glibc-doc-reference-2.19.orig/ 0000775 0001750 0001750 00000000000 12301305370 016267 5 ustar adconrad adconrad glibc-doc-reference-2.19.orig/manual/ 0000775 0001750 0001750 00000000000 12275120646 017557 5 ustar adconrad adconrad glibc-doc-reference-2.19.orig/manual/examples/ 0000775 0001750 0001750 00000000000 12275120646 021375 5 ustar adconrad adconrad glibc-doc-reference-2.19.orig/manual/examples/fmtmsgexpl.c 0000664 0001750 0001750 00000002044 12275120646 023727 0 ustar adconrad adconrad /* How to use fmtmsg and addseverity.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
int
main (void)
{
addseverity (5, "NOTE2");
fmtmsg (MM_PRINT, "only1field", MM_INFO, "text2", "action2", "tag2");
fmtmsg (MM_PRINT, "UX:cat", 5, "invalid syntax", "refer to manual",
"UX:cat:001");
fmtmsg (MM_PRINT, "label:foo", 6, "text", "action", "tag");
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/filesrv.c 0000664 0001750 0001750 00000003344 12275120646 023217 0 ustar adconrad adconrad /* Datagram Socket Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
#define SERVER "/tmp/serversocket"
#define MAXMSG 512
int
main (void)
{
int sock;
char message[MAXMSG];
struct sockaddr_un name;
size_t size;
int nbytes;
/* Remove the filename first, it's ok if the call fails */
unlink (SERVER);
/* Make the socket, then loop endlessly. */
sock = make_named_socket (SERVER);
while (1)
{
/* Wait for a datagram. */
size = sizeof (name);
nbytes = recvfrom (sock, message, MAXMSG, 0,
(struct sockaddr *) & name, &size);
if (nbytes < 0)
{
perror ("recfrom (server)");
exit (EXIT_FAILURE);
}
/* Give a diagnostic message. */
fprintf (stderr, "Server: got message: %s\n", message);
/* Bounce the message back to the sender. */
nbytes = sendto (sock, message, nbytes, 0,
(struct sockaddr *) & name, size);
if (nbytes < 0)
{
perror ("sendto (server)");
exit (EXIT_FAILURE);
}
}
}
glibc-doc-reference-2.19.orig/manual/examples/swapcontext.c 0000664 0001750 0001750 00000006145 12275120646 024126 0 ustar adconrad adconrad /* Complete Context Control
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
/* Set by the signal handler. */
static volatile int expired;
/* The contexts. */
static ucontext_t uc[3];
/* We do only a certain number of switches. */
static int switches;
/* This is the function doing the work. It is just a
skeleton, real code has to be filled in. */
static void
f (int n)
{
int m = 0;
while (1)
{
/* This is where the work would be done. */
if (++m % 100 == 0)
{
putchar ('.');
fflush (stdout);
}
/* Regularly the @var{expire} variable must be checked. */
if (expired)
{
/* We do not want the program to run forever. */
if (++switches == 20)
return;
printf ("\nswitching from %d to %d\n", n, 3 - n);
expired = 0;
/* Switch to the other context, saving the current one. */
swapcontext (&uc[n], &uc[3 - n]);
}
}
}
/* This is the signal handler which simply set the variable. */
void
handler (int signal)
{
expired = 1;
}
int
main (void)
{
struct sigaction sa;
struct itimerval it;
char st1[8192];
char st2[8192];
/* Initialize the data structures for the interval timer. */
sa.sa_flags = SA_RESTART;
sigfillset (&sa.sa_mask);
sa.sa_handler = handler;
it.it_interval.tv_sec = 0;
it.it_interval.tv_usec = 1;
it.it_value = it.it_interval;
/* Install the timer and get the context we can manipulate. */
if (sigaction (SIGPROF, &sa, NULL) < 0
|| setitimer (ITIMER_PROF, &it, NULL) < 0
|| getcontext (&uc[1]) == -1
|| getcontext (&uc[2]) == -1)
abort ();
/* Create a context with a separate stack which causes the
function @code{f} to be call with the parameter @code{1}.
Note that the @code{uc_link} points to the main context
which will cause the program to terminate once the function
return. */
uc[1].uc_link = &uc[0];
uc[1].uc_stack.ss_sp = st1;
uc[1].uc_stack.ss_size = sizeof st1;
makecontext (&uc[1], (void (*) (void)) f, 1, 1);
/* Similarly, but @code{2} is passed as the parameter to @code{f}. */
uc[2].uc_link = &uc[0];
uc[2].uc_stack.ss_sp = st2;
uc[2].uc_stack.ss_size = sizeof st2;
makecontext (&uc[2], (void (*) (void)) f, 1, 2);
/* Start running. */
swapcontext (&uc[0], &uc[1]);
putchar ('\n');
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/pipe.c 0000664 0001750 0001750 00000003754 12275120646 022507 0 ustar adconrad adconrad /* Creating a Pipe
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
/* Read characters from the pipe and echo them to @code{stdout}. */
void
read_from_pipe (int file)
{
FILE *stream;
int c;
stream = fdopen (file, "r");
while ((c = fgetc (stream)) != EOF)
putchar (c);
fclose (stream);
}
/* Write some random text to the pipe. */
void
write_to_pipe (int file)
{
FILE *stream;
stream = fdopen (file, "w");
fprintf (stream, "hello, world!\n");
fprintf (stream, "goodbye, world!\n");
fclose (stream);
}
int
main (void)
{
pid_t pid;
int mypipe[2];
/*@group*/
/* Create the pipe. */
if (pipe (mypipe))
{
fprintf (stderr, "Pipe failed.\n");
return EXIT_FAILURE;
}
/*@end group*/
/* Create the child process. */
pid = fork ();
if (pid == (pid_t) 0)
{
/* This is the child process.
Close other end first. */
close (mypipe[1]);
read_from_pipe (mypipe[0]);
return EXIT_SUCCESS;
}
else if (pid < (pid_t) 0)
{
/* The fork failed. */
fprintf (stderr, "Fork failed.\n");
return EXIT_FAILURE;
}
else
{
/* This is the parent process.
Close other end first. */
close (mypipe[0]);
write_to_pipe (mypipe[1]);
return EXIT_SUCCESS;
}
}
glibc-doc-reference-2.19.orig/manual/examples/add.c 0000664 0001750 0001750 00000002362 12275120646 022274 0 ustar adconrad adconrad /* Example of a Variadic Function
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
int
add_em_up (int count,...)
{
va_list ap;
int i, sum;
va_start (ap, count); /* Initialize the argument list. */
sum = 0;
for (i = 0; i < count; i++)
sum += va_arg (ap, int); /* Get the next argument value. */
va_end (ap); /* Clean up. */
return sum;
}
int
main (void)
{
/* This call prints 16. */
printf ("%d\n", add_em_up (3, 5, 5, 6));
/* This call prints 55. */
printf ("%d\n", add_em_up (10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10));
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/atexit.c 0000664 0001750 0001750 00000001571 12275120646 023043 0 ustar adconrad adconrad /* Cleanups on Exit
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
void
bye (void)
{
puts ("Goodbye, cruel world....");
}
int
main (void)
{
atexit (bye);
exit (EXIT_SUCCESS);
}
glibc-doc-reference-2.19.orig/manual/examples/testpass.c 0000664 0001750 0001750 00000002377 12275120646 023420 0 ustar adconrad adconrad /* Verify a password.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
int
main(void)
{
/* Hashed form of "GNU libc manual". */
const char *const pass = "$1$/iSaq7rB$EoUw5jJPPvAPECNaaWzMK/";
char *result;
int ok;
/*@group*/
/* Read in the user's password and encrypt it,
passing the expected password in as the salt. */
result = crypt(getpass("Password:"), pass);
/*@end group*/
/* Test the result. */
ok = strcmp (result, pass) == 0;
puts(ok ? "Access granted." : "Access denied.");
return ok ? 0 : 1;
}
glibc-doc-reference-2.19.orig/manual/examples/popen.c 0000664 0001750 0001750 00000002547 12275120646 022672 0 ustar adconrad adconrad /* Pipe to a Subprocess
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
void
write_data (FILE * stream)
{
int i;
for (i = 0; i < 100; i++)
fprintf (stream, "%d\n", i);
if (ferror (stream))
{
fprintf (stderr, "Output to stream failed.\n");
exit (EXIT_FAILURE);
}
}
/*@group*/
int
main (void)
{
FILE *output;
output = popen ("more", "w");
if (!output)
{
fprintf (stderr,
"incorrect parameters or too many files.\n");
return EXIT_FAILURE;
}
write_data (output);
if (pclose (output) != 0)
{
fprintf (stderr,
"Could not run more or other error.\n");
}
return EXIT_SUCCESS;
}
/*@end group*/
glibc-doc-reference-2.19.orig/manual/examples/stpcpy.c 0000664 0001750 0001750 00000001622 12275120646 023064 0 ustar adconrad adconrad /* stpcpy example.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
int
main (void)
{
char buffer[10];
char *to = buffer;
to = stpcpy (to, "foo");
to = stpcpy (to, "bar");
puts (buffer);
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/dir.c 0000664 0001750 0001750 00000002101 12275120646 022311 0 ustar adconrad adconrad /* Simple Program to List a Directory
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/*@group*/
#include
#include
#include
/*@end group*/
int
main (void)
{
DIR *dp;
struct dirent *ep;
dp = opendir ("./");
if (dp != NULL)
{
while (ep = readdir (dp))
puts (ep->d_name);
(void) closedir (dp);
}
else
perror ("Couldn't open the directory");
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/termios.c 0000664 0001750 0001750 00000003473 12275120646 023232 0 ustar adconrad adconrad /* Noncanonical Mode Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
/* Use this variable to remember original terminal attributes. */
struct termios saved_attributes;
void
reset_input_mode (void)
{
tcsetattr (STDIN_FILENO, TCSANOW, &saved_attributes);
}
void
set_input_mode (void)
{
struct termios tattr;
char *name;
/* Make sure stdin is a terminal. */
if (!isatty (STDIN_FILENO))
{
fprintf (stderr, "Not a terminal.\n");
exit (EXIT_FAILURE);
}
/* Save the terminal attributes so we can restore them later. */
tcgetattr (STDIN_FILENO, &saved_attributes);
atexit (reset_input_mode);
/*@group*/
/* Set the funny terminal modes. */
tcgetattr (STDIN_FILENO, &tattr);
tattr.c_lflag &= ~(ICANON|ECHO); /* Clear ICANON and ECHO. */
tattr.c_cc[VMIN] = 1;
tattr.c_cc[VTIME] = 0;
tcsetattr (STDIN_FILENO, TCSAFLUSH, &tattr);
}
/*@end group*/
int
main (void)
{
char c;
set_input_mode ();
while (1)
{
read (STDIN_FILENO, &c, 1);
if (c == '\004') /* @kbd{C-d} */
break;
else
putchar (c);
}
return EXIT_SUCCESS;
}
glibc-doc-reference-2.19.orig/manual/examples/inetcli.c 0000664 0001750 0001750 00000003545 12275120646 023177 0 ustar adconrad adconrad /* Byte Stream Socket Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
#include
#include
#include
#define PORT 5555
#define MESSAGE "Yow!!! Are we having fun yet?!?"
#define SERVERHOST "www.gnu.org"
void
write_to_server (int filedes)
{
int nbytes;
nbytes = write (filedes, MESSAGE, strlen (MESSAGE) + 1);
if (nbytes < 0)
{
perror ("write");
exit (EXIT_FAILURE);
}
}
int
main (void)
{
extern void init_sockaddr (struct sockaddr_in *name,
const char *hostname,
uint16_t port);
int sock;
struct sockaddr_in servername;
/* Create the socket. */
sock = socket (PF_INET, SOCK_STREAM, 0);
if (sock < 0)
{
perror ("socket (client)");
exit (EXIT_FAILURE);
}
/* Connect to the server. */
init_sockaddr (&servername, SERVERHOST, PORT);
if (0 > connect (sock,
(struct sockaddr *) &servername,
sizeof (servername)))
{
perror ("connect (client)");
exit (EXIT_FAILURE);
}
/* Send data to the server. */
write_to_server (sock);
close (sock);
exit (EXIT_SUCCESS);
}
glibc-doc-reference-2.19.orig/manual/examples/filecli.c 0000664 0001750 0001750 00000003627 12275120646 023160 0 ustar adconrad adconrad /* Example of Reading Datagrams
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
#include
#define SERVER "/tmp/serversocket"
#define CLIENT "/tmp/mysocket"
#define MAXMSG 512
#define MESSAGE "Yow!!! Are we having fun yet?!?"
int
main (void)
{
extern int make_named_socket (const char *name);
int sock;
char message[MAXMSG];
struct sockaddr_un name;
size_t size;
int nbytes;
/* Make the socket. */
sock = make_named_socket (CLIENT);
/* Initialize the server socket address. */
name.sun_family = AF_LOCAL;
strcpy (name.sun_path, SERVER);
size = strlen (name.sun_path) + sizeof (name.sun_family);
/* Send the datagram. */
nbytes = sendto (sock, MESSAGE, strlen (MESSAGE) + 1, 0,
(struct sockaddr *) & name, size);
if (nbytes < 0)
{
perror ("sendto (client)");
exit (EXIT_FAILURE);
}
/* Wait for a reply. */
nbytes = recvfrom (sock, message, MAXMSG, 0, NULL, 0);
if (nbytes < 0)
{
perror ("recfrom (client)");
exit (EXIT_FAILURE);
}
/* Print a diagnostic message. */
fprintf (stderr, "Client: got message: %s\n", message);
/* Clean up. */
remove (CLIENT);
close (sock);
}
glibc-doc-reference-2.19.orig/manual/examples/execinfo.c 0000664 0001750 0001750 00000002470 12275120646 023344 0 ustar adconrad adconrad /* Obtain a backtrace and print it.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
/* Obtain a backtrace and print it to @code{stdout}. */
void
print_trace (void)
{
void *array[10];
size_t size;
char **strings;
size_t i;
size = backtrace (array, 10);
strings = backtrace_symbols (array, size);
printf ("Obtained %zd stack frames.\n", size);
for (i = 0; i < size; i++)
printf ("%s\n", strings[i]);
free (strings);
}
/* A dummy function to make the backtrace more interesting. */
void
dummy_function (void)
{
print_trace ();
}
int
main (void)
{
dummy_function ();
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/memopen.c 0000664 0001750 0001750 00000001727 12275120646 023210 0 ustar adconrad adconrad /* String Streams
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
static char buffer[] = "foobar";
int
main (void)
{
int ch;
FILE *stream;
stream = fmemopen (buffer, strlen (buffer), "r");
while ((ch = fgetc (stream)) != EOF)
printf ("Got %c\n", ch);
fclose (stream);
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/testopt.c 0000664 0001750 0001750 00000003512 12275120646 023244 0 ustar adconrad adconrad /* Example of Parsing Arguments with getopt.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/*@group*/
#include
#include
#include
#include
int
main (int argc, char **argv)
{
int aflag = 0;
int bflag = 0;
char *cvalue = NULL;
int index;
int c;
opterr = 0;
/*@end group*/
/*@group*/
while ((c = getopt (argc, argv, "abc:")) != -1)
switch (c)
{
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
case 'c':
cvalue = optarg;
break;
case '?':
if (optopt == 'c')
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint (optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr,
"Unknown option character `\\x%x'.\n",
optopt);
return 1;
default:
abort ();
}
/*@end group*/
/*@group*/
printf ("aflag = %d, bflag = %d, cvalue = %s\n",
aflag, bflag, cvalue);
for (index = optind; index < argc; index++)
printf ("Non-option argument %s\n", argv[index]);
return 0;
}
/*@end group*/
glibc-doc-reference-2.19.orig/manual/examples/db.c 0000664 0001750 0001750 00000003747 12275120646 022141 0 ustar adconrad adconrad /* User and Group Database Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
int
main (void)
{
uid_t me;
struct passwd *my_passwd;
struct group *my_group;
char **members;
/* Get information about the user ID. */
me = getuid ();
my_passwd = getpwuid (me);
if (!my_passwd)
{
printf ("Couldn't find out about user %d.\n", (int) me);
exit (EXIT_FAILURE);
}
/* Print the information. */
printf ("I am %s.\n", my_passwd->pw_gecos);
printf ("My login name is %s.\n", my_passwd->pw_name);
printf ("My uid is %d.\n", (int) (my_passwd->pw_uid));
printf ("My home directory is %s.\n", my_passwd->pw_dir);
printf ("My default shell is %s.\n", my_passwd->pw_shell);
/* Get information about the default group ID. */
my_group = getgrgid (my_passwd->pw_gid);
if (!my_group)
{
printf ("Couldn't find out about group %d.\n",
(int) my_passwd->pw_gid);
exit (EXIT_FAILURE);
}
/* Print the information. */
printf ("My default group is %s (%d).\n",
my_group->gr_name, (int) (my_passwd->pw_gid));
printf ("The members of this group are:\n");
members = my_group->gr_mem;
while (*members)
{
printf (" %s\n", *(members));
members++;
}
return EXIT_SUCCESS;
}
glibc-doc-reference-2.19.orig/manual/examples/memstrm.c 0000664 0001750 0001750 00000002056 12275120646 023230 0 ustar adconrad adconrad /* open_memstream example.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
int
main (void)
{
char *bp;
size_t size;
FILE *stream;
stream = open_memstream (&bp, &size);
fprintf (stream, "hello");
fflush (stream);
printf ("buf = `%s', size = %d\n", bp, size);
fprintf (stream, ", world");
fclose (stream);
printf ("buf = `%s', size = %d\n", bp, size);
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/argp-ex1.c 0000664 0001750 0001750 00000002127 12275120646 023167 0 ustar adconrad adconrad /* Argp example #1 -- a minimal program using argp
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/* This is (probably) the smallest possible program that
uses argp. It won't do much except give an error
messages and exit when there are any arguments, and print
a (rather pointless) messages for --help. */
#include
#include
int
main (int argc, char **argv)
{
argp_parse (0, argc, argv, 0, 0, 0);
exit (0);
}
glibc-doc-reference-2.19.orig/manual/examples/argp-ex2.c 0000664 0001750 0001750 00000004560 12275120646 023173 0 ustar adconrad adconrad /* Argp example #2 -- a pretty minimal program using argp
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/* This program doesn't use any options or arguments, but uses
argp to be compliant with the GNU standard command line
format.
In addition to making sure no arguments are given, and
implementing a --help option, this example will have a
--version option, and will put the given documentation string
and bug address in the --help output, as per GNU standards.
The variable ARGP contains the argument parser specification;
adding fields to this structure is the way most parameters are
passed to argp_parse (the first three fields are usually used,
but not in this small program). There are also two global
variables that argp knows about defined here,
ARGP_PROGRAM_VERSION and ARGP_PROGRAM_BUG_ADDRESS (they are
global variables because they will almost always be constant
for a given program, even if it uses different argument
parsers for various tasks). */
#include
#include
const char *argp_program_version =
"argp-ex2 1.0";
const char *argp_program_bug_address =
"";
/* Program documentation. */
static char doc[] =
"Argp example #2 -- a pretty minimal program using argp";
/* Our argument parser. The @code{options}, @code{parser}, and
@code{args_doc} fields are zero because we have neither options or
arguments; @code{doc} and @code{argp_program_bug_address} will be
used in the output for @samp{--help}, and the @samp{--version}
option will print out @code{argp_program_version}. */
static struct argp argp = { 0, 0, 0, doc };
int
main (int argc, char **argv)
{
argp_parse (&argp, argc, argv, 0, 0, 0);
exit (0);
}
glibc-doc-reference-2.19.orig/manual/examples/search.c 0000664 0001750 0001750 00000004720 12275120646 023011 0 ustar adconrad adconrad /* Searching and Sorting Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
/* Define an array of critters to sort. */
struct critter
{
const char *name;
const char *species;
};
struct critter muppets[] =
{
{"Kermit", "frog"},
{"Piggy", "pig"},
{"Gonzo", "whatever"},
{"Fozzie", "bear"},
{"Sam", "eagle"},
{"Robin", "frog"},
{"Animal", "animal"},
{"Camilla", "chicken"},
{"Sweetums", "monster"},
{"Dr. Strangepork", "pig"},
{"Link Hogthrob", "pig"},
{"Zoot", "human"},
{"Dr. Bunsen Honeydew", "human"},
{"Beaker", "human"},
{"Swedish Chef", "human"}
};
int count = sizeof (muppets) / sizeof (struct critter);
/* This is the comparison function used for sorting and searching. */
int
critter_cmp (const void *v1, const void *v2)
{
const struct critter *c1 = v1;
const struct critter *c2 = v2;
return strcmp (c1->name, c2->name);
}
/* Print information about a critter. */
void
print_critter (const struct critter *c)
{
printf ("%s, the %s\n", c->name, c->species);
}
/*@group*/
/* Do the lookup into the sorted array. */
void
find_critter (const char *name)
{
struct critter target, *result;
target.name = name;
result = bsearch (&target, muppets, count, sizeof (struct critter),
critter_cmp);
if (result)
print_critter (result);
else
printf ("Couldn't find %s.\n", name);
}
/*@end group*/
/* Main program. */
int
main (void)
{
int i;
for (i = 0; i < count; i++)
print_critter (&muppets[i]);
printf ("\n");
qsort (muppets, count, sizeof (struct critter), critter_cmp);
for (i = 0; i < count; i++)
print_critter (&muppets[i]);
printf ("\n");
find_critter ("Kermit");
find_critter ("Gonzo");
find_critter ("Janice");
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/strftim.c 0000664 0001750 0001750 00000002530 12275120646 023231 0 ustar adconrad adconrad /* Time Functions Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#define SIZE 256
int
main (void)
{
char buffer[SIZE];
time_t curtime;
struct tm *loctime;
/* Get the current time. */
curtime = time (NULL);
/* Convert it to local time representation. */
loctime = localtime (&curtime);
/* Print out the date and time in the standard format. */
fputs (asctime (loctime), stdout);
/*@group*/
/* Print it out in a nice format. */
strftime (buffer, SIZE, "Today is %A, %B %d.\n", loctime);
fputs (buffer, stdout);
strftime (buffer, SIZE, "The time is %I:%M %p.\n", loctime);
fputs (buffer, stdout);
return 0;
}
/*@end group*/
glibc-doc-reference-2.19.orig/manual/examples/dir2.c 0000664 0001750 0001750 00000002177 12275120646 022410 0 ustar adconrad adconrad /* Simple Program to List a Directory, Mark II
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/*@group*/
#include
#include
/*@end group*/
static int
one (const struct dirent *unused)
{
return 1;
}
int
main (void)
{
struct dirent **eps;
int n;
n = scandir ("./", &eps, one, alphasort);
if (n >= 0)
{
int cnt;
for (cnt = 0; cnt < n; ++cnt)
puts (eps[cnt]->d_name);
}
else
perror ("Couldn't open the directory");
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/README 0000664 0001750 0001750 00000000605 12275120646 022256 0 ustar adconrad adconrad These are source files for example code that appears in The GNU C
Library Reference Manual.
While the manual itself is licensed under the terms of the GNU Free
Documentation License, you can use these source files on their own
under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License, or (at your
option) any later version.
glibc-doc-reference-2.19.orig/manual/examples/strncat.c 0000664 0001750 0001750 00000001704 12275120646 023221 0 ustar adconrad adconrad /* strncat example.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#define SIZE 10
static char buffer[SIZE];
int
main (void)
{
strncpy (buffer, "hello", SIZE);
puts (buffer);
strncat (buffer, ", world", SIZE - strlen (buffer) - 1);
puts (buffer);
}
glibc-doc-reference-2.19.orig/manual/examples/sigh1.c 0000664 0001750 0001750 00000002604 12275120646 022556 0 ustar adconrad adconrad /* Signal Handlers that Return
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
/* This flag controls termination of the main loop. */
volatile sig_atomic_t keep_going = 1;
/* The signal handler just clears the flag and re-enables itself. */
void
catch_alarm (int sig)
{
keep_going = 0;
signal (sig, catch_alarm);
}
void
do_stuff (void)
{
puts ("Doing stuff while waiting for alarm....");
}
int
main (void)
{
/* Establish a handler for SIGALRM signals. */
signal (SIGALRM, catch_alarm);
/* Set an alarm to go off in a little while. */
alarm (2);
/* Check the flag once in a while to see when to quit. */
while (keep_going)
do_stuff ();
return EXIT_SUCCESS;
}
glibc-doc-reference-2.19.orig/manual/examples/genpass.c 0000664 0001750 0001750 00000002726 12275120646 023210 0 ustar adconrad adconrad /* Encrypting Passwords
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
int
main(void)
{
unsigned long seed[2];
char salt[] = "$1$........";
const char *const seedchars =
"./0123456789ABCDEFGHIJKLMNOPQRST"
"UVWXYZabcdefghijklmnopqrstuvwxyz";
char *password;
int i;
/* Generate a (not very) random seed.
You should do it better than this... */
seed[0] = time(NULL);
seed[1] = getpid() ^ (seed[0] >> 14 & 0x30000);
/* Turn it into printable characters from `seedchars'. */
for (i = 0; i < 8; i++)
salt[3+i] = seedchars[(seed[i/5] >> (i%5)*6) & 0x3f];
/* Read in the user's password and encrypt it. */
password = crypt(getpass("Password:"), salt);
/* Print the results. */
puts(password);
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/sigusr.c 0000664 0001750 0001750 00000003622 12275120646 023060 0 ustar adconrad adconrad /* Using kill for Communication
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/*@group*/
#include
#include
#include
#include
/*@end group*/
/* When a @code{SIGUSR1} signal arrives, set this variable. */
volatile sig_atomic_t usr_interrupt = 0;
void
synch_signal (int sig)
{
usr_interrupt = 1;
}
/* The child process executes this function. */
void
child_function (void)
{
/* Perform initialization. */
printf ("I'm here!!! My pid is %d.\n", (int) getpid ());
/* Let parent know you're done. */
kill (getppid (), SIGUSR1);
/* Continue with execution. */
puts ("Bye, now....");
exit (0);
}
int
main (void)
{
struct sigaction usr_action;
sigset_t block_mask;
pid_t child_id;
/* Establish the signal handler. */
sigfillset (&block_mask);
usr_action.sa_handler = synch_signal;
usr_action.sa_mask = block_mask;
usr_action.sa_flags = 0;
sigaction (SIGUSR1, &usr_action, NULL);
/* Create the child process. */
child_id = fork ();
if (child_id == 0)
child_function (); /* Does not return. */
/*@group*/
/* Busy wait for the child to send a signal. */
while (!usr_interrupt)
;
/*@end group*/
/* Now continue execution. */
puts ("That's all, folks!");
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/longopt.c 0000664 0001750 0001750 00000005471 12275120646 023232 0 ustar adconrad adconrad /* Example of Parsing Long Options with getopt_long.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
/* Flag set by @samp{--verbose}. */
static int verbose_flag;
int
main (int argc, char **argv)
{
int c;
while (1)
{
static struct option long_options[] =
{
/* These options set a flag. */
{"verbose", no_argument, &verbose_flag, 1},
{"brief", no_argument, &verbose_flag, 0},
/* These options don't set a flag.
We distinguish them by their indices. */
{"add", no_argument, 0, 'a'},
{"append", no_argument, 0, 'b'},
{"delete", required_argument, 0, 'd'},
{"create", required_argument, 0, 'c'},
{"file", required_argument, 0, 'f'},
{0, 0, 0, 0}
};
/* @code{getopt_long} stores the option index here. */
int option_index = 0;
c = getopt_long (argc, argv, "abc:d:f:",
long_options, &option_index);
/* Detect the end of the options. */
if (c == -1)
break;
switch (c)
{
case 0:
/* If this option set a flag, do nothing else now. */
if (long_options[option_index].flag != 0)
break;
printf ("option %s", long_options[option_index].name);
if (optarg)
printf (" with arg %s", optarg);
printf ("\n");
break;
case 'a':
puts ("option -a\n");
break;
case 'b':
puts ("option -b\n");
break;
case 'c':
printf ("option -c with value `%s'\n", optarg);
break;
case 'd':
printf ("option -d with value `%s'\n", optarg);
break;
case 'f':
printf ("option -f with value `%s'\n", optarg);
break;
case '?':
/* @code{getopt_long} already printed an error message. */
break;
default:
abort ();
}
}
/* Instead of reporting @samp{--verbose}
and @samp{--brief} as they are encountered,
we report the final status resulting from them. */
if (verbose_flag)
puts ("verbose flag is set");
/* Print any remaining command line arguments (not options). */
if (optind < argc)
{
printf ("non-option ARGV-elements: ");
while (optind < argc)
printf ("%s ", argv[optind++]);
putchar ('\n');
}
exit (0);
}
glibc-doc-reference-2.19.orig/manual/examples/timeval_subtract.c 0000664 0001750 0001750 00000003066 12275120646 025116 0 ustar adconrad adconrad /* struct timeval subtraction.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/* Subtract the `struct timeval' values X and Y,
storing the result in RESULT.
Return 1 if the difference is negative, otherwise 0. */
int
timeval_subtract (result, x, y)
struct timeval *result, *x, *y;
{
/* Perform the carry for the later subtraction by updating @var{y}. */
if (x->tv_usec < y->tv_usec) {
int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
y->tv_usec -= 1000000 * nsec;
y->tv_sec += nsec;
}
if (x->tv_usec - y->tv_usec > 1000000) {
int nsec = (x->tv_usec - y->tv_usec) / 1000000;
y->tv_usec += 1000000 * nsec;
y->tv_sec -= nsec;
}
/* Compute the time remaining to wait.
@code{tv_usec} is certainly positive. */
result->tv_sec = x->tv_sec - y->tv_sec;
result->tv_usec = x->tv_usec - y->tv_usec;
/* Return 1 if result is negative. */
return x->tv_sec < y->tv_sec;
}
glibc-doc-reference-2.19.orig/manual/examples/inetsrv.c 0000664 0001750 0001750 00000005442 12275120646 023240 0 ustar adconrad adconrad /* Byte Stream Connection Server Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
#include
#include
#include
#define PORT 5555
#define MAXMSG 512
int
read_from_client (int filedes)
{
char buffer[MAXMSG];
int nbytes;
nbytes = read (filedes, buffer, MAXMSG);
if (nbytes < 0)
{
/* Read error. */
perror ("read");
exit (EXIT_FAILURE);
}
else if (nbytes == 0)
/* End-of-file. */
return -1;
else
{
/* Data read. */
fprintf (stderr, "Server: got message: `%s'\n", buffer);
return 0;
}
}
int
main (void)
{
extern int make_socket (uint16_t port);
int sock;
fd_set active_fd_set, read_fd_set;
int i;
struct sockaddr_in clientname;
size_t size;
/* Create the socket and set it up to accept connections. */
sock = make_socket (PORT);
if (listen (sock, 1) < 0)
{
perror ("listen");
exit (EXIT_FAILURE);
}
/* Initialize the set of active sockets. */
FD_ZERO (&active_fd_set);
FD_SET (sock, &active_fd_set);
while (1)
{
/* Block until input arrives on one or more active sockets. */
read_fd_set = active_fd_set;
if (select (FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0)
{
perror ("select");
exit (EXIT_FAILURE);
}
/* Service all the sockets with input pending. */
for (i = 0; i < FD_SETSIZE; ++i)
if (FD_ISSET (i, &read_fd_set))
{
if (i == sock)
{
/* Connection request on original socket. */
int new;
size = sizeof (clientname);
new = accept (sock,
(struct sockaddr *) &clientname,
&size);
if (new < 0)
{
perror ("accept");
exit (EXIT_FAILURE);
}
fprintf (stderr,
"Server: connect from host %s, port %hd.\n",
inet_ntoa (clientname.sin_addr),
ntohs (clientname.sin_port));
FD_SET (new, &active_fd_set);
}
else
{
/* Data arriving on an already-connected socket. */
if (read_from_client (i) < 0)
{
close (i);
FD_CLR (i, &active_fd_set);
}
}
}
}
}
glibc-doc-reference-2.19.orig/manual/examples/strdupa.c 0000664 0001750 0001750 00000001763 12275120646 023232 0 ustar adconrad adconrad /* strdupa example.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
const char path[] = _PATH_STDPATH;
int
main (void)
{
char *wr_path = strdupa (path);
char *cp = strtok (wr_path, ":");
while (cp != NULL)
{
puts (cp);
cp = strtok (NULL, ":");
}
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/mygetpass.c 0000664 0001750 0001750 00000002363 12275120646 023561 0 ustar adconrad adconrad /* Reading Passwords
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
ssize_t
my_getpass (char **lineptr, size_t *n, FILE *stream)
{
struct termios old, new;
int nread;
/* Turn echoing off and fail if we can't. */
if (tcgetattr (fileno (stream), &old) != 0)
return -1;
new = old;
new.c_lflag &= ~ECHO;
if (tcsetattr (fileno (stream), TCSAFLUSH, &new) != 0)
return -1;
/* Read the password. */
nread = getline (lineptr, n, stream);
/* Restore terminal. */
(void) tcsetattr (fileno (stream), TCSAFLUSH, &old);
return nread;
}
glibc-doc-reference-2.19.orig/manual/examples/argp-ex3.c 0000664 0001750 0001750 00000014002 12275120646 023164 0 ustar adconrad adconrad /* Argp example #3 -- a program with options and arguments using argp
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/* This program uses the same features as example 2, and uses options and
arguments.
We now use the first four fields in ARGP, so here's a description of them:
OPTIONS -- A pointer to a vector of struct argp_option (see below)
PARSER -- A function to parse a single option, called by argp
ARGS_DOC -- A string describing how the non-option arguments should look
DOC -- A descriptive string about this program; if it contains a
vertical tab character (\v), the part after it will be
printed *following* the options
The function PARSER takes the following arguments:
KEY -- An integer specifying which option this is (taken
from the KEY field in each struct argp_option), or
a special key specifying something else; the only
special keys we use here are ARGP_KEY_ARG, meaning
a non-option argument, and ARGP_KEY_END, meaning
that all arguments have been parsed
ARG -- For an option KEY, the string value of its
argument, or NULL if it has none
STATE-- A pointer to a struct argp_state, containing
various useful information about the parsing state; used here
are the INPUT field, which reflects the INPUT argument to
argp_parse, and the ARG_NUM field, which is the number of the
current non-option argument being parsed
It should return either 0, meaning success, ARGP_ERR_UNKNOWN, meaning the
given KEY wasn't recognized, or an errno value indicating some other
error.
Note that in this example, main uses a structure to communicate with the
parse_opt function, a pointer to which it passes in the INPUT argument to
argp_parse. Of course, it's also possible to use global variables
instead, but this is somewhat more flexible.
The OPTIONS field contains a pointer to a vector of struct argp_option's;
that structure has the following fields (if you assign your option
structures using array initialization like this example, unspecified
fields will be defaulted to 0, and need not be specified):
NAME -- The name of this option's long option (may be zero)
KEY -- The KEY to pass to the PARSER function when parsing this option,
*and* the name of this option's short option, if it is a
printable ascii character
ARG -- The name of this option's argument, if any
FLAGS -- Flags describing this option; some of them are:
OPTION_ARG_OPTIONAL -- The argument to this option is optional
OPTION_ALIAS -- This option is an alias for the
previous option
OPTION_HIDDEN -- Don't show this option in --help output
DOC -- A documentation string for this option, shown in --help output
An options vector should be terminated by an option with all fields zero. */
#include
#include
const char *argp_program_version =
"argp-ex3 1.0";
const char *argp_program_bug_address =
"";
/* Program documentation. */
static char doc[] =
"Argp example #3 -- a program with options and arguments using argp";
/* A description of the arguments we accept. */
static char args_doc[] = "ARG1 ARG2";
/* The options we understand. */
static struct argp_option options[] = {
{"verbose", 'v', 0, 0, "Produce verbose output" },
{"quiet", 'q', 0, 0, "Don't produce any output" },
{"silent", 's', 0, OPTION_ALIAS },
{"output", 'o', "FILE", 0,
"Output to FILE instead of standard output" },
{ 0 }
};
/* Used by @code{main} to communicate with @code{parse_opt}. */
struct arguments
{
char *args[2]; /* @var{arg1} & @var{arg2} */
int silent, verbose;
char *output_file;
};
/* Parse a single option. */
static error_t
parse_opt (int key, char *arg, struct argp_state *state)
{
/* Get the @var{input} argument from @code{argp_parse}, which we
know is a pointer to our arguments structure. */
struct arguments *arguments = state->input;
switch (key)
{
case 'q': case 's':
arguments->silent = 1;
break;
case 'v':
arguments->verbose = 1;
break;
case 'o':
arguments->output_file = arg;
break;
case ARGP_KEY_ARG:
if (state->arg_num >= 2)
/* Too many arguments. */
argp_usage (state);
arguments->args[state->arg_num] = arg;
break;
case ARGP_KEY_END:
if (state->arg_num < 2)
/* Not enough arguments. */
argp_usage (state);
break;
default:
return ARGP_ERR_UNKNOWN;
}
return 0;
}
/* Our argp parser. */
static struct argp argp = { options, parse_opt, args_doc, doc };
int
main (int argc, char **argv)
{
struct arguments arguments;
/* Default values. */
arguments.silent = 0;
arguments.verbose = 0;
arguments.output_file = "-";
/* Parse our arguments; every option seen by @code{parse_opt} will
be reflected in @code{arguments}. */
argp_parse (&argp, argc, argv, 0, 0, &arguments);
printf ("ARG1 = %s\nARG2 = %s\nOUTPUT_FILE = %s\n"
"VERBOSE = %s\nSILENT = %s\n",
arguments.args[0], arguments.args[1],
arguments.output_file,
arguments.verbose ? "yes" : "no",
arguments.silent ? "yes" : "no");
exit (0);
}
glibc-doc-reference-2.19.orig/manual/examples/setjmp.c 0000664 0001750 0001750 00000002234 12275120646 023044 0 ustar adconrad adconrad /* Introduction to Non-Local Exits
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
jmp_buf main_loop;
void
abort_to_main_loop (int status)
{
longjmp (main_loop, status);
}
int
main (void)
{
while (1)
if (setjmp (main_loop))
puts ("Back at main loop....");
else
do_command ();
}
void
do_command (void)
{
char buffer[128];
if (fgets (buffer, 128, stdin) == NULL)
abort_to_main_loop (-1);
else
exit (EXIT_SUCCESS);
}
glibc-doc-reference-2.19.orig/manual/examples/subopt.c 0000664 0001750 0001750 00000004324 12275120646 023060 0 ustar adconrad adconrad /* Parsing of Suboptions Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
int do_all;
const char *type;
int read_size;
int write_size;
int read_only;
enum
{
RO_OPTION = 0,
RW_OPTION,
READ_SIZE_OPTION,
WRITE_SIZE_OPTION,
THE_END
};
const char *mount_opts[] =
{
[RO_OPTION] = "ro",
[RW_OPTION] = "rw",
[READ_SIZE_OPTION] = "rsize",
[WRITE_SIZE_OPTION] = "wsize",
[THE_END] = NULL
};
int
main (int argc, char **argv)
{
char *subopts, *value;
int opt;
while ((opt = getopt (argc, argv, "at:o:")) != -1)
switch (opt)
{
case 'a':
do_all = 1;
break;
case 't':
type = optarg;
break;
case 'o':
subopts = optarg;
while (*subopts != '\0')
switch (getsubopt (&subopts, mount_opts, &value))
{
case RO_OPTION:
read_only = 1;
break;
case RW_OPTION:
read_only = 0;
break;
case READ_SIZE_OPTION:
if (value == NULL)
abort ();
read_size = atoi (value);
break;
case WRITE_SIZE_OPTION:
if (value == NULL)
abort ();
write_size = atoi (value);
break;
default:
/* Unknown suboption. */
printf ("Unknown suboption `%s'\n", value);
break;
}
break;
default:
abort ();
}
/* Do the real work. */
return 0;
}
glibc-doc-reference-2.19.orig/manual/examples/select.c 0000664 0001750 0001750 00000002771 12275120646 023027 0 ustar adconrad adconrad /* Waiting for Input or Output
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/*@group*/
#include
#include
#include
#include
#include
/*@end group*/
/*@group*/
int
input_timeout (int filedes, unsigned int seconds)
{
fd_set set;
struct timeval timeout;
/*@end group*/
/* Initialize the file descriptor set. */
FD_ZERO (&set);
FD_SET (filedes, &set);
/* Initialize the timeout data structure. */
timeout.tv_sec = seconds;
timeout.tv_usec = 0;
/*@group*/
/* @code{select} returns 0 if timeout, 1 if input available, -1 if error. */
return TEMP_FAILURE_RETRY (select (FD_SETSIZE,
&set, NULL, NULL,
&timeout));
}
/*@end group*/
/*@group*/
int
main (void)
{
fprintf (stderr, "select returned %d.\n",
input_timeout (STDIN_FILENO, 5));
return 0;
}
/*@end group*/
glibc-doc-reference-2.19.orig/manual/examples/isockad.c 0000664 0001750 0001750 00000002373 12275120646 023163 0 ustar adconrad adconrad /* Internet Socket Example using sockaddr_in.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
void
init_sockaddr (struct sockaddr_in *name,
const char *hostname,
uint16_t port)
{
struct hostent *hostinfo;
name->sin_family = AF_INET;
name->sin_port = htons (port);
hostinfo = gethostbyname (hostname);
if (hostinfo == NULL)
{
fprintf (stderr, "Unknown host %s.\n", hostname);
exit (EXIT_FAILURE);
}
name->sin_addr = *(struct in_addr *) hostinfo->h_addr;
}
glibc-doc-reference-2.19.orig/manual/examples/argp-ex4.c 0000664 0001750 0001750 00000013724 12275120646 023177 0 ustar adconrad adconrad /* Argp example #4 -- a program with somewhat more complicated options
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
/* This program uses the same features as example 3, but has more
options, and somewhat more structure in the -help output. It
also shows how you can `steal' the remainder of the input
arguments past a certain point, for programs that accept a
list of items. It also shows the special argp KEY value
ARGP_KEY_NO_ARGS, which is only given if no non-option
arguments were supplied to the program.
For structuring the help output, two features are used,
*headers* which are entries in the options vector with the
first four fields being zero, and a two part documentation
string (in the variable DOC), which allows documentation both
before and after the options; the two parts of DOC are
separated by a vertical-tab character ('\v', or '\013'). By
convention, the documentation before the options is just a
short string saying what the program does, and that afterwards
is longer, describing the behavior in more detail. All
documentation strings are automatically filled for output,
although newlines may be included to force a line break at a
particular point. All documentation strings are also passed to
the `gettext' function, for possible translation into the
current locale. */
#include
#include
#include
const char *argp_program_version =
"argp-ex4 1.0";
const char *argp_program_bug_address =
"";
/* Program documentation. */
static char doc[] =
"Argp example #4 -- a program with somewhat more complicated\
options\
\vThis part of the documentation comes *after* the options;\
note that the text is automatically filled, but it's possible\
to force a line-break, e.g.\n<-- here.";
/* A description of the arguments we accept. */
static char args_doc[] = "ARG1 [STRING...]";
/* Keys for options without short-options. */
#define OPT_ABORT 1 /* --abort */
/* The options we understand. */
static struct argp_option options[] = {
{"verbose", 'v', 0, 0, "Produce verbose output" },
{"quiet", 'q', 0, 0, "Don't produce any output" },
{"silent", 's', 0, OPTION_ALIAS },
{"output", 'o', "FILE", 0,
"Output to FILE instead of standard output" },
{0,0,0,0, "The following options should be grouped together:" },
{"repeat", 'r', "COUNT", OPTION_ARG_OPTIONAL,
"Repeat the output COUNT (default 10) times"},
{"abort", OPT_ABORT, 0, 0, "Abort before showing any output"},
{ 0 }
};
/* Used by @code{main} to communicate with @code{parse_opt}. */
struct arguments
{
char *arg1; /* @var{arg1} */
char **strings; /* [@var{string}@dots{}] */
int silent, verbose, abort; /* @samp{-s}, @samp{-v}, @samp{--abort} */
char *output_file; /* @var{file} arg to @samp{--output} */
int repeat_count; /* @var{count} arg to @samp{--repeat} */
};
/* Parse a single option. */
static error_t
parse_opt (int key, char *arg, struct argp_state *state)
{
/* Get the @code{input} argument from @code{argp_parse}, which we
know is a pointer to our arguments structure. */
struct arguments *arguments = state->input;
switch (key)
{
case 'q': case 's':
arguments->silent = 1;
break;
case 'v':
arguments->verbose = 1;
break;
case 'o':
arguments->output_file = arg;
break;
case 'r':
arguments->repeat_count = arg ? atoi (arg) : 10;
break;
case OPT_ABORT:
arguments->abort = 1;
break;
case ARGP_KEY_NO_ARGS:
argp_usage (state);
case ARGP_KEY_ARG:
/* Here we know that @code{state->arg_num == 0}, since we
force argument parsing to end before any more arguments can
get here. */
arguments->arg1 = arg;
/* Now we consume all the rest of the arguments.
@code{state->next} is the index in @code{state->argv} of the
next argument to be parsed, which is the first @var{string}
we're interested in, so we can just use
@code{&state->argv[state->next]} as the value for
arguments->strings.
@emph{In addition}, by setting @code{state->next} to the end
of the arguments, we can force argp to stop parsing here and
return. */
arguments->strings = &state->argv[state->next];
state->next = state->argc;
break;
default:
return ARGP_ERR_UNKNOWN;
}
return 0;
}
/* Our argp parser. */
static struct argp argp = { options, parse_opt, args_doc, doc };
int
main (int argc, char **argv)
{
int i, j;
struct arguments arguments;
/* Default values. */
arguments.silent = 0;
arguments.verbose = 0;
arguments.output_file = "-";
arguments.repeat_count = 1;
arguments.abort = 0;
/* Parse our arguments; every option seen by @code{parse_opt} will be
reflected in @code{arguments}. */
argp_parse (&argp, argc, argv, 0, 0, &arguments);
if (arguments.abort)
error (10, 0, "ABORTED");
for (i = 0; i < arguments.repeat_count; i++)
{
printf ("ARG1 = %s\n", arguments.arg1);
printf ("STRINGS = ");
for (j = 0; arguments.strings[j]; j++)
printf (j == 0 ? "%s" : ", %s", arguments.strings[j]);
printf ("\n");
printf ("OUTPUT_FILE = %s\nVERBOSE = %s\nSILENT = %s\n",
arguments.output_file,
arguments.verbose ? "yes" : "no",
arguments.silent ? "yes" : "no");
}
exit (0);
}
glibc-doc-reference-2.19.orig/manual/examples/mkisock.c 0000664 0001750 0001750 00000002467 12275120646 023212 0 ustar adconrad adconrad /* Internet Socket Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
int
make_socket (uint16_t port)
{
int sock;
struct sockaddr_in name;
/* Create the socket. */
sock = socket (PF_INET, SOCK_STREAM, 0);
if (sock < 0)
{
perror ("socket");
exit (EXIT_FAILURE);
}
/* Give the socket a name. */
name.sin_family = AF_INET;
name.sin_port = htons (port);
name.sin_addr.s_addr = htonl (INADDR_ANY);
if (bind (sock, (struct sockaddr *) &name, sizeof (name)) < 0)
{
perror ("bind");
exit (EXIT_FAILURE);
}
return sock;
}
glibc-doc-reference-2.19.orig/manual/examples/mkfsock.c 0000664 0001750 0001750 00000003334 12275120646 023201 0 ustar adconrad adconrad /* Example of Local-Namespace Sockets
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
#include
#include
#include
#include
int
make_named_socket (const char *filename)
{
struct sockaddr_un name;
int sock;
size_t size;
/* Create the socket. */
sock = socket (PF_LOCAL, SOCK_DGRAM, 0);
if (sock < 0)
{
perror ("socket");
exit (EXIT_FAILURE);
}
/* Bind a name to the socket. */
name.sun_family = AF_LOCAL;
strncpy (name.sun_path, filename, sizeof (name.sun_path));
name.sun_path[sizeof (name.sun_path) - 1] = '\0';
/* The size of the address is
the offset of the start of the filename,
plus its length (not including the terminating null byte).
Alternatively you can just do:
size = SUN_LEN (&name);
*/
size = (offsetof (struct sockaddr_un, sun_path)
+ strlen (name.sun_path));
if (bind (sock, (struct sockaddr *) &name, size) < 0)
{
perror ("bind");
exit (EXIT_FAILURE);
}
return sock;
}
glibc-doc-reference-2.19.orig/manual/examples/rprintf.c 0000664 0001750 0001750 00000003761 12275120646 023234 0 ustar adconrad adconrad /* Printf Extension Example
Copyright (C) 1991-2014 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, if not, see .
*/
#include
#include
#include
/*@group*/
typedef struct
{
char *name;
}
Widget;
/*@end group*/
int
print_widget (FILE *stream,
const struct printf_info *info,
const void *const *args)
{
const Widget *w;
char *buffer;
int len;
/* Format the output into a string. */
w = *((const Widget **) (args[0]));
len = asprintf (&buffer, "", w, w->name);
if (len == -1)
return -1;
/* Pad to the minimum field width and print to the stream. */
len = fprintf (stream, "%*s",
(info->left ? -info->width : info->width),
buffer);
/* Clean up and return. */
free (buffer);
return len;
}
int
print_widget_arginfo (const struct printf_info *info, size_t n,
int *argtypes)
{
/* We always take exactly one argument and this is a pointer to the
structure.. */
if (n > 0)
argtypes[0] = PA_POINTER;
return 1;
}
int
main (void)
{
/* Make a widget to print. */
Widget mywidget;
mywidget.name = "mywidget";
/* Register the print function for widgets. */
register_printf_function ('W', print_widget, print_widget_arginfo);
/* Now print the widget. */
printf ("|%W|\n", &mywidget);
printf ("|%35W|\n", &mywidget);
printf ("|%-35W|\n", &mywidget);
return 0;
}
glibc-doc-reference-2.19.orig/manual/time.texi 0000664 0001750 0001750 00000340127 12275120646 021417 0 ustar adconrad adconrad @node Date and Time, Resource Usage And Limitation, Arithmetic, Top
@c %MENU% Functions for getting the date and time and formatting them nicely
@chapter Date and Time
This chapter describes functions for manipulating dates and times,
including functions for determining what time it is and conversion
between different time representations.
@menu
* Time Basics:: Concepts and definitions.
* Elapsed Time:: Data types to represent elapsed times
* Processor And CPU Time:: Time a program has spent executing.
* Calendar Time:: Manipulation of ``real'' dates and times.
* Setting an Alarm:: Sending a signal after a specified time.
* Sleeping:: Waiting for a period of time.
@end menu
@node Time Basics
@section Time Basics
@cindex time
Discussing time in a technical manual can be difficult because the word
``time'' in English refers to lots of different things. In this manual,
we use a rigorous terminology to avoid confusion, and the only thing we
use the simple word ``time'' for is to talk about the abstract concept.
A @dfn{calendar time} is a point in the time continuum, for example
November 4, 1990 at 18:02.5 UTC. Sometimes this is called ``absolute
time''.
@cindex calendar time
We don't speak of a ``date'', because that is inherent in a calendar
time.
@cindex date
An @dfn{interval} is a contiguous part of the time continuum between two
calendar times, for example the hour between 9:00 and 10:00 on July 4,
1980.
@cindex interval
An @dfn{elapsed time} is the length of an interval, for example, 35
minutes. People sometimes sloppily use the word ``interval'' to refer
to the elapsed time of some interval.
@cindex elapsed time
@cindex time, elapsed
An @dfn{amount of time} is a sum of elapsed times, which need not be of
any specific intervals. For example, the amount of time it takes to
read a book might be 9 hours, independently of when and in how many
sittings it is read.
A @dfn{period} is the elapsed time of an interval between two events,
especially when they are part of a sequence of regularly repeating
events.
@cindex period of time
@dfn{CPU time} is like calendar time, except that it is based on the
subset of the time continuum when a particular process is actively
using a CPU. CPU time is, therefore, relative to a process.
@cindex CPU time
@dfn{Processor time} is an amount of time that a CPU is in use. In
fact, it's a basic system resource, since there's a limit to how much
can exist in any given interval (that limit is the elapsed time of the
interval times the number of CPUs in the processor). People often call
this CPU time, but we reserve the latter term in this manual for the
definition above.
@cindex processor time
@node Elapsed Time
@section Elapsed Time
@cindex elapsed time
One way to represent an elapsed time is with a simple arithmetic data
type, as with the following function to compute the elapsed time between
two calendar times. This function is declared in @file{time.h}.
@comment time.h
@comment ISO
@deftypefun double difftime (time_t @var{time1}, time_t @var{time0})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{difftime} function returns the number of seconds of elapsed
time between calendar time @var{time1} and calendar time @var{time0}, as
a value of type @code{double}. The difference ignores leap seconds
unless leap second support is enabled.
In @theglibc{}, you can simply subtract @code{time_t} values. But on
other systems, the @code{time_t} data type might use some other encoding
where subtraction doesn't work directly.
@end deftypefun
@Theglibc{} provides two data types specifically for representing
an elapsed time. They are used by various @glibcadj{} functions, and
you can use them for your own purposes too. They're exactly the same
except that one has a resolution in microseconds, and the other, newer
one, is in nanoseconds.
@comment sys/time.h
@comment BSD
@deftp {Data Type} {struct timeval}
@cindex timeval
The @code{struct timeval} structure represents an elapsed time. It is
declared in @file{sys/time.h} and has the following members:
@table @code
@item long int tv_sec
This represents the number of whole seconds of elapsed time.
@item long int tv_usec
This is the rest of the elapsed time (a fraction of a second),
represented as the number of microseconds. It is always less than one
million.
@end table
@end deftp
@comment sys/time.h
@comment POSIX.1
@deftp {Data Type} {struct timespec}
@cindex timespec
The @code{struct timespec} structure represents an elapsed time. It is
declared in @file{time.h} and has the following members:
@table @code
@item long int tv_sec
This represents the number of whole seconds of elapsed time.
@item long int tv_nsec
This is the rest of the elapsed time (a fraction of a second),
represented as the number of nanoseconds. It is always less than one
billion.
@end table
@end deftp
It is often necessary to subtract two values of type @w{@code{struct
timeval}} or @w{@code{struct timespec}}. Here is the best way to do
this. It works even on some peculiar operating systems where the
@code{tv_sec} member has an unsigned type.
@smallexample
@include timeval_subtract.c.texi
@end smallexample
Common functions that use @code{struct timeval} are @code{gettimeofday}
and @code{settimeofday}.
There are no @glibcadj{} functions specifically oriented toward
dealing with elapsed times, but the calendar time, processor time, and
alarm and sleeping functions have a lot to do with them.
@node Processor And CPU Time
@section Processor And CPU Time
If you're trying to optimize your program or measure its efficiency,
it's very useful to know how much processor time it uses. For that,
calendar time and elapsed times are useless because a process may spend
time waiting for I/O or for other processes to use the CPU. However,
you can get the information with the functions in this section.
CPU time (@pxref{Time Basics}) is represented by the data type
@code{clock_t}, which is a number of @dfn{clock ticks}. It gives the
total amount of time a process has actively used a CPU since some
arbitrary event. On @gnusystems{}, that event is the creation of the
process. While arbitrary in general, the event is always the same event
for any particular process, so you can always measure how much time on
the CPU a particular computation takes by examining the process' CPU
time before and after the computation.
@cindex CPU time
@cindex clock ticks
@cindex ticks, clock
On @gnulinuxhurdsystems{}, @code{clock_t} is equivalent to @code{long int} and
@code{CLOCKS_PER_SEC} is an integer value. But in other systems, both
@code{clock_t} and the macro @code{CLOCKS_PER_SEC} can be either integer
or floating-point types. Casting CPU time values to @code{double}, as
in the example above, makes sure that operations such as arithmetic and
printing work properly and consistently no matter what the underlying
representation is.
Note that the clock can wrap around. On a 32bit system with
@code{CLOCKS_PER_SEC} set to one million this function will return the
same value approximately every 72 minutes.
For additional functions to examine a process' use of processor time,
and to control it, see @ref{Resource Usage And Limitation}.
@menu
* CPU Time:: The @code{clock} function.
* Processor Time:: The @code{times} function.
@end menu
@node CPU Time
@subsection CPU Time Inquiry
To get a process' CPU time, you can use the @code{clock} function. This
facility is declared in the header file @file{time.h}.
@pindex time.h
In typical usage, you call the @code{clock} function at the beginning
and end of the interval you want to time, subtract the values, and then
divide by @code{CLOCKS_PER_SEC} (the number of clock ticks per second)
to get processor time, like this:
@smallexample
@group
#include
clock_t start, end;
double cpu_time_used;
start = clock();
@dots{} /* @r{Do the work.} */
end = clock();
cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;
@end group
@end smallexample
Do not use a single CPU time as an amount of time; it doesn't work that
way. Either do a subtraction as shown above or query processor time
directly. @xref{Processor Time}.
Different computers and operating systems vary wildly in how they keep
track of CPU time. It's common for the internal processor clock
to have a resolution somewhere between a hundredth and millionth of a
second.
@comment time.h
@comment ISO
@deftypevr Macro int CLOCKS_PER_SEC
The value of this macro is the number of clock ticks per second measured
by the @code{clock} function. POSIX requires that this value be one
million independent of the actual resolution.
@end deftypevr
@comment time.h
@comment ISO
@deftp {Data Type} clock_t
This is the type of the value returned by the @code{clock} function.
Values of type @code{clock_t} are numbers of clock ticks.
@end deftp
@comment time.h
@comment ISO
@deftypefun clock_t clock (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On Hurd, this calls task_info twice and adds user and system time
@c from both basic and thread time info structs. On generic posix,
@c calls times and adds utime and stime. On bsd, calls getrusage and
@c safely converts stime and utime to clock. On linux, calls
@c clock_gettime.
This function returns the calling process' current CPU time. If the CPU
time is not available or cannot be represented, @code{clock} returns the
value @code{(clock_t)(-1)}.
@end deftypefun
@node Processor Time
@subsection Processor Time Inquiry
The @code{times} function returns information about a process'
consumption of processor time in a @w{@code{struct tms}} object, in
addition to the process' CPU time. @xref{Time Basics}. You should
include the header file @file{sys/times.h} to use this facility.
@cindex processor time
@cindex CPU time
@pindex sys/times.h
@comment sys/times.h
@comment POSIX.1
@deftp {Data Type} {struct tms}
The @code{tms} structure is used to return information about process
times. It contains at least the following members:
@table @code
@item clock_t tms_utime
This is the total processor time the calling process has used in
executing the instructions of its program.
@item clock_t tms_stime
This is the processor time the system has used on behalf of the calling
process.
@item clock_t tms_cutime
This is the sum of the @code{tms_utime} values and the @code{tms_cutime}
values of all terminated child processes of the calling process, whose
status has been reported to the parent process by @code{wait} or
@code{waitpid}; see @ref{Process Completion}. In other words, it
represents the total processor time used in executing the instructions
of all the terminated child processes of the calling process, excluding
child processes which have not yet been reported by @code{wait} or
@code{waitpid}.
@cindex child process
@item clock_t tms_cstime
This is similar to @code{tms_cutime}, but represents the total processor
time system has used on behalf of all the terminated child processes
of the calling process.
@end table
All of the times are given in numbers of clock ticks. Unlike CPU time,
these are the actual amounts of time; not relative to any event.
@xref{Creating a Process}.
@end deftp
@comment time.h
@comment POSIX.1
@deftypevr Macro int CLK_TCK
This is an obsolete name for the number of clock ticks per second. Use
@code{sysconf (_SC_CLK_TCK)} instead.
@end deftypevr
@comment sys/times.h
@comment POSIX.1
@deftypefun clock_t times (struct tms *@var{buffer})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On HURD, this calls task_info twice, for basic and thread times info,
@c adding user and system times into tms, and then gettimeofday, to
@c compute the real time. On BSD, it calls getclktck, getrusage (twice)
@c and time. On Linux, it's a syscall with special handling to account
@c for clock_t counts that look like error values.
The @code{times} function stores the processor time information for
the calling process in @var{buffer}.
The return value is the number of clock ticks since an arbitrary point
in the past, e.g. since system start-up. @code{times} returns
@code{(clock_t)(-1)} to indicate failure.
@end deftypefun
@strong{Portability Note:} The @code{clock} function described in
@ref{CPU Time} is specified by the @w{ISO C} standard. The
@code{times} function is a feature of POSIX.1. On @gnusystems{}, the
CPU time is defined to be equivalent to the sum of the @code{tms_utime}
and @code{tms_stime} fields returned by @code{times}.
@node Calendar Time
@section Calendar Time
This section describes facilities for keeping track of calendar time.
@xref{Time Basics}.
@Theglibc{} represents calendar time three ways:
@itemize @bullet
@item
@dfn{Simple time} (the @code{time_t} data type) is a compact
representation, typically giving the number of seconds of elapsed time
since some implementation-specific base time.
@cindex simple time
@item
There is also a "high-resolution time" representation. Like simple
time, this represents a calendar time as an elapsed time since a base
time, but instead of measuring in whole seconds, it uses a @code{struct
timeval} data type, which includes fractions of a second. Use this time
representation instead of simple time when you need greater precision.
@cindex high-resolution time
@item
@dfn{Local time} or @dfn{broken-down time} (the @code{struct tm} data
type) represents a calendar time as a set of components specifying the
year, month, and so on in the Gregorian calendar, for a specific time
zone. This calendar time representation is usually used only to
communicate with people.
@cindex local time
@cindex broken-down time
@cindex Gregorian calendar
@cindex calendar, Gregorian
@end itemize
@menu
* Simple Calendar Time:: Facilities for manipulating calendar time.
* High-Resolution Calendar:: A time representation with greater precision.
* Broken-down Time:: Facilities for manipulating local time.
* High Accuracy Clock:: Maintaining a high accuracy system clock.
* Formatting Calendar Time:: Converting times to strings.
* Parsing Date and Time:: Convert textual time and date information back
into broken-down time values.
* TZ Variable:: How users specify the time zone.
* Time Zone Functions:: Functions to examine or specify the time zone.
* Time Functions Example:: An example program showing use of some of
the time functions.
@end menu
@node Simple Calendar Time
@subsection Simple Calendar Time
This section describes the @code{time_t} data type for representing calendar
time as simple time, and the functions which operate on simple time objects.
These facilities are declared in the header file @file{time.h}.
@pindex time.h
@cindex epoch
@comment time.h
@comment ISO
@deftp {Data Type} time_t
This is the data type used to represent simple time. Sometimes, it also
represents an elapsed time. When interpreted as a calendar time value,
it represents the number of seconds elapsed since 00:00:00 on January 1,
1970, Coordinated Universal Time. (This calendar time is sometimes
referred to as the @dfn{epoch}.) POSIX requires that this count not
include leap seconds, but on some systems this count includes leap seconds
if you set @code{TZ} to certain values (@pxref{TZ Variable}).
Note that a simple time has no concept of local time zone. Calendar
Time @var{T} is the same instant in time regardless of where on the
globe the computer is.
In @theglibc{}, @code{time_t} is equivalent to @code{long int}.
In other systems, @code{time_t} might be either an integer or
floating-point type.
@end deftp
The function @code{difftime} tells you the elapsed time between two
simple calendar times, which is not always as easy to compute as just
subtracting. @xref{Elapsed Time}.
@comment time.h
@comment ISO
@deftypefun time_t time (time_t *@var{result})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{time} function returns the current calendar time as a value of
type @code{time_t}. If the argument @var{result} is not a null pointer,
the calendar time value is also stored in @code{*@var{result}}. If the
current calendar time is not available, the value
@w{@code{(time_t)(-1)}} is returned.
@end deftypefun
@c The GNU C library implements stime() with a call to settimeofday() on
@c Linux.
@comment time.h
@comment SVID, XPG
@deftypefun int stime (const time_t *@var{newtime})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On unix, this is implemented in terms of settimeofday.
@code{stime} sets the system clock, i.e., it tells the system that the
current calendar time is @var{newtime}, where @code{newtime} is
interpreted as described in the above definition of @code{time_t}.
@code{settimeofday} is a newer function which sets the system clock to
better than one second precision. @code{settimeofday} is generally a
better choice than @code{stime}. @xref{High-Resolution Calendar}.
Only the superuser can set the system clock.
If the function succeeds, the return value is zero. Otherwise, it is
@code{-1} and @code{errno} is set accordingly:
@table @code
@item EPERM
The process is not superuser.
@end table
@end deftypefun
@node High-Resolution Calendar
@subsection High-Resolution Calendar
The @code{time_t} data type used to represent simple times has a
resolution of only one second. Some applications need more precision.
So, @theglibc{} also contains functions which are capable of
representing calendar times to a higher resolution than one second. The
functions and the associated data types described in this section are
declared in @file{sys/time.h}.
@pindex sys/time.h
@comment sys/time.h
@comment BSD
@deftp {Data Type} {struct timezone}
The @code{struct timezone} structure is used to hold minimal information
about the local time zone. It has the following members:
@table @code
@item int tz_minuteswest
This is the number of minutes west of UTC.
@item int tz_dsttime
If nonzero, Daylight Saving Time applies during some part of the year.
@end table
The @code{struct timezone} type is obsolete and should never be used.
Instead, use the facilities described in @ref{Time Zone Functions}.
@end deftp
@comment sys/time.h
@comment BSD
@deftypefun int gettimeofday (struct timeval *@var{tp}, struct timezone *@var{tzp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On most GNU/Linux systems this is a direct syscall, but the posix/
@c implementation (not used on GNU/Linux or GNU/Hurd) relies on time and
@c localtime_r, saving and restoring tzname in an unsafe manner.
@c On some GNU/Linux variants, ifunc resolvers are used in shared libc
@c for vdso resolution. ifunc-vdso-revisit.
The @code{gettimeofday} function returns the current calendar time as
the elapsed time since the epoch in the @code{struct timeval} structure
indicated by @var{tp}. (@pxref{Elapsed Time} for a description of
@code{struct timeval}). Information about the time zone is returned in
the structure pointed at @var{tzp}. If the @var{tzp} argument is a null
pointer, time zone information is ignored.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error condition is defined for this function:
@table @code
@item ENOSYS
The operating system does not support getting time zone information, and
@var{tzp} is not a null pointer. @gnusystems{} do not
support using @w{@code{struct timezone}} to represent time zone
information; that is an obsolete feature of 4.3 BSD.
Instead, use the facilities described in @ref{Time Zone Functions}.
@end table
@end deftypefun
@comment sys/time.h
@comment BSD
@deftypefun int settimeofday (const struct timeval *@var{tp}, const struct timezone *@var{tzp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On HURD, it calls host_set_time with a privileged port. On other
@c unix systems, it's a syscall.
The @code{settimeofday} function sets the current calendar time in the
system clock according to the arguments. As for @code{gettimeofday},
the calendar time is represented as the elapsed time since the epoch.
As for @code{gettimeofday}, time zone information is ignored if
@var{tzp} is a null pointer.
You must be a privileged user in order to use @code{settimeofday}.
Some kernels automatically set the system clock from some source such as
a hardware clock when they start up. Others, including Linux, place the
system clock in an ``invalid'' state (in which attempts to read the clock
fail). A call of @code{stime} removes the system clock from an invalid
state, and system startup scripts typically run a program that calls
@code{stime}.
@code{settimeofday} causes a sudden jump forwards or backwards, which
can cause a variety of problems in a system. Use @code{adjtime} (below)
to make a smooth transition from one time to another by temporarily
speeding up or slowing down the clock.
With a Linux kernel, @code{adjtimex} does the same thing and can also
make permanent changes to the speed of the system clock so it doesn't
need to be corrected as often.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EPERM
This process cannot set the clock because it is not privileged.
@item ENOSYS
The operating system does not support setting time zone information, and
@var{tzp} is not a null pointer.
@end table
@end deftypefun
@c On Linux, GNU libc implements adjtime() as a call to adjtimex().
@comment sys/time.h
@comment BSD
@deftypefun int adjtime (const struct timeval *@var{delta}, struct timeval *@var{olddelta})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On hurd and mach, call host_adjust_time with a privileged port. On
@c Linux, it's implemented in terms of adjtimex. On other unixen, it's
@c a syscall.
This function speeds up or slows down the system clock in order to make
a gradual adjustment. This ensures that the calendar time reported by
the system clock is always monotonically increasing, which might not
happen if you simply set the clock.
The @var{delta} argument specifies a relative adjustment to be made to
the clock time. If negative, the system clock is slowed down for a
while until it has lost this much elapsed time. If positive, the system
clock is speeded up for a while.
If the @var{olddelta} argument is not a null pointer, the @code{adjtime}
function returns information about any previous time adjustment that
has not yet completed.
This function is typically used to synchronize the clocks of computers
in a local network. You must be a privileged user to use it.
With a Linux kernel, you can use the @code{adjtimex} function to
permanently change the clock speed.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error condition is defined for this function:
@table @code
@item EPERM
You do not have privilege to set the time.
@end table
@end deftypefun
@strong{Portability Note:} The @code{gettimeofday}, @code{settimeofday},
and @code{adjtime} functions are derived from BSD.
Symbols for the following function are declared in @file{sys/timex.h}.
@comment sys/timex.h
@comment GNU
@deftypefun int adjtimex (struct timex *@var{timex})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c It's a syscall, only available on linux.
@code{adjtimex} is functionally identical to @code{ntp_adjtime}.
@xref{High Accuracy Clock}.
This function is present only with a Linux kernel.
@end deftypefun
@node Broken-down Time
@subsection Broken-down Time
@cindex broken-down time
@cindex calendar time and broken-down time
Calendar time is represented by the usual @glibcadj{} functions as an
elapsed time since a fixed base calendar time. This is convenient for
computation, but has no relation to the way people normally think of
calendar time. By contrast, @dfn{broken-down time} is a binary
representation of calendar time separated into year, month, day, and so
on. Broken-down time values are not useful for calculations, but they
are useful for printing human readable time information.
A broken-down time value is always relative to a choice of time
zone, and it also indicates which time zone that is.
The symbols in this section are declared in the header file @file{time.h}.
@comment time.h
@comment ISO
@deftp {Data Type} {struct tm}
This is the data type used to represent a broken-down time. The structure
contains at least the following members, which can appear in any order.
@table @code
@item int tm_sec
This is the number of full seconds since the top of the minute (normally
in the range @code{0} through @code{59}, but the actual upper limit is
@code{60}, to allow for leap seconds if leap second support is
available).
@cindex leap second
@item int tm_min
This is the number of full minutes since the top of the hour (in the
range @code{0} through @code{59}).
@item int tm_hour
This is the number of full hours past midnight (in the range @code{0} through
@code{23}).
@item int tm_mday
This is the ordinal day of the month (in the range @code{1} through @code{31}).
Watch out for this one! As the only ordinal number in the structure, it is
inconsistent with the rest of the structure.
@item int tm_mon
This is the number of full calendar months since the beginning of the
year (in the range @code{0} through @code{11}). Watch out for this one!
People usually use ordinal numbers for month-of-year (where January = 1).
@item int tm_year
This is the number of full calendar years since 1900.
@item int tm_wday
This is the number of full days since Sunday (in the range @code{0} through
@code{6}).
@item int tm_yday
This is the number of full days since the beginning of the year (in the
range @code{0} through @code{365}).
@item int tm_isdst
@cindex Daylight Saving Time
@cindex summer time
This is a flag that indicates whether Daylight Saving Time is (or was, or
will be) in effect at the time described. The value is positive if
Daylight Saving Time is in effect, zero if it is not, and negative if the
information is not available.
@item long int tm_gmtoff
This field describes the time zone that was used to compute this
broken-down time value, including any adjustment for daylight saving; it
is the number of seconds that you must add to UTC to get local time.
You can also think of this as the number of seconds east of UTC. For
example, for U.S. Eastern Standard Time, the value is @code{-5*60*60}.
The @code{tm_gmtoff} field is derived from BSD and is a GNU library
extension; it is not visible in a strict @w{ISO C} environment.
@item const char *tm_zone
This field is the name for the time zone that was used to compute this
broken-down time value. Like @code{tm_gmtoff}, this field is a BSD and
GNU extension, and is not visible in a strict @w{ISO C} environment.
@end table
@end deftp
@comment time.h
@comment ISO
@deftypefun {struct tm *} localtime (const time_t *@var{time})
@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c Calls tz_convert with a static buffer.
@c localtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
The @code{localtime} function converts the simple time pointed to by
@var{time} to broken-down time representation, expressed relative to the
user's specified time zone.
The return value is a pointer to a static broken-down time structure, which
might be overwritten by subsequent calls to @code{ctime}, @code{gmtime},
or @code{localtime}. (But no other library function overwrites the contents
of this object.)
The return value is the null pointer if @var{time} cannot be represented
as a broken-down time; typically this is because the year cannot fit into
an @code{int}.
Calling @code{localtime} also sets the current time zone as if
@code{tzset} were called. @xref{Time Zone Functions}.
@end deftypefun
Using the @code{localtime} function is a big problem in multi-threaded
programs. The result is returned in a static buffer and this is used in
all threads. POSIX.1c introduced a variant of this function.
@comment time.h
@comment POSIX.1c
@deftypefun {struct tm *} localtime_r (const time_t *@var{time}, struct tm *@var{resultp})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c localtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tz_convert(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c tzset_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c always called with tzset_lock held
@c sets static is_initialized before initialization;
@c reads and sets old_tz; sets tz_rules.
@c some of the issues only apply on the first call.
@c subsequent calls only trigger these when called by localtime;
@c otherwise, they're ok.
@c getenv dup @mtsenv
@c strcmp dup ok
@c strdup @ascuheap
@c tzfile_read @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c memcmp dup ok
@c strstr dup ok
@c getenv dup @mtsenv
@c asprintf dup @mtslocale @ascuheap @acsmem
@c stat64 dup ok
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fileno dup ok
@c fstat64 dup ok
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c free dup @ascuheap @acsmem
@c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive]
@c fread_unlocked dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
@c memcpy dup ok
@c decode ok
@c bswap_32 dup ok
@c fseek dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
@c ftello dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
@c malloc dup @ascuheap @acsmem
@c decode64 ok
@c bswap_64 dup ok
@c getc_unlocked ok [no @mtasurace:stream @asucorrupt @acucorrupt]
@c tzstring dup @ascuheap @acsmem
@c compute_tzname_max dup ok [guarded by tzset_lock]
@c memset dup ok
@c update_vars ok [guarded by tzset_lock]
@c sets daylight, timezone, tzname and tzname_cur_max;
@c called only with tzset_lock held, unless tzset_parse_tz
@c (internal, but not static) gets called by users; given the its
@c double-underscore-prefixed name, this interface violation could
@c be regarded as undefined behavior.
@c strlen ok
@c tzset_parse_tz @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c sscanf dup @mtslocale @ascuheap @acsmem
@c isalnum dup @mtsenv
@c tzstring @ascuheap @acsmem
@c reads and changes tzstring_list without synchronization, but
@c only called with tzset_lock held (save for interface violations)
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c strcpy dup ok
@c isdigit dup @mtslocale
@c compute_offset ok
@c tzfile_default @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c sets tzname, timezone, types, zone_names, rule_*off, etc; no guards
@c strlen dup ok
@c tzfile_read dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c mempcpy dup ok
@c compute_tzname_max ok [if guarded by tzset_lock]
@c iterates over zone_names; no guards
@c free dup @ascuheap @acsmem
@c strtoul dup @mtslocale
@c update_vars dup ok
@c tzfile_compute(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c sets tzname; no guards. with !use_localtime, as in gmtime, it's ok
@c tzstring dup @acsuheap @acsmem
@c tzset_parse_tz dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c offtime dup ok
@c tz_compute dup ok
@c strcmp dup ok
@c offtime ok
@c isleap dup ok
@c tz_compute ok
@c compute_change ok
@c isleap ok
@c libc_lock_unlock dup @aculock
The @code{localtime_r} function works just like the @code{localtime}
function. It takes a pointer to a variable containing a simple time
and converts it to the broken-down time format.
But the result is not placed in a static buffer. Instead it is placed
in the object of type @code{struct tm} to which the parameter
@var{resultp} points.
If the conversion is successful the function returns a pointer to the
object the result was written into, i.e., it returns @var{resultp}.
@end deftypefun
@comment time.h
@comment ISO
@deftypefun {struct tm *} gmtime (const time_t *@var{time})
@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c gmtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
This function is similar to @code{localtime}, except that the broken-down
time is expressed as Coordinated Universal Time (UTC) (formerly called
Greenwich Mean Time (GMT)) rather than relative to a local time zone.
@end deftypefun
As for the @code{localtime} function we have the problem that the result
is placed in a static variable. POSIX.1c also provides a replacement for
@code{gmtime}.
@comment time.h
@comment POSIX.1c
@deftypefun {struct tm *} gmtime_r (const time_t *@var{time}, struct tm *@var{resultp})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c You'd think tz_convert could avoid some safety issues with
@c !use_localtime, but no such luck: tzset_internal will always bring
@c about all possible AS and AC problems when it's first called.
@c Calling any of localtime,gmtime_r once would run the initialization
@c and avoid the heap, mem and fd issues in gmtime* in subsequent calls,
@c but the unsafe locking would remain.
@c gmtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tz_convert(gmtime_r) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
This function is similar to @code{localtime_r}, except that it converts
just like @code{gmtime} the given time as Coordinated Universal Time.
If the conversion is successful the function returns a pointer to the
object the result was written into, i.e., it returns @var{resultp}.
@end deftypefun
@comment time.h
@comment ISO
@deftypefun time_t mktime (struct tm *@var{brokentime})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c mktime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c passes a static localtime_offset to mktime_internal; it is read
@c once, used as an initial guess, and updated at the end, but not
@c used except as a guess for subsequent calls, so it should be safe.
@c Even though a compiler might delay the load and perform it multiple
@c times (bug 16346), there are at least two unconditional uses of the
@c auto variable in which the first load is stored, separated by a
@c call to an external function, and a conditional change of the
@c variable before the external call, so refraining from allocating a
@c local variable at the first load would be a very bad optimization.
@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c mktime_internal(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c ydhms_diff ok
@c ranged_convert(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c *convert = localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c time_t_avg dup ok
@c guess_time_tm dup ok
@c ydhms_diff dup ok
@c time_t_add_ok ok
@c time_t_avg ok
@c isdst_differ ok
@c time_t_int_add_ok ok
The @code{mktime} function converts a broken-down time structure to a
simple time representation. It also normalizes the contents of the
broken-down time structure, and fills in some components based on the
values of the others.
The @code{mktime} function ignores the specified contents of the
@code{tm_wday}, @code{tm_yday}, @code{tm_gmtoff}, and @code{tm_zone}
members of the broken-down time
structure. It uses the values of the other components to determine the
calendar time; it's permissible for these components to have
unnormalized values outside their normal ranges. The last thing that
@code{mktime} does is adjust the components of the @var{brokentime}
structure, including the members that were initially ignored.
If the specified broken-down time cannot be represented as a simple time,
@code{mktime} returns a value of @code{(time_t)(-1)} and does not modify
the contents of @var{brokentime}.
Calling @code{mktime} also sets the current time zone as if
@code{tzset} were called; @code{mktime} uses this information instead
of @var{brokentime}'s initial @code{tm_gmtoff} and @code{tm_zone}
members. @xref{Time Zone Functions}.
@end deftypefun
@comment time.h
@comment ???
@deftypefun time_t timelocal (struct tm *@var{brokentime})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c Alias to mktime.
@code{timelocal} is functionally identical to @code{mktime}, but more
mnemonically named. Note that it is the inverse of the @code{localtime}
function.
@strong{Portability note:} @code{mktime} is essentially universally
available. @code{timelocal} is rather rare.
@end deftypefun
@comment time.h
@comment ???
@deftypefun time_t timegm (struct tm *@var{brokentime})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c timegm @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c gmtime_offset triggers the same caveats as localtime_offset in mktime.
@c although gmtime_r, as called by mktime, might save some issues,
@c tzset calls tzset_internal with always, which forces
@c reinitialization, so all issues may arise.
@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c mktime_internal(gmtime_r) @asulock @aculock
@c ..gmtime_r @asulock @aculock
@c ... dup ok
@c tz_convert(!use_localtime) @asulock @aculock
@c ... dup @asulock @aculock
@c tzfile_compute(!use_localtime) ok
@code{timegm} is functionally identical to @code{mktime} except it
always takes the input values to be Coordinated Universal Time (UTC)
regardless of any local time zone setting.
Note that @code{timegm} is the inverse of @code{gmtime}.
@strong{Portability note:} @code{mktime} is essentially universally
available. @code{timegm} is rather rare. For the most portable
conversion from a UTC broken-down time to a simple time, set
the @code{TZ} environment variable to UTC, call @code{mktime}, then set
@code{TZ} back.
@end deftypefun
@node High Accuracy Clock
@subsection High Accuracy Clock
@cindex time, high precision
@cindex clock, high accuracy
@pindex sys/timex.h
@c On Linux, GNU libc implements ntp_gettime() and npt_adjtime() as calls
@c to adjtimex().
The @code{ntp_gettime} and @code{ntp_adjtime} functions provide an
interface to monitor and manipulate the system clock to maintain high
accuracy time. For example, you can fine tune the speed of the clock
or synchronize it with another time source.
A typical use of these functions is by a server implementing the Network
Time Protocol to synchronize the clocks of multiple systems and high
precision clocks.
These functions are declared in @file{sys/timex.h}.
@tindex struct ntptimeval
@deftp {Data Type} {struct ntptimeval}
This structure is used for information about the system clock. It
contains the following members:
@table @code
@item struct timeval time
This is the current calendar time, expressed as the elapsed time since
the epoch. The @code{struct timeval} data type is described in
@ref{Elapsed Time}.
@item long int maxerror
This is the maximum error, measured in microseconds. Unless updated
via @code{ntp_adjtime} periodically, this value will reach some
platform-specific maximum value.
@item long int esterror
This is the estimated error, measured in microseconds. This value can
be set by @code{ntp_adjtime} to indicate the estimated offset of the
system clock from the true calendar time.
@end table
@end deftp
@comment sys/timex.h
@comment GNU
@deftypefun int ntp_gettime (struct ntptimeval *@var{tptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Wrapper for adjtimex.
The @code{ntp_gettime} function sets the structure pointed to by
@var{tptr} to current values. The elements of the structure afterwards
contain the values the timer implementation in the kernel assumes. They
might or might not be correct. If they are not a @code{ntp_adjtime}
call is necessary.
The return value is @code{0} on success and other values on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item TIME_ERROR
The precision clock model is not properly set up at the moment, thus the
clock must be considered unsynchronized, and the values should be
treated with care.
@end table
@end deftypefun
@tindex struct timex
@deftp {Data Type} {struct timex}
This structure is used to control and monitor the system clock. It
contains the following members:
@table @code
@item unsigned int modes
This variable controls whether and which values are set. Several
symbolic constants have to be combined with @emph{binary or} to specify
the effective mode. These constants start with @code{MOD_}.
@item long int offset
This value indicates the current offset of the system clock from the true
calendar time. The value is given in microseconds. If bit
@code{MOD_OFFSET} is set in @code{modes}, the offset (and possibly other
dependent values) can be set. The offset's absolute value must not
exceed @code{MAXPHASE}.
@item long int frequency
This value indicates the difference in frequency between the true
calendar time and the system clock. The value is expressed as scaled
PPM (parts per million, 0.0001%). The scaling is @code{1 <<
SHIFT_USEC}. The value can be set with bit @code{MOD_FREQUENCY}, but
the absolute value must not exceed @code{MAXFREQ}.
@item long int maxerror
This is the maximum error, measured in microseconds. A new value can be
set using bit @code{MOD_MAXERROR}. Unless updated via
@code{ntp_adjtime} periodically, this value will increase steadily
and reach some platform-specific maximum value.
@item long int esterror
This is the estimated error, measured in microseconds. This value can
be set using bit @code{MOD_ESTERROR}.
@item int status
This variable reflects the various states of the clock machinery. There
are symbolic constants for the significant bits, starting with
@code{STA_}. Some of these flags can be updated using the
@code{MOD_STATUS} bit.
@item long int constant
This value represents the bandwidth or stiffness of the PLL (phase
locked loop) implemented in the kernel. The value can be changed using
bit @code{MOD_TIMECONST}.
@item long int precision
This value represents the accuracy or the maximum error when reading the
system clock. The value is expressed in microseconds.
@item long int tolerance
This value represents the maximum frequency error of the system clock in
scaled PPM. This value is used to increase the @code{maxerror} every
second.
@item struct timeval time
The current calendar time.
@item long int tick
The elapsed time between clock ticks in microseconds. A clock tick is a
periodic timer interrupt on which the system clock is based.
@item long int ppsfreq
This is the first of a few optional variables that are present only if
the system clock can use a PPS (pulse per second) signal to discipline
the system clock. The value is expressed in scaled PPM and it denotes
the difference in frequency between the system clock and the PPS signal.
@item long int jitter
This value expresses a median filtered average of the PPS signal's
dispersion in microseconds.
@item int shift
This value is a binary exponent for the duration of the PPS calibration
interval, ranging from @code{PPS_SHIFT} to @code{PPS_SHIFTMAX}.
@item long int stabil
This value represents the median filtered dispersion of the PPS
frequency in scaled PPM.
@item long int jitcnt
This counter represents the number of pulses where the jitter exceeded
the allowed maximum @code{MAXTIME}.
@item long int calcnt
This counter reflects the number of successful calibration intervals.
@item long int errcnt
This counter represents the number of calibration errors (caused by
large offsets or jitter).
@item long int stbcnt
This counter denotes the number of calibrations where the stability
exceeded the threshold.
@end table
@end deftp
@comment sys/timex.h
@comment GNU
@deftypefun int ntp_adjtime (struct timex *@var{tptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Alias to adjtimex syscall.
The @code{ntp_adjtime} function sets the structure specified by
@var{tptr} to current values.
In addition, @code{ntp_adjtime} updates some settings to match what you
pass to it in *@var{tptr}. Use the @code{modes} element of *@var{tptr}
to select what settings to update. You can set @code{offset},
@code{freq}, @code{maxerror}, @code{esterror}, @code{status},
@code{constant}, and @code{tick}.
@code{modes} = zero means set nothing.
Only the superuser can update settings.
@c On Linux, ntp_adjtime() also does the adjtime() function if you set
@c modes = ADJ_OFFSET_SINGLESHOT (in fact, that is how GNU libc implements
@c adjtime()). But this should be considered an internal function because
@c it's so inconsistent with the rest of what ntp_adjtime() does and is
@c forced in an ugly way into the struct timex. So we don't document it
@c and instead document adjtime() as the way to achieve the function.
The return value is @code{0} on success and other values on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item TIME_ERROR
The high accuracy clock model is not properly set up at the moment, thus the
clock must be considered unsynchronized, and the values should be
treated with care. Another reason could be that the specified new values
are not allowed.
@item EPERM
The process specified a settings update, but is not superuser.
@end table
For more details see RFC1305 (Network Time Protocol, Version 3) and
related documents.
@strong{Portability note:} Early versions of @theglibc{} did not
have this function but did have the synonymous @code{adjtimex}.
@end deftypefun
@node Formatting Calendar Time
@subsection Formatting Calendar Time
The functions described in this section format calendar time values as
strings. These functions are declared in the header file @file{time.h}.
@pindex time.h
@comment time.h
@comment ISO
@deftypefun {char *} asctime (const struct tm *@var{brokentime})
@safety{@prelim{}@mtunsafe{@mtasurace{:asctime} @mtslocale{}}@asunsafe{}@acsafe{}}
@c asctime @mtasurace:asctime @mtslocale
@c Uses a static buffer.
@c asctime_internal @mtslocale
@c snprintf dup @mtslocale [no @acsuheap @acsmem]
@c ab_day_name @mtslocale
@c ab_month_name @mtslocale
The @code{asctime} function converts the broken-down time value that
@var{brokentime} points to into a string in a standard format:
@smallexample
"Tue May 21 13:46:22 1991\n"
@end smallexample
The abbreviations for the days of week are: @samp{Sun}, @samp{Mon},
@samp{Tue}, @samp{Wed}, @samp{Thu}, @samp{Fri}, and @samp{Sat}.
The abbreviations for the months are: @samp{Jan}, @samp{Feb},
@samp{Mar}, @samp{Apr}, @samp{May}, @samp{Jun}, @samp{Jul}, @samp{Aug},
@samp{Sep}, @samp{Oct}, @samp{Nov}, and @samp{Dec}.
The return value points to a statically allocated string, which might be
overwritten by subsequent calls to @code{asctime} or @code{ctime}.
(But no other library function overwrites the contents of this
string.)
@end deftypefun
@comment time.h
@comment POSIX.1c
@deftypefun {char *} asctime_r (const struct tm *@var{brokentime}, char *@var{buffer})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c asctime_r @mtslocale
@c asctime_internal dup @mtslocale
This function is similar to @code{asctime} but instead of placing the
result in a static buffer it writes the string in the buffer pointed to
by the parameter @var{buffer}. This buffer should have room
for at least 26 bytes, including the terminating null.
If no error occurred the function returns a pointer to the string the
result was written into, i.e., it returns @var{buffer}. Otherwise
return @code{NULL}.
@end deftypefun
@comment time.h
@comment ISO
@deftypefun {char *} ctime (const time_t *@var{time})
@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtasurace{:asctime} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c ctime @mtasurace:tmbuf @mtasurace:asctime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c localtime dup @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c asctime dup @mtasurace:asctime @mtslocale
The @code{ctime} function is similar to @code{asctime}, except that you
specify the calendar time argument as a @code{time_t} simple time value
rather than in broken-down local time format. It is equivalent to
@smallexample
asctime (localtime (@var{time}))
@end smallexample
Calling @code{ctime} also sets the current time zone as if
@code{tzset} were called. @xref{Time Zone Functions}.
@end deftypefun
@comment time.h
@comment POSIX.1c
@deftypefun {char *} ctime_r (const time_t *@var{time}, char *@var{buffer})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c ctime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c asctime_r dup @mtslocale
This function is similar to @code{ctime}, but places the result in the
string pointed to by @var{buffer}. It is equivalent to (written using
gcc extensions, @pxref{Statement Exprs,,,gcc,Porting and Using gcc}):
@smallexample
(@{ struct tm tm; asctime_r (localtime_r (time, &tm), buf); @})
@end smallexample
If no error occurred the function returns a pointer to the string the
result was written into, i.e., it returns @var{buffer}. Otherwise
return @code{NULL}.
@end deftypefun
@comment time.h
@comment ISO
@deftypefun size_t strftime (char *@var{s}, size_t @var{size}, const char *@var{template}, const struct tm *@var{brokentime})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c strftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c strftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c strftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c add ok
@c memset_zero dup ok
@c memset_space dup ok
@c strlen dup ok
@c mbrlen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps]
@c mbsinit dup ok
@c cpy ok
@c add dup ok
@c memcpy_lowcase ok
@c TOLOWER ok
@c tolower_l ok
@c memcpy_uppcase ok
@c TOUPPER ok
@c toupper_l ok
@c MEMCPY ok
@c memcpy dup ok
@c ISDIGIT ok
@c STRLEN ok
@c strlen dup ok
@c strftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c TOUPPER dup ok
@c nl_get_era_entry @ascuheap @asulock @acsmem @aculock
@c nl_init_era_entries @ascuheap @asulock @acsmem @aculock
@c libc_rwlock_wrlock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c memset dup ok
@c free dup @ascuheap @acsmem
@c realloc dup @ascuheap @acsmem
@c memcpy dup ok
@c strchr dup ok
@c wcschr dup ok
@c libc_rwlock_unlock dup @asulock @aculock
@c ERA_DATE_CMP ok
@c DO_NUMBER ok
@c DO_NUMBER_SPACEPAD ok
@c nl_get_alt_digit @ascuheap @asulock @acsmem @aculock
@c libc_rwlock_wrlock dup @asulock @aculock
@c nl_init_alt_digit @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c memset dup ok
@c strchr dup ok
@c libc_rwlock_unlock dup @aculock
@c memset_space ok
@c memset dup ok
@c memset_zero ok
@c memset dup ok
@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c iso_week_days ok
@c isleap ok
@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tm_diff ok
This function is similar to the @code{sprintf} function (@pxref{Formatted
Input}), but the conversion specifications that can appear in the format
template @var{template} are specialized for printing components of the date
and time @var{brokentime} according to the locale currently specified for
time conversion (@pxref{Locales}) and the current time zone
(@pxref{Time Zone Functions}).
Ordinary characters appearing in the @var{template} are copied to the
output string @var{s}; this can include multibyte character sequences.
Conversion specifiers are introduced by a @samp{%} character, followed
by an optional flag which can be one of the following. These flags
are all GNU extensions. The first three affect only the output of
numbers:
@table @code
@item _
The number is padded with spaces.
@item -
The number is not padded at all.
@item 0
The number is padded with zeros even if the format specifies padding
with spaces.
@item ^
The output uses uppercase characters, but only if this is possible
(@pxref{Case Conversion}).
@end table
The default action is to pad the number with zeros to keep it a constant
width. Numbers that do not have a range indicated below are never
padded, since there is no natural width for them.
Following the flag an optional specification of the width is possible.
This is specified in decimal notation. If the natural size of the
output is of the field has less than the specified number of characters,
the result is written right adjusted and space padded to the given
size.
An optional modifier can follow the optional flag and width
specification. The modifiers, which were first standardized by
POSIX.2-1992 and by @w{ISO C99}, are:
@table @code
@item E
Use the locale's alternate representation for date and time. This
modifier applies to the @code{%c}, @code{%C}, @code{%x}, @code{%X},
@code{%y} and @code{%Y} format specifiers. In a Japanese locale, for
example, @code{%Ex} might yield a date format based on the Japanese
Emperors' reigns.
@item O
Use the locale's alternate numeric symbols for numbers. This modifier
applies only to numeric format specifiers.
@end table
If the format supports the modifier but no alternate representation
is available, it is ignored.
The conversion specifier ends with a format specifier taken from the
following list. The whole @samp{%} sequence is replaced in the output
string as follows:
@table @code
@item %a
The abbreviated weekday name according to the current locale.
@item %A
The full weekday name according to the current locale.
@item %b
The abbreviated month name according to the current locale.
@item %B
The full month name according to the current locale.
Using @code{%B} together with @code{%d} produces grammatically
incorrect results for some locales.
@item %c
The preferred calendar time representation for the current locale.
@item %C
The century of the year. This is equivalent to the greatest integer not
greater than the year divided by 100.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %d
The day of the month as a decimal number (range @code{01} through @code{31}).
@item %D
The date using the format @code{%m/%d/%y}.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %e
The day of the month like with @code{%d}, but padded with blank (range
@code{ 1} through @code{31}).
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %F
The date using the format @code{%Y-%m-%d}. This is the form specified
in the @w{ISO 8601} standard and is the preferred form for all uses.
This format was first standardized by @w{ISO C99} and by POSIX.1-2001.
@item %g
The year corresponding to the ISO week number, but without the century
(range @code{00} through @code{99}). This has the same format and value
as @code{%y}, except that if the ISO week number (see @code{%V}) belongs
to the previous or next year, that year is used instead.
This format was first standardized by @w{ISO C99} and by POSIX.1-2001.
@item %G
The year corresponding to the ISO week number. This has the same format
and value as @code{%Y}, except that if the ISO week number (see
@code{%V}) belongs to the previous or next year, that year is used
instead.
This format was first standardized by @w{ISO C99} and by POSIX.1-2001
but was previously available as a GNU extension.
@item %h
The abbreviated month name according to the current locale. The action
is the same as for @code{%b}.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %H
The hour as a decimal number, using a 24-hour clock (range @code{00} through
@code{23}).
@item %I
The hour as a decimal number, using a 12-hour clock (range @code{01} through
@code{12}).
@item %j
The day of the year as a decimal number (range @code{001} through @code{366}).
@item %k
The hour as a decimal number, using a 24-hour clock like @code{%H}, but
padded with blank (range @code{ 0} through @code{23}).
This format is a GNU extension.
@item %l
The hour as a decimal number, using a 12-hour clock like @code{%I}, but
padded with blank (range @code{ 1} through @code{12}).
This format is a GNU extension.
@item %m
The month as a decimal number (range @code{01} through @code{12}).
@item %M
The minute as a decimal number (range @code{00} through @code{59}).
@item %n
A single @samp{\n} (newline) character.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %p
Either @samp{AM} or @samp{PM}, according to the given time value; or the
corresponding strings for the current locale. Noon is treated as
@samp{PM} and midnight as @samp{AM}. In most locales
@samp{AM}/@samp{PM} format is not supported, in such cases @code{"%p"}
yields an empty string.
@ignore
We currently have a problem with makeinfo. Write @samp{AM} and @samp{am}
both results in `am'. I.e., the difference in case is not visible anymore.
@end ignore
@item %P
Either @samp{am} or @samp{pm}, according to the given time value; or the
corresponding strings for the current locale, printed in lowercase
characters. Noon is treated as @samp{pm} and midnight as @samp{am}. In
most locales @samp{AM}/@samp{PM} format is not supported, in such cases
@code{"%P"} yields an empty string.
This format is a GNU extension.
@item %r
The complete calendar time using the AM/PM format of the current locale.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
In the POSIX locale, this format is equivalent to @code{%I:%M:%S %p}.
@item %R
The hour and minute in decimal numbers using the format @code{%H:%M}.
This format was first standardized by @w{ISO C99} and by POSIX.1-2001
but was previously available as a GNU extension.
@item %s
The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
Leap seconds are not counted unless leap second support is available.
This format is a GNU extension.
@item %S
The seconds as a decimal number (range @code{00} through @code{60}).
@item %t
A single @samp{\t} (tabulator) character.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %T
The time of day using decimal numbers using the format @code{%H:%M:%S}.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %u
The day of the week as a decimal number (range @code{1} through
@code{7}), Monday being @code{1}.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %U
The week number of the current year as a decimal number (range @code{00}
through @code{53}), starting with the first Sunday as the first day of
the first week. Days preceding the first Sunday in the year are
considered to be in week @code{00}.
@item %V
The @w{ISO 8601:1988} week number as a decimal number (range @code{01}
through @code{53}). ISO weeks start with Monday and end with Sunday.
Week @code{01} of a year is the first week which has the majority of its
days in that year; this is equivalent to the week containing the year's
first Thursday, and it is also equivalent to the week containing January
4. Week @code{01} of a year can contain days from the previous year.
The week before week @code{01} of a year is the last week (@code{52} or
@code{53}) of the previous year even if it contains days from the new
year.
This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
@item %w
The day of the week as a decimal number (range @code{0} through
@code{6}), Sunday being @code{0}.
@item %W
The week number of the current year as a decimal number (range @code{00}
through @code{53}), starting with the first Monday as the first day of
the first week. All days preceding the first Monday in the year are
considered to be in week @code{00}.
@item %x
The preferred date representation for the current locale.
@item %X
The preferred time of day representation for the current locale.
@item %y
The year without a century as a decimal number (range @code{00} through
@code{99}). This is equivalent to the year modulo 100.
@item %Y
The year as a decimal number, using the Gregorian calendar. Years
before the year @code{1} are numbered @code{0}, @code{-1}, and so on.
@item %z
@w{RFC 822}/@w{ISO 8601:1988} style numeric time zone (e.g.,
@code{-0600} or @code{+0100}), or nothing if no time zone is
determinable.
This format was first standardized by @w{ISO C99} and by POSIX.1-2001
but was previously available as a GNU extension.
In the POSIX locale, a full @w{RFC 822} timestamp is generated by the format
@w{@samp{"%a, %d %b %Y %H:%M:%S %z"}} (or the equivalent
@w{@samp{"%a, %d %b %Y %T %z"}}).
@item %Z
The time zone abbreviation (empty if the time zone can't be determined).
@item %%
A literal @samp{%} character.
@end table
The @var{size} parameter can be used to specify the maximum number of
characters to be stored in the array @var{s}, including the terminating
null character. If the formatted time requires more than @var{size}
characters, @code{strftime} returns zero and the contents of the array
@var{s} are undefined. Otherwise the return value indicates the
number of characters placed in the array @var{s}, not including the
terminating null character.
@emph{Warning:} This convention for the return value which is prescribed
in @w{ISO C} can lead to problems in some situations. For certain
format strings and certain locales the output really can be the empty
string and this cannot be discovered by testing the return value only.
E.g., in most locales the AM/PM time format is not supported (most of
the world uses the 24 hour time representation). In such locales
@code{"%p"} will return the empty string, i.e., the return value is
zero. To detect situations like this something similar to the following
code should be used:
@smallexample
buf[0] = '\1';
len = strftime (buf, bufsize, format, tp);
if (len == 0 && buf[0] != '\0')
@{
/* Something went wrong in the strftime call. */
@dots{}
@}
@end smallexample
If @var{s} is a null pointer, @code{strftime} does not actually write
anything, but instead returns the number of characters it would have written.
Calling @code{strftime} also sets the current time zone as if
@code{tzset} were called; @code{strftime} uses this information
instead of @var{brokentime}'s @code{tm_gmtoff} and @code{tm_zone}
members. @xref{Time Zone Functions}.
For an example of @code{strftime}, see @ref{Time Functions Example}.
@end deftypefun
@comment time.h
@comment ISO/Amend1
@deftypefun size_t wcsftime (wchar_t *@var{s}, size_t @var{size}, const wchar_t *@var{template}, const struct tm *@var{brokentime})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c wcsftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c wcsftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c wcsftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c add ok
@c memset_zero dup ok
@c memset_space dup ok
@c wcslen dup ok
@c cpy ok
@c add dup ok
@c memcpy_lowcase ok
@c TOLOWER ok
@c towlower_l dup ok
@c memcpy_uppcase ok
@c TOUPPER ok
@c towupper_l dup ok
@c MEMCPY ok
@c wmemcpy dup ok
@c widen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c memset dup ok
@c mbsrtowcs_l @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps]
@c ISDIGIT ok
@c STRLEN ok
@c wcslen dup ok
@c wcsftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c TOUPPER dup ok
@c nl_get_era_entry dup @ascuheap @asulock @acsmem @aculock
@c DO_NUMBER ok
@c DO_NUMBER_SPACEPAD ok
@c nl_get_walt_digit dup @ascuheap @asulock @acsmem @aculock
@c libc_rwlock_wrlock dup @asulock @aculock
@c nl_init_alt_digit dup @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c memset dup ok
@c wcschr dup ok
@c libc_rwlock_unlock dup @aculock
@c memset_space ok
@c wmemset dup ok
@c memset_zero ok
@c wmemset dup ok
@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c iso_week_days ok
@c isleap ok
@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c tm_diff ok
The @code{wcsftime} function is equivalent to the @code{strftime}
function with the difference that it operates on wide character
strings. The buffer where the result is stored, pointed to by @var{s},
must be an array of wide characters. The parameter @var{size} which
specifies the size of the output buffer gives the number of wide
character, not the number of bytes.
Also the format string @var{template} is a wide character string. Since
all characters needed to specify the format string are in the basic
character set it is portably possible to write format strings in the C
source code using the @code{L"@dots{}"} notation. The parameter
@var{brokentime} has the same meaning as in the @code{strftime} call.
The @code{wcsftime} function supports the same flags, modifiers, and
format specifiers as the @code{strftime} function.
The return value of @code{wcsftime} is the number of wide characters
stored in @code{s}. When more characters would have to be written than
can be placed in the buffer @var{s} the return value is zero, with the
same problems indicated in the @code{strftime} documentation.
@end deftypefun
@node Parsing Date and Time
@subsection Convert textual time and date information back
The @w{ISO C} standard does not specify any functions which can convert
the output of the @code{strftime} function back into a binary format.
This led to a variety of more-or-less successful implementations with
different interfaces over the years. Then the Unix standard was
extended by the addition of two functions: @code{strptime} and
@code{getdate}. Both have strange interfaces but at least they are
widely available.
@menu
* Low-Level Time String Parsing:: Interpret string according to given format.
* General Time String Parsing:: User-friendly function to parse data and
time strings.
@end menu
@node Low-Level Time String Parsing
@subsubsection Interpret string according to given format
The first function is rather low-level. It is nevertheless frequently
used in software since it is better known. Its interface and
implementation are heavily influenced by the @code{getdate} function,
which is defined and implemented in terms of calls to @code{strptime}.
@comment time.h
@comment XPG4
@deftypefun {char *} strptime (const char *@var{s}, const char *@var{fmt}, struct tm *@var{tp})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c strptime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c strptime_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c memset dup ok
@c ISSPACE ok
@c isspace_l dup ok
@c match_char ok
@c match_string ok
@c strlen dup ok
@c strncasecmp_l dup ok
@c strcmp dup ok
@c recursive @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c strptime_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c get_number ok
@c ISSPACE dup ok
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c nl_select_era_entry @ascuheap @asulock @acsmem @aculock
@c nl_init_era_entries dup @ascuheap @asulock @acsmem @aculock
@c get_alt_number dup @ascuheap @asulock @acsmem @aculock
@c nl_parse_alt_digit dup @ascuheap @asulock @acsmem @aculock
@c libc_rwlock_wrlock dup @asulock @aculock
@c nl_init_alt_digit dup @ascuheap @acsmem
@c libc_rwlock_unlock dup @aculock
@c get_number dup ok
@c day_of_the_week ok
@c day_of_the_year ok
The @code{strptime} function parses the input string @var{s} according
to the format string @var{fmt} and stores its results in the
structure @var{tp}.
The input string could be generated by a @code{strftime} call or
obtained any other way. It does not need to be in a human-recognizable
format; e.g. a date passed as @code{"02:1999:9"} is acceptable, even
though it is ambiguous without context. As long as the format string
@var{fmt} matches the input string the function will succeed.
The user has to make sure, though, that the input can be parsed in a
unambiguous way. The string @code{"1999112"} can be parsed using the
format @code{"%Y%m%d"} as 1999-1-12, 1999-11-2, or even 19991-1-2. It
is necessary to add appropriate separators to reliably get results.
The format string consists of the same components as the format string
of the @code{strftime} function. The only difference is that the flags
@code{_}, @code{-}, @code{0}, and @code{^} are not allowed.
@comment Is this really the intention? --drepper
Several of the distinct formats of @code{strftime} do the same work in
@code{strptime} since differences like case of the input do not matter.
For reasons of symmetry all formats are supported, though.
The modifiers @code{E} and @code{O} are also allowed everywhere the
@code{strftime} function allows them.
The formats are:
@table @code
@item %a
@itemx %A
The weekday name according to the current locale, in abbreviated form or
the full name.
@item %b
@itemx %B
@itemx %h
The month name according to the current locale, in abbreviated form or
the full name.
@item %c
The date and time representation for the current locale.
@item %Ec
Like @code{%c} but the locale's alternative date and time format is used.
@item %C
The century of the year.
It makes sense to use this format only if the format string also
contains the @code{%y} format.
@item %EC
The locale's representation of the period.
Unlike @code{%C} it sometimes makes sense to use this format since some
cultures represent years relative to the beginning of eras instead of
using the Gregorian years.
@item %d
@item %e
The day of the month as a decimal number (range @code{1} through @code{31}).
Leading zeroes are permitted but not required.
@item %Od
@itemx %Oe
Same as @code{%d} but using the locale's alternative numeric symbols.
Leading zeroes are permitted but not required.
@item %D
Equivalent to @code{%m/%d/%y}.
@item %F
Equivalent to @code{%Y-%m-%d}, which is the @w{ISO 8601} date
format.
This is a GNU extension following an @w{ISO C99} extension to
@code{strftime}.
@item %g
The year corresponding to the ISO week number, but without the century
(range @code{00} through @code{99}).
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
This format is a GNU extension following a GNU extension of @code{strftime}.
@item %G
The year corresponding to the ISO week number.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
This format is a GNU extension following a GNU extension of @code{strftime}.
@item %H
@itemx %k
The hour as a decimal number, using a 24-hour clock (range @code{00} through
@code{23}).
@code{%k} is a GNU extension following a GNU extension of @code{strftime}.
@item %OH
Same as @code{%H} but using the locale's alternative numeric symbols.
@item %I
@itemx %l
The hour as a decimal number, using a 12-hour clock (range @code{01} through
@code{12}).
@code{%l} is a GNU extension following a GNU extension of @code{strftime}.
@item %OI
Same as @code{%I} but using the locale's alternative numeric symbols.
@item %j
The day of the year as a decimal number (range @code{1} through @code{366}).
Leading zeroes are permitted but not required.
@item %m
The month as a decimal number (range @code{1} through @code{12}).
Leading zeroes are permitted but not required.
@item %Om
Same as @code{%m} but using the locale's alternative numeric symbols.
@item %M
The minute as a decimal number (range @code{0} through @code{59}).
Leading zeroes are permitted but not required.
@item %OM
Same as @code{%M} but using the locale's alternative numeric symbols.
@item %n
@itemx %t
Matches any white space.
@item %p
@item %P
The locale-dependent equivalent to @samp{AM} or @samp{PM}.
This format is not useful unless @code{%I} or @code{%l} is also used.
Another complication is that the locale might not define these values at
all and therefore the conversion fails.
@code{%P} is a GNU extension following a GNU extension to @code{strftime}.
@item %r
The complete time using the AM/PM format of the current locale.
A complication is that the locale might not define this format at all
and therefore the conversion fails.
@item %R
The hour and minute in decimal numbers using the format @code{%H:%M}.
@code{%R} is a GNU extension following a GNU extension to @code{strftime}.
@item %s
The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
Leap seconds are not counted unless leap second support is available.
@code{%s} is a GNU extension following a GNU extension to @code{strftime}.
@item %S
The seconds as a decimal number (range @code{0} through @code{60}).
Leading zeroes are permitted but not required.
@strong{NB:} The Unix specification says the upper bound on this value
is @code{61}, a result of a decision to allow double leap seconds. You
will not see the value @code{61} because no minute has more than one
leap second, but the myth persists.
@item %OS
Same as @code{%S} but using the locale's alternative numeric symbols.
@item %T
Equivalent to the use of @code{%H:%M:%S} in this place.
@item %u
The day of the week as a decimal number (range @code{1} through
@code{7}), Monday being @code{1}.
Leading zeroes are permitted but not required.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
@item %U
The week number of the current year as a decimal number (range @code{0}
through @code{53}).
Leading zeroes are permitted but not required.
@item %OU
Same as @code{%U} but using the locale's alternative numeric symbols.
@item %V
The @w{ISO 8601:1988} week number as a decimal number (range @code{1}
through @code{53}).
Leading zeroes are permitted but not required.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
@item %w
The day of the week as a decimal number (range @code{0} through
@code{6}), Sunday being @code{0}.
Leading zeroes are permitted but not required.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
@item %Ow
Same as @code{%w} but using the locale's alternative numeric symbols.
@item %W
The week number of the current year as a decimal number (range @code{0}
through @code{53}).
Leading zeroes are permitted but not required.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
@item %OW
Same as @code{%W} but using the locale's alternative numeric symbols.
@item %x
The date using the locale's date format.
@item %Ex
Like @code{%x} but the locale's alternative data representation is used.
@item %X
The time using the locale's time format.
@item %EX
Like @code{%X} but the locale's alternative time representation is used.
@item %y
The year without a century as a decimal number (range @code{0} through
@code{99}).
Leading zeroes are permitted but not required.
Note that it is questionable to use this format without
the @code{%C} format. The @code{strptime} function does regard input
values in the range @math{68} to @math{99} as the years @math{1969} to
@math{1999} and the values @math{0} to @math{68} as the years
@math{2000} to @math{2068}. But maybe this heuristic fails for some
input data.
Therefore it is best to avoid @code{%y} completely and use @code{%Y}
instead.
@item %Ey
The offset from @code{%EC} in the locale's alternative representation.
@item %Oy
The offset of the year (from @code{%C}) using the locale's alternative
numeric symbols.
@item %Y
The year as a decimal number, using the Gregorian calendar.
@item %EY
The full alternative year representation.
@item %z
The offset from GMT in @w{ISO 8601}/RFC822 format.
@item %Z
The timezone name.
@emph{Note:} Currently, this is not fully implemented. The format is
recognized, input is consumed but no field in @var{tm} is set.
@item %%
A literal @samp{%} character.
@end table
All other characters in the format string must have a matching character
in the input string. Exceptions are white spaces in the input string
which can match zero or more whitespace characters in the format string.
@strong{Portability Note:} The XPG standard advises applications to use
at least one whitespace character (as specified by @code{isspace}) or
other non-alphanumeric characters between any two conversion
specifications. @Theglibc{} does not have this limitation but
other libraries might have trouble parsing formats like
@code{"%d%m%Y%H%M%S"}.
The @code{strptime} function processes the input string from right to
left. Each of the three possible input elements (white space, literal,
or format) are handled one after the other. If the input cannot be
matched to the format string the function stops. The remainder of the
format and input strings are not processed.
The function returns a pointer to the first character it was unable to
process. If the input string contains more characters than required by
the format string the return value points right after the last consumed
input character. If the whole input string is consumed the return value
points to the @code{NULL} byte at the end of the string. If an error
occurs, i.e., @code{strptime} fails to match all of the format string,
the function returns @code{NULL}.
@end deftypefun
The specification of the function in the XPG standard is rather vague,
leaving out a few important pieces of information. Most importantly, it
does not specify what happens to those elements of @var{tm} which are
not directly initialized by the different formats. The
implementations on different Unix systems vary here.
The @glibcadj{} implementation does not touch those fields which are not
directly initialized. Exceptions are the @code{tm_wday} and
@code{tm_yday} elements, which are recomputed if any of the year, month,
or date elements changed. This has two implications:
@itemize @bullet
@item
Before calling the @code{strptime} function for a new input string, you
should prepare the @var{tm} structure you pass. Normally this will mean
initializing all values are to zero. Alternatively, you can set all
fields to values like @code{INT_MAX}, allowing you to determine which
elements were set by the function call. Zero does not work here since
it is a valid value for many of the fields.
Careful initialization is necessary if you want to find out whether a
certain field in @var{tm} was initialized by the function call.
@item
You can construct a @code{struct tm} value with several consecutive
@code{strptime} calls. A useful application of this is e.g. the parsing
of two separate strings, one containing date information and the other
time information. By parsing one after the other without clearing the
structure in-between, you can construct a complete broken-down time.
@end itemize
The following example shows a function which parses a string which is
contains the date information in either US style or @w{ISO 8601} form:
@smallexample
const char *
parse_date (const char *input, struct tm *tm)
@{
const char *cp;
/* @r{First clear the result structure.} */
memset (tm, '\0', sizeof (*tm));
/* @r{Try the ISO format first.} */
cp = strptime (input, "%F", tm);
if (cp == NULL)
@{
/* @r{Does not match. Try the US form.} */
cp = strptime (input, "%D", tm);
@}
return cp;
@}
@end smallexample
@node General Time String Parsing
@subsubsection A More User-friendly Way to Parse Times and Dates
The Unix standard defines another function for parsing date strings.
The interface is weird, but if the function happens to suit your
application it is just fine. It is problematic to use this function
in multi-threaded programs or libraries, since it returns a pointer to
a static variable, and uses a global variable and global state (an
environment variable).
@comment time.h
@comment Unix98
@defvar getdate_err
This variable of type @code{int} contains the error code of the last
unsuccessful call to @code{getdate}. Defined values are:
@table @math
@item 1
The environment variable @code{DATEMSK} is not defined or null.
@item 2
The template file denoted by the @code{DATEMSK} environment variable
cannot be opened.
@item 3
Information about the template file cannot retrieved.
@item 4
The template file is not a regular file.
@item 5
An I/O error occurred while reading the template file.
@item 6
Not enough memory available to execute the function.
@item 7
The template file contains no matching template.
@item 8
The input date is invalid, but would match a template otherwise. This
includes dates like February 31st, and dates which cannot be represented
in a @code{time_t} variable.
@end table
@end defvar
@comment time.h
@comment Unix98
@deftypefun {struct tm *} getdate (const char *@var{string})
@safety{@prelim{}@mtunsafe{@mtasurace{:getdate} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c getdate @mtasurace:getdate @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c getdate_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
The interface to @code{getdate} is the simplest possible for a function
to parse a string and return the value. @var{string} is the input
string and the result is returned in a statically-allocated variable.
The details about how the string is processed are hidden from the user.
In fact, they can be outside the control of the program. Which formats
are recognized is controlled by the file named by the environment
variable @code{DATEMSK}. This file should contain
lines of valid format strings which could be passed to @code{strptime}.
The @code{getdate} function reads these format strings one after the
other and tries to match the input string. The first line which
completely matches the input string is used.
Elements not initialized through the format string retain the values
present at the time of the @code{getdate} function call.
The formats recognized by @code{getdate} are the same as for
@code{strptime}. See above for an explanation. There are only a few
extensions to the @code{strptime} behavior:
@itemize @bullet
@item
If the @code{%Z} format is given the broken-down time is based on the
current time of the timezone matched, not of the current timezone of the
runtime environment.
@emph{Note}: This is not implemented (currently). The problem is that
timezone names are not unique. If a fixed timezone is assumed for a
given string (say @code{EST} meaning US East Coast time), then uses for
countries other than the USA will fail. So far we have found no good
solution to this.
@item
If only the weekday is specified the selected day depends on the current
date. If the current weekday is greater or equal to the @code{tm_wday}
value the current week's day is chosen, otherwise the day next week is chosen.
@item
A similar heuristic is used when only the month is given and not the
year. If the month is greater than or equal to the current month, then
the current year is used. Otherwise it wraps to next year. The first
day of the month is assumed if one is not explicitly specified.
@item
The current hour, minute, and second are used if the appropriate value is
not set through the format.
@item
If no date is given tomorrow's date is used if the time is
smaller than the current time. Otherwise today's date is taken.
@end itemize
It should be noted that the format in the template file need not only
contain format elements. The following is a list of possible format
strings (taken from the Unix standard):
@smallexample
%m
%A %B %d, %Y %H:%M:%S
%A
%B
%m/%d/%y %I %p
%d,%m,%Y %H:%M
at %A the %dst of %B in %Y
run job at %I %p,%B %dnd
%A den %d. %B %Y %H.%M Uhr
@end smallexample
As you can see, the template list can contain very specific strings like
@code{run job at %I %p,%B %dnd}. Using the above list of templates and
assuming the current time is Mon Sep 22 12:19:47 EDT 1986 we can obtain the
following results for the given input.
@multitable {xxxxxxxxxxxx} {xxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}
@item Input @tab Match @tab Result
@item Mon @tab %a @tab Mon Sep 22 12:19:47 EDT 1986
@item Sun @tab %a @tab Sun Sep 28 12:19:47 EDT 1986
@item Fri @tab %a @tab Fri Sep 26 12:19:47 EDT 1986
@item September @tab %B @tab Mon Sep 1 12:19:47 EDT 1986
@item January @tab %B @tab Thu Jan 1 12:19:47 EST 1987
@item December @tab %B @tab Mon Dec 1 12:19:47 EST 1986
@item Sep Mon @tab %b %a @tab Mon Sep 1 12:19:47 EDT 1986
@item Jan Fri @tab %b %a @tab Fri Jan 2 12:19:47 EST 1987
@item Dec Mon @tab %b %a @tab Mon Dec 1 12:19:47 EST 1986
@item Jan Wed 1989 @tab %b %a %Y @tab Wed Jan 4 12:19:47 EST 1989
@item Fri 9 @tab %a %H @tab Fri Sep 26 09:00:00 EDT 1986
@item Feb 10:30 @tab %b %H:%S @tab Sun Feb 1 10:00:30 EST 1987
@item 10:30 @tab %H:%M @tab Tue Sep 23 10:30:00 EDT 1986
@item 13:30 @tab %H:%M @tab Mon Sep 22 13:30:00 EDT 1986
@end multitable
The return value of the function is a pointer to a static variable of
type @w{@code{struct tm}}, or a null pointer if an error occurred. The
result is only valid until the next @code{getdate} call, making this
function unusable in multi-threaded applications.
The @code{errno} variable is @emph{not} changed. Error conditions are
stored in the global variable @code{getdate_err}. See the
description above for a list of the possible error values.
@emph{Warning:} The @code{getdate} function should @emph{never} be
used in SUID-programs. The reason is obvious: using the
@code{DATEMSK} environment variable you can get the function to open
any arbitrary file and chances are high that with some bogus input
(such as a binary file) the program will crash.
@end deftypefun
@comment time.h
@comment GNU
@deftypefun int getdate_r (const char *@var{string}, struct tm *@var{tp})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c getdate_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c getenv dup @mtsenv
@c stat64 dup ok
@c access dup ok
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive]
@c isspace dup @mtslocale
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c memcpy dup ok
@c getline dup @ascuheap @acsmem [no @asucorrupt @aculock @acucorrupt, exclusive]
@c strptime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c feof_unlocked dup ok
@c free dup @ascuheap @acsmem
@c ferror_unlocked dup dup ok
@c time dup ok
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c first_wday @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c memset dup ok
@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c check_mday ok
@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
The @code{getdate_r} function is the reentrant counterpart of
@code{getdate}. It does not use the global variable @code{getdate_err}
to signal an error, but instead returns an error code. The same error
codes as described in the @code{getdate_err} documentation above are
used, with 0 meaning success.
Moreover, @code{getdate_r} stores the broken-down time in the variable
of type @code{struct tm} pointed to by the second argument, rather than
in a static variable.
This function is not defined in the Unix standard. Nevertheless it is
available on some other Unix systems as well.
The warning against using @code{getdate} in SUID-programs applies to
@code{getdate_r} as well.
@end deftypefun
@node TZ Variable
@subsection Specifying the Time Zone with @code{TZ}
In POSIX systems, a user can specify the time zone by means of the
@code{TZ} environment variable. For information about how to set
environment variables, see @ref{Environment Variables}. The functions
for accessing the time zone are declared in @file{time.h}.
@pindex time.h
@cindex time zone
You should not normally need to set @code{TZ}. If the system is
configured properly, the default time zone will be correct. You might
set @code{TZ} if you are using a computer over a network from a
different time zone, and would like times reported to you in the time
zone local to you, rather than what is local to the computer.
In POSIX.1 systems the value of the @code{TZ} variable can be in one of
three formats. With @theglibc{}, the most common format is the
last one, which can specify a selection from a large database of time
zone information for many regions of the world. The first two formats
are used to describe the time zone information directly, which is both
more cumbersome and less precise. But the POSIX.1 standard only
specifies the details of the first two formats, so it is good to be
familiar with them in case you come across a POSIX.1 system that doesn't
support a time zone information database.
The first format is used when there is no Daylight Saving Time (or
summer time) in the local time zone:
@smallexample
@r{@var{std} @var{offset}}
@end smallexample
The @var{std} string specifies the name of the time zone. It must be
three or more characters long and must not contain a leading colon,
embedded digits, commas, nor plus and minus signs. There is no space
character separating the time zone name from the @var{offset}, so these
restrictions are necessary to parse the specification correctly.
The @var{offset} specifies the time value you must add to the local time
to get a Coordinated Universal Time value. It has syntax like
[@code{+}|@code{-}]@var{hh}[@code{:}@var{mm}[@code{:}@var{ss}]]. This
is positive if the local time zone is west of the Prime Meridian and
negative if it is east. The hour must be between @code{0} and
@code{24}, and the minute and seconds between @code{0} and @code{59}.
For example, here is how we would specify Eastern Standard Time, but
without any Daylight Saving Time alternative:
@smallexample
EST+5
@end smallexample
The second format is used when there is Daylight Saving Time:
@smallexample
@r{@var{std} @var{offset} @var{dst} [@var{offset}]@code{,}@var{start}[@code{/}@var{time}]@code{,}@var{end}[@code{/}@var{time}]}
@end smallexample
The initial @var{std} and @var{offset} specify the standard time zone, as
described above. The @var{dst} string and @var{offset} specify the name
and offset for the corresponding Daylight Saving Time zone; if the
@var{offset} is omitted, it defaults to one hour ahead of standard time.
The remainder of the specification describes when Daylight Saving Time is
in effect. The @var{start} field is when Daylight Saving Time goes into
effect and the @var{end} field is when the change is made back to standard
time. The following formats are recognized for these fields:
@table @code
@item J@var{n}
This specifies the Julian day, with @var{n} between @code{1} and @code{365}.
February 29 is never counted, even in leap years.
@item @var{n}
This specifies the Julian day, with @var{n} between @code{0} and @code{365}.
February 29 is counted in leap years.
@item M@var{m}.@var{w}.@var{d}
This specifies day @var{d} of week @var{w} of month @var{m}. The day
@var{d} must be between @code{0} (Sunday) and @code{6}. The week
@var{w} must be between @code{1} and @code{5}; week @code{1} is the
first week in which day @var{d} occurs, and week @code{5} specifies the
@emph{last} @var{d} day in the month. The month @var{m} should be
between @code{1} and @code{12}.
@end table
The @var{time} fields specify when, in the local time currently in
effect, the change to the other time occurs. If omitted, the default is
@code{02:00:00}. The hours part of the time fields can range from
@minus{}167 through 167; this is an extension to POSIX.1, which allows
only the range 0 through 24.
Here are some example @code{TZ} values, including the appropriate
Daylight Saving Time and its dates of applicability. In North
American Eastern Standard Time (EST) and Eastern Daylight Time (EDT),
the normal offset from UTC is 5 hours; since this is
west of the prime meridian, the sign is positive. Summer time begins on
March's second Sunday at 2:00am, and ends on November's first Sunday
at 2:00am.
@smallexample
EST+5EDT,M3.2.0/2,M11.1.0/2
@end smallexample
Israel Standard Time (IST) and Israel Daylight Time (IDT) are 2 hours
ahead of the prime meridian in winter, springing forward an hour on
March's fourth Tuesday at 26:00 (i.e., 02:00 on the first Friday on or
after March 23), and falling back on October's last Sunday at 02:00.
@smallexample
IST-2IDT,M3.4.4/26,M10.5.0
@end smallexample
Western Argentina Summer Time (WARST) is 3 hours behind the prime
meridian all year. There is a dummy fall-back transition on December
31 at 25:00 daylight saving time (i.e., 24:00 standard time,
equivalent to January 1 at 00:00 standard time), and a simultaneous
spring-forward transition on January 1 at 00:00 standard time, so
daylight saving time is in effect all year and the initial @code{WART}
is a placeholder.
@smallexample
WART4WARST,J1/0,J365/25
@end smallexample
Western Greenland Time (WGT) and Western Greenland Summer Time (WGST)
are 3 hours behind UTC in the winter. Its clocks follow the European
Union rules of springing forward by one hour on March's last Sunday at
01:00 UTC (@minus{}02:00 local time) and falling back on October's
last Sunday at 01:00 UTC (@minus{}01:00 local time).
@smallexample
WGT3WGST,M3.5.0/-2,M10.5.0/-1
@end smallexample
The schedule of Daylight Saving Time in any particular jurisdiction has
changed over the years. To be strictly correct, the conversion of dates
and times in the past should be based on the schedule that was in effect
then. However, this format has no facilities to let you specify how the
schedule has changed from year to year. The most you can do is specify
one particular schedule---usually the present day schedule---and this is
used to convert any date, no matter when. For precise time zone
specifications, it is best to use the time zone information database
(see below).
The third format looks like this:
@smallexample
:@var{characters}
@end smallexample
Each operating system interprets this format differently; in
@theglibc{}, @var{characters} is the name of a file which describes the time
zone.
@pindex /etc/localtime
@pindex localtime
If the @code{TZ} environment variable does not have a value, the
operation chooses a time zone by default. In @theglibc{}, the
default time zone is like the specification @samp{TZ=:/etc/localtime}
(or @samp{TZ=:/usr/local/etc/localtime}, depending on how @theglibc{}
was configured; @pxref{Installation}). Other C libraries use their own
rule for choosing the default time zone, so there is little we can say
about them.
@cindex time zone database
@pindex /share/lib/zoneinfo
@pindex zoneinfo
If @var{characters} begins with a slash, it is an absolute file name;
otherwise the library looks for the file
@w{@file{/share/lib/zoneinfo/@var{characters}}}. The @file{zoneinfo}
directory contains data files describing local time zones in many
different parts of the world. The names represent major cities, with
subdirectories for geographical areas; for example,
@file{America/New_York}, @file{Europe/London}, @file{Asia/Hong_Kong}.
These data files are installed by the system administrator, who also
sets @file{/etc/localtime} to point to the data file for the local time
zone. @Theglibc{} comes with a large database of time zone
information for most regions of the world, which is maintained by a
community of volunteers and put in the public domain.
@node Time Zone Functions
@subsection Functions and Variables for Time Zones
@comment time.h
@comment POSIX.1
@deftypevar {char *} tzname [2]
The array @code{tzname} contains two strings, which are the standard
names of the pair of time zones (standard and Daylight
Saving) that the user has selected. @code{tzname[0]} is the name of
the standard time zone (for example, @code{"EST"}), and @code{tzname[1]}
is the name for the time zone when Daylight Saving Time is in use (for
example, @code{"EDT"}). These correspond to the @var{std} and @var{dst}
strings (respectively) from the @code{TZ} environment variable. If
Daylight Saving Time is never used, @code{tzname[1]} is the empty string.
The @code{tzname} array is initialized from the @code{TZ} environment
variable whenever @code{tzset}, @code{ctime}, @code{strftime},
@code{mktime}, or @code{localtime} is called. If multiple abbreviations
have been used (e.g. @code{"EWT"} and @code{"EDT"} for U.S. Eastern War
Time and Eastern Daylight Time), the array contains the most recent
abbreviation.
The @code{tzname} array is required for POSIX.1 compatibility, but in
GNU programs it is better to use the @code{tm_zone} member of the
broken-down time structure, since @code{tm_zone} reports the correct
abbreviation even when it is not the latest one.
Though the strings are declared as @code{char *} the user must refrain
from modifying these strings. Modifying the strings will almost certainly
lead to trouble.
@end deftypevar
@comment time.h
@comment POSIX.1
@deftypefun void tzset (void)
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c tzset @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c tzset_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_unlock dup @aculock
The @code{tzset} function initializes the @code{tzname} variable from
the value of the @code{TZ} environment variable. It is not usually
necessary for your program to call this function, because it is called
automatically when you use the other time conversion functions that
depend on the time zone.
@end deftypefun
The following variables are defined for compatibility with System V
Unix. Like @code{tzname}, these variables are set by calling
@code{tzset} or the other time conversion functions.
@comment time.h
@comment SVID
@deftypevar {long int} timezone
This contains the difference between UTC and the latest local standard
time, in seconds west of UTC. For example, in the U.S. Eastern time
zone, the value is @code{5*60*60}. Unlike the @code{tm_gmtoff} member
of the broken-down time structure, this value is not adjusted for
daylight saving, and its sign is reversed. In GNU programs it is better
to use @code{tm_gmtoff}, since it contains the correct offset even when
it is not the latest one.
@end deftypevar
@comment time.h
@comment SVID
@deftypevar int daylight
This variable has a nonzero value if Daylight Saving Time rules apply.
A nonzero value does not necessarily mean that Daylight Saving Time is
now in effect; it means only that Daylight Saving Time is sometimes in
effect.
@end deftypevar
@node Time Functions Example
@subsection Time Functions Example
Here is an example program showing the use of some of the calendar time
functions.
@smallexample
@include strftim.c.texi
@end smallexample
It produces output like this:
@smallexample
Wed Jul 31 13:02:36 1991
Today is Wednesday, July 31.
The time is 01:02 PM.
@end smallexample
@node Setting an Alarm
@section Setting an Alarm
The @code{alarm} and @code{setitimer} functions provide a mechanism for a
process to interrupt itself in the future. They do this by setting a
timer; when the timer expires, the process receives a signal.
@cindex setting an alarm
@cindex interval timer, setting
@cindex alarms, setting
@cindex timers, setting
Each process has three independent interval timers available:
@itemize @bullet
@item
A real-time timer that counts elapsed time. This timer sends a
@code{SIGALRM} signal to the process when it expires.
@cindex real-time timer
@cindex timer, real-time
@item
A virtual timer that counts processor time used by the process. This timer
sends a @code{SIGVTALRM} signal to the process when it expires.
@cindex virtual timer
@cindex timer, virtual
@item
A profiling timer that counts both processor time used by the process,
and processor time spent in system calls on behalf of the process. This
timer sends a @code{SIGPROF} signal to the process when it expires.
@cindex profiling timer
@cindex timer, profiling
This timer is useful for profiling in interpreters. The interval timer
mechanism does not have the fine granularity necessary for profiling
native code.
@c @xref{profil} !!!
@end itemize
You can only have one timer of each kind set at any given time. If you
set a timer that has not yet expired, that timer is simply reset to the
new value.
You should establish a handler for the appropriate alarm signal using
@code{signal} or @code{sigaction} before issuing a call to
@code{setitimer} or @code{alarm}. Otherwise, an unusual chain of events
could cause the timer to expire before your program establishes the
handler. In this case it would be terminated, since termination is the
default action for the alarm signals. @xref{Signal Handling}.
To be able to use the alarm function to interrupt a system call which
might block otherwise indefinitely it is important to @emph{not} set the
@code{SA_RESTART} flag when registering the signal handler using
@code{sigaction}. When not using @code{sigaction} things get even
uglier: the @code{signal} function has to fixed semantics with respect
to restarts. The BSD semantics for this function is to set the flag.
Therefore, if @code{sigaction} for whatever reason cannot be used, it is
necessary to use @code{sysv_signal} and not @code{signal}.
The @code{setitimer} function is the primary means for setting an alarm.
This facility is declared in the header file @file{sys/time.h}. The
@code{alarm} function, declared in @file{unistd.h}, provides a somewhat
simpler interface for setting the real-time timer.
@pindex unistd.h
@pindex sys/time.h
@comment sys/time.h
@comment BSD
@deftp {Data Type} {struct itimerval}
This structure is used to specify when a timer should expire. It contains
the following members:
@table @code
@item struct timeval it_interval
This is the period between successive timer interrupts. If zero, the
alarm will only be sent once.
@item struct timeval it_value
This is the period between now and the first timer interrupt. If zero,
the alarm is disabled.
@end table
The @code{struct timeval} data type is described in @ref{Elapsed Time}.
@end deftp
@comment sys/time.h
@comment BSD
@deftypefun int setitimer (int @var{which}, const struct itimerval *@var{new}, struct itimerval *@var{old})
@safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}}
@c This function is marked with @mtstimer because the same set of timers
@c is shared by all threads of a process, so calling it in one thread
@c may interfere with timers set by another thread. This interference
@c is not regarded as destructive, because the interface specification
@c makes this overriding while returning the previous value the expected
@c behavior, and the kernel will serialize concurrent calls so that the
@c last one prevails, with each call getting the timer information from
@c the timer installed by the previous call in that serialization.
The @code{setitimer} function sets the timer specified by @var{which}
according to @var{new}. The @var{which} argument can have a value of
@code{ITIMER_REAL}, @code{ITIMER_VIRTUAL}, or @code{ITIMER_PROF}.
If @var{old} is not a null pointer, @code{setitimer} returns information
about any previous unexpired timer of the same kind in the structure it
points to.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The timer period is too large.
@end table
@end deftypefun
@comment sys/time.h
@comment BSD
@deftypefun int getitimer (int @var{which}, struct itimerval *@var{old})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getitimer} function stores information about the timer specified
by @var{which} in the structure pointed at by @var{old}.
The return value and error conditions are the same as for @code{setitimer}.
@end deftypefun
@comment sys/time.h
@comment BSD
@vtable @code
@item ITIMER_REAL
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the real-time
timer.
@comment sys/time.h
@comment BSD
@item ITIMER_VIRTUAL
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the virtual
timer.
@comment sys/time.h
@comment BSD
@item ITIMER_PROF
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the profiling
timer.
@end vtable
@comment unistd.h
@comment POSIX.1
@deftypefun {unsigned int} alarm (unsigned int @var{seconds})
@safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}}
@c Wrapper for setitimer.
The @code{alarm} function sets the real-time timer to expire in
@var{seconds} seconds. If you want to cancel any existing alarm, you
can do this by calling @code{alarm} with a @var{seconds} argument of
zero.
The return value indicates how many seconds remain before the previous
alarm would have been sent. If there is no previous alarm, @code{alarm}
returns zero.
@end deftypefun
The @code{alarm} function could be defined in terms of @code{setitimer}
like this:
@smallexample
unsigned int
alarm (unsigned int seconds)
@{
struct itimerval old, new;
new.it_interval.tv_usec = 0;
new.it_interval.tv_sec = 0;
new.it_value.tv_usec = 0;
new.it_value.tv_sec = (long int) seconds;
if (setitimer (ITIMER_REAL, &new, &old) < 0)
return 0;
else
return old.it_value.tv_sec;
@}
@end smallexample
There is an example showing the use of the @code{alarm} function in
@ref{Handler Returns}.
If you simply want your process to wait for a given number of seconds,
you should use the @code{sleep} function. @xref{Sleeping}.
You shouldn't count on the signal arriving precisely when the timer
expires. In a multiprocessing environment there is typically some
amount of delay involved.
@strong{Portability Note:} The @code{setitimer} and @code{getitimer}
functions are derived from BSD Unix, while the @code{alarm} function is
specified by the POSIX.1 standard. @code{setitimer} is more powerful than
@code{alarm}, but @code{alarm} is more widely used.
@node Sleeping
@section Sleeping
The function @code{sleep} gives a simple way to make the program wait
for a short interval. If your program doesn't use signals (except to
terminate), then you can expect @code{sleep} to wait reliably throughout
the specified interval. Otherwise, @code{sleep} can return sooner if a
signal arrives; if you want to wait for a given interval regardless of
signals, use @code{select} (@pxref{Waiting for I/O}) and don't specify
any descriptors to wait for.
@c !!! select can get EINTR; using SA_RESTART makes sleep win too.
@comment unistd.h
@comment POSIX.1
@deftypefun {unsigned int} sleep (unsigned int @var{seconds})
@safety{@prelim{}@mtunsafe{@mtascusig{:SIGCHLD/linux}}@asunsafe{}@acunsafe{}}
@c On Mach, it uses ports and calls time. On generic posix, it calls
@c nanosleep. On Linux, it temporarily blocks SIGCHLD, which is MT- and
@c AS-Unsafe, and in a way that makes it AC-Unsafe (C-unsafe, even!).
The @code{sleep} function waits for @var{seconds} or until a signal
is delivered, whichever happens first.
If @code{sleep} function returns because the requested interval is over,
it returns a value of zero. If it returns because of delivery of a
signal, its return value is the remaining time in the sleep interval.
The @code{sleep} function is declared in @file{unistd.h}.
@end deftypefun
Resist the temptation to implement a sleep for a fixed amount of time by
using the return value of @code{sleep}, when nonzero, to call
@code{sleep} again. This will work with a certain amount of accuracy as
long as signals arrive infrequently. But each signal can cause the
eventual wakeup time to be off by an additional second or so. Suppose a
few signals happen to arrive in rapid succession by bad luck---there is
no limit on how much this could shorten or lengthen the wait.
Instead, compute the calendar time at which the program should stop
waiting, and keep trying to wait until that calendar time. This won't
be off by more than a second. With just a little more work, you can use
@code{select} and make the waiting period quite accurate. (Of course,
heavy system load can cause additional unavoidable delays---unless the
machine is dedicated to one application, there is no way you can avoid
this.)
On some systems, @code{sleep} can do strange things if your program uses
@code{SIGALRM} explicitly. Even if @code{SIGALRM} signals are being
ignored or blocked when @code{sleep} is called, @code{sleep} might
return prematurely on delivery of a @code{SIGALRM} signal. If you have
established a handler for @code{SIGALRM} signals and a @code{SIGALRM}
signal is delivered while the process is sleeping, the action taken
might be just to cause @code{sleep} to return instead of invoking your
handler. And, if @code{sleep} is interrupted by delivery of a signal
whose handler requests an alarm or alters the handling of @code{SIGALRM},
this handler and @code{sleep} will interfere.
On @gnusystems{}, it is safe to use @code{sleep} and @code{SIGALRM} in
the same program, because @code{sleep} does not work by means of
@code{SIGALRM}.
@comment time.h
@comment POSIX.1
@deftypefun int nanosleep (const struct timespec *@var{requested_time}, struct timespec *@var{remaining})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On Linux, it's a syscall. On Mach, it calls gettimeofday and uses
@c ports.
If resolution to seconds is not enough the @code{nanosleep} function can
be used. As the name suggests the sleep interval can be specified in
nanoseconds. The actual elapsed time of the sleep interval might be
longer since the system rounds the elapsed time you request up to the
next integer multiple of the actual resolution the system can deliver.
*@code{requested_time} is the elapsed time of the interval you want to
sleep.
The function returns as *@code{remaining} the elapsed time left in the
interval for which you requested to sleep. If the interval completed
without getting interrupted by a signal, this is zero.
@code{struct timespec} is described in @xref{Elapsed Time}.
If the function returns because the interval is over the return value is
zero. If the function returns @math{-1} the global variable @var{errno}
is set to the following values:
@table @code
@item EINTR
The call was interrupted because a signal was delivered to the thread.
If the @var{remaining} parameter is not the null pointer the structure
pointed to by @var{remaining} is updated to contain the remaining
elapsed time.
@item EINVAL
The nanosecond value in the @var{requested_time} parameter contains an
illegal value. Either the value is negative or greater than or equal to
1000 million.
@end table
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{nanosleep} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{nanosleep} should
be protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{nanosleep} function is declared in @file{time.h}.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/fdl-1.3.texi 0000664 0001750 0001750 00000055607 12275120646 021533 0 ustar adconrad adconrad @c The GNU Free Documentation License.
@center Version 1.3, 3 November 2008
@c This file is intended to be included within another document,
@c hence no sectioning command or @node.
@display
Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
@uref{http://fsf.org/}
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
@end display
@enumerate 0
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PREAMBLE
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@item
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@item
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@enumerate A
@item
Use in the Title Page (and on the covers, if any) a title distinct
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@item
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``Massive Multiauthor Collaboration Site'' (or ``MMC Site'') means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server. A
``Massive Multiauthor Collaboration'' (or ``MMC'') contained in the
site means any set of copyrightable works thus published on the MMC
site.
``CC-BY-SA'' means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
``Incorporate'' means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is ``eligible for relicensing'' if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.
@end enumerate
@page
@heading ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:
@smallexample
@group
Copyright (C) @var{year} @var{your name}.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@end group
@end smallexample
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the ``with@dots{}Texts.''@: line with this:
@smallexample
@group
with the Invariant Sections being @var{list their titles}, with
the Front-Cover Texts being @var{list}, and with the Back-Cover Texts
being @var{list}.
@end group
@end smallexample
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.
@c Local Variables:
@c ispell-local-pdict: "ispell-dict"
@c End:
glibc-doc-reference-2.19.orig/manual/maint.texi 0000664 0001750 0001750 00000055715 12275120646 021577 0 ustar adconrad adconrad @node Maintenance, Platform, Installation, Top
@c %MENU% How to enhance and port the GNU C Library
@appendix Library Maintenance
@menu
* Source Layout:: How to add new functions or header files
to the GNU C Library.
* Porting:: How to port the GNU C Library to
a new machine or operating system.
@end menu
@node Source Layout
@appendixsec Adding New Functions
The process of building the library is driven by the makefiles, which
make heavy use of special features of GNU @code{make}. The makefiles
are very complex, and you probably don't want to try to understand them.
But what they do is fairly straightforward, and only requires that you
define a few variables in the right places.
The library sources are divided into subdirectories, grouped by topic.
The @file{string} subdirectory has all the string-manipulation
functions, @file{math} has all the mathematical functions, etc.
Each subdirectory contains a simple makefile, called @file{Makefile},
which defines a few @code{make} variables and then includes the global
makefile @file{Rules} with a line like:
@smallexample
include ../Rules
@end smallexample
@noindent
The basic variables that a subdirectory makefile defines are:
@table @code
@item subdir
The name of the subdirectory, for example @file{stdio}.
This variable @strong{must} be defined.
@item headers
The names of the header files in this section of the library,
such as @file{stdio.h}.
@item routines
@itemx aux
The names of the modules (source files) in this section of the library.
These should be simple names, such as @samp{strlen} (rather than
complete file names, such as @file{strlen.c}). Use @code{routines} for
modules that define functions in the library, and @code{aux} for
auxiliary modules containing things like data definitions. But the
values of @code{routines} and @code{aux} are just concatenated, so there
really is no practical difference.@refill
@item tests
The names of test programs for this section of the library. These
should be simple names, such as @samp{tester} (rather than complete file
names, such as @file{tester.c}). @w{@samp{make tests}} will build and
run all the test programs. If a test program needs input, put the test
data in a file called @file{@var{test-program}.input}; it will be given to
the test program on its standard input. If a test program wants to be
run with arguments, put the arguments (all on a single line) in a file
called @file{@var{test-program}.args}. Test programs should exit with
zero status when the test passes, and nonzero status when the test
indicates a bug in the library or error in building.
@item others
The names of ``other'' programs associated with this section of the
library. These are programs which are not tests per se, but are other
small programs included with the library. They are built by
@w{@samp{make others}}.@refill
@item install-lib
@itemx install-data
@itemx install
Files to be installed by @w{@samp{make install}}. Files listed in
@samp{install-lib} are installed in the directory specified by
@samp{libdir} in @file{configparms} or @file{Makeconfig}
(@pxref{Installation}). Files listed in @code{install-data} are
installed in the directory specified by @samp{datadir} in
@file{configparms} or @file{Makeconfig}. Files listed in @code{install}
are installed in the directory specified by @samp{bindir} in
@file{configparms} or @file{Makeconfig}.@refill
@item distribute
Other files from this subdirectory which should be put into a
distribution tar file. You need not list here the makefile itself or
the source and header files listed in the other standard variables.
Only define @code{distribute} if there are files used in an unusual way
that should go into the distribution.
@item generated
Files which are generated by @file{Makefile} in this subdirectory.
These files will be removed by @w{@samp{make clean}}, and they will
never go into a distribution.
@item extra-objs
Extra object files which are built by @file{Makefile} in this
subdirectory. This should be a list of file names like @file{foo.o};
the files will actually be found in whatever directory object files are
being built in. These files will be removed by @w{@samp{make clean}}.
This variable is used for secondary object files needed to build
@code{others} or @code{tests}.
@end table
@menu
* Platform: Adding Platform-specific. Adding platform-specific
features.
@end menu
@node Adding Platform-specific
@appendixsubsec Platform-specific types, macros and functions
It's sometimes necessary to provide nonstandard, platform-specific
features to developers. The C library is traditionally the
lowest library layer, so it makes sense for it to provide these
low-level features. However, including these features in the C
library may be a disadvantage if another package provides them
as well as there will be two conflicting versions of them. Also,
the features won't be available to projects that do not use
@theglibc{} but use other GNU tools, like GCC.
The current guidelines are:
@itemize @bullet
@item
If the header file provides features that only make sense on a particular
machine architecture and have nothing to do with an operating system, then
the features should ultimately be provided as GCC built-in functions. Until
then, @theglibc{} may provide them in the header file. When the GCC built-in
functions become available, those provided in the header file should be made
conditionally available prior to the GCC version in which the built-in
function was made available.
@item
If the header file provides features that are specific to an operating system,
both GCC and @theglibc{} could provide it, but @theglibc{} is preferred
as it already has a lot of information about the operating system.
@item
If the header file provides features that are specific to an operating system
but used by @theglibc{}, then @theglibc{} should provide them.
@end itemize
The general solution for providing low-level features is to export them as
follows:
@itemize @bullet
@item
A nonstandard, low-level header file that defines macros and inline
functions should be called @file{sys/platform/@var{name}.h}.
@item
Each header file's name should include the platform name, to avoid
users thinking there is anything in common between different the
header files for different platforms. For example, a
@file{sys/platform/@var{arch}.h} name such as
@file{sys/platform/ppc.h} is better than @file{sys/platform.h}.
@item
A platform-specific header file provided by @theglibc{} should coordinate
with GCC such that compiler built-in versions of the functions and macros are
preferred if available. This means that user programs will only ever need to
include @file{sys/platform/@var{arch}.h}, keeping the same names of types,
macros, and functions for convenience and portability.
@item
Each included symbol must have the prefix @code{__@var{arch}_}, such as
@code{__ppc_get_timebase}.
@end itemize
The easiest way to provide a header file is to add it to the
@code{sysdep_headers} variable. For example, the combination of
Linux-specific header files on PowerPC could be provided like this:
@smallexample
sysdep_headers += sys/platform/ppc.h
@end smallexample
Then ensure that you have added a @file{sys/platform/ppc.h}
header file in the machine-specific directory, e.g.,
@file{sysdeps/powerpc/sys/platform/ppc.h}.
@node Porting
@appendixsec Porting @theglibc{}
@Theglibc{} is written to be easily portable to a variety of
machines and operating systems. Machine- and operating system-dependent
functions are well separated to make it easy to add implementations for
new machines or operating systems. This section describes the layout of
the library source tree and explains the mechanisms used to select
machine-dependent code to use.
All the machine-dependent and operating system-dependent files in the
library are in the subdirectory @file{sysdeps} under the top-level
library source directory. This directory contains a hierarchy of
subdirectories (@pxref{Hierarchy Conventions}).
Each subdirectory of @file{sysdeps} contains source files for a
particular machine or operating system, or for a class of machine or
operating system (for example, systems by a particular vendor, or all
machines that use IEEE 754 floating-point format). A configuration
specifies an ordered list of these subdirectories. Each subdirectory
implicitly appends its parent directory to the list. For example,
specifying the list @file{unix/bsd/vax} is equivalent to specifying the
list @file{unix/bsd/vax unix/bsd unix}. A subdirectory can also specify
that it implies other subdirectories which are not directly above it in
the directory hierarchy. If the file @file{Implies} exists in a
subdirectory, it lists other subdirectories of @file{sysdeps} which are
appended to the list, appearing after the subdirectory containing the
@file{Implies} file. Lines in an @file{Implies} file that begin with a
@samp{#} character are ignored as comments. For example,
@file{unix/bsd/Implies} contains:@refill
@smallexample
# BSD has Internet-related things.
unix/inet
@end smallexample
@noindent
and @file{unix/Implies} contains:
@need 300
@smallexample
posix
@end smallexample
@noindent
So the final list is @file{unix/bsd/vax unix/bsd unix/inet unix posix}.
@file{sysdeps} has a ``special'' subdirectory called @file{generic}. It
is always implicitly appended to the list of subdirectories, so you
needn't put it in an @file{Implies} file, and you should not create any
subdirectories under it intended to be new specific categories.
@file{generic} serves two purposes. First, the makefiles do not bother
to look for a system-dependent version of a file that's not in
@file{generic}. This means that any system-dependent source file must
have an analogue in @file{generic}, even if the routines defined by that
file are not implemented on other platforms. Second, the @file{generic}
version of a system-dependent file is used if the makefiles do not find
a version specific to the system you're compiling for.
If it is possible to implement the routines in a @file{generic} file in
machine-independent C, using only other machine-independent functions in
the C library, then you should do so. Otherwise, make them stubs. A
@dfn{stub} function is a function which cannot be implemented on a
particular machine or operating system. Stub functions always return an
error, and set @code{errno} to @code{ENOSYS} (Function not implemented).
@xref{Error Reporting}. If you define a stub function, you must place
the statement @code{stub_warning(@var{function})}, where @var{function}
is the name of your function, after its definition. This causes the
function to be listed in the installed @code{}, and
makes GNU ld warn when the function is used.
Some rare functions are only useful on specific systems and aren't
defined at all on others; these do not appear anywhere in the
system-independent source code or makefiles (including the
@file{generic} directory), only in the system-dependent @file{Makefile}
in the specific system's subdirectory.
If you come across a file that is in one of the main source directories
(@file{string}, @file{stdio}, etc.), and you want to write a machine- or
operating system-dependent version of it, move the file into
@file{sysdeps/generic} and write your new implementation in the
appropriate system-specific subdirectory. Note that if a file is to be
system-dependent, it @strong{must not} appear in one of the main source
directories.@refill
There are a few special files that may exist in each subdirectory of
@file{sysdeps}:
@comment Blank lines after items make the table look better.
@table @file
@item Makefile
A makefile for this machine or operating system, or class of machine or
operating system. This file is included by the library makefile
@file{Makerules}, which is used by the top-level makefile and the
subdirectory makefiles. It can change the variables set in the
including makefile or add new rules. It can use GNU @code{make}
conditional directives based on the variable @samp{subdir} (see above) to
select different sets of variables and rules for different sections of
the library. It can also set the @code{make} variable
@samp{sysdep-routines}, to specify extra modules to be included in the
library. You should use @samp{sysdep-routines} rather than adding
modules to @samp{routines} because the latter is used in determining
what to distribute for each subdirectory of the main source tree.@refill
Each makefile in a subdirectory in the ordered list of subdirectories to
be searched is included in order. Since several system-dependent
makefiles may be included, each should append to @samp{sysdep-routines}
rather than simply setting it:
@smallexample
sysdep-routines := $(sysdep-routines) foo bar
@end smallexample
@need 1000
@item Subdirs
This file contains the names of new whole subdirectories under the
top-level library source tree that should be included for this system.
These subdirectories are treated just like the system-independent
subdirectories in the library source tree, such as @file{stdio} and
@file{math}.
Use this when there are completely new sets of functions and header
files that should go into the library for the system this subdirectory
of @file{sysdeps} implements. For example,
@file{sysdeps/unix/inet/Subdirs} contains @file{inet}; the @file{inet}
directory contains various network-oriented operations which only make
sense to put in the library on systems that support the Internet.@refill
@item configure
This file is a shell script fragment to be run at configuration time.
The top-level @file{configure} script uses the shell @code{.} command to
read the @file{configure} file in each system-dependent directory
chosen, in order. The @file{configure} files are often generated from
@file{configure.ac} files using Autoconf.
A system-dependent @file{configure} script will usually add things to
the shell variables @samp{DEFS} and @samp{config_vars}; see the
top-level @file{configure} script for details. The script can check for
@w{@samp{--with-@var{package}}} options that were passed to the
top-level @file{configure}. For an option
@w{@samp{--with-@var{package}=@var{value}}} @file{configure} sets the
shell variable @w{@samp{with_@var{package}}} (with any dashes in
@var{package} converted to underscores) to @var{value}; if the option is
just @w{@samp{--with-@var{package}}} (no argument), then it sets
@w{@samp{with_@var{package}}} to @samp{yes}.
@item configure.ac
This file is an Autoconf input fragment to be processed into the file
@file{configure} in this subdirectory. @xref{Introduction,,,
autoconf.info, Autoconf: Generating Automatic Configuration Scripts},
for a description of Autoconf. You should write either @file{configure}
or @file{configure.ac}, but not both. The first line of
@file{configure.ac} should invoke the @code{m4} macro
@samp{GLIBC_PROVIDES}. This macro does several @code{AC_PROVIDE} calls
for Autoconf macros which are used by the top-level @file{configure}
script; without this, those macros might be invoked again unnecessarily
by Autoconf.
@end table
That is the general system for how system-dependencies are isolated.
@iftex
The next section explains how to decide what directories in
@file{sysdeps} to use. @ref{Porting to Unix}, has some tips on porting
the library to Unix variants.
@end iftex
@menu
* Hierarchy Conventions:: The layout of the @file{sysdeps} hierarchy.
* Porting to Unix:: Porting the library to an average
Unix-like system.
@end menu
@node Hierarchy Conventions
@appendixsubsec Layout of the @file{sysdeps} Directory Hierarchy
A GNU configuration name has three parts: the CPU type, the
manufacturer's name, and the operating system. @file{configure} uses
these to pick the list of system-dependent directories to look for. If
the @samp{--nfp} option is @emph{not} passed to @file{configure}, the
directory @file{@var{machine}/fpu} is also used. The operating system
often has a @dfn{base operating system}; for example, if the operating
system is @samp{Linux}, the base operating system is @samp{unix/sysv}.
The algorithm used to pick the list of directories is simple:
@file{configure} makes a list of the base operating system,
manufacturer, CPU type, and operating system, in that order. It then
concatenates all these together with slashes in between, to produce a
directory name; for example, the configuration @w{@samp{i686-linux-gnu}}
results in @file{unix/sysv/linux/i386/i686}. @file{configure} then
tries removing each element of the list in turn, so
@file{unix/sysv/linux} and @file{unix/sysv} are also tried, among others.
Since the precise version number of the operating system is often not
important, and it would be very inconvenient, for example, to have
identical @file{irix6.2} and @file{irix6.3} directories,
@file{configure} tries successively less specific operating system names
by removing trailing suffixes starting with a period.
As an example, here is the complete list of directories that would be
tried for the configuration @w{@samp{i686-linux-gnu}} (with the
@file{crypt} and @file{linuxthreads} add-on):
@smallexample
sysdeps/i386/elf
crypt/sysdeps/unix
linuxthreads/sysdeps/unix/sysv/linux
linuxthreads/sysdeps/pthread
linuxthreads/sysdeps/unix/sysv
linuxthreads/sysdeps/unix
linuxthreads/sysdeps/i386/i686
linuxthreads/sysdeps/i386
linuxthreads/sysdeps/pthread/no-cmpxchg
sysdeps/unix/sysv/linux/i386
sysdeps/unix/sysv/linux
sysdeps/gnu
sysdeps/unix/common
sysdeps/unix/mman
sysdeps/unix/inet
sysdeps/unix/sysv/i386/i686
sysdeps/unix/sysv/i386
sysdeps/unix/sysv
sysdeps/unix/i386
sysdeps/unix
sysdeps/posix
sysdeps/i386/i686
sysdeps/i386/i486
sysdeps/libm-i387/i686
sysdeps/i386/fpu
sysdeps/libm-i387
sysdeps/i386
sysdeps/wordsize-32
sysdeps/ieee754
sysdeps/libm-ieee754
sysdeps/generic
@end smallexample
Different machine architectures are conventionally subdirectories at the
top level of the @file{sysdeps} directory tree. For example,
@w{@file{sysdeps/sparc}} and @w{@file{sysdeps/m68k}}. These contain
files specific to those machine architectures, but not specific to any
particular operating system. There might be subdirectories for
specializations of those architectures, such as
@w{@file{sysdeps/m68k/68020}}. Code which is specific to the
floating-point coprocessor used with a particular machine should go in
@w{@file{sysdeps/@var{machine}/fpu}}.
There are a few directories at the top level of the @file{sysdeps}
hierarchy that are not for particular machine architectures.
@table @file
@item generic
As described above (@pxref{Porting}), this is the subdirectory
that every configuration implicitly uses after all others.
@item ieee754
This directory is for code using the IEEE 754 floating-point format,
where the C type @code{float} is IEEE 754 single-precision format, and
@code{double} is IEEE 754 double-precision format. Usually this
directory is referred to in the @file{Implies} file in a machine
architecture-specific directory, such as @file{m68k/Implies}.
@item libm-ieee754
This directory contains an implementation of a mathematical library
usable on platforms which use @w{IEEE 754} conformant floating-point
arithmetic.
@item libm-i387
This is a special case. Ideally the code should be in
@file{sysdeps/i386/fpu} but for various reasons it is kept aside.
@item posix
This directory contains implementations of things in the library in
terms of @sc{POSIX.1} functions. This includes some of the @sc{POSIX.1}
functions themselves. Of course, @sc{POSIX.1} cannot be completely
implemented in terms of itself, so a configuration using just
@file{posix} cannot be complete.
@item unix
This is the directory for Unix-like things. @xref{Porting to Unix}.
@file{unix} implies @file{posix}. There are some special-purpose
subdirectories of @file{unix}:
@table @file
@item unix/common
This directory is for things common to both BSD and System V release 4.
Both @file{unix/bsd} and @file{unix/sysv/sysv4} imply @file{unix/common}.
@item unix/inet
This directory is for @code{socket} and related functions on Unix systems.
@file{unix/inet/Subdirs} enables the @file{inet} top-level subdirectory.
@file{unix/common} implies @file{unix/inet}.
@end table
@item mach
This is the directory for things based on the Mach microkernel from CMU
(including @gnuhurdsystems{}). Other basic operating systems
(VMS, for example) would have their own directories at the top level of
the @file{sysdeps} hierarchy, parallel to @file{unix} and @file{mach}.
@end table
@node Porting to Unix
@appendixsubsec Porting @theglibc{} to Unix Systems
Most Unix systems are fundamentally very similar. There are variations
between different machines, and variations in what facilities are
provided by the kernel. But the interface to the operating system
facilities is, for the most part, pretty uniform and simple.
The code for Unix systems is in the directory @file{unix}, at the top
level of the @file{sysdeps} hierarchy. This directory contains
subdirectories (and subdirectory trees) for various Unix variants.
The functions which are system calls in most Unix systems are
implemented in assembly code, which is generated automatically from
specifications in files named @file{syscalls.list}. There are several
such files, one in @file{sysdeps/unix} and others in its subdirectories.
Some special system calls are implemented in files that are named with a
suffix of @samp{.S}; for example, @file{_exit.S}. Files ending in
@samp{.S} are run through the C preprocessor before being fed to the
assembler.
These files all use a set of macros that should be defined in
@file{sysdep.h}. The @file{sysdep.h} file in @file{sysdeps/unix}
partially defines them; a @file{sysdep.h} file in another directory must
finish defining them for the particular machine and operating system
variant. See @file{sysdeps/unix/sysdep.h} and the machine-specific
@file{sysdep.h} implementations to see what these macros are and what
they should do.@refill
The system-specific makefile for the @file{unix} directory
(@file{sysdeps/unix/Makefile}) gives rules to generate several files
from the Unix system you are building the library on (which is assumed
to be the target system you are building the library @emph{for}). All
the generated files are put in the directory where the object files are
kept; they should not affect the source tree itself. The files
generated are @file{ioctls.h}, @file{errnos.h}, @file{sys/param.h}, and
@file{errlist.c} (for the @file{stdio} section of the library).
@ignore
@c This section might be a good idea if it is finished,
@c but there's no point including it as it stands. --rms
@c @appendixsec Compatibility with Traditional C
@c ??? This section is really short now. Want to keep it? --roland
@c It's not anymore true. glibc 2.1 cannot be used with K&R compilers.
@c --drepper
Although @theglibc{} implements the @w{ISO C} library facilities, you
@emph{can} use @theglibc{} with traditional, ``pre-ISO'' C
compilers. However, you need to be careful because the content and
organization of the @glibcadj{} header files differs from that of
traditional C implementations. This means you may need to make changes
to your program in order to get it to compile.
@end ignore
glibc-doc-reference-2.19.orig/manual/syslog.texi 0000664 0001750 0001750 00000052436 12275120646 022004 0 ustar adconrad adconrad @node Syslog, Mathematics, Low-Level Terminal Interface, Top
@c %MENU% System logging and messaging
@chapter Syslog
This chapter describes facilities for issuing and logging messages of
system administration interest. This chapter has nothing to do with
programs issuing messages to their own users or keeping private logs
(One would typically do that with the facilities described in
@ref{I/O on Streams}).
Most systems have a facility called ``Syslog'' that allows programs to
submit messages of interest to system administrators and can be
configured to pass these messages on in various ways, such as printing
on the console, mailing to a particular person, or recording in a log
file for future reference.
A program uses the facilities in this chapter to submit such messages.
@menu
* Overview of Syslog:: Overview of a system's Syslog facility
* Submitting Syslog Messages:: Functions to submit messages to Syslog
@end menu
@node Overview of Syslog
@section Overview of Syslog
System administrators have to deal with lots of different kinds of
messages from a plethora of subsystems within each system, and usually
lots of systems as well. For example, an FTP server might report every
connection it gets. The kernel might report hardware failures on a disk
drive. A DNS server might report usage statistics at regular intervals.
Some of these messages need to be brought to a system administrator's
attention immediately. And it may not be just any system administrator
-- there may be a particular system administrator who deals with a
particular kind of message. Other messages just need to be recorded for
future reference if there is a problem. Still others may need to have
information extracted from them by an automated process that generates
monthly reports.
To deal with these messages, most Unix systems have a facility called
"Syslog." It is generally based on a daemon called ``Syslogd''
Syslogd listens for messages on a Unix domain socket named
@file{/dev/log}. Based on classification information in the messages
and its configuration file (usually @file{/etc/syslog.conf}), Syslogd
routes them in various ways. Some of the popular routings are:
@itemize @bullet
@item
Write to the system console
@item
Mail to a specific user
@item
Write to a log file
@item
Pass to another daemon
@item
Discard
@end itemize
Syslogd can also handle messages from other systems. It listens on the
@code{syslog} UDP port as well as the local socket for messages.
Syslog can handle messages from the kernel itself. But the kernel
doesn't write to @file{/dev/log}; rather, another daemon (sometimes
called ``Klogd'') extracts messages from the kernel and passes them on to
Syslog as any other process would (and it properly identifies them as
messages from the kernel).
Syslog can even handle messages that the kernel issued before Syslogd or
Klogd was running. A Linux kernel, for example, stores startup messages
in a kernel message ring and they are normally still there when Klogd
later starts up. Assuming Syslogd is running by the time Klogd starts,
Klogd then passes everything in the message ring to it.
In order to classify messages for disposition, Syslog requires any process
that submits a message to it to provide two pieces of classification
information with it:
@table @asis
@item facility
This identifies who submitted the message. There are a small number of
facilities defined. The kernel, the mail subsystem, and an FTP server
are examples of recognized facilities. For the complete list,
@xref{syslog; vsyslog}. Keep in mind that these are
essentially arbitrary classifications. "Mail subsystem" doesn't have any
more meaning than the system administrator gives to it.
@item priority
This tells how important the content of the message is. Examples of
defined priority values are: debug, informational, warning, critical.
For the complete list, see @ref{syslog; vsyslog}. Except for
the fact that the priorities have a defined order, the meaning of each
of these priorities is entirely determined by the system administrator.
@end table
A ``facility/priority'' is a number that indicates both the facility
and the priority.
@strong{Warning:} This terminology is not universal. Some people use
``level'' to refer to the priority and ``priority'' to refer to the
combination of facility and priority. A Linux kernel has a concept of a
message ``level,'' which corresponds both to a Syslog priority and to a
Syslog facility/priority (It can be both because the facility code for
the kernel is zero, and that makes priority and facility/priority the
same value).
@Theglibc{} provides functions to submit messages to Syslog. They
do it by writing to the @file{/dev/log} socket. @xref{Submitting Syslog
Messages}.
The @glibcadj{} functions only work to submit messages to the Syslog
facility on the same system. To submit a message to the Syslog facility
on another system, use the socket I/O functions to write a UDP datagram
to the @code{syslog} UDP port on that system. @xref{Sockets}.
@node Submitting Syslog Messages
@section Submitting Syslog Messages
@Theglibc{} provides functions to submit messages to the Syslog
facility:
@menu
* openlog:: Open connection to Syslog
* syslog; vsyslog:: Submit message to Syslog
* closelog:: Close connection to Syslog
* setlogmask:: Cause certain messages to be ignored
* Syslog Example:: Example of all of the above
@end menu
These functions only work to submit messages to the Syslog facility on
the same system. To submit a message to the Syslog facility on another
system, use the socket I/O functions to write a UDP datagram to the
@code{syslog} UDP port on that system. @xref{Sockets}.
@node openlog
@subsection openlog
The symbols referred to in this section are declared in the file
@file{syslog.h}.
@comment syslog.h
@comment BSD
@deftypefun void openlog (const char *@var{ident}, int @var{option}, int @var{facility})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c openlog @asulock @aculock @acsfd
@c libc_lock_lock @asulock @aculock
@c openlog_internal @acsfd [always guarded by syslog_lock, so no race]
@c strncpy dup ok
@c socket dup @acsfd
@c fcntl dup ok
@c connect dup ok
@c close dup @acsfd
@c cancel_handler(NULL) @aculock
@c libc_lock_unlock @aculock
@code{openlog} opens or reopens a connection to Syslog in preparation
for submitting messages.
@var{ident} is an arbitrary identification string which future
@code{syslog} invocations will prefix to each message. This is intended
to identify the source of the message, and people conventionally set it
to the name of the program that will submit the messages.
If @var{ident} is NULL, or if @code{openlog} is not called, the default
identification string used in Syslog messages will be the program name,
taken from argv[0].
Please note that the string pointer @var{ident} will be retained
internally by the Syslog routines. You must not free the memory that
@var{ident} points to. It is also dangerous to pass a reference to an
automatic variable since leaving the scope would mean ending the
lifetime of the variable. If you want to change the @var{ident} string,
you must call @code{openlog} again; overwriting the string pointed to by
@var{ident} is not thread-safe.
You can cause the Syslog routines to drop the reference to @var{ident} and
go back to the default string (the program name taken from argv[0]), by
calling @code{closelog}: @xref{closelog}.
In particular, if you are writing code for a shared library that might get
loaded and then unloaded (e.g. a PAM module), and you use @code{openlog},
you must call @code{closelog} before any point where your library might
get unloaded, as in this example:
@smallexample
#include
void
shared_library_function (void)
@{
openlog ("mylibrary", option, priority);
syslog (LOG_INFO, "shared library has been invoked");
closelog ();
@}
@end smallexample
Without the call to @code{closelog}, future invocations of @code{syslog}
by the program using the shared library may crash, if the library gets
unloaded and the memory containing the string @code{"mylibrary"} becomes
unmapped. This is a limitation of the BSD syslog interface.
@code{openlog} may or may not open the @file{/dev/log} socket, depending
on @var{option}. If it does, it tries to open it and connect it as a
stream socket. If that doesn't work, it tries to open it and connect it
as a datagram socket. The socket has the ``Close on Exec'' attribute,
so the kernel will close it if the process performs an exec.
You don't have to use @code{openlog}. If you call @code{syslog} without
having called @code{openlog}, @code{syslog} just opens the connection
implicitly and uses defaults for the information in @var{ident} and
@var{options}.
@var{options} is a bit string, with the bits as defined by the following
single bit masks:
@table @code
@item LOG_PERROR
If on, @code{openlog} sets up the connection so that any @code{syslog}
on this connection writes its message to the calling process' Standard
Error stream in addition to submitting it to Syslog. If off, @code{syslog}
does not write the message to Standard Error.
@item LOG_CONS
If on, @code{openlog} sets up the connection so that a @code{syslog} on
this connection that fails to submit a message to Syslog writes the
message instead to system console. If off, @code{syslog} does not write
to the system console (but of course Syslog may write messages it
receives to the console).
@item LOG_PID
When on, @code{openlog} sets up the connection so that a @code{syslog}
on this connection inserts the calling process' Process ID (PID) into
the message. When off, @code{openlog} does not insert the PID.
@item LOG_NDELAY
When on, @code{openlog} opens and connects the @file{/dev/log} socket.
When off, a future @code{syslog} call must open and connect the socket.
@strong{Portability note:} In early systems, the sense of this bit was
exactly the opposite.
@item LOG_ODELAY
This bit does nothing. It exists for backward compatibility.
@end table
If any other bit in @var{options} is on, the result is undefined.
@var{facility} is the default facility code for this connection. A
@code{syslog} on this connection that specifies default facility causes
this facility to be associated with the message. See @code{syslog} for
possible values. A value of zero means the default default, which is
@code{LOG_USER}.
If a Syslog connection is already open when you call @code{openlog},
@code{openlog} ``reopens'' the connection. Reopening is like opening
except that if you specify zero for the default facility code, the
default facility code simply remains unchanged and if you specify
LOG_NDELAY and the socket is already open and connected, @code{openlog}
just leaves it that way.
@c There is a bug in closelog() (glibc 2.1.3) wherein it does not reset the
@c default log facility to LOG_USER, which means the default default log
@c facility could be whatever the default log facility was for a previous
@c Syslog connection. I have documented what the function should be rather
@c than what it is because I think if anyone ever gets concerned, the code
@c will change.
@end deftypefun
@node syslog; vsyslog
@subsection syslog, vsyslog
The symbols referred to in this section are declared in the file
@file{syslog.h}.
@c syslog() is implemented as a call to vsyslog().
@comment syslog.h
@comment BSD
@deftypefun void syslog (int @var{facility_priority}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c syslog @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c va_start dup ok
@c vsyslog_chk @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c syslog(INTERNALLOG) dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c open_memstream @ascuheap @acsmem
@c stpcpy dup ok
@c getpid dup ok
@c mempcpy dup ok
@c fsetlocking [no @mtasurace:stream @asulock for exclusive stream]
@c fprintf @mtslocale @ascuheap @acsmem [no @asucorrupt @aculock @acucorrupt on temp memstream]
@c time dup ok
@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c strftime_l(C) dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c ftell dup ok [no @asucorrupt @aculock @acucorrupt on temp memstream]
@c fputs_unlocked dup ok [no @mtasurace:stream @asucorrupt @acucorrupt on temp memstream]
@c putc_unlocked dup ok [no @mtasurace:stream @asucorrupt @acucorrupt on temp memstream]
@c vfprintf/vfprintf_chk dup @mtslocale @ascuheap @acsmem [no @mtasurace:stream @asucorrupt @acucorrupt on temp memstream]
@c fclose dup @ascuheap @acsmem [no @asulock @aculock @acsfd on caller-locked memstream]
@c writev dup ok
@c libc_lock_lock dup @asulock @aculock
@c memset dup ok
@c sigemptyset dup ok
@c sigaction(SIGPIPE) dup @mtasusig:PIPE @acusig:PIPE
@c openlog_internal dup @acsfd
@c send dup ok
@c closelog_internal dup @acsfd
@c open dup @acsfd
@c dprintf dup ok
@c libc_lock_unlock @asulock @aculock
@c free dup @acsuheap @acsmem
@c va_end dup ok
@code{syslog} submits a message to the Syslog facility. It does this by
writing to the Unix domain socket @code{/dev/log}.
@code{syslog} submits the message with the facility and priority indicated
by @var{facility_priority}. The macro @code{LOG_MAKEPRI} generates a
facility/priority from a facility and a priority, as in the following
example:
@smallexample
LOG_MAKEPRI(LOG_USER, LOG_WARNING)
@end smallexample
The possible values for the facility code are (macros):
@c Internally, there is also LOG_KERN, but LOG_KERN == 0, which means
@c if you try to use it here, just selects default.
@vtable @code
@item LOG_USER
A miscellaneous user process
@item LOG_MAIL
Mail
@item LOG_DAEMON
A miscellaneous system daemon
@item LOG_AUTH
Security (authorization)
@item LOG_SYSLOG
Syslog
@item LOG_LPR
Central printer
@item LOG_NEWS
Network news (e.g. Usenet)
@item LOG_UUCP
UUCP
@item LOG_CRON
Cron and At
@item LOG_AUTHPRIV
Private security (authorization)
@item LOG_FTP
Ftp server
@item LOG_LOCAL0
Locally defined
@item LOG_LOCAL1
Locally defined
@item LOG_LOCAL2
Locally defined
@item LOG_LOCAL3
Locally defined
@item LOG_LOCAL4
Locally defined
@item LOG_LOCAL5
Locally defined
@item LOG_LOCAL6
Locally defined
@item LOG_LOCAL7
Locally defined
@end vtable
Results are undefined if the facility code is anything else.
@strong{NB:} @code{syslog} recognizes one other facility code: that of
the kernel. But you can't specify that facility code with these
functions. If you try, it looks the same to @code{syslog} as if you are
requesting the default facility. But you wouldn't want to anyway,
because any program that uses @theglibc{} is not the kernel.
You can use just a priority code as @var{facility_priority}. In that
case, @code{syslog} assumes the default facility established when the
Syslog connection was opened. @xref{Syslog Example}.
The possible values for the priority code are (macros):
@vtable @code
@item LOG_EMERG
The message says the system is unusable.
@item LOG_ALERT
Action on the message must be taken immediately.
@item LOG_CRIT
The message states a critical condition.
@item LOG_ERR
The message describes an error.
@item LOG_WARNING
The message is a warning.
@item LOG_NOTICE
The message describes a normal but important event.
@item LOG_INFO
The message is purely informational.
@item LOG_DEBUG
The message is only for debugging purposes.
@end vtable
Results are undefined if the priority code is anything else.
If the process does not presently have a Syslog connection open (i.e.,
it did not call @code{openlog}), @code{syslog} implicitly opens the
connection the same as @code{openlog} would, with the following defaults
for information that would otherwise be included in an @code{openlog}
call: The default identification string is the program name. The
default default facility is @code{LOG_USER}. The default for all the
connection options in @var{options} is as if those bits were off.
@code{syslog} leaves the Syslog connection open.
If the @file{/dev/log} socket is not open and connected, @code{syslog}
opens and connects it, the same as @code{openlog} with the
@code{LOG_NDELAY} option would.
@code{syslog} leaves @file{/dev/log} open and connected unless its attempt
to send the message failed, in which case @code{syslog} closes it (with the
hope that a future implicit open will restore the Syslog connection to a
usable state).
Example:
@smallexample
#include
syslog (LOG_MAKEPRI(LOG_LOCAL1, LOG_ERROR),
"Unable to make network connection to %s. Error=%m", host);
@end smallexample
@end deftypefun
@comment syslog.h
@comment BSD
@deftypefun void vsyslog (int @var{facility_priority}, const char *@var{format}, va_list @var{arglist})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c vsyslog @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c vsyslog_chk dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
This is functionally identical to @code{syslog}, with the BSD style variable
length argument.
@end deftypefun
@node closelog
@subsection closelog
The symbols referred to in this section are declared in the file
@file{syslog.h}.
@comment syslog.h
@comment BSD
@deftypefun void closelog (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c closelog @asulock @aculock @acsfd
@c libc_lock_lock @asulock @aculock
@c closelog_internal @acsfd [always guarded by syslog_lock, so no race]
@c close dup@acsfd
@c cancel_handler(NULL) @aculock
@c libc_lock_unlock @aculock
@code{closelog} closes the current Syslog connection, if there is one.
This includes closing the @file{/dev/log} socket, if it is open.
@code{closelog} also sets the identification string for Syslog messages
back to the default, if @code{openlog} was called with a non-NULL argument
to @var{ident}. The default identification string is the program name
taken from argv[0].
If you are writing shared library code that uses @code{openlog} to
generate custom syslog output, you should use @code{closelog} to drop
@theglibc{}'s internal reference to the @var{ident} pointer when you are
done. Please read the section on @code{openlog} for more information:
@xref{openlog}.
@code{closelog} does not flush any buffers. You do not have to call
@code{closelog} before re-opening a Syslog connection with @code{openlog}.
Syslog connections are automatically closed on exec or exit.
@end deftypefun
@node setlogmask
@subsection setlogmask
The symbols referred to in this section are declared in the file
@file{syslog.h}.
@comment syslog.h
@comment BSD
@deftypefun int setlogmask (int @var{mask})
@safety{@prelim{}@mtunsafe{@mtasurace{:LogMask}}@asunsafe{}@acsafe{}}
@c Read and modify are not guarded by syslog_lock, so concurrent changes
@c or even uses are undefined. This should use an atomic swap instead,
@c at least for modifications.
@code{setlogmask} sets a mask (the ``logmask'') that determines which
future @code{syslog} calls shall be ignored. If a program has not
called @code{setlogmask}, @code{syslog} doesn't ignore any calls. You
can use @code{setlogmask} to specify that messages of particular
priorities shall be ignored in the future.
A @code{setlogmask} call overrides any previous @code{setlogmask} call.
Note that the logmask exists entirely independently of opening and
closing of Syslog connections.
Setting the logmask has a similar effect to, but is not the same as,
configuring Syslog. The Syslog configuration may cause Syslog to
discard certain messages it receives, but the logmask causes certain
messages never to get submitted to Syslog in the first place.
@var{mask} is a bit string with one bit corresponding to each of the
possible message priorities. If the bit is on, @code{syslog} handles
messages of that priority normally. If it is off, @code{syslog}
discards messages of that priority. Use the message priority macros
described in @ref{syslog; vsyslog} and the @code{LOG_MASK} to construct
an appropriate @var{mask} value, as in this example:
@smallexample
LOG_MASK(LOG_EMERG) | LOG_MASK(LOG_ERROR)
@end smallexample
or
@smallexample
~(LOG_MASK(LOG_INFO))
@end smallexample
There is also a @code{LOG_UPTO} macro, which generates a mask with the bits
on for a certain priority and all priorities above it:
@smallexample
LOG_UPTO(LOG_ERROR)
@end smallexample
The unfortunate naming of the macro is due to the fact that internally,
higher numbers are used for lower message priorities.
@end deftypefun
@node Syslog Example
@subsection Syslog Example
Here is an example of @code{openlog}, @code{syslog}, and @code{closelog}:
This example sets the logmask so that debug and informational messages
get discarded without ever reaching Syslog. So the second @code{syslog}
in the example does nothing.
@smallexample
#include
setlogmask (LOG_UPTO (LOG_NOTICE));
openlog ("exampleprog", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
syslog (LOG_NOTICE, "Program started by User %d", getuid ());
syslog (LOG_INFO, "A tree falls in a forest");
closelog ();
@end smallexample
glibc-doc-reference-2.19.orig/manual/libdl.texi 0000664 0001750 0001750 00000000176 12275120646 021544 0 ustar adconrad adconrad @c FIXME these are undocumented:
@c dladdr
@c dladdr1
@c dlclose
@c dlerror
@c dlinfo
@c dlmopen
@c dlopen
@c dlsym
@c dlvsym
glibc-doc-reference-2.19.orig/manual/signal.texi 0000664 0001750 0001750 00000411424 12275120646 021735 0 ustar adconrad adconrad @node Signal Handling, Program Basics, Non-Local Exits, Top
@c %MENU% How to send, block, and handle signals
@chapter Signal Handling
@cindex signal
A @dfn{signal} is a software interrupt delivered to a process. The
operating system uses signals to report exceptional situations to an
executing program. Some signals report errors such as references to
invalid memory addresses; others report asynchronous events, such as
disconnection of a phone line.
@Theglibc{} defines a variety of signal types, each for a
particular kind of event. Some kinds of events make it inadvisable or
impossible for the program to proceed as usual, and the corresponding
signals normally abort the program. Other kinds of signals that report
harmless events are ignored by default.
If you anticipate an event that causes signals, you can define a handler
function and tell the operating system to run it when that particular
type of signal arrives.
Finally, one process can send a signal to another process; this allows a
parent process to abort a child, or two related processes to communicate
and synchronize.
@menu
* Concepts of Signals:: Introduction to the signal facilities.
* Standard Signals:: Particular kinds of signals with
standard names and meanings.
* Signal Actions:: Specifying what happens when a
particular signal is delivered.
* Defining Handlers:: How to write a signal handler function.
* Interrupted Primitives:: Signal handlers affect use of @code{open},
@code{read}, @code{write} and other functions.
* Generating Signals:: How to send a signal to a process.
* Blocking Signals:: Making the system hold signals temporarily.
* Waiting for a Signal:: Suspending your program until a signal
arrives.
* Signal Stack:: Using a Separate Signal Stack.
* BSD Signal Handling:: Additional functions for backward
compatibility with BSD.
@end menu
@node Concepts of Signals
@section Basic Concepts of Signals
This section explains basic concepts of how signals are generated, what
happens after a signal is delivered, and how programs can handle
signals.
@menu
* Kinds of Signals:: Some examples of what can cause a signal.
* Signal Generation:: Concepts of why and how signals occur.
* Delivery of Signal:: Concepts of what a signal does to the
process.
@end menu
@node Kinds of Signals
@subsection Some Kinds of Signals
A signal reports the occurrence of an exceptional event. These are some
of the events that can cause (or @dfn{generate}, or @dfn{raise}) a
signal:
@itemize @bullet
@item
A program error such as dividing by zero or issuing an address outside
the valid range.
@item
A user request to interrupt or terminate the program. Most environments
are set up to let a user suspend the program by typing @kbd{C-z}, or
terminate it with @kbd{C-c}. Whatever key sequence is used, the
operating system sends the proper signal to interrupt the process.
@item
The termination of a child process.
@item
Expiration of a timer or alarm.
@item
A call to @code{kill} or @code{raise} by the same process.
@item
A call to @code{kill} from another process. Signals are a limited but
useful form of interprocess communication.
@item
An attempt to perform an I/O operation that cannot be done. Examples
are reading from a pipe that has no writer (@pxref{Pipes and FIFOs}),
and reading or writing to a terminal in certain situations (@pxref{Job
Control}).
@end itemize
Each of these kinds of events (excepting explicit calls to @code{kill}
and @code{raise}) generates its own particular kind of signal. The
various kinds of signals are listed and described in detail in
@ref{Standard Signals}.
@node Signal Generation
@subsection Concepts of Signal Generation
@cindex generation of signals
In general, the events that generate signals fall into three major
categories: errors, external events, and explicit requests.
An error means that a program has done something invalid and cannot
continue execution. But not all kinds of errors generate signals---in
fact, most do not. For example, opening a nonexistent file is an error,
but it does not raise a signal; instead, @code{open} returns @code{-1}.
In general, errors that are necessarily associated with certain library
functions are reported by returning a value that indicates an error.
The errors which raise signals are those which can happen anywhere in
the program, not just in library calls. These include division by zero
and invalid memory addresses.
An external event generally has to do with I/O or other processes.
These include the arrival of input, the expiration of a timer, and the
termination of a child process.
An explicit request means the use of a library function such as
@code{kill} whose purpose is specifically to generate a signal.
Signals may be generated @dfn{synchronously} or @dfn{asynchronously}. A
synchronous signal pertains to a specific action in the program, and is
delivered (unless blocked) during that action. Most errors generate
signals synchronously, and so do explicit requests by a process to
generate a signal for that same process. On some machines, certain
kinds of hardware errors (usually floating-point exceptions) are not
reported completely synchronously, but may arrive a few instructions
later.
Asynchronous signals are generated by events outside the control of the
process that receives them. These signals arrive at unpredictable times
during execution. External events generate signals asynchronously, and
so do explicit requests that apply to some other process.
A given type of signal is either typically synchronous or typically
asynchronous. For example, signals for errors are typically synchronous
because errors generate signals synchronously. But any type of signal
can be generated synchronously or asynchronously with an explicit
request.
@node Delivery of Signal
@subsection How Signals Are Delivered
@cindex delivery of signals
@cindex pending signals
@cindex blocked signals
When a signal is generated, it becomes @dfn{pending}. Normally it
remains pending for just a short period of time and then is
@dfn{delivered} to the process that was signaled. However, if that kind
of signal is currently @dfn{blocked}, it may remain pending
indefinitely---until signals of that kind are @dfn{unblocked}. Once
unblocked, it will be delivered immediately. @xref{Blocking Signals}.
@cindex specified action (for a signal)
@cindex default action (for a signal)
@cindex signal action
@cindex catching signals
When the signal is delivered, whether right away or after a long delay,
the @dfn{specified action} for that signal is taken. For certain
signals, such as @code{SIGKILL} and @code{SIGSTOP}, the action is fixed,
but for most signals, the program has a choice: ignore the signal,
specify a @dfn{handler function}, or accept the @dfn{default action} for
that kind of signal. The program specifies its choice using functions
such as @code{signal} or @code{sigaction} (@pxref{Signal Actions}). We
sometimes say that a handler @dfn{catches} the signal. While the
handler is running, that particular signal is normally blocked.
If the specified action for a kind of signal is to ignore it, then any
such signal which is generated is discarded immediately. This happens
even if the signal is also blocked at the time. A signal discarded in
this way will never be delivered, not even if the program subsequently
specifies a different action for that kind of signal and then unblocks
it.
If a signal arrives which the program has neither handled nor ignored,
its @dfn{default action} takes place. Each kind of signal has its own
default action, documented below (@pxref{Standard Signals}). For most kinds
of signals, the default action is to terminate the process. For certain
kinds of signals that represent ``harmless'' events, the default action
is to do nothing.
When a signal terminates a process, its parent process can determine the
cause of termination by examining the termination status code reported
by the @code{wait} or @code{waitpid} functions. (This is discussed in
more detail in @ref{Process Completion}.) The information it can get
includes the fact that termination was due to a signal and the kind of
signal involved. If a program you run from a shell is terminated by a
signal, the shell typically prints some kind of error message.
The signals that normally represent program errors have a special
property: when one of these signals terminates the process, it also
writes a @dfn{core dump file} which records the state of the process at
the time of termination. You can examine the core dump with a debugger
to investigate what caused the error.
If you raise a ``program error'' signal by explicit request, and this
terminates the process, it makes a core dump file just as if the signal
had been due directly to an error.
@node Standard Signals
@section Standard Signals
@cindex signal names
@cindex names of signals
@pindex signal.h
@cindex signal number
This section lists the names for various standard kinds of signals and
describes what kind of event they mean. Each signal name is a macro
which stands for a positive integer---the @dfn{signal number} for that
kind of signal. Your programs should never make assumptions about the
numeric code for a particular kind of signal, but rather refer to them
always by the names defined here. This is because the number for a
given kind of signal can vary from system to system, but the meanings of
the names are standardized and fairly uniform.
The signal names are defined in the header file @file{signal.h}.
@comment signal.h
@comment BSD
@deftypevr Macro int NSIG
The value of this symbolic constant is the total number of signals
defined. Since the signal numbers are allocated consecutively,
@code{NSIG} is also one greater than the largest defined signal number.
@end deftypevr
@menu
* Program Error Signals:: Used to report serious program errors.
* Termination Signals:: Used to interrupt and/or terminate the
program.
* Alarm Signals:: Used to indicate expiration of timers.
* Asynchronous I/O Signals:: Used to indicate input is available.
* Job Control Signals:: Signals used to support job control.
* Operation Error Signals:: Used to report operational system errors.
* Miscellaneous Signals:: Miscellaneous Signals.
* Signal Messages:: Printing a message describing a signal.
@end menu
@node Program Error Signals
@subsection Program Error Signals
@cindex program error signals
The following signals are generated when a serious program error is
detected by the operating system or the computer itself. In general,
all of these signals are indications that your program is seriously
broken in some way, and there's usually no way to continue the
computation which encountered the error.
Some programs handle program error signals in order to tidy up before
terminating; for example, programs that turn off echoing of terminal
input should handle program error signals in order to turn echoing back
on. The handler should end by specifying the default action for the
signal that happened and then reraising it; this will cause the program
to terminate with that signal, as if it had not had a handler.
(@xref{Termination in Handler}.)
Termination is the sensible ultimate outcome from a program error in
most programs. However, programming systems such as Lisp that can load
compiled user programs might need to keep executing even if a user
program incurs an error. These programs have handlers which use
@code{longjmp} to return control to the command level.
The default action for all of these signals is to cause the process to
terminate. If you block or ignore these signals or establish handlers
for them that return normally, your program will probably break horribly
when such signals happen, unless they are generated by @code{raise} or
@code{kill} instead of a real error.
@vindex COREFILE
When one of these program error signals terminates a process, it also
writes a @dfn{core dump file} which records the state of the process at
the time of termination. The core dump file is named @file{core} and is
written in whichever directory is current in the process at the time.
(On @gnuhurdsystems{}, you can specify the file name for core dumps with
the environment variable @code{COREFILE}.) The purpose of core dump
files is so that you can examine them with a debugger to investigate
what caused the error.
@comment signal.h
@comment ISO
@deftypevr Macro int SIGFPE
The @code{SIGFPE} signal reports a fatal arithmetic error. Although the
name is derived from ``floating-point exception'', this signal actually
covers all arithmetic errors, including division by zero and overflow.
If a program stores integer data in a location which is then used in a
floating-point operation, this often causes an ``invalid operation''
exception, because the processor cannot recognize the data as a
floating-point number.
@cindex exception
@cindex floating-point exception
Actual floating-point exceptions are a complicated subject because there
are many types of exceptions with subtly different meanings, and the
@code{SIGFPE} signal doesn't distinguish between them. The @cite{IEEE
Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std 754-1985
and ANSI/IEEE Std 854-1987)}
defines various floating-point exceptions and requires conforming
computer systems to report their occurrences. However, this standard
does not specify how the exceptions are reported, or what kinds of
handling and control the operating system can offer to the programmer.
@end deftypevr
BSD systems provide the @code{SIGFPE} handler with an extra argument
that distinguishes various causes of the exception. In order to access
this argument, you must define the handler to accept two arguments,
which means you must cast it to a one-argument function type in order to
establish the handler. @Theglibc{} does provide this extra
argument, but the value is meaningful only on operating systems that
provide the information (BSD systems and @gnusystems{}).
@table @code
@comment signal.h
@comment BSD
@item FPE_INTOVF_TRAP
@vindex FPE_INTOVF_TRAP
Integer overflow (impossible in a C program unless you enable overflow
trapping in a hardware-specific fashion).
@comment signal.h
@comment BSD
@item FPE_INTDIV_TRAP
@vindex FPE_INTDIV_TRAP
Integer division by zero.
@comment signal.h
@comment BSD
@item FPE_SUBRNG_TRAP
@vindex FPE_SUBRNG_TRAP
Subscript-range (something that C programs never check for).
@comment signal.h
@comment BSD
@item FPE_FLTOVF_TRAP
@vindex FPE_FLTOVF_TRAP
Floating overflow trap.
@comment signal.h
@comment BSD
@item FPE_FLTDIV_TRAP
@vindex FPE_FLTDIV_TRAP
Floating/decimal division by zero.
@comment signal.h
@comment BSD
@item FPE_FLTUND_TRAP
@vindex FPE_FLTUND_TRAP
Floating underflow trap. (Trapping on floating underflow is not
normally enabled.)
@comment signal.h
@comment BSD
@item FPE_DECOVF_TRAP
@vindex FPE_DECOVF_TRAP
Decimal overflow trap. (Only a few machines have decimal arithmetic and
C never uses it.)
@ignore @c These seem redundant
@comment signal.h
@comment BSD
@item FPE_FLTOVF_FAULT
@vindex FPE_FLTOVF_FAULT
Floating overflow fault.
@comment signal.h
@comment BSD
@item FPE_FLTDIV_FAULT
@vindex FPE_FLTDIV_FAULT
Floating divide by zero fault.
@comment signal.h
@comment BSD
@item FPE_FLTUND_FAULT
@vindex FPE_FLTUND_FAULT
Floating underflow fault.
@end ignore
@end table
@comment signal.h
@comment ISO
@deftypevr Macro int SIGILL
The name of this signal is derived from ``illegal instruction''; it
usually means your program is trying to execute garbage or a privileged
instruction. Since the C compiler generates only valid instructions,
@code{SIGILL} typically indicates that the executable file is corrupted,
or that you are trying to execute data. Some common ways of getting
into the latter situation are by passing an invalid object where a
pointer to a function was expected, or by writing past the end of an
automatic array (or similar problems with pointers to automatic
variables) and corrupting other data on the stack such as the return
address of a stack frame.
@code{SIGILL} can also be generated when the stack overflows, or when
the system has trouble running the handler for a signal.
@end deftypevr
@cindex illegal instruction
@comment signal.h
@comment ISO
@deftypevr Macro int SIGSEGV
@cindex segmentation violation
This signal is generated when a program tries to read or write outside
the memory that is allocated for it, or to write memory that can only be
read. (Actually, the signals only occur when the program goes far
enough outside to be detected by the system's memory protection
mechanism.) The name is an abbreviation for ``segmentation violation''.
Common ways of getting a @code{SIGSEGV} condition include dereferencing
a null or uninitialized pointer, or when you use a pointer to step
through an array, but fail to check for the end of the array. It varies
among systems whether dereferencing a null pointer generates
@code{SIGSEGV} or @code{SIGBUS}.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGBUS
This signal is generated when an invalid pointer is dereferenced. Like
@code{SIGSEGV}, this signal is typically the result of dereferencing an
uninitialized pointer. The difference between the two is that
@code{SIGSEGV} indicates an invalid access to valid memory, while
@code{SIGBUS} indicates an access to an invalid address. In particular,
@code{SIGBUS} signals often result from dereferencing a misaligned
pointer, such as referring to a four-word integer at an address not
divisible by four. (Each kind of computer has its own requirements for
address alignment.)
The name of this signal is an abbreviation for ``bus error''.
@end deftypevr
@cindex bus error
@comment signal.h
@comment ISO
@deftypevr Macro int SIGABRT
@cindex abort signal
This signal indicates an error detected by the program itself and
reported by calling @code{abort}. @xref{Aborting a Program}.
@end deftypevr
@comment signal.h
@comment Unix
@deftypevr Macro int SIGIOT
Generated by the PDP-11 ``iot'' instruction. On most machines, this is
just another name for @code{SIGABRT}.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGTRAP
Generated by the machine's breakpoint instruction, and possibly other
trap instructions. This signal is used by debuggers. Your program will
probably only see @code{SIGTRAP} if it is somehow executing bad
instructions.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGEMT
Emulator trap; this results from certain unimplemented instructions
which might be emulated in software, or the operating system's
failure to properly emulate them.
@end deftypevr
@comment signal.h
@comment Unix
@deftypevr Macro int SIGSYS
Bad system call; that is to say, the instruction to trap to the
operating system was executed, but the code number for the system call
to perform was invalid.
@end deftypevr
@node Termination Signals
@subsection Termination Signals
@cindex program termination signals
These signals are all used to tell a process to terminate, in one way
or another. They have different names because they're used for slightly
different purposes, and programs might want to handle them differently.
The reason for handling these signals is usually so your program can
tidy up as appropriate before actually terminating. For example, you
might want to save state information, delete temporary files, or restore
the previous terminal modes. Such a handler should end by specifying
the default action for the signal that happened and then reraising it;
this will cause the program to terminate with that signal, as if it had
not had a handler. (@xref{Termination in Handler}.)
The (obvious) default action for all of these signals is to cause the
process to terminate.
@comment signal.h
@comment ISO
@deftypevr Macro int SIGTERM
@cindex termination signal
The @code{SIGTERM} signal is a generic signal used to cause program
termination. Unlike @code{SIGKILL}, this signal can be blocked,
handled, and ignored. It is the normal way to politely ask a program to
terminate.
The shell command @code{kill} generates @code{SIGTERM} by default.
@pindex kill
@end deftypevr
@comment signal.h
@comment ISO
@deftypevr Macro int SIGINT
@cindex interrupt signal
The @code{SIGINT} (``program interrupt'') signal is sent when the user
types the INTR character (normally @kbd{C-c}). @xref{Special
Characters}, for information about terminal driver support for
@kbd{C-c}.
@end deftypevr
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGQUIT
@cindex quit signal
@cindex quit signal
The @code{SIGQUIT} signal is similar to @code{SIGINT}, except that it's
controlled by a different key---the QUIT character, usually
@kbd{C-\}---and produces a core dump when it terminates the process,
just like a program error signal. You can think of this as a
program error condition ``detected'' by the user.
@xref{Program Error Signals}, for information about core dumps.
@xref{Special Characters}, for information about terminal driver
support.
Certain kinds of cleanups are best omitted in handling @code{SIGQUIT}.
For example, if the program creates temporary files, it should handle
the other termination requests by deleting the temporary files. But it
is better for @code{SIGQUIT} not to delete them, so that the user can
examine them in conjunction with the core dump.
@end deftypevr
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGKILL
The @code{SIGKILL} signal is used to cause immediate program termination.
It cannot be handled or ignored, and is therefore always fatal. It is
also not possible to block this signal.
This signal is usually generated only by explicit request. Since it
cannot be handled, you should generate it only as a last resort, after
first trying a less drastic method such as @kbd{C-c} or @code{SIGTERM}.
If a process does not respond to any other termination signals, sending
it a @code{SIGKILL} signal will almost always cause it to go away.
In fact, if @code{SIGKILL} fails to terminate a process, that by itself
constitutes an operating system bug which you should report.
The system will generate @code{SIGKILL} for a process itself under some
unusual conditions where the program cannot possibly continue to run
(even to run a signal handler).
@end deftypevr
@cindex kill signal
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGHUP
@cindex hangup signal
The @code{SIGHUP} (``hang-up'') signal is used to report that the user's
terminal is disconnected, perhaps because a network or telephone
connection was broken. For more information about this, see @ref{Control
Modes}.
This signal is also used to report the termination of the controlling
process on a terminal to jobs associated with that session; this
termination effectively disconnects all processes in the session from
the controlling terminal. For more information, see @ref{Termination
Internals}.
@end deftypevr
@node Alarm Signals
@subsection Alarm Signals
These signals are used to indicate the expiration of timers.
@xref{Setting an Alarm}, for information about functions that cause
these signals to be sent.
The default behavior for these signals is to cause program termination.
This default is rarely useful, but no other default would be useful;
most of the ways of using these signals would require handler functions
in any case.
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGALRM
This signal typically indicates expiration of a timer that measures real
or clock time. It is used by the @code{alarm} function, for example.
@end deftypevr
@cindex alarm signal
@comment signal.h
@comment BSD
@deftypevr Macro int SIGVTALRM
This signal typically indicates expiration of a timer that measures CPU
time used by the current process. The name is an abbreviation for
``virtual time alarm''.
@end deftypevr
@cindex virtual time alarm signal
@comment signal.h
@comment BSD
@deftypevr Macro int SIGPROF
This signal typically indicates expiration of a timer that measures
both CPU time used by the current process, and CPU time expended on
behalf of the process by the system. Such a timer is used to implement
code profiling facilities, hence the name of this signal.
@end deftypevr
@cindex profiling alarm signal
@node Asynchronous I/O Signals
@subsection Asynchronous I/O Signals
The signals listed in this section are used in conjunction with
asynchronous I/O facilities. You have to take explicit action by
calling @code{fcntl} to enable a particular file descriptor to generate
these signals (@pxref{Interrupt Input}). The default action for these
signals is to ignore them.
@comment signal.h
@comment BSD
@deftypevr Macro int SIGIO
@cindex input available signal
@cindex output possible signal
This signal is sent when a file descriptor is ready to perform input
or output.
On most operating systems, terminals and sockets are the only kinds of
files that can generate @code{SIGIO}; other kinds, including ordinary
files, never generate @code{SIGIO} even if you ask them to.
On @gnusystems{} @code{SIGIO} will always be generated properly
if you successfully set asynchronous mode with @code{fcntl}.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGURG
@cindex urgent data signal
This signal is sent when ``urgent'' or out-of-band data arrives on a
socket. @xref{Out-of-Band Data}.
@end deftypevr
@comment signal.h
@comment SVID
@deftypevr Macro int SIGPOLL
This is a System V signal name, more or less similar to @code{SIGIO}.
It is defined only for compatibility.
@end deftypevr
@node Job Control Signals
@subsection Job Control Signals
@cindex job control signals
These signals are used to support job control. If your system
doesn't support job control, then these macros are defined but the
signals themselves can't be raised or handled.
You should generally leave these signals alone unless you really
understand how job control works. @xref{Job Control}.
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGCHLD
@cindex child process signal
This signal is sent to a parent process whenever one of its child
processes terminates or stops.
The default action for this signal is to ignore it. If you establish a
handler for this signal while there are child processes that have
terminated but not reported their status via @code{wait} or
@code{waitpid} (@pxref{Process Completion}), whether your new handler
applies to those processes or not depends on the particular operating
system.
@end deftypevr
@comment signal.h
@comment SVID
@deftypevr Macro int SIGCLD
This is an obsolete name for @code{SIGCHLD}.
@end deftypevr
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGCONT
@cindex continue signal
You can send a @code{SIGCONT} signal to a process to make it continue.
This signal is special---it always makes the process continue if it is
stopped, before the signal is delivered. The default behavior is to do
nothing else. You cannot block this signal. You can set a handler, but
@code{SIGCONT} always makes the process continue regardless.
Most programs have no reason to handle @code{SIGCONT}; they simply
resume execution without realizing they were ever stopped. You can use
a handler for @code{SIGCONT} to make a program do something special when
it is stopped and continued---for example, to reprint a prompt when it
is suspended while waiting for input.
@end deftypevr
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGSTOP
The @code{SIGSTOP} signal stops the process. It cannot be handled,
ignored, or blocked.
@end deftypevr
@cindex stop signal
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGTSTP
The @code{SIGTSTP} signal is an interactive stop signal. Unlike
@code{SIGSTOP}, this signal can be handled and ignored.
Your program should handle this signal if you have a special need to
leave files or system tables in a secure state when a process is
stopped. For example, programs that turn off echoing should handle
@code{SIGTSTP} so they can turn echoing back on before stopping.
This signal is generated when the user types the SUSP character
(normally @kbd{C-z}). For more information about terminal driver
support, see @ref{Special Characters}.
@end deftypevr
@cindex interactive stop signal
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGTTIN
A process cannot read from the user's terminal while it is running
as a background job. When any process in a background job tries to
read from the terminal, all of the processes in the job are sent a
@code{SIGTTIN} signal. The default action for this signal is to
stop the process. For more information about how this interacts with
the terminal driver, see @ref{Access to the Terminal}.
@end deftypevr
@cindex terminal input signal
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGTTOU
This is similar to @code{SIGTTIN}, but is generated when a process in a
background job attempts to write to the terminal or set its modes.
Again, the default action is to stop the process. @code{SIGTTOU} is
only generated for an attempt to write to the terminal if the
@code{TOSTOP} output mode is set; @pxref{Output Modes}.
@end deftypevr
@cindex terminal output signal
While a process is stopped, no more signals can be delivered to it until
it is continued, except @code{SIGKILL} signals and (obviously)
@code{SIGCONT} signals. The signals are marked as pending, but not
delivered until the process is continued. The @code{SIGKILL} signal
always causes termination of the process and can't be blocked, handled
or ignored. You can ignore @code{SIGCONT}, but it always causes the
process to be continued anyway if it is stopped. Sending a
@code{SIGCONT} signal to a process causes any pending stop signals for
that process to be discarded. Likewise, any pending @code{SIGCONT}
signals for a process are discarded when it receives a stop signal.
When a process in an orphaned process group (@pxref{Orphaned Process
Groups}) receives a @code{SIGTSTP}, @code{SIGTTIN}, or @code{SIGTTOU}
signal and does not handle it, the process does not stop. Stopping the
process would probably not be very useful, since there is no shell
program that will notice it stop and allow the user to continue it.
What happens instead depends on the operating system you are using.
Some systems may do nothing; others may deliver another signal instead,
such as @code{SIGKILL} or @code{SIGHUP}. On @gnuhurdsystems{}, the process
dies with @code{SIGKILL}; this avoids the problem of many stopped,
orphaned processes lying around the system.
@ignore
On @gnuhurdsystems{}, it is possible to reattach to the orphaned process
group and continue it, so stop signals do stop the process as usual on
@gnuhurdsystems{} unless you have requested POSIX compatibility ``till it
hurts.''
@end ignore
@node Operation Error Signals
@subsection Operation Error Signals
These signals are used to report various errors generated by an
operation done by the program. They do not necessarily indicate a
programming error in the program, but an error that prevents an
operating system call from completing. The default action for all of
them is to cause the process to terminate.
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGPIPE
@cindex pipe signal
@cindex broken pipe signal
Broken pipe. If you use pipes or FIFOs, you have to design your
application so that one process opens the pipe for reading before
another starts writing. If the reading process never starts, or
terminates unexpectedly, writing to the pipe or FIFO raises a
@code{SIGPIPE} signal. If @code{SIGPIPE} is blocked, handled or
ignored, the offending call fails with @code{EPIPE} instead.
Pipes and FIFO special files are discussed in more detail in @ref{Pipes
and FIFOs}.
Another cause of @code{SIGPIPE} is when you try to output to a socket
that isn't connected. @xref{Sending Data}.
@end deftypevr
@comment signal.h
@comment GNU
@deftypevr Macro int SIGLOST
@cindex lost resource signal
Resource lost. This signal is generated when you have an advisory lock
on an NFS file, and the NFS server reboots and forgets about your lock.
On @gnuhurdsystems{}, @code{SIGLOST} is generated when any server program
dies unexpectedly. It is usually fine to ignore the signal; whatever
call was made to the server that died just returns an error.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGXCPU
CPU time limit exceeded. This signal is generated when the process
exceeds its soft resource limit on CPU time. @xref{Limits on Resources}.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGXFSZ
File size limit exceeded. This signal is generated when the process
attempts to extend a file so it exceeds the process's soft resource
limit on file size. @xref{Limits on Resources}.
@end deftypevr
@node Miscellaneous Signals
@subsection Miscellaneous Signals
These signals are used for various other purposes. In general, they
will not affect your program unless it explicitly uses them for something.
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SIGUSR1
@comment signal.h
@comment POSIX.1
@deftypevrx Macro int SIGUSR2
@cindex user signals
The @code{SIGUSR1} and @code{SIGUSR2} signals are set aside for you to
use any way you want. They're useful for simple interprocess
communication, if you write a signal handler for them in the program
that receives the signal.
There is an example showing the use of @code{SIGUSR1} and @code{SIGUSR2}
in @ref{Signaling Another Process}.
The default action is to terminate the process.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGWINCH
Window size change. This is generated on some systems (including GNU)
when the terminal driver's record of the number of rows and columns on
the screen is changed. The default action is to ignore it.
If a program does full-screen display, it should handle @code{SIGWINCH}.
When the signal arrives, it should fetch the new screen size and
reformat its display accordingly.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SIGINFO
Information request. On 4.4 BSD and @gnuhurdsystems{}, this signal is sent
to all the processes in the foreground process group of the controlling
terminal when the user types the STATUS character in canonical mode;
@pxref{Signal Characters}.
If the process is the leader of the process group, the default action is
to print some status information about the system and what the process
is doing. Otherwise the default is to do nothing.
@end deftypevr
@node Signal Messages
@subsection Signal Messages
@cindex signal messages
We mentioned above that the shell prints a message describing the signal
that terminated a child process. The clean way to print a message
describing a signal is to use the functions @code{strsignal} and
@code{psignal}. These functions use a signal number to specify which
kind of signal to describe. The signal number may come from the
termination status of a child process (@pxref{Process Completion}) or it
may come from a signal handler in the same process.
@comment string.h
@comment GNU
@deftypefun {char *} strsignal (int @var{signum})
@safety{@prelim{}@mtunsafe{@mtasurace{:strsignal} @mtslocale{}}@asunsafe{@asuinit{} @ascuintl{} @asucorrupt{} @ascuheap{}}@acunsafe{@acuinit{} @acucorrupt{} @acsmem{}}}
@c strsignal @mtasurace:strsignal @mtslocale @asuinit @ascuintl @asucorrupt @ascuheap @acucorrupt @acsmem
@c uses a static buffer if tsd key creation fails
@c [once] init
@c libc_key_create ok
@c pthread_key_create dup ok
@c getbuffer @asucorrupt @ascuheap @acsmem
@c libc_getspecific ok
@c pthread_getspecific dup ok
@c malloc dup @ascuheap @acsmem
@c libc_setspecific @asucorrupt @ascuheap @acucorrupt @acsmem
@c pthread_setspecific dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c snprintf dup @mtslocale @ascuheap @acsmem
@c _ @ascuintl
This function returns a pointer to a statically-allocated string
containing a message describing the signal @var{signum}. You
should not modify the contents of this string; and, since it can be
rewritten on subsequent calls, you should save a copy of it if you need
to reference it later.
@pindex string.h
This function is a GNU extension, declared in the header file
@file{string.h}.
@end deftypefun
@comment signal.h
@comment BSD
@deftypefun void psignal (int @var{signum}, const char *@var{message})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuintl{} @ascuheap{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{}}}
@c psignal @mtslocale @asucorrupt @ascuintl @ascuheap @aculock @acucorrupt @acsmem
@c _ @ascuintl
@c fxprintf @asucorrupt @aculock @acucorrupt
@c asprintf @mtslocale @ascuheap @acsmem
@c free dup @ascuheap @acsmem
This function prints a message describing the signal @var{signum} to the
standard error output stream @code{stderr}; see @ref{Standard Streams}.
If you call @code{psignal} with a @var{message} that is either a null
pointer or an empty string, @code{psignal} just prints the message
corresponding to @var{signum}, adding a trailing newline.
If you supply a non-null @var{message} argument, then @code{psignal}
prefixes its output with this string. It adds a colon and a space
character to separate the @var{message} from the string corresponding
to @var{signum}.
@pindex stdio.h
This function is a BSD feature, declared in the header file @file{signal.h}.
@end deftypefun
@vindex sys_siglist
There is also an array @code{sys_siglist} which contains the messages
for the various signal codes. This array exists on BSD systems, unlike
@code{strsignal}.
@node Signal Actions
@section Specifying Signal Actions
@cindex signal actions
@cindex establishing a handler
The simplest way to change the action for a signal is to use the
@code{signal} function. You can specify a built-in action (such as to
ignore the signal), or you can @dfn{establish a handler}.
@Theglibc{} also implements the more versatile @code{sigaction}
facility. This section describes both facilities and gives suggestions
on which to use when.
@menu
* Basic Signal Handling:: The simple @code{signal} function.
* Advanced Signal Handling:: The more powerful @code{sigaction} function.
* Signal and Sigaction:: How those two functions interact.
* Sigaction Function Example:: An example of using the sigaction function.
* Flags for Sigaction:: Specifying options for signal handling.
* Initial Signal Actions:: How programs inherit signal actions.
@end menu
@node Basic Signal Handling
@subsection Basic Signal Handling
@cindex @code{signal} function
The @code{signal} function provides a simple interface for establishing
an action for a particular signal. The function and associated macros
are declared in the header file @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment GNU
@deftp {Data Type} sighandler_t
This is the type of signal handler functions. Signal handlers take one
integer argument specifying the signal number, and have return type
@code{void}. So, you should define handler functions like this:
@smallexample
void @var{handler} (int @code{signum}) @{ @dots{} @}
@end smallexample
The name @code{sighandler_t} for this data type is a GNU extension.
@end deftp
@comment signal.h
@comment ISO
@deftypefun sighandler_t signal (int @var{signum}, sighandler_t @var{action})
@safety{@prelim{}@mtsafe{@mtssigintr{}}@assafe{}@acsafe{}}
@c signal ok
@c sigemptyset dup ok
@c sigaddset dup ok
@c sigismember dup ok
@c sigaction dup ok
The @code{signal} function establishes @var{action} as the action for
the signal @var{signum}.
The first argument, @var{signum}, identifies the signal whose behavior
you want to control, and should be a signal number. The proper way to
specify a signal number is with one of the symbolic signal names
(@pxref{Standard Signals})---don't use an explicit number, because
the numerical code for a given kind of signal may vary from operating
system to operating system.
The second argument, @var{action}, specifies the action to use for the
signal @var{signum}. This can be one of the following:
@table @code
@item SIG_DFL
@vindex SIG_DFL
@cindex default action for a signal
@code{SIG_DFL} specifies the default action for the particular signal.
The default actions for various kinds of signals are stated in
@ref{Standard Signals}.
@item SIG_IGN
@vindex SIG_IGN
@cindex ignore action for a signal
@code{SIG_IGN} specifies that the signal should be ignored.
Your program generally should not ignore signals that represent serious
events or that are normally used to request termination. You cannot
ignore the @code{SIGKILL} or @code{SIGSTOP} signals at all. You can
ignore program error signals like @code{SIGSEGV}, but ignoring the error
won't enable the program to continue executing meaningfully. Ignoring
user requests such as @code{SIGINT}, @code{SIGQUIT}, and @code{SIGTSTP}
is unfriendly.
When you do not wish signals to be delivered during a certain part of
the program, the thing to do is to block them, not ignore them.
@xref{Blocking Signals}.
@item @var{handler}
Supply the address of a handler function in your program, to specify
running this handler as the way to deliver the signal.
For more information about defining signal handler functions,
see @ref{Defining Handlers}.
@end table
If you set the action for a signal to @code{SIG_IGN}, or if you set it
to @code{SIG_DFL} and the default action is to ignore that signal, then
any pending signals of that type are discarded (even if they are
blocked). Discarding the pending signals means that they will never be
delivered, not even if you subsequently specify another action and
unblock this kind of signal.
The @code{signal} function returns the action that was previously in
effect for the specified @var{signum}. You can save this value and
restore it later by calling @code{signal} again.
If @code{signal} can't honor the request, it returns @code{SIG_ERR}
instead. The following @code{errno} error conditions are defined for
this function:
@table @code
@item EINVAL
You specified an invalid @var{signum}; or you tried to ignore or provide
a handler for @code{SIGKILL} or @code{SIGSTOP}.
@end table
@end deftypefun
@strong{Compatibility Note:} A problem encountered when working with the
@code{signal} function is that it has different semantics on BSD and
SVID systems. The difference is that on SVID systems the signal handler
is deinstalled after signal delivery. On BSD systems the
handler must be explicitly deinstalled. In @theglibc{} we use the
BSD version by default. To use the SVID version you can either use the
function @code{sysv_signal} (see below) or use the @code{_XOPEN_SOURCE}
feature select macro (@pxref{Feature Test Macros}). In general, use of these
functions should be avoided because of compatibility problems. It
is better to use @code{sigaction} if it is available since the results
are much more reliable.
Here is a simple example of setting up a handler to delete temporary
files when certain fatal signals happen:
@smallexample
#include
void
termination_handler (int signum)
@{
struct temp_file *p;
for (p = temp_file_list; p; p = p->next)
unlink (p->name);
@}
int
main (void)
@{
@dots{}
if (signal (SIGINT, termination_handler) == SIG_IGN)
signal (SIGINT, SIG_IGN);
if (signal (SIGHUP, termination_handler) == SIG_IGN)
signal (SIGHUP, SIG_IGN);
if (signal (SIGTERM, termination_handler) == SIG_IGN)
signal (SIGTERM, SIG_IGN);
@dots{}
@}
@end smallexample
@noindent
Note that if a given signal was previously set to be ignored, this code
avoids altering that setting. This is because non-job-control shells
often ignore certain signals when starting children, and it is important
for the children to respect this.
We do not handle @code{SIGQUIT} or the program error signals in this
example because these are designed to provide information for debugging
(a core dump), and the temporary files may give useful information.
@comment signal.h
@comment GNU
@deftypefun sighandler_t sysv_signal (int @var{signum}, sighandler_t @var{action})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c sysv_signal ok
@c sigemptyset dup ok
@c sigaction dup ok
The @code{sysv_signal} implements the behavior of the standard
@code{signal} function as found on SVID systems. The difference to BSD
systems is that the handler is deinstalled after a delivery of a signal.
@strong{Compatibility Note:} As said above for @code{signal}, this
function should be avoided when possible. @code{sigaction} is the
preferred method.
@end deftypefun
@comment signal.h
@comment SVID
@deftypefun sighandler_t ssignal (int @var{signum}, sighandler_t @var{action})
@safety{@prelim{}@mtsafe{@mtssigintr{}}@assafe{}@acsafe{}}
@c Aliases signal and bsd_signal.
The @code{ssignal} function does the same thing as @code{signal}; it is
provided only for compatibility with SVID.
@end deftypefun
@comment signal.h
@comment ISO
@deftypevr Macro sighandler_t SIG_ERR
The value of this macro is used as the return value from @code{signal}
to indicate an error.
@end deftypevr
@ignore
@comment RMS says that ``we don't do this''.
Implementations might define additional macros for built-in signal
actions that are suitable as a @var{action} argument to @code{signal},
besides @code{SIG_IGN} and @code{SIG_DFL}. Identifiers whose names
begin with @samp{SIG_} followed by an uppercase letter are reserved for
this purpose.
@end ignore
@node Advanced Signal Handling
@subsection Advanced Signal Handling
@cindex @code{sigaction} function
The @code{sigaction} function has the same basic effect as
@code{signal}: to specify how a signal should be handled by the process.
However, @code{sigaction} offers more control, at the expense of more
complexity. In particular, @code{sigaction} allows you to specify
additional flags to control when the signal is generated and how the
handler is invoked.
The @code{sigaction} function is declared in @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment POSIX.1
@deftp {Data Type} {struct sigaction}
Structures of type @code{struct sigaction} are used in the
@code{sigaction} function to specify all the information about how to
handle a particular signal. This structure contains at least the
following members:
@table @code
@item sighandler_t sa_handler
This is used in the same way as the @var{action} argument to the
@code{signal} function. The value can be @code{SIG_DFL},
@code{SIG_IGN}, or a function pointer. @xref{Basic Signal Handling}.
@item sigset_t sa_mask
This specifies a set of signals to be blocked while the handler runs.
Blocking is explained in @ref{Blocking for Handler}. Note that the
signal that was delivered is automatically blocked by default before its
handler is started; this is true regardless of the value in
@code{sa_mask}. If you want that signal not to be blocked within its
handler, you must write code in the handler to unblock it.
@item int sa_flags
This specifies various flags which can affect the behavior of
the signal. These are described in more detail in @ref{Flags for Sigaction}.
@end table
@end deftp
@comment signal.h
@comment POSIX.1
@deftypefun int sigaction (int @var{signum}, const struct sigaction *restrict @var{action}, struct sigaction *restrict @var{old-action})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @var{action} argument is used to set up a new action for the signal
@var{signum}, while the @var{old-action} argument is used to return
information about the action previously associated with this symbol.
(In other words, @var{old-action} has the same purpose as the
@code{signal} function's return value---you can check to see what the
old action in effect for the signal was, and restore it later if you
want.)
Either @var{action} or @var{old-action} can be a null pointer. If
@var{old-action} is a null pointer, this simply suppresses the return
of information about the old action. If @var{action} is a null pointer,
the action associated with the signal @var{signum} is unchanged; this
allows you to inquire about how a signal is being handled without changing
that handling.
The return value from @code{sigaction} is zero if it succeeds, and
@code{-1} on failure. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EINVAL
The @var{signum} argument is not valid, or you are trying to
trap or ignore @code{SIGKILL} or @code{SIGSTOP}.
@end table
@end deftypefun
@node Signal and Sigaction
@subsection Interaction of @code{signal} and @code{sigaction}
It's possible to use both the @code{signal} and @code{sigaction}
functions within a single program, but you have to be careful because
they can interact in slightly strange ways.
The @code{sigaction} function specifies more information than the
@code{signal} function, so the return value from @code{signal} cannot
express the full range of @code{sigaction} possibilities. Therefore, if
you use @code{signal} to save and later reestablish an action, it may
not be able to reestablish properly a handler that was established with
@code{sigaction}.
To avoid having problems as a result, always use @code{sigaction} to
save and restore a handler if your program uses @code{sigaction} at all.
Since @code{sigaction} is more general, it can properly save and
reestablish any action, regardless of whether it was established
originally with @code{signal} or @code{sigaction}.
On some systems if you establish an action with @code{signal} and then
examine it with @code{sigaction}, the handler address that you get may
not be the same as what you specified with @code{signal}. It may not
even be suitable for use as an action argument with @code{signal}. But
you can rely on using it as an argument to @code{sigaction}. This
problem never happens on @gnusystems{}.
So, you're better off using one or the other of the mechanisms
consistently within a single program.
@strong{Portability Note:} The basic @code{signal} function is a feature
of @w{ISO C}, while @code{sigaction} is part of the POSIX.1 standard. If
you are concerned about portability to non-POSIX systems, then you
should use the @code{signal} function instead.
@node Sigaction Function Example
@subsection @code{sigaction} Function Example
In @ref{Basic Signal Handling}, we gave an example of establishing a
simple handler for termination signals using @code{signal}. Here is an
equivalent example using @code{sigaction}:
@smallexample
#include
void
termination_handler (int signum)
@{
struct temp_file *p;
for (p = temp_file_list; p; p = p->next)
unlink (p->name);
@}
int
main (void)
@{
@dots{}
struct sigaction new_action, old_action;
/* @r{Set up the structure to specify the new action.} */
new_action.sa_handler = termination_handler;
sigemptyset (&new_action.sa_mask);
new_action.sa_flags = 0;
sigaction (SIGINT, NULL, &old_action);
if (old_action.sa_handler != SIG_IGN)
sigaction (SIGINT, &new_action, NULL);
sigaction (SIGHUP, NULL, &old_action);
if (old_action.sa_handler != SIG_IGN)
sigaction (SIGHUP, &new_action, NULL);
sigaction (SIGTERM, NULL, &old_action);
if (old_action.sa_handler != SIG_IGN)
sigaction (SIGTERM, &new_action, NULL);
@dots{}
@}
@end smallexample
The program just loads the @code{new_action} structure with the desired
parameters and passes it in the @code{sigaction} call. The usage of
@code{sigemptyset} is described later; see @ref{Blocking Signals}.
As in the example using @code{signal}, we avoid handling signals
previously set to be ignored. Here we can avoid altering the signal
handler even momentarily, by using the feature of @code{sigaction} that
lets us examine the current action without specifying a new one.
Here is another example. It retrieves information about the current
action for @code{SIGINT} without changing that action.
@smallexample
struct sigaction query_action;
if (sigaction (SIGINT, NULL, &query_action) < 0)
/* @r{@code{sigaction} returns -1 in case of error.} */
else if (query_action.sa_handler == SIG_DFL)
/* @r{@code{SIGINT} is handled in the default, fatal manner.} */
else if (query_action.sa_handler == SIG_IGN)
/* @r{@code{SIGINT} is ignored.} */
else
/* @r{A programmer-defined signal handler is in effect.} */
@end smallexample
@node Flags for Sigaction
@subsection Flags for @code{sigaction}
@cindex signal flags
@cindex flags for @code{sigaction}
@cindex @code{sigaction} flags
The @code{sa_flags} member of the @code{sigaction} structure is a
catch-all for special features. Most of the time, @code{SA_RESTART} is
a good value to use for this field.
The value of @code{sa_flags} is interpreted as a bit mask. Thus, you
should choose the flags you want to set, @sc{or} those flags together,
and store the result in the @code{sa_flags} member of your
@code{sigaction} structure.
Each signal number has its own set of flags. Each call to
@code{sigaction} affects one particular signal number, and the flags
that you specify apply only to that particular signal.
In @theglibc{}, establishing a handler with @code{signal} sets all
the flags to zero except for @code{SA_RESTART}, whose value depends on
the settings you have made with @code{siginterrupt}. @xref{Interrupted
Primitives}, to see what this is about.
@pindex signal.h
These macros are defined in the header file @file{signal.h}.
@comment signal.h
@comment POSIX.1
@deftypevr Macro int SA_NOCLDSTOP
This flag is meaningful only for the @code{SIGCHLD} signal. When the
flag is set, the system delivers the signal for a terminated child
process but not for one that is stopped. By default, @code{SIGCHLD} is
delivered for both terminated children and stopped children.
Setting this flag for a signal other than @code{SIGCHLD} has no effect.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SA_ONSTACK
If this flag is set for a particular signal number, the system uses the
signal stack when delivering that kind of signal. @xref{Signal Stack}.
If a signal with this flag arrives and you have not set a signal stack,
the system terminates the program with @code{SIGILL}.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SA_RESTART
This flag controls what happens when a signal is delivered during
certain primitives (such as @code{open}, @code{read} or @code{write}),
and the signal handler returns normally. There are two alternatives:
the library function can resume, or it can return failure with error
code @code{EINTR}.
The choice is controlled by the @code{SA_RESTART} flag for the
particular kind of signal that was delivered. If the flag is set,
returning from a handler resumes the library function. If the flag is
clear, returning from a handler makes the function fail.
@xref{Interrupted Primitives}.
@end deftypevr
@node Initial Signal Actions
@subsection Initial Signal Actions
@cindex initial signal actions
When a new process is created (@pxref{Creating a Process}), it inherits
handling of signals from its parent process. However, when you load a
new process image using the @code{exec} function (@pxref{Executing a
File}), any signals that you've defined your own handlers for revert to
their @code{SIG_DFL} handling. (If you think about it a little, this
makes sense; the handler functions from the old program are specific to
that program, and aren't even present in the address space of the new
program image.) Of course, the new program can establish its own
handlers.
When a program is run by a shell, the shell normally sets the initial
actions for the child process to @code{SIG_DFL} or @code{SIG_IGN}, as
appropriate. It's a good idea to check to make sure that the shell has
not set up an initial action of @code{SIG_IGN} before you establish your
own signal handlers.
Here is an example of how to establish a handler for @code{SIGHUP}, but
not if @code{SIGHUP} is currently ignored:
@smallexample
@group
@dots{}
struct sigaction temp;
sigaction (SIGHUP, NULL, &temp);
if (temp.sa_handler != SIG_IGN)
@{
temp.sa_handler = handle_sighup;
sigemptyset (&temp.sa_mask);
sigaction (SIGHUP, &temp, NULL);
@}
@end group
@end smallexample
@node Defining Handlers
@section Defining Signal Handlers
@cindex signal handler function
This section describes how to write a signal handler function that can
be established with the @code{signal} or @code{sigaction} functions.
A signal handler is just a function that you compile together with the
rest of the program. Instead of directly invoking the function, you use
@code{signal} or @code{sigaction} to tell the operating system to call
it when a signal arrives. This is known as @dfn{establishing} the
handler. @xref{Signal Actions}.
There are two basic strategies you can use in signal handler functions:
@itemize @bullet
@item
You can have the handler function note that the signal arrived by
tweaking some global data structures, and then return normally.
@item
You can have the handler function terminate the program or transfer
control to a point where it can recover from the situation that caused
the signal.
@end itemize
You need to take special care in writing handler functions because they
can be called asynchronously. That is, a handler might be called at any
point in the program, unpredictably. If two signals arrive during a
very short interval, one handler can run within another. This section
describes what your handler should do, and what you should avoid.
@menu
* Handler Returns:: Handlers that return normally, and what
this means.
* Termination in Handler:: How handler functions terminate a program.
* Longjmp in Handler:: Nonlocal transfer of control out of a
signal handler.
* Signals in Handler:: What happens when signals arrive while
the handler is already occupied.
* Merged Signals:: When a second signal arrives before the
first is handled.
* Nonreentrancy:: Do not call any functions unless you know they
are reentrant with respect to signals.
* Atomic Data Access:: A single handler can run in the middle of
reading or writing a single object.
@end menu
@node Handler Returns
@subsection Signal Handlers that Return
Handlers which return normally are usually used for signals such as
@code{SIGALRM} and the I/O and interprocess communication signals. But
a handler for @code{SIGINT} might also return normally after setting a
flag that tells the program to exit at a convenient time.
It is not safe to return normally from the handler for a program error
signal, because the behavior of the program when the handler function
returns is not defined after a program error. @xref{Program Error
Signals}.
Handlers that return normally must modify some global variable in order
to have any effect. Typically, the variable is one that is examined
periodically by the program during normal operation. Its data type
should be @code{sig_atomic_t} for reasons described in @ref{Atomic
Data Access}.
Here is a simple example of such a program. It executes the body of
the loop until it has noticed that a @code{SIGALRM} signal has arrived.
This technique is useful because it allows the iteration in progress
when the signal arrives to complete before the loop exits.
@smallexample
@include sigh1.c.texi
@end smallexample
@node Termination in Handler
@subsection Handlers That Terminate the Process
Handler functions that terminate the program are typically used to cause
orderly cleanup or recovery from program error signals and interactive
interrupts.
The cleanest way for a handler to terminate the process is to raise the
same signal that ran the handler in the first place. Here is how to do
this:
@smallexample
volatile sig_atomic_t fatal_error_in_progress = 0;
void
fatal_error_signal (int sig)
@{
@group
/* @r{Since this handler is established for more than one kind of signal, }
@r{it might still get invoked recursively by delivery of some other kind}
@r{of signal. Use a static variable to keep track of that.} */
if (fatal_error_in_progress)
raise (sig);
fatal_error_in_progress = 1;
@end group
@group
/* @r{Now do the clean up actions:}
@r{- reset terminal modes}
@r{- kill child processes}
@r{- remove lock files} */
@dots{}
@end group
@group
/* @r{Now reraise the signal. We reactivate the signal's}
@r{default handling, which is to terminate the process.}
@r{We could just call @code{exit} or @code{abort},}
@r{but reraising the signal sets the return status}
@r{from the process correctly.} */
signal (sig, SIG_DFL);
raise (sig);
@}
@end group
@end smallexample
@node Longjmp in Handler
@subsection Nonlocal Control Transfer in Handlers
@cindex non-local exit, from signal handler
You can do a nonlocal transfer of control out of a signal handler using
the @code{setjmp} and @code{longjmp} facilities (@pxref{Non-Local
Exits}).
When the handler does a nonlocal control transfer, the part of the
program that was running will not continue. If this part of the program
was in the middle of updating an important data structure, the data
structure will remain inconsistent. Since the program does not
terminate, the inconsistency is likely to be noticed later on.
There are two ways to avoid this problem. One is to block the signal
for the parts of the program that update important data structures.
Blocking the signal delays its delivery until it is unblocked, once the
critical updating is finished. @xref{Blocking Signals}.
The other way is to re-initialize the crucial data structures in the
signal handler, or to make their values consistent.
Here is a rather schematic example showing the reinitialization of one
global variable.
@smallexample
@group
#include
#include
jmp_buf return_to_top_level;
volatile sig_atomic_t waiting_for_input;
void
handle_sigint (int signum)
@{
/* @r{We may have been waiting for input when the signal arrived,}
@r{but we are no longer waiting once we transfer control.} */
waiting_for_input = 0;
longjmp (return_to_top_level, 1);
@}
@end group
@group
int
main (void)
@{
@dots{}
signal (SIGINT, sigint_handler);
@dots{}
while (1) @{
prepare_for_command ();
if (setjmp (return_to_top_level) == 0)
read_and_execute_command ();
@}
@}
@end group
@group
/* @r{Imagine this is a subroutine used by various commands.} */
char *
read_data ()
@{
if (input_from_terminal) @{
waiting_for_input = 1;
@dots{}
waiting_for_input = 0;
@} else @{
@dots{}
@}
@}
@end group
@end smallexample
@node Signals in Handler
@subsection Signals Arriving While a Handler Runs
@cindex race conditions, relating to signals
What happens if another signal arrives while your signal handler
function is running?
When the handler for a particular signal is invoked, that signal is
automatically blocked until the handler returns. That means that if two
signals of the same kind arrive close together, the second one will be
held until the first has been handled. (The handler can explicitly
unblock the signal using @code{sigprocmask}, if you want to allow more
signals of this type to arrive; see @ref{Process Signal Mask}.)
However, your handler can still be interrupted by delivery of another
kind of signal. To avoid this, you can use the @code{sa_mask} member of
the action structure passed to @code{sigaction} to explicitly specify
which signals should be blocked while the signal handler runs. These
signals are in addition to the signal for which the handler was invoked,
and any other signals that are normally blocked by the process.
@xref{Blocking for Handler}.
When the handler returns, the set of blocked signals is restored to the
value it had before the handler ran. So using @code{sigprocmask} inside
the handler only affects what signals can arrive during the execution of
the handler itself, not what signals can arrive once the handler returns.
@strong{Portability Note:} Always use @code{sigaction} to establish a
handler for a signal that you expect to receive asynchronously, if you
want your program to work properly on System V Unix. On this system,
the handling of a signal whose handler was established with
@code{signal} automatically sets the signal's action back to
@code{SIG_DFL}, and the handler must re-establish itself each time it
runs. This practice, while inconvenient, does work when signals cannot
arrive in succession. However, if another signal can arrive right away,
it may arrive before the handler can re-establish itself. Then the
second signal would receive the default handling, which could terminate
the process.
@node Merged Signals
@subsection Signals Close Together Merge into One
@cindex handling multiple signals
@cindex successive signals
@cindex merging of signals
If multiple signals of the same type are delivered to your process
before your signal handler has a chance to be invoked at all, the
handler may only be invoked once, as if only a single signal had
arrived. In effect, the signals merge into one. This situation can
arise when the signal is blocked, or in a multiprocessing environment
where the system is busy running some other processes while the signals
are delivered. This means, for example, that you cannot reliably use a
signal handler to count signals. The only distinction you can reliably
make is whether at least one signal has arrived since a given time in
the past.
Here is an example of a handler for @code{SIGCHLD} that compensates for
the fact that the number of signals received may not equal the number of
child processes that generate them. It assumes that the program keeps track
of all the child processes with a chain of structures as follows:
@smallexample
struct process
@{
struct process *next;
/* @r{The process ID of this child.} */
int pid;
/* @r{The descriptor of the pipe or pseudo terminal}
@r{on which output comes from this child.} */
int input_descriptor;
/* @r{Nonzero if this process has stopped or terminated.} */
sig_atomic_t have_status;
/* @r{The status of this child; 0 if running,}
@r{otherwise a status value from @code{waitpid}.} */
int status;
@};
struct process *process_list;
@end smallexample
This example also uses a flag to indicate whether signals have arrived
since some time in the past---whenever the program last cleared it to
zero.
@smallexample
/* @r{Nonzero means some child's status has changed}
@r{so look at @code{process_list} for the details.} */
int process_status_change;
@end smallexample
Here is the handler itself:
@smallexample
void
sigchld_handler (int signo)
@{
int old_errno = errno;
while (1) @{
register int pid;
int w;
struct process *p;
/* @r{Keep asking for a status until we get a definitive result.} */
do
@{
errno = 0;
pid = waitpid (WAIT_ANY, &w, WNOHANG | WUNTRACED);
@}
while (pid <= 0 && errno == EINTR);
if (pid <= 0) @{
/* @r{A real failure means there are no more}
@r{stopped or terminated child processes, so return.} */
errno = old_errno;
return;
@}
/* @r{Find the process that signaled us, and record its status.} */
for (p = process_list; p; p = p->next)
if (p->pid == pid) @{
p->status = w;
/* @r{Indicate that the @code{status} field}
@r{has data to look at. We do this only after storing it.} */
p->have_status = 1;
/* @r{If process has terminated, stop waiting for its output.} */
if (WIFSIGNALED (w) || WIFEXITED (w))
if (p->input_descriptor)
FD_CLR (p->input_descriptor, &input_wait_mask);
/* @r{The program should check this flag from time to time}
@r{to see if there is any news in @code{process_list}.} */
++process_status_change;
@}
/* @r{Loop around to handle all the processes}
@r{that have something to tell us.} */
@}
@}
@end smallexample
Here is the proper way to check the flag @code{process_status_change}:
@smallexample
if (process_status_change) @{
struct process *p;
process_status_change = 0;
for (p = process_list; p; p = p->next)
if (p->have_status) @{
@dots{} @r{Examine @code{p->status}} @dots{}
@}
@}
@end smallexample
@noindent
It is vital to clear the flag before examining the list; otherwise, if a
signal were delivered just before the clearing of the flag, and after
the appropriate element of the process list had been checked, the status
change would go unnoticed until the next signal arrived to set the flag
again. You could, of course, avoid this problem by blocking the signal
while scanning the list, but it is much more elegant to guarantee
correctness by doing things in the right order.
The loop which checks process status avoids examining @code{p->status}
until it sees that status has been validly stored. This is to make sure
that the status cannot change in the middle of accessing it. Once
@code{p->have_status} is set, it means that the child process is stopped
or terminated, and in either case, it cannot stop or terminate again
until the program has taken notice. @xref{Atomic Usage}, for more
information about coping with interruptions during accesses of a
variable.
Here is another way you can test whether the handler has run since the
last time you checked. This technique uses a counter which is never
changed outside the handler. Instead of clearing the count, the program
remembers the previous value and sees whether it has changed since the
previous check. The advantage of this method is that different parts of
the program can check independently, each part checking whether there
has been a signal since that part last checked.
@smallexample
sig_atomic_t process_status_change;
sig_atomic_t last_process_status_change;
@dots{}
@{
sig_atomic_t prev = last_process_status_change;
last_process_status_change = process_status_change;
if (last_process_status_change != prev) @{
struct process *p;
for (p = process_list; p; p = p->next)
if (p->have_status) @{
@dots{} @r{Examine @code{p->status}} @dots{}
@}
@}
@}
@end smallexample
@node Nonreentrancy
@subsection Signal Handling and Nonreentrant Functions
@cindex restrictions on signal handler functions
Handler functions usually don't do very much. The best practice is to
write a handler that does nothing but set an external variable that the
program checks regularly, and leave all serious work to the program.
This is best because the handler can be called asynchronously, at
unpredictable times---perhaps in the middle of a primitive function, or
even between the beginning and the end of a C operator that requires
multiple instructions. The data structures being manipulated might
therefore be in an inconsistent state when the handler function is
invoked. Even copying one @code{int} variable into another can take two
instructions on most machines.
This means you have to be very careful about what you do in a signal
handler.
@itemize @bullet
@item
@cindex @code{volatile} declarations
If your handler needs to access any global variables from your program,
declare those variables @code{volatile}. This tells the compiler that
the value of the variable might change asynchronously, and inhibits
certain optimizations that would be invalidated by such modifications.
@item
@cindex reentrant functions
If you call a function in the handler, make sure it is @dfn{reentrant}
with respect to signals, or else make sure that the signal cannot
interrupt a call to a related function.
@end itemize
A function can be non-reentrant if it uses memory that is not on the
stack.
@itemize @bullet
@item
If a function uses a static variable or a global variable, or a
dynamically-allocated object that it finds for itself, then it is
non-reentrant and any two calls to the function can interfere.
For example, suppose that the signal handler uses @code{gethostbyname}.
This function returns its value in a static object, reusing the same
object each time. If the signal happens to arrive during a call to
@code{gethostbyname}, or even after one (while the program is still
using the value), it will clobber the value that the program asked for.
However, if the program does not use @code{gethostbyname} or any other
function that returns information in the same object, or if it always
blocks signals around each use, then you are safe.
There are a large number of library functions that return values in a
fixed object, always reusing the same object in this fashion, and all of
them cause the same problem. Function descriptions in this manual
always mention this behavior.
@item
If a function uses and modifies an object that you supply, then it is
potentially non-reentrant; two calls can interfere if they use the same
object.
This case arises when you do I/O using streams. Suppose that the
signal handler prints a message with @code{fprintf}. Suppose that the
program was in the middle of an @code{fprintf} call using the same
stream when the signal was delivered. Both the signal handler's message
and the program's data could be corrupted, because both calls operate on
the same data structure---the stream itself.
However, if you know that the stream that the handler uses cannot
possibly be used by the program at a time when signals can arrive, then
you are safe. It is no problem if the program uses some other stream.
@item
On most systems, @code{malloc} and @code{free} are not reentrant,
because they use a static data structure which records what memory
blocks are free. As a result, no library functions that allocate or
free memory are reentrant. This includes functions that allocate space
to store a result.
The best way to avoid the need to allocate memory in a handler is to
allocate in advance space for signal handlers to use.
The best way to avoid freeing memory in a handler is to flag or record
the objects to be freed, and have the program check from time to time
whether anything is waiting to be freed. But this must be done with
care, because placing an object on a chain is not atomic, and if it is
interrupted by another signal handler that does the same thing, you
could ``lose'' one of the objects.
@ignore
!!! not true
In @theglibc{}, @code{malloc} and @code{free} are safe to use in
signal handlers because they block signals. As a result, the library
functions that allocate space for a result are also safe in signal
handlers. The obstack allocation functions are safe as long as you
don't use the same obstack both inside and outside of a signal handler.
@end ignore
@ignore
@comment Once we have r_alloc again add this paragraph.
The relocating allocation functions (@pxref{Relocating Allocator})
are certainly not safe to use in a signal handler.
@end ignore
@item
Any function that modifies @code{errno} is non-reentrant, but you can
correct for this: in the handler, save the original value of
@code{errno} and restore it before returning normally. This prevents
errors that occur within the signal handler from being confused with
errors from system calls at the point the program is interrupted to run
the handler.
This technique is generally applicable; if you want to call in a handler
a function that modifies a particular object in memory, you can make
this safe by saving and restoring that object.
@item
Merely reading from a memory object is safe provided that you can deal
with any of the values that might appear in the object at a time when
the signal can be delivered. Keep in mind that assignment to some data
types requires more than one instruction, which means that the handler
could run ``in the middle of'' an assignment to the variable if its type
is not atomic. @xref{Atomic Data Access}.
@item
Merely writing into a memory object is safe as long as a sudden change
in the value, at any time when the handler might run, will not disturb
anything.
@end itemize
@node Atomic Data Access
@subsection Atomic Data Access and Signal Handling
Whether the data in your application concerns atoms, or mere text, you
have to be careful about the fact that access to a single datum is not
necessarily @dfn{atomic}. This means that it can take more than one
instruction to read or write a single object. In such cases, a signal
handler might be invoked in the middle of reading or writing the object.
There are three ways you can cope with this problem. You can use data
types that are always accessed atomically; you can carefully arrange
that nothing untoward happens if an access is interrupted, or you can
block all signals around any access that had better not be interrupted
(@pxref{Blocking Signals}).
@menu
* Non-atomic Example:: A program illustrating interrupted access.
* Types: Atomic Types. Data types that guarantee no interruption.
* Usage: Atomic Usage. Proving that interruption is harmless.
@end menu
@node Non-atomic Example
@subsubsection Problems with Non-Atomic Access
Here is an example which shows what can happen if a signal handler runs
in the middle of modifying a variable. (Interrupting the reading of a
variable can also lead to paradoxical results, but here we only show
writing.)
@smallexample
#include
#include
volatile struct two_words @{ int a, b; @} memory;
void
handler(int signum)
@{
printf ("%d,%d\n", memory.a, memory.b);
alarm (1);
@}
@group
int
main (void)
@{
static struct two_words zeros = @{ 0, 0 @}, ones = @{ 1, 1 @};
signal (SIGALRM, handler);
memory = zeros;
alarm (1);
while (1)
@{
memory = zeros;
memory = ones;
@}
@}
@end group
@end smallexample
This program fills @code{memory} with zeros, ones, zeros, ones,
alternating forever; meanwhile, once per second, the alarm signal handler
prints the current contents. (Calling @code{printf} in the handler is
safe in this program because it is certainly not being called outside
the handler when the signal happens.)
Clearly, this program can print a pair of zeros or a pair of ones. But
that's not all it can do! On most machines, it takes several
instructions to store a new value in @code{memory}, and the value is
stored one word at a time. If the signal is delivered in between these
instructions, the handler might find that @code{memory.a} is zero and
@code{memory.b} is one (or vice versa).
On some machines it may be possible to store a new value in
@code{memory} with just one instruction that cannot be interrupted. On
these machines, the handler will always print two zeros or two ones.
@node Atomic Types
@subsubsection Atomic Types
To avoid uncertainty about interrupting access to a variable, you can
use a particular data type for which access is always atomic:
@code{sig_atomic_t}. Reading and writing this data type is guaranteed
to happen in a single instruction, so there's no way for a handler to
run ``in the middle'' of an access.
The type @code{sig_atomic_t} is always an integer data type, but which
one it is, and how many bits it contains, may vary from machine to
machine.
@comment signal.h
@comment ISO
@deftp {Data Type} sig_atomic_t
This is an integer data type. Objects of this type are always accessed
atomically.
@end deftp
In practice, you can assume that @code{int} is atomic.
You can also assume that pointer
types are atomic; that is very convenient. Both of these assumptions
are true on all of the machines that @theglibc{} supports and on
all POSIX systems we know of.
@c ??? This might fail on a 386 that uses 64-bit pointers.
@node Atomic Usage
@subsubsection Atomic Usage Patterns
Certain patterns of access avoid any problem even if an access is
interrupted. For example, a flag which is set by the handler, and
tested and cleared by the main program from time to time, is always safe
even if access actually requires two instructions. To show that this is
so, we must consider each access that could be interrupted, and show
that there is no problem if it is interrupted.
An interrupt in the middle of testing the flag is safe because either it's
recognized to be nonzero, in which case the precise value doesn't
matter, or it will be seen to be nonzero the next time it's tested.
An interrupt in the middle of clearing the flag is no problem because
either the value ends up zero, which is what happens if a signal comes
in just before the flag is cleared, or the value ends up nonzero, and
subsequent events occur as if the signal had come in just after the flag
was cleared. As long as the code handles both of these cases properly,
it can also handle a signal in the middle of clearing the flag. (This
is an example of the sort of reasoning you need to do to figure out
whether non-atomic usage is safe.)
Sometimes you can insure uninterrupted access to one object by
protecting its use with another object, perhaps one whose type
guarantees atomicity. @xref{Merged Signals}, for an example.
@node Interrupted Primitives
@section Primitives Interrupted by Signals
A signal can arrive and be handled while an I/O primitive such as
@code{open} or @code{read} is waiting for an I/O device. If the signal
handler returns, the system faces the question: what should happen next?
POSIX specifies one approach: make the primitive fail right away. The
error code for this kind of failure is @code{EINTR}. This is flexible,
but usually inconvenient. Typically, POSIX applications that use signal
handlers must check for @code{EINTR} after each library function that
can return it, in order to try the call again. Often programmers forget
to check, which is a common source of error.
@Theglibc{} provides a convenient way to retry a call after a
temporary failure, with the macro @code{TEMP_FAILURE_RETRY}:
@comment unistd.h
@comment GNU
@defmac TEMP_FAILURE_RETRY (@var{expression})
This macro evaluates @var{expression} once, and examines its value as
type @code{long int}. If the value equals @code{-1}, that indicates a
failure and @code{errno} should be set to show what kind of failure.
If it fails and reports error code @code{EINTR},
@code{TEMP_FAILURE_RETRY} evaluates it again, and over and over until
the result is not a temporary failure.
The value returned by @code{TEMP_FAILURE_RETRY} is whatever value
@var{expression} produced.
@end defmac
BSD avoids @code{EINTR} entirely and provides a more convenient
approach: to restart the interrupted primitive, instead of making it
fail. If you choose this approach, you need not be concerned with
@code{EINTR}.
You can choose either approach with @theglibc{}. If you use
@code{sigaction} to establish a signal handler, you can specify how that
handler should behave. If you specify the @code{SA_RESTART} flag,
return from that handler will resume a primitive; otherwise, return from
that handler will cause @code{EINTR}. @xref{Flags for Sigaction}.
Another way to specify the choice is with the @code{siginterrupt}
function. @xref{BSD Handler}.
@c !!! not true now about _BSD_SOURCE
When you don't specify with @code{sigaction} or @code{siginterrupt} what
a particular handler should do, it uses a default choice. The default
choice in @theglibc{} depends on the feature test macros you have
defined. If you define @code{_BSD_SOURCE} or @code{_GNU_SOURCE} before
calling @code{signal}, the default is to resume primitives; otherwise,
the default is to make them fail with @code{EINTR}. (The library
contains alternate versions of the @code{signal} function, and the
feature test macros determine which one you really call.) @xref{Feature
Test Macros}.
@cindex EINTR, and restarting interrupted primitives
@cindex restarting interrupted primitives
@cindex interrupting primitives
@cindex primitives, interrupting
@c !!! want to have @cindex system calls @i{see} primitives [no page #]
The description of each primitive affected by this issue
lists @code{EINTR} among the error codes it can return.
There is one situation where resumption never happens no matter which
choice you make: when a data-transfer function such as @code{read} or
@code{write} is interrupted by a signal after transferring part of the
data. In this case, the function returns the number of bytes already
transferred, indicating partial success.
This might at first appear to cause unreliable behavior on
record-oriented devices (including datagram sockets; @pxref{Datagrams}),
where splitting one @code{read} or @code{write} into two would read or
write two records. Actually, there is no problem, because interruption
after a partial transfer cannot happen on such devices; they always
transfer an entire record in one burst, with no waiting once data
transfer has started.
@node Generating Signals
@section Generating Signals
@cindex sending signals
@cindex raising signals
@cindex signals, generating
Besides signals that are generated as a result of a hardware trap or
interrupt, your program can explicitly send signals to itself or to
another process.
@menu
* Signaling Yourself:: A process can send a signal to itself.
* Signaling Another Process:: Send a signal to another process.
* Permission for kill:: Permission for using @code{kill}.
* Kill Example:: Using @code{kill} for Communication.
@end menu
@node Signaling Yourself
@subsection Signaling Yourself
A process can send itself a signal with the @code{raise} function. This
function is declared in @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment ISO
@deftypefun int raise (int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c raise ok
@c [posix]
@c getpid dup ok
@c kill dup ok
@c [linux]
@c syscall(gettid) ok
@c syscall(tgkill) ok
The @code{raise} function sends the signal @var{signum} to the calling
process. It returns zero if successful and a nonzero value if it fails.
About the only reason for failure would be if the value of @var{signum}
is invalid.
@end deftypefun
@comment signal.h
@comment SVID
@deftypefun int gsignal (int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Aliases raise.
The @code{gsignal} function does the same thing as @code{raise}; it is
provided only for compatibility with SVID.
@end deftypefun
One convenient use for @code{raise} is to reproduce the default behavior
of a signal that you have trapped. For instance, suppose a user of your
program types the SUSP character (usually @kbd{C-z}; @pxref{Special
Characters}) to send it an interactive stop signal
(@code{SIGTSTP}), and you want to clean up some internal data buffers
before stopping. You might set this up like this:
@comment RMS suggested getting rid of the handler for SIGCONT in this function.
@comment But that would require that the handler for SIGTSTP unblock the
@comment signal before doing the call to raise. We haven't covered that
@comment topic yet, and I don't want to distract from the main point of
@comment the example with a digression to explain what is going on. As
@comment the example is written, the signal that is raise'd will be delivered
@comment as soon as the SIGTSTP handler returns, which is fine.
@smallexample
#include
/* @r{When a stop signal arrives, set the action back to the default
and then resend the signal after doing cleanup actions.} */
void
tstp_handler (int sig)
@{
signal (SIGTSTP, SIG_DFL);
/* @r{Do cleanup actions here.} */
@dots{}
raise (SIGTSTP);
@}
/* @r{When the process is continued again, restore the signal handler.} */
void
cont_handler (int sig)
@{
signal (SIGCONT, cont_handler);
signal (SIGTSTP, tstp_handler);
@}
@group
/* @r{Enable both handlers during program initialization.} */
int
main (void)
@{
signal (SIGCONT, cont_handler);
signal (SIGTSTP, tstp_handler);
@dots{}
@}
@end group
@end smallexample
@strong{Portability note:} @code{raise} was invented by the @w{ISO C}
committee. Older systems may not support it, so using @code{kill} may
be more portable. @xref{Signaling Another Process}.
@node Signaling Another Process
@subsection Signaling Another Process
@cindex killing a process
The @code{kill} function can be used to send a signal to another process.
In spite of its name, it can be used for a lot of things other than
causing a process to terminate. Some examples of situations where you
might want to send signals between processes are:
@itemize @bullet
@item
A parent process starts a child to perform a task---perhaps having the
child running an infinite loop---and then terminates the child when the
task is no longer needed.
@item
A process executes as part of a group, and needs to terminate or notify
the other processes in the group when an error or other event occurs.
@item
Two processes need to synchronize while working together.
@end itemize
This section assumes that you know a little bit about how processes
work. For more information on this subject, see @ref{Processes}.
The @code{kill} function is declared in @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment POSIX.1
@deftypefun int kill (pid_t @var{pid}, int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c The hurd implementation is not a critical section, so it's not
@c immediately obvious that, in case of cancellation, it won't leak
@c ports or the memory allocated by proc_getpgrppids when pid <= 0.
@c Since none of these make it AC-Unsafe, I'm leaving them out.
The @code{kill} function sends the signal @var{signum} to the process
or process group specified by @var{pid}. Besides the signals listed in
@ref{Standard Signals}, @var{signum} can also have a value of zero to
check the validity of the @var{pid}.
The @var{pid} specifies the process or process group to receive the
signal:
@table @code
@item @var{pid} > 0
The process whose identifier is @var{pid}.
@item @var{pid} == 0
All processes in the same process group as the sender.
@item @var{pid} < -1
The process group whose identifier is @minus{}@var{pid}.
@item @var{pid} == -1
If the process is privileged, send the signal to all processes except
for some special system processes. Otherwise, send the signal to all
processes with the same effective user ID.
@end table
A process can send a signal to itself with a call like @w{@code{kill
(getpid(), @var{signum})}}. If @code{kill} is used by a process to send
a signal to itself, and the signal is not blocked, then @code{kill}
delivers at least one signal (which might be some other pending
unblocked signal instead of the signal @var{signum}) to that process
before it returns.
The return value from @code{kill} is zero if the signal can be sent
successfully. Otherwise, no signal is sent, and a value of @code{-1} is
returned. If @var{pid} specifies sending a signal to several processes,
@code{kill} succeeds if it can send the signal to at least one of them.
There's no way you can tell which of the processes got the signal
or whether all of them did.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The @var{signum} argument is an invalid or unsupported number.
@item EPERM
You do not have the privilege to send a signal to the process or any of
the processes in the process group named by @var{pid}.
@item ESRCH
The @var{pid} argument does not refer to an existing process or group.
@end table
@end deftypefun
@comment signal.h
@comment BSD
@deftypefun int killpg (int @var{pgid}, int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Calls kill with -pgid.
This is similar to @code{kill}, but sends signal @var{signum} to the
process group @var{pgid}. This function is provided for compatibility
with BSD; using @code{kill} to do this is more portable.
@end deftypefun
As a simple example of @code{kill}, the call @w{@code{kill (getpid (),
@var{sig})}} has the same effect as @w{@code{raise (@var{sig})}}.
@node Permission for kill
@subsection Permission for using @code{kill}
There are restrictions that prevent you from using @code{kill} to send
signals to any random process. These are intended to prevent antisocial
behavior such as arbitrarily killing off processes belonging to another
user. In typical use, @code{kill} is used to pass signals between
parent, child, and sibling processes, and in these situations you
normally do have permission to send signals. The only common exception
is when you run a setuid program in a child process; if the program
changes its real UID as well as its effective UID, you may not have
permission to send a signal. The @code{su} program does this.
Whether a process has permission to send a signal to another process
is determined by the user IDs of the two processes. This concept is
discussed in detail in @ref{Process Persona}.
Generally, for a process to be able to send a signal to another process,
either the sending process must belong to a privileged user (like
@samp{root}), or the real or effective user ID of the sending process
must match the real or effective user ID of the receiving process. If
the receiving process has changed its effective user ID from the
set-user-ID mode bit on its process image file, then the owner of the
process image file is used in place of its current effective user ID.
In some implementations, a parent process might be able to send signals
to a child process even if the user ID's don't match, and other
implementations might enforce other restrictions.
The @code{SIGCONT} signal is a special case. It can be sent if the
sender is part of the same session as the receiver, regardless of
user IDs.
@node Kill Example
@subsection Using @code{kill} for Communication
@cindex interprocess communication, with signals
Here is a longer example showing how signals can be used for
interprocess communication. This is what the @code{SIGUSR1} and
@code{SIGUSR2} signals are provided for. Since these signals are fatal
by default, the process that is supposed to receive them must trap them
through @code{signal} or @code{sigaction}.
In this example, a parent process forks a child process and then waits
for the child to complete its initialization. The child process tells
the parent when it is ready by sending it a @code{SIGUSR1} signal, using
the @code{kill} function.
@smallexample
@include sigusr.c.texi
@end smallexample
This example uses a busy wait, which is bad, because it wastes CPU
cycles that other programs could otherwise use. It is better to ask the
system to wait until the signal arrives. See the example in
@ref{Waiting for a Signal}.
@node Blocking Signals
@section Blocking Signals
@cindex blocking signals
Blocking a signal means telling the operating system to hold it and
deliver it later. Generally, a program does not block signals
indefinitely---it might as well ignore them by setting their actions to
@code{SIG_IGN}. But it is useful to block signals briefly, to prevent
them from interrupting sensitive operations. For instance:
@itemize @bullet
@item
You can use the @code{sigprocmask} function to block signals while you
modify global variables that are also modified by the handlers for these
signals.
@item
You can set @code{sa_mask} in your @code{sigaction} call to block
certain signals while a particular signal handler runs. This way, the
signal handler can run without being interrupted itself by signals.
@end itemize
@menu
* Why Block:: The purpose of blocking signals.
* Signal Sets:: How to specify which signals to
block.
* Process Signal Mask:: Blocking delivery of signals to your
process during normal execution.
* Testing for Delivery:: Blocking to Test for Delivery of
a Signal.
* Blocking for Handler:: Blocking additional signals while a
handler is being run.
* Checking for Pending Signals:: Checking for Pending Signals
* Remembering a Signal:: How you can get almost the same
effect as blocking a signal, by
handling it and setting a flag
to be tested later.
@end menu
@node Why Block
@subsection Why Blocking Signals is Useful
Temporary blocking of signals with @code{sigprocmask} gives you a way to
prevent interrupts during critical parts of your code. If signals
arrive in that part of the program, they are delivered later, after you
unblock them.
One example where this is useful is for sharing data between a signal
handler and the rest of the program. If the type of the data is not
@code{sig_atomic_t} (@pxref{Atomic Data Access}), then the signal
handler could run when the rest of the program has only half finished
reading or writing the data. This would lead to confusing consequences.
To make the program reliable, you can prevent the signal handler from
running while the rest of the program is examining or modifying that
data---by blocking the appropriate signal around the parts of the
program that touch the data.
Blocking signals is also necessary when you want to perform a certain
action only if a signal has not arrived. Suppose that the handler for
the signal sets a flag of type @code{sig_atomic_t}; you would like to
test the flag and perform the action if the flag is not set. This is
unreliable. Suppose the signal is delivered immediately after you test
the flag, but before the consequent action: then the program will
perform the action even though the signal has arrived.
The only way to test reliably for whether a signal has yet arrived is to
test while the signal is blocked.
@node Signal Sets
@subsection Signal Sets
All of the signal blocking functions use a data structure called a
@dfn{signal set} to specify what signals are affected. Thus, every
activity involves two stages: creating the signal set, and then passing
it as an argument to a library function.
@cindex signal set
These facilities are declared in the header file @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment POSIX.1
@deftp {Data Type} sigset_t
The @code{sigset_t} data type is used to represent a signal set.
Internally, it may be implemented as either an integer or structure
type.
For portability, use only the functions described in this section to
initialize, change, and retrieve information from @code{sigset_t}
objects---don't try to manipulate them directly.
@end deftp
There are two ways to initialize a signal set. You can initially
specify it to be empty with @code{sigemptyset} and then add specified
signals individually. Or you can specify it to be full with
@code{sigfillset} and then delete specified signals individually.
You must always initialize the signal set with one of these two
functions before using it in any other way. Don't try to set all the
signals explicitly because the @code{sigset_t} object might include some
other information (like a version field) that needs to be initialized as
well. (In addition, it's not wise to put into your program an
assumption that the system has no signals aside from the ones you know
about.)
@comment signal.h
@comment POSIX.1
@deftypefun int sigemptyset (sigset_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Just memsets all of set to zero.
This function initializes the signal set @var{set} to exclude all of the
defined signals. It always returns @code{0}.
@end deftypefun
@comment signal.h
@comment POSIX.1
@deftypefun int sigfillset (sigset_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function initializes the signal set @var{set} to include
all of the defined signals. Again, the return value is @code{0}.
@end deftypefun
@comment signal.h
@comment POSIX.1
@deftypefun int sigaddset (sigset_t *@var{set}, int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function adds the signal @var{signum} to the signal set @var{set}.
All @code{sigaddset} does is modify @var{set}; it does not block or
unblock any signals.
The return value is @code{0} on success and @code{-1} on failure.
The following @code{errno} error condition is defined for this function:
@table @code
@item EINVAL
The @var{signum} argument doesn't specify a valid signal.
@end table
@end deftypefun
@comment signal.h
@comment POSIX.1
@deftypefun int sigdelset (sigset_t *@var{set}, int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function removes the signal @var{signum} from the signal set
@var{set}. All @code{sigdelset} does is modify @var{set}; it does not
block or unblock any signals. The return value and error conditions are
the same as for @code{sigaddset}.
@end deftypefun
Finally, there is a function to test what signals are in a signal set:
@comment signal.h
@comment POSIX.1
@deftypefun int sigismember (const sigset_t *@var{set}, int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{sigismember} function tests whether the signal @var{signum} is
a member of the signal set @var{set}. It returns @code{1} if the signal
is in the set, @code{0} if not, and @code{-1} if there is an error.
The following @code{errno} error condition is defined for this function:
@table @code
@item EINVAL
The @var{signum} argument doesn't specify a valid signal.
@end table
@end deftypefun
@node Process Signal Mask
@subsection Process Signal Mask
@cindex signal mask
@cindex process signal mask
The collection of signals that are currently blocked is called the
@dfn{signal mask}. Each process has its own signal mask. When you
create a new process (@pxref{Creating a Process}), it inherits its
parent's mask. You can block or unblock signals with total flexibility
by modifying the signal mask.
The prototype for the @code{sigprocmask} function is in @file{signal.h}.
@pindex signal.h
Note that you must not use @code{sigprocmask} in multi-threaded processes,
because each thread has its own signal mask and there is no single process
signal mask. According to POSIX, the behavior of @code{sigprocmask} in a
multi-threaded process is ``unspecified''.
Instead, use @code{pthread_sigmask}.
@ifset linuxthreads
@xref{Threads and Signal Handling}.
@end ifset
@comment signal.h
@comment POSIX.1
@deftypefun int sigprocmask (int @var{how}, const sigset_t *restrict @var{set}, sigset_t *restrict @var{oldset})
@safety{@prelim{}@mtunsafe{@mtasurace{:sigprocmask/bsd(SIG_UNBLOCK)}}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c This takes the hurd_self_sigstate-returned object's lock on HURD. On
@c BSD, SIG_UNBLOCK is emulated with two sigblock calls, which
@c introduces a race window.
The @code{sigprocmask} function is used to examine or change the calling
process's signal mask. The @var{how} argument determines how the signal
mask is changed, and must be one of the following values:
@table @code
@comment signal.h
@comment POSIX.1
@vindex SIG_BLOCK
@item SIG_BLOCK
Block the signals in @code{set}---add them to the existing mask. In
other words, the new mask is the union of the existing mask and
@var{set}.
@comment signal.h
@comment POSIX.1
@vindex SIG_UNBLOCK
@item SIG_UNBLOCK
Unblock the signals in @var{set}---remove them from the existing mask.
@comment signal.h
@comment POSIX.1
@vindex SIG_SETMASK
@item SIG_SETMASK
Use @var{set} for the mask; ignore the previous value of the mask.
@end table
The last argument, @var{oldset}, is used to return information about the
old process signal mask. If you just want to change the mask without
looking at it, pass a null pointer as the @var{oldset} argument.
Similarly, if you want to know what's in the mask without changing it,
pass a null pointer for @var{set} (in this case the @var{how} argument
is not significant). The @var{oldset} argument is often used to
remember the previous signal mask in order to restore it later. (Since
the signal mask is inherited over @code{fork} and @code{exec} calls, you
can't predict what its contents are when your program starts running.)
If invoking @code{sigprocmask} causes any pending signals to be
unblocked, at least one of those signals is delivered to the process
before @code{sigprocmask} returns. The order in which pending signals
are delivered is not specified, but you can control the order explicitly
by making multiple @code{sigprocmask} calls to unblock various signals
one at a time.
The @code{sigprocmask} function returns @code{0} if successful, and @code{-1}
to indicate an error. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EINVAL
The @var{how} argument is invalid.
@end table
You can't block the @code{SIGKILL} and @code{SIGSTOP} signals, but
if the signal set includes these, @code{sigprocmask} just ignores
them instead of returning an error status.
Remember, too, that blocking program error signals such as @code{SIGFPE}
leads to undesirable results for signals generated by an actual program
error (as opposed to signals sent with @code{raise} or @code{kill}).
This is because your program may be too broken to be able to continue
executing to a point where the signal is unblocked again.
@xref{Program Error Signals}.
@end deftypefun
@node Testing for Delivery
@subsection Blocking to Test for Delivery of a Signal
Now for a simple example. Suppose you establish a handler for
@code{SIGALRM} signals that sets a flag whenever a signal arrives, and
your main program checks this flag from time to time and then resets it.
You can prevent additional @code{SIGALRM} signals from arriving in the
meantime by wrapping the critical part of the code with calls to
@code{sigprocmask}, like this:
@smallexample
/* @r{This variable is set by the SIGALRM signal handler.} */
volatile sig_atomic_t flag = 0;
int
main (void)
@{
sigset_t block_alarm;
@dots{}
/* @r{Initialize the signal mask.} */
sigemptyset (&block_alarm);
sigaddset (&block_alarm, SIGALRM);
@group
while (1)
@{
/* @r{Check if a signal has arrived; if so, reset the flag.} */
sigprocmask (SIG_BLOCK, &block_alarm, NULL);
if (flag)
@{
@var{actions-if-not-arrived}
flag = 0;
@}
sigprocmask (SIG_UNBLOCK, &block_alarm, NULL);
@dots{}
@}
@}
@end group
@end smallexample
@node Blocking for Handler
@subsection Blocking Signals for a Handler
@cindex blocking signals, in a handler
When a signal handler is invoked, you usually want it to be able to
finish without being interrupted by another signal. From the moment the
handler starts until the moment it finishes, you must block signals that
might confuse it or corrupt its data.
When a handler function is invoked on a signal, that signal is
automatically blocked (in addition to any other signals that are already
in the process's signal mask) during the time the handler is running.
If you set up a handler for @code{SIGTSTP}, for instance, then the
arrival of that signal forces further @code{SIGTSTP} signals to wait
during the execution of the handler.
However, by default, other kinds of signals are not blocked; they can
arrive during handler execution.
The reliable way to block other kinds of signals during the execution of
the handler is to use the @code{sa_mask} member of the @code{sigaction}
structure.
Here is an example:
@smallexample
#include
#include
void catch_stop ();
void
install_handler (void)
@{
struct sigaction setup_action;
sigset_t block_mask;
sigemptyset (&block_mask);
/* @r{Block other terminal-generated signals while handler runs.} */
sigaddset (&block_mask, SIGINT);
sigaddset (&block_mask, SIGQUIT);
setup_action.sa_handler = catch_stop;
setup_action.sa_mask = block_mask;
setup_action.sa_flags = 0;
sigaction (SIGTSTP, &setup_action, NULL);
@}
@end smallexample
This is more reliable than blocking the other signals explicitly in the
code for the handler. If you block signals explicitly in the handler,
you can't avoid at least a short interval at the beginning of the
handler where they are not yet blocked.
You cannot remove signals from the process's current mask using this
mechanism. However, you can make calls to @code{sigprocmask} within
your handler to block or unblock signals as you wish.
In any case, when the handler returns, the system restores the mask that
was in place before the handler was entered. If any signals that become
unblocked by this restoration are pending, the process will receive
those signals immediately, before returning to the code that was
interrupted.
@node Checking for Pending Signals
@subsection Checking for Pending Signals
@cindex pending signals, checking for
@cindex blocked signals, checking for
@cindex checking for pending signals
You can find out which signals are pending at any time by calling
@code{sigpending}. This function is declared in @file{signal.h}.
@pindex signal.h
@comment signal.h
@comment POSIX.1
@deftypefun int sigpending (sigset_t *@var{set})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c Direct rt_sigpending syscall on most systems. On hurd, calls
@c hurd_self_sigstate, it copies the sigstate's pending while holding
@c its lock.
The @code{sigpending} function stores information about pending signals
in @var{set}. If there is a pending signal that is blocked from
delivery, then that signal is a member of the returned set. (You can
test whether a particular signal is a member of this set using
@code{sigismember}; see @ref{Signal Sets}.)
The return value is @code{0} if successful, and @code{-1} on failure.
@end deftypefun
Testing whether a signal is pending is not often useful. Testing when
that signal is not blocked is almost certainly bad design.
Here is an example.
@smallexample
#include
#include
sigset_t base_mask, waiting_mask;
sigemptyset (&base_mask);
sigaddset (&base_mask, SIGINT);
sigaddset (&base_mask, SIGTSTP);
/* @r{Block user interrupts while doing other processing.} */
sigprocmask (SIG_SETMASK, &base_mask, NULL);
@dots{}
/* @r{After a while, check to see whether any signals are pending.} */
sigpending (&waiting_mask);
if (sigismember (&waiting_mask, SIGINT)) @{
/* @r{User has tried to kill the process.} */
@}
else if (sigismember (&waiting_mask, SIGTSTP)) @{
/* @r{User has tried to stop the process.} */
@}
@end smallexample
Remember that if there is a particular signal pending for your process,
additional signals of that same type that arrive in the meantime might
be discarded. For example, if a @code{SIGINT} signal is pending when
another @code{SIGINT} signal arrives, your program will probably only
see one of them when you unblock this signal.
@strong{Portability Note:} The @code{sigpending} function is new in
POSIX.1. Older systems have no equivalent facility.
@node Remembering a Signal
@subsection Remembering a Signal to Act On Later
Instead of blocking a signal using the library facilities, you can get
almost the same results by making the handler set a flag to be tested
later, when you ``unblock''. Here is an example:
@smallexample
/* @r{If this flag is nonzero, don't handle the signal right away.} */
volatile sig_atomic_t signal_pending;
/* @r{This is nonzero if a signal arrived and was not handled.} */
volatile sig_atomic_t defer_signal;
void
handler (int signum)
@{
if (defer_signal)
signal_pending = signum;
else
@dots{} /* @r{``Really'' handle the signal.} */
@}
@dots{}
void
update_mumble (int frob)
@{
/* @r{Prevent signals from having immediate effect.} */
defer_signal++;
/* @r{Now update @code{mumble}, without worrying about interruption.} */
mumble.a = 1;
mumble.b = hack ();
mumble.c = frob;
/* @r{We have updated @code{mumble}. Handle any signal that came in.} */
defer_signal--;
if (defer_signal == 0 && signal_pending != 0)
raise (signal_pending);
@}
@end smallexample
Note how the particular signal that arrives is stored in
@code{signal_pending}. That way, we can handle several types of
inconvenient signals with the same mechanism.
We increment and decrement @code{defer_signal} so that nested critical
sections will work properly; thus, if @code{update_mumble} were called
with @code{signal_pending} already nonzero, signals would be deferred
not only within @code{update_mumble}, but also within the caller. This
is also why we do not check @code{signal_pending} if @code{defer_signal}
is still nonzero.
The incrementing and decrementing of @code{defer_signal} each require more
than one instruction; it is possible for a signal to happen in the
middle. But that does not cause any problem. If the signal happens
early enough to see the value from before the increment or decrement,
that is equivalent to a signal which came before the beginning of the
increment or decrement, which is a case that works properly.
It is absolutely vital to decrement @code{defer_signal} before testing
@code{signal_pending}, because this avoids a subtle bug. If we did
these things in the other order, like this,
@smallexample
if (defer_signal == 1 && signal_pending != 0)
raise (signal_pending);
defer_signal--;
@end smallexample
@noindent
then a signal arriving in between the @code{if} statement and the decrement
would be effectively ``lost'' for an indefinite amount of time. The
handler would merely set @code{defer_signal}, but the program having
already tested this variable, it would not test the variable again.
@cindex timing error in signal handling
Bugs like these are called @dfn{timing errors}. They are especially bad
because they happen only rarely and are nearly impossible to reproduce.
You can't expect to find them with a debugger as you would find a
reproducible bug. So it is worth being especially careful to avoid
them.
(You would not be tempted to write the code in this order, given the use
of @code{defer_signal} as a counter which must be tested along with
@code{signal_pending}. After all, testing for zero is cleaner than
testing for one. But if you did not use @code{defer_signal} as a
counter, and gave it values of zero and one only, then either order
might seem equally simple. This is a further advantage of using a
counter for @code{defer_signal}: it will reduce the chance you will
write the code in the wrong order and create a subtle bug.)
@node Waiting for a Signal
@section Waiting for a Signal
@cindex waiting for a signal
@cindex @code{pause} function
If your program is driven by external events, or uses signals for
synchronization, then when it has nothing to do it should probably wait
until a signal arrives.
@menu
* Using Pause:: The simple way, using @code{pause}.
* Pause Problems:: Why the simple way is often not very good.
* Sigsuspend:: Reliably waiting for a specific signal.
@end menu
@node Using Pause
@subsection Using @code{pause}
The simple way to wait until a signal arrives is to call @code{pause}.
Please read about its disadvantages, in the following section, before
you use it.
@comment unistd.h
@comment POSIX.1
@deftypefun int pause (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:sigprocmask/!bsd!linux}}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c The signal mask read by sigprocmask may be overridden by another
@c thread or by a signal handler before we call sigsuspend. Is this a
@c safety issue? Probably not.
@c pause @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
@c [ports/linux/generic]
@c syscall_pause ok
@c [posix]
@c sigemptyset dup ok
@c sigprocmask(SIG_BLOCK) dup @asulock/hurd @aculock/hurd [no @mtasurace:sigprocmask/bsd(SIG_UNBLOCK)]
@c sigsuspend dup @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
The @code{pause} function suspends program execution until a signal
arrives whose action is either to execute a handler function, or to
terminate the process.
If the signal causes a handler function to be executed, then
@code{pause} returns. This is considered an unsuccessful return (since
``successful'' behavior would be to suspend the program forever), so the
return value is @code{-1}. Even if you specify that other primitives
should resume when a system handler returns (@pxref{Interrupted
Primitives}), this has no effect on @code{pause}; it always fails when a
signal is handled.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EINTR
The function was interrupted by delivery of a signal.
@end table
If the signal causes program termination, @code{pause} doesn't return
(obviously).
This function is a cancellation point in multithreaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{pause} is
called. If the thread gets cancelled these resources stay allocated
until the program ends. To avoid this calls to @code{pause} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{pause} function is declared in @file{unistd.h}.
@end deftypefun
@node Pause Problems
@subsection Problems with @code{pause}
The simplicity of @code{pause} can conceal serious timing errors that
can make a program hang mysteriously.
It is safe to use @code{pause} if the real work of your program is done
by the signal handlers themselves, and the ``main program'' does nothing
but call @code{pause}. Each time a signal is delivered, the handler
will do the next batch of work that is to be done, and then return, so
that the main loop of the program can call @code{pause} again.
You can't safely use @code{pause} to wait until one more signal arrives,
and then resume real work. Even if you arrange for the signal handler
to cooperate by setting a flag, you still can't use @code{pause}
reliably. Here is an example of this problem:
@smallexample
/* @r{@code{usr_interrupt} is set by the signal handler.} */
if (!usr_interrupt)
pause ();
/* @r{Do work once the signal arrives.} */
@dots{}
@end smallexample
@noindent
This has a bug: the signal could arrive after the variable
@code{usr_interrupt} is checked, but before the call to @code{pause}.
If no further signals arrive, the process would never wake up again.
You can put an upper limit on the excess waiting by using @code{sleep}
in a loop, instead of using @code{pause}. (@xref{Sleeping}, for more
about @code{sleep}.) Here is what this looks like:
@smallexample
/* @r{@code{usr_interrupt} is set by the signal handler.}
while (!usr_interrupt)
sleep (1);
/* @r{Do work once the signal arrives.} */
@dots{}
@end smallexample
For some purposes, that is good enough. But with a little more
complexity, you can wait reliably until a particular signal handler is
run, using @code{sigsuspend}.
@ifinfo
@xref{Sigsuspend}.
@end ifinfo
@node Sigsuspend
@subsection Using @code{sigsuspend}
The clean and reliable way to wait for a signal to arrive is to block it
and then use @code{sigsuspend}. By using @code{sigsuspend} in a loop,
you can wait for certain kinds of signals, while letting other kinds of
signals be handled by their handlers.
@comment signal.h
@comment POSIX.1
@deftypefun int sigsuspend (const sigset_t *@var{set})
@safety{@prelim{}@mtunsafe{@mtasurace{:sigprocmask/!bsd!linux}}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c sigsuspend @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
@c [posix] @mtasurace:sigprocmask/!bsd!linux
@c saving and restoring the procmask is racy
@c sigprocmask(SIG_SETMASK) dup @asulock/hurd @aculock/hurd [no @mtasurace:sigprocmask/bsd(SIG_UNBLOCK)]
@c pause @asulock/hurd @aculock/hurd
@c [bsd]
@c sigismember dup ok
@c sigmask dup ok
@c sigpause dup ok [no @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd]
@c [linux]
@c do_sigsuspend ok
This function replaces the process's signal mask with @var{set} and then
suspends the process until a signal is delivered whose action is either
to terminate the process or invoke a signal handling function. In other
words, the program is effectively suspended until one of the signals that
is not a member of @var{set} arrives.
If the process is woken up by delivery of a signal that invokes a handler
function, and the handler function returns, then @code{sigsuspend} also
returns.
The mask remains @var{set} only as long as @code{sigsuspend} is waiting.
The function @code{sigsuspend} always restores the previous signal mask
when it returns.
The return value and error conditions are the same as for @code{pause}.
@end deftypefun
With @code{sigsuspend}, you can replace the @code{pause} or @code{sleep}
loop in the previous section with something completely reliable:
@smallexample
sigset_t mask, oldmask;
@dots{}
/* @r{Set up the mask of signals to temporarily block.} */
sigemptyset (&mask);
sigaddset (&mask, SIGUSR1);
@dots{}
/* @r{Wait for a signal to arrive.} */
sigprocmask (SIG_BLOCK, &mask, &oldmask);
while (!usr_interrupt)
sigsuspend (&oldmask);
sigprocmask (SIG_UNBLOCK, &mask, NULL);
@end smallexample
This last piece of code is a little tricky. The key point to remember
here is that when @code{sigsuspend} returns, it resets the process's
signal mask to the original value, the value from before the call to
@code{sigsuspend}---in this case, the @code{SIGUSR1} signal is once
again blocked. The second call to @code{sigprocmask} is
necessary to explicitly unblock this signal.
One other point: you may be wondering why the @code{while} loop is
necessary at all, since the program is apparently only waiting for one
@code{SIGUSR1} signal. The answer is that the mask passed to
@code{sigsuspend} permits the process to be woken up by the delivery of
other kinds of signals, as well---for example, job control signals. If
the process is woken up by a signal that doesn't set
@code{usr_interrupt}, it just suspends itself again until the ``right''
kind of signal eventually arrives.
This technique takes a few more lines of preparation, but that is needed
just once for each kind of wait criterion you want to use. The code
that actually waits is just four lines.
@node Signal Stack
@section Using a Separate Signal Stack
A signal stack is a special area of memory to be used as the execution
stack during signal handlers. It should be fairly large, to avoid any
danger that it will overflow in turn; the macro @code{SIGSTKSZ} is
defined to a canonical size for signal stacks. You can use
@code{malloc} to allocate the space for the stack. Then call
@code{sigaltstack} or @code{sigstack} to tell the system to use that
space for the signal stack.
You don't need to write signal handlers differently in order to use a
signal stack. Switching from one stack to the other happens
automatically. (Some non-GNU debuggers on some machines may get
confused if you examine a stack trace while a handler that uses the
signal stack is running.)
There are two interfaces for telling the system to use a separate signal
stack. @code{sigstack} is the older interface, which comes from 4.2
BSD. @code{sigaltstack} is the newer interface, and comes from 4.4
BSD. The @code{sigaltstack} interface has the advantage that it does
not require your program to know which direction the stack grows, which
depends on the specific machine and operating system.
@comment signal.h
@comment XPG
@deftp {Data Type} stack_t
This structure describes a signal stack. It contains the following members:
@table @code
@item void *ss_sp
This points to the base of the signal stack.
@item size_t ss_size
This is the size (in bytes) of the signal stack which @samp{ss_sp} points to.
You should set this to however much space you allocated for the stack.
There are two macros defined in @file{signal.h} that you should use in
calculating this size:
@vtable @code
@item SIGSTKSZ
This is the canonical size for a signal stack. It is judged to be
sufficient for normal uses.
@item MINSIGSTKSZ
This is the amount of signal stack space the operating system needs just
to implement signal delivery. The size of a signal stack @strong{must}
be greater than this.
For most cases, just using @code{SIGSTKSZ} for @code{ss_size} is
sufficient. But if you know how much stack space your program's signal
handlers will need, you may want to use a different size. In this case,
you should allocate @code{MINSIGSTKSZ} additional bytes for the signal
stack and increase @code{ss_size} accordingly.
@end vtable
@item int ss_flags
This field contains the bitwise @sc{or} of these flags:
@vtable @code
@item SS_DISABLE
This tells the system that it should not use the signal stack.
@item SS_ONSTACK
This is set by the system, and indicates that the signal stack is
currently in use. If this bit is not set, then signals will be
delivered on the normal user stack.
@end vtable
@end table
@end deftp
@comment signal.h
@comment XPG
@deftypefun int sigaltstack (const stack_t *restrict @var{stack}, stack_t *restrict @var{oldstack})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c Syscall on Linux and BSD; the HURD implementation takes a lock on
@c the hurd_self_sigstate-returned struct.
The @code{sigaltstack} function specifies an alternate stack for use
during signal handling. When a signal is received by the process and
its action indicates that the signal stack is used, the system arranges
a switch to the currently installed signal stack while the handler for
that signal is executed.
If @var{oldstack} is not a null pointer, information about the currently
installed signal stack is returned in the location it points to. If
@var{stack} is not a null pointer, then this is installed as the new
stack for use by signal handlers.
The return value is @code{0} on success and @code{-1} on failure. If
@code{sigaltstack} fails, it sets @code{errno} to one of these values:
@table @code
@item EINVAL
You tried to disable a stack that was in fact currently in use.
@item ENOMEM
The size of the alternate stack was too small.
It must be greater than @code{MINSIGSTKSZ}.
@end table
@end deftypefun
Here is the older @code{sigstack} interface. You should use
@code{sigaltstack} instead on systems that have it.
@comment signal.h
@comment BSD
@deftp {Data Type} {struct sigstack}
This structure describes a signal stack. It contains the following members:
@table @code
@item void *ss_sp
This is the stack pointer. If the stack grows downwards on your
machine, this should point to the top of the area you allocated. If the
stack grows upwards, it should point to the bottom.
@item int ss_onstack
This field is true if the process is currently using this stack.
@end table
@end deftp
@comment signal.h
@comment BSD
@deftypefun int sigstack (struct sigstack *@var{stack}, struct sigstack *@var{oldstack})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c Lossy and dangerous (no size limit) wrapper for sigaltstack.
The @code{sigstack} function specifies an alternate stack for use during
signal handling. When a signal is received by the process and its
action indicates that the signal stack is used, the system arranges a
switch to the currently installed signal stack while the handler for
that signal is executed.
If @var{oldstack} is not a null pointer, information about the currently
installed signal stack is returned in the location it points to. If
@var{stack} is not a null pointer, then this is installed as the new
stack for use by signal handlers.
The return value is @code{0} on success and @code{-1} on failure.
@end deftypefun
@node BSD Signal Handling
@section BSD Signal Handling
This section describes alternative signal handling functions derived
from BSD Unix. These facilities were an advance, in their time; today,
they are mostly obsolete, and supported mainly for compatibility with
BSD Unix.
There are many similarities between the BSD and POSIX signal handling
facilities, because the POSIX facilities were inspired by the BSD
facilities. Besides having different names for all the functions to
avoid conflicts, the main differences between the two are:
@itemize @bullet
@item
BSD Unix represents signal masks as an @code{int} bit mask, rather than
as a @code{sigset_t} object.
@item
The BSD facilities use a different default for whether an interrupted
primitive should fail or resume. The POSIX facilities make system
calls fail unless you specify that they should resume. With the BSD
facility, the default is to make system calls resume unless you say they
should fail. @xref{Interrupted Primitives}.
@end itemize
The BSD facilities are declared in @file{signal.h}.
@pindex signal.h
@menu
* BSD Handler:: BSD Function to Establish a Handler.
* Blocking in BSD:: BSD Functions for Blocking Signals.
@end menu
@node BSD Handler
@subsection BSD Function to Establish a Handler
@comment signal.h
@comment BSD
@deftp {Data Type} {struct sigvec}
This data type is the BSD equivalent of @code{struct sigaction}
(@pxref{Advanced Signal Handling}); it is used to specify signal actions
to the @code{sigvec} function. It contains the following members:
@table @code
@item sighandler_t sv_handler
This is the handler function.
@item int sv_mask
This is the mask of additional signals to be blocked while the handler
function is being called.
@item int sv_flags
This is a bit mask used to specify various flags which affect the
behavior of the signal. You can also refer to this field as
@code{sv_onstack}.
@end table
@end deftp
These symbolic constants can be used to provide values for the
@code{sv_flags} field of a @code{sigvec} structure. This field is a bit
mask value, so you bitwise-OR the flags of interest to you together.
@comment signal.h
@comment BSD
@deftypevr Macro int SV_ONSTACK
If this bit is set in the @code{sv_flags} field of a @code{sigvec}
structure, it means to use the signal stack when delivering the signal.
@end deftypevr
@comment signal.h
@comment BSD
@deftypevr Macro int SV_INTERRUPT
If this bit is set in the @code{sv_flags} field of a @code{sigvec}
structure, it means that system calls interrupted by this kind of signal
should not be restarted if the handler returns; instead, the system
calls should return with a @code{EINTR} error status. @xref{Interrupted
Primitives}.
@end deftypevr
@comment signal.h
@comment Sun
@deftypevr Macro int SV_RESETHAND
If this bit is set in the @code{sv_flags} field of a @code{sigvec}
structure, it means to reset the action for the signal back to
@code{SIG_DFL} when the signal is received.
@end deftypevr
@comment signal.h
@comment BSD
@deftypefun int sigvec (int @var{signum}, const struct sigvec *@var{action}, struct sigvec *@var{old-action})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is mostly a safe wrapper for sigaction. The exception are
@c systems that lack SA_RESETHAND, in which a signal handler wrapper is
@c used that calls sigaction to reset the handler before calling the
@c user-supplied handler; it's unlikely that this emulation is used
@c anywhere, for user-supplied flags and mask don't seem to be used
@c the way one would expect.
This function is the equivalent of @code{sigaction} (@pxref{Advanced Signal
Handling}); it installs the action @var{action} for the signal @var{signum},
returning information about the previous action in effect for that signal
in @var{old-action}.
@end deftypefun
@comment signal.h
@comment BSD
@deftypefun int siginterrupt (int @var{signum}, int @var{failflag})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtssigintr{}}}@asunsafe{}@acunsafe{@acucorrupt{}}}
@c This calls sigaction twice, once to get the current sigaction for the
@c specified signal, another to apply the flags change. This could
@c override the effects of a concurrent sigaction call. It also
@c modifies without any guards the global _sigintr variable, that
@c bsd_signal reads from, and it may leave _sigintr modified without
@c overriding the active handler if cancelled between the two
@c operations.
This function specifies which approach to use when certain primitives
are interrupted by handling signal @var{signum}. If @var{failflag} is
false, signal @var{signum} restarts primitives. If @var{failflag} is
true, handling @var{signum} causes these primitives to fail with error
code @code{EINTR}. @xref{Interrupted Primitives}.
@end deftypefun
@node Blocking in BSD
@subsection BSD Functions for Blocking Signals
@comment signal.h
@comment BSD
@deftypefn Macro int sigmask (int @var{signum})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This just shifts signum.
This macro returns a signal mask that has the bit for signal @var{signum}
set. You can bitwise-OR the results of several calls to @code{sigmask}
together to specify more than one signal. For example,
@smallexample
(sigmask (SIGTSTP) | sigmask (SIGSTOP)
| sigmask (SIGTTIN) | sigmask (SIGTTOU))
@end smallexample
@noindent
specifies a mask that includes all the job-control stop signals.
@end deftypefn
@comment signal.h
@comment BSD
@deftypefun int sigblock (int @var{mask})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c On most POSIX systems, this is a wrapper for sigprocmask(SIG_BLOCK).
@c The exception are BSD systems other than 4.4, where it is a syscall.
@c sigblock @asulock/hurd @aculock/hurd
@c sigprocmask(SIG_BLOCK) dup @asulock/hurd @aculock/hurd [no @mtasurace:sigprocmask/bsd(SIG_UNBLOCK)]
This function is equivalent to @code{sigprocmask} (@pxref{Process Signal
Mask}) with a @var{how} argument of @code{SIG_BLOCK}: it adds the
signals specified by @var{mask} to the calling process's set of blocked
signals. The return value is the previous set of blocked signals.
@end deftypefun
@comment signal.h
@comment BSD
@deftypefun int sigsetmask (int @var{mask})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c On most POSIX systems, this is a wrapper for sigprocmask(SIG_SETMASK).
@c The exception are BSD systems other than 4.4, where it is a syscall.
@c sigsetmask @asulock/hurd @aculock/hurd
@c sigprocmask(SIG_SETMASK) dup @asulock/hurd @aculock/hurd [no @mtasurace:sigprocmask/bsd(SIG_UNBLOCK)]
This function equivalent to @code{sigprocmask} (@pxref{Process
Signal Mask}) with a @var{how} argument of @code{SIG_SETMASK}: it sets
the calling process's signal mask to @var{mask}. The return value is
the previous set of blocked signals.
@end deftypefun
@comment signal.h
@comment BSD
@deftypefun int sigpause (int @var{mask})
@safety{@prelim{}@mtunsafe{@mtasurace{:sigprocmask/!bsd!linux}}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c sigpause @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
@c [posix]
@c __sigpause @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
@c do_sigpause @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
@c sigprocmask(0) dup @asulock/hurd @aculock/hurd [no @mtasurace:sigprocmask/bsd(SIG_UNBLOCK)]
@c sigdelset dup ok
@c sigset_set_old_mask dup ok
@c sigsuspend dup @mtasurace:sigprocmask/!bsd!linux @asulock/hurd @aculock/hurd
This function is the equivalent of @code{sigsuspend} (@pxref{Waiting
for a Signal}): it sets the calling process's signal mask to @var{mask},
and waits for a signal to arrive. On return the previous set of blocked
signals is restored.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/check-safety.sh 0000664 0001750 0001750 00000010567 12275120646 022472 0 ustar adconrad adconrad #! /bin/sh
# Copyright 2014 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# .
# Check that the @safety notes are self-consistent, i.e., that they're
# in proper order (mt then as then ac), that remarks appear within
# corresponding sections (mt within mt, etc), that unsafety always has
# an explicit reason and when there's a reason for unsafety it's not
# safe, and that there aren't duplicates remarks.
success=:
# If no arguments are given, take all *.texi files in the current directory.
test $# != 0 || set *.texi
# Check that all safety remarks have entries for all of MT, AS and AC,
# in this order, with an optional prelim note before them.
grep -n '^@safety' "$@" |
grep -v ':@safety{\(@prelim{}\)\?@mt\(un\)\?safe{.*}'\
'@as\(un\)\?safe{.*}@ac\(un\)\?safe{.*}}' &&
success=false
# Check that @mt-started notes appear within @mtsafe or @mtunsafe,
# that @as-started notes appear within @assafe or @asunsafe, and that
# @ac-started notes appear within @acsafe or @acunsafe. Also check
# that @mt, @as and @ac are followed by an s (for safe) or u (for
# unsafe), but let @mt have as, ac or asc before [su], and let @as
# have a c (for cancel) before [su]. Also make sure blanks separate
# each of the annotations.
grep -n '^@safety' "$@" |
grep -v ':@safety{\(@prelim{}\)\?'\
'@mt\(un\)\?safe{\(@mt\(asc\?\|ac\)\?[su][^ ]*}\)\?'\
'\( @mt\(asc\?\|ac\)\?[su][^ ]*}\)*}'\
'@as\(un\)\?safe{\(@asc\?[su][^ ]*}\)\?'\
'\( @asc\?[su][^ ]*}\)*}'\
'@ac\(un\)\?safe{\(@ac[su][^ ]*}\)\?'\
'\( @ac[su][^ ]*}\)*}}' &&
success=false
# Make sure safety lines marked as @mtsafe do not contain any
# MT-Unsafe remark; that would be @mtu, but there could be as, ac or
# asc between mt and u.
grep -n '^@safety.*@mtsafe' "$@" |
grep '@mt\(asc\?\|ac\)?u' "$@" &&
success=false
# Make sure @mtunsafe lines contain at least one @mtu remark (with
# optional as, ac or asc between mt and u).
grep -n '^@safety.*@mtunsafe' "$@" |
grep -v '@mtunsafe{.*@mt\(asc\?\|ac\)\?u' &&
success=false
# Make sure safety lines marked as @assafe do not contain any AS-Unsafe
# remark, which could be @asu or @mtasu note (with an optional c
# between as and u in both cases).
grep -n '^@safety.*@assafe' "$@" |
grep '@\(mt\)\?asc\?u' &&
success=false
# Make sure @asunsafe lines contain at least one @asu remark (which
# could be @ascu, or @mtasu or even @mtascu).
grep -n '^@safety.*@asunsafe' "$@" |
grep -v '@mtasc\?u.*@asunsafe\|@asunsafe{.*@asc\?u' &&
success=false
# Make sure safety lines marked as @acsafe do not contain any
# AC-Unsafe remark, which could be @acu, @ascu or even @mtacu or
# @mtascu.
grep -n '^@safety.*@acsafe' "$@" |
grep '@\(mt\)\?as\?cu' &&
success=false
# Make sure @acunsafe lines contain at least one @acu remark (possibly
# implied by @ascu, @mtacu or @mtascu).
grep -n '^@safety.*@acunsafe' "$@" |
grep -v '@\(mtas\?\|as\)cu.*@acunsafe\|@acunsafe{.*@acu' &&
success=false
# Make sure there aren't duplicate remarks in the same safety note.
grep -n '^@safety' "$@" |
grep '[^:]\(@\(mt\|a[sc]\)[^ {]*{[^ ]*}\).*[^:]\1' &&
success=false
# Check that comments containing safety remarks do not contain {}s,
# that all @mt remarks appear before @as remarks, that in turn appear
# before @ac remarks, all properly blank-separated, and that an
# optional comment about exclusions is between []s at the end of the
# line.
grep -n '^@c \+[^@ ]\+\( dup\)\?'\
'\( @\(mt\|a[sc]\)[^ ]*\)*\( \[.*\]\)\?$' "$@" |
grep -v ':@c *[^@{}]*\( @mt[^ {}]*\)*'\
'\( @as[^ {}]*\)*\( @ac[^ {}]*\)*\( \[.*\]\)\?$' &&
success=false
# Check that comments containing safety remarks do not contain
# duplicate remarks.
grep -n '^@c \+[^@ ]\+\( dup\)\?'\
'\( @\(mt\|a[sc]\)[^ ]*\)*\( \[.*\]\)\?$' "$@" |
grep '[^:]\(@\(mt\|a[sc]\)[^ ]*\) \(.*[^:]\)\?\1\($\| \)' &&
success=false
$success
glibc-doc-reference-2.19.orig/manual/conf.texi 0000664 0001750 0001750 00000154150 12275120646 021405 0 ustar adconrad adconrad @node System Configuration, Cryptographic Functions, System Management, Top
@c %MENU% Parameters describing operating system limits
@chapter System Configuration Parameters
The functions and macros listed in this chapter give information about
configuration parameters of the operating system---for example, capacity
limits, presence of optional POSIX features, and the default path for
executable files (@pxref{String Parameters}).
@menu
* General Limits:: Constants and functions that describe
various process-related limits that have
one uniform value for any given machine.
* System Options:: Optional POSIX features.
* Version Supported:: Version numbers of POSIX.1 and POSIX.2.
* Sysconf:: Getting specific configuration values
of general limits and system options.
* Minimums:: Minimum values for general limits.
* Limits for Files:: Size limitations that pertain to individual files.
These can vary between file systems
or even from file to file.
* Options for Files:: Optional features that some files may support.
* File Minimums:: Minimum values for file limits.
* Pathconf:: Getting the limit values for a particular file.
* Utility Limits:: Capacity limits of some POSIX.2 utility programs.
* Utility Minimums:: Minimum allowable values of those limits.
* String Parameters:: Getting the default search path.
@end menu
@node General Limits
@section General Capacity Limits
@cindex POSIX capacity limits
@cindex limits, POSIX
@cindex capacity limits, POSIX
The POSIX.1 and POSIX.2 standards specify a number of parameters that
describe capacity limitations of the system. These limits can be fixed
constants for a given operating system, or they can vary from machine to
machine. For example, some limit values may be configurable by the
system administrator, either at run time or by rebuilding the kernel,
and this should not require recompiling application programs.
@pindex limits.h
Each of the following limit parameters has a macro that is defined in
@file{limits.h} only if the system has a fixed, uniform limit for the
parameter in question. If the system allows different file systems or
files to have different limits, then the macro is undefined; use
@code{sysconf} to find out the limit that applies at a particular time
on a particular machine. @xref{Sysconf}.
Each of these parameters also has another macro, with a name starting
with @samp{_POSIX}, which gives the lowest value that the limit is
allowed to have on @emph{any} POSIX system. @xref{Minimums}.
@cindex limits, program argument size
@comment limits.h
@comment POSIX.1
@deftypevr Macro int ARG_MAX
If defined, the unvarying maximum combined length of the @var{argv} and
@var{environ} arguments that can be passed to the @code{exec} functions.
@end deftypevr
@cindex limits, number of processes
@comment limits.h
@comment POSIX.1
@deftypevr Macro int CHILD_MAX
If defined, the unvarying maximum number of processes that can exist
with the same real user ID at any one time. In BSD and GNU, this is
controlled by the @code{RLIMIT_NPROC} resource limit; @pxref{Limits on
Resources}.
@end deftypevr
@cindex limits, number of open files
@comment limits.h
@comment POSIX.1
@deftypevr Macro int OPEN_MAX
If defined, the unvarying maximum number of files that a single process
can have open simultaneously. In BSD and GNU, this is controlled
by the @code{RLIMIT_NOFILE} resource limit; @pxref{Limits on Resources}.
@end deftypevr
@comment limits.h
@comment POSIX.1
@deftypevr Macro int STREAM_MAX
If defined, the unvarying maximum number of streams that a single
process can have open simultaneously. @xref{Opening Streams}.
@end deftypevr
@cindex limits, time zone name length
@comment limits.h
@comment POSIX.1
@deftypevr Macro int TZNAME_MAX
If defined, the unvarying maximum length of a time zone name.
@xref{Time Zone Functions}.
@end deftypevr
These limit macros are always defined in @file{limits.h}.
@cindex limits, number of supplementary group IDs
@comment limits.h
@comment POSIX.1
@deftypevr Macro int NGROUPS_MAX
The maximum number of supplementary group IDs that one process can have.
The value of this macro is actually a lower bound for the maximum. That
is, you can count on being able to have that many supplementary group
IDs, but a particular machine might let you have even more. You can use
@code{sysconf} to see whether a particular machine will let you have
more (@pxref{Sysconf}).
@end deftypevr
@comment limits.h
@comment POSIX.1
@deftypevr Macro ssize_t SSIZE_MAX
The largest value that can fit in an object of type @code{ssize_t}.
Effectively, this is the limit on the number of bytes that can be read
or written in a single operation.
This macro is defined in all POSIX systems because this limit is never
configurable.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int RE_DUP_MAX
The largest number of repetitions you are guaranteed is allowed in the
construct @samp{\@{@var{min},@var{max}\@}} in a regular expression.
The value of this macro is actually a lower bound for the maximum. That
is, you can count on being able to have that many repetitions, but a
particular machine might let you have even more. You can use
@code{sysconf} to see whether a particular machine will let you have
more (@pxref{Sysconf}). And even the value that @code{sysconf} tells
you is just a lower bound---larger values might work.
This macro is defined in all POSIX.2 systems, because POSIX.2 says it
should always be defined even if there is no specific imposed limit.
@end deftypevr
@node System Options
@section Overall System Options
@cindex POSIX optional features
@cindex optional POSIX features
POSIX defines certain system-specific options that not all POSIX systems
support. Since these options are provided in the kernel, not in the
library, simply using @theglibc{} does not guarantee any of these
features is supported; it depends on the system you are using.
@pindex unistd.h
You can test for the availability of a given option using the macros in
this section, together with the function @code{sysconf}. The macros are
defined only if you include @file{unistd.h}.
For the following macros, if the macro is defined in @file{unistd.h},
then the option is supported. Otherwise, the option may or may not be
supported; use @code{sysconf} to find out. @xref{Sysconf}.
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int _POSIX_JOB_CONTROL
If this symbol is defined, it indicates that the system supports job
control. Otherwise, the implementation behaves as if all processes
within a session belong to a single process group. @xref{Job Control}.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int _POSIX_SAVED_IDS
If this symbol is defined, it indicates that the system remembers the
effective user and group IDs of a process before it executes an
executable file with the set-user-ID or set-group-ID bits set, and that
explicitly changing the effective user or group IDs back to these values
is permitted. If this option is not defined, then if a nonprivileged
process changes its effective user or group ID to the real user or group
ID of the process, it can't change it back again. @xref{Enable/Disable
Setuid}.
@end deftypevr
For the following macros, if the macro is defined in @file{unistd.h},
then its value indicates whether the option is supported. A value of
@code{-1} means no, and any other value means yes. If the macro is not
defined, then the option may or may not be supported; use @code{sysconf}
to find out. @xref{Sysconf}.
@comment unistd.h
@comment POSIX.2
@deftypevr Macro int _POSIX2_C_DEV
If this symbol is defined, it indicates that the system has the POSIX.2
C compiler command, @code{c89}. @Theglibc{} always defines this
as @code{1}, on the assumption that you would not have installed it if
you didn't have a C compiler.
@end deftypevr
@comment unistd.h
@comment POSIX.2
@deftypevr Macro int _POSIX2_FORT_DEV
If this symbol is defined, it indicates that the system has the POSIX.2
Fortran compiler command, @code{fort77}. @Theglibc{} never
defines this, because we don't know what the system has.
@end deftypevr
@comment unistd.h
@comment POSIX.2
@deftypevr Macro int _POSIX2_FORT_RUN
If this symbol is defined, it indicates that the system has the POSIX.2
@code{asa} command to interpret Fortran carriage control. @Theglibc{}
never defines this, because we don't know what the system has.
@end deftypevr
@comment unistd.h
@comment POSIX.2
@deftypevr Macro int _POSIX2_LOCALEDEF
If this symbol is defined, it indicates that the system has the POSIX.2
@code{localedef} command. @Theglibc{} never defines this, because
we don't know what the system has.
@end deftypevr
@comment unistd.h
@comment POSIX.2
@deftypevr Macro int _POSIX2_SW_DEV
If this symbol is defined, it indicates that the system has the POSIX.2
commands @code{ar}, @code{make}, and @code{strip}. @Theglibc{}
always defines this as @code{1}, on the assumption that you had to have
@code{ar} and @code{make} to install the library, and it's unlikely that
@code{strip} would be absent when those are present.
@end deftypevr
@node Version Supported
@section Which Version of POSIX is Supported
@comment unistd.h
@comment POSIX.1
@deftypevr Macro {long int} _POSIX_VERSION
This constant represents the version of the POSIX.1 standard to which
the implementation conforms. For an implementation conforming to the
1995 POSIX.1 standard, the value is the integer @code{199506L}.
@code{_POSIX_VERSION} is always defined (in @file{unistd.h}) in any
POSIX system.
@strong{Usage Note:} Don't try to test whether the system supports POSIX
by including @file{unistd.h} and then checking whether
@code{_POSIX_VERSION} is defined. On a non-POSIX system, this will
probably fail because there is no @file{unistd.h}. We do not know of
@emph{any} way you can reliably test at compilation time whether your
target system supports POSIX or whether @file{unistd.h} exists.
@end deftypevr
@comment unistd.h
@comment POSIX.2
@deftypevr Macro {long int} _POSIX2_C_VERSION
This constant represents the version of the POSIX.2 standard which the
library and system kernel support. We don't know what value this will
be for the first version of the POSIX.2 standard, because the value is
based on the year and month in which the standard is officially adopted.
The value of this symbol says nothing about the utilities installed on
the system.
@strong{Usage Note:} You can use this macro to tell whether a POSIX.1
system library supports POSIX.2 as well. Any POSIX.1 system contains
@file{unistd.h}, so include that file and then test @code{defined
(_POSIX2_C_VERSION)}.
@end deftypevr
@node Sysconf
@section Using @code{sysconf}
When your system has configurable system limits, you can use the
@code{sysconf} function to find out the value that applies to any
particular machine. The function and the associated @var{parameter}
constants are declared in the header file @file{unistd.h}.
@menu
* Sysconf Definition:: Detailed specifications of @code{sysconf}.
* Constants for Sysconf:: The list of parameters @code{sysconf} can read.
* Examples of Sysconf:: How to use @code{sysconf} and the parameter
macros properly together.
@end menu
@node Sysconf Definition
@subsection Definition of @code{sysconf}
@comment unistd.h
@comment POSIX.1
@deftypefun {long int} sysconf (int @var{parameter})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c Some parts of the implementation open /proc and /sys files and dirs
@c to collect system details, using fd and stream I/O depending on the
@c case. _SC_TZNAME_MAX calls __tzname_max, that (while holding a lock)
@c calls tzset_internal, that calls getenv if it's called the first
@c time; there are free and strdup calls in there too. The returned max
@c value may change over time for TZNAME_MAX, depending on selected
@c timezones; NPROCS, NPROCS_CONF, PHYS_PAGES, AVPHYS_PAGES,
@c NGROUPS_MAX, SIGQUEUE_MAX, depending on variable values read from
@c /proc at each call, and from rlimit-obtained values CHILD_MAX,
@c OPEN_MAX, ARG_MAX, SIGQUEUE_MAX.
This function is used to inquire about runtime system parameters. The
@var{parameter} argument should be one of the @samp{_SC_} symbols listed
below.
The normal return value from @code{sysconf} is the value you requested.
A value of @code{-1} is returned both if the implementation does not
impose a limit, and in case of an error.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The value of the @var{parameter} is invalid.
@end table
@end deftypefun
@node Constants for Sysconf
@subsection Constants for @code{sysconf} Parameters
Here are the symbolic constants for use as the @var{parameter} argument
to @code{sysconf}. The values are all integer constants (more
specifically, enumeration type values).
@vtable @code
@comment unistd.h
@comment POSIX.1
@item _SC_ARG_MAX
Inquire about the parameter corresponding to @code{ARG_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_CHILD_MAX
Inquire about the parameter corresponding to @code{CHILD_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_OPEN_MAX
Inquire about the parameter corresponding to @code{OPEN_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_STREAM_MAX
Inquire about the parameter corresponding to @code{STREAM_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_TZNAME_MAX
Inquire about the parameter corresponding to @code{TZNAME_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_NGROUPS_MAX
Inquire about the parameter corresponding to @code{NGROUPS_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_JOB_CONTROL
Inquire about the parameter corresponding to @code{_POSIX_JOB_CONTROL}.
@comment unistd.h
@comment POSIX.1
@item _SC_SAVED_IDS
Inquire about the parameter corresponding to @code{_POSIX_SAVED_IDS}.
@comment unistd.h
@comment POSIX.1
@item _SC_VERSION
Inquire about the parameter corresponding to @code{_POSIX_VERSION}.
@comment unistd.h
@comment POSIX.1
@item _SC_CLK_TCK
Inquire about the number of clock ticks per second; @pxref{CPU Time}.
The corresponding parameter @code{CLK_TCK} is obsolete.
@comment unistd.h
@comment GNU
@item _SC_CHARCLASS_NAME_MAX
Inquire about the parameter corresponding to maximal length allowed for
a character class name in an extended locale specification. These
extensions are not yet standardized and so this option is not standardized
as well.
@comment unistdh.h
@comment POSIX.1
@item _SC_REALTIME_SIGNALS
Inquire about the parameter corresponding to @code{_POSIX_REALTIME_SIGNALS}.
@comment unistd.h
@comment POSIX.1
@item _SC_PRIORITY_SCHEDULING
Inquire about the parameter corresponding to @code{_POSIX_PRIORITY_SCHEDULING}.
@comment unistd.h
@comment POSIX.1
@item _SC_TIMERS
Inquire about the parameter corresponding to @code{_POSIX_TIMERS}.
@comment unistd.h
@comment POSIX.1
@item _SC_ASYNCHRONOUS_IO
Inquire about the parameter corresponding to @code{_POSIX_ASYNCHRONOUS_IO}.
@comment unistd.h
@comment POSIX.1
@item _SC_PRIORITIZED_IO
Inquire about the parameter corresponding to @code{_POSIX_PRIORITIZED_IO}.
@comment unistd.h
@comment POSIX.1
@item _SC_SYNCHRONIZED_IO
Inquire about the parameter corresponding to @code{_POSIX_SYNCHRONIZED_IO}.
@comment unistd.h
@comment POSIX.1
@item _SC_FSYNC
Inquire about the parameter corresponding to @code{_POSIX_FSYNC}.
@comment unistd.h
@comment POSIX.1
@item _SC_MAPPED_FILES
Inquire about the parameter corresponding to @code{_POSIX_MAPPED_FILES}.
@comment unistd.h
@comment POSIX.1
@item _SC_MEMLOCK
Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK}.
@comment unistd.h
@comment POSIX.1
@item _SC_MEMLOCK_RANGE
Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK_RANGE}.
@comment unistd.h
@comment POSIX.1
@item _SC_MEMORY_PROTECTION
Inquire about the parameter corresponding to @code{_POSIX_MEMORY_PROTECTION}.
@comment unistd.h
@comment POSIX.1
@item _SC_MESSAGE_PASSING
Inquire about the parameter corresponding to @code{_POSIX_MESSAGE_PASSING}.
@comment unistd.h
@comment POSIX.1
@item _SC_SEMAPHORES
Inquire about the parameter corresponding to @code{_POSIX_SEMAPHORES}.
@comment unistd.h
@comment POSIX.1
@item _SC_SHARED_MEMORY_OBJECTS
Inquire about the parameter corresponding to@*
@code{_POSIX_SHARED_MEMORY_OBJECTS}.
@comment unistd.h
@comment POSIX.1
@item _SC_AIO_LISTIO_MAX
Inquire about the parameter corresponding to @code{_POSIX_AIO_LISTIO_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_AIO_MAX
Inquire about the parameter corresponding to @code{_POSIX_AIO_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_AIO_PRIO_DELTA_MAX
Inquire the value by which a process can decrease its asynchronous I/O
priority level from its own scheduling priority. This corresponds to the
run-time invariant value @code{AIO_PRIO_DELTA_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_DELAYTIMER_MAX
Inquire about the parameter corresponding to @code{_POSIX_DELAYTIMER_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_MQ_OPEN_MAX
Inquire about the parameter corresponding to @code{_POSIX_MQ_OPEN_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_MQ_PRIO_MAX
Inquire about the parameter corresponding to @code{_POSIX_MQ_PRIO_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_RTSIG_MAX
Inquire about the parameter corresponding to @code{_POSIX_RTSIG_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_SEM_NSEMS_MAX
Inquire about the parameter corresponding to @code{_POSIX_SEM_NSEMS_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_SEM_VALUE_MAX
Inquire about the parameter corresponding to @code{_POSIX_SEM_VALUE_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_SIGQUEUE_MAX
Inquire about the parameter corresponding to @code{_POSIX_SIGQUEUE_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_TIMER_MAX
Inquire about the parameter corresponding to @code{_POSIX_TIMER_MAX}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII
Inquire about the parameter corresponding to @code{_POSIX_PII}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_XTI
Inquire about the parameter corresponding to @code{_POSIX_PII_XTI}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_SOCKET
Inquire about the parameter corresponding to @code{_POSIX_PII_SOCKET}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_INTERNET
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_OSI
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI}.
@comment unistd.h
@comment POSIX.1g
@item _SC_SELECT
Inquire about the parameter corresponding to @code{_POSIX_SELECT}.
@comment unistd.h
@comment POSIX.1g
@item _SC_UIO_MAXIOV
Inquire about the parameter corresponding to @code{_POSIX_UIO_MAXIOV}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_INTERNET_STREAM
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_STREAM}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_INTERNET_DGRAM
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_DGRAM}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_OSI_COTS
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_COTS}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_OSI_CLTS
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_CLTS}.
@comment unistd.h
@comment POSIX.1g
@item _SC_PII_OSI_M
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_M}.
@comment unistd.h
@comment POSIX.1g
@item _SC_T_IOV_MAX
Inquire the value of the value associated with the @code{T_IOV_MAX}
variable.
@comment unistd.h
@comment POSIX.1
@item _SC_THREADS
Inquire about the parameter corresponding to @code{_POSIX_THREADS}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_SAFE_FUNCTIONS
Inquire about the parameter corresponding to@*
@code{_POSIX_THREAD_SAFE_FUNCTIONS}.
@comment unistd.h
@comment POSIX.1
@item _SC_GETGR_R_SIZE_MAX
Inquire about the parameter corresponding to @code{_POSIX_GETGR_R_SIZE_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_GETPW_R_SIZE_MAX
Inquire about the parameter corresponding to @code{_POSIX_GETPW_R_SIZE_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_LOGIN_NAME_MAX
Inquire about the parameter corresponding to @code{_POSIX_LOGIN_NAME_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_TTY_NAME_MAX
Inquire about the parameter corresponding to @code{_POSIX_TTY_NAME_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_DESTRUCTOR_ITERATIONS
Inquire about the parameter corresponding to
@code{_POSIX_THREAD_DESTRUCTOR_ITERATIONS}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_KEYS_MAX
Inquire about the parameter corresponding to @code{_POSIX_THREAD_KEYS_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_STACK_MIN
Inquire about the parameter corresponding to @code{_POSIX_THREAD_STACK_MIN}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_THREADS_MAX
Inquire about the parameter corresponding to @code{_POSIX_THREAD_THREADS_MAX}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_ATTR_STACKADDR
Inquire about the parameter corresponding to@*a
@code{_POSIX_THREAD_ATTR_STACKADDR}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_ATTR_STACKSIZE
Inquire about the parameter corresponding to@*
@code{_POSIX_THREAD_ATTR_STACKSIZE}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_PRIORITY_SCHEDULING
Inquire about the parameter corresponding to
@code{_POSIX_THREAD_PRIORITY_SCHEDULING}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_PRIO_INHERIT
Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_INHERIT}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_PRIO_PROTECT
Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_PROTECT}.
@comment unistd.h
@comment POSIX.1
@item _SC_THREAD_PROCESS_SHARED
Inquire about the parameter corresponding to
@code{_POSIX_THREAD_PROCESS_SHARED}.
@comment unistd.h
@comment POSIX.2
@item _SC_2_C_DEV
Inquire about whether the system has the POSIX.2 C compiler command,
@code{c89}.
@comment unistd.h
@comment POSIX.2
@item _SC_2_FORT_DEV
Inquire about whether the system has the POSIX.2 Fortran compiler
command, @code{fort77}.
@comment unistd.h
@comment POSIX.2
@item _SC_2_FORT_RUN
Inquire about whether the system has the POSIX.2 @code{asa} command to
interpret Fortran carriage control.
@comment unistd.h
@comment POSIX.2
@item _SC_2_LOCALEDEF
Inquire about whether the system has the POSIX.2 @code{localedef}
command.
@comment unistd.h
@comment POSIX.2
@item _SC_2_SW_DEV
Inquire about whether the system has the POSIX.2 commands @code{ar},
@code{make}, and @code{strip}.
@comment unistd.h
@comment POSIX.2
@item _SC_BC_BASE_MAX
Inquire about the maximum value of @code{obase} in the @code{bc}
utility.
@comment unistd.h
@comment POSIX.2
@item _SC_BC_DIM_MAX
Inquire about the maximum size of an array in the @code{bc}
utility.
@comment unistd.h
@comment POSIX.2
@item _SC_BC_SCALE_MAX
Inquire about the maximum value of @code{scale} in the @code{bc}
utility.
@comment unistd.h
@comment POSIX.2
@item _SC_BC_STRING_MAX
Inquire about the maximum size of a string constant in the
@code{bc} utility.
@comment unistd.h
@comment POSIX.2
@item _SC_COLL_WEIGHTS_MAX
Inquire about the maximum number of weights that can necessarily
be used in defining the collating sequence for a locale.
@comment unistd.h
@comment POSIX.2
@item _SC_EXPR_NEST_MAX
Inquire about the maximum number of expressions nested within
parentheses when using the @code{expr} utility.
@comment unistd.h
@comment POSIX.2
@item _SC_LINE_MAX
Inquire about the maximum size of a text line that the POSIX.2 text
utilities can handle.
@comment unistd.h
@comment POSIX.2
@item _SC_EQUIV_CLASS_MAX
Inquire about the maximum number of weights that can be assigned to an
entry of the @code{LC_COLLATE} category @samp{order} keyword in a locale
definition. @Theglibc{} does not presently support locale
definitions.
@comment unistd.h
@comment POSIX.2
@item _SC_VERSION
Inquire about the version number of POSIX.1 that the library and kernel
support.
@comment unistd.h
@comment POSIX.2
@item _SC_2_VERSION
Inquire about the version number of POSIX.2 that the system utilities
support.
@comment unistd.h
@comment GNU
@item _SC_PAGESIZE
Inquire about the virtual memory page size of the machine.
@code{getpagesize} returns the same value (@pxref{Query Memory Parameters}).
@comment unistd.h
@comment GNU
@item _SC_NPROCESSORS_CONF
Inquire about the number of configured processors.
@comment unistd.h
@comment GNU
@item _SC_NPROCESSORS_ONLN
Inquire about the number of processors online.
@comment unistd.h
@comment GNU
@item _SC_PHYS_PAGES
Inquire about the number of physical pages in the system.
@comment unistd.h
@comment GNU
@item _SC_AVPHYS_PAGES
Inquire about the number of available physical pages in the system.
@comment unistd.h
@comment GNU
@item _SC_ATEXIT_MAX
Inquire about the number of functions which can be registered as termination
functions for @code{atexit}; @pxref{Cleanups on Exit}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_VERSION
Inquire about the parameter corresponding to @code{_XOPEN_VERSION}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_XCU_VERSION
Inquire about the parameter corresponding to @code{_XOPEN_XCU_VERSION}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_UNIX
Inquire about the parameter corresponding to @code{_XOPEN_UNIX}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_REALTIME
Inquire about the parameter corresponding to @code{_XOPEN_REALTIME}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_REALTIME_THREADS
Inquire about the parameter corresponding to @code{_XOPEN_REALTIME_THREADS}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_LEGACY
Inquire about the parameter corresponding to @code{_XOPEN_LEGACY}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_CRYPT
Inquire about the parameter corresponding to @code{_XOPEN_CRYPT}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_ENH_I18N
Inquire about the parameter corresponding to @code{_XOPEN_ENH_I18N}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_SHM
Inquire about the parameter corresponding to @code{_XOPEN_SHM}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_XPG2
Inquire about the parameter corresponding to @code{_XOPEN_XPG2}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_XPG3
Inquire about the parameter corresponding to @code{_XOPEN_XPG3}.
@comment unistd.h
@comment X/Open
@item _SC_XOPEN_XPG4
Inquire about the parameter corresponding to @code{_XOPEN_XPG4}.
@comment unistd.h
@comment X/Open
@item _SC_CHAR_BIT
Inquire about the number of bits in a variable of type @code{char}.
@comment unistd.h
@comment X/Open
@item _SC_CHAR_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{char}.
@comment unistd.h
@comment X/Open
@item _SC_CHAR_MIN
Inquire about the minimum value which can be stored in a variable of type
@code{char}.
@comment unistd.h
@comment X/Open
@item _SC_INT_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{int}.
@comment unistd.h
@comment X/Open
@item _SC_INT_MIN
Inquire about the minimum value which can be stored in a variable of type
@code{int}.
@comment unistd.h
@comment X/Open
@item _SC_LONG_BIT
Inquire about the number of bits in a variable of type @code{long int}.
@comment unistd.h
@comment X/Open
@item _SC_WORD_BIT
Inquire about the number of bits in a variable of a register word.
@comment unistd.h
@comment X/Open
@item _SC_MB_LEN_MAX
Inquire the maximum length of a multi-byte representation of a wide
character value.
@comment unistd.h
@comment X/Open
@item _SC_NZERO
Inquire about the value used to internally represent the zero priority level for
the process execution.
@comment unistd.h
@comment X/Open
@item SC_SSIZE_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{ssize_t}.
@comment unistd.h
@comment X/Open
@item _SC_SCHAR_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{signed char}.
@comment unistd.h
@comment X/Open
@item _SC_SCHAR_MIN
Inquire about the minimum value which can be stored in a variable of type
@code{signed char}.
@comment unistd.h
@comment X/Open
@item _SC_SHRT_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{short int}.
@comment unistd.h
@comment X/Open
@item _SC_SHRT_MIN
Inquire about the minimum value which can be stored in a variable of type
@code{short int}.
@comment unistd.h
@comment X/Open
@item _SC_UCHAR_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{unsigned char}.
@comment unistd.h
@comment X/Open
@item _SC_UINT_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{unsigned int}.
@comment unistd.h
@comment X/Open
@item _SC_ULONG_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{unsigned long int}.
@comment unistd.h
@comment X/Open
@item _SC_USHRT_MAX
Inquire about the maximum value which can be stored in a variable of type
@code{unsigned short int}.
@comment unistd.h
@comment X/Open
@item _SC_NL_ARGMAX
Inquire about the parameter corresponding to @code{NL_ARGMAX}.
@comment unistd.h
@comment X/Open
@item _SC_NL_LANGMAX
Inquire about the parameter corresponding to @code{NL_LANGMAX}.
@comment unistd.h
@comment X/Open
@item _SC_NL_MSGMAX
Inquire about the parameter corresponding to @code{NL_MSGMAX}.
@comment unistd.h
@comment X/Open
@item _SC_NL_NMAX
Inquire about the parameter corresponding to @code{NL_NMAX}.
@comment unistd.h
@comment X/Open
@item _SC_NL_SETMAX
Inquire about the parameter corresponding to @code{NL_SETMAX}.
@comment unistd.h
@comment X/Open
@item _SC_NL_TEXTMAX
Inquire about the parameter corresponding to @code{NL_TEXTMAX}.
@end vtable
@node Examples of Sysconf
@subsection Examples of @code{sysconf}
We recommend that you first test for a macro definition for the
parameter you are interested in, and call @code{sysconf} only if the
macro is not defined. For example, here is how to test whether job
control is supported:
@smallexample
@group
int
have_job_control (void)
@{
#ifdef _POSIX_JOB_CONTROL
return 1;
#else
int value = sysconf (_SC_JOB_CONTROL);
if (value < 0)
/* @r{If the system is that badly wedged,}
@r{there's no use trying to go on.} */
fatal (strerror (errno));
return value;
#endif
@}
@end group
@end smallexample
Here is how to get the value of a numeric limit:
@smallexample
int
get_child_max ()
@{
#ifdef CHILD_MAX
return CHILD_MAX;
#else
int value = sysconf (_SC_CHILD_MAX);
if (value < 0)
fatal (strerror (errno));
return value;
#endif
@}
@end smallexample
@node Minimums
@section Minimum Values for General Capacity Limits
Here are the names for the POSIX minimum upper bounds for the system
limit parameters. The significance of these values is that you can
safely push to these limits without checking whether the particular
system you are using can go that far.
@table @code
@comment limits.h
@comment POSIX.1
@item _POSIX_AIO_LISTIO_MAX
The most restrictive limit permitted by POSIX for the maximum number of
I/O operations that can be specified in a list I/O call. The value of
this constant is @code{2}; thus you can add up to two new entries
of the list of outstanding operations.
@comment limits.h
@comment POSIX.1
@item _POSIX_AIO_MAX
The most restrictive limit permitted by POSIX for the maximum number of
outstanding asynchronous I/O operations. The value of this constant is
@code{1}. So you cannot expect that you can issue more than one
operation and immediately continue with the normal work, receiving the
notifications asynchronously.
@comment limits.h
@comment POSIX.1
@item _POSIX_ARG_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum combined length of the @var{argv} and @var{environ}
arguments that can be passed to the @code{exec} functions.
Its value is @code{4096}.
@comment limits.h
@comment POSIX.1
@item _POSIX_CHILD_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of simultaneous processes per real user ID. Its
value is @code{6}.
@comment limits.h
@comment POSIX.1
@item _POSIX_NGROUPS_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of supplementary group IDs per process. Its
value is @code{0}.
@comment limits.h
@comment POSIX.1
@item _POSIX_OPEN_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of files that a single process can have open
simultaneously. Its value is @code{16}.
@comment limits.h
@comment POSIX.1
@item _POSIX_SSIZE_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum value that can be stored in an object of type
@code{ssize_t}. Its value is @code{32767}.
@comment limits.h
@comment POSIX.1
@item _POSIX_STREAM_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of streams that a single process can have open
simultaneously. Its value is @code{8}.
@comment limits.h
@comment POSIX.1
@item _POSIX_TZNAME_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the maximum length of a time zone name. Its value is @code{3}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_RE_DUP_MAX
The value of this macro is the most restrictive limit permitted by POSIX
for the numbers used in the @samp{\@{@var{min},@var{max}\@}} construct
in a regular expression. Its value is @code{255}.
@end table
@node Limits for Files
@section Limits on File System Capacity
The POSIX.1 standard specifies a number of parameters that describe the
limitations of the file system. It's possible for the system to have a
fixed, uniform limit for a parameter, but this isn't the usual case. On
most systems, it's possible for different file systems (and, for some
parameters, even different files) to have different maximum limits. For
example, this is very likely if you use NFS to mount some of the file
systems from other machines.
@pindex limits.h
Each of the following macros is defined in @file{limits.h} only if the
system has a fixed, uniform limit for the parameter in question. If the
system allows different file systems or files to have different limits,
then the macro is undefined; use @code{pathconf} or @code{fpathconf} to
find out the limit that applies to a particular file. @xref{Pathconf}.
Each parameter also has another macro, with a name starting with
@samp{_POSIX}, which gives the lowest value that the limit is allowed to
have on @emph{any} POSIX system. @xref{File Minimums}.
@cindex limits, link count of files
@comment limits.h (optional)
@comment POSIX.1
@deftypevr Macro int LINK_MAX
The uniform system limit (if any) for the number of names for a given
file. @xref{Hard Links}.
@end deftypevr
@cindex limits, terminal input queue
@comment limits.h
@comment POSIX.1
@deftypevr Macro int MAX_CANON
The uniform system limit (if any) for the amount of text in a line of
input when input editing is enabled. @xref{Canonical or Not}.
@end deftypevr
@comment limits.h
@comment POSIX.1
@deftypevr Macro int MAX_INPUT
The uniform system limit (if any) for the total number of characters
typed ahead as input. @xref{I/O Queues}.
@end deftypevr
@cindex limits, file name length
@comment limits.h
@comment POSIX.1
@deftypevr Macro int NAME_MAX
The uniform system limit (if any) for the length of a file name component, not
including the terminating null character.
@strong{Portability Note:} On some systems, @theglibc{} defines
@code{NAME_MAX}, but does not actually enforce this limit.
@end deftypevr
@comment limits.h
@comment POSIX.1
@deftypevr Macro int PATH_MAX
The uniform system limit (if any) for the length of an entire file name (that
is, the argument given to system calls such as @code{open}), including the
terminating null character.
@strong{Portability Note:} @Theglibc{} does not enforce this limit
even if @code{PATH_MAX} is defined.
@end deftypevr
@cindex limits, pipe buffer size
@comment limits.h
@comment POSIX.1
@deftypevr Macro int PIPE_BUF
The uniform system limit (if any) for the number of bytes that can be
written atomically to a pipe. If multiple processes are writing to the
same pipe simultaneously, output from different processes might be
interleaved in chunks of this size. @xref{Pipes and FIFOs}.
@end deftypevr
These are alternative macro names for some of the same information.
@comment dirent.h
@comment BSD
@deftypevr Macro int MAXNAMLEN
This is the BSD name for @code{NAME_MAX}. It is defined in
@file{dirent.h}.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int FILENAME_MAX
The value of this macro is an integer constant expression that
represents the maximum length of a file name string. It is defined in
@file{stdio.h}.
Unlike @code{PATH_MAX}, this macro is defined even if there is no actual
limit imposed. In such a case, its value is typically a very large
number. @strong{This is always the case on @gnuhurdsystems{}.}
@strong{Usage Note:} Don't use @code{FILENAME_MAX} as the size of an
array in which to store a file name! You can't possibly make an array
that big! Use dynamic allocation (@pxref{Memory Allocation}) instead.
@end deftypevr
@node Options for Files
@section Optional Features in File Support
POSIX defines certain system-specific options in the system calls for
operating on files. Some systems support these options and others do
not. Since these options are provided in the kernel, not in the
library, simply using @theglibc{} does not guarantee that any of these
features is supported; it depends on the system you are using. They can
also vary between file systems on a single machine.
@pindex unistd.h
This section describes the macros you can test to determine whether a
particular option is supported on your machine. If a given macro is
defined in @file{unistd.h}, then its value says whether the
corresponding feature is supported. (A value of @code{-1} indicates no;
any other value indicates yes.) If the macro is undefined, it means
particular files may or may not support the feature.
Since all the machines that support @theglibc{} also support NFS,
one can never make a general statement about whether all file systems
support the @code{_POSIX_CHOWN_RESTRICTED} and @code{_POSIX_NO_TRUNC}
features. So these names are never defined as macros in @theglibc{}.
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int _POSIX_CHOWN_RESTRICTED
If this option is in effect, the @code{chown} function is restricted so
that the only changes permitted to nonprivileged processes is to change
the group owner of a file to either be the effective group ID of the
process, or one of its supplementary group IDs. @xref{File Owner}.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int _POSIX_NO_TRUNC
If this option is in effect, file name components longer than
@code{NAME_MAX} generate an @code{ENAMETOOLONG} error. Otherwise, file
name components that are too long are silently truncated.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro {unsigned char} _POSIX_VDISABLE
This option is only meaningful for files that are terminal devices.
If it is enabled, then handling for special control characters can
be disabled individually. @xref{Special Characters}.
@end deftypevr
@pindex unistd.h
If one of these macros is undefined, that means that the option might be
in effect for some files and not for others. To inquire about a
particular file, call @code{pathconf} or @code{fpathconf}.
@xref{Pathconf}.
@node File Minimums
@section Minimum Values for File System Limits
Here are the names for the POSIX minimum upper bounds for some of the
above parameters. The significance of these values is that you can
safely push to these limits without checking whether the particular
system you are using can go that far. In most cases @gnusystems{} do not
have these strict limitations. The actual limit should be requested if
necessary.
@table @code
@comment limits.h
@comment POSIX.1
@item _POSIX_LINK_MAX
The most restrictive limit permitted by POSIX for the maximum value of a
file's link count. The value of this constant is @code{8}; thus, you
can always make up to eight names for a file without running into a
system limit.
@comment limits.h
@comment POSIX.1
@item _POSIX_MAX_CANON
The most restrictive limit permitted by POSIX for the maximum number of
bytes in a canonical input line from a terminal device. The value of
this constant is @code{255}.
@comment limits.h
@comment POSIX.1
@item _POSIX_MAX_INPUT
The most restrictive limit permitted by POSIX for the maximum number of
bytes in a terminal device input queue (or typeahead buffer).
@xref{Input Modes}. The value of this constant is @code{255}.
@comment limits.h
@comment POSIX.1
@item _POSIX_NAME_MAX
The most restrictive limit permitted by POSIX for the maximum number of
bytes in a file name component. The value of this constant is
@code{14}.
@comment limits.h
@comment POSIX.1
@item _POSIX_PATH_MAX
The most restrictive limit permitted by POSIX for the maximum number of
bytes in a file name. The value of this constant is @code{256}.
@comment limits.h
@comment POSIX.1
@item _POSIX_PIPE_BUF
The most restrictive limit permitted by POSIX for the maximum number of
bytes that can be written atomically to a pipe. The value of this
constant is @code{512}.
@comment limits.h
@comment POSIX.1
@item SYMLINK_MAX
Maximum number of bytes in a symbolic link.
@comment limits.h
@comment POSIX.1
@item POSIX_REC_INCR_XFER_SIZE
Recommended increment for file transfer sizes between the
@code{POSIX_REC_MIN_XFER_SIZE} and @code{POSIX_REC_MAX_XFER_SIZE}
values.
@comment limits.h
@comment POSIX.1
@item POSIX_REC_MAX_XFER_SIZE
Maximum recommended file transfer size.
@comment limits.h
@comment POSIX.1
@item POSIX_REC_MIN_XFER_SIZE
Minimum recommended file transfer size.
@comment limits.h
@comment POSIX.1
@item POSIX_REC_XFER_ALIGN
Recommended file transfer buffer alignment.
@end table
@node Pathconf
@section Using @code{pathconf}
When your machine allows different files to have different values for a
file system parameter, you can use the functions in this section to find
out the value that applies to any particular file.
These functions and the associated constants for the @var{parameter}
argument are declared in the header file @file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun {long int} pathconf (const char *@var{filename}, int @var{parameter})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c When __statfs_link_max finds an ext* filesystem, it may read
@c /proc/mounts or similar as a mntent stream.
@c __statfs_chown_restricted may read from
@c /proc/sys/fs/xfs/restrict_chown as a file descriptor.
This function is used to inquire about the limits that apply to
the file named @var{filename}.
The @var{parameter} argument should be one of the @samp{_PC_} constants
listed below.
The normal return value from @code{pathconf} is the value you requested.
A value of @code{-1} is returned both if the implementation does not
impose a limit, and in case of an error. In the former case,
@code{errno} is not set, while in the latter case, @code{errno} is set
to indicate the cause of the problem. So the only way to use this
function robustly is to store @code{0} into @code{errno} just before
calling it.
Besides the usual file name errors (@pxref{File Name Errors}),
the following error condition is defined for this function:
@table @code
@item EINVAL
The value of @var{parameter} is invalid, or the implementation doesn't
support the @var{parameter} for the specific file.
@end table
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun {long int} fpathconf (int @var{filedes}, int @var{parameter})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Same caveats as pathconf.
This is just like @code{pathconf} except that an open file descriptor
is used to specify the file for which information is requested, instead
of a file name.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The value of @var{parameter} is invalid, or the implementation doesn't
support the @var{parameter} for the specific file.
@end table
@end deftypefun
Here are the symbolic constants that you can use as the @var{parameter}
argument to @code{pathconf} and @code{fpathconf}. The values are all
integer constants.
@table @code
@comment unistd.h
@comment POSIX.1
@item _PC_LINK_MAX
Inquire about the value of @code{LINK_MAX}.
@comment unistd.h
@comment POSIX.1
@item _PC_MAX_CANON
Inquire about the value of @code{MAX_CANON}.
@comment unistd.h
@comment POSIX.1
@item _PC_MAX_INPUT
Inquire about the value of @code{MAX_INPUT}.
@comment unistd.h
@comment POSIX.1
@item _PC_NAME_MAX
Inquire about the value of @code{NAME_MAX}.
@comment unistd.h
@comment POSIX.1
@item _PC_PATH_MAX
Inquire about the value of @code{PATH_MAX}.
@comment unistd.h
@comment POSIX.1
@item _PC_PIPE_BUF
Inquire about the value of @code{PIPE_BUF}.
@comment unistd.h
@comment POSIX.1
@item _PC_CHOWN_RESTRICTED
Inquire about the value of @code{_POSIX_CHOWN_RESTRICTED}.
@comment unistd.h
@comment POSIX.1
@item _PC_NO_TRUNC
Inquire about the value of @code{_POSIX_NO_TRUNC}.
@comment unistd.h
@comment POSIX.1
@item _PC_VDISABLE
Inquire about the value of @code{_POSIX_VDISABLE}.
@comment unistd.h
@comment POSIX.1
@item _PC_SYNC_IO
Inquire about the value of @code{_POSIX_SYNC_IO}.
@comment unistd.h
@comment POSIX.1
@item _PC_ASYNC_IO
Inquire about the value of @code{_POSIX_ASYNC_IO}.
@comment unistd.h
@comment POSIX.1
@item _PC_PRIO_IO
Inquire about the value of @code{_POSIX_PRIO_IO}.
@comment unistd.h
@comment LFS
@item _PC_FILESIZEBITS
Inquire about the availability of large files on the filesystem.
@comment unistd.h
@comment POSIX.1
@item _PC_REC_INCR_XFER_SIZE
Inquire about the value of @code{POSIX_REC_INCR_XFER_SIZE}.
@comment unistd.h
@comment POSIX.1
@item _PC_REC_MAX_XFER_SIZE
Inquire about the value of @code{POSIX_REC_MAX_XFER_SIZE}.
@comment unistd.h
@comment POSIX.1
@item _PC_REC_MIN_XFER_SIZE
Inquire about the value of @code{POSIX_REC_MIN_XFER_SIZE}.
@comment unistd.h
@comment POSIX.1
@item _PC_REC_XFER_ALIGN
Inquire about the value of @code{POSIX_REC_XFER_ALIGN}.
@end table
@strong{Portability Note:} On some systems, @theglibc{} does not
enforce @code{_PC_NAME_MAX} or @code{_PC_PATH_MAX} limits.
@node Utility Limits
@section Utility Program Capacity Limits
The POSIX.2 standard specifies certain system limits that you can access
through @code{sysconf} that apply to utility behavior rather than the
behavior of the library or the operating system.
@Theglibc{} defines macros for these limits, and @code{sysconf}
returns values for them if you ask; but these values convey no
meaningful information. They are simply the smallest values that
POSIX.2 permits.
@comment limits.h
@comment POSIX.2
@deftypevr Macro int BC_BASE_MAX
The largest value of @code{obase} that the @code{bc} utility is
guaranteed to support.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int BC_DIM_MAX
The largest number of elements in one array that the @code{bc} utility
is guaranteed to support.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int BC_SCALE_MAX
The largest value of @code{scale} that the @code{bc} utility is
guaranteed to support.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int BC_STRING_MAX
The largest number of characters in one string constant that the
@code{bc} utility is guaranteed to support.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int COLL_WEIGHTS_MAX
The largest number of weights that can necessarily be used in defining
the collating sequence for a locale.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int EXPR_NEST_MAX
The maximum number of expressions that can be nested within parenthesis
by the @code{expr} utility.
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int LINE_MAX
The largest text line that the text-oriented POSIX.2 utilities can
support. (If you are using the GNU versions of these utilities, then
there is no actual limit except that imposed by the available virtual
memory, but there is no way that the library can tell you this.)
@end deftypevr
@comment limits.h
@comment POSIX.2
@deftypevr Macro int EQUIV_CLASS_MAX
The maximum number of weights that can be assigned to an entry of the
@code{LC_COLLATE} category @samp{order} keyword in a locale definition.
@Theglibc{} does not presently support locale definitions.
@end deftypevr
@node Utility Minimums
@section Minimum Values for Utility Limits
@table @code
@comment limits.h
@comment POSIX.2
@item _POSIX2_BC_BASE_MAX
The most restrictive limit permitted by POSIX.2 for the maximum value of
@code{obase} in the @code{bc} utility. Its value is @code{99}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_BC_DIM_MAX
The most restrictive limit permitted by POSIX.2 for the maximum size of
an array in the @code{bc} utility. Its value is @code{2048}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_BC_SCALE_MAX
The most restrictive limit permitted by POSIX.2 for the maximum value of
@code{scale} in the @code{bc} utility. Its value is @code{99}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_BC_STRING_MAX
The most restrictive limit permitted by POSIX.2 for the maximum size of
a string constant in the @code{bc} utility. Its value is @code{1000}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_COLL_WEIGHTS_MAX
The most restrictive limit permitted by POSIX.2 for the maximum number
of weights that can necessarily be used in defining the collating
sequence for a locale. Its value is @code{2}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_EXPR_NEST_MAX
The most restrictive limit permitted by POSIX.2 for the maximum number
of expressions nested within parenthesis when using the @code{expr} utility.
Its value is @code{32}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_LINE_MAX
The most restrictive limit permitted by POSIX.2 for the maximum size of
a text line that the text utilities can handle. Its value is
@code{2048}.
@comment limits.h
@comment POSIX.2
@item _POSIX2_EQUIV_CLASS_MAX
The most restrictive limit permitted by POSIX.2 for the maximum number
of weights that can be assigned to an entry of the @code{LC_COLLATE}
category @samp{order} keyword in a locale definition. Its value is
@code{2}. @Theglibc{} does not presently support locale
definitions.
@end table
@node String Parameters
@section String-Valued Parameters
POSIX.2 defines a way to get string-valued parameters from the operating
system with the function @code{confstr}:
@comment unistd.h
@comment POSIX.2
@deftypefun size_t confstr (int @var{parameter}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function reads the value of a string-valued system parameter,
storing the string into @var{len} bytes of memory space starting at
@var{buf}. The @var{parameter} argument should be one of the
@samp{_CS_} symbols listed below.
The normal return value from @code{confstr} is the length of the string
value that you asked for. If you supply a null pointer for @var{buf},
then @code{confstr} does not try to store the string; it just returns
its length. A value of @code{0} indicates an error.
If the string you asked for is too long for the buffer (that is, longer
than @code{@var{len} - 1}), then @code{confstr} stores just that much
(leaving room for the terminating null character). You can tell that
this has happened because @code{confstr} returns a value greater than or
equal to @var{len}.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The value of the @var{parameter} is invalid.
@end table
@end deftypefun
Currently there is just one parameter you can read with @code{confstr}:
@table @code
@comment unistd.h
@comment POSIX.2
@item _CS_PATH
This parameter's value is the recommended default path for searching for
executable files. This is the path that a user has by default just
after logging in.
@comment unistd.h
@comment Unix98
@item _CS_LFS_CFLAGS
The returned string specifies which additional flags must be given to
the C compiler if a source is compiled using the
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS_LDFLAGS
The returned string specifies which additional flags must be given to
the linker if a source is compiled using the
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS_LIBS
The returned string specifies which additional libraries must be linked
to the application if a source is compiled using the
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS_LINTFLAGS
The returned string specifies which additional flags must be given to
the lint tool if a source is compiled using the
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS64_CFLAGS
The returned string specifies which additional flags must be given to
the C compiler if a source is compiled using the
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS64_LDFLAGS
The returned string specifies which additional flags must be given to
the linker if a source is compiled using the
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS64_LIBS
The returned string specifies which additional libraries must be linked
to the application if a source is compiled using the
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@comment unistd.h
@comment Unix98
@item _CS_LFS64_LINTFLAGS
The returned string specifies which additional flags must be given to
the lint tool if a source is compiled using the
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
@end table
The way to use @code{confstr} without any arbitrary limit on string size
is to call it twice: first call it to get the length, allocate the
buffer accordingly, and then call @code{confstr} again to fill the
buffer, like this:
@smallexample
@group
char *
get_default_path (void)
@{
size_t len = confstr (_CS_PATH, NULL, 0);
char *buffer = (char *) xmalloc (len);
if (confstr (_CS_PATH, buf, len + 1) == 0)
@{
free (buffer);
return NULL;
@}
return buffer;
@}
@end group
@end smallexample
glibc-doc-reference-2.19.orig/manual/arith.texi 0000664 0001750 0001750 00000311520 12275120646 021563 0 ustar adconrad adconrad @node Arithmetic, Date and Time, Mathematics, Top
@c %MENU% Low level arithmetic functions
@chapter Arithmetic Functions
This chapter contains information about functions for doing basic
arithmetic operations, such as splitting a float into its integer and
fractional parts or retrieving the imaginary part of a complex value.
These functions are declared in the header files @file{math.h} and
@file{complex.h}.
@menu
* Integers:: Basic integer types and concepts
* Integer Division:: Integer division with guaranteed rounding.
* Floating Point Numbers:: Basic concepts. IEEE 754.
* Floating Point Classes:: The five kinds of floating-point number.
* Floating Point Errors:: When something goes wrong in a calculation.
* Rounding:: Controlling how results are rounded.
* Control Functions:: Saving and restoring the FPU's state.
* Arithmetic Functions:: Fundamental operations provided by the library.
* Complex Numbers:: The types. Writing complex constants.
* Operations on Complex:: Projection, conjugation, decomposition.
* Parsing of Numbers:: Converting strings to numbers.
* System V Number Conversion:: An archaic way to convert numbers to strings.
@end menu
@node Integers
@section Integers
@cindex integer
The C language defines several integer data types: integer, short integer,
long integer, and character, all in both signed and unsigned varieties.
The GNU C compiler extends the language to contain long long integers
as well.
@cindex signedness
The C integer types were intended to allow code to be portable among
machines with different inherent data sizes (word sizes), so each type
may have different ranges on different machines. The problem with
this is that a program often needs to be written for a particular range
of integers, and sometimes must be written for a particular size of
storage, regardless of what machine the program runs on.
To address this problem, @theglibc{} contains C type definitions
you can use to declare integers that meet your exact needs. Because the
@glibcadj{} header files are customized to a specific machine, your
program source code doesn't have to be.
These @code{typedef}s are in @file{stdint.h}.
@pindex stdint.h
If you require that an integer be represented in exactly N bits, use one
of the following types, with the obvious mapping to bit size and signedness:
@itemize @bullet
@item int8_t
@item int16_t
@item int32_t
@item int64_t
@item uint8_t
@item uint16_t
@item uint32_t
@item uint64_t
@end itemize
If your C compiler and target machine do not allow integers of a certain
size, the corresponding above type does not exist.
If you don't need a specific storage size, but want the smallest data
structure with @emph{at least} N bits, use one of these:
@itemize @bullet
@item int_least8_t
@item int_least16_t
@item int_least32_t
@item int_least64_t
@item uint_least8_t
@item uint_least16_t
@item uint_least32_t
@item uint_least64_t
@end itemize
If you don't need a specific storage size, but want the data structure
that allows the fastest access while having at least N bits (and
among data structures with the same access speed, the smallest one), use
one of these:
@itemize @bullet
@item int_fast8_t
@item int_fast16_t
@item int_fast32_t
@item int_fast64_t
@item uint_fast8_t
@item uint_fast16_t
@item uint_fast32_t
@item uint_fast64_t
@end itemize
If you want an integer with the widest range possible on the platform on
which it is being used, use one of the following. If you use these,
you should write code that takes into account the variable size and range
of the integer.
@itemize @bullet
@item intmax_t
@item uintmax_t
@end itemize
@Theglibc{} also provides macros that tell you the maximum and
minimum possible values for each integer data type. The macro names
follow these examples: @code{INT32_MAX}, @code{UINT8_MAX},
@code{INT_FAST32_MIN}, @code{INT_LEAST64_MIN}, @code{UINTMAX_MAX},
@code{INTMAX_MAX}, @code{INTMAX_MIN}. Note that there are no macros for
unsigned integer minima. These are always zero.
@cindex maximum possible integer
@cindex minimum possible integer
There are similar macros for use with C's built in integer types which
should come with your C compiler. These are described in @ref{Data Type
Measurements}.
Don't forget you can use the C @code{sizeof} function with any of these
data types to get the number of bytes of storage each uses.
@node Integer Division
@section Integer Division
@cindex integer division functions
This section describes functions for performing integer division. These
functions are redundant when GNU CC is used, because in GNU C the
@samp{/} operator always rounds towards zero. But in other C
implementations, @samp{/} may round differently with negative arguments.
@code{div} and @code{ldiv} are useful because they specify how to round
the quotient: towards zero. The remainder has the same sign as the
numerator.
These functions are specified to return a result @var{r} such that the value
@code{@var{r}.quot*@var{denominator} + @var{r}.rem} equals
@var{numerator}.
@pindex stdlib.h
To use these facilities, you should include the header file
@file{stdlib.h} in your program.
@comment stdlib.h
@comment ISO
@deftp {Data Type} div_t
This is a structure type used to hold the result returned by the @code{div}
function. It has the following members:
@table @code
@item int quot
The quotient from the division.
@item int rem
The remainder from the division.
@end table
@end deftp
@comment stdlib.h
@comment ISO
@deftypefun div_t div (int @var{numerator}, int @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Functions in this section are pure, and thus safe.
This function @code{div} computes the quotient and remainder from
the division of @var{numerator} by @var{denominator}, returning the
result in a structure of type @code{div_t}.
If the result cannot be represented (as in a division by zero), the
behavior is undefined.
Here is an example, albeit not a very useful one.
@smallexample
div_t result;
result = div (20, -6);
@end smallexample
@noindent
Now @code{result.quot} is @code{-3} and @code{result.rem} is @code{2}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftp {Data Type} ldiv_t
This is a structure type used to hold the result returned by the @code{ldiv}
function. It has the following members:
@table @code
@item long int quot
The quotient from the division.
@item long int rem
The remainder from the division.
@end table
(This is identical to @code{div_t} except that the components are of
type @code{long int} rather than @code{int}.)
@end deftp
@comment stdlib.h
@comment ISO
@deftypefun ldiv_t ldiv (long int @var{numerator}, long int @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{ldiv} function is similar to @code{div}, except that the
arguments are of type @code{long int} and the result is returned as a
structure of type @code{ldiv_t}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftp {Data Type} lldiv_t
This is a structure type used to hold the result returned by the @code{lldiv}
function. It has the following members:
@table @code
@item long long int quot
The quotient from the division.
@item long long int rem
The remainder from the division.
@end table
(This is identical to @code{div_t} except that the components are of
type @code{long long int} rather than @code{int}.)
@end deftp
@comment stdlib.h
@comment ISO
@deftypefun lldiv_t lldiv (long long int @var{numerator}, long long int @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{lldiv} function is like the @code{div} function, but the
arguments are of type @code{long long int} and the result is returned as
a structure of type @code{lldiv_t}.
The @code{lldiv} function was added in @w{ISO C99}.
@end deftypefun
@comment inttypes.h
@comment ISO
@deftp {Data Type} imaxdiv_t
This is a structure type used to hold the result returned by the @code{imaxdiv}
function. It has the following members:
@table @code
@item intmax_t quot
The quotient from the division.
@item intmax_t rem
The remainder from the division.
@end table
(This is identical to @code{div_t} except that the components are of
type @code{intmax_t} rather than @code{int}.)
See @ref{Integers} for a description of the @code{intmax_t} type.
@end deftp
@comment inttypes.h
@comment ISO
@deftypefun imaxdiv_t imaxdiv (intmax_t @var{numerator}, intmax_t @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{imaxdiv} function is like the @code{div} function, but the
arguments are of type @code{intmax_t} and the result is returned as
a structure of type @code{imaxdiv_t}.
See @ref{Integers} for a description of the @code{intmax_t} type.
The @code{imaxdiv} function was added in @w{ISO C99}.
@end deftypefun
@node Floating Point Numbers
@section Floating Point Numbers
@cindex floating point
@cindex IEEE 754
@cindex IEEE floating point
Most computer hardware has support for two different kinds of numbers:
integers (@math{@dots{}-3, -2, -1, 0, 1, 2, 3@dots{}}) and
floating-point numbers. Floating-point numbers have three parts: the
@dfn{mantissa}, the @dfn{exponent}, and the @dfn{sign bit}. The real
number represented by a floating-point value is given by
@tex
$(s \mathrel? -1 \mathrel: 1) \cdot 2^e \cdot M$
@end tex
@ifnottex
@math{(s ? -1 : 1) @mul{} 2^e @mul{} M}
@end ifnottex
where @math{s} is the sign bit, @math{e} the exponent, and @math{M}
the mantissa. @xref{Floating Point Concepts}, for details. (It is
possible to have a different @dfn{base} for the exponent, but all modern
hardware uses @math{2}.)
Floating-point numbers can represent a finite subset of the real
numbers. While this subset is large enough for most purposes, it is
important to remember that the only reals that can be represented
exactly are rational numbers that have a terminating binary expansion
shorter than the width of the mantissa. Even simple fractions such as
@math{1/5} can only be approximated by floating point.
Mathematical operations and functions frequently need to produce values
that are not representable. Often these values can be approximated
closely enough for practical purposes, but sometimes they can't.
Historically there was no way to tell when the results of a calculation
were inaccurate. Modern computers implement the @w{IEEE 754} standard
for numerical computations, which defines a framework for indicating to
the program when the results of calculation are not trustworthy. This
framework consists of a set of @dfn{exceptions} that indicate why a
result could not be represented, and the special values @dfn{infinity}
and @dfn{not a number} (NaN).
@node Floating Point Classes
@section Floating-Point Number Classification Functions
@cindex floating-point classes
@cindex classes, floating-point
@pindex math.h
@w{ISO C99} defines macros that let you determine what sort of
floating-point number a variable holds.
@comment math.h
@comment ISO
@deftypefn {Macro} int fpclassify (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is a generic macro which works on all floating-point types and
which returns a value of type @code{int}. The possible values are:
@vtable @code
@item FP_NAN
The floating-point number @var{x} is ``Not a Number'' (@pxref{Infinity
and NaN})
@item FP_INFINITE
The value of @var{x} is either plus or minus infinity (@pxref{Infinity
and NaN})
@item FP_ZERO
The value of @var{x} is zero. In floating-point formats like @w{IEEE
754}, where zero can be signed, this value is also returned if
@var{x} is negative zero.
@item FP_SUBNORMAL
Numbers whose absolute value is too small to be represented in the
normal format are represented in an alternate, @dfn{denormalized} format
(@pxref{Floating Point Concepts}). This format is less precise but can
represent values closer to zero. @code{fpclassify} returns this value
for values of @var{x} in this alternate format.
@item FP_NORMAL
This value is returned for all other values of @var{x}. It indicates
that there is nothing special about the number.
@end vtable
@end deftypefn
@code{fpclassify} is most useful if more than one property of a number
must be tested. There are more specific macros which only test one
property at a time. Generally these macros execute faster than
@code{fpclassify}, since there is special hardware support for them.
You should therefore use the specific macros whenever possible.
@comment math.h
@comment ISO
@deftypefn {Macro} int isfinite (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if @var{x} is finite: not plus or
minus infinity, and not NaN. It is equivalent to
@smallexample
(fpclassify (x) != FP_NAN && fpclassify (x) != FP_INFINITE)
@end smallexample
@code{isfinite} is implemented as a macro which accepts any
floating-point type.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn {Macro} int isnormal (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if @var{x} is finite and normalized.
It is equivalent to
@smallexample
(fpclassify (x) == FP_NORMAL)
@end smallexample
@end deftypefn
@comment math.h
@comment ISO
@deftypefn {Macro} int isnan (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if @var{x} is NaN. It is equivalent
to
@smallexample
(fpclassify (x) == FP_NAN)
@end smallexample
@end deftypefn
@comment math.h
@comment GNU
@deftypefn {Macro} int issignaling (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if @var{x} is a signaling NaN
(sNaN). It is based on draft TS 18661 and currently enabled as a GNU
extension.
@end deftypefn
Another set of floating-point classification functions was provided by
BSD. @Theglibc{} also supports these functions; however, we
recommend that you use the ISO C99 macros in new code. Those are standard
and will be available more widely. Also, since they are macros, you do
not have to worry about the type of their argument.
@comment math.h
@comment BSD
@deftypefun int isinf (double @var{x})
@comment math.h
@comment BSD
@deftypefunx int isinff (float @var{x})
@comment math.h
@comment BSD
@deftypefunx int isinfl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns @code{-1} if @var{x} represents negative infinity,
@code{1} if @var{x} represents positive infinity, and @code{0} otherwise.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun int isnan (double @var{x})
@comment math.h
@comment BSD
@deftypefunx int isnanf (float @var{x})
@comment math.h
@comment BSD
@deftypefunx int isnanl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns a nonzero value if @var{x} is a ``not a number''
value, and zero otherwise.
@strong{NB:} The @code{isnan} macro defined by @w{ISO C99} overrides
the BSD function. This is normally not a problem, because the two
routines behave identically. However, if you really need to get the BSD
function for some reason, you can write
@smallexample
(isnan) (x)
@end smallexample
@end deftypefun
@comment math.h
@comment BSD
@deftypefun int finite (double @var{x})
@comment math.h
@comment BSD
@deftypefunx int finitef (float @var{x})
@comment math.h
@comment BSD
@deftypefunx int finitel (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns a nonzero value if @var{x} is finite or a ``not a
number'' value, and zero otherwise.
@end deftypefun
@strong{Portability Note:} The functions listed in this section are BSD
extensions.
@node Floating Point Errors
@section Errors in Floating-Point Calculations
@menu
* FP Exceptions:: IEEE 754 math exceptions and how to detect them.
* Infinity and NaN:: Special values returned by calculations.
* Status bit operations:: Checking for exceptions after the fact.
* Math Error Reporting:: How the math functions report errors.
@end menu
@node FP Exceptions
@subsection FP Exceptions
@cindex exception
@cindex signal
@cindex zero divide
@cindex division by zero
@cindex inexact exception
@cindex invalid exception
@cindex overflow exception
@cindex underflow exception
The @w{IEEE 754} standard defines five @dfn{exceptions} that can occur
during a calculation. Each corresponds to a particular sort of error,
such as overflow.
When exceptions occur (when exceptions are @dfn{raised}, in the language
of the standard), one of two things can happen. By default the
exception is simply noted in the floating-point @dfn{status word}, and
the program continues as if nothing had happened. The operation
produces a default value, which depends on the exception (see the table
below). Your program can check the status word to find out which
exceptions happened.
Alternatively, you can enable @dfn{traps} for exceptions. In that case,
when an exception is raised, your program will receive the @code{SIGFPE}
signal. The default action for this signal is to terminate the
program. @xref{Signal Handling}, for how you can change the effect of
the signal.
@findex matherr
In the System V math library, the user-defined function @code{matherr}
is called when certain exceptions occur inside math library functions.
However, the Unix98 standard deprecates this interface. We support it
for historical compatibility, but recommend that you do not use it in
new programs. When this interface is used, exceptions may not be
raised.
@noindent
The exceptions defined in @w{IEEE 754} are:
@table @samp
@item Invalid Operation
This exception is raised if the given operands are invalid for the
operation to be performed. Examples are
(see @w{IEEE 754}, @w{section 7}):
@enumerate
@item
Addition or subtraction: @math{@infinity{} - @infinity{}}. (But
@math{@infinity{} + @infinity{} = @infinity{}}).
@item
Multiplication: @math{0 @mul{} @infinity{}}.
@item
Division: @math{0/0} or @math{@infinity{}/@infinity{}}.
@item
Remainder: @math{x} REM @math{y}, where @math{y} is zero or @math{x} is
infinite.
@item
Square root if the operand is less then zero. More generally, any
mathematical function evaluated outside its domain produces this
exception.
@item
Conversion of a floating-point number to an integer or decimal
string, when the number cannot be represented in the target format (due
to overflow, infinity, or NaN).
@item
Conversion of an unrecognizable input string.
@item
Comparison via predicates involving @math{<} or @math{>}, when one or
other of the operands is NaN. You can prevent this exception by using
the unordered comparison functions instead; see @ref{FP Comparison Functions}.
@end enumerate
If the exception does not trap, the result of the operation is NaN.
@item Division by Zero
This exception is raised when a finite nonzero number is divided
by zero. If no trap occurs the result is either @math{+@infinity{}} or
@math{-@infinity{}}, depending on the signs of the operands.
@item Overflow
This exception is raised whenever the result cannot be represented
as a finite value in the precision format of the destination. If no trap
occurs the result depends on the sign of the intermediate result and the
current rounding mode (@w{IEEE 754}, @w{section 7.3}):
@enumerate
@item
Round to nearest carries all overflows to @math{@infinity{}}
with the sign of the intermediate result.
@item
Round toward @math{0} carries all overflows to the largest representable
finite number with the sign of the intermediate result.
@item
Round toward @math{-@infinity{}} carries positive overflows to the
largest representable finite number and negative overflows to
@math{-@infinity{}}.
@item
Round toward @math{@infinity{}} carries negative overflows to the
most negative representable finite number and positive overflows
to @math{@infinity{}}.
@end enumerate
Whenever the overflow exception is raised, the inexact exception is also
raised.
@item Underflow
The underflow exception is raised when an intermediate result is too
small to be calculated accurately, or if the operation's result rounded
to the destination precision is too small to be normalized.
When no trap is installed for the underflow exception, underflow is
signaled (via the underflow flag) only when both tininess and loss of
accuracy have been detected. If no trap handler is installed the
operation continues with an imprecise small value, or zero if the
destination precision cannot hold the small exact result.
@item Inexact
This exception is signalled if a rounded result is not exact (such as
when calculating the square root of two) or a result overflows without
an overflow trap.
@end table
@node Infinity and NaN
@subsection Infinity and NaN
@cindex infinity
@cindex not a number
@cindex NaN
@w{IEEE 754} floating point numbers can represent positive or negative
infinity, and @dfn{NaN} (not a number). These three values arise from
calculations whose result is undefined or cannot be represented
accurately. You can also deliberately set a floating-point variable to
any of them, which is sometimes useful. Some examples of calculations
that produce infinity or NaN:
@ifnottex
@smallexample
@math{1/0 = @infinity{}}
@math{log (0) = -@infinity{}}
@math{sqrt (-1) = NaN}
@end smallexample
@end ifnottex
@tex
$${1\over0} = \infty$$
$$\log 0 = -\infty$$
$$\sqrt{-1} = \hbox{NaN}$$
@end tex
When a calculation produces any of these values, an exception also
occurs; see @ref{FP Exceptions}.
The basic operations and math functions all accept infinity and NaN and
produce sensible output. Infinities propagate through calculations as
one would expect: for example, @math{2 + @infinity{} = @infinity{}},
@math{4/@infinity{} = 0}, atan @math{(@infinity{}) = @pi{}/2}. NaN, on
the other hand, infects any calculation that involves it. Unless the
calculation would produce the same result no matter what real value
replaced NaN, the result is NaN.
In comparison operations, positive infinity is larger than all values
except itself and NaN, and negative infinity is smaller than all values
except itself and NaN. NaN is @dfn{unordered}: it is not equal to,
greater than, or less than anything, @emph{including itself}. @code{x ==
x} is false if the value of @code{x} is NaN. You can use this to test
whether a value is NaN or not, but the recommended way to test for NaN
is with the @code{isnan} function (@pxref{Floating Point Classes}). In
addition, @code{<}, @code{>}, @code{<=}, and @code{>=} will raise an
exception when applied to NaNs.
@file{math.h} defines macros that allow you to explicitly set a variable
to infinity or NaN.
@comment math.h
@comment ISO
@deftypevr Macro float INFINITY
An expression representing positive infinity. It is equal to the value
produced by mathematical operations like @code{1.0 / 0.0}.
@code{-INFINITY} represents negative infinity.
You can test whether a floating-point value is infinite by comparing it
to this macro. However, this is not recommended; you should use the
@code{isfinite} macro instead. @xref{Floating Point Classes}.
This macro was introduced in the @w{ISO C99} standard.
@end deftypevr
@comment math.h
@comment GNU
@deftypevr Macro float NAN
An expression representing a value which is ``not a number''. This
macro is a GNU extension, available only on machines that support the
``not a number'' value---that is to say, on all machines that support
IEEE floating point.
You can use @samp{#ifdef NAN} to test whether the machine supports
NaN. (Of course, you must arrange for GNU extensions to be visible,
such as by defining @code{_GNU_SOURCE}, and then you must include
@file{math.h}.)
@end deftypevr
@w{IEEE 754} also allows for another unusual value: negative zero. This
value is produced when you divide a positive number by negative
infinity, or when a negative result is smaller than the limits of
representation.
@node Status bit operations
@subsection Examining the FPU status word
@w{ISO C99} defines functions to query and manipulate the
floating-point status word. You can use these functions to check for
untrapped exceptions when it's convenient, rather than worrying about
them in the middle of a calculation.
These constants represent the various @w{IEEE 754} exceptions. Not all
FPUs report all the different exceptions. Each constant is defined if
and only if the FPU you are compiling for supports that exception, so
you can test for FPU support with @samp{#ifdef}. They are defined in
@file{fenv.h}.
@vtable @code
@comment fenv.h
@comment ISO
@item FE_INEXACT
The inexact exception.
@comment fenv.h
@comment ISO
@item FE_DIVBYZERO
The divide by zero exception.
@comment fenv.h
@comment ISO
@item FE_UNDERFLOW
The underflow exception.
@comment fenv.h
@comment ISO
@item FE_OVERFLOW
The overflow exception.
@comment fenv.h
@comment ISO
@item FE_INVALID
The invalid exception.
@end vtable
The macro @code{FE_ALL_EXCEPT} is the bitwise OR of all exception macros
which are supported by the FP implementation.
These functions allow you to clear exception flags, test for exceptions,
and save and restore the set of exceptions flagged.
@comment fenv.h
@comment ISO
@deftypefun int feclearexcept (int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{@assposix{}}@acsafe{@acsposix{}}}
@c The other functions in this section that modify FP status register
@c mostly do so with non-atomic load-modify-store sequences, but since
@c the register is thread-specific, this should be fine, and safe for
@c cancellation. As long as the FP environment is restored before the
@c signal handler returns control to the interrupted thread (like any
@c kernel should do), the functions are also safe for use in signal
@c handlers.
This function clears all of the supported exception flags indicated by
@var{excepts}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@comment fenv.h
@comment ISO
@deftypefun int feraiseexcept (int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function raises the supported exceptions indicated by
@var{excepts}. If more than one exception bit in @var{excepts} is set
the order in which the exceptions are raised is undefined except that
overflow (@code{FE_OVERFLOW}) or underflow (@code{FE_UNDERFLOW}) are
raised before inexact (@code{FE_INEXACT}). Whether for overflow or
underflow the inexact exception is also raised is also implementation
dependent.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@comment fenv.h
@comment ISO
@deftypefun int fetestexcept (int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Test whether the exception flags indicated by the parameter @var{except}
are currently set. If any of them are, a nonzero value is returned
which specifies which exceptions are set. Otherwise the result is zero.
@end deftypefun
To understand these functions, imagine that the status word is an
integer variable named @var{status}. @code{feclearexcept} is then
equivalent to @samp{status &= ~excepts} and @code{fetestexcept} is
equivalent to @samp{(status & excepts)}. The actual implementation may
be very different, of course.
Exception flags are only cleared when the program explicitly requests it,
by calling @code{feclearexcept}. If you want to check for exceptions
from a set of calculations, you should clear all the flags first. Here
is a simple example of the way to use @code{fetestexcept}:
@smallexample
@{
double f;
int raised;
feclearexcept (FE_ALL_EXCEPT);
f = compute ();
raised = fetestexcept (FE_OVERFLOW | FE_INVALID);
if (raised & FE_OVERFLOW) @{ /* @dots{} */ @}
if (raised & FE_INVALID) @{ /* @dots{} */ @}
/* @dots{} */
@}
@end smallexample
You cannot explicitly set bits in the status word. You can, however,
save the entire status word and restore it later. This is done with the
following functions:
@comment fenv.h
@comment ISO
@deftypefun int fegetexceptflag (fexcept_t *@var{flagp}, int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function stores in the variable pointed to by @var{flagp} an
implementation-defined value representing the current setting of the
exception flags indicated by @var{excepts}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@comment fenv.h
@comment ISO
@deftypefun int fesetexceptflag (const fexcept_t *@var{flagp}, int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function restores the flags for the exceptions indicated by
@var{excepts} to the values stored in the variable pointed to by
@var{flagp}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
Note that the value stored in @code{fexcept_t} bears no resemblance to
the bit mask returned by @code{fetestexcept}. The type may not even be
an integer. Do not attempt to modify an @code{fexcept_t} variable.
@node Math Error Reporting
@subsection Error Reporting by Mathematical Functions
@cindex errors, mathematical
@cindex domain error
@cindex range error
Many of the math functions are defined only over a subset of the real or
complex numbers. Even if they are mathematically defined, their result
may be larger or smaller than the range representable by their return
type without loss of accuracy. These are known as @dfn{domain errors},
@dfn{overflows}, and
@dfn{underflows}, respectively. Math functions do several things when
one of these errors occurs. In this manual we will refer to the
complete response as @dfn{signalling} a domain error, overflow, or
underflow.
When a math function suffers a domain error, it raises the invalid
exception and returns NaN. It also sets @var{errno} to @code{EDOM};
this is for compatibility with old systems that do not support @w{IEEE
754} exception handling. Likewise, when overflow occurs, math
functions raise the overflow exception and, in the default rounding
mode, return @math{@infinity{}} or @math{-@infinity{}} as appropriate
(in other rounding modes, the largest finite value of the appropriate
sign is returned when appropriate for that rounding mode). They also
set @var{errno} to @code{ERANGE} if returning @math{@infinity{}} or
@math{-@infinity{}}; @var{errno} may or may not be set to
@code{ERANGE} when a finite value is returned on overflow. When
underflow occurs, the underflow exception is raised, and zero
(appropriately signed) or a subnormal value, as appropriate for the
mathematical result of the function and the rounding mode, is
returned. @var{errno} may be set to @code{ERANGE}, but this is not
guaranteed; it is intended that @theglibc{} should set it when the
underflow is to an appropriately signed zero, but not necessarily for
other underflows.
Some of the math functions are defined mathematically to result in a
complex value over parts of their domains. The most familiar example of
this is taking the square root of a negative number. The complex math
functions, such as @code{csqrt}, will return the appropriate complex value
in this case. The real-valued functions, such as @code{sqrt}, will
signal a domain error.
Some older hardware does not support infinities. On that hardware,
overflows instead return a particular very large number (usually the
largest representable number). @file{math.h} defines macros you can use
to test for overflow on both old and new hardware.
@comment math.h
@comment ISO
@deftypevr Macro double HUGE_VAL
@comment math.h
@comment ISO
@deftypevrx Macro float HUGE_VALF
@comment math.h
@comment ISO
@deftypevrx Macro {long double} HUGE_VALL
An expression representing a particular very large number. On machines
that use @w{IEEE 754} floating point format, @code{HUGE_VAL} is infinity.
On other machines, it's typically the largest positive number that can
be represented.
Mathematical functions return the appropriately typed version of
@code{HUGE_VAL} or @code{@minus{}HUGE_VAL} when the result is too large
to be represented.
@end deftypevr
@node Rounding
@section Rounding Modes
Floating-point calculations are carried out internally with extra
precision, and then rounded to fit into the destination type. This
ensures that results are as precise as the input data. @w{IEEE 754}
defines four possible rounding modes:
@table @asis
@item Round to nearest.
This is the default mode. It should be used unless there is a specific
need for one of the others. In this mode results are rounded to the
nearest representable value. If the result is midway between two
representable values, the even representable is chosen. @dfn{Even} here
means the lowest-order bit is zero. This rounding mode prevents
statistical bias and guarantees numeric stability: round-off errors in a
lengthy calculation will remain smaller than half of @code{FLT_EPSILON}.
@c @item Round toward @math{+@infinity{}}
@item Round toward plus Infinity.
All results are rounded to the smallest representable value
which is greater than the result.
@c @item Round toward @math{-@infinity{}}
@item Round toward minus Infinity.
All results are rounded to the largest representable value which is less
than the result.
@item Round toward zero.
All results are rounded to the largest representable value whose
magnitude is less than that of the result. In other words, if the
result is negative it is rounded up; if it is positive, it is rounded
down.
@end table
@noindent
@file{fenv.h} defines constants which you can use to refer to the
various rounding modes. Each one will be defined if and only if the FPU
supports the corresponding rounding mode.
@table @code
@comment fenv.h
@comment ISO
@vindex FE_TONEAREST
@item FE_TONEAREST
Round to nearest.
@comment fenv.h
@comment ISO
@vindex FE_UPWARD
@item FE_UPWARD
Round toward @math{+@infinity{}}.
@comment fenv.h
@comment ISO
@vindex FE_DOWNWARD
@item FE_DOWNWARD
Round toward @math{-@infinity{}}.
@comment fenv.h
@comment ISO
@vindex FE_TOWARDZERO
@item FE_TOWARDZERO
Round toward zero.
@end table
Underflow is an unusual case. Normally, @w{IEEE 754} floating point
numbers are always normalized (@pxref{Floating Point Concepts}).
Numbers smaller than @math{2^r} (where @math{r} is the minimum exponent,
@code{FLT_MIN_RADIX-1} for @var{float}) cannot be represented as
normalized numbers. Rounding all such numbers to zero or @math{2^r}
would cause some algorithms to fail at 0. Therefore, they are left in
denormalized form. That produces loss of precision, since some bits of
the mantissa are stolen to indicate the decimal point.
If a result is too small to be represented as a denormalized number, it
is rounded to zero. However, the sign of the result is preserved; if
the calculation was negative, the result is @dfn{negative zero}.
Negative zero can also result from some operations on infinity, such as
@math{4/-@infinity{}}.
At any time one of the above four rounding modes is selected. You can
find out which one with this function:
@comment fenv.h
@comment ISO
@deftypefun int fegetround (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns the currently selected rounding mode, represented by one of the
values of the defined rounding mode macros.
@end deftypefun
@noindent
To change the rounding mode, use this function:
@comment fenv.h
@comment ISO
@deftypefun int fesetround (int @var{round})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Changes the currently selected rounding mode to @var{round}. If
@var{round} does not correspond to one of the supported rounding modes
nothing is changed. @code{fesetround} returns zero if it changed the
rounding mode, a nonzero value if the mode is not supported.
@end deftypefun
You should avoid changing the rounding mode if possible. It can be an
expensive operation; also, some hardware requires you to compile your
program differently for it to work. The resulting code may run slower.
See your compiler documentation for details.
@c This section used to claim that functions existed to round one number
@c in a specific fashion. I can't find any functions in the library
@c that do that. -zw
@node Control Functions
@section Floating-Point Control Functions
@w{IEEE 754} floating-point implementations allow the programmer to
decide whether traps will occur for each of the exceptions, by setting
bits in the @dfn{control word}. In C, traps result in the program
receiving the @code{SIGFPE} signal; see @ref{Signal Handling}.
@strong{NB:} @w{IEEE 754} says that trap handlers are given details of
the exceptional situation, and can set the result value. C signals do
not provide any mechanism to pass this information back and forth.
Trapping exceptions in C is therefore not very useful.
It is sometimes necessary to save the state of the floating-point unit
while you perform some calculation. The library provides functions
which save and restore the exception flags, the set of exceptions that
generate traps, and the rounding mode. This information is known as the
@dfn{floating-point environment}.
The functions to save and restore the floating-point environment all use
a variable of type @code{fenv_t} to store information. This type is
defined in @file{fenv.h}. Its size and contents are
implementation-defined. You should not attempt to manipulate a variable
of this type directly.
To save the state of the FPU, use one of these functions:
@comment fenv.h
@comment ISO
@deftypefun int fegetenv (fenv_t *@var{envp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Store the floating-point environment in the variable pointed to by
@var{envp}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@comment fenv.h
@comment ISO
@deftypefun int feholdexcept (fenv_t *@var{envp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Store the current floating-point environment in the object pointed to by
@var{envp}. Then clear all exception flags, and set the FPU to trap no
exceptions. Not all FPUs support trapping no exceptions; if
@code{feholdexcept} cannot set this mode, it returns nonzero value. If it
succeeds, it returns zero.
@end deftypefun
The functions which restore the floating-point environment can take these
kinds of arguments:
@itemize @bullet
@item
Pointers to @code{fenv_t} objects, which were initialized previously by a
call to @code{fegetenv} or @code{feholdexcept}.
@item
@vindex FE_DFL_ENV
The special macro @code{FE_DFL_ENV} which represents the floating-point
environment as it was available at program start.
@item
Implementation defined macros with names starting with @code{FE_} and
having type @code{fenv_t *}.
@vindex FE_NOMASK_ENV
If possible, @theglibc{} defines a macro @code{FE_NOMASK_ENV}
which represents an environment where every exception raised causes a
trap to occur. You can test for this macro using @code{#ifdef}. It is
only defined if @code{_GNU_SOURCE} is defined.
Some platforms might define other predefined environments.
@end itemize
@noindent
To set the floating-point environment, you can use either of these
functions:
@comment fenv.h
@comment ISO
@deftypefun int fesetenv (const fenv_t *@var{envp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Set the floating-point environment to that described by @var{envp}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@comment fenv.h
@comment ISO
@deftypefun int feupdateenv (const fenv_t *@var{envp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Like @code{fesetenv}, this function sets the floating-point environment
to that described by @var{envp}. However, if any exceptions were
flagged in the status word before @code{feupdateenv} was called, they
remain flagged after the call. In other words, after @code{feupdateenv}
is called, the status word is the bitwise OR of the previous status word
and the one saved in @var{envp}.
The function returns zero in case the operation was successful, a
non-zero value otherwise.
@end deftypefun
@noindent
To control for individual exceptions if raising them causes a trap to
occur, you can use the following two functions.
@strong{Portability Note:} These functions are all GNU extensions.
@comment fenv.h
@comment GNU
@deftypefun int feenableexcept (int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This functions enables traps for each of the exceptions as indicated by
the parameter @var{except}. The individual exceptions are described in
@ref{Status bit operations}. Only the specified exceptions are
enabled, the status of the other exceptions is not changed.
The function returns the previous enabled exceptions in case the
operation was successful, @code{-1} otherwise.
@end deftypefun
@comment fenv.h
@comment GNU
@deftypefun int fedisableexcept (int @var{excepts})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This functions disables traps for each of the exceptions as indicated by
the parameter @var{except}. The individual exceptions are described in
@ref{Status bit operations}. Only the specified exceptions are
disabled, the status of the other exceptions is not changed.
The function returns the previous enabled exceptions in case the
operation was successful, @code{-1} otherwise.
@end deftypefun
@comment fenv.h
@comment GNU
@deftypefun int fegetexcept (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function returns a bitmask of all currently enabled exceptions. It
returns @code{-1} in case of failure.
@end deftypefun
@node Arithmetic Functions
@section Arithmetic Functions
The C library provides functions to do basic operations on
floating-point numbers. These include absolute value, maximum and minimum,
normalization, bit twiddling, rounding, and a few others.
@menu
* Absolute Value:: Absolute values of integers and floats.
* Normalization Functions:: Extracting exponents and putting them back.
* Rounding Functions:: Rounding floats to integers.
* Remainder Functions:: Remainders on division, precisely defined.
* FP Bit Twiddling:: Sign bit adjustment. Adding epsilon.
* FP Comparison Functions:: Comparisons without risk of exceptions.
* Misc FP Arithmetic:: Max, min, positive difference, multiply-add.
@end menu
@node Absolute Value
@subsection Absolute Value
@cindex absolute value functions
These functions are provided for obtaining the @dfn{absolute value} (or
@dfn{magnitude}) of a number. The absolute value of a real number
@var{x} is @var{x} if @var{x} is positive, @minus{}@var{x} if @var{x} is
negative. For a complex number @var{z}, whose real part is @var{x} and
whose imaginary part is @var{y}, the absolute value is @w{@code{sqrt
(@var{x}*@var{x} + @var{y}*@var{y})}}.
@pindex math.h
@pindex stdlib.h
Prototypes for @code{abs}, @code{labs} and @code{llabs} are in @file{stdlib.h};
@code{imaxabs} is declared in @file{inttypes.h};
@code{fabs}, @code{fabsf} and @code{fabsl} are declared in @file{math.h}.
@code{cabs}, @code{cabsf} and @code{cabsl} are declared in @file{complex.h}.
@comment stdlib.h
@comment ISO
@deftypefun int abs (int @var{number})
@comment stdlib.h
@comment ISO
@deftypefunx {long int} labs (long int @var{number})
@comment stdlib.h
@comment ISO
@deftypefunx {long long int} llabs (long long int @var{number})
@comment inttypes.h
@comment ISO
@deftypefunx intmax_t imaxabs (intmax_t @var{number})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the absolute value of @var{number}.
Most computers use a two's complement integer representation, in which
the absolute value of @code{INT_MIN} (the smallest possible @code{int})
cannot be represented; thus, @w{@code{abs (INT_MIN)}} is not defined.
@code{llabs} and @code{imaxdiv} are new to @w{ISO C99}.
See @ref{Integers} for a description of the @code{intmax_t} type.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double fabs (double @var{number})
@comment math.h
@comment ISO
@deftypefunx float fabsf (float @var{number})
@comment math.h
@comment ISO
@deftypefunx {long double} fabsl (long double @var{number})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns the absolute value of the floating-point number
@var{number}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun double cabs (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx float cabsf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {long double} cabsl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the absolute value of the complex number @var{z}
(@pxref{Complex Numbers}). The absolute value of a complex number is:
@smallexample
sqrt (creal (@var{z}) * creal (@var{z}) + cimag (@var{z}) * cimag (@var{z}))
@end smallexample
This function should always be used instead of the direct formula
because it takes special care to avoid losing precision. It may also
take advantage of hardware support for this operation. See @code{hypot}
in @ref{Exponents and Logarithms}.
@end deftypefun
@node Normalization Functions
@subsection Normalization Functions
@cindex normalization functions (floating-point)
The functions described in this section are primarily provided as a way
to efficiently perform certain low-level manipulations on floating point
numbers that are represented internally using a binary radix;
see @ref{Floating Point Concepts}. These functions are required to
have equivalent behavior even if the representation does not use a radix
of 2, but of course they are unlikely to be particularly efficient in
those cases.
@pindex math.h
All these functions are declared in @file{math.h}.
@comment math.h
@comment ISO
@deftypefun double frexp (double @var{value}, int *@var{exponent})
@comment math.h
@comment ISO
@deftypefunx float frexpf (float @var{value}, int *@var{exponent})
@comment math.h
@comment ISO
@deftypefunx {long double} frexpl (long double @var{value}, int *@var{exponent})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are used to split the number @var{value}
into a normalized fraction and an exponent.
If the argument @var{value} is not zero, the return value is @var{value}
times a power of two, and its magnitude is always in the range 1/2
(inclusive) to 1 (exclusive). The corresponding exponent is stored in
@code{*@var{exponent}}; the return value multiplied by 2 raised to this
exponent equals the original number @var{value}.
For example, @code{frexp (12.8, &exponent)} returns @code{0.8} and
stores @code{4} in @code{exponent}.
If @var{value} is zero, then the return value is zero and
zero is stored in @code{*@var{exponent}}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double ldexp (double @var{value}, int @var{exponent})
@comment math.h
@comment ISO
@deftypefunx float ldexpf (float @var{value}, int @var{exponent})
@comment math.h
@comment ISO
@deftypefunx {long double} ldexpl (long double @var{value}, int @var{exponent})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the result of multiplying the floating-point
number @var{value} by 2 raised to the power @var{exponent}. (It can
be used to reassemble floating-point numbers that were taken apart
by @code{frexp}.)
For example, @code{ldexp (0.8, 4)} returns @code{12.8}.
@end deftypefun
The following functions, which come from BSD, provide facilities
equivalent to those of @code{ldexp} and @code{frexp}. See also the
@w{ISO C} function @code{logb} which originally also appeared in BSD.
@comment math.h
@comment BSD
@deftypefun double scalb (double @var{value}, double @var{exponent})
@comment math.h
@comment BSD
@deftypefunx float scalbf (float @var{value}, float @var{exponent})
@comment math.h
@comment BSD
@deftypefunx {long double} scalbl (long double @var{value}, long double @var{exponent})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{scalb} function is the BSD name for @code{ldexp}.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun double scalbn (double @var{x}, int @var{n})
@comment math.h
@comment BSD
@deftypefunx float scalbnf (float @var{x}, int @var{n})
@comment math.h
@comment BSD
@deftypefunx {long double} scalbnl (long double @var{x}, int @var{n})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{scalbn} is identical to @code{scalb}, except that the exponent
@var{n} is an @code{int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun double scalbln (double @var{x}, long int @var{n})
@comment math.h
@comment BSD
@deftypefunx float scalblnf (float @var{x}, long int @var{n})
@comment math.h
@comment BSD
@deftypefunx {long double} scalblnl (long double @var{x}, long int @var{n})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{scalbln} is identical to @code{scalb}, except that the exponent
@var{n} is a @code{long int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun double significand (double @var{x})
@comment math.h
@comment BSD
@deftypefunx float significandf (float @var{x})
@comment math.h
@comment BSD
@deftypefunx {long double} significandl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{significand} returns the mantissa of @var{x} scaled to the range
@math{[1, 2)}.
It is equivalent to @w{@code{scalb (@var{x}, (double) -ilogb (@var{x}))}}.
This function exists mainly for use in certain standardized tests
of @w{IEEE 754} conformance.
@end deftypefun
@node Rounding Functions
@subsection Rounding Functions
@cindex converting floats to integers
@pindex math.h
The functions listed here perform operations such as rounding and
truncation of floating-point values. Some of these functions convert
floating point numbers to integer values. They are all declared in
@file{math.h}.
You can also convert floating-point numbers to integers simply by
casting them to @code{int}. This discards the fractional part,
effectively rounding towards zero. However, this only works if the
result can actually be represented as an @code{int}---for very large
numbers, this is impossible. The functions listed here return the
result as a @code{double} instead to get around this problem.
@comment math.h
@comment ISO
@deftypefun double ceil (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float ceilf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} ceill (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions round @var{x} upwards to the nearest integer,
returning that value as a @code{double}. Thus, @code{ceil (1.5)}
is @code{2.0}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double floor (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float floorf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} floorl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions round @var{x} downwards to the nearest
integer, returning that value as a @code{double}. Thus, @code{floor
(1.5)} is @code{1.0} and @code{floor (-1.5)} is @code{-2.0}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double trunc (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float truncf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} truncl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{trunc} functions round @var{x} towards zero to the nearest
integer (returned in floating-point format). Thus, @code{trunc (1.5)}
is @code{1.0} and @code{trunc (-1.5)} is @code{-1.0}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double rint (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float rintf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} rintl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions round @var{x} to an integer value according to the
current rounding mode. @xref{Floating Point Parameters}, for
information about the various rounding modes. The default
rounding mode is to round to the nearest integer; some machines
support other modes, but round-to-nearest is always used unless
you explicitly select another.
If @var{x} was not initially an integer, these functions raise the
inexact exception.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double nearbyint (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float nearbyintf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} nearbyintl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the same value as the @code{rint} functions, but
do not raise the inexact exception if @var{x} is not an integer.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double round (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float roundf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} roundl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are similar to @code{rint}, but they round halfway
cases away from zero instead of to the nearest integer (or other
current rounding mode).
@end deftypefun
@comment math.h
@comment ISO
@deftypefun {long int} lrint (double @var{x})
@comment math.h
@comment ISO
@deftypefunx {long int} lrintf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long int} lrintl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are just like @code{rint}, but they return a
@code{long int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun {long long int} llrint (double @var{x})
@comment math.h
@comment ISO
@deftypefunx {long long int} llrintf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long long int} llrintl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are just like @code{rint}, but they return a
@code{long long int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun {long int} lround (double @var{x})
@comment math.h
@comment ISO
@deftypefunx {long int} lroundf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long int} lroundl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are just like @code{round}, but they return a
@code{long int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun {long long int} llround (double @var{x})
@comment math.h
@comment ISO
@deftypefunx {long long int} llroundf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long long int} llroundl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are just like @code{round}, but they return a
@code{long long int} instead of a floating-point number.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double modf (double @var{value}, double *@var{integer-part})
@comment math.h
@comment ISO
@deftypefunx float modff (float @var{value}, float *@var{integer-part})
@comment math.h
@comment ISO
@deftypefunx {long double} modfl (long double @var{value}, long double *@var{integer-part})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions break the argument @var{value} into an integer part and a
fractional part (between @code{-1} and @code{1}, exclusive). Their sum
equals @var{value}. Each of the parts has the same sign as @var{value},
and the integer part is always rounded toward zero.
@code{modf} stores the integer part in @code{*@var{integer-part}}, and
returns the fractional part. For example, @code{modf (2.5, &intpart)}
returns @code{0.5} and stores @code{2.0} into @code{intpart}.
@end deftypefun
@node Remainder Functions
@subsection Remainder Functions
The functions in this section compute the remainder on division of two
floating-point numbers. Each is a little different; pick the one that
suits your problem.
@comment math.h
@comment ISO
@deftypefun double fmod (double @var{numerator}, double @var{denominator})
@comment math.h
@comment ISO
@deftypefunx float fmodf (float @var{numerator}, float @var{denominator})
@comment math.h
@comment ISO
@deftypefunx {long double} fmodl (long double @var{numerator}, long double @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the remainder from the division of
@var{numerator} by @var{denominator}. Specifically, the return value is
@code{@var{numerator} - @w{@var{n} * @var{denominator}}}, where @var{n}
is the quotient of @var{numerator} divided by @var{denominator}, rounded
towards zero to an integer. Thus, @w{@code{fmod (6.5, 2.3)}} returns
@code{1.9}, which is @code{6.5} minus @code{4.6}.
The result has the same sign as the @var{numerator} and has magnitude
less than the magnitude of the @var{denominator}.
If @var{denominator} is zero, @code{fmod} signals a domain error.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun double drem (double @var{numerator}, double @var{denominator})
@comment math.h
@comment BSD
@deftypefunx float dremf (float @var{numerator}, float @var{denominator})
@comment math.h
@comment BSD
@deftypefunx {long double} dreml (long double @var{numerator}, long double @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are like @code{fmod} except that they round the
internal quotient @var{n} to the nearest integer instead of towards zero
to an integer. For example, @code{drem (6.5, 2.3)} returns @code{-0.4},
which is @code{6.5} minus @code{6.9}.
The absolute value of the result is less than or equal to half the
absolute value of the @var{denominator}. The difference between
@code{fmod (@var{numerator}, @var{denominator})} and @code{drem
(@var{numerator}, @var{denominator})} is always either
@var{denominator}, minus @var{denominator}, or zero.
If @var{denominator} is zero, @code{drem} signals a domain error.
@end deftypefun
@comment math.h
@comment BSD
@deftypefun double remainder (double @var{numerator}, double @var{denominator})
@comment math.h
@comment BSD
@deftypefunx float remainderf (float @var{numerator}, float @var{denominator})
@comment math.h
@comment BSD
@deftypefunx {long double} remainderl (long double @var{numerator}, long double @var{denominator})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is another name for @code{drem}.
@end deftypefun
@node FP Bit Twiddling
@subsection Setting and modifying single bits of FP values
@cindex FP arithmetic
There are some operations that are too complicated or expensive to
perform by hand on floating-point numbers. @w{ISO C99} defines
functions to do these operations, which mostly involve changing single
bits.
@comment math.h
@comment ISO
@deftypefun double copysign (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float copysignf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} copysignl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return @var{x} but with the sign of @var{y}. They work
even if @var{x} or @var{y} are NaN or zero. Both of these can carry a
sign (although not all implementations support it) and this is one of
the few operations that can tell the difference.
@code{copysign} never raises an exception.
@c except signalling NaNs
This function is defined in @w{IEC 559} (and the appendix with
recommended functions in @w{IEEE 754}/@w{IEEE 854}).
@end deftypefun
@comment math.h
@comment ISO
@deftypefun int signbit (@emph{float-type} @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{signbit} is a generic macro which can work on all floating-point
types. It returns a nonzero value if the value of @var{x} has its sign
bit set.
This is not the same as @code{x < 0.0}, because @w{IEEE 754} floating
point allows zero to be signed. The comparison @code{-0.0 < 0.0} is
false, but @code{signbit (-0.0)} will return a nonzero value.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double nextafter (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float nextafterf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} nextafterl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{nextafter} function returns the next representable neighbor of
@var{x} in the direction towards @var{y}. The size of the step between
@var{x} and the result depends on the type of the result. If
@math{@var{x} = @var{y}} the function simply returns @var{y}. If either
value is @code{NaN}, @code{NaN} is returned. Otherwise
a value corresponding to the value of the least significant bit in the
mantissa is added or subtracted, depending on the direction.
@code{nextafter} will signal overflow or underflow if the result goes
outside of the range of normalized numbers.
This function is defined in @w{IEC 559} (and the appendix with
recommended functions in @w{IEEE 754}/@w{IEEE 854}).
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double nexttoward (double @var{x}, long double @var{y})
@comment math.h
@comment ISO
@deftypefunx float nexttowardf (float @var{x}, long double @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} nexttowardl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are identical to the corresponding versions of
@code{nextafter} except that their second argument is a @code{long
double}.
@end deftypefun
@cindex NaN
@comment math.h
@comment ISO
@deftypefun double nan (const char *@var{tagp})
@comment math.h
@comment ISO
@deftypefunx float nanf (const char *@var{tagp})
@comment math.h
@comment ISO
@deftypefunx {long double} nanl (const char *@var{tagp})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c The unsafe-but-ruled-safe locale use comes from strtod.
The @code{nan} function returns a representation of NaN, provided that
NaN is supported by the target platform.
@code{nan ("@var{n-char-sequence}")} is equivalent to
@code{strtod ("NAN(@var{n-char-sequence})")}.
The argument @var{tagp} is used in an unspecified manner. On @w{IEEE
754} systems, there are many representations of NaN, and @var{tagp}
selects one. On other systems it may do nothing.
@end deftypefun
@node FP Comparison Functions
@subsection Floating-Point Comparison Functions
@cindex unordered comparison
The standard C comparison operators provoke exceptions when one or other
of the operands is NaN. For example,
@smallexample
int v = a < 1.0;
@end smallexample
@noindent
will raise an exception if @var{a} is NaN. (This does @emph{not}
happen with @code{==} and @code{!=}; those merely return false and true,
respectively, when NaN is examined.) Frequently this exception is
undesirable. @w{ISO C99} therefore defines comparison functions that
do not raise exceptions when NaN is examined. All of the functions are
implemented as macros which allow their arguments to be of any
floating-point type. The macros are guaranteed to evaluate their
arguments only once.
@comment math.h
@comment ISO
@deftypefn Macro int isgreater (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether the argument @var{x} is greater than
@var{y}. It is equivalent to @code{(@var{x}) > (@var{y})}, but no
exception is raised if @var{x} or @var{y} are NaN.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn Macro int isgreaterequal (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether the argument @var{x} is greater than or
equal to @var{y}. It is equivalent to @code{(@var{x}) >= (@var{y})}, but no
exception is raised if @var{x} or @var{y} are NaN.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn Macro int isless (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether the argument @var{x} is less than @var{y}.
It is equivalent to @code{(@var{x}) < (@var{y})}, but no exception is
raised if @var{x} or @var{y} are NaN.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn Macro int islessequal (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether the argument @var{x} is less than or equal
to @var{y}. It is equivalent to @code{(@var{x}) <= (@var{y})}, but no
exception is raised if @var{x} or @var{y} are NaN.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn Macro int islessgreater (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether the argument @var{x} is less or greater
than @var{y}. It is equivalent to @code{(@var{x}) < (@var{y}) ||
(@var{x}) > (@var{y})} (although it only evaluates @var{x} and @var{y}
once), but no exception is raised if @var{x} or @var{y} are NaN.
This macro is not equivalent to @code{@var{x} != @var{y}}, because that
expression is true if @var{x} or @var{y} are NaN.
@end deftypefn
@comment math.h
@comment ISO
@deftypefn Macro int isunordered (@emph{real-floating} @var{x}, @emph{real-floating} @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro determines whether its arguments are unordered. In other
words, it is true if @var{x} or @var{y} are NaN, and false otherwise.
@end deftypefn
Not all machines provide hardware support for these operations. On
machines that don't, the macros can be very slow. Therefore, you should
not use these functions when NaN is not a concern.
@strong{NB:} There are no macros @code{isequal} or @code{isunequal}.
They are unnecessary, because the @code{==} and @code{!=} operators do
@emph{not} throw an exception if one or both of the operands are NaN.
@node Misc FP Arithmetic
@subsection Miscellaneous FP arithmetic functions
@cindex minimum
@cindex maximum
@cindex positive difference
@cindex multiply-add
The functions in this section perform miscellaneous but common
operations that are awkward to express with C operators. On some
processors these functions can use special machine instructions to
perform these operations faster than the equivalent C code.
@comment math.h
@comment ISO
@deftypefun double fmin (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float fminf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} fminl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fmin} function returns the lesser of the two values @var{x}
and @var{y}. It is similar to the expression
@smallexample
((x) < (y) ? (x) : (y))
@end smallexample
except that @var{x} and @var{y} are only evaluated once.
If an argument is NaN, the other argument is returned. If both arguments
are NaN, NaN is returned.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double fmax (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float fmaxf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} fmaxl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fmax} function returns the greater of the two values @var{x}
and @var{y}.
If an argument is NaN, the other argument is returned. If both arguments
are NaN, NaN is returned.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double fdim (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float fdimf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} fdiml (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fdim} function returns the positive difference between
@var{x} and @var{y}. The positive difference is @math{@var{x} -
@var{y}} if @var{x} is greater than @var{y}, and @math{0} otherwise.
If @var{x}, @var{y}, or both are NaN, NaN is returned.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double fma (double @var{x}, double @var{y}, double @var{z})
@comment math.h
@comment ISO
@deftypefunx float fmaf (float @var{x}, float @var{y}, float @var{z})
@comment math.h
@comment ISO
@deftypefunx {long double} fmal (long double @var{x}, long double @var{y}, long double @var{z})
@cindex butterfly
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fma} function performs floating-point multiply-add. This is
the operation @math{(@var{x} @mul{} @var{y}) + @var{z}}, but the
intermediate result is not rounded to the destination type. This can
sometimes improve the precision of a calculation.
This function was introduced because some processors have a special
instruction to perform multiply-add. The C compiler cannot use it
directly, because the expression @samp{x*y + z} is defined to round the
intermediate result. @code{fma} lets you choose when you want to round
only once.
@vindex FP_FAST_FMA
On processors which do not implement multiply-add in hardware,
@code{fma} can be very slow since it must avoid intermediate rounding.
@file{math.h} defines the symbols @code{FP_FAST_FMA},
@code{FP_FAST_FMAF}, and @code{FP_FAST_FMAL} when the corresponding
version of @code{fma} is no slower than the expression @samp{x*y + z}.
In @theglibc{}, this always means the operation is implemented in
hardware.
@end deftypefun
@node Complex Numbers
@section Complex Numbers
@pindex complex.h
@cindex complex numbers
@w{ISO C99} introduces support for complex numbers in C. This is done
with a new type qualifier, @code{complex}. It is a keyword if and only
if @file{complex.h} has been included. There are three complex types,
corresponding to the three real types: @code{float complex},
@code{double complex}, and @code{long double complex}.
To construct complex numbers you need a way to indicate the imaginary
part of a number. There is no standard notation for an imaginary
floating point constant. Instead, @file{complex.h} defines two macros
that can be used to create complex numbers.
@deftypevr Macro {const float complex} _Complex_I
This macro is a representation of the complex number ``@math{0+1i}''.
Multiplying a real floating-point value by @code{_Complex_I} gives a
complex number whose value is purely imaginary. You can use this to
construct complex constants:
@smallexample
@math{3.0 + 4.0i} = @code{3.0 + 4.0 * _Complex_I}
@end smallexample
Note that @code{_Complex_I * _Complex_I} has the value @code{-1}, but
the type of that value is @code{complex}.
@end deftypevr
@c Put this back in when gcc supports _Imaginary_I. It's too confusing.
@ignore
@noindent
Without an optimizing compiler this is more expensive than the use of
@code{_Imaginary_I} but with is better than nothing. You can avoid all
the hassles if you use the @code{I} macro below if the name is not
problem.
@deftypevr Macro {const float imaginary} _Imaginary_I
This macro is a representation of the value ``@math{1i}''. I.e., it is
the value for which
@smallexample
_Imaginary_I * _Imaginary_I = -1
@end smallexample
@noindent
The result is not of type @code{float imaginary} but instead @code{float}.
One can use it to easily construct complex number like in
@smallexample
3.0 - _Imaginary_I * 4.0
@end smallexample
@noindent
which results in the complex number with a real part of 3.0 and a
imaginary part -4.0.
@end deftypevr
@end ignore
@noindent
@code{_Complex_I} is a bit of a mouthful. @file{complex.h} also defines
a shorter name for the same constant.
@deftypevr Macro {const float complex} I
This macro has exactly the same value as @code{_Complex_I}. Most of the
time it is preferable. However, it causes problems if you want to use
the identifier @code{I} for something else. You can safely write
@smallexample
#include
#undef I
@end smallexample
@noindent
if you need @code{I} for your own purposes. (In that case we recommend
you also define some other short name for @code{_Complex_I}, such as
@code{J}.)
@ignore
If the implementation does not support the @code{imaginary} types
@code{I} is defined as @code{_Complex_I} which is the second best
solution. It still can be used in the same way but requires a most
clever compiler to get the same results.
@end ignore
@end deftypevr
@node Operations on Complex
@section Projections, Conjugates, and Decomposing of Complex Numbers
@cindex project complex numbers
@cindex conjugate complex numbers
@cindex decompose complex numbers
@pindex complex.h
@w{ISO C99} also defines functions that perform basic operations on
complex numbers, such as decomposition and conjugation. The prototypes
for all these functions are in @file{complex.h}. All functions are
available in three variants, one for each of the three complex types.
@comment complex.h
@comment ISO
@deftypefun double creal (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx float crealf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {long double} creall (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the real part of the complex number @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun double cimag (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx float cimagf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {long double} cimagl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the imaginary part of the complex number @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} conj (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} conjf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} conjl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the conjugate value of the complex number
@var{z}. The conjugate of a complex number has the same real part and a
negated imaginary part. In other words, @samp{conj(a + bi) = a + -bi}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun double carg (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx float cargf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {long double} cargl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the argument of the complex number @var{z}.
The argument of a complex number is the angle in the complex plane
between the positive real axis and a line passing through zero and the
number. This angle is measured in the usual fashion and ranges from
@math{-@pi{}} to @math{@pi{}}.
@code{carg} has a branch cut along the negative real axis.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} cproj (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} cprojf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} cprojl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the projection of the complex value @var{z} onto
the Riemann sphere. Values with an infinite imaginary part are projected
to positive infinity on the real axis, even if the real part is NaN. If
the real part is infinite, the result is equivalent to
@smallexample
INFINITY + I * copysign (0.0, cimag (z))
@end smallexample
@end deftypefun
@node Parsing of Numbers
@section Parsing of Numbers
@cindex parsing numbers (in formatted input)
@cindex converting strings to numbers
@cindex number syntax, parsing
@cindex syntax, for reading numbers
This section describes functions for ``reading'' integer and
floating-point numbers from a string. It may be more convenient in some
cases to use @code{sscanf} or one of the related functions; see
@ref{Formatted Input}. But often you can make a program more robust by
finding the tokens in the string by hand, then converting the numbers
one by one.
@menu
* Parsing of Integers:: Functions for conversion of integer values.
* Parsing of Floats:: Functions for conversion of floating-point
values.
@end menu
@node Parsing of Integers
@subsection Parsing of Integers
@pindex stdlib.h
@pindex wchar.h
The @samp{str} functions are declared in @file{stdlib.h} and those
beginning with @samp{wcs} are declared in @file{wchar.h}. One might
wonder about the use of @code{restrict} in the prototypes of the
functions in this section. It is seemingly useless but the @w{ISO C}
standard uses it (for the functions defined there) so we have to do it
as well.
@comment stdlib.h
@comment ISO
@deftypefun {long int} strtol (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c strtol uses the thread-local pointer to the locale in effect, and
@c strtol_l loads the LC_NUMERIC locale data from it early on and once,
@c but if the locale is the global locale, and another thread calls
@c setlocale in a way that modifies the pointer to the LC_CTYPE locale
@c category, the behavior of e.g. IS*, TOUPPER will vary throughout the
@c execution of the function, because they re-read the locale data from
@c the given locale pointer. We solved this by documenting setlocale as
@c MT-Unsafe.
The @code{strtol} (``string-to-long'') function converts the initial
part of @var{string} to a signed integer, which is returned as a value
of type @code{long int}.
This function attempts to decompose @var{string} as follows:
@itemize @bullet
@item
A (possibly empty) sequence of whitespace characters. Which characters
are whitespace is determined by the @code{isspace} function
(@pxref{Classification of Characters}). These are discarded.
@item
An optional plus or minus sign (@samp{+} or @samp{-}).
@item
A nonempty sequence of digits in the radix specified by @var{base}.
If @var{base} is zero, decimal radix is assumed unless the series of
digits begins with @samp{0} (specifying octal radix), or @samp{0x} or
@samp{0X} (specifying hexadecimal radix); in other words, the same
syntax used for integer constants in C.
Otherwise @var{base} must have a value between @code{2} and @code{36}.
If @var{base} is @code{16}, the digits may optionally be preceded by
@samp{0x} or @samp{0X}. If base has no legal value the value returned
is @code{0l} and the global variable @code{errno} is set to @code{EINVAL}.
@item
Any remaining characters in the string. If @var{tailptr} is not a null
pointer, @code{strtol} stores a pointer to this tail in
@code{*@var{tailptr}}.
@end itemize
If the string is empty, contains only whitespace, or does not contain an
initial substring that has the expected syntax for an integer in the
specified @var{base}, no conversion is performed. In this case,
@code{strtol} returns a value of zero and the value stored in
@code{*@var{tailptr}} is the value of @var{string}.
In a locale other than the standard @code{"C"} locale, this function
may recognize additional implementation-dependent syntax.
If the string has valid syntax for an integer but the value is not
representable because of overflow, @code{strtol} returns either
@code{LONG_MAX} or @code{LONG_MIN} (@pxref{Range of Type}), as
appropriate for the sign of the value. It also sets @code{errno}
to @code{ERANGE} to indicate there was overflow.
You should not check for errors by examining the return value of
@code{strtol}, because the string might be a valid representation of
@code{0l}, @code{LONG_MAX}, or @code{LONG_MIN}. Instead, check whether
@var{tailptr} points to what you expect after the number
(e.g. @code{'\0'} if the string should end after the number). You also
need to clear @var{errno} before the call and check it afterward, in
case there was overflow.
There is an example at the end of this section.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {long int} wcstol (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstol} function is equivalent to the @code{strtol} function
in nearly all aspects but handles wide character strings.
The @code{wcstol} function was introduced in @w{Amendment 1} of @w{ISO C90}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun {unsigned long int} strtoul (const char *retrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{strtoul} (``string-to-unsigned-long'') function is like
@code{strtol} except it converts to an @code{unsigned long int} value.
The syntax is the same as described above for @code{strtol}. The value
returned on overflow is @code{ULONG_MAX} (@pxref{Range of Type}).
If @var{string} depicts a negative number, @code{strtoul} acts the same
as @var{strtol} but casts the result to an unsigned integer. That means
for example that @code{strtoul} on @code{"-1"} returns @code{ULONG_MAX}
and an input more negative than @code{LONG_MIN} returns
(@code{ULONG_MAX} + 1) / 2.
@code{strtoul} sets @var{errno} to @code{EINVAL} if @var{base} is out of
range, or @code{ERANGE} on overflow.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {unsigned long int} wcstoul (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoul} function is equivalent to the @code{strtoul} function
in nearly all aspects but handles wide character strings.
The @code{wcstoul} function was introduced in @w{Amendment 1} of @w{ISO C90}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun {long long int} strtoll (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{strtoll} function is like @code{strtol} except that it returns
a @code{long long int} value, and accepts numbers with a correspondingly
larger range.
If the string has valid syntax for an integer but the value is not
representable because of overflow, @code{strtoll} returns either
@code{LLONG_MAX} or @code{LLONG_MIN} (@pxref{Range of Type}), as
appropriate for the sign of the value. It also sets @code{errno} to
@code{ERANGE} to indicate there was overflow.
The @code{strtoll} function was introduced in @w{ISO C99}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {long long int} wcstoll (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoll} function is equivalent to the @code{strtoll} function
in nearly all aspects but handles wide character strings.
The @code{wcstoll} function was introduced in @w{Amendment 1} of @w{ISO C90}.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun {long long int} strtoq (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@code{strtoq} (``string-to-quad-word'') is the BSD name for @code{strtoll}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {long long int} wcstoq (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoq} function is equivalent to the @code{strtoq} function
in nearly all aspects but handles wide character strings.
The @code{wcstoq} function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun {unsigned long long int} strtoull (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{strtoull} function is related to @code{strtoll} the same way
@code{strtoul} is related to @code{strtol}.
The @code{strtoull} function was introduced in @w{ISO C99}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {unsigned long long int} wcstoull (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoull} function is equivalent to the @code{strtoull} function
in nearly all aspects but handles wide character strings.
The @code{wcstoull} function was introduced in @w{Amendment 1} of @w{ISO C90}.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun {unsigned long long int} strtouq (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@code{strtouq} is the BSD name for @code{strtoull}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {unsigned long long int} wcstouq (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstouq} function is equivalent to the @code{strtouq} function
in nearly all aspects but handles wide character strings.
The @code{wcstouq} function is a GNU extension.
@end deftypefun
@comment inttypes.h
@comment ISO
@deftypefun intmax_t strtoimax (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{strtoimax} function is like @code{strtol} except that it returns
a @code{intmax_t} value, and accepts numbers of a corresponding range.
If the string has valid syntax for an integer but the value is not
representable because of overflow, @code{strtoimax} returns either
@code{INTMAX_MAX} or @code{INTMAX_MIN} (@pxref{Integers}), as
appropriate for the sign of the value. It also sets @code{errno} to
@code{ERANGE} to indicate there was overflow.
See @ref{Integers} for a description of the @code{intmax_t} type. The
@code{strtoimax} function was introduced in @w{ISO C99}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun intmax_t wcstoimax (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoimax} function is equivalent to the @code{strtoimax} function
in nearly all aspects but handles wide character strings.
The @code{wcstoimax} function was introduced in @w{ISO C99}.
@end deftypefun
@comment inttypes.h
@comment ISO
@deftypefun uintmax_t strtoumax (const char *restrict @var{string}, char **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{strtoumax} function is related to @code{strtoimax}
the same way that @code{strtoul} is related to @code{strtol}.
See @ref{Integers} for a description of the @code{intmax_t} type. The
@code{strtoumax} function was introduced in @w{ISO C99}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun uintmax_t wcstoumax (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr}, int @var{base})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstoumax} function is equivalent to the @code{strtoumax} function
in nearly all aspects but handles wide character strings.
The @code{wcstoumax} function was introduced in @w{ISO C99}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun {long int} atol (const char *@var{string})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is similar to the @code{strtol} function with a @var{base}
argument of @code{10}, except that it need not detect overflow errors.
The @code{atol} function is provided mostly for compatibility with
existing code; using @code{strtol} is more robust.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun int atoi (const char *@var{string})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is like @code{atol}, except that it returns an @code{int}.
The @code{atoi} function is also considered obsolete; use @code{strtol}
instead.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun {long long int} atoll (const char *@var{string})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is similar to @code{atol}, except it returns a @code{long
long int}.
The @code{atoll} function was introduced in @w{ISO C99}. It too is
obsolete (despite having just been added); use @code{strtoll} instead.
@end deftypefun
All the functions mentioned in this section so far do not handle
alternative representations of characters as described in the locale
data. Some locales specify thousands separator and the way they have to
be used which can help to make large numbers more readable. To read
such numbers one has to use the @code{scanf} functions with the @samp{'}
flag.
Here is a function which parses a string as a sequence of integers and
returns the sum of them:
@smallexample
int
sum_ints_from_string (char *string)
@{
int sum = 0;
while (1) @{
char *tail;
int next;
/* @r{Skip whitespace by hand, to detect the end.} */
while (isspace (*string)) string++;
if (*string == 0)
break;
/* @r{There is more nonwhitespace,} */
/* @r{so it ought to be another number.} */
errno = 0;
/* @r{Parse it.} */
next = strtol (string, &tail, 0);
/* @r{Add it in, if not overflow.} */
if (errno)
printf ("Overflow\n");
else
sum += next;
/* @r{Advance past it.} */
string = tail;
@}
return sum;
@}
@end smallexample
@node Parsing of Floats
@subsection Parsing of Floats
@pindex stdlib.h
The @samp{str} functions are declared in @file{stdlib.h} and those
beginning with @samp{wcs} are declared in @file{wchar.h}. One might
wonder about the use of @code{restrict} in the prototypes of the
functions in this section. It is seemingly useless but the @w{ISO C}
standard uses it (for the functions defined there) so we have to do it
as well.
@comment stdlib.h
@comment ISO
@deftypefun double strtod (const char *restrict @var{string}, char **restrict @var{tailptr})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Besides the unsafe-but-ruled-safe locale uses, this uses a lot of
@c mpn, but it's all safe.
@c
@c round_and_return
@c get_rounding_mode ok
@c mpn_add_1 ok
@c mpn_rshift ok
@c MPN_ZERO ok
@c MPN2FLOAT -> mpn_construct_(float|double|long_double) ok
@c str_to_mpn
@c mpn_mul_1 -> umul_ppmm ok
@c mpn_add_1 ok
@c mpn_lshift_1 -> mpn_lshift ok
@c STRTOF_INTERNAL
@c MPN_VAR ok
@c SET_MANTISSA ok
@c STRNCASECMP ok, wide and narrow
@c round_and_return ok
@c mpn_mul ok
@c mpn_addmul_1 ok
@c ... mpn_sub
@c mpn_lshift ok
@c udiv_qrnnd ok
@c count_leading_zeros ok
@c add_ssaaaa ok
@c sub_ddmmss ok
@c umul_ppmm ok
@c mpn_submul_1 ok
The @code{strtod} (``string-to-double'') function converts the initial
part of @var{string} to a floating-point number, which is returned as a
value of type @code{double}.
This function attempts to decompose @var{string} as follows:
@itemize @bullet
@item
A (possibly empty) sequence of whitespace characters. Which characters
are whitespace is determined by the @code{isspace} function
(@pxref{Classification of Characters}). These are discarded.
@item
An optional plus or minus sign (@samp{+} or @samp{-}).
@item A floating point number in decimal or hexadecimal format. The
decimal format is:
@itemize @minus
@item
A nonempty sequence of digits optionally containing a decimal-point
character---normally @samp{.}, but it depends on the locale
(@pxref{General Numeric}).
@item
An optional exponent part, consisting of a character @samp{e} or
@samp{E}, an optional sign, and a sequence of digits.
@end itemize
The hexadecimal format is as follows:
@itemize @minus
@item
A 0x or 0X followed by a nonempty sequence of hexadecimal digits
optionally containing a decimal-point character---normally @samp{.}, but
it depends on the locale (@pxref{General Numeric}).
@item
An optional binary-exponent part, consisting of a character @samp{p} or
@samp{P}, an optional sign, and a sequence of digits.
@end itemize
@item
Any remaining characters in the string. If @var{tailptr} is not a null
pointer, a pointer to this tail of the string is stored in
@code{*@var{tailptr}}.
@end itemize
If the string is empty, contains only whitespace, or does not contain an
initial substring that has the expected syntax for a floating-point
number, no conversion is performed. In this case, @code{strtod} returns
a value of zero and the value returned in @code{*@var{tailptr}} is the
value of @var{string}.
In a locale other than the standard @code{"C"} or @code{"POSIX"} locales,
this function may recognize additional locale-dependent syntax.
If the string has valid syntax for a floating-point number but the value
is outside the range of a @code{double}, @code{strtod} will signal
overflow or underflow as described in @ref{Math Error Reporting}.
@code{strtod} recognizes four special input strings. The strings
@code{"inf"} and @code{"infinity"} are converted to @math{@infinity{}},
or to the largest representable value if the floating-point format
doesn't support infinities. You can prepend a @code{"+"} or @code{"-"}
to specify the sign. Case is ignored when scanning these strings.
The strings @code{"nan"} and @code{"nan(@var{chars@dots{}})"} are converted
to NaN. Again, case is ignored. If @var{chars@dots{}} are provided, they
are used in some unspecified fashion to select a particular
representation of NaN (there can be several).
Since zero is a valid result as well as the value returned on error, you
should check for errors in the same way as for @code{strtol}, by
examining @var{errno} and @var{tailptr}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun float strtof (const char *@var{string}, char **@var{tailptr})
@comment stdlib.h
@comment ISO
@deftypefunx {long double} strtold (const char *@var{string}, char **@var{tailptr})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
These functions are analogous to @code{strtod}, but return @code{float}
and @code{long double} values respectively. They report errors in the
same way as @code{strtod}. @code{strtof} can be substantially faster
than @code{strtod}, but has less precision; conversely, @code{strtold}
can be much slower but has more precision (on systems where @code{long
double} is a separate type).
These functions have been GNU extensions and are new to @w{ISO C99}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun double wcstod (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr})
@comment stdlib.h
@comment ISO
@deftypefunx float wcstof (const wchar_t *@var{string}, wchar_t **@var{tailptr})
@comment stdlib.h
@comment ISO
@deftypefunx {long double} wcstold (const wchar_t *@var{string}, wchar_t **@var{tailptr})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
The @code{wcstod}, @code{wcstof}, and @code{wcstol} functions are
equivalent in nearly all aspect to the @code{strtod}, @code{strtof}, and
@code{strtold} functions but it handles wide character string.
The @code{wcstod} function was introduced in @w{Amendment 1} of @w{ISO
C90}. The @code{wcstof} and @code{wcstold} functions were introduced in
@w{ISO C99}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun double atof (const char *@var{string})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is similar to the @code{strtod} function, except that it
need not detect overflow and underflow errors. The @code{atof} function
is provided mostly for compatibility with existing code; using
@code{strtod} is more robust.
@end deftypefun
@Theglibc{} also provides @samp{_l} versions of these functions,
which take an additional argument, the locale to use in conversion.
See also @ref{Parsing of Integers}.
@node System V Number Conversion
@section Old-fashioned System V number-to-string functions
The old @w{System V} C library provided three functions to convert
numbers to strings, with unusual and hard-to-use semantics. @Theglibc{}
also provides these functions and some natural extensions.
These functions are only available in @theglibc{} and on systems descended
from AT&T Unix. Therefore, unless these functions do precisely what you
need, it is better to use @code{sprintf}, which is standard.
All these functions are defined in @file{stdlib.h}.
@comment stdlib.h
@comment SVID, Unix98
@deftypefun {char *} ecvt (double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg})
@safety{@prelim{}@mtunsafe{@mtasurace{:ecvt}}@asunsafe{}@acsafe{}}
The function @code{ecvt} converts the floating-point number @var{value}
to a string with at most @var{ndigit} decimal digits. The
returned string contains no decimal point or sign. The first digit of
the string is non-zero (unless @var{value} is actually zero) and the
last digit is rounded to nearest. @code{*@var{decpt}} is set to the
index in the string of the first digit after the decimal point.
@code{*@var{neg}} is set to a nonzero value if @var{value} is negative,
zero otherwise.
If @var{ndigit} decimal digits would exceed the precision of a
@code{double} it is reduced to a system-specific value.
The returned string is statically allocated and overwritten by each call
to @code{ecvt}.
If @var{value} is zero, it is implementation defined whether
@code{*@var{decpt}} is @code{0} or @code{1}.
For example: @code{ecvt (12.3, 5, &d, &n)} returns @code{"12300"}
and sets @var{d} to @code{2} and @var{n} to @code{0}.
@end deftypefun
@comment stdlib.h
@comment SVID, Unix98
@deftypefun {char *} fcvt (double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg})
@safety{@prelim{}@mtunsafe{@mtasurace{:fcvt}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The function @code{fcvt} is like @code{ecvt}, but @var{ndigit} specifies
the number of digits after the decimal point. If @var{ndigit} is less
than zero, @var{value} is rounded to the @math{@var{ndigit}+1}'th place to the
left of the decimal point. For example, if @var{ndigit} is @code{-1},
@var{value} will be rounded to the nearest 10. If @var{ndigit} is
negative and larger than the number of digits to the left of the decimal
point in @var{value}, @var{value} will be rounded to one significant digit.
If @var{ndigit} decimal digits would exceed the precision of a
@code{double} it is reduced to a system-specific value.
The returned string is statically allocated and overwritten by each call
to @code{fcvt}.
@end deftypefun
@comment stdlib.h
@comment SVID, Unix98
@deftypefun {char *} gcvt (double @var{value}, int @var{ndigit}, char *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c gcvt calls sprintf, that ultimately calls vfprintf, which malloc()s
@c args_value if it's too large, but gcvt never exercises this path.
@code{gcvt} is functionally equivalent to @samp{sprintf(buf, "%*g",
ndigit, value}. It is provided only for compatibility's sake. It
returns @var{buf}.
If @var{ndigit} decimal digits would exceed the precision of a
@code{double} it is reduced to a system-specific value.
@end deftypefun
As extensions, @theglibc{} provides versions of these three
functions that take @code{long double} arguments.
@comment stdlib.h
@comment GNU
@deftypefun {char *} qecvt (long double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg})
@safety{@prelim{}@mtunsafe{@mtasurace{:qecvt}}@asunsafe{}@acsafe{}}
This function is equivalent to @code{ecvt} except that it takes a
@code{long double} for the first parameter and that @var{ndigit} is
restricted by the precision of a @code{long double}.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun {char *} qfcvt (long double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg})
@safety{@prelim{}@mtunsafe{@mtasurace{:qfcvt}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function is equivalent to @code{fcvt} except that it
takes a @code{long double} for the first parameter and that @var{ndigit} is
restricted by the precision of a @code{long double}.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun {char *} qgcvt (long double @var{value}, int @var{ndigit}, char *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is equivalent to @code{gcvt} except that it takes a
@code{long double} for the first parameter and that @var{ndigit} is
restricted by the precision of a @code{long double}.
@end deftypefun
@cindex gcvt_r
The @code{ecvt} and @code{fcvt} functions, and their @code{long double}
equivalents, all return a string located in a static buffer which is
overwritten by the next call to the function. @Theglibc{}
provides another set of extended functions which write the converted
string into a user-supplied buffer. These have the conventional
@code{_r} suffix.
@code{gcvt_r} is not necessary, because @code{gcvt} already uses a
user-supplied buffer.
@comment stdlib.h
@comment GNU
@deftypefun int ecvt_r (double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{ecvt_r} function is the same as @code{ecvt}, except
that it places its result into the user-specified buffer pointed to by
@var{buf}, with length @var{len}. The return value is @code{-1} in
case of an error and zero otherwise.
This function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment SVID, Unix98
@deftypefun int fcvt_r (double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fcvt_r} function is the same as @code{fcvt}, except that it
places its result into the user-specified buffer pointed to by
@var{buf}, with length @var{len}. The return value is @code{-1} in
case of an error and zero otherwise.
This function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int qecvt_r (long double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{qecvt_r} function is the same as @code{qecvt}, except
that it places its result into the user-specified buffer pointed to by
@var{buf}, with length @var{len}. The return value is @code{-1} in
case of an error and zero otherwise.
This function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int qfcvt_r (long double @var{value}, int @var{ndigit}, int *@var{decpt}, int *@var{neg}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{qfcvt_r} function is the same as @code{qfcvt}, except
that it places its result into the user-specified buffer pointed to by
@var{buf}, with length @var{len}. The return value is @code{-1} in
case of an error and zero otherwise.
This function is a GNU extension.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/tsort.awk 0000664 0001750 0001750 00000001360 12275120646 021436 0 ustar adconrad adconrad #! /usr/bin/awk -f
# Generate topologically sorted list of manual chapters.
# Copyright (C) 1998-2014 Free Software Foundation, Inc.
# Written by Ulrich Drepper , 1998.
BEGIN {
cnt = 0
dnt = 0
}
{
to[dnt] = $1
from[dnt] = $2
++dnt
all[cnt++] = $1
}
END {
do {
moved = 0
for (i = 0; i < dnt; ++i) {
for (j = 0; j < cnt; ++j) {
if (all[j] == from[i]) {
for (k = j + 1; k < cnt; ++k) {
if (all[k] == to[i]) {
break;
}
}
if (k < cnt) {
for (l = k - 1; l >= j; --l) {
all[l + 1] = all[l]
}
all[j] = to[i]
break;
}
}
}
if (j < cnt) {
moved = 1
break
}
}
} while (moved)
for (i = 0; i < cnt; ++i) {
print all[i];
}
}
glibc-doc-reference-2.19.orig/manual/sysinfo.texi 0000664 0001750 0001750 00000145371 12275120646 022157 0 ustar adconrad adconrad @node System Management, System Configuration, Users and Groups, Top
@c %MENU% Controlling the system and getting information about it
@chapter System Management
This chapter describes facilities for controlling the system that
underlies a process (including the operating system and hardware) and
for getting information about it. Anyone can generally use the
informational facilities, but usually only a properly privileged process
can make changes.
@menu
* Host Identification:: Determining the name of the machine.
* Platform Type:: Determining operating system and basic
machine type
* Filesystem Handling:: Controlling/querying mounts
* System Parameters:: Getting and setting various system parameters
@end menu
To get information on parameters of the system that are built into the
system, such as the maximum length of a filename, @ref{System
Configuration}.
@node Host Identification
@section Host Identification
This section explains how to identify the particular system on which your
program is running. First, let's review the various ways computer systems
are named, which is a little complicated because of the history of the
development of the Internet.
Every Unix system (also known as a host) has a host name, whether it's
connected to a network or not. In its simplest form, as used before
computer networks were an issue, it's just a word like @samp{chicken}.
@cindex host name
But any system attached to the Internet or any network like it conforms
to a more rigorous naming convention as part of the Domain Name System
(DNS). In DNS, every host name is composed of two parts:
@cindex DNS
@cindex Domain Name System
@enumerate
@item
hostname
@cindex hostname
@item
domain name
@cindex domain name
@end enumerate
You will note that ``hostname'' looks a lot like ``host name'', but is
not the same thing, and that people often incorrectly refer to entire
host names as ``domain names.''
In DNS, the full host name is properly called the FQDN (Fully Qualified
Domain Name) and consists of the hostname, then a period, then the
domain name. The domain name itself usually has multiple components
separated by periods. So for example, a system's hostname may be
@samp{chicken} and its domain name might be @samp{ai.mit.edu}, so
its FQDN (which is its host name) is @samp{chicken.ai.mit.edu}.
@cindex FQDN
Adding to the confusion, though, is that DNS is not the only name space
in which a computer needs to be known. Another name space is the
NIS (aka YP) name space. For NIS purposes, there is another domain
name, which is called the NIS domain name or the YP domain name. It
need not have anything to do with the DNS domain name.
@cindex YP
@cindex NIS
@cindex NIS domain name
@cindex YP domain name
Confusing things even more is the fact that in DNS, it is possible for
multiple FQDNs to refer to the same system. However, there is always
exactly one of them that is the true host name, and it is called the
canonical FQDN.
In some contexts, the host name is called a ``node name.''
For more information on DNS host naming, see @ref{Host Names}.
@pindex hostname
@pindex hostid
@pindex unistd.h
Prototypes for these functions appear in @file{unistd.h}.
The programs @code{hostname}, @code{hostid}, and @code{domainname} work
by calling these functions.
@comment unistd.h
@comment BSD
@deftypefun int gethostname (char *@var{name}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on unix; implemented in terms of uname on posix and of
@c hurd_get_host_config on hurd.
This function returns the host name of the system on which it is called,
in the array @var{name}. The @var{size} argument specifies the size of
this array, in bytes. Note that this is @emph{not} the DNS hostname.
If the system participates in DNS, this is the FQDN (see above).
The return value is @code{0} on success and @code{-1} on failure. In
@theglibc{}, @code{gethostname} fails if @var{size} is not large
enough; then you can try again with a larger array. The following
@code{errno} error condition is defined for this function:
@table @code
@item ENAMETOOLONG
The @var{size} argument is less than the size of the host name plus one.
@end table
@pindex sys/param.h
On some systems, there is a symbol for the maximum possible host name
length: @code{MAXHOSTNAMELEN}. It is defined in @file{sys/param.h}.
But you can't count on this to exist, so it is cleaner to handle
failure and try again.
@code{gethostname} stores the beginning of the host name in @var{name}
even if the host name won't entirely fit. For some purposes, a
truncated host name is good enough. If it is, you can ignore the
error code.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int sethostname (const char *@var{name}, size_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on unix; implemented in terms of hurd_set_host_config
@c on hurd.
The @code{sethostname} function sets the host name of the system that
calls it to @var{name}, a string with length @var{length}. Only
privileged processes are permitted to do this.
Usually @code{sethostname} gets called just once, at system boot time.
Often, the program that calls it sets it to the value it finds in the
file @code{/etc/hostname}.
@cindex /etc/hostname
Be sure to set the host name to the full host name, not just the DNS
hostname (see above).
The return value is @code{0} on success and @code{-1} on failure.
The following @code{errno} error condition is defined for this function:
@table @code
@item EPERM
This process cannot set the host name because it is not privileged.
@end table
@end deftypefun
@comment unistd.h
@comment ???
@deftypefun int getdomainnname (char *@var{name}, size_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Syscalls uname, then strlen and memcpy.
@cindex NIS domain name
@cindex YP domain name
@code{getdomainname} returns the NIS (aka YP) domain name of the system
on which it is called. Note that this is not the more popular DNS
domain name. Get that with @code{gethostname}.
The specifics of this function are analogous to @code{gethostname}, above.
@end deftypefun
@comment unistd.h
@comment ???
@deftypefun int setdomainname (const char *@var{name}, size_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall.
@cindex NIS domain name
@cindex YP domain name
@code{getdomainname} sets the NIS (aka YP) domain name of the system
on which it is called. Note that this is not the more popular DNS
domain name. Set that with @code{sethostname}.
The specifics of this function are analogous to @code{sethostname}, above.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun {long int} gethostid (void)
@safety{@prelim{}@mtsafe{@mtshostid{} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c On HURD, calls _hurd_get_host_config and strtol. On Linux, open
@c HOSTIDFILE, reads an int32_t and closes; if that fails, it calls
@c gethostname and gethostbyname_r to use the h_addr.
This function returns the ``host ID'' of the machine the program is
running on. By convention, this is usually the primary Internet IP address
of that machine, converted to a @w{@code{long int}}. However, on some
systems it is a meaningless but unique number which is hard-coded for
each machine.
This is not widely used. It arose in BSD 4.2, but was dropped in BSD 4.4.
It is not required by POSIX.
The proper way to query the IP address is to use @code{gethostbyname}
on the results of @code{gethostname}. For more information on IP addresses,
@xref{Host Addresses}.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int sethostid (long int @var{id})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtshostid{}}}@asunsafe{}@acunsafe{@acucorrupt{} @acsfd{}}}
The @code{sethostid} function sets the ``host ID'' of the host machine
to @var{id}. Only privileged processes are permitted to do this. Usually
it happens just once, at system boot time.
The proper way to establish the primary IP address of a system
is to configure the IP address resolver to associate that IP address with
the system's host name as returned by @code{gethostname}. For example,
put a record for the system in @file{/etc/hosts}.
See @code{gethostid} above for more information on host ids.
The return value is @code{0} on success and @code{-1} on failure.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EPERM
This process cannot set the host name because it is not privileged.
@item ENOSYS
The operating system does not support setting the host ID. On some
systems, the host ID is a meaningless but unique number hard-coded for
each machine.
@end table
@end deftypefun
@node Platform Type
@section Platform Type Identification
You can use the @code{uname} function to find out some information about
the type of computer your program is running on. This function and the
associated data type are declared in the header file
@file{sys/utsname.h}.
@pindex sys/utsname.h
As a bonus, @code{uname} also gives some information identifying the
particular system your program is running on. This is the same information
which you can get with functions targeted to this purpose described in
@ref{Host Identification}.
@comment sys/utsname.h
@comment POSIX.1
@deftp {Data Type} {struct utsname}
The @code{utsname} structure is used to hold information returned
by the @code{uname} function. It has the following members:
@table @code
@item char sysname[]
This is the name of the operating system in use.
@item char release[]
This is the current release level of the operating system implementation.
@item char version[]
This is the current version level within the release of the operating
system.
@item char machine[]
This is a description of the type of hardware that is in use.
Some systems provide a mechanism to interrogate the kernel directly for
this information. On systems without such a mechanism, @theglibc{}
fills in this field based on the configuration name that was
specified when building and installing the library.
GNU uses a three-part name to describe a system configuration; the three
parts are @var{cpu}, @var{manufacturer} and @var{system-type}, and they
are separated with dashes. Any possible combination of three names is
potentially meaningful, but most such combinations are meaningless in
practice and even the meaningful ones are not necessarily supported by
any particular GNU program.
Since the value in @code{machine} is supposed to describe just the
hardware, it consists of the first two parts of the configuration name:
@samp{@var{cpu}-@var{manufacturer}}. For example, it might be one of these:
@quotation
@code{"sparc-sun"},
@code{"i386-@var{anything}"},
@code{"m68k-hp"},
@code{"m68k-sony"},
@code{"m68k-sun"},
@code{"mips-dec"}
@end quotation
@item char nodename[]
This is the host name of this particular computer. In @theglibc{},
the value is the same as that returned by @code{gethostname};
see @ref{Host Identification}.
@ gethostname() is implemented with a call to uname().
@item char domainname[]
This is the NIS or YP domain name. It is the same value returned by
@code{getdomainname}; see @ref{Host Identification}. This element
is a relatively recent invention and use of it is not as portable as
use of the rest of the structure.
@c getdomainname() is implemented with a call to uname().
@end table
@end deftp
@comment sys/utsname.h
@comment POSIX.1
@deftypefun int uname (struct utsname *@var{info})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on unix; the posix fallback is to call gethostname and
@c then fills in the other fields with constants; on HURD, it calls
@c proc_uname and then gethostname.
The @code{uname} function fills in the structure pointed to by
@var{info} with information about the operating system and host machine.
A non-negative value indicates that the data was successfully stored.
@code{-1} as the value indicates an error. The only error possible is
@code{EFAULT}, which we normally don't mention as it is always a
possibility.
@end deftypefun
@node Filesystem Handling
@section Controlling and Querying Mounts
All files are in filesystems, and before you can access any file, its
filesystem must be mounted. Because of Unix's concept of
@emph{Everything is a file}, mounting of filesystems is central to doing
almost anything. This section explains how to find out what filesystems
are currently mounted and what filesystems are available for mounting,
and how to change what is mounted.
The classic filesystem is the contents of a disk drive. The concept is
considerably more abstract, though, and lots of things other than disk
drives can be mounted.
Some block devices don't correspond to traditional devices like disk
drives. For example, a loop device is a block device whose driver uses
a regular file in another filesystem as its medium. So if that regular
file contains appropriate data for a filesystem, you can by mounting the
loop device essentially mount a regular file.
Some filesystems aren't based on a device of any kind. The ``proc''
filesystem, for example, contains files whose data is made up by the
filesystem driver on the fly whenever you ask for it. And when you
write to it, the data you write causes changes in the system. No data
gets stored.
@c It would be good to mention NFS mounts here.
@menu
* Mount Information:: What is or could be mounted?
* Mount-Unmount-Remount:: Controlling what is mounted and how
@end menu
@node Mount Information, Mount-Unmount-Remount, , Filesystem Handling
@subsection Mount Information
For some programs it is desirable and necessary to access information
about whether a certain filesystem is mounted and, if it is, where, or
simply to get lists of all the available filesystems. @Theglibc{}
provides some functions to retrieve this information portably.
Traditionally Unix systems have a file named @file{/etc/fstab} which
describes all possibly mounted filesystems. The @code{mount} program
uses this file to mount at startup time of the system all the
necessary filesystems. The information about all the filesystems
actually mounted is normally kept in a file named either
@file{/var/run/mtab} or @file{/etc/mtab}. Both files share the same
syntax and it is crucial that this syntax is followed all the time.
Therefore it is best to never directly write the files. The functions
described in this section can do this and they also provide the
functionality to convert the external textual representation to the
internal representation.
Note that the @file{fstab} and @file{mtab} files are maintained on a
system by @emph{convention}. It is possible for the files not to exist
or not to be consistent with what is really mounted or available to
mount, if the system's administration policy allows it. But programs
that mount and unmount filesystems typically maintain and use these
files as described herein.
@vindex _PATH_FSTAB
@vindex _PATH_MNTTAB
@vindex _PATH_MOUNTED
@vindex FSTAB
@vindex MNTTAB
@vindex MOUNTED
The filenames given above should never be used directly. The portable
way to handle these file is to use the macro @code{_PATH_FSTAB},
defined in @file{fstab.h}, or @code{_PATH_MNTTAB}, defined in
@file{mntent.h} and @file{paths.h}, for @file{fstab}; and the macro
@code{_PATH_MOUNTED}, also defined in @file{mntent.h} and
@file{paths.h}, for @file{mtab}. There are also two alternate macro
names @code{FSTAB}, @code{MNTTAB}, and @code{MOUNTED} defined but
these names are deprecated and kept only for backward compatibility.
The names @code{_PATH_MNTTAB} and @code{_PATH_MOUNTED} should always be used.
@menu
* fstab:: The @file{fstab} file
* mtab:: The @file{mtab} file
* Other Mount Information:: Other (non-libc) sources of mount information
@end menu
@node fstab
@subsubsection The @file{fstab} file
The internal representation for entries of the file is @w{@code{struct
fstab}}, defined in @file{fstab.h}.
@comment fstab.h
@comment BSD
@deftp {Data Type} {struct fstab}
This structure is used with the @code{getfsent}, @code{getfsspec}, and
@code{getfsfile} functions.
@table @code
@item char *fs_spec
This element describes the device from which the filesystem is mounted.
Normally this is the name of a special device, such as a hard disk
partition, but it could also be a more or less generic string. For
@dfn{NFS} it would be a hostname and directory name combination.
Even though the element is not declared @code{const} it shouldn't be
modified. The missing @code{const} has historic reasons, since this
function predates @w{ISO C}. The same is true for the other string
elements of this structure.
@item char *fs_file
This describes the mount point on the local system. I.e., accessing any
file in this filesystem has implicitly or explicitly this string as a
prefix.
@item char *fs_vfstype
This is the type of the filesystem. Depending on what the underlying
kernel understands it can be any string.
@item char *fs_mntops
This is a string containing options passed to the kernel with the
@code{mount} call. Again, this can be almost anything. There can be
more than one option, separated from the others by a comma. Each option
consists of a name and an optional value part, introduced by an @code{=}
character.
If the value of this element must be processed it should ideally be done
using the @code{getsubopt} function; see @ref{Suboptions}.
@item const char *fs_type
This name is poorly chosen. This element points to a string (possibly
in the @code{fs_mntops} string) which describes the modes with which the
filesystem is mounted. @file{fstab} defines five macros to describe the
possible values:
@vtable @code
@item FSTAB_RW
The filesystems gets mounted with read and write enabled.
@item FSTAB_RQ
The filesystems gets mounted with read and write enabled. Write access
is restricted by quotas.
@item FSTAB_RO
The filesystem gets mounted read-only.
@item FSTAB_SW
This is not a real filesystem, it is a swap device.
@item FSTAB_XX
This entry from the @file{fstab} file is totally ignored.
@end vtable
Testing for equality with these value must happen using @code{strcmp}
since these are all strings. Comparing the pointer will probably always
fail.
@item int fs_freq
This element describes the dump frequency in days.
@item int fs_passno
This element describes the pass number on parallel dumps. It is closely
related to the @code{dump} utility used on Unix systems.
@end table
@end deftp
To read the entire content of the of the @file{fstab} file @theglibc{}
contains a set of three functions which are designed in the usual way.
@comment fstab.h
@comment BSD
@deftypefun int setfsent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:fsent}}@asunsafe{@ascuheap{} @asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c setfsent @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c fstab_init(1) @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c malloc dup @ascuheap @acsmem
@c rewind dup @asucorrupt @acucorrupt [no @aculock]
@c setmntent dup @ascuheap @asulock @acsmem @acsfd @aculock
This function makes sure that the internal read pointer for the
@file{fstab} file is at the beginning of the file. This is done by
either opening the file or resetting the read pointer.
Since the file handle is internal to the libc this function is not
thread-safe.
This function returns a non-zero value if the operation was successful
and the @code{getfs*} functions can be used to read the entries of the
file.
@end deftypefun
@comment fstab.h
@comment BSD
@deftypefun void endfsent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:fsent}}@asunsafe{@ascuheap{} @asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c endfsent @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c endmntent dup @ascuheap @asulock @aculock @acsmem @acsfd
This function makes sure that all resources acquired by a prior call to
@code{setfsent} (explicitly or implicitly by calling @code{getfsent}) are
freed.
@end deftypefun
@comment fstab.h
@comment BSD
@deftypefun {struct fstab *} getfsent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:fsent} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c getfsent @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @asulock @acucorrupt @aculock @acsmem
@c fstab_init(0) dup @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c fstab_fetch @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
@c getmntent_r dup @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
@c fstab_convert @mtasurace:fsent
@c hasmntopt dup ok
This function returns the next entry of the @file{fstab} file. If this
is the first call to any of the functions handling @file{fstab} since
program start or the last call of @code{endfsent}, the file will be
opened.
The function returns a pointer to a variable of type @code{struct
fstab}. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred @code{getfsent}
returns a @code{NULL} pointer.
@end deftypefun
@comment fstab.h
@comment BSD
@deftypefun {struct fstab *} getfsspec (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:fsent} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c getffsspec @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @asulock @acucorrupt @aculock @acsmem
@c fstab_init(1) dup @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c fstab_fetch dup @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
@c strcmp dup ok
@c fstab_convert dup @mtasurace:fsent
This function returns the next entry of the @file{fstab} file which has
a string equal to @var{name} pointed to by the @code{fs_spec} element.
Since there is normally exactly one entry for each special device it
makes no sense to call this function more than once for the same
argument. If this is the first call to any of the functions handling
@file{fstab} since program start or the last call of @code{endfsent},
the file will be opened.
The function returns a pointer to a variable of type @code{struct
fstab}. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred @code{getfsent}
returns a @code{NULL} pointer.
@end deftypefun
@comment fstab.h
@comment BSD
@deftypefun {struct fstab *} getfsfile (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:fsent} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c getffsfile @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @asulock @acucorrupt @aculock @acsmem
@c fstab_init(1) dup @mtasurace:fsent @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsmem @acsfd
@c fstab_fetch dup @mtasurace:fsent @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
@c strcmp dup ok
@c fstab_convert dup @mtasurace:fsent
This function returns the next entry of the @file{fstab} file which has
a string equal to @var{name} pointed to by the @code{fs_file} element.
Since there is normally exactly one entry for each mount point it
makes no sense to call this function more than once for the same
argument. If this is the first call to any of the functions handling
@file{fstab} since program start or the last call of @code{endfsent},
the file will be opened.
The function returns a pointer to a variable of type @code{struct
fstab}. This variable is shared by all threads and therefore this
function is not thread-safe. If an error occurred @code{getfsent}
returns a @code{NULL} pointer.
@end deftypefun
@node mtab
@subsubsection The @file{mtab} file
The following functions and data structure access the @file{mtab} file.
@comment mntent.h
@comment BSD
@deftp {Data Type} {struct mntent}
This structure is used with the @code{getmntent}, @code{getmntent_t},
@code{addmntent}, and @code{hasmntopt} functions.
@table @code
@item char *mnt_fsname
This element contains a pointer to a string describing the name of the
special device from which the filesystem is mounted. It corresponds to
the @code{fs_spec} element in @code{struct fstab}.
@item char *mnt_dir
This element points to a string describing the mount point of the
filesystem. It corresponds to the @code{fs_file} element in
@code{struct fstab}.
@item char *mnt_type
@code{mnt_type} describes the filesystem type and is therefore
equivalent to @code{fs_vfstype} in @code{struct fstab}. @file{mntent.h}
defines a few symbolic names for some of the values this string can have.
But since the kernel can support arbitrary filesystems it does not
make much sense to give them symbolic names. If one knows the symbol
name one also knows the filesystem name. Nevertheless here follows the
list of the symbols provided in @file{mntent.h}.
@vtable @code
@item MNTTYPE_IGNORE
This symbol expands to @code{"ignore"}. The value is sometime used in
@file{fstab} files to make sure entries are not used without removing them.
@item MNTTYPE_NFS
Expands to @code{"nfs"}. Using this macro sometimes could make sense
since it names the default NFS implementation, in case both version 2
and 3 are supported.
@item MNTTYPE_SWAP
This symbol expands to @code{"swap"}. It names the special @file{fstab}
entry which names one of the possibly multiple swap partitions.
@end vtable
@item char *mnt_opts
The element contains a string describing the options used while mounting
the filesystem. As for the equivalent element @code{fs_mntops} of
@code{struct fstab} it is best to use the function @code{getsubopt}
(@pxref{Suboptions}) to access the parts of this string.
The @file{mntent.h} file defines a number of macros with string values
which correspond to some of the options understood by the kernel. There
might be many more options which are possible so it doesn't make much sense
to rely on these macros but to be consistent here is the list:
@vtable @code
@item MNTOPT_DEFAULTS
Expands to @code{"defaults"}. This option should be used alone since it
indicates all values for the customizable values are chosen to be the
default.
@item MNTOPT_RO
Expands to @code{"ro"}. See the @code{FSTAB_RO} value, it means the
filesystem is mounted read-only.
@item MNTOPT_RW
Expand to @code{"rw"}. See the @code{FSTAB_RW} value, it means the
filesystem is mounted with read and write permissions.
@item MNTOPT_SUID
Expands to @code{"suid"}. This means that the SUID bit (@pxref{How
Change Persona}) is respected when a program from the filesystem is
started.
@item MNTOPT_NOSUID
Expands to @code{"nosuid"}. This is the opposite of @code{MNTOPT_SUID},
the SUID bit for all files from the filesystem is ignored.
@item MNTOPT_NOAUTO
Expands to @code{"noauto"}. At startup time the @code{mount} program
will ignore this entry if it is started with the @code{-a} option to
mount all filesystems mentioned in the @file{fstab} file.
@end vtable
As for the @code{FSTAB_*} entries introduced above it is important to
use @code{strcmp} to check for equality.
@item mnt_freq
This elements corresponds to @code{fs_freq} and also specifies the
frequency in days in which dumps are made.
@item mnt_passno
This element is equivalent to @code{fs_passno} with the same meaning
which is uninteresting for all programs beside @code{dump}.
@end table
@end deftp
For accessing the @file{mtab} file there is again a set of three
functions to access all entries in a row. Unlike the functions to
handle @file{fstab} these functions do not access a fixed file and there
is even a thread safe variant of the get function. Beside this @theglibc
contains functions to alter the file and test for specific options.
@comment mntent.h
@comment BSD
@deftypefun {FILE *} setmntent (const char *@var{file}, const char *@var{mode})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @acsfd{} @aculock{}}}
@c setmntent @ascuheap @asulock @acsmem @acsfd @aculock
@c strlen dup ok
@c mempcpy dup ok
@c memcpy dup ok
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking dup ok [no @mtasurace:stream @asulock: exclusive stream]
The @code{setmntent} function prepares the file named @var{FILE} which
must be in the format of a @file{fstab} and @file{mtab} file for the
upcoming processing through the other functions of the family. The
@var{mode} parameter can be chosen in the way the @var{opentype}
parameter for @code{fopen} (@pxref{Opening Streams}) can be chosen. If
the file is opened for writing the file is also allowed to be empty.
If the file was successfully opened @code{setmntent} returns a file
descriptor for future use. Otherwise the return value is @code{NULL}
and @code{errno} is set accordingly.
@end deftypefun
@comment mntent.h
@comment BSD
@deftypefun int endmntent (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c endmntent @ascuheap @asulock @aculock @acsmem @acsfd
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
This function takes for the @var{stream} parameter a file handle which
previously was returned from the @code{setmntent} call.
@code{endmntent} closes the stream and frees all resources.
The return value is @math{1} unless an error occurred in which case it
is @math{0}.
@end deftypefun
@comment mntent.h
@comment BSD
@deftypefun {struct mntent *} getmntent (FILE *@var{stream})
@safety{@prelim{}@mtunsafe{@mtasurace{:mntentbuf} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asuinit{}}@acunsafe{@acuinit{} @acucorrupt{} @aculock{} @acsmem{}}}
@c getmntent @mtasurace:mntentbuf @mtslocale @asucorrupt @ascuheap @asuinit @acuinit @acucorrupt @aculock @acsmem
@c libc_once @ascuheap @asuinit @acuinit @acsmem
@c allocate @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c getmntent_r dup @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
The @code{getmntent} function takes as the parameter a file handle
previously returned by successful call to @code{setmntent}. It returns
a pointer to a static variable of type @code{struct mntent} which is
filled with the information from the next entry from the file currently
read.
The file format used prescribes the use of spaces or tab characters to
separate the fields. This makes it harder to use name containing one
of these characters (e.g., mount points using spaces). Therefore
these characters are encoded in the files and the @code{getmntent}
function takes care of the decoding while reading the entries back in.
@code{'\040'} is used to encode a space character, @code{'\011'} to
encode a tab character, @code{'\012'} to encode a newline character,
and @code{'\\'} to encode a backslash.
If there was an error or the end of the file is reached the return value
is @code{NULL}.
This function is not thread-safe since all calls to this function return
a pointer to the same static variable. @code{getmntent_r} should be
used in situations where multiple threads access the file.
@end deftypefun
@comment mntent.h
@comment BSD
@deftypefun {struct mntent *} getmntent_r (FILE *@var{stream}, struct mntent *@var{result}, char *@var{buffer}, int @var{bufsize})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c getmntent_r @mtslocale @asucorrupt @ascuheap @acucorrupt @aculock @acsmem
@c flockfile dup @aculock
@c fgets_unlocked dup @asucorrupt @acucorrupt [locked, so no @mtsrace:stream]
@c funlockfile dup @aculock
@c strchr dup ok
@c strspn dup ok
@c strsep dup ok
@c decode_name ok
@c sscanf dup @mtslocale @ascuheap @acsmem
The @code{getmntent_r} function is the reentrant variant of
@code{getmntent}. It also returns the next entry from the file and
returns a pointer. The actual variable the values are stored in is not
static, though. Instead the function stores the values in the variable
pointed to by the @var{result} parameter. Additional information (e.g.,
the strings pointed to by the elements of the result) are kept in the
buffer of size @var{bufsize} pointed to by @var{buffer}.
Escaped characters (space, tab, backslash) are converted back in the
same way as it happens for @code{getmentent}.
The function returns a @code{NULL} pointer in error cases. Errors could be:
@itemize @bullet
@item
error while reading the file,
@item
end of file reached,
@item
@var{bufsize} is too small for reading a complete new entry.
@end itemize
@end deftypefun
@comment mntent.h
@comment BSD
@deftypefun int addmntent (FILE *@var{stream}, const struct mntent *@var{mnt})
@safety{@prelim{}@mtunsafe{@mtasurace{:stream} @mtslocale{}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c addmntent @mtasurace:stream @mtslocale @asucorrupt @acucorrupt
@c fseek dup @asucorrupt @acucorrupt [no @aculock]
@c encode_name ok
@c fprintf dup @mtslocale @asucorrupt @acucorrupt [no @ascuheap @acsmem, no @aculock]
@c fflush dup @asucorrupt @acucorrupt [no @aculock]
The @code{addmntent} function allows adding a new entry to the file
previously opened with @code{setmntent}. The new entries are always
appended. I.e., even if the position of the file descriptor is not at
the end of the file this function does not overwrite an existing entry
following the current position.
The implication of this is that to remove an entry from a file one has
to create a new file while leaving out the entry to be removed and after
closing the file remove the old one and rename the new file to the
chosen name.
This function takes care of spaces and tab characters in the names to be
written to the file. It converts them and the backslash character into
the format describe in the @code{getmntent} description above.
This function returns @math{0} in case the operation was successful.
Otherwise the return value is @math{1} and @code{errno} is set
appropriately.
@end deftypefun
@comment mntent.h
@comment BSD
@deftypefun {char *} hasmntopt (const struct mntent *@var{mnt}, const char *@var{opt})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c hasmntopt ok
@c strlen dup ok
@c strstr dup ok
@c strchr dup ok
This function can be used to check whether the string pointed to by the
@code{mnt_opts} element of the variable pointed to by @var{mnt} contains
the option @var{opt}. If this is true a pointer to the beginning of the
option in the @code{mnt_opts} element is returned. If no such option
exists the function returns @code{NULL}.
This function is useful to test whether a specific option is present but
when all options have to be processed one is better off with using the
@code{getsubopt} function to iterate over all options in the string.
@end deftypefun
@node Other Mount Information
@subsubsection Other (Non-libc) Sources of Mount Information
On a system with a Linux kernel and the @code{proc} filesystem, you can
get information on currently mounted filesystems from the file
@file{mounts} in the @code{proc} filesystem. Its format is similar to
that of the @file{mtab} file, but represents what is truly mounted
without relying on facilities outside the kernel to keep @file{mtab} up
to date.
@node Mount-Unmount-Remount, , Mount Information, Filesystem Handling
@subsection Mount, Unmount, Remount
This section describes the functions for mounting, unmounting, and
remounting filesystems.
Only the superuser can mount, unmount, or remount a filesystem.
These functions do not access the @file{fstab} and @file{mtab} files. You
should maintain and use these separately. @xref{Mount Information}.
The symbols in this section are declared in @file{sys/mount.h}.
@comment sys/mount.h
@comment SVID, BSD
@deftypefun {int} mount (const char *@var{special_file}, const char *@var{dir}, const char *@var{fstype}, unsigned long int @var{options}, const void *@var{data})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall.
@code{mount} mounts or remounts a filesystem. The two operations are
quite different and are merged rather unnaturally into this one function.
The @code{MS_REMOUNT} option, explained below, determines whether
@code{mount} mounts or remounts.
For a mount, the filesystem on the block device represented by the
device special file named @var{special_file} gets mounted over the mount
point @var{dir}. This means that the directory @var{dir} (along with any
files in it) is no longer visible; in its place (and still with the name
@var{dir}) is the root directory of the filesystem on the device.
As an exception, if the filesystem type (see below) is one which is not
based on a device (e.g. ``proc''), @code{mount} instantiates a
filesystem and mounts it over @var{dir} and ignores @var{special_file}.
For a remount, @var{dir} specifies the mount point where the filesystem
to be remounted is (and remains) mounted and @var{special_file} is
ignored. Remounting a filesystem means changing the options that control
operations on the filesystem while it is mounted. It does not mean
unmounting and mounting again.
For a mount, you must identify the type of the filesystem as
@var{fstype}. This type tells the kernel how to access the filesystem
and can be thought of as the name of a filesystem driver. The
acceptable values are system dependent. On a system with a Linux kernel
and the @code{proc} filesystem, the list of possible values is in the
file @file{filesystems} in the @code{proc} filesystem (e.g. type
@kbd{cat /proc/filesystems} to see the list). With a Linux kernel, the
types of filesystems that @code{mount} can mount, and their type names,
depends on what filesystem drivers are configured into the kernel or
loaded as loadable kernel modules. An example of a common value for
@var{fstype} is @code{ext2}.
For a remount, @code{mount} ignores @var{fstype}.
@c This is traditionally called "rwflag" for historical reasons.
@c No point in confusing people today, though.
@var{options} specifies a variety of options that apply until the
filesystem is unmounted or remounted. The precise meaning of an option
depends on the filesystem and with some filesystems, an option may have
no effect at all. Furthermore, for some filesystems, some of these
options (but never @code{MS_RDONLY}) can be overridden for individual
file accesses via @code{ioctl}.
@var{options} is a bit string with bit fields defined using the
following mask and masked value macros:
@table @code
@item MS_MGC_MASK
This multibit field contains a magic number. If it does not have the value
@code{MS_MGC_VAL}, @code{mount} assumes all the following bits are zero and
the @var{data} argument is a null string, regardless of their actual values.
@item MS_REMOUNT
This bit on means to remount the filesystem. Off means to mount it.
@c There is a mask MS_RMT_MASK in mount.h that says only two of the options
@c can be reset by remount. But the Linux kernel has its own version of
@c MS_RMT_MASK that says they all can be reset. As far as I can tell,
@c libc just passes the arguments straight through to the kernel.
@item MS_RDONLY
This bit on specifies that no writing to the filesystem shall be allowed
while it is mounted. This cannot be overridden by @code{ioctl}. This
option is available on nearly all filesystems.
@item S_IMMUTABLE
This bit on specifies that no writing to the files in the filesystem
shall be allowed while it is mounted. This can be overridden for a
particular file access by a properly privileged call to @code{ioctl}.
This option is a relatively new invention and is not available on many
filesystems.
@item S_APPEND
This bit on specifies that the only file writing that shall be allowed
while the filesystem is mounted is appending. Some filesystems allow
this to be overridden for a particular process by a properly privileged
call to @code{ioctl}. This is a relatively new invention and is not
available on many filesystems.
@item MS_NOSUID
This bit on specifies that Setuid and Setgid permissions on files in the
filesystem shall be ignored while it is mounted.
@item MS_NOEXEC
This bit on specifies that no files in the filesystem shall be executed
while the filesystem is mounted.
@item MS_NODEV
This bit on specifies that no device special files in the filesystem
shall be accessible while the filesystem is mounted.
@item MS_SYNCHRONOUS
This bit on specifies that all writes to the filesystem while it is
mounted shall be synchronous; i.e., data shall be synced before each
write completes rather than held in the buffer cache.
@item MS_MANDLOCK
This bit on specifies that mandatory locks on files shall be permitted while
the filesystem is mounted.
@item MS_NOATIME
This bit on specifies that access times of files shall not be updated when
the files are accessed while the filesystem is mounted.
@item MS_NODIRATIME
This bit on specifies that access times of directories shall not be updated
when the directories are accessed while the filesystem in mounted.
@c there is also S_QUOTA Linux fs.h (mount.h still uses its former name
@c S_WRITE), but I can't see what it does. Turns on quotas, I guess.
@end table
Any bits not covered by the above masks should be set off; otherwise,
results are undefined.
The meaning of @var{data} depends on the filesystem type and is controlled
entirely by the filesystem driver in the kernel.
Example:
@smallexample
@group
#include
mount("/dev/hdb", "/cdrom", MS_MGC_VAL | MS_RDONLY | MS_NOSUID, "");
mount("/dev/hda2", "/mnt", MS_MGC_VAL | MS_REMOUNT, "");
@end group
@end smallexample
Appropriate arguments for @code{mount} are conventionally recorded in
the @file{fstab} table. @xref{Mount Information}.
The return value is zero if the mount or remount is successful. Otherwise,
it is @code{-1} and @code{errno} is set appropriately. The values of
@code{errno} are filesystem dependent, but here is a general list:
@table @code
@item EPERM
The process is not superuser.
@item ENODEV
The file system type @var{fstype} is not known to the kernel.
@item ENOTBLK
The file @var{dev} is not a block device special file.
@item EBUSY
@itemize @bullet
@item
The device is already mounted.
@item
The mount point is busy. (E.g. it is some process' working directory or
has a filesystem mounted on it already).
@item
The request is to remount read-only, but there are files open for write.
@end itemize
@item EINVAL
@itemize @bullet
@item
A remount was attempted, but there is no filesystem mounted over the
specified mount point.
@item
The supposed filesystem has an invalid superblock.
@end itemize
@item EACCES
@itemize @bullet
@item
The filesystem is inherently read-only (possibly due to a switch on the
device) and the process attempted to mount it read/write (by setting the
@code{MS_RDONLY} bit off).
@item
@var{special_file} or @var{dir} is not accessible due to file permissions.
@item
@var{special_file} is not accessible because it is in a filesystem that is
mounted with the @code{MS_NODEV} option.
@end itemize
@item EM_FILE
The table of dummy devices is full. @code{mount} needs to create a
dummy device (aka ``unnamed'' device) if the filesystem being mounted is
not one that uses a device.
@end table
@end deftypefun
@comment sys/mount.h
@comment GNU
@deftypefun {int} umount2 (const char *@var{file}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall.
@code{umount2} unmounts a filesystem.
You can identify the filesystem to unmount either by the device special
file that contains the filesystem or by the mount point. The effect is
the same. Specify either as the string @var{file}.
@var{flags} contains the one-bit field identified by the following
mask macro:
@table @code
@item MNT_FORCE
This bit on means to force the unmounting even if the filesystem is
busy, by making it unbusy first. If the bit is off and the filesystem is
busy, @code{umount2} fails with @code{errno} = @code{EBUSY}. Depending
on the filesystem, this may override all, some, or no busy conditions.
@end table
All other bits in @var{flags} should be set to zero; otherwise, the result
is undefined.
Example:
@smallexample
@group
#include
umount2("/mnt", MNT_FORCE);
umount2("/dev/hdd1", 0);
@end group
@end smallexample
After the filesystem is unmounted, the directory that was the mount point
is visible, as are any files in it.
As part of unmounting, @code{umount2} syncs the filesystem.
If the unmounting is successful, the return value is zero. Otherwise, it
is @code{-1} and @code{errno} is set accordingly:
@table @code
@item EPERM
The process is not superuser.
@item EBUSY
The filesystem cannot be unmounted because it is busy. E.g. it contains
a directory that is some process's working directory or a file that some
process has open. With some filesystems in some cases, you can avoid
this failure with the @code{MNT_FORCE} option.
@item EINVAL
@var{file} validly refers to a file, but that file is neither a mount
point nor a device special file of a currently mounted filesystem.
@end table
This function is not available on all systems.
@end deftypefun
@comment sys/mount.h
@comment SVID, GNU
@deftypefun {int} umount (const char *@var{file})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall or wrapper for umount2.
@code{umount} does the same thing as @code{umount2} with @var{flags} set
to zeroes. It is more widely available than @code{umount2} but since it
lacks the possibility to forcefully unmount a filesystem is deprecated
when @code{umount2} is also available.
@end deftypefun
@node System Parameters
@section System Parameters
This section describes the @code{sysctl} function, which gets and sets
a variety of system parameters.
The symbols used in this section are declared in the file @file{sys/sysctl.h}.
@comment sys/sysctl.h
@comment BSD
@deftypefun int sysctl (int *@var{names}, int @var{nlen}, void *@var{oldval}, size_t *@var{oldlenp}, void *@var{newval}, size_t @var{newlen})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
@code{sysctl} gets or sets a specified system parameter. There are so
many of these parameters that it is not practical to list them all here,
but here are some examples:
@itemize @bullet
@item network domain name
@item paging parameters
@item network Address Resolution Protocol timeout time
@item maximum number of files that may be open
@item root filesystem device
@item when kernel was built
@end itemize
The set of available parameters depends on the kernel configuration and
can change while the system is running, particularly when you load and
unload loadable kernel modules.
The system parameters with which @code{syslog} is concerned are arranged
in a hierarchical structure like a hierarchical filesystem. To identify
a particular parameter, you specify a path through the structure in a
way analogous to specifying the pathname of a file. Each component of
the path is specified by an integer and each of these integers has a
macro defined for it by @file{sys/sysctl.h}. @var{names} is the path, in
the form of an array of integers. Each component of the path is one
element of the array, in order. @var{nlen} is the number of components
in the path.
For example, the first component of the path for all the paging
parameters is the value @code{CTL_VM}. For the free page thresholds, the
second component of the path is @code{VM_FREEPG}. So to get the free
page threshold values, make @var{names} an array containing the two
elements @code{CTL_VM} and @code{VM_FREEPG} and make @var{nlen} = 2.
The format of the value of a parameter depends on the parameter.
Sometimes it is an integer; sometimes it is an ASCII string; sometimes
it is an elaborate structure. In the case of the free page thresholds
used in the example above, the parameter value is a structure containing
several integers.
In any case, you identify a place to return the parameter's value with
@var{oldval} and specify the amount of storage available at that
location as *@var{oldlenp}. *@var{oldlenp} does double duty because it
is also the output location that contains the actual length of the
returned value.
If you don't want the parameter value returned, specify a null pointer
for @var{oldval}.
To set the parameter, specify the address and length of the new value
as @var{newval} and @var{newlen}. If you don't want to set the parameter,
specify a null pointer as @var{newval}.
If you get and set a parameter in the same @code{sysctl} call, the value
returned is the value of the parameter before it was set.
Each system parameter has a set of permissions similar to the
permissions for a file (including the permissions on directories in its
path) that determine whether you may get or set it. For the purposes of
these permissions, every parameter is considered to be owned by the
superuser and Group 0 so processes with that effective uid or gid may
have more access to system parameters. Unlike with files, the superuser
does not invariably have full permission to all system parameters, because
some of them are designed not to be changed ever.
@code{sysctl} returns a zero return value if it succeeds. Otherwise, it
returns @code{-1} and sets @code{errno} appropriately. Besides the
failures that apply to all system calls, the following are the
@code{errno} codes for all possible failures:
@table @code
@item EPERM
The process is not permitted to access one of the components of the
path of the system parameter or is not permitted to access the system parameter
itself in the way (read or write) that it requested.
@c There is some indication in the Linux 2.2 code that the code is trying to
@c return EACCES here, but the EACCES value never actually makes it to the
@c user.
@item ENOTDIR
There is no system parameter corresponding to @var{name}.
@item EFAULT
@var{oldval} is not null, which means the process wanted to read the parameter,
but *@var{oldlenp} is zero, so there is no place to return it.
@item EINVAL
@itemize @bullet
@item
The process attempted to set a system parameter to a value that is not valid
for that parameter.
@item
The space provided for the return of the system parameter is not the right
size for that parameter.
@end itemize
@item ENOMEM
This value may be returned instead of the more correct @code{EINVAL} in some
cases where the space provided for the return of the system parameter is too
small.
@end table
@end deftypefun
If you have a Linux kernel with the @code{proc} filesystem, you can get
and set most of the same parameters by reading and writing to files in
the @code{sys} directory of the @code{proc} filesystem. In the @code{sys}
directory, the directory structure represents the hierarchical structure
of the parameters. E.g. you can display the free page thresholds with
@smallexample
cat /proc/sys/vm/freepages
@end smallexample
@c In Linux, the sysctl() and /proc instances of the parameter are created
@c together. The proc filesystem accesses the same data structure as
@c sysctl(), which has special fields in it for /proc. But it is still
@c possible to create a sysctl-only parameter.
Some more traditional and more widely available, though less general,
@glibcadj{} functions for getting and setting some of the same system
parameters are:
@itemize @bullet
@item
@code{getdomainname}, @code{setdomainname}
@item
@code{gethostname}, @code{sethostname} (@xref{Host Identification}.)
@item
@code{uname} (@xref{Platform Type}.)
@item
@code{bdflush}
@end itemize
glibc-doc-reference-2.19.orig/manual/search.texi 0000664 0001750 0001750 00000066750 12275120646 021735 0 ustar adconrad adconrad @node Searching and Sorting, Pattern Matching, Message Translation, Top
@c %MENU% General searching and sorting functions
@chapter Searching and Sorting
This chapter describes functions for searching and sorting arrays of
arbitrary objects. You pass the appropriate comparison function to be
applied as an argument, along with the size of the objects in the array
and the total number of elements.
@menu
* Comparison Functions:: Defining how to compare two objects.
Since the sort and search facilities
are general, you have to specify the
ordering.
* Array Search Function:: The @code{bsearch} function.
* Array Sort Function:: The @code{qsort} function.
* Search/Sort Example:: An example program.
* Hash Search Function:: The @code{hsearch} function.
* Tree Search Function:: The @code{tsearch} function.
@end menu
@node Comparison Functions
@section Defining the Comparison Function
@cindex Comparison Function
In order to use the sorted array library functions, you have to describe
how to compare the elements of the array.
To do this, you supply a comparison function to compare two elements of
the array. The library will call this function, passing as arguments
pointers to two array elements to be compared. Your comparison function
should return a value the way @code{strcmp} (@pxref{String/Array
Comparison}) does: negative if the first argument is ``less'' than the
second, zero if they are ``equal'', and positive if the first argument
is ``greater''.
Here is an example of a comparison function which works with an array of
numbers of type @code{double}:
@smallexample
int
compare_doubles (const void *a, const void *b)
@{
const double *da = (const double *) a;
const double *db = (const double *) b;
return (*da > *db) - (*da < *db);
@}
@end smallexample
The header file @file{stdlib.h} defines a name for the data type of
comparison functions. This type is a GNU extension.
@comment stdlib.h
@comment GNU
@tindex comparison_fn_t
@smallexample
int comparison_fn_t (const void *, const void *);
@end smallexample
@node Array Search Function
@section Array Search Function
@cindex search function (for arrays)
@cindex binary search function (for arrays)
@cindex array search function
Generally searching for a specific element in an array means that
potentially all elements must be checked. @Theglibc{} contains
functions to perform linear search. The prototypes for the following
two functions can be found in @file{search.h}.
@comment search.h
@comment SVID
@deftypefun {void *} lfind (const void *@var{key}, const void *@var{base}, size_t *@var{nmemb}, size_t @var{size}, comparison_fn_t @var{compar})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{lfind} function searches in the array with @code{*@var{nmemb}}
elements of @var{size} bytes pointed to by @var{base} for an element
which matches the one pointed to by @var{key}. The function pointed to
by @var{compar} is used decide whether two elements match.
The return value is a pointer to the matching element in the array
starting at @var{base} if it is found. If no matching element is
available @code{NULL} is returned.
The mean runtime of this function is @code{*@var{nmemb}}/2. This
function should only be used if elements often get added to or deleted from
the array in which case it might not be useful to sort the array before
searching.
@end deftypefun
@comment search.h
@comment SVID
@deftypefun {void *} lsearch (const void *@var{key}, void *@var{base}, size_t *@var{nmemb}, size_t @var{size}, comparison_fn_t @var{compar})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c A signal handler that interrupted an insertion and performed an
@c insertion itself would leave the array in a corrupt state (e.g. one
@c new element initialized twice, with parts of both initializations
@c prevailing, and another uninitialized element), but this is just a
@c special case of races on user-controlled objects, that have to be
@c avoided by users.
@c In case of cancellation, we know the array won't be left in a corrupt
@c state; the new element is initialized before the element count is
@c incremented, and the compiler can't reorder these operations because
@c it can't know that they don't alias. So, we'll either cancel after
@c the increment and the initialization are both complete, or the
@c increment won't have taken place, and so how far the initialization
@c got doesn't matter.
The @code{lsearch} function is similar to the @code{lfind} function. It
searches the given array for an element and returns it if found. The
difference is that if no matching element is found the @code{lsearch}
function adds the object pointed to by @var{key} (with a size of
@var{size} bytes) at the end of the array and it increments the value of
@code{*@var{nmemb}} to reflect this addition.
This means for the caller that if it is not sure that the array contains
the element one is searching for the memory allocated for the array
starting at @var{base} must have room for at least @var{size} more
bytes. If one is sure the element is in the array it is better to use
@code{lfind} so having more room in the array is always necessary when
calling @code{lsearch}.
@end deftypefun
To search a sorted array for an element matching the key, use the
@code{bsearch} function. The prototype for this function is in
the header file @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment ISO
@deftypefun {void *} bsearch (const void *@var{key}, const void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{bsearch} function searches the sorted array @var{array} for an object
that is equivalent to @var{key}. The array contains @var{count} elements,
each of which is of size @var{size} bytes.
The @var{compare} function is used to perform the comparison. This
function is called with two pointer arguments and should return an
integer less than, equal to, or greater than zero corresponding to
whether its first argument is considered less than, equal to, or greater
than its second argument. The elements of the @var{array} must already
be sorted in ascending order according to this comparison function.
The return value is a pointer to the matching array element, or a null
pointer if no match is found. If the array contains more than one element
that matches, the one that is returned is unspecified.
This function derives its name from the fact that it is implemented
using the binary search algorithm.
@end deftypefun
@node Array Sort Function
@section Array Sort Function
@cindex sort function (for arrays)
@cindex quick sort function (for arrays)
@cindex array sort function
To sort an array using an arbitrary comparison function, use the
@code{qsort} function. The prototype for this function is in
@file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment ISO
@deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}}
The @var{qsort} function sorts the array @var{array}. The array contains
@var{count} elements, each of which is of size @var{size}.
The @var{compare} function is used to perform the comparison on the
array elements. This function is called with two pointer arguments and
should return an integer less than, equal to, or greater than zero
corresponding to whether its first argument is considered less than,
equal to, or greater than its second argument.
@cindex stable sorting
@strong{Warning:} If two objects compare as equal, their order after
sorting is unpredictable. That is to say, the sorting is not stable.
This can make a difference when the comparison considers only part of
the elements. Two elements with the same sort key may differ in other
respects.
If you want the effect of a stable sort, you can get this result by
writing the comparison function so that, lacking other reason
distinguish between two elements, it compares them by their addresses.
Note that doing this may make the sorting algorithm less efficient, so
do it only if necessary.
Here is a simple example of sorting an array of doubles in numerical
order, using the comparison function defined above (@pxref{Comparison
Functions}):
@smallexample
@{
double *array;
int size;
@dots{}
qsort (array, size, sizeof (double), compare_doubles);
@}
@end smallexample
The @code{qsort} function derives its name from the fact that it was
originally implemented using the ``quick sort'' algorithm.
The implementation of @code{qsort} in this library might not be an
in-place sort and might thereby use an extra amount of memory to store
the array.
@end deftypefun
@node Search/Sort Example
@section Searching and Sorting Example
Here is an example showing the use of @code{qsort} and @code{bsearch}
with an array of structures. The objects in the array are sorted
by comparing their @code{name} fields with the @code{strcmp} function.
Then, we can look up individual objects based on their names.
@comment This example is dedicated to the memory of Jim Henson. RIP.
@smallexample
@include search.c.texi
@end smallexample
@cindex Kermit the frog
The output from this program looks like:
@smallexample
Kermit, the frog
Piggy, the pig
Gonzo, the whatever
Fozzie, the bear
Sam, the eagle
Robin, the frog
Animal, the animal
Camilla, the chicken
Sweetums, the monster
Dr. Strangepork, the pig
Link Hogthrob, the pig
Zoot, the human
Dr. Bunsen Honeydew, the human
Beaker, the human
Swedish Chef, the human
Animal, the animal
Beaker, the human
Camilla, the chicken
Dr. Bunsen Honeydew, the human
Dr. Strangepork, the pig
Fozzie, the bear
Gonzo, the whatever
Kermit, the frog
Link Hogthrob, the pig
Piggy, the pig
Robin, the frog
Sam, the eagle
Swedish Chef, the human
Sweetums, the monster
Zoot, the human
Kermit, the frog
Gonzo, the whatever
Couldn't find Janice.
@end smallexample
@node Hash Search Function
@section The @code{hsearch} function.
The functions mentioned so far in this chapter are for searching in a sorted
or unsorted array. There are other methods to organize information
which later should be searched. The costs of insert, delete and search
differ. One possible implementation is using hashing tables.
The following functions are declared in the header file @file{search.h}.
@comment search.h
@comment SVID
@deftypefun int hcreate (size_t @var{nel})
@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c hcreate @mtasurace:hsearch @ascuheap @acucorrupt @acsmem
@c hcreate_r dup @mtsrace:htab @ascuheap @acucorrupt @acsmem
The @code{hcreate} function creates a hashing table which can contain at
least @var{nel} elements. There is no possibility to grow this table so
it is necessary to choose the value for @var{nel} wisely. The method
used to implement this function might make it necessary to make the
number of elements in the hashing table larger than the expected maximal
number of elements. Hashing tables usually work inefficiently if they are
filled 80% or more. The constant access time guaranteed by hashing can
only be achieved if few collisions exist. See Knuth's ``The Art of
Computer Programming, Part 3: Searching and Sorting'' for more
information.
The weakest aspect of this function is that there can be at most one
hashing table used through the whole program. The table is allocated
in local memory out of control of the programmer. As an extension @theglibc{}
provides an additional set of functions with a reentrant
interface which provide a similar interface but which allow to keep
arbitrarily many hashing tables.
It is possible to use more than one hashing table in the program run if
the former table is first destroyed by a call to @code{hdestroy}.
The function returns a non-zero value if successful. If it return zero
something went wrong. This could either mean there is already a hashing
table in use or the program runs out of memory.
@end deftypefun
@comment search.h
@comment SVID
@deftypefun void hdestroy (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c hdestroy @mtasurace:hsearch @ascuheap @acucorrupt @acsmem
@c hdestroy_r dup @mtsrace:htab @ascuheap @acucorrupt @acsmem
The @code{hdestroy} function can be used to free all the resources
allocated in a previous call of @code{hcreate}. After a call to this
function it is again possible to call @code{hcreate} and allocate a new
table with possibly different size.
It is important to remember that the elements contained in the hashing
table at the time @code{hdestroy} is called are @emph{not} freed by this
function. It is the responsibility of the program code to free those
strings (if necessary at all). Freeing all the element memory is not
possible without extra, separately kept information since there is no
function to iterate through all available elements in the hashing table.
If it is really necessary to free a table and all elements the
programmer has to keep a list of all table elements and before calling
@code{hdestroy} s/he has to free all element's data using this list.
This is a very unpleasant mechanism and it also shows that this kind of
hashing tables is mainly meant for tables which are created once and
used until the end of the program run.
@end deftypefun
Entries of the hashing table and keys for the search are defined using
this type:
@deftp {Data type} {struct ENTRY}
Both elements of this structure are pointers to zero-terminated strings.
This is a limiting restriction of the functionality of the
@code{hsearch} functions. They can only be used for data sets which use
the NUL character always and solely to terminate the records. It is not
possible to handle general binary data.
@table @code
@item char *key
Pointer to a zero-terminated string of characters describing the key for
the search or the element in the hashing table.
@item char *data
Pointer to a zero-terminated string of characters describing the data.
If the functions will be called only for searching an existing entry
this element might stay undefined since it is not used.
@end table
@end deftp
@comment search.h
@comment SVID
@deftypefun {ENTRY *} hsearch (ENTRY @var{item}, ACTION @var{action})
@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{}@acunsafe{@acucorrupt{/action==ENTER}}}
@c hsearch @mtasurace:hsearch @acucorrupt/action==ENTER
@c hsearch_r dup @mtsrace:htab @acucorrupt/action==ENTER
To search in a hashing table created using @code{hcreate} the
@code{hsearch} function must be used. This function can perform simple
search for an element (if @var{action} has the @code{FIND}) or it can
alternatively insert the key element into the hashing table. Entries
are never replaced.
The key is denoted by a pointer to an object of type @code{ENTRY}. For
locating the corresponding position in the hashing table only the
@code{key} element of the structure is used.
If an entry with matching key is found the @var{action} parameter is
irrelevant. The found entry is returned. If no matching entry is found
and the @var{action} parameter has the value @code{FIND} the function
returns a @code{NULL} pointer. If no entry is found and the
@var{action} parameter has the value @code{ENTER} a new entry is added
to the hashing table which is initialized with the parameter @var{item}.
A pointer to the newly added entry is returned.
@end deftypefun
As mentioned before the hashing table used by the functions described so
far is global and there can be at any time at most one hashing table in
the program. A solution is to use the following functions which are a
GNU extension. All have in common that they operate on a hashing table
which is described by the content of an object of the type @code{struct
hsearch_data}. This type should be treated as opaque, none of its
members should be changed directly.
@comment search.h
@comment GNU
@deftypefun int hcreate_r (size_t @var{nel}, struct hsearch_data *@var{htab})
@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c Unlike the lsearch array, the htab is (at least in part) opaque, so
@c let's make it absolutely clear that ensuring exclusive access is a
@c caller responsibility.
@c Cancellation is unlikely to leave the htab in a corrupt state: the
@c last field to be initialized is the one that tells whether the entire
@c data structure was initialized, and there's a function call (calloc)
@c in between that will often ensure all other fields are written before
@c the table. However, should this call be inlined (say with LTO), this
@c assumption may not hold. The calloc call doesn't cross our library
@c interface barrier, so let's consider this could happen and mark this
@c with @acucorrupt. It's no safety loss, since we already have
@c @ascuheap anyway...
@c hcreate_r @mtsrace:htab @ascuheap @acucorrupt @acsmem
@c isprime ok
@c calloc dup @ascuheap @acsmem
The @code{hcreate_r} function initializes the object pointed to by
@var{htab} to contain a hashing table with at least @var{nel} elements.
So this function is equivalent to the @code{hcreate} function except
that the initialized data structure is controlled by the user.
This allows having more than one hashing table at one time. The memory
necessary for the @code{struct hsearch_data} object can be allocated
dynamically. It must be initialized with zero before calling this
function.
The return value is non-zero if the operation was successful. If the
return value is zero, something went wrong, which probably means the
programs ran out of memory.
@end deftypefun
@comment search.h
@comment GNU
@deftypefun void hdestroy_r (struct hsearch_data *@var{htab})
@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c The table is released while the table pointer still points to it.
@c Async cancellation is thus unsafe, but it already was because we call
@c free(). Using the table in a handler while it's being released would
@c also be dangerous, but calling free() already makes it unsafe, and
@c the requirement on the caller to ensure exclusive access already
@c guarantees this doesn't happen, so we don't get @asucorrupt.
@c hdestroy_r @mtsrace:htab @ascuheap @acucorrupt @acsmem
@c free dup @ascuheap @acsmem
The @code{hdestroy_r} function frees all resources allocated by the
@code{hcreate_r} function for this very same object @var{htab}. As for
@code{hdestroy} it is the programs responsibility to free the strings
for the elements of the table.
@end deftypefun
@comment search.h
@comment GNU
@deftypefun int hsearch_r (ENTRY @var{item}, ACTION @var{action}, ENTRY **@var{retval}, struct hsearch_data *@var{htab})
@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@assafe{}@acunsafe{@acucorrupt{/action==ENTER}}}
@c Callers have to ensure mutual exclusion; insertion, if cancelled,
@c leaves the table in a corrupt state.
@c hsearch_r @mtsrace:htab @acucorrupt/action==ENTER
@c strlen dup ok
@c strcmp dup ok
The @code{hsearch_r} function is equivalent to @code{hsearch}. The
meaning of the first two arguments is identical. But instead of
operating on a single global hashing table the function works on the
table described by the object pointed to by @var{htab} (which is
initialized by a call to @code{hcreate_r}).
Another difference to @code{hcreate} is that the pointer to the found
entry in the table is not the return value of the functions. It is
returned by storing it in a pointer variables pointed to by the
@var{retval} parameter. The return value of the function is an integer
value indicating success if it is non-zero and failure if it is zero.
In the latter case the global variable @var{errno} signals the reason for
the failure.
@table @code
@item ENOMEM
The table is filled and @code{hsearch_r} was called with a so far
unknown key and @var{action} set to @code{ENTER}.
@item ESRCH
The @var{action} parameter is @code{FIND} and no corresponding element
is found in the table.
@end table
@end deftypefun
@node Tree Search Function
@section The @code{tsearch} function.
Another common form to organize data for efficient search is to use
trees. The @code{tsearch} function family provides a nice interface to
functions to organize possibly large amounts of data by providing a mean
access time proportional to the logarithm of the number of elements.
@Theglibc{} implementation even guarantees that this bound is
never exceeded even for input data which cause problems for simple
binary tree implementations.
The functions described in the chapter are all described in the @w{System
V} and X/Open specifications and are therefore quite portable.
In contrast to the @code{hsearch} functions the @code{tsearch} functions
can be used with arbitrary data and not only zero-terminated strings.
The @code{tsearch} functions have the advantage that no function to
initialize data structures is necessary. A simple pointer of type
@code{void *} initialized to @code{NULL} is a valid tree and can be
extended or searched. The prototypes for these functions can be found
in the header file @file{search.h}.
@comment search.h
@comment SVID
@deftypefun {void *} tsearch (const void *@var{key}, void **@var{rootp}, comparison_fn_t @var{compar})
@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c The tree is not modified in a thread-safe manner, and rotations may
@c leave the tree in an inconsistent state that could be observed in an
@c asynchronous signal handler (except for the caller-synchronization
@c requirement) or after asynchronous cancellation of the thread
@c performing the rotation or the insertion.
The @code{tsearch} function searches in the tree pointed to by
@code{*@var{rootp}} for an element matching @var{key}. The function
pointed to by @var{compar} is used to determine whether two elements
match. @xref{Comparison Functions}, for a specification of the functions
which can be used for the @var{compar} parameter.
If the tree does not contain a matching entry the @var{key} value will
be added to the tree. @code{tsearch} does not make a copy of the object
pointed to by @var{key} (how could it since the size is unknown).
Instead it adds a reference to this object which means the object must
be available as long as the tree data structure is used.
The tree is represented by a pointer to a pointer since it is sometimes
necessary to change the root node of the tree. So it must not be
assumed that the variable pointed to by @var{rootp} has the same value
after the call. This also shows that it is not safe to call the
@code{tsearch} function more than once at the same time using the same
tree. It is no problem to run it more than once at a time on different
trees.
The return value is a pointer to the matching element in the tree. If a
new element was created the pointer points to the new data (which is in
fact @var{key}). If an entry had to be created and the program ran out
of space @code{NULL} is returned.
@end deftypefun
@comment search.h
@comment SVID
@deftypefun {void *} tfind (const void *@var{key}, void *const *@var{rootp}, comparison_fn_t @var{compar})
@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@assafe{}@acsafe{}}
The @code{tfind} function is similar to the @code{tsearch} function. It
locates an element matching the one pointed to by @var{key} and returns
a pointer to this element. But if no matching element is available no
new element is entered (note that the @var{rootp} parameter points to a
constant pointer). Instead the function returns @code{NULL}.
@end deftypefun
Another advantage of the @code{tsearch} function in contrast to the
@code{hsearch} functions is that there is an easy way to remove
elements.
@comment search.h
@comment SVID
@deftypefun {void *} tdelete (const void *@var{key}, void **@var{rootp}, comparison_fn_t @var{compar})
@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
To remove a specific element matching @var{key} from the tree
@code{tdelete} can be used. It locates the matching element using the
same method as @code{tfind}. The corresponding element is then removed
and a pointer to the parent of the deleted node is returned by the
function. If there is no matching entry in the tree nothing can be
deleted and the function returns @code{NULL}. If the root of the tree
is deleted @code{tdelete} returns some unspecified value not equal to
@code{NULL}.
@end deftypefun
@comment search.h
@comment GNU
@deftypefun void tdestroy (void *@var{vroot}, __free_fn_t @var{freefct})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
If the complete search tree has to be removed one can use
@code{tdestroy}. It frees all resources allocated by the @code{tsearch}
function to generate the tree pointed to by @var{vroot}.
For the data in each tree node the function @var{freefct} is called.
The pointer to the data is passed as the argument to the function. If
no such work is necessary @var{freefct} must point to a function doing
nothing. It is called in any case.
This function is a GNU extension and not covered by the @w{System V} or
X/Open specifications.
@end deftypefun
In addition to the function to create and destroy the tree data
structure, there is another function which allows you to apply a
function to all elements of the tree. The function must have this type:
@smallexample
void __action_fn_t (const void *nodep, VISIT value, int level);
@end smallexample
The @var{nodep} is the data value of the current node (once given as the
@var{key} argument to @code{tsearch}). @var{level} is a numeric value
which corresponds to the depth of the current node in the tree. The
root node has the depth @math{0} and its children have a depth of
@math{1} and so on. The @code{VISIT} type is an enumeration type.
@deftp {Data Type} VISIT
The @code{VISIT} value indicates the status of the current node in the
tree and how the function is called. The status of a node is either
`leaf' or `internal node'. For each leaf node the function is called
exactly once, for each internal node it is called three times: before
the first child is processed, after the first child is processed and
after both children are processed. This makes it possible to handle all
three methods of tree traversal (or even a combination of them).
@table @code
@item preorder
The current node is an internal node and the function is called before
the first child was processed.
@item postorder
The current node is an internal node and the function is called after
the first child was processed.
@item endorder
The current node is an internal node and the function is called after
the second child was processed.
@item leaf
The current node is a leaf.
@end table
@end deftp
@comment search.h
@comment SVID
@deftypefun void twalk (const void *@var{root}, __action_fn_t @var{action})
@safety{@prelim{}@mtsafe{@mtsrace{:root}}@assafe{}@acsafe{}}
For each node in the tree with a node pointed to by @var{root}, the
@code{twalk} function calls the function provided by the parameter
@var{action}. For leaf nodes the function is called exactly once with
@var{value} set to @code{leaf}. For internal nodes the function is
called three times, setting the @var{value} parameter or @var{action} to
the appropriate value. The @var{level} argument for the @var{action}
function is computed while descending the tree with increasing the value
by one for the descend to a child, starting with the value @math{0} for
the root node.
Since the functions used for the @var{action} parameter to @code{twalk}
must not modify the tree data, it is safe to run @code{twalk} in more
than one thread at the same time, working on the same tree. It is also
safe to call @code{tfind} in parallel. Functions which modify the tree
must not be used, otherwise the behavior is undefined.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/setjmp.texi 0000664 0001750 0001750 00000053342 12275120646 021763 0 ustar adconrad adconrad @node Non-Local Exits, Signal Handling, Resource Usage And Limitation, Top
@c %MENU% Jumping out of nested function calls
@chapter Non-Local Exits
@cindex non-local exits
@cindex long jumps
Sometimes when your program detects an unusual situation inside a deeply
nested set of function calls, you would like to be able to immediately
return to an outer level of control. This section describes how you can
do such @dfn{non-local exits} using the @code{setjmp} and @code{longjmp}
functions.
@menu
* Intro: Non-Local Intro. When and how to use these facilities.
* Details: Non-Local Details. Functions for non-local exits.
* Non-Local Exits and Signals:: Portability issues.
* System V contexts:: Complete context control a la System V.
@end menu
@node Non-Local Intro, Non-Local Details, , Non-Local Exits
@section Introduction to Non-Local Exits
As an example of a situation where a non-local exit can be useful,
suppose you have an interactive program that has a ``main loop'' that
prompts for and executes commands. Suppose the ``read'' command reads
input from a file, doing some lexical analysis and parsing of the input
while processing it. If a low-level input error is detected, it would
be useful to be able to return immediately to the ``main loop'' instead
of having to make each of the lexical analysis, parsing, and processing
phases all have to explicitly deal with error situations initially
detected by nested calls.
(On the other hand, if each of these phases has to do a substantial
amount of cleanup when it exits---such as closing files, deallocating
buffers or other data structures, and the like---then it can be more
appropriate to do a normal return and have each phase do its own
cleanup, because a non-local exit would bypass the intervening phases and
their associated cleanup code entirely. Alternatively, you could use a
non-local exit but do the cleanup explicitly either before or after
returning to the ``main loop''.)
In some ways, a non-local exit is similar to using the @samp{return}
statement to return from a function. But while @samp{return} abandons
only a single function call, transferring control back to the point at
which it was called, a non-local exit can potentially abandon many
levels of nested function calls.
You identify return points for non-local exits by calling the function
@code{setjmp}. This function saves information about the execution
environment in which the call to @code{setjmp} appears in an object of
type @code{jmp_buf}. Execution of the program continues normally after
the call to @code{setjmp}, but if an exit is later made to this return
point by calling @code{longjmp} with the corresponding @w{@code{jmp_buf}}
object, control is transferred back to the point where @code{setjmp} was
called. The return value from @code{setjmp} is used to distinguish
between an ordinary return and a return made by a call to
@code{longjmp}, so calls to @code{setjmp} usually appear in an @samp{if}
statement.
Here is how the example program described above might be set up:
@smallexample
@include setjmp.c.texi
@end smallexample
The function @code{abort_to_main_loop} causes an immediate transfer of
control back to the main loop of the program, no matter where it is
called from.
The flow of control inside the @code{main} function may appear a little
mysterious at first, but it is actually a common idiom with
@code{setjmp}. A normal call to @code{setjmp} returns zero, so the
``else'' clause of the conditional is executed. If
@code{abort_to_main_loop} is called somewhere within the execution of
@code{do_command}, then it actually appears as if the @emph{same} call
to @code{setjmp} in @code{main} were returning a second time with a value
of @code{-1}.
@need 250
So, the general pattern for using @code{setjmp} looks something like:
@smallexample
if (setjmp (@var{buffer}))
/* @r{Code to clean up after premature return.} */
@dots{}
else
/* @r{Code to be executed normally after setting up the return point.} */
@dots{}
@end smallexample
@node Non-Local Details, Non-Local Exits and Signals, Non-Local Intro, Non-Local Exits
@section Details of Non-Local Exits
Here are the details on the functions and data structures used for
performing non-local exits. These facilities are declared in
@file{setjmp.h}.
@pindex setjmp.h
@comment setjmp.h
@comment ISO
@deftp {Data Type} jmp_buf
Objects of type @code{jmp_buf} hold the state information to
be restored by a non-local exit. The contents of a @code{jmp_buf}
identify a specific place to return to.
@end deftp
@comment setjmp.h
@comment ISO
@deftypefn Macro int setjmp (jmp_buf @var{state})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c _setjmp ok
@c __sigsetjmp(!savemask) ok
@c __sigjmp_save(!savemask) ok, does not call sigprocmask
When called normally, @code{setjmp} stores information about the
execution state of the program in @var{state} and returns zero. If
@code{longjmp} is later used to perform a non-local exit to this
@var{state}, @code{setjmp} returns a nonzero value.
@end deftypefn
@comment setjmp.h
@comment ISO
@deftypefun void longjmp (jmp_buf @var{state}, int @var{value})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{} @asucorrupt{} @asulock{/hurd}}@acunsafe{@acucorrupt{} @aculock{/hurd}}}
@c __libc_siglongjmp @ascuplugin @asucorrupt @asulock/hurd @acucorrupt @aculock/hurd
@c _longjmp_unwind @ascuplugin @asucorrupt @acucorrupt
@c __pthread_cleanup_upto @ascuplugin @asucorrupt @acucorrupt
@c plugins may be unsafe themselves, but even if they weren't, this
@c function isn't robust WRT async signals and cancellation:
@c cleanups aren't taken off the stack right away, only after all
@c cleanups have been run. This means that async-cancelling
@c longjmp, or interrupting longjmp with an async signal handler
@c that calls longjmp may run the same cleanups multiple times.
@c _JMPBUF_UNWINDS_ADJ ok
@c *cleanup_buf->__routine @ascuplugin
@c sigprocmask(SIG_SETMASK) dup @asulock/hurd @aculock/hurd
@c __longjmp ok
This function restores current execution to the state saved in
@var{state}, and continues execution from the call to @code{setjmp} that
established that return point. Returning from @code{setjmp} by means of
@code{longjmp} returns the @var{value} argument that was passed to
@code{longjmp}, rather than @code{0}. (But if @var{value} is given as
@code{0}, @code{setjmp} returns @code{1}).@refill
@end deftypefun
There are a lot of obscure but important restrictions on the use of
@code{setjmp} and @code{longjmp}. Most of these restrictions are
present because non-local exits require a fair amount of magic on the
part of the C compiler and can interact with other parts of the language
in strange ways.
The @code{setjmp} function is actually a macro without an actual
function definition, so you shouldn't try to @samp{#undef} it or take
its address. In addition, calls to @code{setjmp} are safe in only the
following contexts:
@itemize @bullet
@item
As the test expression of a selection or iteration
statement (such as @samp{if}, @samp{switch}, or @samp{while}).
@item
As one operand of an equality or comparison operator that appears as the
test expression of a selection or iteration statement. The other
operand must be an integer constant expression.
@item
As the operand of a unary @samp{!} operator, that appears as the
test expression of a selection or iteration statement.
@item
By itself as an expression statement.
@end itemize
Return points are valid only during the dynamic extent of the function
that called @code{setjmp} to establish them. If you @code{longjmp} to
a return point that was established in a function that has already
returned, unpredictable and disastrous things are likely to happen.
You should use a nonzero @var{value} argument to @code{longjmp}. While
@code{longjmp} refuses to pass back a zero argument as the return value
from @code{setjmp}, this is intended as a safety net against accidental
misuse and is not really good programming style.
When you perform a non-local exit, accessible objects generally retain
whatever values they had at the time @code{longjmp} was called. The
exception is that the values of automatic variables local to the
function containing the @code{setjmp} call that have been changed since
the call to @code{setjmp} are indeterminate, unless you have declared
them @code{volatile}.
@node Non-Local Exits and Signals, System V contexts, Non-Local Details, Non-Local Exits
@section Non-Local Exits and Signals
In BSD Unix systems, @code{setjmp} and @code{longjmp} also save and
restore the set of blocked signals; see @ref{Blocking Signals}. However,
the POSIX.1 standard requires @code{setjmp} and @code{longjmp} not to
change the set of blocked signals, and provides an additional pair of
functions (@code{sigsetjmp} and @code{siglongjmp}) to get the BSD
behavior.
The behavior of @code{setjmp} and @code{longjmp} in @theglibc{} is
controlled by feature test macros; see @ref{Feature Test Macros}. The
default in @theglibc{} is the POSIX.1 behavior rather than the BSD
behavior.
The facilities in this section are declared in the header file
@file{setjmp.h}.
@pindex setjmp.h
@comment setjmp.h
@comment POSIX.1
@deftp {Data Type} sigjmp_buf
This is similar to @code{jmp_buf}, except that it can also store state
information about the set of blocked signals.
@end deftp
@comment setjmp.h
@comment POSIX.1
@deftypefun int sigsetjmp (sigjmp_buf @var{state}, int @var{savesigs})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{/hurd}}@acunsafe{@aculock{/hurd}}}
@c sigsetjmp @asulock/hurd @aculock/hurd
@c __sigsetjmp(savemask) @asulock/hurd @aculock/hurd
@c __sigjmp_save(savemask) @asulock/hurd @aculock/hurd
@c sigprocmask(SIG_BLOCK probe) dup @asulock/hurd @aculock/hurd
This is similar to @code{setjmp}. If @var{savesigs} is nonzero, the set
of blocked signals is saved in @var{state} and will be restored if a
@code{siglongjmp} is later performed with this @var{state}.
@end deftypefun
@comment setjmp.h
@comment POSIX.1
@deftypefun void siglongjmp (sigjmp_buf @var{state}, int @var{value})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{} @asucorrupt{} @asulock{/hurd}}@acunsafe{@acucorrupt{} @aculock{/hurd}}}
@c Alias to longjmp.
This is similar to @code{longjmp} except for the type of its @var{state}
argument. If the @code{sigsetjmp} call that set this @var{state} used a
nonzero @var{savesigs} flag, @code{siglongjmp} also restores the set of
blocked signals.
@end deftypefun
@node System V contexts,, Non-Local Exits and Signals, Non-Local Exits
@section Complete Context Control
The Unix standard provides one more set of functions to control the
execution path and these functions are more powerful than those
discussed in this chapter so far. These function were part of the
original @w{System V} API and by this route were added to the Unix
API. Beside on branded Unix implementations these interfaces are not
widely available. Not all platforms and/or architectures @theglibc{}
is available on provide this interface. Use @file{configure} to
detect the availability.
Similar to the @code{jmp_buf} and @code{sigjmp_buf} types used for the
variables to contain the state of the @code{longjmp} functions the
interfaces of interest here have an appropriate type as well. Objects
of this type are normally much larger since more information is
contained. The type is also used in a few more places as we will see.
The types and functions described in this section are all defined and
declared respectively in the @file{ucontext.h} header file.
@comment ucontext.h
@comment SVID
@deftp {Data Type} ucontext_t
The @code{ucontext_t} type is defined as a structure with as least the
following elements:
@table @code
@item ucontext_t *uc_link
This is a pointer to the next context structure which is used if the
context described in the current structure returns.
@item sigset_t uc_sigmask
Set of signals which are blocked when this context is used.
@item stack_t uc_stack
Stack used for this context. The value need not be (and normally is
not) the stack pointer. @xref{Signal Stack}.
@item mcontext_t uc_mcontext
This element contains the actual state of the process. The
@code{mcontext_t} type is also defined in this header but the definition
should be treated as opaque. Any use of knowledge of the type makes
applications less portable.
@end table
@end deftp
Objects of this type have to be created by the user. The initialization
and modification happens through one of the following functions:
@comment ucontext.h
@comment SVID
@deftypefun int getcontext (ucontext_t *@var{ucp})
@safety{@prelim{}@mtsafe{@mtsrace{:ucp}}@assafe{}@acsafe{}}
@c Linux-only implementations in assembly, including sigprocmask
@c syscall. A few cases call the sigprocmask function, but that's safe
@c too. The ppc case is implemented in terms of a swapcontext syscall.
The @code{getcontext} function initializes the variable pointed to by
@var{ucp} with the context of the calling thread. The context contains
the content of the registers, the signal mask, and the current stack.
Executing the contents would start at the point where the
@code{getcontext} call just returned.
The function returns @code{0} if successful. Otherwise it returns
@code{-1} and sets @var{errno} accordingly.
@end deftypefun
The @code{getcontext} function is similar to @code{setjmp} but it does
not provide an indication of whether the function returns for the first
time or whether the initialized context was used and the execution is
resumed at just that point. If this is necessary the user has to take
determine this herself. This must be done carefully since the context
contains registers which might contain register variables. This is a
good situation to define variables with @code{volatile}.
Once the context variable is initialized it can be used as is or it can
be modified. The latter is normally done to implement co-routines or
similar constructs. The @code{makecontext} function is what has to be
used to do that.
@comment ucontext.h
@comment SVID
@deftypefun void makecontext (ucontext_t *@var{ucp}, void (*@var{func}) (void), int @var{argc}, @dots{})
@safety{@prelim{}@mtsafe{@mtsrace{:ucp}}@assafe{}@acsafe{}}
@c Linux-only implementations mostly in assembly, nothing unsafe.
The @var{ucp} parameter passed to the @code{makecontext} shall be
initialized by a call to @code{getcontext}. The context will be
modified to in a way so that if the context is resumed it will start by
calling the function @code{func} which gets @var{argc} integer arguments
passed. The integer arguments which are to be passed should follow the
@var{argc} parameter in the call to @code{makecontext}.
Before the call to this function the @code{uc_stack} and @code{uc_link}
element of the @var{ucp} structure should be initialized. The
@code{uc_stack} element describes the stack which is used for this
context. No two contexts which are used at the same time should use the
same memory region for a stack.
The @code{uc_link} element of the object pointed to by @var{ucp} should
be a pointer to the context to be executed when the function @var{func}
returns or it should be a null pointer. See @code{setcontext} for more
information about the exact use.
@end deftypefun
While allocating the memory for the stack one has to be careful. Most
modern processors keep track of whether a certain memory region is
allowed to contain code which is executed or not. Data segments and
heap memory is normally not tagged to allow this. The result is that
programs would fail. Examples for such code include the calling
sequences the GNU C compiler generates for calls to nested functions.
Safe ways to allocate stacks correctly include using memory on the
original threads stack or explicitly allocate memory tagged for
execution using (@pxref{Memory-mapped I/O}).
@strong{Compatibility note}: The current Unix standard is very imprecise
about the way the stack is allocated. All implementations seem to agree
that the @code{uc_stack} element must be used but the values stored in
the elements of the @code{stack_t} value are unclear. @Theglibc{}
and most other Unix implementations require the @code{ss_sp} value of
the @code{uc_stack} element to point to the base of the memory region
allocated for the stack and the size of the memory region is stored in
@code{ss_size}. There are implements out there which require
@code{ss_sp} to be set to the value the stack pointer will have (which
can depending on the direction the stack grows be different). This
difference makes the @code{makecontext} function hard to use and it
requires detection of the platform at compile time.
@comment ucontext.h
@comment SVID
@deftypefun int setcontext (const ucontext_t *@var{ucp})
@safety{@prelim{}@mtsafe{@mtsrace{:ucp}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c Linux-only implementations mostly in assembly. Some ports use
@c sigreturn or swapcontext syscalls; others restore the signal mask
@c first and then proceed restore other registers in userland, which
@c leaves a window for cancellation or async signals with misaligned or
@c otherwise corrupt stack. ??? Switching to a different stack, or even
@c to an earlier state on the same stack, may conflict with pthread
@c cleanups. This is not quite MT-Unsafe, it's a different kind of
@c safety issue.
The @code{setcontext} function restores the context described by
@var{ucp}. The context is not modified and can be reused as often as
wanted.
If the context was created by @code{getcontext} execution resumes with
the registers filled with the same values and the same stack as if the
@code{getcontext} call just returned.
If the context was modified with a call to @code{makecontext} execution
continues with the function passed to @code{makecontext} which gets the
specified parameters passed. If this function returns execution is
resumed in the context which was referenced by the @code{uc_link}
element of the context structure passed to @code{makecontext} at the
time of the call. If @code{uc_link} was a null pointer the application
terminates normally with an exit status value of @code{EXIT_SUCCESS}
(@pxref{Program Termination}).
Since the context contains information about the stack no two threads
should use the same context at the same time. The result in most cases
would be disastrous.
The @code{setcontext} function does not return unless an error occurred
in which case it returns @code{-1}.
@end deftypefun
The @code{setcontext} function simply replaces the current context with
the one described by the @var{ucp} parameter. This is often useful but
there are situations where the current context has to be preserved.
@comment ucontext.h
@comment SVID
@deftypefun int swapcontext (ucontext_t *restrict @var{oucp}, const ucontext_t *restrict @var{ucp})
@safety{@prelim{}@mtsafe{@mtsrace{:oucp} @mtsrace{:ucp}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c Linux-only implementations mostly in assembly. Some ports call or
@c inline getcontext and/or setcontext, adjusting the saved context in
@c between, so we inherit the potential issues of both.
The @code{swapcontext} function is similar to @code{setcontext} but
instead of just replacing the current context the latter is first saved
in the object pointed to by @var{oucp} as if this was a call to
@code{getcontext}. The saved context would resume after the call to
@code{swapcontext}.
Once the current context is saved the context described in @var{ucp} is
installed and execution continues as described in this context.
If @code{swapcontext} succeeds the function does not return unless the
context @var{oucp} is used without prior modification by
@code{makecontext}. The return value in this case is @code{0}. If the
function fails it returns @code{-1} and set @var{errno} accordingly.
@end deftypefun
@heading Example for SVID Context Handling
The easiest way to use the context handling functions is as a
replacement for @code{setjmp} and @code{longjmp}. The context contains
on most platforms more information which might lead to less surprises
but this also means using these functions is more expensive (beside
being less portable).
@smallexample
int
random_search (int n, int (*fp) (int, ucontext_t *))
@{
volatile int cnt = 0;
ucontext_t uc;
/* @r{Safe current context.} */
if (getcontext (&uc) < 0)
return -1;
/* @r{If we have not tried @var{n} times try again.} */
if (cnt++ < n)
/* @r{Call the function with a new random number}
@r{and the context}. */
if (fp (rand (), &uc) != 0)
/* @r{We found what we were looking for.} */
return 1;
/* @r{Not found.} */
return 0;
@}
@end smallexample
Using contexts in such a way enables emulating exception handling. The
search functions passed in the @var{fp} parameter could be very large,
nested, and complex which would make it complicated (or at least would
require a lot of code) to leave the function with an error value which
has to be passed down to the caller. By using the context it is
possible to leave the search function in one step and allow restarting
the search which also has the nice side effect that it can be
significantly faster.
Something which is harder to implement with @code{setjmp} and
@code{longjmp} is to switch temporarily to a different execution path
and then resume where execution was stopped.
@smallexample
@include swapcontext.c.texi
@end smallexample
This an example how the context functions can be used to implement
co-routines or cooperative multi-threading. All that has to be done is
to call every once in a while @code{swapcontext} to continue running a
different context. It is not allowed to do the context switching from
the signal handler directly since neither @code{setcontext} nor
@code{swapcontext} are functions which can be called from a signal
handler. But setting a variable in the signal handler and checking it
in the body of the functions which are executed. Since
@code{swapcontext} is saving the current context it is possible to have
multiple different scheduling points in the code. Execution will always
resume where it was left.
glibc-doc-reference-2.19.orig/manual/resource.texi 0000664 0001750 0001750 00000176007 12275120646 022314 0 ustar adconrad adconrad @node Resource Usage And Limitation, Non-Local Exits, Date and Time, Top
@c %MENU% Functions for examining resource usage and getting and setting limits
@chapter Resource Usage And Limitation
This chapter describes functions for examining how much of various kinds of
resources (CPU time, memory, etc.) a process has used and getting and setting
limits on future usage.
@menu
* Resource Usage:: Measuring various resources used.
* Limits on Resources:: Specifying limits on resource usage.
* Priority:: Reading or setting process run priority.
* Memory Resources:: Querying memory available resources.
* Processor Resources:: Learn about the processors available.
@end menu
@node Resource Usage
@section Resource Usage
@pindex sys/resource.h
The function @code{getrusage} and the data type @code{struct rusage}
are used to examine the resource usage of a process. They are declared
in @file{sys/resource.h}.
@comment sys/resource.h
@comment BSD
@deftypefun int getrusage (int @var{processes}, struct rusage *@var{rusage})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On HURD, this calls task_info 3 times. On UNIX, it's a syscall.
This function reports resource usage totals for processes specified by
@var{processes}, storing the information in @code{*@var{rusage}}.
In most systems, @var{processes} has only two valid values:
@table @code
@comment sys/resource.h
@comment BSD
@item RUSAGE_SELF
Just the current process.
@comment sys/resource.h
@comment BSD
@item RUSAGE_CHILDREN
All child processes (direct and indirect) that have already terminated.
@end table
The return value of @code{getrusage} is zero for success, and @code{-1}
for failure.
@table @code
@item EINVAL
The argument @var{processes} is not valid.
@end table
@end deftypefun
One way of getting resource usage for a particular child process is with
the function @code{wait4}, which returns totals for a child when it
terminates. @xref{BSD Wait Functions}.
@comment sys/resource.h
@comment BSD
@deftp {Data Type} {struct rusage}
This data type stores various resource usage statistics. It has the
following members, and possibly others:
@table @code
@item struct timeval ru_utime
Time spent executing user instructions.
@item struct timeval ru_stime
Time spent in operating system code on behalf of @var{processes}.
@item long int ru_maxrss
The maximum resident set size used, in kilobytes. That is, the maximum
number of kilobytes of physical memory that @var{processes} used
simultaneously.
@item long int ru_ixrss
An integral value expressed in kilobytes times ticks of execution, which
indicates the amount of memory used by text that was shared with other
processes.
@item long int ru_idrss
An integral value expressed the same way, which is the amount of
unshared memory used for data.
@item long int ru_isrss
An integral value expressed the same way, which is the amount of
unshared memory used for stack space.
@item long int ru_minflt
The number of page faults which were serviced without requiring any I/O.
@item long int ru_majflt
The number of page faults which were serviced by doing I/O.
@item long int ru_nswap
The number of times @var{processes} was swapped entirely out of main memory.
@item long int ru_inblock
The number of times the file system had to read from the disk on behalf
of @var{processes}.
@item long int ru_oublock
The number of times the file system had to write to the disk on behalf
of @var{processes}.
@item long int ru_msgsnd
Number of IPC messages sent.
@item long int ru_msgrcv
Number of IPC messages received.
@item long int ru_nsignals
Number of signals received.
@item long int ru_nvcsw
The number of times @var{processes} voluntarily invoked a context switch
(usually to wait for some service).
@item long int ru_nivcsw
The number of times an involuntary context switch took place (because
a time slice expired, or another process of higher priority was
scheduled).
@end table
@end deftp
@code{vtimes} is a historical function that does some of what
@code{getrusage} does. @code{getrusage} is a better choice.
@code{vtimes} and its @code{vtimes} data structure are declared in
@file{sys/vtimes.h}.
@pindex sys/vtimes.h
@comment sys/vtimes.h
@deftypefun int vtimes (struct vtimes *@var{current}, struct vtimes *@var{child})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Calls getrusage twice.
@code{vtimes} reports resource usage totals for a process.
If @var{current} is non-null, @code{vtimes} stores resource usage totals for
the invoking process alone in the structure to which it points. If
@var{child} is non-null, @code{vtimes} stores resource usage totals for all
past children (which have terminated) of the invoking process in the structure
to which it points.
@deftp {Data Type} {struct vtimes}
This data type contains information about the resource usage of a process.
Each member corresponds to a member of the @code{struct rusage} data type
described above.
@table @code
@item vm_utime
User CPU time. Analogous to @code{ru_utime} in @code{struct rusage}
@item vm_stime
System CPU time. Analogous to @code{ru_stime} in @code{struct rusage}
@item vm_idsrss
Data and stack memory. The sum of the values that would be reported as
@code{ru_idrss} and @code{ru_isrss} in @code{struct rusage}
@item vm_ixrss
Shared memory. Analogous to @code{ru_ixrss} in @code{struct rusage}
@item vm_maxrss
Maximent resident set size. Analogous to @code{ru_maxrss} in
@code{struct rusage}
@item vm_majflt
Major page faults. Analogous to @code{ru_majflt} in @code{struct rusage}
@item vm_minflt
Minor page faults. Analogous to @code{ru_minflt} in @code{struct rusage}
@item vm_nswap
Swap count. Analogous to @code{ru_nswap} in @code{struct rusage}
@item vm_inblk
Disk reads. Analogous to @code{ru_inblk} in @code{struct rusage}
@item vm_oublk
Disk writes. Analogous to @code{ru_oublk} in @code{struct rusage}
@end table
@end deftp
The return value is zero if the function succeeds; @code{-1} otherwise.
@end deftypefun
An additional historical function for examining resource usage,
@code{vtimes}, is supported but not documented here. It is declared in
@file{sys/vtimes.h}.
@node Limits on Resources
@section Limiting Resource Usage
@cindex resource limits
@cindex limits on resource usage
@cindex usage limits
You can specify limits for the resource usage of a process. When the
process tries to exceed a limit, it may get a signal, or the system call
by which it tried to do so may fail, depending on the resource. Each
process initially inherits its limit values from its parent, but it can
subsequently change them.
There are two per-process limits associated with a resource:
@cindex limit
@table @dfn
@item current limit
The current limit is the value the system will not allow usage to
exceed. It is also called the ``soft limit'' because the process being
limited can generally raise the current limit at will.
@cindex current limit
@cindex soft limit
@item maximum limit
The maximum limit is the maximum value to which a process is allowed to
set its current limit. It is also called the ``hard limit'' because
there is no way for a process to get around it. A process may lower
its own maximum limit, but only the superuser may increase a maximum
limit.
@cindex maximum limit
@cindex hard limit
@end table
@pindex sys/resource.h
The symbols for use with @code{getrlimit}, @code{setrlimit},
@code{getrlimit64}, and @code{setrlimit64} are defined in
@file{sys/resource.h}.
@comment sys/resource.h
@comment BSD
@deftypefun int getrlimit (int @var{resource}, struct rlimit *@var{rlp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on most systems.
Read the current and maximum limits for the resource @var{resource}
and store them in @code{*@var{rlp}}.
The return value is @code{0} on success and @code{-1} on failure. The
only possible @code{errno} error condition is @code{EFAULT}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{getrlimit64}. Thus, the
LFS interface transparently replaces the old interface.
@end deftypefun
@comment sys/resource.h
@comment Unix98
@deftypefun int getrlimit64 (int @var{resource}, struct rlimit64 *@var{rlp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on most systems, wrapper to getrlimit otherwise.
This function is similar to @code{getrlimit} but its second parameter is
a pointer to a variable of type @code{struct rlimit64}, which allows it
to read values which wouldn't fit in the member of a @code{struct
rlimit}.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit machine, this function is available under the name
@code{getrlimit} and so transparently replaces the old interface.
@end deftypefun
@comment sys/resource.h
@comment BSD
@deftypefun int setrlimit (int @var{resource}, const struct rlimit *@var{rlp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on most systems; lock-taking critical section on HURD.
Store the current and maximum limits for the resource @var{resource}
in @code{*@var{rlp}}.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error condition is possible:
@table @code
@item EPERM
@itemize @bullet
@item
The process tried to raise a current limit beyond the maximum limit.
@item
The process tried to raise a maximum limit, but is not superuser.
@end itemize
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{setrlimit64}. Thus, the
LFS interface transparently replaces the old interface.
@end deftypefun
@comment sys/resource.h
@comment Unix98
@deftypefun int setrlimit64 (int @var{resource}, const struct rlimit64 *@var{rlp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Wrapper for setrlimit or direct syscall.
This function is similar to @code{setrlimit} but its second parameter is
a pointer to a variable of type @code{struct rlimit64} which allows it
to set values which wouldn't fit in the member of a @code{struct
rlimit}.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit machine this function is available under the name
@code{setrlimit} and so transparently replaces the old interface.
@end deftypefun
@comment sys/resource.h
@comment BSD
@deftp {Data Type} {struct rlimit}
This structure is used with @code{getrlimit} to receive limit values,
and with @code{setrlimit} to specify limit values for a particular process
and resource. It has two fields:
@table @code
@item rlim_t rlim_cur
The current limit
@item rlim_t rlim_max
The maximum limit.
@end table
For @code{getrlimit}, the structure is an output; it receives the current
values. For @code{setrlimit}, it specifies the new values.
@end deftp
For the LFS functions a similar type is defined in @file{sys/resource.h}.
@comment sys/resource.h
@comment Unix98
@deftp {Data Type} {struct rlimit64}
This structure is analogous to the @code{rlimit} structure above, but
its components have wider ranges. It has two fields:
@table @code
@item rlim64_t rlim_cur
This is analogous to @code{rlimit.rlim_cur}, but with a different type.
@item rlim64_t rlim_max
This is analogous to @code{rlimit.rlim_max}, but with a different type.
@end table
@end deftp
Here is a list of resources for which you can specify a limit. Memory
and file sizes are measured in bytes.
@table @code
@comment sys/resource.h
@comment BSD
@item RLIMIT_CPU
@vindex RLIMIT_CPU
The maximum amount of CPU time the process can use. If it runs for
longer than this, it gets a signal: @code{SIGXCPU}. The value is
measured in seconds. @xref{Operation Error Signals}.
@comment sys/resource.h
@comment BSD
@item RLIMIT_FSIZE
@vindex RLIMIT_FSIZE
The maximum size of file the process can create. Trying to write a
larger file causes a signal: @code{SIGXFSZ}. @xref{Operation Error
Signals}.
@comment sys/resource.h
@comment BSD
@item RLIMIT_DATA
@vindex RLIMIT_DATA
The maximum size of data memory for the process. If the process tries
to allocate data memory beyond this amount, the allocation function
fails.
@comment sys/resource.h
@comment BSD
@item RLIMIT_STACK
@vindex RLIMIT_STACK
The maximum stack size for the process. If the process tries to extend
its stack past this size, it gets a @code{SIGSEGV} signal.
@xref{Program Error Signals}.
@comment sys/resource.h
@comment BSD
@item RLIMIT_CORE
@vindex RLIMIT_CORE
The maximum size core file that this process can create. If the process
terminates and would dump a core file larger than this, then no core
file is created. So setting this limit to zero prevents core files from
ever being created.
@comment sys/resource.h
@comment BSD
@item RLIMIT_RSS
@vindex RLIMIT_RSS
The maximum amount of physical memory that this process should get.
This parameter is a guide for the system's scheduler and memory
allocator; the system may give the process more memory when there is a
surplus.
@comment sys/resource.h
@comment BSD
@item RLIMIT_MEMLOCK
The maximum amount of memory that can be locked into physical memory (so
it will never be paged out).
@comment sys/resource.h
@comment BSD
@item RLIMIT_NPROC
The maximum number of processes that can be created with the same user ID.
If you have reached the limit for your user ID, @code{fork} will fail
with @code{EAGAIN}. @xref{Creating a Process}.
@comment sys/resource.h
@comment BSD
@item RLIMIT_NOFILE
@vindex RLIMIT_NOFILE
@itemx RLIMIT_OFILE
@vindex RLIMIT_OFILE
The maximum number of files that the process can open. If it tries to
open more files than this, its open attempt fails with @code{errno}
@code{EMFILE}. @xref{Error Codes}. Not all systems support this limit;
GNU does, and 4.4 BSD does.
@comment sys/resource.h
@comment Unix98
@item RLIMIT_AS
@vindex RLIMIT_AS
The maximum size of total memory that this process should get. If the
process tries to allocate more memory beyond this amount with, for
example, @code{brk}, @code{malloc}, @code{mmap} or @code{sbrk}, the
allocation function fails.
@comment sys/resource.h
@comment BSD
@item RLIM_NLIMITS
@vindex RLIM_NLIMITS
The number of different resource limits. Any valid @var{resource}
operand must be less than @code{RLIM_NLIMITS}.
@end table
@comment sys/resource.h
@comment BSD
@deftypevr Constant rlim_t RLIM_INFINITY
This constant stands for a value of ``infinity'' when supplied as
the limit value in @code{setrlimit}.
@end deftypevr
The following are historical functions to do some of what the functions
above do. The functions above are better choices.
@code{ulimit} and the command symbols are declared in @file{ulimit.h}.
@pindex ulimit.h
@comment ulimit.h
@comment BSD
@deftypefun {long int} ulimit (int @var{cmd}, @dots{})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Wrapper for getrlimit, setrlimit or
@c sysconf(_SC_OPEN_MAX)->getdtablesize->getrlimit.
@code{ulimit} gets the current limit or sets the current and maximum
limit for a particular resource for the calling process according to the
command @var{cmd}.a
If you are getting a limit, the command argument is the only argument.
If you are setting a limit, there is a second argument:
@code{long int} @var{limit} which is the value to which you are setting
the limit.
The @var{cmd} values and the operations they specify are:
@table @code
@item GETFSIZE
Get the current limit on the size of a file, in units of 512 bytes.
@item SETFSIZE
Set the current and maximum limit on the size of a file to @var{limit} *
512 bytes.
@end table
There are also some other @var{cmd} values that may do things on some
systems, but they are not supported.
Only the superuser may increase a maximum limit.
When you successfully get a limit, the return value of @code{ulimit} is
that limit, which is never negative. When you successfully set a limit,
the return value is zero. When the function fails, the return value is
@code{-1} and @code{errno} is set according to the reason:
@table @code
@item EPERM
A process tried to increase a maximum limit, but is not superuser.
@end table
@end deftypefun
@code{vlimit} and its resource symbols are declared in @file{sys/vlimit.h}.
@pindex sys/vlimit.h
@comment sys/vlimit.h
@comment BSD
@deftypefun int vlimit (int @var{resource}, int @var{limit})
@safety{@prelim{}@mtunsafe{@mtasurace{:setrlimit}}@asunsafe{}@acsafe{}}
@c It calls getrlimit and modifies the rlim_cur field before calling
@c setrlimit. There's a window for a concurrent call to setrlimit that
@c modifies e.g. rlim_max, which will be lost if running as super-user.
@code{vlimit} sets the current limit for a resource for a process.
@var{resource} identifies the resource:
@table @code
@item LIM_CPU
Maximum CPU time. Same as @code{RLIMIT_CPU} for @code{setrlimit}.
@item LIM_FSIZE
Maximum file size. Same as @code{RLIMIT_FSIZE} for @code{setrlimit}.
@item LIM_DATA
Maximum data memory. Same as @code{RLIMIT_DATA} for @code{setrlimit}.
@item LIM_STACK
Maximum stack size. Same as @code{RLIMIT_STACK} for @code{setrlimit}.
@item LIM_CORE
Maximum core file size. Same as @code{RLIMIT_COR} for @code{setrlimit}.
@item LIM_MAXRSS
Maximum physical memory. Same as @code{RLIMIT_RSS} for @code{setrlimit}.
@end table
The return value is zero for success, and @code{-1} with @code{errno} set
accordingly for failure:
@table @code
@item EPERM
The process tried to set its current limit beyond its maximum limit.
@end table
@end deftypefun
@node Priority
@section Process CPU Priority And Scheduling
@cindex process priority
@cindex cpu priority
@cindex priority of a process
When multiple processes simultaneously require CPU time, the system's
scheduling policy and process CPU priorities determine which processes
get it. This section describes how that determination is made and
@glibcadj{} functions to control it.
It is common to refer to CPU scheduling simply as scheduling and a
process' CPU priority simply as the process' priority, with the CPU
resource being implied. Bear in mind, though, that CPU time is not the
only resource a process uses or that processes contend for. In some
cases, it is not even particularly important. Giving a process a high
``priority'' may have very little effect on how fast a process runs with
respect to other processes. The priorities discussed in this section
apply only to CPU time.
CPU scheduling is a complex issue and different systems do it in wildly
different ways. New ideas continually develop and find their way into
the intricacies of the various systems' scheduling algorithms. This
section discusses the general concepts, some specifics of systems
that commonly use @theglibc{}, and some standards.
For simplicity, we talk about CPU contention as if there is only one CPU
in the system. But all the same principles apply when a processor has
multiple CPUs, and knowing that the number of processes that can run at
any one time is equal to the number of CPUs, you can easily extrapolate
the information.
The functions described in this section are all defined by the POSIX.1
and POSIX.1b standards (the @code{sched@dots{}} functions are POSIX.1b).
However, POSIX does not define any semantics for the values that these
functions get and set. In this chapter, the semantics are based on the
Linux kernel's implementation of the POSIX standard. As you will see,
the Linux implementation is quite the inverse of what the authors of the
POSIX syntax had in mind.
@menu
* Absolute Priority:: The first tier of priority. Posix
* Realtime Scheduling:: Scheduling among the process nobility
* Basic Scheduling Functions:: Get/set scheduling policy, priority
* Traditional Scheduling:: Scheduling among the vulgar masses
* CPU Affinity:: Limiting execution to certain CPUs
@end menu
@node Absolute Priority
@subsection Absolute Priority
@cindex absolute priority
@cindex priority, absolute
Every process has an absolute priority, and it is represented by a number.
The higher the number, the higher the absolute priority.
@cindex realtime CPU scheduling
On systems of the past, and most systems today, all processes have
absolute priority 0 and this section is irrelevant. In that case,
@xref{Traditional Scheduling}. Absolute priorities were invented to
accommodate realtime systems, in which it is vital that certain processes
be able to respond to external events happening in real time, which
means they cannot wait around while some other process that @emph{wants
to}, but doesn't @emph{need to} run occupies the CPU.
@cindex ready to run
@cindex preemptive scheduling
When two processes are in contention to use the CPU at any instant, the
one with the higher absolute priority always gets it. This is true even if the
process with the lower priority is already using the CPU (i.e., the
scheduling is preemptive). Of course, we're only talking about
processes that are running or ``ready to run,'' which means they are
ready to execute instructions right now. When a process blocks to wait
for something like I/O, its absolute priority is irrelevant.
@cindex runnable process
@strong{NB:} The term ``runnable'' is a synonym for ``ready to run.''
When two processes are running or ready to run and both have the same
absolute priority, it's more interesting. In that case, who gets the
CPU is determined by the scheduling policy. If the processes have
absolute priority 0, the traditional scheduling policy described in
@ref{Traditional Scheduling} applies. Otherwise, the policies described
in @ref{Realtime Scheduling} apply.
You normally give an absolute priority above 0 only to a process that
can be trusted not to hog the CPU. Such processes are designed to block
(or terminate) after relatively short CPU runs.
A process begins life with the same absolute priority as its parent
process. Functions described in @ref{Basic Scheduling Functions} can
change it.
Only a privileged process can change a process' absolute priority to
something other than @code{0}. Only a privileged process or the
target process' owner can change its absolute priority at all.
POSIX requires absolute priority values used with the realtime
scheduling policies to be consecutive with a range of at least 32. On
Linux, they are 1 through 99. The functions
@code{sched_get_priority_max} and @code{sched_set_priority_min} portably
tell you what the range is on a particular system.
@subsubsection Using Absolute Priority
One thing you must keep in mind when designing real time applications is
that having higher absolute priority than any other process doesn't
guarantee the process can run continuously. Two things that can wreck a
good CPU run are interrupts and page faults.
Interrupt handlers live in that limbo between processes. The CPU is
executing instructions, but they aren't part of any process. An
interrupt will stop even the highest priority process. So you must
allow for slight delays and make sure that no device in the system has
an interrupt handler that could cause too long a delay between
instructions for your process.
Similarly, a page fault causes what looks like a straightforward
sequence of instructions to take a long time. The fact that other
processes get to run while the page faults in is of no consequence,
because as soon as the I/O is complete, the high priority process will
kick them out and run again, but the wait for the I/O itself could be a
problem. To neutralize this threat, use @code{mlock} or
@code{mlockall}.
There are a few ramifications of the absoluteness of this priority on a
single-CPU system that you need to keep in mind when you choose to set a
priority and also when you're working on a program that runs with high
absolute priority. Consider a process that has higher absolute priority
than any other process in the system and due to a bug in its program, it
gets into an infinite loop. It will never cede the CPU. You can't run
a command to kill it because your command would need to get the CPU in
order to run. The errant program is in complete control. It controls
the vertical, it controls the horizontal.
There are two ways to avoid this: 1) keep a shell running somewhere with
a higher absolute priority. 2) keep a controlling terminal attached to
the high priority process group. All the priority in the world won't
stop an interrupt handler from running and delivering a signal to the
process if you hit Control-C.
Some systems use absolute priority as a means of allocating a fixed
percentage of CPU time to a process. To do this, a super high priority
privileged process constantly monitors the process' CPU usage and raises
its absolute priority when the process isn't getting its entitled share
and lowers it when the process is exceeding it.
@strong{NB:} The absolute priority is sometimes called the ``static
priority.'' We don't use that term in this manual because it misses the
most important feature of the absolute priority: its absoluteness.
@node Realtime Scheduling
@subsection Realtime Scheduling
@cindex realtime scheduling
Whenever two processes with the same absolute priority are ready to run,
the kernel has a decision to make, because only one can run at a time.
If the processes have absolute priority 0, the kernel makes this decision
as described in @ref{Traditional Scheduling}. Otherwise, the decision
is as described in this section.
If two processes are ready to run but have different absolute priorities,
the decision is much simpler, and is described in @ref{Absolute
Priority}.
Each process has a scheduling policy. For processes with absolute
priority other than zero, there are two available:
@enumerate
@item
First Come First Served
@item
Round Robin
@end enumerate
The most sensible case is where all the processes with a certain
absolute priority have the same scheduling policy. We'll discuss that
first.
In Round Robin, processes share the CPU, each one running for a small
quantum of time (``time slice'') and then yielding to another in a
circular fashion. Of course, only processes that are ready to run and
have the same absolute priority are in this circle.
In First Come First Served, the process that has been waiting the
longest to run gets the CPU, and it keeps it until it voluntarily
relinquishes the CPU, runs out of things to do (blocks), or gets
preempted by a higher priority process.
First Come First Served, along with maximal absolute priority and
careful control of interrupts and page faults, is the one to use when a
process absolutely, positively has to run at full CPU speed or not at
all.
Judicious use of @code{sched_yield} function invocations by processes
with First Come First Served scheduling policy forms a good compromise
between Round Robin and First Come First Served.
To understand how scheduling works when processes of different scheduling
policies occupy the same absolute priority, you have to know the nitty
gritty details of how processes enter and exit the ready to run list:
In both cases, the ready to run list is organized as a true queue, where
a process gets pushed onto the tail when it becomes ready to run and is
popped off the head when the scheduler decides to run it. Note that
ready to run and running are two mutually exclusive states. When the
scheduler runs a process, that process is no longer ready to run and no
longer in the ready to run list. When the process stops running, it
may go back to being ready to run again.
The only difference between a process that is assigned the Round Robin
scheduling policy and a process that is assigned First Come First Serve
is that in the former case, the process is automatically booted off the
CPU after a certain amount of time. When that happens, the process goes
back to being ready to run, which means it enters the queue at the tail.
The time quantum we're talking about is small. Really small. This is
not your father's timesharing. For example, with the Linux kernel, the
round robin time slice is a thousand times shorter than its typical
time slice for traditional scheduling.
A process begins life with the same scheduling policy as its parent process.
Functions described in @ref{Basic Scheduling Functions} can change it.
Only a privileged process can set the scheduling policy of a process
that has absolute priority higher than 0.
@node Basic Scheduling Functions
@subsection Basic Scheduling Functions
This section describes functions in @theglibc{} for setting the
absolute priority and scheduling policy of a process.
@strong{Portability Note:} On systems that have the functions in this
section, the macro _POSIX_PRIORITY_SCHEDULING is defined in
@file{}.
For the case that the scheduling policy is traditional scheduling, more
functions to fine tune the scheduling are in @ref{Traditional Scheduling}.
Don't try to make too much out of the naming and structure of these
functions. They don't match the concepts described in this manual
because the functions are as defined by POSIX.1b, but the implementation
on systems that use @theglibc{} is the inverse of what the POSIX
structure contemplates. The POSIX scheme assumes that the primary
scheduling parameter is the scheduling policy and that the priority
value, if any, is a parameter of the scheduling policy. In the
implementation, though, the priority value is king and the scheduling
policy, if anything, only fine tunes the effect of that priority.
The symbols in this section are declared by including file @file{sched.h}.
@comment sched.h
@comment POSIX
@deftp {Data Type} {struct sched_param}
This structure describes an absolute priority.
@table @code
@item int sched_priority
absolute priority value
@end table
@end deftp
@comment sched.h
@comment POSIX
@deftypefun int sched_setscheduler (pid_t @var{pid}, int @var{policy}, const struct sched_param *@var{param})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function sets both the absolute priority and the scheduling policy
for a process.
It assigns the absolute priority value given by @var{param} and the
scheduling policy @var{policy} to the process with Process ID @var{pid},
or the calling process if @var{pid} is zero. If @var{policy} is
negative, @code{sched_setscheduler} keeps the existing scheduling policy.
The following macros represent the valid values for @var{policy}:
@table @code
@item SCHED_OTHER
Traditional Scheduling
@item SCHED_FIFO
First In First Out
@item SCHED_RR
Round Robin
@end table
@c The Linux kernel code (in sched.c) actually reschedules the process,
@c but it puts it at the head of the run queue, so I'm not sure just what
@c the effect is, but it must be subtle.
On success, the return value is @code{0}. Otherwise, it is @code{-1}
and @code{ERRNO} is set accordingly. The @code{errno} values specific
to this function are:
@table @code
@item EPERM
@itemize @bullet
@item
The calling process does not have @code{CAP_SYS_NICE} permission and
@var{policy} is not @code{SCHED_OTHER} (or it's negative and the
existing policy is not @code{SCHED_OTHER}.
@item
The calling process does not have @code{CAP_SYS_NICE} permission and its
owner is not the target process' owner. I.e., the effective uid of the
calling process is neither the effective nor the real uid of process
@var{pid}.
@c We need a cross reference to the capabilities section, when written.
@end itemize
@item ESRCH
There is no process with pid @var{pid} and @var{pid} is not zero.
@item EINVAL
@itemize @bullet
@item
@var{policy} does not identify an existing scheduling policy.
@item
The absolute priority value identified by *@var{param} is outside the
valid range for the scheduling policy @var{policy} (or the existing
scheduling policy if @var{policy} is negative) or @var{param} is
null. @code{sched_get_priority_max} and @code{sched_get_priority_min}
tell you what the valid range is.
@item
@var{pid} is negative.
@end itemize
@end table
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_getscheduler (pid_t @var{pid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function returns the scheduling policy assigned to the process with
Process ID (pid) @var{pid}, or the calling process if @var{pid} is zero.
The return value is the scheduling policy. See
@code{sched_setscheduler} for the possible values.
If the function fails, the return value is instead @code{-1} and
@code{errno} is set accordingly.
The @code{errno} values specific to this function are:
@table @code
@item ESRCH
There is no process with pid @var{pid} and it is not zero.
@item EINVAL
@var{pid} is negative.
@end table
Note that this function is not an exact mate to @code{sched_setscheduler}
because while that function sets the scheduling policy and the absolute
priority, this function gets only the scheduling policy. To get the
absolute priority, use @code{sched_getparam}.
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_setparam (pid_t @var{pid}, const struct sched_param *@var{param})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function sets a process' absolute priority.
It is functionally identical to @code{sched_setscheduler} with
@var{policy} = @code{-1}.
@c in fact, that's how it's implemented in Linux.
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_getparam (pid_t @var{pid}, struct sched_param *@var{param})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function returns a process' absolute priority.
@var{pid} is the Process ID (pid) of the process whose absolute priority
you want to know.
@var{param} is a pointer to a structure in which the function stores the
absolute priority of the process.
On success, the return value is @code{0}. Otherwise, it is @code{-1}
and @code{ERRNO} is set accordingly. The @code{errno} values specific
to this function are:
@table @code
@item ESRCH
There is no process with pid @var{pid} and it is not zero.
@item EINVAL
@var{pid} is negative.
@end table
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_get_priority_min (int @var{policy})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function returns the lowest absolute priority value that is
allowable for a process with scheduling policy @var{policy}.
On Linux, it is 0 for SCHED_OTHER and 1 for everything else.
On success, the return value is @code{0}. Otherwise, it is @code{-1}
and @code{ERRNO} is set accordingly. The @code{errno} values specific
to this function are:
@table @code
@item EINVAL
@var{policy} does not identify an existing scheduling policy.
@end table
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_get_priority_max (int @var{policy})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function returns the highest absolute priority value that is
allowable for a process that with scheduling policy @var{policy}.
On Linux, it is 0 for SCHED_OTHER and 99 for everything else.
On success, the return value is @code{0}. Otherwise, it is @code{-1}
and @code{ERRNO} is set accordingly. The @code{errno} values specific
to this function are:
@table @code
@item EINVAL
@var{policy} does not identify an existing scheduling policy.
@end table
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_rr_get_interval (pid_t @var{pid}, struct timespec *@var{interval})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, Linux only.
This function returns the length of the quantum (time slice) used with
the Round Robin scheduling policy, if it is used, for the process with
Process ID @var{pid}.
It returns the length of time as @var{interval}.
@c We need a cross-reference to where timespec is explained. But that
@c section doesn't exist yet, and the time chapter needs to be slightly
@c reorganized so there is a place to put it (which will be right next
@c to timeval, which is presently misplaced). 2000.05.07.
With a Linux kernel, the round robin time slice is always 150
microseconds, and @var{pid} need not even be a real pid.
The return value is @code{0} on success and in the pathological case
that it fails, the return value is @code{-1} and @code{errno} is set
accordingly. There is nothing specific that can go wrong with this
function, so there are no specific @code{errno} values.
@end deftypefun
@comment sched.h
@comment POSIX
@deftypefun int sched_yield (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on Linux; alias to swtch on HURD.
This function voluntarily gives up the process' claim on the CPU.
Technically, @code{sched_yield} causes the calling process to be made
immediately ready to run (as opposed to running, which is what it was
before). This means that if it has absolute priority higher than 0, it
gets pushed onto the tail of the queue of processes that share its
absolute priority and are ready to run, and it will run again when its
turn next arrives. If its absolute priority is 0, it is more
complicated, but still has the effect of yielding the CPU to other
processes.
If there are no other processes that share the calling process' absolute
priority, this function doesn't have any effect.
To the extent that the containing program is oblivious to what other
processes in the system are doing and how fast it executes, this
function appears as a no-op.
The return value is @code{0} on success and in the pathological case
that it fails, the return value is @code{-1} and @code{errno} is set
accordingly. There is nothing specific that can go wrong with this
function, so there are no specific @code{errno} values.
@end deftypefun
@node Traditional Scheduling
@subsection Traditional Scheduling
@cindex scheduling, traditional
This section is about the scheduling among processes whose absolute
priority is 0. When the system hands out the scraps of CPU time that
are left over after the processes with higher absolute priority have
taken all they want, the scheduling described herein determines who
among the great unwashed processes gets them.
@menu
* Traditional Scheduling Intro::
* Traditional Scheduling Functions::
@end menu
@node Traditional Scheduling Intro
@subsubsection Introduction To Traditional Scheduling
Long before there was absolute priority (See @ref{Absolute Priority}),
Unix systems were scheduling the CPU using this system. When Posix came
in like the Romans and imposed absolute priorities to accommodate the
needs of realtime processing, it left the indigenous Absolute Priority
Zero processes to govern themselves by their own familiar scheduling
policy.
Indeed, absolute priorities higher than zero are not available on many
systems today and are not typically used when they are, being intended
mainly for computers that do realtime processing. So this section
describes the only scheduling many programmers need to be concerned
about.
But just to be clear about the scope of this scheduling: Any time a
process with an absolute priority of 0 and a process with an absolute
priority higher than 0 are ready to run at the same time, the one with
absolute priority 0 does not run. If it's already running when the
higher priority ready-to-run process comes into existence, it stops
immediately.
In addition to its absolute priority of zero, every process has another
priority, which we will refer to as "dynamic priority" because it changes
over time. The dynamic priority is meaningless for processes with
an absolute priority higher than zero.
The dynamic priority sometimes determines who gets the next turn on the
CPU. Sometimes it determines how long turns last. Sometimes it
determines whether a process can kick another off the CPU.
In Linux, the value is a combination of these things, but mostly it is
just determines the length of the time slice. The higher a process'
dynamic priority, the longer a shot it gets on the CPU when it gets one.
If it doesn't use up its time slice before giving up the CPU to do
something like wait for I/O, it is favored for getting the CPU back when
it's ready for it, to finish out its time slice. Other than that,
selection of processes for new time slices is basically round robin.
But the scheduler does throw a bone to the low priority processes: A
process' dynamic priority rises every time it is snubbed in the
scheduling process. In Linux, even the fat kid gets to play.
The fluctuation of a process' dynamic priority is regulated by another
value: The ``nice'' value. The nice value is an integer, usually in the
range -20 to 20, and represents an upper limit on a process' dynamic
priority. The higher the nice number, the lower that limit.
On a typical Linux system, for example, a process with a nice value of
20 can get only 10 milliseconds on the CPU at a time, whereas a process
with a nice value of -20 can achieve a high enough priority to get 400
milliseconds.
The idea of the nice value is deferential courtesy. In the beginning,
in the Unix garden of Eden, all processes shared equally in the bounty
of the computer system. But not all processes really need the same
share of CPU time, so the nice value gave a courteous process the
ability to refuse its equal share of CPU time that others might prosper.
Hence, the higher a process' nice value, the nicer the process is.
(Then a snake came along and offered some process a negative nice value
and the system became the crass resource allocation system we know
today).
Dynamic priorities tend upward and downward with an objective of
smoothing out allocation of CPU time and giving quick response time to
infrequent requests. But they never exceed their nice limits, so on a
heavily loaded CPU, the nice value effectively determines how fast a
process runs.
In keeping with the socialistic heritage of Unix process priority, a
process begins life with the same nice value as its parent process and
can raise it at will. A process can also raise the nice value of any
other process owned by the same user (or effective user). But only a
privileged process can lower its nice value. A privileged process can
also raise or lower another process' nice value.
@glibcadj{} functions for getting and setting nice values are described in
@xref{Traditional Scheduling Functions}.
@node Traditional Scheduling Functions
@subsubsection Functions For Traditional Scheduling
@pindex sys/resource.h
This section describes how you can read and set the nice value of a
process. All these symbols are declared in @file{sys/resource.h}.
The function and macro names are defined by POSIX, and refer to
"priority," but the functions actually have to do with nice values, as
the terms are used both in the manual and POSIX.
The range of valid nice values depends on the kernel, but typically it
runs from @code{-20} to @code{20}. A lower nice value corresponds to
higher priority for the process. These constants describe the range of
priority values:
@vtable @code
@comment sys/resource.h
@comment BSD
@item PRIO_MIN
The lowest valid nice value.
@comment sys/resource.h
@comment BSD
@item PRIO_MAX
The highest valid nice value.
@end vtable
@comment sys/resource.h
@comment BSD,POSIX
@deftypefun int getpriority (int @var{class}, int @var{id})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on UNIX. On HURD, calls _hurd_priority_which_map.
Return the nice value of a set of processes; @var{class} and @var{id}
specify which ones (see below). If the processes specified do not all
have the same nice value, this returns the lowest value that any of them
has.
On success, the return value is @code{0}. Otherwise, it is @code{-1}
and @code{ERRNO} is set accordingly. The @code{errno} values specific
to this function are:
@table @code
@item ESRCH
The combination of @var{class} and @var{id} does not match any existing
process.
@item EINVAL
The value of @var{class} is not valid.
@end table
If the return value is @code{-1}, it could indicate failure, or it could
be the nice value. The only way to make certain is to set @code{errno =
0} before calling @code{getpriority}, then use @code{errno != 0}
afterward as the criterion for failure.
@end deftypefun
@comment sys/resource.h
@comment BSD,POSIX
@deftypefun int setpriority (int @var{class}, int @var{id}, int @var{niceval})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall on UNIX. On HURD, calls _hurd_priority_which_map.
Set the nice value of a set of processes to @var{niceval}; @var{class}
and @var{id} specify which ones (see below).
The return value is @code{0} on success, and @code{-1} on
failure. The following @code{errno} error condition are possible for
this function:
@table @code
@item ESRCH
The combination of @var{class} and @var{id} does not match any existing
process.
@item EINVAL
The value of @var{class} is not valid.
@item EPERM
The call would set the nice value of a process which is owned by a different
user than the calling process (i.e., the target process' real or effective
uid does not match the calling process' effective uid) and the calling
process does not have @code{CAP_SYS_NICE} permission.
@item EACCES
The call would lower the process' nice value and the process does not have
@code{CAP_SYS_NICE} permission.
@end table
@end deftypefun
The arguments @var{class} and @var{id} together specify a set of
processes in which you are interested. These are the possible values of
@var{class}:
@vtable @code
@comment sys/resource.h
@comment BSD
@item PRIO_PROCESS
One particular process. The argument @var{id} is a process ID (pid).
@comment sys/resource.h
@comment BSD
@item PRIO_PGRP
All the processes in a particular process group. The argument @var{id} is
a process group ID (pgid).
@comment sys/resource.h
@comment BSD
@item PRIO_USER
All the processes owned by a particular user (i.e., whose real uid
indicates the user). The argument @var{id} is a user ID (uid).
@end vtable
If the argument @var{id} is 0, it stands for the calling process, its
process group, or its owner (real uid), according to @var{class}.
@comment unistd.h
@comment BSD
@deftypefun int nice (int @var{increment})
@safety{@prelim{}@mtunsafe{@mtasurace{:setpriority}}@asunsafe{}@acsafe{}}
@c Calls getpriority before and after setpriority, using the result of
@c the first call to compute the argument for setpriority. This creates
@c a window for a concurrent setpriority (or nice) call to be lost or
@c exhibit surprising behavior.
Increment the nice value of the calling process by @var{increment}.
The return value is the new nice value on success, and @code{-1} on
failure. In the case of failure, @code{errno} will be set to the
same values as for @code{setpriority}.
Here is an equivalent definition of @code{nice}:
@smallexample
int
nice (int increment)
@{
int result, old = getpriority (PRIO_PROCESS, 0);
result = setpriority (PRIO_PROCESS, 0, old + increment);
if (result != -1)
return old + increment;
else
return -1;
@}
@end smallexample
@end deftypefun
@node CPU Affinity
@subsection Limiting execution to certain CPUs
On a multi-processor system the operating system usually distributes
the different processes which are runnable on all available CPUs in a
way which allows the system to work most efficiently. Which processes
and threads run can be to some extend be control with the scheduling
functionality described in the last sections. But which CPU finally
executes which process or thread is not covered.
There are a number of reasons why a program might want to have control
over this aspect of the system as well:
@itemize @bullet
@item
One thread or process is responsible for absolutely critical work
which under no circumstances must be interrupted or hindered from
making process by other process or threads using CPU resources. In
this case the special process would be confined to a CPU which no
other process or thread is allowed to use.
@item
The access to certain resources (RAM, I/O ports) has different costs
from different CPUs. This is the case in NUMA (Non-Uniform Memory
Architecture) machines. Preferably memory should be accessed locally
but this requirement is usually not visible to the scheduler.
Therefore forcing a process or thread to the CPUs which have local
access to the mostly used memory helps to significantly boost the
performance.
@item
In controlled runtimes resource allocation and book-keeping work (for
instance garbage collection) is performance local to processors. This
can help to reduce locking costs if the resources do not have to be
protected from concurrent accesses from different processors.
@end itemize
The POSIX standard up to this date is of not much help to solve this
problem. The Linux kernel provides a set of interfaces to allow
specifying @emph{affinity sets} for a process. The scheduler will
schedule the thread or process on CPUs specified by the affinity
masks. The interfaces which @theglibc{} define follow to some
extend the Linux kernel interface.
@comment sched.h
@comment GNU
@deftp {Data Type} cpu_set_t
This data set is a bitset where each bit represents a CPU. How the
system's CPUs are mapped to bits in the bitset is system dependent.
The data type has a fixed size; in the unlikely case that the number
of bits are not sufficient to describe the CPUs of the system a
different interface has to be used.
This type is a GNU extension and is defined in @file{sched.h}.
@end deftp
To manipulate the bitset, to set and reset bits, a number of macros is
defined. Some of the macros take a CPU number as a parameter. Here
it is important to never exceed the size of the bitset. The following
macro specifies the number of bits in the @code{cpu_set_t} bitset.
@comment sched.h
@comment GNU
@deftypevr Macro int CPU_SETSIZE
The value of this macro is the maximum number of CPUs which can be
handled with a @code{cpu_set_t} object.
@end deftypevr
The type @code{cpu_set_t} should be considered opaque; all
manipulation should happen via the next four macros.
@comment sched.h
@comment GNU
@deftypefn Macro void CPU_ZERO (cpu_set_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c CPU_ZERO ok
@c __CPU_ZERO_S ok
@c memset dup ok
This macro initializes the CPU set @var{set} to be the empty set.
This macro is a GNU extension and is defined in @file{sched.h}.
@end deftypefn
@comment sched.h
@comment GNU
@deftypefn Macro void CPU_SET (int @var{cpu}, cpu_set_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c CPU_SET ok
@c __CPU_SET_S ok
@c __CPUELT ok
@c __CPUMASK ok
This macro adds @var{cpu} to the CPU set @var{set}.
The @var{cpu} parameter must not have side effects since it is
evaluated more than once.
This macro is a GNU extension and is defined in @file{sched.h}.
@end deftypefn
@comment sched.h
@comment GNU
@deftypefn Macro void CPU_CLR (int @var{cpu}, cpu_set_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c CPU_CLR ok
@c __CPU_CLR_S ok
@c __CPUELT dup ok
@c __CPUMASK dup ok
This macro removes @var{cpu} from the CPU set @var{set}.
The @var{cpu} parameter must not have side effects since it is
evaluated more than once.
This macro is a GNU extension and is defined in @file{sched.h}.
@end deftypefn
@comment sched.h
@comment GNU
@deftypefn Macro int CPU_ISSET (int @var{cpu}, const cpu_set_t *@var{set})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c CPU_ISSET ok
@c __CPU_ISSET_S ok
@c __CPUELT dup ok
@c __CPUMASK dup ok
This macro returns a nonzero value (true) if @var{cpu} is a member
of the CPU set @var{set}, and zero (false) otherwise.
The @var{cpu} parameter must not have side effects since it is
evaluated more than once.
This macro is a GNU extension and is defined in @file{sched.h}.
@end deftypefn
CPU bitsets can be constructed from scratch or the currently installed
affinity mask can be retrieved from the system.
@comment sched.h
@comment GNU
@deftypefun int sched_getaffinity (pid_t @var{pid}, size_t @var{cpusetsize}, cpu_set_t *@var{cpuset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Wrapped syscall to zero out past the kernel cpu set size; Linux
@c only.
This functions stores the CPU affinity mask for the process or thread
with the ID @var{pid} in the @var{cpusetsize} bytes long bitmap
pointed to by @var{cpuset}. If successful, the function always
initializes all bits in the @code{cpu_set_t} object and returns zero.
If @var{pid} does not correspond to a process or thread on the system
the or the function fails for some other reason, it returns @code{-1}
and @code{errno} is set to represent the error condition.
@table @code
@item ESRCH
No process or thread with the given ID found.
@item EFAULT
The pointer @var{cpuset} is does not point to a valid object.
@end table
This function is a GNU extension and is declared in @file{sched.h}.
@end deftypefun
Note that it is not portably possible to use this information to
retrieve the information for different POSIX threads. A separate
interface must be provided for that.
@comment sched.h
@comment GNU
@deftypefun int sched_setaffinity (pid_t @var{pid}, size_t @var{cpusetsize}, const cpu_set_t *@var{cpuset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Wrapped syscall to detect attempts to set bits past the kernel cpu
@c set size; Linux only.
This function installs the @var{cpusetsize} bytes long affinity mask
pointed to by @var{cpuset} for the process or thread with the ID @var{pid}.
If successful the function returns zero and the scheduler will in future
take the affinity information into account.
If the function fails it will return @code{-1} and @code{errno} is set
to the error code:
@table @code
@item ESRCH
No process or thread with the given ID found.
@item EFAULT
The pointer @var{cpuset} is does not point to a valid object.
@item EINVAL
The bitset is not valid. This might mean that the affinity set might
not leave a processor for the process or thread to run on.
@end table
This function is a GNU extension and is declared in @file{sched.h}.
@end deftypefun
@node Memory Resources
@section Querying memory available resources
The amount of memory available in the system and the way it is organized
determines oftentimes the way programs can and have to work. For
functions like @code{mmap} it is necessary to know about the size of
individual memory pages and knowing how much memory is available enables
a program to select appropriate sizes for, say, caches. Before we get
into these details a few words about memory subsystems in traditional
Unix systems will be given.
@menu
* Memory Subsystem:: Overview about traditional Unix memory handling.
* Query Memory Parameters:: How to get information about the memory
subsystem?
@end menu
@node Memory Subsystem
@subsection Overview about traditional Unix memory handling
@cindex address space
@cindex physical memory
@cindex physical address
Unix systems normally provide processes virtual address spaces. This
means that the addresses of the memory regions do not have to correspond
directly to the addresses of the actual physical memory which stores the
data. An extra level of indirection is introduced which translates
virtual addresses into physical addresses. This is normally done by the
hardware of the processor.
@cindex shared memory
Using a virtual address space has several advantage. The most important
is process isolation. The different processes running on the system
cannot interfere directly with each other. No process can write into
the address space of another process (except when shared memory is used
but then it is wanted and controlled).
Another advantage of virtual memory is that the address space the
processes see can actually be larger than the physical memory available.
The physical memory can be extended by storage on an external media
where the content of currently unused memory regions is stored. The
address translation can then intercept accesses to these memory regions
and make memory content available again by loading the data back into
memory. This concept makes it necessary that programs which have to use
lots of memory know the difference between available virtual address
space and available physical memory. If the working set of virtual
memory of all the processes is larger than the available physical memory
the system will slow down dramatically due to constant swapping of
memory content from the memory to the storage media and back. This is
called ``thrashing''.
@cindex thrashing
@cindex memory page
@cindex page, memory
A final aspect of virtual memory which is important and follows from
what is said in the last paragraph is the granularity of the virtual
address space handling. When we said that the virtual address handling
stores memory content externally it cannot do this on a byte-by-byte
basis. The administrative overhead does not allow this (leaving alone
the processor hardware). Instead several thousand bytes are handled
together and form a @dfn{page}. The size of each page is always a power
of two byte. The smallest page size in use today is 4096, with 8192,
16384, and 65536 being other popular sizes.
@node Query Memory Parameters
@subsection How to get information about the memory subsystem?
The page size of the virtual memory the process sees is essential to
know in several situations. Some programming interface (e.g.,
@code{mmap}, @pxref{Memory-mapped I/O}) require the user to provide
information adjusted to the page size. In the case of @code{mmap} is it
necessary to provide a length argument which is a multiple of the page
size. Another place where the knowledge about the page size is useful
is in memory allocation. If one allocates pieces of memory in larger
chunks which are then subdivided by the application code it is useful to
adjust the size of the larger blocks to the page size. If the total
memory requirement for the block is close (but not larger) to a multiple
of the page size the kernel's memory handling can work more effectively
since it only has to allocate memory pages which are fully used. (To do
this optimization it is necessary to know a bit about the memory
allocator which will require a bit of memory itself for each block and
this overhead must not push the total size over the page size multiple.
The page size traditionally was a compile time constant. But recent
development of processors changed this. Processors now support
different page sizes and they can possibly even vary among different
processes on the same system. Therefore the system should be queried at
runtime about the current page size and no assumptions (except about it
being a power of two) should be made.
@vindex _SC_PAGESIZE
The correct interface to query about the page size is @code{sysconf}
(@pxref{Sysconf Definition}) with the parameter @code{_SC_PAGESIZE}.
There is a much older interface available, too.
@comment unistd.h
@comment BSD
@deftypefun int getpagesize (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Obtained from the aux vec at program startup time. GNU/Linux/m68k is
@c the exception, with the possibility of a syscall.
The @code{getpagesize} function returns the page size of the process.
This value is fixed for the runtime of the process but can vary in
different runs of the application.
The function is declared in @file{unistd.h}.
@end deftypefun
Widely available on @w{System V} derived systems is a method to get
information about the physical memory the system has. The call
@vindex _SC_PHYS_PAGES
@cindex sysconf
@smallexample
sysconf (_SC_PHYS_PAGES)
@end smallexample
@noindent
returns the total number of pages of physical the system has.
This does not mean all this memory is available. This information can
be found using
@vindex _SC_AVPHYS_PAGES
@cindex sysconf
@smallexample
sysconf (_SC_AVPHYS_PAGES)
@end smallexample
These two values help to optimize applications. The value returned for
@code{_SC_AVPHYS_PAGES} is the amount of memory the application can use
without hindering any other process (given that no other process
increases its memory usage). The value returned for
@code{_SC_PHYS_PAGES} is more or less a hard limit for the working set.
If all applications together constantly use more than that amount of
memory the system is in trouble.
@Theglibc{} provides in addition to these already described way to
get this information two functions. They are declared in the file
@file{sys/sysinfo.h}. Programmers should prefer to use the
@code{sysconf} method described above.
@comment sys/sysinfo.h
@comment GNU
@deftypefun {long int} get_phys_pages (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c This fopens a /proc file and scans it for the requested information.
The @code{get_phys_pages} function returns the total number of pages of
physical the system has. To get the amount of memory this number has to
be multiplied by the page size.
This function is a GNU extension.
@end deftypefun
@comment sys/sysinfo.h
@comment GNU
@deftypefun {long int} get_avphys_pages (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
The @code{get_phys_pages} function returns the number of available pages of
physical the system has. To get the amount of memory this number has to
be multiplied by the page size.
This function is a GNU extension.
@end deftypefun
@node Processor Resources
@section Learn about the processors available
The use of threads or processes with shared memory allows an application
to take advantage of all the processing power a system can provide. If
the task can be parallelized the optimal way to write an application is
to have at any time as many processes running as there are processors.
To determine the number of processors available to the system one can
run
@vindex _SC_NPROCESSORS_CONF
@cindex sysconf
@smallexample
sysconf (_SC_NPROCESSORS_CONF)
@end smallexample
@noindent
which returns the number of processors the operating system configured.
But it might be possible for the operating system to disable individual
processors and so the call
@vindex _SC_NPROCESSORS_ONLN
@cindex sysconf
@smallexample
sysconf (_SC_NPROCESSORS_ONLN)
@end smallexample
@noindent
returns the number of processors which are currently online (i.e.,
available).
For these two pieces of information @theglibc{} also provides
functions to get the information directly. The functions are declared
in @file{sys/sysinfo.h}.
@comment sys/sysinfo.h
@comment GNU
@deftypefun int get_nprocs_conf (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c This function reads from from /sys using dir streams (single user, so
@c no @mtasurace issue), and on some arches, from /proc using streams.
The @code{get_nprocs_conf} function returns the number of processors the
operating system configured.
This function is a GNU extension.
@end deftypefun
@comment sys/sysinfo.h
@comment GNU
@deftypefun int get_nprocs (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
@c This function reads from /proc using file descriptor I/O.
The @code{get_nprocs} function returns the number of available processors.
This function is a GNU extension.
@end deftypefun
@cindex load average
Before starting more threads it should be checked whether the processors
are not already overused. Unix systems calculate something called the
@dfn{load average}. This is a number indicating how many processes were
running. This number is average over different periods of times
(normally 1, 5, and 15 minutes).
@comment stdlib.h
@comment BSD
@deftypefun int getloadavg (double @var{loadavg}[], int @var{nelem})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
@c Calls host_info on HURD; on Linux, opens /proc/loadavg, reads from
@c it, closes it, without cancellation point, and calls strtod_l with
@c the C locale to convert the strings to doubles.
This function gets the 1, 5 and 15 minute load averages of the
system. The values are placed in @var{loadavg}. @code{getloadavg} will
place at most @var{nelem} elements into the array but never more than
three elements. The return value is the number of elements written to
@var{loadavg}, or -1 on error.
This function is declared in @file{stdlib.h}.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/pattern.texi 0000664 0001750 0001750 00000264112 12275120646 022135 0 ustar adconrad adconrad @node Pattern Matching, I/O Overview, Searching and Sorting, Top
@c %MENU% Matching shell ``globs'' and regular expressions
@chapter Pattern Matching
@Theglibc{} provides pattern matching facilities for two kinds of
patterns: regular expressions and file-name wildcards. The library also
provides a facility for expanding variable and command references and
parsing text into words in the way the shell does.
@menu
* Wildcard Matching:: Matching a wildcard pattern against a single string.
* Globbing:: Finding the files that match a wildcard pattern.
* Regular Expressions:: Matching regular expressions against strings.
* Word Expansion:: Expanding shell variables, nested commands,
arithmetic, and wildcards.
This is what the shell does with shell commands.
@end menu
@node Wildcard Matching
@section Wildcard Matching
@pindex fnmatch.h
This section describes how to match a wildcard pattern against a
particular string. The result is a yes or no answer: does the
string fit the pattern or not. The symbols described here are all
declared in @file{fnmatch.h}.
@comment fnmatch.h
@comment POSIX.2
@deftypefun int fnmatch (const char *@var{pattern}, const char *@var{string}, int @var{flags})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c fnmatch @mtsenv @mtslocale @ascuheap @acsmem
@c strnlen dup ok
@c mbsrtowcs
@c memset dup ok
@c malloc dup @ascuheap @acsmem
@c mbsinit dup ok
@c free dup @ascuheap @acsmem
@c FCT = internal_fnwmatch @mtsenv @mtslocale @ascuheap @acsmem
@c FOLD @mtslocale
@c towlower @mtslocale
@c EXT @mtsenv @mtslocale @ascuheap @acsmem
@c STRLEN = wcslen dup ok
@c getenv @mtsenv
@c malloc dup @ascuheap @acsmem
@c MEMPCPY = wmempcpy dup ok
@c FCT dup @mtsenv @mtslocale @ascuheap @acsmem
@c STRCAT = wcscat dup ok
@c free dup @ascuheap @acsmem
@c END @mtsenv
@c getenv @mtsenv
@c MEMCHR = wmemchr dup ok
@c getenv @mtsenv
@c IS_CHAR_CLASS = is_char_class @mtslocale
@c wctype @mtslocale
@c BTOWC ok
@c ISWCTYPE ok
@c auto findidx dup ok
@c elem_hash dup ok
@c memcmp dup ok
@c collseq_table_lookup dup ok
@c NO_LEADING_PERIOD ok
This function tests whether the string @var{string} matches the pattern
@var{pattern}. It returns @code{0} if they do match; otherwise, it
returns the nonzero value @code{FNM_NOMATCH}. The arguments
@var{pattern} and @var{string} are both strings.
The argument @var{flags} is a combination of flag bits that alter the
details of matching. See below for a list of the defined flags.
In @theglibc{}, @code{fnmatch} might sometimes report ``errors'' by
returning nonzero values that are not equal to @code{FNM_NOMATCH}.
@end deftypefun
These are the available flags for the @var{flags} argument:
@table @code
@comment fnmatch.h
@comment GNU
@item FNM_FILE_NAME
Treat the @samp{/} character specially, for matching file names. If
this flag is set, wildcard constructs in @var{pattern} cannot match
@samp{/} in @var{string}. Thus, the only way to match @samp{/} is with
an explicit @samp{/} in @var{pattern}.
@comment fnmatch.h
@comment POSIX.2
@item FNM_PATHNAME
This is an alias for @code{FNM_FILE_NAME}; it comes from POSIX.2. We
don't recommend this name because we don't use the term ``pathname'' for
file names.
@comment fnmatch.h
@comment POSIX.2
@item FNM_PERIOD
Treat the @samp{.} character specially if it appears at the beginning of
@var{string}. If this flag is set, wildcard constructs in @var{pattern}
cannot match @samp{.} as the first character of @var{string}.
If you set both @code{FNM_PERIOD} and @code{FNM_FILE_NAME}, then the
special treatment applies to @samp{.} following @samp{/} as well as to
@samp{.} at the beginning of @var{string}. (The shell uses the
@code{FNM_PERIOD} and @code{FNM_FILE_NAME} flags together for matching
file names.)
@comment fnmatch.h
@comment POSIX.2
@item FNM_NOESCAPE
Don't treat the @samp{\} character specially in patterns. Normally,
@samp{\} quotes the following character, turning off its special meaning
(if any) so that it matches only itself. When quoting is enabled, the
pattern @samp{\?} matches only the string @samp{?}, because the question
mark in the pattern acts like an ordinary character.
If you use @code{FNM_NOESCAPE}, then @samp{\} is an ordinary character.
@comment fnmatch.h
@comment GNU
@item FNM_LEADING_DIR
Ignore a trailing sequence of characters starting with a @samp{/} in
@var{string}; that is to say, test whether @var{string} starts with a
directory name that @var{pattern} matches.
If this flag is set, either @samp{foo*} or @samp{foobar} as a pattern
would match the string @samp{foobar/frobozz}.
@comment fnmatch.h
@comment GNU
@item FNM_CASEFOLD
Ignore case in comparing @var{string} to @var{pattern}.
@comment fnmatch.h
@comment GNU
@item FNM_EXTMATCH
@cindex Korn Shell
@pindex ksh
Recognize beside the normal patterns also the extended patterns
introduced in @file{ksh}. The patterns are written in the form
explained in the following table where @var{pattern-list} is a @code{|}
separated list of patterns.
@table @code
@item ?(@var{pattern-list})
The pattern matches if zero or one occurrences of any of the patterns
in the @var{pattern-list} allow matching the input string.
@item *(@var{pattern-list})
The pattern matches if zero or more occurrences of any of the patterns
in the @var{pattern-list} allow matching the input string.
@item +(@var{pattern-list})
The pattern matches if one or more occurrences of any of the patterns
in the @var{pattern-list} allow matching the input string.
@item @@(@var{pattern-list})
The pattern matches if exactly one occurrence of any of the patterns in
the @var{pattern-list} allows matching the input string.
@item !(@var{pattern-list})
The pattern matches if the input string cannot be matched with any of
the patterns in the @var{pattern-list}.
@end table
@end table
@node Globbing
@section Globbing
@cindex globbing
The archetypal use of wildcards is for matching against the files in a
directory, and making a list of all the matches. This is called
@dfn{globbing}.
You could do this using @code{fnmatch}, by reading the directory entries
one by one and testing each one with @code{fnmatch}. But that would be
slow (and complex, since you would have to handle subdirectories by
hand).
The library provides a function @code{glob} to make this particular use
of wildcards convenient. @code{glob} and the other symbols in this
section are declared in @file{glob.h}.
@menu
* Calling Glob:: Basic use of @code{glob}.
* Flags for Globbing:: Flags that enable various options in @code{glob}.
* More Flags for Globbing:: GNU specific extensions to @code{glob}.
@end menu
@node Calling Glob
@subsection Calling @code{glob}
The result of globbing is a vector of file names (strings). To return
this vector, @code{glob} uses a special data type, @code{glob_t}, which
is a structure. You pass @code{glob} the address of the structure, and
it fills in the structure's fields to tell you about the results.
@comment glob.h
@comment POSIX.2
@deftp {Data Type} glob_t
This data type holds a pointer to a word vector. More precisely, it
records both the address of the word vector and its size. The GNU
implementation contains some more fields which are non-standard
extensions.
@table @code
@item gl_pathc
The number of elements in the vector, excluding the initial null entries
if the GLOB_DOOFFS flag is used (see gl_offs below).
@item gl_pathv
The address of the vector. This field has type @w{@code{char **}}.
@item gl_offs
The offset of the first real element of the vector, from its nominal
address in the @code{gl_pathv} field. Unlike the other fields, this
is always an input to @code{glob}, rather than an output from it.
If you use a nonzero offset, then that many elements at the beginning of
the vector are left empty. (The @code{glob} function fills them with
null pointers.)
The @code{gl_offs} field is meaningful only if you use the
@code{GLOB_DOOFFS} flag. Otherwise, the offset is always zero
regardless of what is in this field, and the first real element comes at
the beginning of the vector.
@item gl_closedir
The address of an alternative implementation of the @code{closedir}
function. It is used if the @code{GLOB_ALTDIRFUNC} bit is set in
the flag parameter. The type of this field is
@w{@code{void (*) (void *)}}.
This is a GNU extension.
@item gl_readdir
The address of an alternative implementation of the @code{readdir}
function used to read the contents of a directory. It is used if the
@code{GLOB_ALTDIRFUNC} bit is set in the flag parameter. The type of
this field is @w{@code{struct dirent *(*) (void *)}}.
This is a GNU extension.
@item gl_opendir
The address of an alternative implementation of the @code{opendir}
function. It is used if the @code{GLOB_ALTDIRFUNC} bit is set in
the flag parameter. The type of this field is
@w{@code{void *(*) (const char *)}}.
This is a GNU extension.
@item gl_stat
The address of an alternative implementation of the @code{stat} function
to get information about an object in the filesystem. It is used if the
@code{GLOB_ALTDIRFUNC} bit is set in the flag parameter. The type of
this field is @w{@code{int (*) (const char *, struct stat *)}}.
This is a GNU extension.
@item gl_lstat
The address of an alternative implementation of the @code{lstat}
function to get information about an object in the filesystems, not
following symbolic links. It is used if the @code{GLOB_ALTDIRFUNC} bit
is set in the flag parameter. The type of this field is @code{@w{int
(*) (const char *,} @w{struct stat *)}}.
This is a GNU extension.
@item gl_flags
The flags used when @code{glob} was called. In addition, @code{GLOB_MAGCHAR}
might be set. See @ref{Flags for Globbing} for more details.
This is a GNU extension.
@end table
@end deftp
For use in the @code{glob64} function @file{glob.h} contains another
definition for a very similar type. @code{glob64_t} differs from
@code{glob_t} only in the types of the members @code{gl_readdir},
@code{gl_stat}, and @code{gl_lstat}.
@comment glob.h
@comment GNU
@deftp {Data Type} glob64_t
This data type holds a pointer to a word vector. More precisely, it
records both the address of the word vector and its size. The GNU
implementation contains some more fields which are non-standard
extensions.
@table @code
@item gl_pathc
The number of elements in the vector, excluding the initial null entries
if the GLOB_DOOFFS flag is used (see gl_offs below).
@item gl_pathv
The address of the vector. This field has type @w{@code{char **}}.
@item gl_offs
The offset of the first real element of the vector, from its nominal
address in the @code{gl_pathv} field. Unlike the other fields, this
is always an input to @code{glob}, rather than an output from it.
If you use a nonzero offset, then that many elements at the beginning of
the vector are left empty. (The @code{glob} function fills them with
null pointers.)
The @code{gl_offs} field is meaningful only if you use the
@code{GLOB_DOOFFS} flag. Otherwise, the offset is always zero
regardless of what is in this field, and the first real element comes at
the beginning of the vector.
@item gl_closedir
The address of an alternative implementation of the @code{closedir}
function. It is used if the @code{GLOB_ALTDIRFUNC} bit is set in
the flag parameter. The type of this field is
@w{@code{void (*) (void *)}}.
This is a GNU extension.
@item gl_readdir
The address of an alternative implementation of the @code{readdir64}
function used to read the contents of a directory. It is used if the
@code{GLOB_ALTDIRFUNC} bit is set in the flag parameter. The type of
this field is @w{@code{struct dirent64 *(*) (void *)}}.
This is a GNU extension.
@item gl_opendir
The address of an alternative implementation of the @code{opendir}
function. It is used if the @code{GLOB_ALTDIRFUNC} bit is set in
the flag parameter. The type of this field is
@w{@code{void *(*) (const char *)}}.
This is a GNU extension.
@item gl_stat
The address of an alternative implementation of the @code{stat64} function
to get information about an object in the filesystem. It is used if the
@code{GLOB_ALTDIRFUNC} bit is set in the flag parameter. The type of
this field is @w{@code{int (*) (const char *, struct stat64 *)}}.
This is a GNU extension.
@item gl_lstat
The address of an alternative implementation of the @code{lstat64}
function to get information about an object in the filesystems, not
following symbolic links. It is used if the @code{GLOB_ALTDIRFUNC} bit
is set in the flag parameter. The type of this field is @code{@w{int
(*) (const char *,} @w{struct stat64 *)}}.
This is a GNU extension.
@item gl_flags
The flags used when @code{glob} was called. In addition, @code{GLOB_MAGCHAR}
might be set. See @ref{Flags for Globbing} for more details.
This is a GNU extension.
@end table
@end deftp
@comment glob.h
@comment POSIX.2
@deftypefun int glob (const char *@var{pattern}, int @var{flags}, int (*@var{errfunc}) (const char *@var{filename}, int @var{error-code}), glob_t *@var{vector-ptr})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtsenv{} @mtascusig{:ALRM} @mtascutimer{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c glob @mtasurace:utent @mtsenv @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c strlen dup ok
@c strchr dup ok
@c malloc dup @ascuheap @acsmem
@c mempcpy dup ok
@c next_brace_sub ok
@c free dup @ascuheap @acsmem
@c globfree dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c glob_pattern_p ok
@c glob_pattern_type dup ok
@c getenv dup @mtsenv
@c GET_LOGIN_NAME_MAX ok
@c getlogin_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c GETPW_R_SIZE_MAX ok
@c getpwnam_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c memcpy dup ok
@c memchr dup ok
@c *pglob->gl_stat user-supplied
@c stat64 dup ok
@c S_ISDIR dup ok
@c strdup dup @ascuheap @acsmem
@c glob_pattern_type ok
@c glob_in_dir @mtsenv @mtslocale @asucorrupt @ascuheap @acucorrupt @acsfd @acsmem
@c strlen dup ok
@c glob_pattern_type dup ok
@c malloc dup @ascuheap @acsmem
@c mempcpy dup ok
@c *pglob->gl_stat user-supplied
@c stat64 dup ok
@c free dup @ascuheap @acsmem
@c *pglob->gl_opendir user-supplied
@c opendir dup @ascuheap @acsmem @acsfd
@c dirfd dup ok
@c *pglob->gl_readdir user-supplied
@c CONVERT_DIRENT_DIRENT64 ok
@c readdir64 ok [protected by exclusive use of the stream]
@c REAL_DIR_ENTRY ok
@c DIRENT_MIGHT_BE_DIR ok
@c fnmatch dup @mtsenv @mtslocale @ascuheap @acsmem
@c DIRENT_MIGHT_BE_SYMLINK ok
@c link_exists_p ok
@c link_exists2_p ok
@c strlen dup ok
@c mempcpy dup ok
@c *pglob->gl_stat user-supplied
@c fxstatat64 dup ok
@c realloc dup @ascuheap @acsmem
@c pglob->gl_closedir user-supplied
@c closedir @ascuheap @acsmem @acsfd
@c prefix_array dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c mempcpy dup ok
@c strcpy dup ok
The function @code{glob} does globbing using the pattern @var{pattern}
in the current directory. It puts the result in a newly allocated
vector, and stores the size and address of this vector into
@code{*@var{vector-ptr}}. The argument @var{flags} is a combination of
bit flags; see @ref{Flags for Globbing}, for details of the flags.
The result of globbing is a sequence of file names. The function
@code{glob} allocates a string for each resulting word, then
allocates a vector of type @code{char **} to store the addresses of
these strings. The last element of the vector is a null pointer.
This vector is called the @dfn{word vector}.
To return this vector, @code{glob} stores both its address and its
length (number of elements, not counting the terminating null pointer)
into @code{*@var{vector-ptr}}.
Normally, @code{glob} sorts the file names alphabetically before
returning them. You can turn this off with the flag @code{GLOB_NOSORT}
if you want to get the information as fast as possible. Usually it's
a good idea to let @code{glob} sort them---if you process the files in
alphabetical order, the users will have a feel for the rate of progress
that your application is making.
If @code{glob} succeeds, it returns 0. Otherwise, it returns one
of these error codes:
@vtable @code
@comment glob.h
@comment POSIX.2
@item GLOB_ABORTED
There was an error opening a directory, and you used the flag
@code{GLOB_ERR} or your specified @var{errfunc} returned a nonzero
value.
@iftex
See below
@end iftex
@ifinfo
@xref{Flags for Globbing},
@end ifinfo
for an explanation of the @code{GLOB_ERR} flag and @var{errfunc}.
@comment glob.h
@comment POSIX.2
@item GLOB_NOMATCH
The pattern didn't match any existing files. If you use the
@code{GLOB_NOCHECK} flag, then you never get this error code, because
that flag tells @code{glob} to @emph{pretend} that the pattern matched
at least one file.
@comment glob.h
@comment POSIX.2
@item GLOB_NOSPACE
It was impossible to allocate memory to hold the result.
@end vtable
In the event of an error, @code{glob} stores information in
@code{*@var{vector-ptr}} about all the matches it has found so far.
It is important to notice that the @code{glob} function will not fail if
it encounters directories or files which cannot be handled without the
LFS interfaces. The implementation of @code{glob} is supposed to use
these functions internally. This at least is the assumptions made by
the Unix standard. The GNU extension of allowing the user to provide
own directory handling and @code{stat} functions complicates things a
bit. If these callback functions are used and a large file or directory
is encountered @code{glob} @emph{can} fail.
@end deftypefun
@comment glob.h
@comment GNU
@deftypefun int glob64 (const char *@var{pattern}, int @var{flags}, int (*@var{errfunc}) (const char *@var{filename}, int @var{error-code}), glob64_t *@var{vector-ptr})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtsenv{} @mtascusig{:ALRM} @mtascutimer{} @mtslocale{}}@asunsafe{@ascudlopen{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Same code as glob, but with glob64_t #defined as glob_t.
The @code{glob64} function was added as part of the Large File Summit
extensions but is not part of the original LFS proposal. The reason for
this is simple: it is not necessary. The necessity for a @code{glob64}
function is added by the extensions of the GNU @code{glob}
implementation which allows the user to provide own directory handling
and @code{stat} functions. The @code{readdir} and @code{stat} functions
do depend on the choice of @code{_FILE_OFFSET_BITS} since the definition
of the types @code{struct dirent} and @code{struct stat} will change
depending on the choice.
Beside this difference the @code{glob64} works just like @code{glob} in
all aspects.
This function is a GNU extension.
@end deftypefun
@node Flags for Globbing
@subsection Flags for Globbing
This section describes the standard flags that you can specify in the
@var{flags} argument to @code{glob}. Choose the flags you want,
and combine them with the C bitwise OR operator @code{|}.
Note that there are @ref{More Flags for Globbing} available as GNU extensions.
@vtable @code
@comment glob.h
@comment POSIX.2
@item GLOB_APPEND
Append the words from this expansion to the vector of words produced by
previous calls to @code{glob}. This way you can effectively expand
several words as if they were concatenated with spaces between them.
In order for appending to work, you must not modify the contents of the
word vector structure between calls to @code{glob}. And, if you set
@code{GLOB_DOOFFS} in the first call to @code{glob}, you must also
set it when you append to the results.
Note that the pointer stored in @code{gl_pathv} may no longer be valid
after you call @code{glob} the second time, because @code{glob} might
have relocated the vector. So always fetch @code{gl_pathv} from the
@code{glob_t} structure after each @code{glob} call; @strong{never} save
the pointer across calls.
@comment glob.h
@comment POSIX.2
@item GLOB_DOOFFS
Leave blank slots at the beginning of the vector of words.
The @code{gl_offs} field says how many slots to leave.
The blank slots contain null pointers.
@comment glob.h
@comment POSIX.2
@item GLOB_ERR
Give up right away and report an error if there is any difficulty
reading the directories that must be read in order to expand @var{pattern}
fully. Such difficulties might include a directory in which you don't
have the requisite access. Normally, @code{glob} tries its best to keep
on going despite any errors, reading whatever directories it can.
You can exercise even more control than this by specifying an
error-handler function @var{errfunc} when you call @code{glob}. If
@var{errfunc} is not a null pointer, then @code{glob} doesn't give up
right away when it can't read a directory; instead, it calls
@var{errfunc} with two arguments, like this:
@smallexample
(*@var{errfunc}) (@var{filename}, @var{error-code})
@end smallexample
@noindent
The argument @var{filename} is the name of the directory that
@code{glob} couldn't open or couldn't read, and @var{error-code} is the
@code{errno} value that was reported to @code{glob}.
If the error handler function returns nonzero, then @code{glob} gives up
right away. Otherwise, it continues.
@comment glob.h
@comment POSIX.2
@item GLOB_MARK
If the pattern matches the name of a directory, append @samp{/} to the
directory's name when returning it.
@comment glob.h
@comment POSIX.2
@item GLOB_NOCHECK
If the pattern doesn't match any file names, return the pattern itself
as if it were a file name that had been matched. (Normally, when the
pattern doesn't match anything, @code{glob} returns that there were no
matches.)
@comment glob.h
@comment POSIX.2
@item GLOB_NOESCAPE
Don't treat the @samp{\} character specially in patterns. Normally,
@samp{\} quotes the following character, turning off its special meaning
(if any) so that it matches only itself. When quoting is enabled, the
pattern @samp{\?} matches only the string @samp{?}, because the question
mark in the pattern acts like an ordinary character.
If you use @code{GLOB_NOESCAPE}, then @samp{\} is an ordinary character.
@code{glob} does its work by calling the function @code{fnmatch}
repeatedly. It handles the flag @code{GLOB_NOESCAPE} by turning on the
@code{FNM_NOESCAPE} flag in calls to @code{fnmatch}.
@comment glob.h
@comment POSIX.2
@item GLOB_NOSORT
Don't sort the file names; return them in no particular order.
(In practice, the order will depend on the order of the entries in
the directory.) The only reason @emph{not} to sort is to save time.
@end vtable
@node More Flags for Globbing
@subsection More Flags for Globbing
Beside the flags described in the last section, the GNU implementation of
@code{glob} allows a few more flags which are also defined in the
@file{glob.h} file. Some of the extensions implement functionality
which is available in modern shell implementations.
@vtable @code
@comment glob.h
@comment GNU
@item GLOB_PERIOD
The @code{.} character (period) is treated special. It cannot be
matched by wildcards. @xref{Wildcard Matching}, @code{FNM_PERIOD}.
@comment glob.h
@comment GNU
@item GLOB_MAGCHAR
The @code{GLOB_MAGCHAR} value is not to be given to @code{glob} in the
@var{flags} parameter. Instead, @code{glob} sets this bit in the
@var{gl_flags} element of the @var{glob_t} structure provided as the
result if the pattern used for matching contains any wildcard character.
@comment glob.h
@comment GNU
@item GLOB_ALTDIRFUNC
Instead of the using the using the normal functions for accessing the
filesystem the @code{glob} implementation uses the user-supplied
functions specified in the structure pointed to by @var{pglob}
parameter. For more information about the functions refer to the
sections about directory handling see @ref{Accessing Directories}, and
@ref{Reading Attributes}.
@comment glob.h
@comment GNU
@item GLOB_BRACE
If this flag is given the handling of braces in the pattern is changed.
It is now required that braces appear correctly grouped. I.e., for each
opening brace there must be a closing one. Braces can be used
recursively. So it is possible to define one brace expression in
another one. It is important to note that the range of each brace
expression is completely contained in the outer brace expression (if
there is one).
The string between the matching braces is separated into single
expressions by splitting at @code{,} (comma) characters. The commas
themselves are discarded. Please note what we said above about recursive
brace expressions. The commas used to separate the subexpressions must
be at the same level. Commas in brace subexpressions are not matched.
They are used during expansion of the brace expression of the deeper
level. The example below shows this
@smallexample
glob ("@{foo/@{,bar,biz@},baz@}", GLOB_BRACE, NULL, &result)
@end smallexample
@noindent
is equivalent to the sequence
@smallexample
glob ("foo/", GLOB_BRACE, NULL, &result)
glob ("foo/bar", GLOB_BRACE|GLOB_APPEND, NULL, &result)
glob ("foo/biz", GLOB_BRACE|GLOB_APPEND, NULL, &result)
glob ("baz", GLOB_BRACE|GLOB_APPEND, NULL, &result)
@end smallexample
@noindent
if we leave aside error handling.
@comment glob.h
@comment GNU
@item GLOB_NOMAGIC
If the pattern contains no wildcard constructs (it is a literal file name),
return it as the sole ``matching'' word, even if no file exists by that name.
@comment glob.h
@comment GNU
@item GLOB_TILDE
If this flag is used the character @code{~} (tilde) is handled special
if it appears at the beginning of the pattern. Instead of being taken
verbatim it is used to represent the home directory of a known user.
If @code{~} is the only character in pattern or it is followed by a
@code{/} (slash), the home directory of the process owner is
substituted. Using @code{getlogin} and @code{getpwnam} the information
is read from the system databases. As an example take user @code{bart}
with his home directory at @file{/home/bart}. For him a call like
@smallexample
glob ("~/bin/*", GLOB_TILDE, NULL, &result)
@end smallexample
@noindent
would return the contents of the directory @file{/home/bart/bin}.
Instead of referring to the own home directory it is also possible to
name the home directory of other users. To do so one has to append the
user name after the tilde character. So the contents of user
@code{homer}'s @file{bin} directory can be retrieved by
@smallexample
glob ("~homer/bin/*", GLOB_TILDE, NULL, &result)
@end smallexample
If the user name is not valid or the home directory cannot be determined
for some reason the pattern is left untouched and itself used as the
result. I.e., if in the last example @code{home} is not available the
tilde expansion yields to @code{"~homer/bin/*"} and @code{glob} is not
looking for a directory named @code{~homer}.
This functionality is equivalent to what is available in C-shells if the
@code{nonomatch} flag is set.
@comment glob.h
@comment GNU
@item GLOB_TILDE_CHECK
If this flag is used @code{glob} behaves like as if @code{GLOB_TILDE} is
given. The only difference is that if the user name is not available or
the home directory cannot be determined for other reasons this leads to
an error. @code{glob} will return @code{GLOB_NOMATCH} instead of using
the pattern itself as the name.
This functionality is equivalent to what is available in C-shells if
@code{nonomatch} flag is not set.
@comment glob.h
@comment GNU
@item GLOB_ONLYDIR
If this flag is used the globbing function takes this as a
@strong{hint} that the caller is only interested in directories
matching the pattern. If the information about the type of the file
is easily available non-directories will be rejected but no extra
work will be done to determine the information for each file. I.e.,
the caller must still be able to filter directories out.
This functionality is only available with the GNU @code{glob}
implementation. It is mainly used internally to increase the
performance but might be useful for a user as well and therefore is
documented here.
@end vtable
Calling @code{glob} will in most cases allocate resources which are used
to represent the result of the function call. If the same object of
type @code{glob_t} is used in multiple call to @code{glob} the resources
are freed or reused so that no leaks appear. But this does not include
the time when all @code{glob} calls are done.
@comment glob.h
@comment POSIX.2
@deftypefun void globfree (glob_t *@var{pglob})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c globfree dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c free dup @ascuheap @acsmem
The @code{globfree} function frees all resources allocated by previous
calls to @code{glob} associated with the object pointed to by
@var{pglob}. This function should be called whenever the currently used
@code{glob_t} typed object isn't used anymore.
@end deftypefun
@comment glob.h
@comment GNU
@deftypefun void globfree64 (glob64_t *@var{pglob})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
This function is equivalent to @code{globfree} but it frees records of
type @code{glob64_t} which were allocated by @code{glob64}.
@end deftypefun
@node Regular Expressions
@section Regular Expression Matching
@Theglibc{} supports two interfaces for matching regular
expressions. One is the standard POSIX.2 interface, and the other is
what @theglibc{} has had for many years.
Both interfaces are declared in the header file @file{regex.h}.
If you define @w{@code{_POSIX_C_SOURCE}}, then only the POSIX.2
functions, structures, and constants are declared.
@c !!! we only document the POSIX.2 interface here!!
@menu
* POSIX Regexp Compilation:: Using @code{regcomp} to prepare to match.
* Flags for POSIX Regexps:: Syntax variations for @code{regcomp}.
* Matching POSIX Regexps:: Using @code{regexec} to match the compiled
pattern that you get from @code{regcomp}.
* Regexp Subexpressions:: Finding which parts of the string were matched.
* Subexpression Complications:: Find points of which parts were matched.
* Regexp Cleanup:: Freeing storage; reporting errors.
@end menu
@node POSIX Regexp Compilation
@subsection POSIX Regular Expression Compilation
Before you can actually match a regular expression, you must
@dfn{compile} it. This is not true compilation---it produces a special
data structure, not machine instructions. But it is like ordinary
compilation in that its purpose is to enable you to ``execute'' the
pattern fast. (@xref{Matching POSIX Regexps}, for how to use the
compiled regular expression for matching.)
There is a special data type for compiled regular expressions:
@comment regex.h
@comment POSIX.2
@deftp {Data Type} regex_t
This type of object holds a compiled regular expression.
It is actually a structure. It has just one field that your programs
should look at:
@table @code
@item re_nsub
This field holds the number of parenthetical subexpressions in the
regular expression that was compiled.
@end table
There are several other fields, but we don't describe them here, because
only the functions in the library should use them.
@end deftp
After you create a @code{regex_t} object, you can compile a regular
expression into it by calling @code{regcomp}.
@comment regex.h
@comment POSIX.2
@deftypefun int regcomp (regex_t *restrict @var{compiled}, const char *restrict @var{pattern}, int @var{cflags})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c All of the issues have to do with memory allocation and multi-byte
@c character handling present in the input string, or implied by ranges
@c or inverted character classes.
@c (re_)malloc @ascuheap @acsmem
@c re_compile_internal @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c (re_)realloc @ascuheap @acsmem [no @asucorrupt @acucorrupt for we zero the buffer]
@c init_dfa @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c (re_)malloc @ascuheap @acsmem
@c calloc @ascuheap @acsmem
@c _NL_CURRENT ok
@c _NL_CURRENT_WORD ok
@c btowc @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c libc_lock_init ok
@c re_string_construct @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_construct_common ok
@c re_string_realloc_buffers @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c build_wcs_upper_buffer @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c isascii ok
@c mbsinit ok
@c toupper ok
@c mbrtowc dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c iswlower @mtslocale
@c towupper @mtslocale
@c wcrtomb dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c (re_)malloc dup @ascuheap @acsmem
@c build_upper_buffer ok (@mtslocale but optimized)
@c islower ok
@c toupper ok
@c build_wcs_buffer @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c mbrtowc dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_translate_buffer ok
@c parse @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c fetch_token @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c peek_token @mtslocale
@c re_string_eoi ok
@c re_string_peek_byte ok
@c re_string_cur_idx ok
@c re_string_length ok
@c re_string_peek_byte_case @mtslocale
@c re_string_peek_byte dup ok
@c re_string_is_single_byte_char ok
@c isascii ok
@c re_string_peek_byte dup ok
@c re_string_wchar_at ok
@c re_string_skip_bytes ok
@c re_string_skip_bytes dup ok
@c parse_reg_exp @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c parse_branch @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c parse_expression @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c create_token_tree dup @ascuheap @acsmem
@c re_string_eoi dup ok
@c re_string_first_byte ok
@c fetch_token dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c create_tree dup @ascuheap @acsmem
@c parse_sub_exp @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c fetch_token dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c parse_reg_exp dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c postorder() @ascuheap @acsmem
@c free_tree @ascuheap @acsmem
@c free_token dup @ascuheap @acsmem
@c create_tree dup @ascuheap @acsmem
@c parse_bracket_exp @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c _NL_CURRENT dup ok
@c _NL_CURRENT_WORD dup ok
@c calloc dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c peek_token_bracket ok
@c re_string_eoi dup ok
@c re_string_peek_byte dup ok
@c re_string_first_byte dup ok
@c re_string_cur_idx dup ok
@c re_string_length dup ok
@c re_string_skip_bytes dup ok
@c bitset_set ok
@c re_string_skip_bytes ok
@c parse_bracket_element @mtslocale
@c re_string_char_size_at ok
@c re_string_wchar_at dup ok
@c re_string_skip_bytes dup ok
@c parse_bracket_symbol @mtslocale
@c re_string_eoi dup ok
@c re_string_fetch_byte_case @mtslocale
@c re_string_fetch_byte ok
@c re_string_first_byte dup ok
@c isascii ok
@c re_string_char_size_at dup ok
@c re_string_skip_bytes dup ok
@c re_string_fetch_byte dup ok
@c re_string_peek_byte dup ok
@c re_string_skip_bytes dup ok
@c peek_token_bracket dup ok
@c auto build_range_exp @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c auto lookup_collation_sequence_value @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c btowc dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c collseq_table_lookup ok
@c auto seek_collating_symbol_entry dup ok
@c (re_)realloc dup @ascuheap @acsmem
@c collseq_table_lookup dup ok
@c bitset_set dup ok
@c (re_)realloc dup @ascuheap @acsmem
@c build_equiv_class @mtslocale @ascuheap @acsmem
@c _NL_CURRENT ok
@c auto findidx ok
@c bitset_set dup ok
@c (re_)realloc dup @ascuheap @acsmem
@c auto build_collating_symbol @ascuheap @acsmem
@c auto seek_collating_symbol_entry ok
@c bitset_set dup ok
@c (re_)realloc dup @ascuheap @acsmem
@c build_charclass @mtslocale @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c bitset_set dup ok
@c isalnum ok
@c iscntrl ok
@c isspace ok
@c isalpha ok
@c isdigit ok
@c isprint ok
@c isupper ok
@c isblank ok
@c isgraph ok
@c ispunct ok
@c isxdigit ok
@c bitset_not ok
@c bitset_mask ok
@c create_token_tree dup @ascuheap @acsmem
@c create_tree dup @ascuheap @acsmem
@c free_charset dup @ascuheap @acsmem
@c init_word_char @mtslocale
@c isalnum ok
@c build_charclass_op @mtslocale @ascuheap @acsmem
@c calloc dup @ascuheap @acsmem
@c build_charclass dup @mtslocale @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c free_charset dup @ascuheap @acsmem
@c bitset_set dup ok
@c bitset_not dup ok
@c bitset_mask dup ok
@c create_token_tree dup @ascuheap @acsmem
@c create_tree dup @ascuheap @acsmem
@c parse_dup_op @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_cur_idx dup ok
@c fetch_number @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c fetch_token dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_set_index ok
@c postorder() @ascuheap @acsmem
@c free_tree dup @ascuheap @acsmem
@c mark_opt_subexp ok
@c duplicate_tree @ascuheap @acsmem
@c create_token_tree dup @ascuheap @acsmem
@c create_tree dup @ascuheap @acsmem
@c postorder() @ascuheap @acsmem
@c free_tree dup @ascuheap @acsmem
@c fetch_token dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c parse_branch dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c create_tree dup @ascuheap @acsmem
@c create_tree @ascuheap @acsmem
@c create_token_tree @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c analyze @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c preorder() @ascuheap @acsmem
@c optimize_subexps ok
@c calc_next ok
@c link_nfa_nodes @ascuheap @acsmem
@c re_node_set_init_1 @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c re_node_set_init_2 @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c postorder() @ascuheap @acsmem
@c lower_subexps @ascuheap @acsmem
@c lower_subexp @ascuheap @acsmem
@c create_tree dup @ascuheap @acsmem
@c calc_first @ascuheap @acsmem
@c re_dfa_add_node @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c re_node_set_init_empty ok
@c calc_eclosure @ascuheap @acsmem
@c calc_eclosure_iter @ascuheap @acsmem
@c re_node_set_alloc @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c duplicate_node_closure @ascuheap @acsmem
@c re_node_set_empty ok
@c duplicate_node @ascuheap @acsmem
@c re_dfa_add_node dup @ascuheap @acsmem
@c re_node_set_insert @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c search_duplicated_node ok
@c re_node_set_merge @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c re_node_set_free @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c re_node_set_insert dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c calc_inveclosure @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c re_node_set_insert_last @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c optimize_utf8 ok
@c create_initial_state @ascuheap @acsmem
@c re_node_set_init_copy @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c re_node_set_contains ok
@c re_node_set_merge dup @ascuheap @acsmem
@c re_acquire_state_context @ascuheap @acsmem
@c calc_state_hash ok
@c re_node_set_compare ok
@c create_cd_newstate @ascuheap @acsmem
@c calloc dup @ascuheap @acsmem
@c re_node_set_init_copy dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c free_state @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c NOT_SATISFY_PREV_CONSTRAINT ok
@c re_node_set_remove_at ok
@c register_state @ascuheap @acsmem
@c re_node_set_alloc dup @ascuheap @acsmem
@c re_node_set_insert_last dup @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c free_workarea_compile @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c re_string_destruct @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c free_dfa_content @ascuheap @acsmem
@c free_token @ascuheap @acsmem
@c free_charset @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_compile_fastmap @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_compile_fastmap_iter @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_set_fastmap ok
@c tolower ok
@c mbrtowc dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c wcrtomb dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c towlower @mtslocale
@c _NL_CURRENT ok
@c (re_)free @ascuheap @acsmem
The function @code{regcomp} ``compiles'' a regular expression into a
data structure that you can use with @code{regexec} to match against a
string. The compiled regular expression format is designed for
efficient matching. @code{regcomp} stores it into @code{*@var{compiled}}.
It's up to you to allocate an object of type @code{regex_t} and pass its
address to @code{regcomp}.
The argument @var{cflags} lets you specify various options that control
the syntax and semantics of regular expressions. @xref{Flags for POSIX
Regexps}.
If you use the flag @code{REG_NOSUB}, then @code{regcomp} omits from
the compiled regular expression the information necessary to record
how subexpressions actually match. In this case, you might as well
pass @code{0} for the @var{matchptr} and @var{nmatch} arguments when
you call @code{regexec}.
If you don't use @code{REG_NOSUB}, then the compiled regular expression
does have the capacity to record how subexpressions match. Also,
@code{regcomp} tells you how many subexpressions @var{pattern} has, by
storing the number in @code{@var{compiled}->re_nsub}. You can use that
value to decide how long an array to allocate to hold information about
subexpression matches.
@code{regcomp} returns @code{0} if it succeeds in compiling the regular
expression; otherwise, it returns a nonzero error code (see the table
below). You can use @code{regerror} to produce an error message string
describing the reason for a nonzero value; see @ref{Regexp Cleanup}.
@end deftypefun
Here are the possible nonzero values that @code{regcomp} can return:
@table @code
@comment regex.h
@comment POSIX.2
@item REG_BADBR
There was an invalid @samp{\@{@dots{}\@}} construct in the regular
expression. A valid @samp{\@{@dots{}\@}} construct must contain either
a single number, or two numbers in increasing order separated by a
comma.
@comment regex.h
@comment POSIX.2
@item REG_BADPAT
There was a syntax error in the regular expression.
@comment regex.h
@comment POSIX.2
@item REG_BADRPT
A repetition operator such as @samp{?} or @samp{*} appeared in a bad
position (with no preceding subexpression to act on).
@comment regex.h
@comment POSIX.2
@item REG_ECOLLATE
The regular expression referred to an invalid collating element (one not
defined in the current locale for string collation). @xref{Locale
Categories}.
@comment regex.h
@comment POSIX.2
@item REG_ECTYPE
The regular expression referred to an invalid character class name.
@comment regex.h
@comment POSIX.2
@item REG_EESCAPE
The regular expression ended with @samp{\}.
@comment regex.h
@comment POSIX.2
@item REG_ESUBREG
There was an invalid number in the @samp{\@var{digit}} construct.
@comment regex.h
@comment POSIX.2
@item REG_EBRACK
There were unbalanced square brackets in the regular expression.
@comment regex.h
@comment POSIX.2
@item REG_EPAREN
An extended regular expression had unbalanced parentheses,
or a basic regular expression had unbalanced @samp{\(} and @samp{\)}.
@comment regex.h
@comment POSIX.2
@item REG_EBRACE
The regular expression had unbalanced @samp{\@{} and @samp{\@}}.
@comment regex.h
@comment POSIX.2
@item REG_ERANGE
One of the endpoints in a range expression was invalid.
@comment regex.h
@comment POSIX.2
@item REG_ESPACE
@code{regcomp} ran out of memory.
@end table
@node Flags for POSIX Regexps
@subsection Flags for POSIX Regular Expressions
These are the bit flags that you can use in the @var{cflags} operand when
compiling a regular expression with @code{regcomp}.
@table @code
@comment regex.h
@comment POSIX.2
@item REG_EXTENDED
Treat the pattern as an extended regular expression, rather than as a
basic regular expression.
@comment regex.h
@comment POSIX.2
@item REG_ICASE
Ignore case when matching letters.
@comment regex.h
@comment POSIX.2
@item REG_NOSUB
Don't bother storing the contents of the @var{matches-ptr} array.
@comment regex.h
@comment POSIX.2
@item REG_NEWLINE
Treat a newline in @var{string} as dividing @var{string} into multiple
lines, so that @samp{$} can match before the newline and @samp{^} can
match after. Also, don't permit @samp{.} to match a newline, and don't
permit @samp{[^@dots{}]} to match a newline.
Otherwise, newline acts like any other ordinary character.
@end table
@node Matching POSIX Regexps
@subsection Matching a Compiled POSIX Regular Expression
Once you have compiled a regular expression, as described in @ref{POSIX
Regexp Compilation}, you can match it against strings using
@code{regexec}. A match anywhere inside the string counts as success,
unless the regular expression contains anchor characters (@samp{^} or
@samp{$}).
@comment regex.h
@comment POSIX.2
@deftypefun int regexec (const regex_t *restrict @var{compiled}, const char *restrict @var{string}, size_t @var{nmatch}, regmatch_t @var{matchptr}[restrict], int @var{eflags})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c libc_lock_lock @asulock @aculock
@c re_search_internal @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_allocate @ascuheap @acsmem
@c re_string_construct_common dup ok
@c re_string_realloc_buffers dup @ascuheap @acsmem
@c match_ctx_init @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c re_string_byte_at ok
@c re_string_first_byte dup ok
@c check_matching @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_cur_idx dup ok
@c acquire_init_state_context dup @ascuheap @acsmem
@c re_string_context_at ok
@c re_string_byte_at dup ok
@c bitset_contain ok
@c re_acquire_state_context dup @ascuheap @acsmem
@c check_subexp_matching_top @ascuheap @acsmem
@c match_ctx_add_subtop @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c calloc dup @ascuheap @acsmem
@c transit_state_bkref @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_cur_idx dup ok
@c re_string_context_at dup ok
@c NOT_SATISFY_NEXT_CONSTRAINT ok
@c get_subexp @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_get_buffer ok
@c search_cur_bkref_entry ok
@c clean_state_log_if_needed @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c extend_buffers @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_realloc_buffers dup @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c build_wcs_upper_buffer dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c build_upper_buffer dup ok (@mtslocale but optimized)
@c build_wcs_buffer dup @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_translate_buffer dup ok
@c get_subexp_sub @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c check_arrival @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c (re_)realloc dup @ascuheap @acsmem
@c re_string_context_at dup ok
@c re_node_set_init_1 dup @ascuheap @acsmem
@c check_arrival_expand_ecl @ascuheap @acsmem
@c re_node_set_alloc dup @ascuheap @acsmem
@c find_subexp_node ok
@c re_node_set_merge dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c check_arrival_expand_ecl_sub @ascuheap @acsmem
@c re_node_set_contains dup ok
@c re_node_set_insert dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_init_copy dup @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c expand_bkref_cache @ascuheap @acsmem
@c search_cur_bkref_entry dup ok
@c re_node_set_contains dup ok
@c re_node_set_init_1 dup @ascuheap @acsmem
@c check_arrival_expand_ecl dup @ascuheap @acsmem
@c re_node_set_merge dup @ascuheap @acsmem
@c re_node_set_init_copy dup @ascuheap @acsmem
@c re_node_set_insert dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_acquire_state @ascuheap @acsmem
@c calc_state_hash dup ok
@c re_node_set_compare dup ok
@c create_ci_newstate @ascuheap @acsmem
@c calloc dup @ascuheap @acsmem
@c re_node_set_init_copy dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c register_state dup @ascuheap @acsmem
@c free_state dup @ascuheap @acsmem
@c re_acquire_state_context dup @ascuheap @acsmem
@c re_node_set_merge dup @ascuheap @acsmem
@c check_arrival_add_next_nodes @mtslocale @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c check_node_accept_bytes @mtslocale @ascuheap @acsmem
@c re_string_byte_at dup ok
@c re_string_char_size_at dup ok
@c re_string_elem_size_at @mtslocale
@c _NL_CURRENT_WORD dup ok
@c _NL_CURRENT dup ok
@c auto findidx dup ok
@c _NL_CURRENT_WORD dup ok
@c _NL_CURRENT dup ok
@c collseq_table_lookup dup ok
@c find_collation_sequence_value @mtslocale
@c _NL_CURRENT_WORD dup ok
@c _NL_CURRENT dup ok
@c auto findidx dup ok
@c wcscoll @mtslocale @ascuheap @acsmem
@c re_node_set_empty dup ok
@c re_node_set_merge dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_insert dup @ascuheap @acsmem
@c re_acquire_state dup @ascuheap @acsmem
@c check_node_accept ok
@c re_string_byte_at dup ok
@c bitset_contain dup ok
@c re_string_context_at dup ok
@c NOT_SATISFY_NEXT_CONSTRAINT dup ok
@c match_ctx_add_entry @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c clean_state_log_if_needed dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c extend_buffers dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c find_subexp_node dup ok
@c calloc dup @ascuheap @acsmem
@c check_arrival dup ***
@c match_ctx_add_sublast @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c re_acquire_state_context dup @ascuheap @acsmem
@c re_node_set_init_union @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c re_node_set_init_copy dup @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c re_node_set_free dup @ascuheap @acsmem
@c check_subexp_matching_top dup @ascuheap @acsmem
@c check_halt_state_context ok
@c re_string_context_at dup ok
@c check_halt_node_context ok
@c NOT_SATISFY_NEXT_CONSTRAINT dup ok
@c re_string_eoi dup ok
@c extend_buffers dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c transit_state @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c transit_state_mb @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_context_at dup ok
@c NOT_SATISFY_NEXT_CONSTRAINT dup ok
@c check_node_accept_bytes dup @mtslocale @ascuheap @acsmem
@c re_string_cur_idx dup ok
@c clean_state_log_if_needed @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_node_set_init_union dup @ascuheap @acsmem
@c re_acquire_state_context dup @ascuheap @acsmem
@c re_string_fetch_byte dup ok
@c re_string_context_at dup ok
@c build_trtable @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c group_nodes_into_DFAstates @ascuheap @acsmem
@c bitset_empty dup ok
@c bitset_set dup ok
@c bitset_merge dup ok
@c bitset_set_all ok
@c bitset_clear ok
@c bitset_contain dup ok
@c bitset_copy ok
@c re_node_set_init_copy dup @ascuheap @acsmem
@c re_node_set_insert dup @ascuheap @acsmem
@c re_node_set_init_1 dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_alloc dup @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c bitset_empty ok
@c re_node_set_empty dup ok
@c re_node_set_merge dup @ascuheap @acsmem
@c re_acquire_state_context dup @ascuheap @acsmem
@c bitset_merge ok
@c calloc dup @ascuheap @acsmem
@c bitset_contain dup ok
@c merge_state_with_log @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c re_string_cur_idx dup ok
@c re_node_set_init_union dup @ascuheap @acsmem
@c re_string_context_at dup ok
@c re_node_set_free dup @ascuheap @acsmem
@c check_subexp_matching_top @ascuheap @acsmem
@c match_ctx_add_subtop dup @ascuheap @acsmem
@c transit_state_bkref dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c find_recover_state
@c re_string_cur_idx dup ok
@c re_string_skip_bytes dup ok
@c merge_state_with_log dup @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c check_halt_state_context dup ok
@c prune_impossible_nodes @mtslocale @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c sift_ctx_init ok
@c re_node_set_init_empty dup ok
@c sift_states_backward @mtslocale @ascuheap @acsmem
@c re_node_set_init_1 dup @ascuheap @acsmem
@c update_cur_sifted_state @mtslocale @ascuheap @acsmem
@c add_epsilon_src_nodes @ascuheap @acsmem
@c re_acquire_state dup @ascuheap @acsmem
@c re_node_set_alloc dup @ascuheap @acsmem
@c re_node_set_merge dup @ascuheap @acsmem
@c re_node_set_add_intersect @ascuheap @acsmem
@c (re_)realloc dup @ascuheap @acsmem
@c check_subexp_limits @ascuheap @acsmem
@c sub_epsilon_src_nodes @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c re_node_set_contains dup ok
@c re_node_set_add_intersect dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_remove_at dup ok
@c re_node_set_contains dup ok
@c re_acquire_state dup @ascuheap @acsmem
@c sift_states_bkref @mtslocale @ascuheap @acsmem
@c search_cur_bkref_entry dup ok
@c check_dst_limits ok
@c search_cur_bkref_entry dup ok
@c check_dst_limits_calc_pos ok
@c check_dst_limits_calc_pos_1 ok
@c re_node_set_init_copy dup @ascuheap @acsmem
@c re_node_set_insert dup @ascuheap @acsmem
@c sift_states_backward dup @mtslocale @ascuheap @acsmem
@c merge_state_array dup @ascuheap @acsmem
@c re_node_set_remove ok
@c re_node_set_contains dup ok
@c re_node_set_remove_at dup ok
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c re_node_set_empty dup ok
@c build_sifted_states @mtslocale @ascuheap @acsmem
@c sift_states_iter_mb @mtslocale @ascuheap @acsmem
@c check_node_accept_bytes dup @mtslocale @ascuheap @acsmem
@c check_node_accept dup ok
@c check_dst_limits dup ok
@c re_node_set_insert dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c check_halt_state_context dup ok
@c merge_state_array @ascuheap @acsmem
@c re_node_set_init_union dup @ascuheap @acsmem
@c re_acquire_state dup @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c set_regs @ascuheap @acsmem
@c (re_)malloc dup @ascuheap @acsmem
@c re_node_set_init_empty dup ok
@c free_fail_stack_return @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c update_regs ok
@c re_node_set_free dup @ascuheap @acsmem
@c pop_fail_stack @ascuheap @acsmem
@c re_node_set_free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c match_ctx_free @ascuheap @acsmem
@c match_ctx_clean @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c (re_)free dup @ascuheap @acsmem
@c re_string_destruct dup @ascuheap @acsmem
@c libc_lock_unlock @aculock
This function tries to match the compiled regular expression
@code{*@var{compiled}} against @var{string}.
@code{regexec} returns @code{0} if the regular expression matches;
otherwise, it returns a nonzero value. See the table below for
what nonzero values mean. You can use @code{regerror} to produce an
error message string describing the reason for a nonzero value;
see @ref{Regexp Cleanup}.
The argument @var{eflags} is a word of bit flags that enable various
options.
If you want to get information about what part of @var{string} actually
matched the regular expression or its subexpressions, use the arguments
@var{matchptr} and @var{nmatch}. Otherwise, pass @code{0} for
@var{nmatch}, and @code{NULL} for @var{matchptr}. @xref{Regexp
Subexpressions}.
@end deftypefun
You must match the regular expression with the same set of current
locales that were in effect when you compiled the regular expression.
The function @code{regexec} accepts the following flags in the
@var{eflags} argument:
@table @code
@comment regex.h
@comment POSIX.2
@item REG_NOTBOL
Do not regard the beginning of the specified string as the beginning of
a line; more generally, don't make any assumptions about what text might
precede it.
@comment regex.h
@comment POSIX.2
@item REG_NOTEOL
Do not regard the end of the specified string as the end of a line; more
generally, don't make any assumptions about what text might follow it.
@end table
Here are the possible nonzero values that @code{regexec} can return:
@table @code
@comment regex.h
@comment POSIX.2
@item REG_NOMATCH
The pattern didn't match the string. This isn't really an error.
@comment regex.h
@comment POSIX.2
@item REG_ESPACE
@code{regexec} ran out of memory.
@end table
@node Regexp Subexpressions
@subsection Match Results with Subexpressions
When @code{regexec} matches parenthetical subexpressions of
@var{pattern}, it records which parts of @var{string} they match. It
returns that information by storing the offsets into an array whose
elements are structures of type @code{regmatch_t}. The first element of
the array (index @code{0}) records the part of the string that matched
the entire regular expression. Each other element of the array records
the beginning and end of the part that matched a single parenthetical
subexpression.
@comment regex.h
@comment POSIX.2
@deftp {Data Type} regmatch_t
This is the data type of the @var{matcharray} array that you pass to
@code{regexec}. It contains two structure fields, as follows:
@table @code
@item rm_so
The offset in @var{string} of the beginning of a substring. Add this
value to @var{string} to get the address of that part.
@item rm_eo
The offset in @var{string} of the end of the substring.
@end table
@end deftp
@comment regex.h
@comment POSIX.2
@deftp {Data Type} regoff_t
@code{regoff_t} is an alias for another signed integer type.
The fields of @code{regmatch_t} have type @code{regoff_t}.
@end deftp
The @code{regmatch_t} elements correspond to subexpressions
positionally; the first element (index @code{1}) records where the first
subexpression matched, the second element records the second
subexpression, and so on. The order of the subexpressions is the order
in which they begin.
When you call @code{regexec}, you specify how long the @var{matchptr}
array is, with the @var{nmatch} argument. This tells @code{regexec} how
many elements to store. If the actual regular expression has more than
@var{nmatch} subexpressions, then you won't get offset information about
the rest of them. But this doesn't alter whether the pattern matches a
particular string or not.
If you don't want @code{regexec} to return any information about where
the subexpressions matched, you can either supply @code{0} for
@var{nmatch}, or use the flag @code{REG_NOSUB} when you compile the
pattern with @code{regcomp}.
@node Subexpression Complications
@subsection Complications in Subexpression Matching
Sometimes a subexpression matches a substring of no characters. This
happens when @samp{f\(o*\)} matches the string @samp{fum}. (It really
matches just the @samp{f}.) In this case, both of the offsets identify
the point in the string where the null substring was found. In this
example, the offsets are both @code{1}.
Sometimes the entire regular expression can match without using some of
its subexpressions at all---for example, when @samp{ba\(na\)*} matches the
string @samp{ba}, the parenthetical subexpression is not used. When
this happens, @code{regexec} stores @code{-1} in both fields of the
element for that subexpression.
Sometimes matching the entire regular expression can match a particular
subexpression more than once---for example, when @samp{ba\(na\)*}
matches the string @samp{bananana}, the parenthetical subexpression
matches three times. When this happens, @code{regexec} usually stores
the offsets of the last part of the string that matched the
subexpression. In the case of @samp{bananana}, these offsets are
@code{6} and @code{8}.
But the last match is not always the one that is chosen. It's more
accurate to say that the last @emph{opportunity} to match is the one
that takes precedence. What this means is that when one subexpression
appears within another, then the results reported for the inner
subexpression reflect whatever happened on the last match of the outer
subexpression. For an example, consider @samp{\(ba\(na\)*s \)*} matching
the string @samp{bananas bas }. The last time the inner expression
actually matches is near the end of the first word. But it is
@emph{considered} again in the second word, and fails to match there.
@code{regexec} reports nonuse of the ``na'' subexpression.
Another place where this rule applies is when the regular expression
@smallexample
\(ba\(na\)*s \|nefer\(ti\)* \)*
@end smallexample
@noindent
matches @samp{bananas nefertiti}. The ``na'' subexpression does match
in the first word, but it doesn't match in the second word because the
other alternative is used there. Once again, the second repetition of
the outer subexpression overrides the first, and within that second
repetition, the ``na'' subexpression is not used. So @code{regexec}
reports nonuse of the ``na'' subexpression.
@node Regexp Cleanup
@subsection POSIX Regexp Matching Cleanup
When you are finished using a compiled regular expression, you can
free the storage it uses by calling @code{regfree}.
@comment regex.h
@comment POSIX.2
@deftypefun void regfree (regex_t *@var{compiled})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c (re_)free dup @ascuheap @acsmem
@c free_dfa_content dup @ascuheap @acsmem
Calling @code{regfree} frees all the storage that @code{*@var{compiled}}
points to. This includes various internal fields of the @code{regex_t}
structure that aren't documented in this manual.
@code{regfree} does not free the object @code{*@var{compiled}} itself.
@end deftypefun
You should always free the space in a @code{regex_t} structure with
@code{regfree} before using the structure to compile another regular
expression.
When @code{regcomp} or @code{regexec} reports an error, you can use
the function @code{regerror} to turn it into an error message string.
@comment regex.h
@comment POSIX.2
@deftypefun size_t regerror (int @var{errcode}, const regex_t *restrict @var{compiled}, char *restrict @var{buffer}, size_t @var{length})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c regerror calls gettext, strcmp and mempcpy or memcpy.
This function produces an error message string for the error code
@var{errcode}, and stores the string in @var{length} bytes of memory
starting at @var{buffer}. For the @var{compiled} argument, supply the
same compiled regular expression structure that @code{regcomp} or
@code{regexec} was working with when it got the error. Alternatively,
you can supply @code{NULL} for @var{compiled}; you will still get a
meaningful error message, but it might not be as detailed.
If the error message can't fit in @var{length} bytes (including a
terminating null character), then @code{regerror} truncates it.
The string that @code{regerror} stores is always null-terminated
even if it has been truncated.
The return value of @code{regerror} is the minimum length needed to
store the entire error message. If this is less than @var{length}, then
the error message was not truncated, and you can use it. Otherwise, you
should call @code{regerror} again with a larger buffer.
Here is a function which uses @code{regerror}, but always dynamically
allocates a buffer for the error message:
@smallexample
char *get_regerror (int errcode, regex_t *compiled)
@{
size_t length = regerror (errcode, compiled, NULL, 0);
char *buffer = xmalloc (length);
(void) regerror (errcode, compiled, buffer, length);
return buffer;
@}
@end smallexample
@end deftypefun
@node Word Expansion
@section Shell-Style Word Expansion
@cindex word expansion
@cindex expansion of shell words
@dfn{Word expansion} means the process of splitting a string into
@dfn{words} and substituting for variables, commands, and wildcards
just as the shell does.
For example, when you write @samp{ls -l foo.c}, this string is split
into three separate words---@samp{ls}, @samp{-l} and @samp{foo.c}.
This is the most basic function of word expansion.
When you write @samp{ls *.c}, this can become many words, because
the word @samp{*.c} can be replaced with any number of file names.
This is called @dfn{wildcard expansion}, and it is also a part of
word expansion.
When you use @samp{echo $PATH} to print your path, you are taking
advantage of @dfn{variable substitution}, which is also part of word
expansion.
Ordinary programs can perform word expansion just like the shell by
calling the library function @code{wordexp}.
@menu
* Expansion Stages:: What word expansion does to a string.
* Calling Wordexp:: How to call @code{wordexp}.
* Flags for Wordexp:: Options you can enable in @code{wordexp}.
* Wordexp Example:: A sample program that does word expansion.
* Tilde Expansion:: Details of how tilde expansion works.
* Variable Substitution:: Different types of variable substitution.
@end menu
@node Expansion Stages
@subsection The Stages of Word Expansion
When word expansion is applied to a sequence of words, it performs the
following transformations in the order shown here:
@enumerate
@item
@cindex tilde expansion
@dfn{Tilde expansion}: Replacement of @samp{~foo} with the name of
the home directory of @samp{foo}.
@item
Next, three different transformations are applied in the same step,
from left to right:
@itemize @bullet
@item
@cindex variable substitution
@cindex substitution of variables and commands
@dfn{Variable substitution}: Environment variables are substituted for
references such as @samp{$foo}.
@item
@cindex command substitution
@dfn{Command substitution}: Constructs such as @w{@samp{`cat foo`}} and
the equivalent @w{@samp{$(cat foo)}} are replaced with the output from
the inner command.
@item
@cindex arithmetic expansion
@dfn{Arithmetic expansion}: Constructs such as @samp{$(($x-1))} are
replaced with the result of the arithmetic computation.
@end itemize
@item
@cindex field splitting
@dfn{Field splitting}: subdivision of the text into @dfn{words}.
@item
@cindex wildcard expansion
@dfn{Wildcard expansion}: The replacement of a construct such as @samp{*.c}
with a list of @samp{.c} file names. Wildcard expansion applies to an
entire word at a time, and replaces that word with 0 or more file names
that are themselves words.
@item
@cindex quote removal
@cindex removal of quotes
@dfn{Quote removal}: The deletion of string-quotes, now that they have
done their job by inhibiting the above transformations when appropriate.
@end enumerate
For the details of these transformations, and how to write the constructs
that use them, see @w{@cite{The BASH Manual}} (to appear).
@node Calling Wordexp
@subsection Calling @code{wordexp}
All the functions, constants and data types for word expansion are
declared in the header file @file{wordexp.h}.
Word expansion produces a vector of words (strings). To return this
vector, @code{wordexp} uses a special data type, @code{wordexp_t}, which
is a structure. You pass @code{wordexp} the address of the structure,
and it fills in the structure's fields to tell you about the results.
@comment wordexp.h
@comment POSIX.2
@deftp {Data Type} {wordexp_t}
This data type holds a pointer to a word vector. More precisely, it
records both the address of the word vector and its size.
@table @code
@item we_wordc
The number of elements in the vector.
@item we_wordv
The address of the vector. This field has type @w{@code{char **}}.
@item we_offs
The offset of the first real element of the vector, from its nominal
address in the @code{we_wordv} field. Unlike the other fields, this
is always an input to @code{wordexp}, rather than an output from it.
If you use a nonzero offset, then that many elements at the beginning of
the vector are left empty. (The @code{wordexp} function fills them with
null pointers.)
The @code{we_offs} field is meaningful only if you use the
@code{WRDE_DOOFFS} flag. Otherwise, the offset is always zero
regardless of what is in this field, and the first real element comes at
the beginning of the vector.
@end table
@end deftp
@comment wordexp.h
@comment POSIX.2
@deftypefun int wordexp (const char *@var{words}, wordexp_t *@var{word-vector-ptr}, int @var{flags})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtasuconst{:@mtsenv{}} @mtsenv{} @mtascusig{:ALRM} @mtascutimer{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuintl{} @ascuheap{} @asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c wordexp @mtasurace:utent @mtasuconst:@mtsenv @mtsenv @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuintl @ascuheap @asucorrupt @asulock @acucorrupt @aculock @acsfd @acsmem
@c w_newword ok
@c wordfree dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c calloc dup @ascuheap @acsmem
@c getenv dup @mtsenv
@c strcpy dup ok
@c parse_backslash @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c parse_dollars @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c w_addchar dup @ascuheap @acsmem
@c parse_arith @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c w_newword dup ok
@c parse_dollars dup @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_backtick dup @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c parse_qtd_backslash dup @ascuheap @acsmem
@c eval_expr @mtslocale
@c eval_expr_multidiv @mtslocale
@c eval_expr_val @mtslocale
@c isspace dup @mtslocale
@c eval_expr dup @mtslocale
@c isspace dup @mtslocale
@c isspace dup @mtslocale
@c free dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c w_addstr dup @ascuheap @acsmem
@c itoa_word dup ok
@c parse_comm @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c w_newword dup ok
@c pthread_setcancelstate @ascuplugin @ascuheap @acsmem
@c (disable cancellation around exec_comm; it may do_cancel the
@c second time, if async cancel is enabled)
@c THREAD_ATOMIC_CMPXCHG_VAL dup ok
@c CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS dup ok
@c do_cancel @ascuplugin @ascuheap @acsmem
@c THREAD_ATOMIC_BIT_SET dup ok
@c pthread_unwind @ascuplugin @ascuheap @acsmem
@c Unwind_ForcedUnwind if available @ascuplugin @ascuheap @acsmem
@c libc_unwind_longjmp otherwise
@c cleanups
@c exec_comm @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c pipe2 dup ok
@c pipe dup ok
@c fork dup @ascuplugin @aculock
@c close dup @acsfd
@c on child: exec_comm_child -> exec or abort
@c waitpid dup ok
@c read dup ok
@c w_addmem dup @ascuheap @acsmem
@c strchr dup ok
@c w_addword dup @ascuheap @acsmem
@c w_newword dup ok
@c w_addchar dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c kill dup ok
@c free dup @ascuheap @acsmem
@c parse_param @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c reads from __libc_argc and __libc_argv without guards
@c w_newword dup ok
@c isalpha dup @mtslocale^^
@c w_addchar dup @ascuheap @acsmem
@c isalnum dup @mtslocale^^
@c isdigit dup @mtslocale^^
@c strchr dup ok
@c itoa_word dup ok
@c atoi dup @mtslocale
@c getpid dup ok
@c w_addstr dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c stpcpy dup ok
@c w_addword dup @ascuheap @acsmem
@c strdup dup @ascuheap @acsmem
@c getenv dup @mtsenv
@c parse_dollars dup @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_tilde dup @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c fnmatch dup @mtsenv @mtslocale @ascuheap @acsmem
@c mempcpy dup ok
@c _ dup @ascuintl
@c fxprintf dup @aculock
@c setenv dup @mtasuconst:@mtsenv @ascuheap @asulock @acucorrupt @aculock @acsmem
@c strspn dup ok
@c strcspn dup ok
@c parse_backtick @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c w_newword dup ok
@c exec_comm dup @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c free dup @ascuheap @acsmem
@c parse_qtd_backslash dup @ascuheap @acsmem
@c parse_backslash dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c parse_dquote @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_dollars dup @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_backtick dup @ascuplugin @ascuheap @aculock @acsfd @acsmem
@c parse_qtd_backslash dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c w_addword dup @ascuheap @acsmem
@c strdup dup @ascuheap @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c parse_squote dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c parse_tilde @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c strchr dup ok
@c w_addchar dup @ascuheap @acsmem
@c getenv dup @mtsenv
@c w_addstr dup @ascuheap @acsmem
@c strlen dup ok
@c w_addmem dup @ascuheap @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c mempcpy dup ok
@c getuid dup ok
@c getpwuid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getpwnam_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_glob @mtasurace:utent @mtasuconst:@mtsenv @mtsenv @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c strchr dup ok
@c parse_dollars dup @mtasuconst:@mtsenv @mtslocale @mtsenv @ascudlopen @ascuplugin @ascuintl @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c parse_qtd_backslash @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c parse_backslash dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c w_addword dup @ascuheap @acsmem
@c w_newword dup ok
@c do_parse_glob @mtasurace:utent @mtsenv @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @aculock @acsfd @acsmem
@c glob dup @mtasurace:utent @mtsenv @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @aculock @acsfd @acsmem [auto glob_t avoids @asucorrupt @acucorrupt]
@c w_addstr dup @ascuheap @acsmem
@c w_addchar dup @ascuheap @acsmem
@c globfree dup @ascuheap @acsmem [auto glob_t avoids @asucorrupt @acucorrupt]
@c free dup @ascuheap @acsmem
@c w_newword dup ok
@c strdup dup @ascuheap @acsmem
@c w_addword dup @ascuheap @acsmem
@c wordfree dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c strchr dup ok
@c w_addchar dup @ascuheap @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
Perform word expansion on the string @var{words}, putting the result in
a newly allocated vector, and store the size and address of this vector
into @code{*@var{word-vector-ptr}}. The argument @var{flags} is a
combination of bit flags; see @ref{Flags for Wordexp}, for details of
the flags.
You shouldn't use any of the characters @samp{|&;<>} in the string
@var{words} unless they are quoted; likewise for newline. If you use
these characters unquoted, you will get the @code{WRDE_BADCHAR} error
code. Don't use parentheses or braces unless they are quoted or part of
a word expansion construct. If you use quotation characters @samp{'"`},
they should come in pairs that balance.
The results of word expansion are a sequence of words. The function
@code{wordexp} allocates a string for each resulting word, then
allocates a vector of type @code{char **} to store the addresses of
these strings. The last element of the vector is a null pointer.
This vector is called the @dfn{word vector}.
To return this vector, @code{wordexp} stores both its address and its
length (number of elements, not counting the terminating null pointer)
into @code{*@var{word-vector-ptr}}.
If @code{wordexp} succeeds, it returns 0. Otherwise, it returns one
of these error codes:
@table @code
@comment wordexp.h
@comment POSIX.2
@item WRDE_BADCHAR
The input string @var{words} contains an unquoted invalid character such
as @samp{|}.
@comment wordexp.h
@comment POSIX.2
@item WRDE_BADVAL
The input string refers to an undefined shell variable, and you used the flag
@code{WRDE_UNDEF} to forbid such references.
@comment wordexp.h
@comment POSIX.2
@item WRDE_CMDSUB
The input string uses command substitution, and you used the flag
@code{WRDE_NOCMD} to forbid command substitution.
@comment wordexp.h
@comment POSIX.2
@item WRDE_NOSPACE
It was impossible to allocate memory to hold the result. In this case,
@code{wordexp} can store part of the results---as much as it could
allocate room for.
@comment wordexp.h
@comment POSIX.2
@item WRDE_SYNTAX
There was a syntax error in the input string. For example, an unmatched
quoting character is a syntax error.
@end table
@end deftypefun
@comment wordexp.h
@comment POSIX.2
@deftypefun void wordfree (wordexp_t *@var{word-vector-ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c wordfree dup @asucorrupt @ascuheap @acucorrupt @acsmem
@c free dup @ascuheap @acsmem
Free the storage used for the word-strings and vector that
@code{*@var{word-vector-ptr}} points to. This does not free the
structure @code{*@var{word-vector-ptr}} itself---only the other
data it points to.
@end deftypefun
@node Flags for Wordexp
@subsection Flags for Word Expansion
This section describes the flags that you can specify in the
@var{flags} argument to @code{wordexp}. Choose the flags you want,
and combine them with the C operator @code{|}.
@table @code
@comment wordexp.h
@comment POSIX.2
@item WRDE_APPEND
Append the words from this expansion to the vector of words produced by
previous calls to @code{wordexp}. This way you can effectively expand
several words as if they were concatenated with spaces between them.
In order for appending to work, you must not modify the contents of the
word vector structure between calls to @code{wordexp}. And, if you set
@code{WRDE_DOOFFS} in the first call to @code{wordexp}, you must also
set it when you append to the results.
@comment wordexp.h
@comment POSIX.2
@item WRDE_DOOFFS
Leave blank slots at the beginning of the vector of words.
The @code{we_offs} field says how many slots to leave.
The blank slots contain null pointers.
@comment wordexp.h
@comment POSIX.2
@item WRDE_NOCMD
Don't do command substitution; if the input requests command substitution,
report an error.
@comment wordexp.h
@comment POSIX.2
@item WRDE_REUSE
Reuse a word vector made by a previous call to @code{wordexp}.
Instead of allocating a new vector of words, this call to @code{wordexp}
will use the vector that already exists (making it larger if necessary).
Note that the vector may move, so it is not safe to save an old pointer
and use it again after calling @code{wordexp}. You must fetch
@code{we_pathv} anew after each call.
@comment wordexp.h
@comment POSIX.2
@item WRDE_SHOWERR
Do show any error messages printed by commands run by command substitution.
More precisely, allow these commands to inherit the standard error output
stream of the current process. By default, @code{wordexp} gives these
commands a standard error stream that discards all output.
@comment wordexp.h
@comment POSIX.2
@item WRDE_UNDEF
If the input refers to a shell variable that is not defined, report an
error.
@end table
@node Wordexp Example
@subsection @code{wordexp} Example
Here is an example of using @code{wordexp} to expand several strings
and use the results to run a shell command. It also shows the use of
@code{WRDE_APPEND} to concatenate the expansions and of @code{wordfree}
to free the space allocated by @code{wordexp}.
@smallexample
int
expand_and_execute (const char *program, const char **options)
@{
wordexp_t result;
pid_t pid
int status, i;
/* @r{Expand the string for the program to run.} */
switch (wordexp (program, &result, 0))
@{
case 0: /* @r{Successful}. */
break;
case WRDE_NOSPACE:
/* @r{If the error was @code{WRDE_NOSPACE},}
@r{then perhaps part of the result was allocated.} */
wordfree (&result);
default: /* @r{Some other error.} */
return -1;
@}
/* @r{Expand the strings specified for the arguments.} */
for (i = 0; options[i] != NULL; i++)
@{
if (wordexp (options[i], &result, WRDE_APPEND))
@{
wordfree (&result);
return -1;
@}
@}
pid = fork ();
if (pid == 0)
@{
/* @r{This is the child process. Execute the command.} */
execv (result.we_wordv[0], result.we_wordv);
exit (EXIT_FAILURE);
@}
else if (pid < 0)
/* @r{The fork failed. Report failure.} */
status = -1;
else
/* @r{This is the parent process. Wait for the child to complete.} */
if (waitpid (pid, &status, 0) != pid)
status = -1;
wordfree (&result);
return status;
@}
@end smallexample
@node Tilde Expansion
@subsection Details of Tilde Expansion
It's a standard part of shell syntax that you can use @samp{~} at the
beginning of a file name to stand for your own home directory. You
can use @samp{~@var{user}} to stand for @var{user}'s home directory.
@dfn{Tilde expansion} is the process of converting these abbreviations
to the directory names that they stand for.
Tilde expansion applies to the @samp{~} plus all following characters up
to whitespace or a slash. It takes place only at the beginning of a
word, and only if none of the characters to be transformed is quoted in
any way.
Plain @samp{~} uses the value of the environment variable @code{HOME}
as the proper home directory name. @samp{~} followed by a user name
uses @code{getpwname} to look up that user in the user database, and
uses whatever directory is recorded there. Thus, @samp{~} followed
by your own name can give different results from plain @samp{~}, if
the value of @code{HOME} is not really your home directory.
@node Variable Substitution
@subsection Details of Variable Substitution
Part of ordinary shell syntax is the use of @samp{$@var{variable}} to
substitute the value of a shell variable into a command. This is called
@dfn{variable substitution}, and it is one part of doing word expansion.
There are two basic ways you can write a variable reference for
substitution:
@table @code
@item $@{@var{variable}@}
If you write braces around the variable name, then it is completely
unambiguous where the variable name ends. You can concatenate
additional letters onto the end of the variable value by writing them
immediately after the close brace. For example, @samp{$@{foo@}s}
expands into @samp{tractors}.
@item $@var{variable}
If you do not put braces around the variable name, then the variable
name consists of all the alphanumeric characters and underscores that
follow the @samp{$}. The next punctuation character ends the variable
name. Thus, @samp{$foo-bar} refers to the variable @code{foo} and expands
into @samp{tractor-bar}.
@end table
When you use braces, you can also use various constructs to modify the
value that is substituted, or test it in various ways.
@table @code
@item $@{@var{variable}:-@var{default}@}
Substitute the value of @var{variable}, but if that is empty or
undefined, use @var{default} instead.
@item $@{@var{variable}:=@var{default}@}
Substitute the value of @var{variable}, but if that is empty or
undefined, use @var{default} instead and set the variable to
@var{default}.
@item $@{@var{variable}:?@var{message}@}
If @var{variable} is defined and not empty, substitute its value.
Otherwise, print @var{message} as an error message on the standard error
stream, and consider word expansion a failure.
@c ??? How does wordexp report such an error?
@c WRDE_BADVAL is returned.
@item $@{@var{variable}:+@var{replacement}@}
Substitute @var{replacement}, but only if @var{variable} is defined and
nonempty. Otherwise, substitute nothing for this construct.
@end table
@table @code
@item $@{#@var{variable}@}
Substitute a numeral which expresses in base ten the number of
characters in the value of @var{variable}. @samp{$@{#foo@}} stands for
@samp{7}, because @samp{tractor} is seven characters.
@end table
These variants of variable substitution let you remove part of the
variable's value before substituting it. The @var{prefix} and
@var{suffix} are not mere strings; they are wildcard patterns, just
like the patterns that you use to match multiple file names. But
in this context, they match against parts of the variable value
rather than against file names.
@table @code
@item $@{@var{variable}%%@var{suffix}@}
Substitute the value of @var{variable}, but first discard from that
variable any portion at the end that matches the pattern @var{suffix}.
If there is more than one alternative for how to match against
@var{suffix}, this construct uses the longest possible match.
Thus, @samp{$@{foo%%r*@}} substitutes @samp{t}, because the largest
match for @samp{r*} at the end of @samp{tractor} is @samp{ractor}.
@item $@{@var{variable}%@var{suffix}@}
Substitute the value of @var{variable}, but first discard from that
variable any portion at the end that matches the pattern @var{suffix}.
If there is more than one alternative for how to match against
@var{suffix}, this construct uses the shortest possible alternative.
Thus, @samp{$@{foo%r*@}} substitutes @samp{tracto}, because the shortest
match for @samp{r*} at the end of @samp{tractor} is just @samp{r}.
@item $@{@var{variable}##@var{prefix}@}
Substitute the value of @var{variable}, but first discard from that
variable any portion at the beginning that matches the pattern @var{prefix}.
If there is more than one alternative for how to match against
@var{prefix}, this construct uses the longest possible match.
Thus, @samp{$@{foo##*t@}} substitutes @samp{or}, because the largest
match for @samp{*t} at the beginning of @samp{tractor} is @samp{tract}.
@item $@{@var{variable}#@var{prefix}@}
Substitute the value of @var{variable}, but first discard from that
variable any portion at the beginning that matches the pattern @var{prefix}.
If there is more than one alternative for how to match against
@var{prefix}, this construct uses the shortest possible alternative.
Thus, @samp{$@{foo#*t@}} substitutes @samp{ractor}, because the shortest
match for @samp{*t} at the beginning of @samp{tractor} is just @samp{t}.
@end table
glibc-doc-reference-2.19.orig/manual/summary.awk 0000664 0001750 0001750 00000007067 12275120646 021772 0 ustar adconrad adconrad # awk script to create summary.texinfo from the library texinfo files.
# Copyright (C) 1992-2014 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# .
# This script recognizes sequences that look like:
# @comment HEADER.h
# @comment STANDARD
# @def... ITEM | @item ITEM | @vindex ITEM
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print "@c DO NOT EDIT THIS FILE!"
print "@c This file is generated by summary.awk from the Texinfo sources."
}
$1 == "@node" { node=$2;
for (i = 3; i <= NF; ++i)
{ node=node " " $i; if ( $i ~ /,/ ) break; }
sub (/,[, ]*$/, "", node);
}
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for (i = 3; i <= NF; ++i)
header=header ", @file{" $i "}"
}
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header != 0 && $1 ~ /@def|@item|@vindex/ \
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if (!curly) {
if (n >= firstword[$1])
defn=defn " " word
if (n == nameword[$1])
name=word
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}
}
}
printf "@comment %s%c", name, 12 # FF
printf "@item%s%c%c", defn, 12, 12
if (header != -1) printf "%s ", header;
printf "(%s): @ref{%s}.%c\n", std, node, 12;
header = 0 }
glibc-doc-reference-2.19.orig/manual/math.texi 0000664 0001750 0001750 00000220064 12275120646 021407 0 ustar adconrad adconrad @c We need some definitions here.
@ifclear mult
@ifhtml
@set mult ·
@set infty ∞
@set pie π
@end ifhtml
@iftex
@set mult @cdot
@set infty @infty
@end iftex
@ifclear mult
@set mult *
@set infty oo
@set pie pi
@end ifclear
@macro mul
@value{mult}
@end macro
@macro infinity
@value{infty}
@end macro
@ifnottex
@macro pi
@value{pie}
@end macro
@end ifnottex
@end ifclear
@node Mathematics, Arithmetic, Syslog, Top
@c %MENU% Math functions, useful constants, random numbers
@chapter Mathematics
This chapter contains information about functions for performing
mathematical computations, such as trigonometric functions. Most of
these functions have prototypes declared in the header file
@file{math.h}. The complex-valued functions are defined in
@file{complex.h}.
@pindex math.h
@pindex complex.h
All mathematical functions which take a floating-point argument
have three variants, one each for @code{double}, @code{float}, and
@code{long double} arguments. The @code{double} versions are mostly
defined in @w{ISO C89}. The @code{float} and @code{long double}
versions are from the numeric extensions to C included in @w{ISO C99}.
Which of the three versions of a function should be used depends on the
situation. For most calculations, the @code{float} functions are the
fastest. On the other hand, the @code{long double} functions have the
highest precision. @code{double} is somewhere in between. It is
usually wise to pick the narrowest type that can accommodate your data.
Not all machines have a distinct @code{long double} type; it may be the
same as @code{double}.
@menu
* Mathematical Constants:: Precise numeric values for often-used
constants.
* Trig Functions:: Sine, cosine, tangent, and friends.
* Inverse Trig Functions:: Arcsine, arccosine, etc.
* Exponents and Logarithms:: Also pow and sqrt.
* Hyperbolic Functions:: sinh, cosh, tanh, etc.
* Special Functions:: Bessel, gamma, erf.
* Errors in Math Functions:: Known Maximum Errors in Math Functions.
* Pseudo-Random Numbers:: Functions for generating pseudo-random
numbers.
* FP Function Optimizations:: Fast code or small code.
@end menu
@node Mathematical Constants
@section Predefined Mathematical Constants
@cindex constants
@cindex mathematical constants
The header @file{math.h} defines several useful mathematical constants.
All values are defined as preprocessor macros starting with @code{M_}.
The values provided are:
@vtable @code
@item M_E
The base of natural logarithms.
@item M_LOG2E
The logarithm to base @code{2} of @code{M_E}.
@item M_LOG10E
The logarithm to base @code{10} of @code{M_E}.
@item M_LN2
The natural logarithm of @code{2}.
@item M_LN10
The natural logarithm of @code{10}.
@item M_PI
Pi, the ratio of a circle's circumference to its diameter.
@item M_PI_2
Pi divided by two.
@item M_PI_4
Pi divided by four.
@item M_1_PI
The reciprocal of pi (1/pi)
@item M_2_PI
Two times the reciprocal of pi.
@item M_2_SQRTPI
Two times the reciprocal of the square root of pi.
@item M_SQRT2
The square root of two.
@item M_SQRT1_2
The reciprocal of the square root of two (also the square root of 1/2).
@end vtable
These constants come from the Unix98 standard and were also available in
4.4BSD; therefore they are only defined if @code{_BSD_SOURCE} or
@code{_XOPEN_SOURCE=500}, or a more general feature select macro, is
defined. The default set of features includes these constants.
@xref{Feature Test Macros}.
All values are of type @code{double}. As an extension, @theglibc{}
also defines these constants with type @code{long double}. The
@code{long double} macros have a lowercase @samp{l} appended to their
names: @code{M_El}, @code{M_PIl}, and so forth. These are only
available if @code{_GNU_SOURCE} is defined.
@vindex PI
@emph{Note:} Some programs use a constant named @code{PI} which has the
same value as @code{M_PI}. This constant is not standard; it may have
appeared in some old AT&T headers, and is mentioned in Stroustrup's book
on C++. It infringes on the user's name space, so @theglibc{}
does not define it. Fixing programs written to expect it is simple:
replace @code{PI} with @code{M_PI} throughout, or put @samp{-DPI=M_PI}
on the compiler command line.
@node Trig Functions
@section Trigonometric Functions
@cindex trigonometric functions
These are the familiar @code{sin}, @code{cos}, and @code{tan} functions.
The arguments to all of these functions are in units of radians; recall
that pi radians equals 180 degrees.
@cindex pi (trigonometric constant)
The math library normally defines @code{M_PI} to a @code{double}
approximation of pi. If strict ISO and/or POSIX compliance
are requested this constant is not defined, but you can easily define it
yourself:
@smallexample
#define M_PI 3.14159265358979323846264338327
@end smallexample
@noindent
You can also compute the value of pi with the expression @code{acos
(-1.0)}.
@comment math.h
@comment ISO
@deftypefun double sin (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float sinf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} sinl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the sine of @var{x}, where @var{x} is given in
radians. The return value is in the range @code{-1} to @code{1}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double cos (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float cosf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} cosl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the cosine of @var{x}, where @var{x} is given in
radians. The return value is in the range @code{-1} to @code{1}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double tan (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float tanf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} tanl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the tangent of @var{x}, where @var{x} is given in
radians.
Mathematically, the tangent function has singularities at odd multiples
of pi/2. If the argument @var{x} is too close to one of these
singularities, @code{tan} will signal overflow.
@end deftypefun
In many applications where @code{sin} and @code{cos} are used, the sine
and cosine of the same angle are needed at the same time. It is more
efficient to compute them simultaneously, so the library provides a
function to do that.
@comment math.h
@comment GNU
@deftypefun void sincos (double @var{x}, double *@var{sinx}, double *@var{cosx})
@comment math.h
@comment GNU
@deftypefunx void sincosf (float @var{x}, float *@var{sinx}, float *@var{cosx})
@comment math.h
@comment GNU
@deftypefunx void sincosl (long double @var{x}, long double *@var{sinx}, long double *@var{cosx})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the sine of @var{x} in @code{*@var{sinx}} and the
cosine of @var{x} in @code{*@var{cos}}, where @var{x} is given in
radians. Both values, @code{*@var{sinx}} and @code{*@var{cosx}}, are in
the range of @code{-1} to @code{1}.
This function is a GNU extension. Portable programs should be prepared
to cope with its absence.
@end deftypefun
@cindex complex trigonometric functions
@w{ISO C99} defines variants of the trig functions which work on
complex numbers. @Theglibc{} provides these functions, but they
are only useful if your compiler supports the new complex types defined
by the standard.
@c XXX Change this when gcc is fixed. -zw
(As of this writing GCC supports complex numbers, but there are bugs in
the implementation.)
@comment complex.h
@comment ISO
@deftypefun {complex double} csin (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} csinf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} csinl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c There are calls to nan* that could trigger @mtslocale if they didn't get
@c empty strings.
These functions return the complex sine of @var{z}.
The mathematical definition of the complex sine is
@ifnottex
@math{sin (z) = 1/(2*i) * (exp (z*i) - exp (-z*i))}.
@end ifnottex
@tex
$$\sin(z) = {1\over 2i} (e^{zi} - e^{-zi})$$
@end tex
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} ccos (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} ccosf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} ccosl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex cosine of @var{z}.
The mathematical definition of the complex cosine is
@ifnottex
@math{cos (z) = 1/2 * (exp (z*i) + exp (-z*i))}
@end ifnottex
@tex
$$\cos(z) = {1\over 2} (e^{zi} + e^{-zi})$$
@end tex
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} ctan (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} ctanf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} ctanl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex tangent of @var{z}.
The mathematical definition of the complex tangent is
@ifnottex
@math{tan (z) = -i * (exp (z*i) - exp (-z*i)) / (exp (z*i) + exp (-z*i))}
@end ifnottex
@tex
$$\tan(z) = -i \cdot {e^{zi} - e^{-zi}\over e^{zi} + e^{-zi}}$$
@end tex
@noindent
The complex tangent has poles at @math{pi/2 + 2n}, where @math{n} is an
integer. @code{ctan} may signal overflow if @var{z} is too close to a
pole.
@end deftypefun
@node Inverse Trig Functions
@section Inverse Trigonometric Functions
@cindex inverse trigonometric functions
These are the usual arc sine, arc cosine and arc tangent functions,
which are the inverses of the sine, cosine and tangent functions
respectively.
@comment math.h
@comment ISO
@deftypefun double asin (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float asinf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} asinl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the arc sine of @var{x}---that is, the value whose
sine is @var{x}. The value is in units of radians. Mathematically,
there are infinitely many such values; the one actually returned is the
one between @code{-pi/2} and @code{pi/2} (inclusive).
The arc sine function is defined mathematically only
over the domain @code{-1} to @code{1}. If @var{x} is outside the
domain, @code{asin} signals a domain error.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double acos (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float acosf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} acosl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the arc cosine of @var{x}---that is, the value
whose cosine is @var{x}. The value is in units of radians.
Mathematically, there are infinitely many such values; the one actually
returned is the one between @code{0} and @code{pi} (inclusive).
The arc cosine function is defined mathematically only
over the domain @code{-1} to @code{1}. If @var{x} is outside the
domain, @code{acos} signals a domain error.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double atan (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float atanf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} atanl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the arc tangent of @var{x}---that is, the value
whose tangent is @var{x}. The value is in units of radians.
Mathematically, there are infinitely many such values; the one actually
returned is the one between @code{-pi/2} and @code{pi/2} (inclusive).
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double atan2 (double @var{y}, double @var{x})
@comment math.h
@comment ISO
@deftypefunx float atan2f (float @var{y}, float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} atan2l (long double @var{y}, long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function computes the arc tangent of @var{y}/@var{x}, but the signs
of both arguments are used to determine the quadrant of the result, and
@var{x} is permitted to be zero. The return value is given in radians
and is in the range @code{-pi} to @code{pi}, inclusive.
If @var{x} and @var{y} are coordinates of a point in the plane,
@code{atan2} returns the signed angle between the line from the origin
to that point and the x-axis. Thus, @code{atan2} is useful for
converting Cartesian coordinates to polar coordinates. (To compute the
radial coordinate, use @code{hypot}; see @ref{Exponents and
Logarithms}.)
@c This is experimentally true. Should it be so? -zw
If both @var{x} and @var{y} are zero, @code{atan2} returns zero.
@end deftypefun
@cindex inverse complex trigonometric functions
@w{ISO C99} defines complex versions of the inverse trig functions.
@comment complex.h
@comment ISO
@deftypefun {complex double} casin (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} casinf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} casinl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the complex arc sine of @var{z}---that is, the
value whose sine is @var{z}. The value returned is in radians.
Unlike the real-valued functions, @code{casin} is defined for all
values of @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} cacos (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} cacosf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} cacosl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the complex arc cosine of @var{z}---that is, the
value whose cosine is @var{z}. The value returned is in radians.
Unlike the real-valued functions, @code{cacos} is defined for all
values of @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} catan (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} catanf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} catanl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the complex arc tangent of @var{z}---that is,
the value whose tangent is @var{z}. The value is in units of radians.
@end deftypefun
@node Exponents and Logarithms
@section Exponentiation and Logarithms
@cindex exponentiation functions
@cindex power functions
@cindex logarithm functions
@comment math.h
@comment ISO
@deftypefun double exp (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float expf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} expl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute @code{e} (the base of natural logarithms) raised
to the power @var{x}.
If the magnitude of the result is too large to be representable,
@code{exp} signals overflow.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double exp2 (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float exp2f (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} exp2l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute @code{2} raised to the power @var{x}.
Mathematically, @code{exp2 (x)} is the same as @code{exp (x * log (2))}.
@end deftypefun
@comment math.h
@comment GNU
@deftypefun double exp10 (double @var{x})
@comment math.h
@comment GNU
@deftypefunx float exp10f (float @var{x})
@comment math.h
@comment GNU
@deftypefunx {long double} exp10l (long double @var{x})
@comment math.h
@comment GNU
@deftypefunx double pow10 (double @var{x})
@comment math.h
@comment GNU
@deftypefunx float pow10f (float @var{x})
@comment math.h
@comment GNU
@deftypefunx {long double} pow10l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute @code{10} raised to the power @var{x}.
Mathematically, @code{exp10 (x)} is the same as @code{exp (x * log (10))}.
These functions are GNU extensions. The name @code{exp10} is
preferred, since it is analogous to @code{exp} and @code{exp2}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double log (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float logf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} logl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions compute the natural logarithm of @var{x}. @code{exp (log
(@var{x}))} equals @var{x}, exactly in mathematics and approximately in
C.
If @var{x} is negative, @code{log} signals a domain error. If @var{x}
is zero, it returns negative infinity; if @var{x} is too close to zero,
it may signal overflow.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double log10 (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float log10f (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} log10l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the base-10 logarithm of @var{x}.
@code{log10 (@var{x})} equals @code{log (@var{x}) / log (10)}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double log2 (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float log2f (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} log2l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the base-2 logarithm of @var{x}.
@code{log2 (@var{x})} equals @code{log (@var{x}) / log (2)}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double logb (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float logbf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} logbl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions extract the exponent of @var{x} and return it as a
floating-point value. If @code{FLT_RADIX} is two, @code{logb} is equal
to @code{floor (log2 (x))}, except it's probably faster.
If @var{x} is de-normalized, @code{logb} returns the exponent @var{x}
would have if it were normalized. If @var{x} is infinity (positive or
negative), @code{logb} returns @math{@infinity{}}. If @var{x} is zero,
@code{logb} returns @math{@infinity{}}. It does not signal.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun int ilogb (double @var{x})
@comment math.h
@comment ISO
@deftypefunx int ilogbf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx int ilogbl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions are equivalent to the corresponding @code{logb}
functions except that they return signed integer values.
@end deftypefun
@noindent
Since integers cannot represent infinity and NaN, @code{ilogb} instead
returns an integer that can't be the exponent of a normal floating-point
number. @file{math.h} defines constants so you can check for this.
@comment math.h
@comment ISO
@deftypevr Macro int FP_ILOGB0
@code{ilogb} returns this value if its argument is @code{0}. The
numeric value is either @code{INT_MIN} or @code{-INT_MAX}.
This macro is defined in @w{ISO C99}.
@end deftypevr
@comment math.h
@comment ISO
@deftypevr Macro int FP_ILOGBNAN
@code{ilogb} returns this value if its argument is @code{NaN}. The
numeric value is either @code{INT_MIN} or @code{INT_MAX}.
This macro is defined in @w{ISO C99}.
@end deftypevr
These values are system specific. They might even be the same. The
proper way to test the result of @code{ilogb} is as follows:
@smallexample
i = ilogb (f);
if (i == FP_ILOGB0 || i == FP_ILOGBNAN)
@{
if (isnan (f))
@{
/* @r{Handle NaN.} */
@}
else if (f == 0.0)
@{
/* @r{Handle 0.0.} */
@}
else
@{
/* @r{Some other value with large exponent,}
@r{perhaps +Inf.} */
@}
@}
@end smallexample
@comment math.h
@comment ISO
@deftypefun double pow (double @var{base}, double @var{power})
@comment math.h
@comment ISO
@deftypefunx float powf (float @var{base}, float @var{power})
@comment math.h
@comment ISO
@deftypefunx {long double} powl (long double @var{base}, long double @var{power})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These are general exponentiation functions, returning @var{base} raised
to @var{power}.
Mathematically, @code{pow} would return a complex number when @var{base}
is negative and @var{power} is not an integral value. @code{pow} can't
do that, so instead it signals a domain error. @code{pow} may also
underflow or overflow the destination type.
@end deftypefun
@cindex square root function
@comment math.h
@comment ISO
@deftypefun double sqrt (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float sqrtf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} sqrtl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the nonnegative square root of @var{x}.
If @var{x} is negative, @code{sqrt} signals a domain error.
Mathematically, it should return a complex number.
@end deftypefun
@cindex cube root function
@comment math.h
@comment BSD
@deftypefun double cbrt (double @var{x})
@comment math.h
@comment BSD
@deftypefunx float cbrtf (float @var{x})
@comment math.h
@comment BSD
@deftypefunx {long double} cbrtl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the cube root of @var{x}. They cannot
fail; every representable real value has a representable real cube root.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double hypot (double @var{x}, double @var{y})
@comment math.h
@comment ISO
@deftypefunx float hypotf (float @var{x}, float @var{y})
@comment math.h
@comment ISO
@deftypefunx {long double} hypotl (long double @var{x}, long double @var{y})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return @code{sqrt (@var{x}*@var{x} +
@var{y}*@var{y})}. This is the length of the hypotenuse of a right
triangle with sides of length @var{x} and @var{y}, or the distance
of the point (@var{x}, @var{y}) from the origin. Using this function
instead of the direct formula is wise, since the error is
much smaller. See also the function @code{cabs} in @ref{Absolute Value}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double expm1 (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float expm1f (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} expm1l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return a value equivalent to @code{exp (@var{x}) - 1}.
They are computed in a way that is accurate even if @var{x} is
near zero---a case where @code{exp (@var{x}) - 1} would be inaccurate owing
to subtraction of two numbers that are nearly equal.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double log1p (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float log1pf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} log1pl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions returns a value equivalent to @w{@code{log (1 + @var{x})}}.
They are computed in a way that is accurate even if @var{x} is
near zero.
@end deftypefun
@cindex complex exponentiation functions
@cindex complex logarithm functions
@w{ISO C99} defines complex variants of some of the exponentiation and
logarithm functions.
@comment complex.h
@comment ISO
@deftypefun {complex double} cexp (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} cexpf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} cexpl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return @code{e} (the base of natural
logarithms) raised to the power of @var{z}.
Mathematically, this corresponds to the value
@ifnottex
@math{exp (z) = exp (creal (z)) * (cos (cimag (z)) + I * sin (cimag (z)))}
@end ifnottex
@tex
$$\exp(z) = e^z = e^{{\rm Re}\,z} (\cos ({\rm Im}\,z) + i \sin ({\rm Im}\,z))$$
@end tex
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} clog (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} clogf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} clogl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the natural logarithm of @var{z}.
Mathematically, this corresponds to the value
@ifnottex
@math{log (z) = log (cabs (z)) + I * carg (z)}
@end ifnottex
@tex
$$\log(z) = \log |z| + i \arg z$$
@end tex
@noindent
@code{clog} has a pole at 0, and will signal overflow if @var{z} equals
or is very close to 0. It is well-defined for all other values of
@var{z}.
@end deftypefun
@comment complex.h
@comment GNU
@deftypefun {complex double} clog10 (complex double @var{z})
@comment complex.h
@comment GNU
@deftypefunx {complex float} clog10f (complex float @var{z})
@comment complex.h
@comment GNU
@deftypefunx {complex long double} clog10l (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the base 10 logarithm of the complex value
@var{z}. Mathematically, this corresponds to the value
@ifnottex
@math{log (z) = log10 (cabs (z)) + I * carg (z)}
@end ifnottex
@tex
$$\log_{10}(z) = \log_{10}|z| + i \arg z$$
@end tex
These functions are GNU extensions.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} csqrt (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} csqrtf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} csqrtl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex square root of the argument @var{z}. Unlike
the real-valued functions, they are defined for all values of @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} cpow (complex double @var{base}, complex double @var{power})
@comment complex.h
@comment ISO
@deftypefunx {complex float} cpowf (complex float @var{base}, complex float @var{power})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} cpowl (complex long double @var{base}, complex long double @var{power})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return @var{base} raised to the power of
@var{power}. This is equivalent to @w{@code{cexp (y * clog (x))}}
@end deftypefun
@node Hyperbolic Functions
@section Hyperbolic Functions
@cindex hyperbolic functions
The functions in this section are related to the exponential functions;
see @ref{Exponents and Logarithms}.
@comment math.h
@comment ISO
@deftypefun double sinh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float sinhf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} sinhl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the hyperbolic sine of @var{x}, defined
mathematically as @w{@code{(exp (@var{x}) - exp (-@var{x})) / 2}}. They
may signal overflow if @var{x} is too large.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double cosh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float coshf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} coshl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These function return the hyperbolic cosine of @var{x},
defined mathematically as @w{@code{(exp (@var{x}) + exp (-@var{x})) / 2}}.
They may signal overflow if @var{x} is too large.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double tanh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float tanhf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} tanhl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the hyperbolic tangent of @var{x},
defined mathematically as @w{@code{sinh (@var{x}) / cosh (@var{x})}}.
They may signal overflow if @var{x} is too large.
@end deftypefun
@cindex hyperbolic functions
There are counterparts for the hyperbolic functions which take
complex arguments.
@comment complex.h
@comment ISO
@deftypefun {complex double} csinh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} csinhf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} csinhl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex hyperbolic sine of @var{z}, defined
mathematically as @w{@code{(exp (@var{z}) - exp (-@var{z})) / 2}}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} ccosh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} ccoshf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} ccoshl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex hyperbolic cosine of @var{z}, defined
mathematically as @w{@code{(exp (@var{z}) + exp (-@var{z})) / 2}}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} ctanh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} ctanhf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} ctanhl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the complex hyperbolic tangent of @var{z},
defined mathematically as @w{@code{csinh (@var{z}) / ccosh (@var{z})}}.
@end deftypefun
@cindex inverse hyperbolic functions
@comment math.h
@comment ISO
@deftypefun double asinh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float asinhf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} asinhl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse hyperbolic sine of @var{x}---the
value whose hyperbolic sine is @var{x}.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double acosh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float acoshf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} acoshl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse hyperbolic cosine of @var{x}---the
value whose hyperbolic cosine is @var{x}. If @var{x} is less than
@code{1}, @code{acosh} signals a domain error.
@end deftypefun
@comment math.h
@comment ISO
@deftypefun double atanh (double @var{x})
@comment math.h
@comment ISO
@deftypefunx float atanhf (float @var{x})
@comment math.h
@comment ISO
@deftypefunx {long double} atanhl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse hyperbolic tangent of @var{x}---the
value whose hyperbolic tangent is @var{x}. If the absolute value of
@var{x} is greater than @code{1}, @code{atanh} signals a domain error;
if it is equal to 1, @code{atanh} returns infinity.
@end deftypefun
@cindex inverse complex hyperbolic functions
@comment complex.h
@comment ISO
@deftypefun {complex double} casinh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} casinhf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} casinhl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse complex hyperbolic sine of
@var{z}---the value whose complex hyperbolic sine is @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} cacosh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} cacoshf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} cacoshl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse complex hyperbolic cosine of
@var{z}---the value whose complex hyperbolic cosine is @var{z}. Unlike
the real-valued functions, there are no restrictions on the value of @var{z}.
@end deftypefun
@comment complex.h
@comment ISO
@deftypefun {complex double} catanh (complex double @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex float} catanhf (complex float @var{z})
@comment complex.h
@comment ISO
@deftypefunx {complex long double} catanhl (complex long double @var{z})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
These functions return the inverse complex hyperbolic tangent of
@var{z}---the value whose complex hyperbolic tangent is @var{z}. Unlike
the real-valued functions, there are no restrictions on the value of
@var{z}.
@end deftypefun
@node Special Functions
@section Special Functions
@cindex special functions
@cindex Bessel functions
@cindex gamma function
These are some more exotic mathematical functions which are sometimes
useful. Currently they only have real-valued versions.
@comment math.h
@comment SVID
@deftypefun double erf (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float erff (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} erfl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{erf} returns the error function of @var{x}. The error
function is defined as
@tex
$$\hbox{erf}(x) = {2\over\sqrt{\pi}}\cdot\int_0^x e^{-t^2} \hbox{d}t$$
@end tex
@ifnottex
@smallexample
erf (x) = 2/sqrt(pi) * integral from 0 to x of exp(-t^2) dt
@end smallexample
@end ifnottex
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double erfc (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float erfcf (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} erfcl (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{erfc} returns @code{1.0 - erf(@var{x})}, but computed in a
fashion that avoids round-off error when @var{x} is large.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double lgamma (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float lgammaf (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} lgammal (long double @var{x})
@safety{@prelim{}@mtunsafe{@mtasurace{:signgam}}@asunsafe{}@acsafe{}}
@code{lgamma} returns the natural logarithm of the absolute value of
the gamma function of @var{x}. The gamma function is defined as
@tex
$$\Gamma(x) = \int_0^\infty t^{x-1} e^{-t} \hbox{d}t$$
@end tex
@ifnottex
@smallexample
gamma (x) = integral from 0 to @infinity{} of t^(x-1) e^-t dt
@end smallexample
@end ifnottex
@vindex signgam
The sign of the gamma function is stored in the global variable
@var{signgam}, which is declared in @file{math.h}. It is @code{1} if
the intermediate result was positive or zero, or @code{-1} if it was
negative.
To compute the real gamma function you can use the @code{tgamma}
function or you can compute the values as follows:
@smallexample
lgam = lgamma(x);
gam = signgam*exp(lgam);
@end smallexample
The gamma function has singularities at the non-positive integers.
@code{lgamma} will raise the zero divide exception if evaluated at a
singularity.
@end deftypefun
@comment math.h
@comment XPG
@deftypefun double lgamma_r (double @var{x}, int *@var{signp})
@comment math.h
@comment XPG
@deftypefunx float lgammaf_r (float @var{x}, int *@var{signp})
@comment math.h
@comment XPG
@deftypefunx {long double} lgammal_r (long double @var{x}, int *@var{signp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{lgamma_r} is just like @code{lgamma}, but it stores the sign of
the intermediate result in the variable pointed to by @var{signp}
instead of in the @var{signgam} global. This means it is reentrant.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double gamma (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float gammaf (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} gammal (long double @var{x})
@safety{@prelim{}@mtunsafe{@mtasurace{:signgam}}@asunsafe{}@acsafe{}}
These functions exist for compatibility reasons. They are equivalent to
@code{lgamma} etc. It is better to use @code{lgamma} since for one the
name reflects better the actual computation, moreover @code{lgamma} is
standardized in @w{ISO C99} while @code{gamma} is not.
@end deftypefun
@comment math.h
@comment XPG, ISO
@deftypefun double tgamma (double @var{x})
@comment math.h
@comment XPG, ISO
@deftypefunx float tgammaf (float @var{x})
@comment math.h
@comment XPG, ISO
@deftypefunx {long double} tgammal (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{tgamma} applies the gamma function to @var{x}. The gamma
function is defined as
@tex
$$\Gamma(x) = \int_0^\infty t^{x-1} e^{-t} \hbox{d}t$$
@end tex
@ifnottex
@smallexample
gamma (x) = integral from 0 to @infinity{} of t^(x-1) e^-t dt
@end smallexample
@end ifnottex
This function was introduced in @w{ISO C99}.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double j0 (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float j0f (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} j0l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{j0} returns the Bessel function of the first kind of order 0 of
@var{x}. It may signal underflow if @var{x} is too large.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double j1 (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float j1f (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} j1l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{j1} returns the Bessel function of the first kind of order 1 of
@var{x}. It may signal underflow if @var{x} is too large.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double jn (int @var{n}, double @var{x})
@comment math.h
@comment SVID
@deftypefunx float jnf (int @var{n}, float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} jnl (int @var{n}, long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{jn} returns the Bessel function of the first kind of order
@var{n} of @var{x}. It may signal underflow if @var{x} is too large.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double y0 (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float y0f (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} y0l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{y0} returns the Bessel function of the second kind of order 0 of
@var{x}. It may signal underflow if @var{x} is too large. If @var{x}
is negative, @code{y0} signals a domain error; if it is zero,
@code{y0} signals overflow and returns @math{-@infinity}.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double y1 (double @var{x})
@comment math.h
@comment SVID
@deftypefunx float y1f (float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} y1l (long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{y1} returns the Bessel function of the second kind of order 1 of
@var{x}. It may signal underflow if @var{x} is too large. If @var{x}
is negative, @code{y1} signals a domain error; if it is zero,
@code{y1} signals overflow and returns @math{-@infinity}.
@end deftypefun
@comment math.h
@comment SVID
@deftypefun double yn (int @var{n}, double @var{x})
@comment math.h
@comment SVID
@deftypefunx float ynf (int @var{n}, float @var{x})
@comment math.h
@comment SVID
@deftypefunx {long double} ynl (int @var{n}, long double @var{x})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{yn} returns the Bessel function of the second kind of order @var{n} of
@var{x}. It may signal underflow if @var{x} is too large. If @var{x}
is negative, @code{yn} signals a domain error; if it is zero,
@code{yn} signals overflow and returns @math{-@infinity}.
@end deftypefun
@node Errors in Math Functions
@section Known Maximum Errors in Math Functions
@cindex math errors
@cindex ulps
This section lists the known errors of the functions in the math
library. Errors are measured in ``units of the last place''. This is a
measure for the relative error. For a number @math{z} with the
representation @math{d.d@dots{}d@mul{}2^e} (we assume IEEE
floating-point numbers with base 2) the ULP is represented by
@tex
$${|d.d\dots d - (z/2^e)|}\over {2^{p-1}}$$
@end tex
@ifnottex
@smallexample
|d.d...d - (z / 2^e)| / 2^(p - 1)
@end smallexample
@end ifnottex
@noindent
where @math{p} is the number of bits in the mantissa of the
floating-point number representation. Ideally the error for all
functions is always less than 0.5ulps in round-to-nearest mode. Using
rounding bits this is also
possible and normally implemented for the basic operations. Except
for certain functions such as @code{sqrt}, @code{fma} and @code{rint}
whose results are fully specified by reference to corresponding IEEE
754 floating-point operations, and conversions between strings and
floating point, @theglibc{} does not aim for correctly rounded results
for functions in the math library, and does not aim for correctness in
whether ``inexact'' exceptions are raised. Instead, the goals for
accuracy of functions without fully specified results are as follows;
some functions have bugs meaning they do not meet these goals in all
cases. In future, @theglibc{} may provide some other correctly
rounding functions under the names such as @code{crsin} proposed for
an extension to ISO C.
@itemize @bullet
@item
Each function with a floating-point result behaves as if it computes
an infinite-precision result that is within a few ulp (in both real
and complex parts, for functions with complex results) of the
mathematically correct value of the function (interpreted together
with ISO C or POSIX semantics for the function in question) at the
exact value passed as the input. Exceptions are raised appropriately
for this value and in accordance with IEEE 754 / ISO C / POSIX
semantics, and it is then rounded according to the current rounding
direction to the result that is returned to the user. @code{errno}
may also be set (@pxref{Math Error Reporting}).
@item
For the IBM @code{long double} format, as used on PowerPC GNU/Linux,
the accuracy goal is weaker for input values not exactly representable
in 106 bits of precision; it is as if the input value is some value
within 0.5ulp of the value actually passed, where ``ulp'' is
interpreted in terms of a fixed-precision 106-bit mantissa, but not
necessarily the exact value actually passed with discontiguous
mantissa bits.
@item
Functions behave as if the infinite-precision result computed is zero,
infinity or NaN if and only if that is the mathematically correct
infinite-precision result. They behave as if the infinite-precision
result computed always has the same sign as the mathematically correct
result.
@item
If the mathematical result is more than a few ulp above the overflow
threshold for the current rounding direction, the value returned is
the appropriate overflow value for the current rounding direction,
with the overflow exception raised.
@item
If the mathematical result has magnitude well below half the least
subnormal magnitude, the returned value is either zero or the least
subnormal (in each case, with the correct sign), according to the
current rounding direction and with the underflow exception raised.
@item
Where the mathematical result underflows and is not exactly
representable as a floating-point value, the underflow exception is
raised (so there may be spurious underflow exceptions in cases where
the underflowing result is exact, but not missing underflow exceptions
in cases where it is inexact).
@item
@Theglibc{} does not aim for functions to satisfy other properties of
the underlying mathematical function, such as monotonicity, where not
implied by the above goals.
@item
All the above applies to both real and complex parts, for complex
functions.
@end itemize
Therefore many of the functions in the math library have errors. The
table lists the maximum error for each function which is exposed by one
of the existing tests in the test suite. The table tries to cover as much
as possible and list the actual maximum error (or at least a ballpark
figure) but this is often not achieved due to the large search space.
The table lists the ULP values for different architectures. Different
architectures have different results since their hardware support for
floating-point operations varies and also the existing hardware support
is different.
@page
@c This multitable does not fit on a single page
@include libm-err.texi
@node Pseudo-Random Numbers
@section Pseudo-Random Numbers
@cindex random numbers
@cindex pseudo-random numbers
@cindex seed (for random numbers)
This section describes the GNU facilities for generating a series of
pseudo-random numbers. The numbers generated are not truly random;
typically, they form a sequence that repeats periodically, with a period
so large that you can ignore it for ordinary purposes. The random
number generator works by remembering a @dfn{seed} value which it uses
to compute the next random number and also to compute a new seed.
Although the generated numbers look unpredictable within one run of a
program, the sequence of numbers is @emph{exactly the same} from one run
to the next. This is because the initial seed is always the same. This
is convenient when you are debugging a program, but it is unhelpful if
you want the program to behave unpredictably. If you want a different
pseudo-random series each time your program runs, you must specify a
different seed each time. For ordinary purposes, basing the seed on the
current time works well.
You can obtain repeatable sequences of numbers on a particular machine type
by specifying the same initial seed value for the random number
generator. There is no standard meaning for a particular seed value;
the same seed, used in different C libraries or on different CPU types,
will give you different random numbers.
@Theglibc{} supports the standard @w{ISO C} random number functions
plus two other sets derived from BSD and SVID. The BSD and @w{ISO C}
functions provide identical, somewhat limited functionality. If only a
small number of random bits are required, we recommend you use the
@w{ISO C} interface, @code{rand} and @code{srand}. The SVID functions
provide a more flexible interface, which allows better random number
generator algorithms, provides more random bits (up to 48) per call, and
can provide random floating-point numbers. These functions are required
by the XPG standard and therefore will be present in all modern Unix
systems.
@menu
* ISO Random:: @code{rand} and friends.
* BSD Random:: @code{random} and friends.
* SVID Random:: @code{drand48} and friends.
@end menu
@node ISO Random
@subsection ISO C Random Number Functions
This section describes the random number functions that are part of
the @w{ISO C} standard.
To use these facilities, you should include the header file
@file{stdlib.h} in your program.
@pindex stdlib.h
@comment stdlib.h
@comment ISO
@deftypevr Macro int RAND_MAX
The value of this macro is an integer constant representing the largest
value the @code{rand} function can return. In @theglibc{}, it is
@code{2147483647}, which is the largest signed integer representable in
32 bits. In other libraries, it may be as low as @code{32767}.
@end deftypevr
@comment stdlib.h
@comment ISO
@deftypefun int rand (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Just calls random.
The @code{rand} function returns the next pseudo-random number in the
series. The value ranges from @code{0} to @code{RAND_MAX}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun void srand (unsigned int @var{seed})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Alias to srandom.
This function establishes @var{seed} as the seed for a new series of
pseudo-random numbers. If you call @code{rand} before a seed has been
established with @code{srand}, it uses the value @code{1} as a default
seed.
To produce a different pseudo-random series each time your program is
run, do @code{srand (time (0))}.
@end deftypefun
POSIX.1 extended the C standard functions to support reproducible random
numbers in multi-threaded programs. However, the extension is badly
designed and unsuitable for serious work.
@comment stdlib.h
@comment POSIX.1
@deftypefun int rand_r (unsigned int *@var{seed})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns a random number in the range 0 to @code{RAND_MAX}
just as @code{rand} does. However, all its state is stored in the
@var{seed} argument. This means the RNG's state can only have as many
bits as the type @code{unsigned int} has. This is far too few to
provide a good RNG.
If your program requires a reentrant RNG, we recommend you use the
reentrant GNU extensions to the SVID random number generator. The
POSIX.1 interface should only be used when the GNU extensions are not
available.
@end deftypefun
@node BSD Random
@subsection BSD Random Number Functions
This section describes a set of random number generation functions that
are derived from BSD. There is no advantage to using these functions
with @theglibc{}; we support them for BSD compatibility only.
The prototypes for these functions are in @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment BSD
@deftypefun {long int} random (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Takes a lock and calls random_r with an automatic variable and the
@c global state, while holding a lock.
This function returns the next pseudo-random number in the sequence.
The value returned ranges from @code{0} to @code{2147483647}.
@strong{NB:} Temporarily this function was defined to return a
@code{int32_t} value to indicate that the return value always contains
32 bits even if @code{long int} is wider. The standard demands it
differently. Users must always be aware of the 32-bit limitation,
though.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun void srandom (unsigned int @var{seed})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Takes a lock and calls srandom_r with an automatic variable and a
@c static buffer. There's no MT-safety issue because the static buffer
@c is internally protected by a lock, although other threads may modify
@c the set state before it is used.
The @code{srandom} function sets the state of the random number
generator based on the integer @var{seed}. If you supply a @var{seed} value
of @code{1}, this will cause @code{random} to reproduce the default set
of random numbers.
To produce a different set of pseudo-random numbers each time your
program runs, do @code{srandom (time (0))}.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun {char *} initstate (unsigned int @var{seed}, char *@var{state}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
The @code{initstate} function is used to initialize the random number
generator state. The argument @var{state} is an array of @var{size}
bytes, used to hold the state information. It is initialized based on
@var{seed}. The size must be between 8 and 256 bytes, and should be a
power of two. The bigger the @var{state} array, the better.
The return value is the previous value of the state information array.
You can use this value later as an argument to @code{setstate} to
restore that state.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun {char *} setstate (char *@var{state})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
The @code{setstate} function restores the random number state
information @var{state}. The argument must have been the result of
a previous call to @var{initstate} or @var{setstate}.
The return value is the previous value of the state information array.
You can use this value later as an argument to @code{setstate} to
restore that state.
If the function fails the return value is @code{NULL}.
@end deftypefun
The four functions described so far in this section all work on a state
which is shared by all threads. The state is not directly accessible to
the user and can only be modified by these functions. This makes it
hard to deal with situations where each thread should have its own
pseudo-random number generator.
@Theglibc{} contains four additional functions which contain the
state as an explicit parameter and therefore make it possible to handle
thread-local PRNGs. Beside this there is no difference. In fact, the
four functions already discussed are implemented internally using the
following interfaces.
The @file{stdlib.h} header contains a definition of the following type:
@comment stdlib.h
@comment GNU
@deftp {Data Type} {struct random_data}
Objects of type @code{struct random_data} contain the information
necessary to represent the state of the PRNG. Although a complete
definition of the type is present the type should be treated as opaque.
@end deftp
The functions modifying the state follow exactly the already described
functions.
@comment stdlib.h
@comment GNU
@deftypefun int random_r (struct random_data *restrict @var{buf}, int32_t *restrict @var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buf}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{random_r} function behaves exactly like the @code{random}
function except that it uses and modifies the state in the object
pointed to by the first parameter instead of the global state.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int srandom_r (unsigned int @var{seed}, struct random_data *@var{buf})
@safety{@prelim{}@mtsafe{@mtsrace{:buf}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{srandom_r} function behaves exactly like the @code{srandom}
function except that it uses and modifies the state in the object
pointed to by the second parameter instead of the global state.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int initstate_r (unsigned int @var{seed}, char *restrict @var{statebuf}, size_t @var{statelen}, struct random_data *restrict @var{buf})
@safety{@prelim{}@mtsafe{@mtsrace{:buf}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{initstate_r} function behaves exactly like the @code{initstate}
function except that it uses and modifies the state in the object
pointed to by the fourth parameter instead of the global state.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int setstate_r (char *restrict @var{statebuf}, struct random_data *restrict @var{buf})
@safety{@prelim{}@mtsafe{@mtsrace{:buf}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{setstate_r} function behaves exactly like the @code{setstate}
function except that it uses and modifies the state in the object
pointed to by the first parameter instead of the global state.
@end deftypefun
@node SVID Random
@subsection SVID Random Number Function
The C library on SVID systems contains yet another kind of random number
generator functions. They use a state of 48 bits of data. The user can
choose among a collection of functions which return the random bits
in different forms.
Generally there are two kinds of function. The first uses a state of
the random number generator which is shared among several functions and
by all threads of the process. The second requires the user to handle
the state.
All functions have in common that they use the same congruential
formula with the same constants. The formula is
@smallexample
Y = (a * X + c) mod m
@end smallexample
@noindent
where @var{X} is the state of the generator at the beginning and
@var{Y} the state at the end. @code{a} and @code{c} are constants
determining the way the generator works. By default they are
@smallexample
a = 0x5DEECE66D = 25214903917
c = 0xb = 11
@end smallexample
@noindent
but they can also be changed by the user. @code{m} is of course 2^48
since the state consists of a 48-bit array.
The prototypes for these functions are in @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment SVID
@deftypefun double drand48 (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
@c Uses of the static state buffer are not guarded by a lock (thus
@c @mtasurace:drand48), so they may be found or left at a
@c partially-updated state in case of calls from within signal handlers
@c or cancellation. None of this will break safety rules or invoke
@c undefined behavior, but it may affect randomness.
This function returns a @code{double} value in the range of @code{0.0}
to @code{1.0} (exclusive). The random bits are determined by the global
state of the random number generator in the C library.
Since the @code{double} type according to @w{IEEE 754} has a 52-bit
mantissa this means 4 bits are not initialized by the random number
generator. These are (of course) chosen to be the least significant
bits and they are initialized to @code{0}.
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun double erand48 (unsigned short int @var{xsubi}[3])
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
@c The static buffer is just initialized with default parameters, which
@c are later read to advance the state held in xsubi.
This function returns a @code{double} value in the range of @code{0.0}
to @code{1.0} (exclusive), similarly to @code{drand48}. The argument is
an array describing the state of the random number generator.
This function can be called subsequently since it updates the array to
guarantee random numbers. The array should have been initialized before
initial use to obtain reproducible results.
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun {long int} lrand48 (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{lrand48} function returns an integer value in the range of
@code{0} to @code{2^31} (exclusive). Even if the size of the @code{long
int} type can take more than 32 bits, no higher numbers are returned.
The random bits are determined by the global state of the random number
generator in the C library.
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun {long int} nrand48 (unsigned short int @var{xsubi}[3])
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
This function is similar to the @code{lrand48} function in that it
returns a number in the range of @code{0} to @code{2^31} (exclusive) but
the state of the random number generator used to produce the random bits
is determined by the array provided as the parameter to the function.
The numbers in the array are updated afterwards so that subsequent calls
to this function yield different results (as is expected of a random
number generator). The array should have been initialized before the
first call to obtain reproducible results.
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun {long int} mrand48 (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{mrand48} function is similar to @code{lrand48}. The only
difference is that the numbers returned are in the range @code{-2^31} to
@code{2^31} (exclusive).
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun {long int} jrand48 (unsigned short int @var{xsubi}[3])
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{jrand48} function is similar to @code{nrand48}. The only
difference is that the numbers returned are in the range @code{-2^31} to
@code{2^31} (exclusive). For the @code{xsubi} parameter the same
requirements are necessary.
@end deftypefun
The internal state of the random number generator can be initialized in
several ways. The methods differ in the completeness of the
information provided.
@comment stdlib.h
@comment SVID
@deftypefun void srand48 (long int @var{seedval})
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{srand48} function sets the most significant 32 bits of the
internal state of the random number generator to the least
significant 32 bits of the @var{seedval} parameter. The lower 16 bits
are initialized to the value @code{0x330E}. Even if the @code{long
int} type contains more than 32 bits only the lower 32 bits are used.
Owing to this limitation, initialization of the state of this
function is not very useful. But it makes it easy to use a construct
like @code{srand48 (time (0))}.
A side-effect of this function is that the values @code{a} and @code{c}
from the internal state, which are used in the congruential formula,
are reset to the default values given above. This is of importance once
the user has called the @code{lcong48} function (see below).
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun {unsigned short int *} seed48 (unsigned short int @var{seed16v}[3])
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{seed48} function initializes all 48 bits of the state of the
internal random number generator from the contents of the parameter
@var{seed16v}. Here the lower 16 bits of the first element of
@var{see16v} initialize the least significant 16 bits of the internal
state, the lower 16 bits of @code{@var{seed16v}[1]} initialize the mid-order
16 bits of the state and the 16 lower bits of @code{@var{seed16v}[2]}
initialize the most significant 16 bits of the state.
Unlike @code{srand48} this function lets the user initialize all 48 bits
of the state.
The value returned by @code{seed48} is a pointer to an array containing
the values of the internal state before the change. This might be
useful to restart the random number generator at a certain state.
Otherwise the value can simply be ignored.
As for @code{srand48}, the values @code{a} and @code{c} from the
congruential formula are reset to the default values.
@end deftypefun
There is one more function to initialize the random number generator
which enables you to specify even more information by allowing you to
change the parameters in the congruential formula.
@comment stdlib.h
@comment SVID
@deftypefun void lcong48 (unsigned short int @var{param}[7])
@safety{@prelim{}@mtunsafe{@mtasurace{:drand48}}@asunsafe{}@acunsafe{@acucorrupt{}}}
The @code{lcong48} function allows the user to change the complete state
of the random number generator. Unlike @code{srand48} and
@code{seed48}, this function also changes the constants in the
congruential formula.
From the seven elements in the array @var{param} the least significant
16 bits of the entries @code{@var{param}[0]} to @code{@var{param}[2]}
determine the initial state, the least significant 16 bits of
@code{@var{param}[3]} to @code{@var{param}[5]} determine the 48 bit
constant @code{a} and @code{@var{param}[6]} determines the 16-bit value
@code{c}.
@end deftypefun
All the above functions have in common that they use the global
parameters for the congruential formula. In multi-threaded programs it
might sometimes be useful to have different parameters in different
threads. For this reason all the above functions have a counterpart
which works on a description of the random number generator in the
user-supplied buffer instead of the global state.
Please note that it is no problem if several threads use the global
state if all threads use the functions which take a pointer to an array
containing the state. The random numbers are computed following the
same loop but if the state in the array is different all threads will
obtain an individual random number generator.
The user-supplied buffer must be of type @code{struct drand48_data}.
This type should be regarded as opaque and not manipulated directly.
@comment stdlib.h
@comment GNU
@deftypefun int drand48_r (struct drand48_data *@var{buffer}, double *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
This function is equivalent to the @code{drand48} function with the
difference that it does not modify the global random number generator
parameters but instead the parameters in the buffer supplied through the
pointer @var{buffer}. The random number is returned in the variable
pointed to by @var{result}.
The return value of the function indicates whether the call succeeded.
If the value is less than @code{0} an error occurred and @var{errno} is
set to indicate the problem.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int erand48_r (unsigned short int @var{xsubi}[3], struct drand48_data *@var{buffer}, double *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{erand48_r} function works like @code{erand48}, but in addition
it takes an argument @var{buffer} which describes the random number
generator. The state of the random number generator is taken from the
@code{xsubi} array, the parameters for the congruential formula from the
global random number generator data. The random number is returned in
the variable pointed to by @var{result}.
The return value is non-negative if the call succeeded.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int lrand48_r (struct drand48_data *@var{buffer}, long int *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
This function is similar to @code{lrand48}, but in addition it takes a
pointer to a buffer describing the state of the random number generator
just like @code{drand48}.
If the return value of the function is non-negative the variable pointed
to by @var{result} contains the result. Otherwise an error occurred.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int nrand48_r (unsigned short int @var{xsubi}[3], struct drand48_data *@var{buffer}, long int *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{nrand48_r} function works like @code{nrand48} in that it
produces a random number in the range @code{0} to @code{2^31}. But instead
of using the global parameters for the congruential formula it uses the
information from the buffer pointed to by @var{buffer}. The state is
described by the values in @var{xsubi}.
If the return value is non-negative the variable pointed to by
@var{result} contains the result.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int mrand48_r (struct drand48_data *@var{buffer}, long int *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
This function is similar to @code{mrand48} but like the other reentrant
functions it uses the random number generator described by the value in
the buffer pointed to by @var{buffer}.
If the return value is non-negative the variable pointed to by
@var{result} contains the result.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int jrand48_r (unsigned short int @var{xsubi}[3], struct drand48_data *@var{buffer}, long int *@var{result})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
The @code{jrand48_r} function is similar to @code{jrand48}. Like the
other reentrant functions of this function family it uses the
congruential formula parameters from the buffer pointed to by
@var{buffer}.
If the return value is non-negative the variable pointed to by
@var{result} contains the result.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
Before any of the above functions are used the buffer of type
@code{struct drand48_data} should be initialized. The easiest way to do
this is to fill the whole buffer with null bytes, e.g. by
@smallexample
memset (buffer, '\0', sizeof (struct drand48_data));
@end smallexample
@noindent
Using any of the reentrant functions of this family now will
automatically initialize the random number generator to the default
values for the state and the parameters of the congruential formula.
The other possibility is to use any of the functions which explicitly
initialize the buffer. Though it might be obvious how to initialize the
buffer from looking at the parameter to the function, it is highly
recommended to use these functions since the result might not always be
what you expect.
@comment stdlib.h
@comment GNU
@deftypefun int srand48_r (long int @var{seedval}, struct drand48_data *@var{buffer})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
The description of the random number generator represented by the
information in @var{buffer} is initialized similarly to what the function
@code{srand48} does. The state is initialized from the parameter
@var{seedval} and the parameters for the congruential formula are
initialized to their default values.
If the return value is non-negative the function call succeeded.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int seed48_r (unsigned short int @var{seed16v}[3], struct drand48_data *@var{buffer})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
This function is similar to @code{srand48_r} but like @code{seed48} it
initializes all 48 bits of the state from the parameter @var{seed16v}.
If the return value is non-negative the function call succeeded. It
does not return a pointer to the previous state of the random number
generator like the @code{seed48} function does. If the user wants to
preserve the state for a later re-run s/he can copy the whole buffer
pointed to by @var{buffer}.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int lcong48_r (unsigned short int @var{param}[7], struct drand48_data *@var{buffer})
@safety{@prelim{}@mtsafe{@mtsrace{:buffer}}@assafe{}@acunsafe{@acucorrupt{}}}
This function initializes all aspects of the random number generator
described in @var{buffer} with the data in @var{param}. Here it is
especially true that the function does more than just copying the
contents of @var{param} and @var{buffer}. More work is required and
therefore it is important to use this function rather than initializing
the random number generator directly.
If the return value is non-negative the function call succeeded.
This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
@node FP Function Optimizations
@section Is Fast Code or Small Code preferred?
@cindex Optimization
If an application uses many floating point functions it is often the case
that the cost of the function calls themselves is not negligible.
Modern processors can often execute the operations themselves
very fast, but the function call disrupts the instruction pipeline.
For this reason @theglibc{} provides optimizations for many of the
frequently-used math functions. When GNU CC is used and the user
activates the optimizer, several new inline functions and macros are
defined. These new functions and macros have the same names as the
library functions and so are used instead of the latter. In the case of
inline functions the compiler will decide whether it is reasonable to
use them, and this decision is usually correct.
This means that no calls to the library functions may be necessary, and
can increase the speed of generated code significantly. The drawback is
that code size will increase, and the increase is not always negligible.
There are two kind of inline functions: Those that give the same result
as the library functions and others that might not set @code{errno} and
might have a reduced precision and/or argument range in comparison with
the library functions. The latter inline functions are only available
if the flag @code{-ffast-math} is given to GNU CC.
In cases where the inline functions and macros are not wanted the symbol
@code{__NO_MATH_INLINES} should be defined before any system header is
included. This will ensure that only library functions are used. Of
course, it can be determined for each file in the project whether
giving this option is preferable or not.
Not all hardware implements the entire @w{IEEE 754} standard, and even
if it does there may be a substantial performance penalty for using some
of its features. For example, enabling traps on some processors forces
the FPU to run un-pipelined, which can more than double calculation time.
@c ***Add explanation of -lieee, -mieee.
glibc-doc-reference-2.19.orig/manual/argp.texi 0000664 0001750 0001750 00000151372 12275120646 021414 0 ustar adconrad adconrad @node Argp, Suboptions, Getopt, Parsing Program Arguments
@need 5000
@section Parsing Program Options with Argp
@cindex argp (program argument parser)
@cindex argument parsing with argp
@cindex option parsing with argp
@dfn{Argp} is an interface for parsing unix-style argument vectors.
@xref{Program Arguments}.
Argp provides features unavailable in the more commonly used
@code{getopt} interface. These features include automatically producing
output in response to the @samp{--help} and @samp{--version} options, as
described in the GNU coding standards. Using argp makes it less likely
that programmers will neglect to implement these additional options or
keep them up to date.
Argp also provides the ability to merge several independently defined
option parsers into one, mediating conflicts between them and making the
result appear seamless. A library can export an argp option parser that
user programs might employ in conjunction with their own option parsers,
resulting in less work for the user programs. Some programs may use only
argument parsers exported by libraries, thereby achieving consistent and
efficient option-parsing for abstractions implemented by the libraries.
@pindex argp.h
The header file @file{} should be included to use argp.
@subsection The @code{argp_parse} Function
The main interface to argp is the @code{argp_parse} function. In many
cases, calling @code{argp_parse} is the only argument-parsing code
needed in @code{main}.
@xref{Program Arguments}.
@comment argp.h
@comment GNU
@deftypefun {error_t} argp_parse (const struct argp *@var{argp}, int @var{argc}, char **@var{argv}, unsigned @var{flags}, int *@var{arg_index}, void *@var{input})
@safety{@prelim{}@mtunsafe{@mtasurace{:argpbuf} @mtslocale{} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c Optionally alloca()tes standard help options, initializes the parser,
@c then parses individual args in a loop, and then finalizes.
@c parser_init
@c calc_sizes ok
@c option_is_end ok
@c malloc @ascuheap @acsmem
@c parser_convert @mtslocale
@c convert_options @mtslocale
@c option_is_end ok
@c option_is_short ok
@c isprint, but locale may change within the loop
@c find_long_option ok
@c group_parse
@c group->parser (from argp->parser)
@c parser_parse_next
@c getopt_long(_only)_r many issues, same as non_r minus @mtasurace
@c parser_parse_arg
@c group_parse dup
@c parser_parse_opt
@c group_parse dup
@c argp_error dup @mtasurace:argpbuf @mtsenv @mtslocale @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c dgettext (bad key error) dup @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c parser_finalize
@c group_parse
@c fprintf dup @mtslocale @asucorrupt @aculock @acucorrupt [no @ascuheap @acsmem]
@c dgettext dup @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c arg_state_help
@c free dup @ascuhelp @acsmem
The @code{argp_parse} function parses the arguments in @var{argv}, of
length @var{argc}, using the argp parser @var{argp}. @xref{Argp
Parsers}. Passing a null pointer for @var{argp} is the same as using
a @code{struct argp} containing all zeros.
@var{flags} is a set of flag bits that modify the parsing behavior.
@xref{Argp Flags}. @var{input} is passed through to the argp parser
@var{argp}, and has meaning defined by @var{argp}. A typical usage is
to pass a pointer to a structure which is used for specifying
parameters to the parser and passing back the results.
Unless the @code{ARGP_NO_EXIT} or @code{ARGP_NO_HELP} flags are included
in @var{flags}, calling @code{argp_parse} may result in the program
exiting. This behavior is true if an error is detected, or when an
unknown option is encountered. @xref{Program Termination}.
If @var{arg_index} is non-null, the index of the first unparsed option
in @var{argv} is returned as a value.
The return value is zero for successful parsing, or an error code
(@pxref{Error Codes}) if an error is detected. Different argp parsers
may return arbitrary error codes, but the standard error codes are:
@code{ENOMEM} if a memory allocation error occurred, or @code{EINVAL} if
an unknown option or option argument is encountered.
@end deftypefun
@menu
* Globals: Argp Global Variables. Global argp parameters.
* Parsers: Argp Parsers. Defining parsers for use with @code{argp_parse}.
* Flags: Argp Flags. Flags that modify the behavior of @code{argp_parse}.
* Help: Argp Help. Printing help messages when not parsing.
* Examples: Argp Examples. Simple examples of programs using argp.
* Customization: Argp User Customization.
Users may control the @samp{--help} output format.
@end menu
@node Argp Global Variables, Argp Parsers, , Argp
@subsection Argp Global Variables
These variables make it easy for user programs to implement the
@samp{--version} option and provide a bug-reporting address in the
@samp{--help} output. These are implemented in argp by default.
@comment argp.h
@comment GNU
@deftypevar {const char *} argp_program_version
If defined or set by the user program to a non-zero value, then a
@samp{--version} option is added when parsing with @code{argp_parse},
which will print the @samp{--version} string followed by a newline and
exit. The exception to this is if the @code{ARGP_NO_EXIT} flag is used.
@end deftypevar
@comment argp.h
@comment GNU
@deftypevar {const char *} argp_program_bug_address
If defined or set by the user program to a non-zero value,
@code{argp_program_bug_address} should point to a string that will be
printed at the end of the standard output for the @samp{--help} option,
embedded in a sentence that says @samp{Report bugs to @var{address}.}.
@end deftypevar
@need 1500
@comment argp.h
@comment GNU
@defvar argp_program_version_hook
If defined or set by the user program to a non-zero value, a
@samp{--version} option is added when parsing with @code{arg_parse},
which prints the program version and exits with a status of zero. This
is not the case if the @code{ARGP_NO_HELP} flag is used. If the
@code{ARGP_NO_EXIT} flag is set, the exit behavior of the program is
suppressed or modified, as when the argp parser is going to be used by
other programs.
It should point to a function with this type of signature:
@smallexample
void @var{print-version} (FILE *@var{stream}, struct argp_state *@var{state})
@end smallexample
@noindent
@xref{Argp Parsing State}, for an explanation of @var{state}.
This variable takes precedence over @code{argp_program_version}, and is
useful if a program has version information not easily expressed in a
simple string.
@end defvar
@comment argp.h
@comment GNU
@deftypevar error_t argp_err_exit_status
This is the exit status used when argp exits due to a parsing error. If
not defined or set by the user program, this defaults to:
@code{EX_USAGE} from @file{}.
@end deftypevar
@node Argp Parsers, Argp Flags, Argp Global Variables, Argp
@subsection Specifying Argp Parsers
The first argument to the @code{argp_parse} function is a pointer to a
@code{struct argp}, which is known as an @dfn{argp parser}:
@comment argp.h
@comment GNU
@deftp {Data Type} {struct argp}
This structure specifies how to parse a given set of options and
arguments, perhaps in conjunction with other argp parsers. It has the
following fields:
@table @code
@item const struct argp_option *options
A pointer to a vector of @code{argp_option} structures specifying which
options this argp parser understands; it may be zero if there are no
options at all. @xref{Argp Option Vectors}.
@item argp_parser_t parser
A pointer to a function that defines actions for this parser; it is
called for each option parsed, and at other well-defined points in the
parsing process. A value of zero is the same as a pointer to a function
that always returns @code{ARGP_ERR_UNKNOWN}. @xref{Argp Parser
Functions}.
@item const char *args_doc
If non-zero, a string describing what non-option arguments are called by
this parser. This is only used to print the @samp{Usage:} message. If
it contains newlines, the strings separated by them are considered
alternative usage patterns and printed on separate lines. Lines after
the first are prefixed by @samp{ or: } instead of @samp{Usage:}.
@item const char *doc
If non-zero, a string containing extra text to be printed before and
after the options in a long help message, with the two sections
separated by a vertical tab (@code{'\v'}, @code{'\013'}) character. By
convention, the documentation before the options is just a short string
explaining what the program does. Documentation printed after the
options describe behavior in more detail.
@item const struct argp_child *children
A pointer to a vector of @code{argp_children} structures. This pointer
specifies which additional argp parsers should be combined with this
one. @xref{Argp Children}.
@item char *(*help_filter)(int @var{key}, const char *@var{text}, void *@var{input})
If non-zero, a pointer to a function that filters the output of help
messages. @xref{Argp Help Filtering}.
@item const char *argp_domain
If non-zero, the strings used in the argp library are translated using
the domain described by this string. If zero, the current default domain
is used.
@end table
@end deftp
Of the above group, @code{options}, @code{parser}, @code{args_doc}, and
the @code{doc} fields are usually all that are needed. If an argp
parser is defined as an initialized C variable, only the fields used
need be specified in the initializer. The rest will default to zero due
to the way C structure initialization works. This design is exploited in
most argp structures; the most-used fields are grouped near the
beginning, the unused fields left unspecified.
@menu
* Options: Argp Option Vectors. Specifying options in an argp parser.
* Argp Parser Functions:: Defining actions for an argp parser.
* Children: Argp Children. Combining multiple argp parsers.
* Help Filtering: Argp Help Filtering. Customizing help output for an argp parser.
@end menu
@node Argp Option Vectors, Argp Parser Functions, Argp Parsers, Argp Parsers
@subsection Specifying Options in an Argp Parser
The @code{options} field in a @code{struct argp} points to a vector of
@code{struct argp_option} structures, each of which specifies an option
that the argp parser supports. Multiple entries may be used for a single
option provided it has multiple names. This should be terminated by an
entry with zero in all fields. Note that when using an initialized C
array for options, writing @code{@{ 0 @}} is enough to achieve this.
@comment argp.h
@comment GNU
@deftp {Data Type} {struct argp_option}
This structure specifies a single option that an argp parser
understands, as well as how to parse and document that option. It has
the following fields:
@table @code
@item const char *name
The long name for this option, corresponding to the long option
@samp{--@var{name}}; this field may be zero if this option @emph{only}
has a short name. To specify multiple names for an option, additional
entries may follow this one, with the @code{OPTION_ALIAS} flag
set. @xref{Argp Option Flags}.
@item int key
The integer key provided by the current option to the option parser. If
@var{key} has a value that is a printable @sc{ascii} character (i.e.,
@code{isascii (@var{key})} is true), it @emph{also} specifies a short
option @samp{-@var{char}}, where @var{char} is the @sc{ascii} character
with the code @var{key}.
@item const char *arg
If non-zero, this is the name of an argument associated with this
option, which must be provided (e.g., with the
@samp{--@var{name}=@var{value}} or @samp{-@var{char} @var{value}}
syntaxes), unless the @code{OPTION_ARG_OPTIONAL} flag (@pxref{Argp
Option Flags}) is set, in which case it @emph{may} be provided.
@item int flags
Flags associated with this option, some of which are referred to above.
@xref{Argp Option Flags}.
@item const char *doc
A documentation string for this option, for printing in help messages.
If both the @code{name} and @code{key} fields are zero, this string
will be printed tabbed left from the normal option column, making it
useful as a group header. This will be the first thing printed in its
group. In this usage, it's conventional to end the string with a
@samp{:} character.
@item int group
Group identity for this option.
In a long help message, options are sorted alphabetically within each
group, and the groups presented in the order 0, 1, 2, @dots{}, @var{n},
@minus{}@var{m}, @dots{}, @minus{}2, @minus{}1.
Every entry in an options array with this field 0 will inherit the group
number of the previous entry, or zero if it's the first one. If it's a
group header with @code{name} and @code{key} fields both zero, the
previous entry + 1 is the default. Automagic options such as
@samp{--help} are put into group @minus{}1.
Note that because of C structure initialization rules, this field often
need not be specified, because 0 is the correct value.
@end table
@end deftp
@menu
* Flags: Argp Option Flags. Flags for options.
@end menu
@node Argp Option Flags, , , Argp Option Vectors
@subsubsection Flags for Argp Options
The following flags may be or'd together in the @code{flags} field of a
@code{struct argp_option}. These flags control various aspects of how
that option is parsed or displayed in help messages:
@vtable @code
@comment argp.h
@comment GNU
@item OPTION_ARG_OPTIONAL
The argument associated with this option is optional.
@comment argp.h
@comment GNU
@item OPTION_HIDDEN
This option isn't displayed in any help messages.
@comment argp.h
@comment GNU
@item OPTION_ALIAS
This option is an alias for the closest previous non-alias option. This
means that it will be displayed in the same help entry, and will inherit
fields other than @code{name} and @code{key} from the option being
aliased.
@comment argp.h
@comment GNU
@item OPTION_DOC
This option isn't actually an option and should be ignored by the actual
option parser. It is an arbitrary section of documentation that should
be displayed in much the same manner as the options. This is known as a
@dfn{documentation option}.
If this flag is set, then the option @code{name} field is displayed
unmodified (e.g., no @samp{--} prefix is added) at the left-margin where
a @emph{short} option would normally be displayed, and this
documentation string is left in it's usual place. For purposes of
sorting, any leading whitespace and punctuation is ignored, unless the
first non-whitespace character is @samp{-}. This entry is displayed
after all options, after @code{OPTION_DOC} entries with a leading
@samp{-}, in the same group.
@comment argp.h
@comment GNU
@item OPTION_NO_USAGE
This option shouldn't be included in `long' usage messages, but should
still be included in other help messages. This is intended for options
that are completely documented in an argp's @code{args_doc}
field. @xref{Argp Parsers}. Including this option in the generic usage
list would be redundant, and should be avoided.
For instance, if @code{args_doc} is @code{"FOO BAR\n-x BLAH"}, and the
@samp{-x} option's purpose is to distinguish these two cases, @samp{-x}
should probably be marked @code{OPTION_NO_USAGE}.
@end vtable
@node Argp Parser Functions, Argp Children, Argp Option Vectors, Argp Parsers
@subsection Argp Parser Functions
The function pointed to by the @code{parser} field in a @code{struct
argp} (@pxref{Argp Parsers}) defines what actions take place in response
to each option or argument parsed. It is also used as a hook, allowing a
parser to perform tasks at certain other points during parsing.
@need 2000
Argp parser functions have the following type signature:
@cindex argp parser functions
@smallexample
error_t @var{parser} (int @var{key}, char *@var{arg}, struct argp_state *@var{state})
@end smallexample
@noindent
where the arguments are as follows:
@table @var
@item key
For each option that is parsed, @var{parser} is called with a value of
@var{key} from that option's @code{key} field in the option
vector. @xref{Argp Option Vectors}. @var{parser} is also called at
other times with special reserved keys, such as @code{ARGP_KEY_ARG} for
non-option arguments. @xref{Argp Special Keys}.
@item arg
If @var{key} is an option, @var{arg} is its given value. This defaults
to zero if no value is specified. Only options that have a non-zero
@code{arg} field can ever have a value. These must @emph{always} have a
value unless the @code{OPTION_ARG_OPTIONAL} flag is specified. If the
input being parsed specifies a value for an option that doesn't allow
one, an error results before @var{parser} ever gets called.
If @var{key} is @code{ARGP_KEY_ARG}, @var{arg} is a non-option
argument. Other special keys always have a zero @var{arg}.
@item state
@var{state} points to a @code{struct argp_state}, containing useful
information about the current parsing state for use by
@var{parser}. @xref{Argp Parsing State}.
@end table
When @var{parser} is called, it should perform whatever action is
appropriate for @var{key}, and return @code{0} for success,
@code{ARGP_ERR_UNKNOWN} if the value of @var{key} is not handled by this
parser function, or a unix error code if a real error
occurred. @xref{Error Codes}.
@comment argp.h
@comment GNU
@deftypevr Macro int ARGP_ERR_UNKNOWN
Argp parser functions should return @code{ARGP_ERR_UNKNOWN} for any
@var{key} value they do not recognize, or for non-option arguments
(@code{@var{key} == ARGP_KEY_ARG}) that they are not equipped to handle.
@end deftypevr
@need 3000
A typical parser function uses a switch statement on @var{key}:
@smallexample
error_t
parse_opt (int key, char *arg, struct argp_state *state)
@{
switch (key)
@{
case @var{option_key}:
@var{action}
break;
@dots{}
default:
return ARGP_ERR_UNKNOWN;
@}
return 0;
@}
@end smallexample
@menu
* Keys: Argp Special Keys. Special values for the @var{key} argument.
* State: Argp Parsing State. What the @var{state} argument refers to.
* Functions: Argp Helper Functions. Functions to help during argp parsing.
@end menu
@node Argp Special Keys, Argp Parsing State, , Argp Parser Functions
@subsubsection Special Keys for Argp Parser Functions
In addition to key values corresponding to user options, the @var{key}
argument to argp parser functions may have a number of other special
values. In the following example @var{arg} and @var{state} refer to
parser function arguments. @xref{Argp Parser Functions}.
@vtable @code
@comment argp.h
@comment GNU
@item ARGP_KEY_ARG
This is not an option at all, but rather a command line argument, whose
value is pointed to by @var{arg}.
When there are multiple parser functions in play due to argp parsers
being combined, it's impossible to know which one will handle a specific
argument. Each is called until one returns 0 or an error other than
@code{ARGP_ERR_UNKNOWN}; if an argument is not handled,
@code{argp_parse} immediately returns success, without parsing any more
arguments.
Once a parser function returns success for this key, that fact is
recorded, and the @code{ARGP_KEY_NO_ARGS} case won't be
used. @emph{However}, if while processing the argument a parser function
decrements the @code{next} field of its @var{state} argument, the option
won't be considered processed; this is to allow you to actually modify
the argument, perhaps into an option, and have it processed again.
@comment argp.h
@comment GNU
@item ARGP_KEY_ARGS
If a parser function returns @code{ARGP_ERR_UNKNOWN} for
@code{ARGP_KEY_ARG}, it is immediately called again with the key
@code{ARGP_KEY_ARGS}, which has a similar meaning, but is slightly more
convenient for consuming all remaining arguments. @var{arg} is 0, and
the tail of the argument vector may be found at @code{@var{state}->argv
+ @var{state}->next}. If success is returned for this key, and
@code{@var{state}->next} is unchanged, all remaining arguments are
considered to have been consumed. Otherwise, the amount by which
@code{@var{state}->next} has been adjusted indicates how many were used.
Here's an example that uses both, for different args:
@smallexample
@dots{}
case ARGP_KEY_ARG:
if (@var{state}->arg_num == 0)
/* First argument */
first_arg = @var{arg};
else
/* Let the next case parse it. */
return ARGP_KEY_UNKNOWN;
break;
case ARGP_KEY_ARGS:
remaining_args = @var{state}->argv + @var{state}->next;
num_remaining_args = @var{state}->argc - @var{state}->next;
break;
@end smallexample
@comment argp.h
@comment GNU
@item ARGP_KEY_END
This indicates that there are no more command line arguments. Parser
functions are called in a different order, children first. This allows
each parser to clean up its state for the parent.
@comment argp.h
@comment GNU
@item ARGP_KEY_NO_ARGS
Because it's common to do some special processing if there aren't any
non-option args, parser functions are called with this key if they
didn't successfully process any non-option arguments. This is called
just before @code{ARGP_KEY_END}, where more general validity checks on
previously parsed arguments take place.
@comment argp.h
@comment GNU
@item ARGP_KEY_INIT
This is passed in before any parsing is done. Afterwards, the values of
each element of the @code{child_input} field of @var{state}, if any, are
copied to each child's state to be the initial value of the @code{input}
when @emph{their} parsers are called.
@comment argp.h
@comment GNU
@item ARGP_KEY_SUCCESS
Passed in when parsing has successfully been completed, even if
arguments remain.
@comment argp.h
@comment GNU
@item ARGP_KEY_ERROR
Passed in if an error has occurred and parsing is terminated. In this
case a call with a key of @code{ARGP_KEY_SUCCESS} is never made.
@comment argp.h
@comment GNU
@item ARGP_KEY_FINI
The final key ever seen by any parser, even after
@code{ARGP_KEY_SUCCESS} and @code{ARGP_KEY_ERROR}. Any resources
allocated by @code{ARGP_KEY_INIT} may be freed here. At times, certain
resources allocated are to be returned to the caller after a successful
parse. In that case, those particular resources can be freed in the
@code{ARGP_KEY_ERROR} case.
@end vtable
In all cases, @code{ARGP_KEY_INIT} is the first key seen by parser
functions, and @code{ARGP_KEY_FINI} the last, unless an error was
returned by the parser for @code{ARGP_KEY_INIT}. Other keys can occur
in one the following orders. @var{opt} refers to an arbitrary option
key:
@table @asis
@item @var{opt}@dots{} @code{ARGP_KEY_NO_ARGS} @code{ARGP_KEY_END} @code{ARGP_KEY_SUCCESS}
The arguments being parsed did not contain any non-option arguments.
@item ( @var{opt} | @code{ARGP_KEY_ARG} )@dots{} @code{ARGP_KEY_END} @code{ARGP_KEY_SUCCESS}
All non-option arguments were successfully handled by a parser
function. There may be multiple parser functions if multiple argp
parsers were combined.
@item ( @var{opt} | @code{ARGP_KEY_ARG} )@dots{} @code{ARGP_KEY_SUCCESS}
Some non-option argument went unrecognized.
This occurs when every parser function returns @code{ARGP_KEY_UNKNOWN}
for an argument, in which case parsing stops at that argument if
@var{arg_index} is a null pointer. Otherwise an error occurs.
@end table
In all cases, if a non-null value for @var{arg_index} gets passed to
@code{argp_parse}, the index of the first unparsed command-line argument
is passed back in that value.
If an error occurs and is either detected by argp or because a parser
function returned an error value, each parser is called with
@code{ARGP_KEY_ERROR}. No further calls are made, except the final call
with @code{ARGP_KEY_FINI}.
@node Argp Parsing State, Argp Helper Functions, Argp Special Keys, Argp Parser Functions
@subsubsection Argp Parsing State
The third argument to argp parser functions (@pxref{Argp Parser
Functions}) is a pointer to a @code{struct argp_state}, which contains
information about the state of the option parsing.
@comment argp.h
@comment GNU
@deftp {Data Type} {struct argp_state}
This structure has the following fields, which may be modified as noted:
@table @code
@item const struct argp *const root_argp
The top level argp parser being parsed. Note that this is often
@emph{not} the same @code{struct argp} passed into @code{argp_parse} by
the invoking program. @xref{Argp}. It is an internal argp parser that
contains options implemented by @code{argp_parse} itself, such as
@samp{--help}.
@item int argc
@itemx char **argv
The argument vector being parsed. This may be modified.
@item int next
The index in @code{argv} of the next argument to be parsed. This may be
modified.
One way to consume all remaining arguments in the input is to set
@code{@var{state}->next = @var{state}->argc}, perhaps after recording
the value of the @code{next} field to find the consumed arguments. The
current option can be re-parsed immediately by decrementing this field,
then modifying @code{@var{state}->argv[@var{state}->next]} to reflect
the option that should be reexamined.
@item unsigned flags
The flags supplied to @code{argp_parse}. These may be modified, although
some flags may only take effect when @code{argp_parse} is first
invoked. @xref{Argp Flags}.
@item unsigned arg_num
While calling a parsing function with the @var{key} argument
@code{ARGP_KEY_ARG}, this represents the number of the current arg,
starting at 0. It is incremented after each @code{ARGP_KEY_ARG} call
returns. At all other times, this is the number of @code{ARGP_KEY_ARG}
arguments that have been processed.
@item int quoted
If non-zero, the index in @code{argv} of the first argument following a
special @samp{--} argument. This prevents anything that follows from
being interpreted as an option. It is only set after argument parsing
has proceeded past this point.
@item void *input
An arbitrary pointer passed in from the caller of @code{argp_parse}, in
the @var{input} argument.
@item void **child_inputs
These are values that will be passed to child parsers. This vector will
be the same length as the number of children in the current parser. Each
child parser will be given the value of
@code{@var{state}->child_inputs[@var{i}]} as @emph{its}
@code{@var{state}->input} field, where @var{i} is the index of the child
in the this parser's @code{children} field. @xref{Argp Children}.
@item void *hook
For the parser function's use. Initialized to 0, but otherwise ignored
by argp.
@item char *name
The name used when printing messages. This is initialized to
@code{argv[0]}, or @code{program_invocation_name} if @code{argv[0]} is
unavailable.
@item FILE *err_stream
@itemx FILE *out_stream
The stdio streams used when argp prints. Error messages are printed to
@code{err_stream}, all other output, such as @samp{--help} output) to
@code{out_stream}. These are initialized to @code{stderr} and
@code{stdout} respectively. @xref{Standard Streams}.
@item void *pstate
Private, for use by the argp implementation.
@end table
@end deftp
@node Argp Helper Functions, , Argp Parsing State, Argp Parser Functions
@subsubsection Functions For Use in Argp Parsers
Argp provides a number of functions available to the user of argp
(@pxref{Argp Parser Functions}), mostly for producing error messages.
These take as their first argument the @var{state} argument to the
parser function. @xref{Argp Parsing State}.
@cindex usage messages, in argp
@comment argp.h
@comment GNU
@deftypefun void argp_usage (const struct argp_state *@var{state})
@safety{@prelim{}@mtunsafe{@mtasurace{:argpbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @ascuintl{} @asucorrupt{}}@acunsafe{@acsmem{} @acucorrupt{} @aculock{}}}
@c Just calls argp_state_help with stderr and ARGP_HELP_STD_USAGE.
Outputs the standard usage message for the argp parser referred to by
@var{state} to @code{@var{state}->err_stream} and terminate the program
with @code{exit (argp_err_exit_status)}. @xref{Argp Global Variables}.
@end deftypefun
@cindex syntax error messages, in argp
@comment argp.h
@comment GNU
@deftypefun void argp_error (const struct argp_state *@var{state}, const char *@var{fmt}, @dots{})
@safety{@prelim{}@mtunsafe{@mtasurace{:argpbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @ascuintl{} @asucorrupt{}}@acunsafe{@acsmem{} @acucorrupt{} @aculock{}}}
@c Lock stream, vasprintf the formatted message into a buffer, print the
@c buffer prefixed by the short program name (in libc,
@c argp_short_program_name is a macro that expands to
@c program_invocation_short_name), releases the buffer, then call
@c argp_state_help with stream and ARGP_HELP_STD_ERR, unlocking the
@c stream at the end.
Prints the printf format string @var{fmt} and following args, preceded
by the program name and @samp{:}, and followed by a @w{@samp{Try @dots{}
--help}} message, and terminates the program with an exit status of
@code{argp_err_exit_status}. @xref{Argp Global Variables}.
@end deftypefun
@cindex error messages, in argp
@comment argp.h
@comment GNU
@deftypefun void argp_failure (const struct argp_state *@var{state}, int @var{status}, int @var{errnum}, const char *@var{fmt}, @dots{})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{}}}
@c Lock stream, write out the short program name, vasprintf the optional
@c formatted message to a buffer, print the buffer prefixed by colon and
@c blank, release the buffer, call strerror_r with an automatic buffer,
@c print it out after colon and blank, put[w]c a line break, unlock the
@c stream, then exit unless ARGP_NO_EXIT.
Similar to the standard gnu error-reporting function @code{error}, this
prints the program name and @samp{:}, the printf format string
@var{fmt}, and the appropriate following args. If it is non-zero, the
standard unix error text for @var{errnum} is printed. If @var{status} is
non-zero, it terminates the program with that value as its exit status.
The difference between @code{argp_failure} and @code{argp_error} is that
@code{argp_error} is for @emph{parsing errors}, whereas
@code{argp_failure} is for other problems that occur during parsing but
don't reflect a syntactic problem with the input, such as illegal values
for options, bad phase of the moon, etc.
@end deftypefun
@comment argp.h
@comment GNU
@deftypefun void argp_state_help (const struct argp_state *@var{state}, FILE *@var{stream}, unsigned @var{flags})
@safety{@prelim{}@mtunsafe{@mtasurace{:argpbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @ascuintl{} @asucorrupt{}}@acunsafe{@acsmem{} @acucorrupt{} @aculock{}}}
@c Just calls _help with the short program name and optionally exit.
@c The main problems in _help, besides the usual issues with stream I/O
@c and translation, are the use of a static buffer (uparams, thus
@c @mtasurace:argpbuf) that makes the whole thing thread-unsafe, reading
@c from the environment for ARGP_HELP_FMT, accessing the locale object
@c multiple times.
@c _help @mtsenv @mtasurace:argpbuf @mtslocale @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c dgettext @ascuintl
@c flockfile @aculock
@c funlockfile @aculock
@c fill_in_uparams @mtsenv @mtasurace:argpbuf @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c argp_failure dup (status = errnum = 0)
@c atoi dup @mtslocale
@c argp_hol @ascuheap @acsmem
@c make_hol @ascuheap @acsmem
@c hol_add_cluster @ascuheap @acsmem
@c hol_append @ascuheap @acsmem
@c hol_set_group ok
@c hol_find_entry ok
@c hol_sort @mtslocale @acucorrupt
@c qsort dup @acucorrupt
@c hol_entry_qcmp @mtslocale
@c hol_entry_cmp @mtslocale
@c group_cmp ok
@c hol_cluster_cmp ok
@c group_cmp ok
@c hol_entry_first_short @mtslocale
@c hol_entry_short_iterate [@mtslocale]
@c until_short ok
@c oshort ok
@c isprint ok
@c odoc ok
@c hol_entry_first_long ok
@c canon_doc_option @mtslocale
@c tolower dup
@c hol_usage @mtslocale @ascuintl @ascuheap @acsmem
@c hol_entry_short_iterate ok
@c add_argless_short_opt ok
@c argp_fmtstream_printf dup
@c hol_entry_short_iterate @mtslocale @ascuintl @ascuheap @acsmem
@c usage_argful_short_opt @mtslocale @ascuintl @ascuheap @acsmem
@c dgettext dup
@c argp_fmtstream_printf dup
@c hol_entry_long_iterate @mtslocale @ascuintl @ascuheap @acsmem
@c usage_long_opt @mtslocale @ascuintl @ascuheap @acsmem
@c dgettext dup
@c argp_fmtstream_printf dup
@c hol_help @mtslocale @mtasurace:argpbuf @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c hol_entry_help @mtslocale @mtasurace:argpbuf @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_set_lmargin dup
@c argp_fmtstream_wmargin dup
@c argp_fmtstream_set_wmargin dup
@c comma @mtslocale @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_putc dup
@c hol_cluster_is_child ok
@c argp_fmtstream_wmargin dup
@c print_header dup
@c argp_fmtstream_set_wmargin dup
@c argp_fmtstream_puts dup
@c indent_to dup
@c argp_fmtstream_putc dup
@c arg @mtslocale @ascuheap @acsmem
@c argp_fmtstream_printf dup
@c odoc dup
@c argp_fmtstream_puts dup
@c argp_fmtstream_printf dup
@c print_header @mtslocale @mtasurace:argpbuf @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c dgettext dup
@c filter_doc dup
@c argp_fmtstream_putc dup
@c indent_to dup
@c argp_fmtstream_set_lmargin dup
@c argp_fmtstream_set_wmargin dup
@c argp_fmtstream_puts dup
@c free dup
@c filter_doc dup
@c argp_fmtstream_point dup
@c indent_to @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_point dup
@c argp_fmtstream_putc dup
@c dgettext dup
@c filter_doc dup
@c argp_fmtstream_putc dup
@c argp_fmtstream_puts dup
@c free dup
@c hol_free @ascuheap @acsmem
@c free dup
@c argp_args_levels ok
@c argp_args_usage @mtslocale @ascuintl @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c dgettext dup
@c filter_doc ok
@c argp_input ok
@c argp->help_filter
@c space @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_point dup
@c argp_fmtstream_rmargin @mtslocale @asucorrupt @acucorrupt @aculock
@c argp_fmtstream_update dup
@c argp_fmtstream_putc dup
@c argp_fmtstream_write dup
@c free dup
@c argp_doc @mtslocale @ascuheap @ascuintl @asucorrupt @acsmem @acucorrupt @aculock
@c dgettext @ascuintl
@c strndup @ascuheap @acsmem
@c argp_input dup
@c argp->help_filter
@c argp_fmtstream_putc @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_ensure dup
@c argp_fmtstream_write dup
@c argp_fmtstream_puts dup
@c argp_fmtstream_point @mtslocale @asucorrupt @acucorrupt @aculock
@c argp_fmtstream_update dup
@c argp_fmtstream_lmargin dup
@c free dup
@c argp_make_fmtstream @ascuheap @acsmem
@c argp_fmtstream_free @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_update @mtslocale @asucorrupt @acucorrupt @aculock
@c put[w]c_unlocked dup
@c isblank in loop @mtslocale
@c fxprintf @aculock
@c fxprintf @aculock
@c free dup
@c argp_fmtstream_set_wmargin @mtslocale @asucorrupt @acucorrupt @aculock
@c argp_fmtstream_update dup
@c argp_fmtstream_printf @mtslocale @ascuheap @acsmem
@c argp_fmtstream_ensure dup
@c vsnprintf dup
@c argp_fmtstream_set_lmargin @mtslocale @asucorrupt @acucorrupt @aculock
@c argp_fmtstream_update dup
@c argp_fmtstream_puts @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_write @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_ensure @mtslocale @ascuheap @asucorrupt @acsmem @acucorrupt @aculock
@c argp_fmtstream_update dup
@c fxprintf @aculock
@c realloc @ascuheap @acsmem
Outputs a help message for the argp parser referred to by @var{state},
to @var{stream}. The @var{flags} argument determines what sort of help
message is produced. @xref{Argp Help Flags}.
@end deftypefun
Error output is sent to @code{@var{state}->err_stream}, and the program
name printed is @code{@var{state}->name}.
The output or program termination behavior of these functions may be
suppressed if the @code{ARGP_NO_EXIT} or @code{ARGP_NO_ERRS} flags are
passed to @code{argp_parse}. @xref{Argp Flags}.
This behavior is useful if an argp parser is exported for use by other
programs (e.g., by a library), and may be used in a context where it is
not desirable to terminate the program in response to parsing errors. In
argp parsers intended for such general use, and for the case where the
program @emph{doesn't} terminate, calls to any of these functions should
be followed by code that returns the appropriate error code:
@smallexample
if (@var{bad argument syntax})
@{
argp_usage (@var{state});
return EINVAL;
@}
@end smallexample
@noindent
If a parser function will @emph{only} be used when @code{ARGP_NO_EXIT}
is not set, the return may be omitted.
@node Argp Children, Argp Help Filtering, Argp Parser Functions, Argp Parsers
@subsection Combining Multiple Argp Parsers
The @code{children} field in a @code{struct argp} enables other argp
parsers to be combined with the referencing one for the parsing of a
single set of arguments. This field should point to a vector of
@code{struct argp_child}, which is terminated by an entry having a value
of zero in the @code{argp} field.
Where conflicts between combined parsers arise, as when two specify an
option with the same name, the parser conflicts are resolved in favor of
the parent argp parser(s), or the earlier of the argp parsers in the
list of children.
@comment argp.h
@comment GNU
@deftp {Data Type} {struct argp_child}
An entry in the list of subsidiary argp parsers pointed to by the
@code{children} field in a @code{struct argp}. The fields are as
follows:
@table @code
@item const struct argp *argp
The child argp parser, or zero to end of the list.
@item int flags
Flags for this child.
@item const char *header
If non-zero, this is an optional header to be printed within help output
before the child options. As a side-effect, a non-zero value forces the
child options to be grouped together. To achieve this effect without
actually printing a header string, use a value of @code{""}. As with
header strings specified in an option entry, the conventional value of
the last character is @samp{:}. @xref{Argp Option Vectors}.
@item int group
This is where the child options are grouped relative to the other
`consolidated' options in the parent argp parser. The values are the
same as the @code{group} field in @code{struct argp_option}. @xref{Argp
Option Vectors}. All child-groupings follow parent options at a
particular group level. If both this field and @code{header} are zero,
then the child's options aren't grouped together, they are merged with
parent options at the parent option group level.
@end table
@end deftp
@node Argp Flags, Argp Help, Argp Parsers, Argp
@subsection Flags for @code{argp_parse}
The default behavior of @code{argp_parse} is designed to be convenient
for the most common case of parsing program command line argument. To
modify these defaults, the following flags may be or'd together in the
@var{flags} argument to @code{argp_parse}:
@vtable @code
@comment argp.h
@comment GNU
@item ARGP_PARSE_ARGV0
Don't ignore the first element of the @var{argv} argument to
@code{argp_parse}. Unless @code{ARGP_NO_ERRS} is set, the first element
of the argument vector is skipped for option parsing purposes, as it
corresponds to the program name in a command line.
@comment argp.h
@comment GNU
@item ARGP_NO_ERRS
Don't print error messages for unknown options to @code{stderr}; unless
this flag is set, @code{ARGP_PARSE_ARGV0} is ignored, as @code{argv[0]}
is used as the program name in the error messages. This flag implies
@code{ARGP_NO_EXIT}. This is based on the assumption that silent exiting
upon errors is bad behavior.
@comment argp.h
@comment GNU
@item ARGP_NO_ARGS
Don't parse any non-option args. Normally these are parsed by calling
the parse functions with a key of @code{ARGP_KEY_ARG}, the actual
argument being the value. This flag needn't normally be set, as the
default behavior is to stop parsing as soon as an argument fails to be
parsed. @xref{Argp Parser Functions}.
@comment argp.h
@comment GNU
@item ARGP_IN_ORDER
Parse options and arguments in the same order they occur on the command
line. Normally they're rearranged so that all options come first.
@comment argp.h
@comment GNU
@item ARGP_NO_HELP
Don't provide the standard long option @samp{--help}, which ordinarily
causes usage and option help information to be output to @code{stdout}
and @code{exit (0)}.
@comment argp.h
@comment GNU
@item ARGP_NO_EXIT
Don't exit on errors, although they may still result in error messages.
@comment argp.h
@comment GNU
@item ARGP_LONG_ONLY
Use the gnu getopt `long-only' rules for parsing arguments. This allows
long-options to be recognized with only a single @samp{-}
(i.e., @samp{-help}). This results in a less useful interface, and its
use is discouraged as it conflicts with the way most GNU programs work
as well as the GNU coding standards.
@comment argp.h
@comment GNU
@item ARGP_SILENT
Turns off any message-printing/exiting options, specifically
@code{ARGP_NO_EXIT}, @code{ARGP_NO_ERRS}, and @code{ARGP_NO_HELP}.
@end vtable
@node Argp Help Filtering, , Argp Children, Argp Parsers
@need 2000
@subsection Customizing Argp Help Output
The @code{help_filter} field in a @code{struct argp} is a pointer to a
function that filters the text of help messages before displaying
them. They have a function signature like:
@smallexample
char *@var{help-filter} (int @var{key}, const char *@var{text}, void *@var{input})
@end smallexample
@noindent
Where @var{key} is either a key from an option, in which case @var{text}
is that option's help text. @xref{Argp Option Vectors}. Alternately, one
of the special keys with names beginning with @samp{ARGP_KEY_HELP_}
might be used, describing which other help text @var{text} will contain.
@xref{Argp Help Filter Keys}.
The function should return either @var{text} if it remains as-is, or a
replacement string allocated using @code{malloc}. This will be either be
freed by argp or zero, which prints nothing. The value of @var{text} is
supplied @emph{after} any translation has been done, so if any of the
replacement text needs translation, it will be done by the filter
function. @var{input} is either the input supplied to @code{argp_parse}
or it is zero, if @code{argp_help} was called directly by the user.
@menu
* Keys: Argp Help Filter Keys. Special @var{key} values for help filter functions.
@end menu
@node Argp Help Filter Keys, , , Argp Help Filtering
@subsubsection Special Keys for Argp Help Filter Functions
The following special values may be passed to an argp help filter
function as the first argument in addition to key values for user
options. They specify which help text the @var{text} argument contains:
@vtable @code
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_PRE_DOC
The help text preceding options.
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_POST_DOC
The help text following options.
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_HEADER
The option header string.
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_EXTRA
This is used after all other documentation; @var{text} is zero for this key.
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_DUP_ARGS_NOTE
The explanatory note printed when duplicate option arguments have been suppressed.
@comment argp.h
@comment GNU
@item ARGP_KEY_HELP_ARGS_DOC
The argument doc string; formally the @code{args_doc} field from the argp parser. @xref{Argp Parsers}.
@end vtable
@node Argp Help, Argp Examples, Argp Flags, Argp
@subsection The @code{argp_help} Function
Normally programs using argp need not be written with particular
printing argument-usage-type help messages in mind as the standard
@samp{--help} option is handled automatically by argp. Typical error
cases can be handled using @code{argp_usage} and
@code{argp_error}. @xref{Argp Helper Functions}. However, if it's
desirable to print a help message in some context other than parsing the
program options, argp offers the @code{argp_help} interface.
@comment argp.h
@comment GNU
@deftypefun void argp_help (const struct argp *@var{argp}, FILE *@var{stream}, unsigned @var{flags}, char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:argpbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @ascuintl{} @asucorrupt{}}@acunsafe{@acsmem{} @acucorrupt{} @aculock{}}}
@c Just calls _help.
This outputs a help message for the argp parser @var{argp} to
@var{stream}. The type of messages printed will be determined by
@var{flags}.
Any options such as @samp{--help} that are implemented automatically by
argp itself will @emph{not} be present in the help output; for this
reason it is best to use @code{argp_state_help} if calling from within
an argp parser function. @xref{Argp Helper Functions}.
@end deftypefun
@menu
* Flags: Argp Help Flags. Specifying what sort of help message to print.
@end menu
@node Argp Help Flags, , , Argp Help
@subsection Flags for the @code{argp_help} Function
When calling @code{argp_help} (@pxref{Argp Help}) or
@code{argp_state_help} (@pxref{Argp Helper Functions}) the exact output
is determined by the @var{flags} argument. This should consist of any of
the following flags, or'd together:
@vtable @code
@item ARGP_HELP_USAGE
A unix @samp{Usage:} message that explicitly lists all options.
@item ARGP_HELP_SHORT_USAGE
A unix @samp{Usage:} message that displays an appropriate placeholder to
indicate where the options go; useful for showing the non-option
argument syntax.
@item ARGP_HELP_SEE
A @samp{Try @dots{} for more help} message; @samp{@dots{}} contains the
program name and @samp{--help}.
@item ARGP_HELP_LONG
A verbose option help message that gives each option available along
with its documentation string.
@item ARGP_HELP_PRE_DOC
The part of the argp parser doc string preceding the verbose option help.
@item ARGP_HELP_POST_DOC
The part of the argp parser doc string that following the verbose option help.
@item ARGP_HELP_DOC
@code{(ARGP_HELP_PRE_DOC | ARGP_HELP_POST_DOC)}
@item ARGP_HELP_BUG_ADDR
A message that prints where to report bugs for this program, if the
@code{argp_program_bug_address} variable contains this information.
@item ARGP_HELP_LONG_ONLY
This will modify any output to reflect the @code{ARGP_LONG_ONLY} mode.
@end vtable
The following flags are only understood when used with
@code{argp_state_help}. They control whether the function returns after
printing its output, or terminates the program:
@vtable @code
@item ARGP_HELP_EXIT_ERR
This will terminate the program with @code{exit (argp_err_exit_status)}.
@item ARGP_HELP_EXIT_OK
This will terminate the program with @code{exit (0)}.
@end vtable
The following flags are combinations of the basic flags for printing
standard messages:
@vtable @code
@item ARGP_HELP_STD_ERR
Assuming that an error message for a parsing error has printed, this
prints a message on how to get help, and terminates the program with an
error.
@item ARGP_HELP_STD_USAGE
This prints a standard usage message and terminates the program with an
error. This is used when no other specific error messages are
appropriate or available.
@item ARGP_HELP_STD_HELP
This prints the standard response for a @samp{--help} option, and
terminates the program successfully.
@end vtable
@node Argp Examples, Argp User Customization, Argp Help, Argp
@subsection Argp Examples
These example programs demonstrate the basic usage of argp.
@menu
* 1: Argp Example 1. A minimal program using argp.
* 2: Argp Example 2. A program using only default options.
* 3: Argp Example 3. A simple program with user options.
* 4: Argp Example 4. Combining multiple argp parsers.
@end menu
@node Argp Example 1, Argp Example 2, , Argp Examples
@subsubsection A Minimal Program Using Argp
This is perhaps the smallest program possible that uses argp. It won't
do much except give an error messages and exit when there are any
arguments, and prints a rather pointless message for @samp{--help}.
@smallexample
@include argp-ex1.c.texi
@end smallexample
@node Argp Example 2, Argp Example 3, Argp Example 1, Argp Examples
@subsubsection A Program Using Argp with Only Default Options
This program doesn't use any options or arguments, it uses argp to be
compliant with the GNU standard command line format.
In addition to giving no arguments and implementing a @samp{--help}
option, this example has a @samp{--version} option, which will put the
given documentation string and bug address in the @samp{--help} output,
as per GNU standards.
The variable @code{argp} contains the argument parser
specification. Adding fields to this structure is the way most
parameters are passed to @code{argp_parse}. The first three fields are
normally used, but they are not in this small program. There are also
two global variables that argp can use defined here,
@code{argp_program_version} and @code{argp_program_bug_address}. They
are considered global variables because they will almost always be
constant for a given program, even if they use different argument
parsers for various tasks.
@smallexample
@include argp-ex2.c.texi
@end smallexample
@node Argp Example 3, Argp Example 4, Argp Example 2, Argp Examples
@subsubsection A Program Using Argp with User Options
This program uses the same features as example 2, adding user options
and arguments.
We now use the first four fields in @code{argp} (@pxref{Argp Parsers})
and specify @code{parse_opt} as the parser function. @xref{Argp Parser
Functions}.
Note that in this example, @code{main} uses a structure to communicate
with the @code{parse_opt} function, a pointer to which it passes in the
@code{input} argument to @code{argp_parse}. @xref{Argp}. It is retrieved
by @code{parse_opt} through the @code{input} field in its @code{state}
argument. @xref{Argp Parsing State}. Of course, it's also possible to
use global variables instead, but using a structure like this is
somewhat more flexible and clean.
@smallexample
@include argp-ex3.c.texi
@end smallexample
@node Argp Example 4, , Argp Example 3, Argp Examples
@subsubsection A Program Using Multiple Combined Argp Parsers
This program uses the same features as example 3, but has more options,
and presents more structure in the @samp{--help} output. It also
illustrates how you can `steal' the remainder of the input arguments
past a certain point for programs that accept a list of items. It also
illustrates the @var{key} value @code{ARGP_KEY_NO_ARGS}, which is only
given if no non-option arguments were supplied to the
program. @xref{Argp Special Keys}.
For structuring help output, two features are used: @emph{headers} and a
two part option string. The @emph{headers} are entries in the options
vector. @xref{Argp Option Vectors}. The first four fields are zero. The
two part documentation string are in the variable @code{doc}, which
allows documentation both before and after the options. @xref{Argp
Parsers}, the two parts of @code{doc} are separated by a vertical-tab
character (@code{'\v'}, or @code{'\013'}). By convention, the
documentation before the options is a short string stating what the
program does, and after any options it is longer, describing the
behavior in more detail. All documentation strings are automatically
filled for output, although newlines may be included to force a line
break at a particular point. In addition, documentation strings are
passed to the @code{gettext} function, for possible translation into the
current locale.
@smallexample
@include argp-ex4.c.texi
@end smallexample
@node Argp User Customization, , Argp Examples, Argp
@subsection Argp User Customization
@cindex ARGP_HELP_FMT environment variable
The formatting of argp @samp{--help} output may be controlled to some
extent by a program's users, by setting the @code{ARGP_HELP_FMT}
environment variable to a comma-separated list of tokens. Whitespace is
ignored:
@table @samp
@item dup-args
@itemx no-dup-args
These turn @dfn{duplicate-argument-mode} on or off. In duplicate
argument mode, if an option that accepts an argument has multiple names,
the argument is shown for each name. Otherwise, it is only shown for the
first long option. A note is subsequently printed so the user knows that
it applies to other names as well. The default is @samp{no-dup-args},
which is less consistent, but prettier.
@item dup-args-note
@item no-dup-args-note
These will enable or disable the note informing the user of suppressed
option argument duplication. The default is @samp{dup-args-note}.
@item short-opt-col=@var{n}
This prints the first short option in column @var{n}. The default is 2.
@item long-opt-col=@var{n}
This prints the first long option in column @var{n}. The default is 6.
@item doc-opt-col=@var{n}
This prints `documentation options' (@pxref{Argp Option Flags}) in
column @var{n}. The default is 2.
@item opt-doc-col=@var{n}
This prints the documentation for options starting in column
@var{n}. The default is 29.
@item header-col=@var{n}
This will indent the group headers that document groups of options to
column @var{n}. The default is 1.
@item usage-indent=@var{n}
This will indent continuation lines in @samp{Usage:} messages to column
@var{n}. The default is 12.
@item rmargin=@var{n}
This will word wrap help output at or before column @var{n}. The default
is 79.
@end table
glibc-doc-reference-2.19.orig/manual/string.texi 0000664 0001750 0001750 00000335365 12275120646 021777 0 ustar adconrad adconrad @node String and Array Utilities, Character Set Handling, Character Handling, Top
@c %MENU% Utilities for copying and comparing strings and arrays
@chapter String and Array Utilities
Operations on strings (or arrays of characters) are an important part of
many programs. @Theglibc{} provides an extensive set of string
utility functions, including functions for copying, concatenating,
comparing, and searching strings. Many of these functions can also
operate on arbitrary regions of storage; for example, the @code{memcpy}
function can be used to copy the contents of any kind of array.
It's fairly common for beginning C programmers to ``reinvent the wheel''
by duplicating this functionality in their own code, but it pays to
become familiar with the library functions and to make use of them,
since this offers benefits in maintenance, efficiency, and portability.
For instance, you could easily compare one string to another in two
lines of C code, but if you use the built-in @code{strcmp} function,
you're less likely to make a mistake. And, since these library
functions are typically highly optimized, your program may run faster
too.
@menu
* Representation of Strings:: Introduction to basic concepts.
* String/Array Conventions:: Whether to use a string function or an
arbitrary array function.
* String Length:: Determining the length of a string.
* Copying and Concatenation:: Functions to copy the contents of strings
and arrays.
* String/Array Comparison:: Functions for byte-wise and character-wise
comparison.
* Collation Functions:: Functions for collating strings.
* Search Functions:: Searching for a specific element or substring.
* Finding Tokens in a String:: Splitting a string into tokens by looking
for delimiters.
* strfry:: Function for flash-cooking a string.
* Trivial Encryption:: Obscuring data.
* Encode Binary Data:: Encoding and Decoding of Binary Data.
* Argz and Envz Vectors:: Null-separated string vectors.
@end menu
@node Representation of Strings
@section Representation of Strings
@cindex string, representation of
This section is a quick summary of string concepts for beginning C
programmers. It describes how character strings are represented in C
and some common pitfalls. If you are already familiar with this
material, you can skip this section.
@cindex string
@cindex multibyte character string
A @dfn{string} is an array of @code{char} objects. But string-valued
variables are usually declared to be pointers of type @code{char *}.
Such variables do not include space for the text of a string; that has
to be stored somewhere else---in an array variable, a string constant,
or dynamically allocated memory (@pxref{Memory Allocation}). It's up to
you to store the address of the chosen memory space into the pointer
variable. Alternatively you can store a @dfn{null pointer} in the
pointer variable. The null pointer does not point anywhere, so
attempting to reference the string it points to gets an error.
@cindex wide character string
``string'' normally refers to multibyte character strings as opposed to
wide character strings. Wide character strings are arrays of type
@code{wchar_t} and as for multibyte character strings usually pointers
of type @code{wchar_t *} are used.
@cindex null character
@cindex null wide character
By convention, a @dfn{null character}, @code{'\0'}, marks the end of a
multibyte character string and the @dfn{null wide character},
@code{L'\0'}, marks the end of a wide character string. For example, in
testing to see whether the @code{char *} variable @var{p} points to a
null character marking the end of a string, you can write
@code{!*@var{p}} or @code{*@var{p} == '\0'}.
A null character is quite different conceptually from a null pointer,
although both are represented by the integer @code{0}.
@cindex string literal
@dfn{String literals} appear in C program source as strings of
characters between double-quote characters (@samp{"}) where the initial
double-quote character is immediately preceded by a capital @samp{L}
(ell) character (as in @code{L"foo"}). In @w{ISO C}, string literals
can also be formed by @dfn{string concatenation}: @code{"a" "b"} is the
same as @code{"ab"}. For wide character strings one can either use
@code{L"a" L"b"} or @code{L"a" "b"}. Modification of string literals is
not allowed by the GNU C compiler, because literals are placed in
read-only storage.
Character arrays that are declared @code{const} cannot be modified
either. It's generally good style to declare non-modifiable string
pointers to be of type @code{const char *}, since this often allows the
C compiler to detect accidental modifications as well as providing some
amount of documentation about what your program intends to do with the
string.
The amount of memory allocated for the character array may extend past
the null character that normally marks the end of the string. In this
document, the term @dfn{allocated size} is always used to refer to the
total amount of memory allocated for the string, while the term
@dfn{length} refers to the number of characters up to (but not
including) the terminating null character.
@cindex length of string
@cindex allocation size of string
@cindex size of string
@cindex string length
@cindex string allocation
A notorious source of program bugs is trying to put more characters in a
string than fit in its allocated size. When writing code that extends
strings or moves characters into a pre-allocated array, you should be
very careful to keep track of the length of the text and make explicit
checks for overflowing the array. Many of the library functions
@emph{do not} do this for you! Remember also that you need to allocate
an extra byte to hold the null character that marks the end of the
string.
@cindex single-byte string
@cindex multibyte string
Originally strings were sequences of bytes where each byte represents a
single character. This is still true today if the strings are encoded
using a single-byte character encoding. Things are different if the
strings are encoded using a multibyte encoding (for more information on
encodings see @ref{Extended Char Intro}). There is no difference in
the programming interface for these two kind of strings; the programmer
has to be aware of this and interpret the byte sequences accordingly.
But since there is no separate interface taking care of these
differences the byte-based string functions are sometimes hard to use.
Since the count parameters of these functions specify bytes a call to
@code{strncpy} could cut a multibyte character in the middle and put an
incomplete (and therefore unusable) byte sequence in the target buffer.
@cindex wide character string
To avoid these problems later versions of the @w{ISO C} standard
introduce a second set of functions which are operating on @dfn{wide
characters} (@pxref{Extended Char Intro}). These functions don't have
the problems the single-byte versions have since every wide character is
a legal, interpretable value. This does not mean that cutting wide
character strings at arbitrary points is without problems. It normally
is for alphabet-based languages (except for non-normalized text) but
languages based on syllables still have the problem that more than one
wide character is necessary to complete a logical unit. This is a
higher level problem which the @w{C library} functions are not designed
to solve. But it is at least good that no invalid byte sequences can be
created. Also, the higher level functions can also much easier operate
on wide character than on multibyte characters so that a general advise
is to use wide characters internally whenever text is more than simply
copied.
The remaining of this chapter will discuss the functions for handling
wide character strings in parallel with the discussion of the multibyte
character strings since there is almost always an exact equivalent
available.
@node String/Array Conventions
@section String and Array Conventions
This chapter describes both functions that work on arbitrary arrays or
blocks of memory, and functions that are specific to null-terminated
arrays of characters and wide characters.
Functions that operate on arbitrary blocks of memory have names
beginning with @samp{mem} and @samp{wmem} (such as @code{memcpy} and
@code{wmemcpy}) and invariably take an argument which specifies the size
(in bytes and wide characters respectively) of the block of memory to
operate on. The array arguments and return values for these functions
have type @code{void *} or @code{wchar_t}. As a matter of style, the
elements of the arrays used with the @samp{mem} functions are referred
to as ``bytes''. You can pass any kind of pointer to these functions,
and the @code{sizeof} operator is useful in computing the value for the
size argument. Parameters to the @samp{wmem} functions must be of type
@code{wchar_t *}. These functions are not really usable with anything
but arrays of this type.
In contrast, functions that operate specifically on strings and wide
character strings have names beginning with @samp{str} and @samp{wcs}
respectively (such as @code{strcpy} and @code{wcscpy}) and look for a
null character to terminate the string instead of requiring an explicit
size argument to be passed. (Some of these functions accept a specified
maximum length, but they also check for premature termination with a
null character.) The array arguments and return values for these
functions have type @code{char *} and @code{wchar_t *} respectively, and
the array elements are referred to as ``characters'' and ``wide
characters''.
In many cases, there are both @samp{mem} and @samp{str}/@samp{wcs}
versions of a function. The one that is more appropriate to use depends
on the exact situation. When your program is manipulating arbitrary
arrays or blocks of storage, then you should always use the @samp{mem}
functions. On the other hand, when you are manipulating null-terminated
strings it is usually more convenient to use the @samp{str}/@samp{wcs}
functions, unless you already know the length of the string in advance.
The @samp{wmem} functions should be used for wide character arrays with
known size.
@cindex wint_t
@cindex parameter promotion
Some of the memory and string functions take single characters as
arguments. Since a value of type @code{char} is automatically promoted
into a value of type @code{int} when used as a parameter, the functions
are declared with @code{int} as the type of the parameter in question.
In case of the wide character function the situation is similarly: the
parameter type for a single wide character is @code{wint_t} and not
@code{wchar_t}. This would for many implementations not be necessary
since the @code{wchar_t} is large enough to not be automatically
promoted, but since the @w{ISO C} standard does not require such a
choice of types the @code{wint_t} type is used.
@node String Length
@section String Length
You can get the length of a string using the @code{strlen} function.
This function is declared in the header file @file{string.h}.
@pindex string.h
@comment string.h
@comment ISO
@deftypefun size_t strlen (const char *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strlen} function returns the length of the null-terminated
string @var{s} in bytes. (In other words, it returns the offset of the
terminating null character within the array.)
For example,
@smallexample
strlen ("hello, world")
@result{} 12
@end smallexample
When applied to a character array, the @code{strlen} function returns
the length of the string stored there, not its allocated size. You can
get the allocated size of the character array that holds a string using
the @code{sizeof} operator:
@smallexample
char string[32] = "hello, world";
sizeof (string)
@result{} 32
strlen (string)
@result{} 12
@end smallexample
But beware, this will not work unless @var{string} is the character
array itself, not a pointer to it. For example:
@smallexample
char string[32] = "hello, world";
char *ptr = string;
sizeof (string)
@result{} 32
sizeof (ptr)
@result{} 4 /* @r{(on a machine with 4 byte pointers)} */
@end smallexample
This is an easy mistake to make when you are working with functions that
take string arguments; those arguments are always pointers, not arrays.
It must also be noted that for multibyte encoded strings the return
value does not have to correspond to the number of characters in the
string. To get this value the string can be converted to wide
characters and @code{wcslen} can be used or something like the following
code can be used:
@smallexample
/* @r{The input is in @code{string}.}
@r{The length is expected in @code{n}.} */
@{
mbstate_t t;
char *scopy = string;
/* In initial state. */
memset (&t, '\0', sizeof (t));
/* Determine number of characters. */
n = mbsrtowcs (NULL, &scopy, strlen (scopy), &t);
@}
@end smallexample
This is cumbersome to do so if the number of characters (as opposed to
bytes) is needed often it is better to work with wide characters.
@end deftypefun
The wide character equivalent is declared in @file{wchar.h}.
@comment wchar.h
@comment ISO
@deftypefun size_t wcslen (const wchar_t *@var{ws})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcslen} function is the wide character equivalent to
@code{strlen}. The return value is the number of wide characters in the
wide character string pointed to by @var{ws} (this is also the offset of
the terminating null wide character of @var{ws}).
Since there are no multi wide character sequences making up one
character the return value is not only the offset in the array, it is
also the number of wide characters.
This function was introduced in @w{Amendment 1} to @w{ISO C90}.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun size_t strnlen (const char *@var{s}, size_t @var{maxlen})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strnlen} function returns the length of the string @var{s} in
bytes if this length is smaller than @var{maxlen} bytes. Otherwise it
returns @var{maxlen}. Therefore this function is equivalent to
@code{(strlen (@var{s}) < @var{maxlen} ? strlen (@var{s}) : @var{maxlen})}
but it
is more efficient and works even if the string @var{s} is not
null-terminated.
@smallexample
char string[32] = "hello, world";
strnlen (string, 32)
@result{} 12
strnlen (string, 5)
@result{} 5
@end smallexample
This function is a GNU extension and is declared in @file{string.h}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun size_t wcsnlen (const wchar_t *@var{ws}, size_t @var{maxlen})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{wcsnlen} is the wide character equivalent to @code{strnlen}. The
@var{maxlen} parameter specifies the maximum number of wide characters.
This function is a GNU extension and is declared in @file{wchar.h}.
@end deftypefun
@node Copying and Concatenation
@section Copying and Concatenation
You can use the functions described in this section to copy the contents
of strings and arrays, or to append the contents of one string to
another. The @samp{str} and @samp{mem} functions are declared in the
header file @file{string.h} while the @samp{wstr} and @samp{wmem}
functions are declared in the file @file{wchar.h}.
@pindex string.h
@pindex wchar.h
@cindex copying strings and arrays
@cindex string copy functions
@cindex array copy functions
@cindex concatenating strings
@cindex string concatenation functions
A helpful way to remember the ordering of the arguments to the functions
in this section is that it corresponds to an assignment expression, with
the destination array specified to the left of the source array. All
of these functions return the address of the destination array.
Most of these functions do not work properly if the source and
destination arrays overlap. For example, if the beginning of the
destination array overlaps the end of the source array, the original
contents of that part of the source array may get overwritten before it
is copied. Even worse, in the case of the string functions, the null
character marking the end of the string may be lost, and the copy
function might get stuck in a loop trashing all the memory allocated to
your program.
All functions that have problems copying between overlapping arrays are
explicitly identified in this manual. In addition to functions in this
section, there are a few others like @code{sprintf} (@pxref{Formatted
Output Functions}) and @code{scanf} (@pxref{Formatted Input
Functions}).
@comment string.h
@comment ISO
@deftypefun {void *} memcpy (void *restrict @var{to}, const void *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{memcpy} function copies @var{size} bytes from the object
beginning at @var{from} into the object beginning at @var{to}. The
behavior of this function is undefined if the two arrays @var{to} and
@var{from} overlap; use @code{memmove} instead if overlapping is possible.
The value returned by @code{memcpy} is the value of @var{to}.
Here is an example of how you might use @code{memcpy} to copy the
contents of an array:
@smallexample
struct foo *oldarray, *newarray;
int arraysize;
@dots{}
memcpy (new, old, arraysize * sizeof (struct foo));
@end smallexample
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wmemcpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wmemcpy} function copies @var{size} wide characters from the object
beginning at @var{wfrom} into the object beginning at @var{wto}. The
behavior of this function is undefined if the two arrays @var{wto} and
@var{wfrom} overlap; use @code{wmemmove} instead if overlapping is possible.
The following is a possible implementation of @code{wmemcpy} but there
are more optimizations possible.
@smallexample
wchar_t *
wmemcpy (wchar_t *restrict wto, const wchar_t *restrict wfrom,
size_t size)
@{
return (wchar_t *) memcpy (wto, wfrom, size * sizeof (wchar_t));
@}
@end smallexample
The value returned by @code{wmemcpy} is the value of @var{wto}.
This function was introduced in @w{Amendment 1} to @w{ISO C90}.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {void *} mempcpy (void *restrict @var{to}, const void *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{mempcpy} function is nearly identical to the @code{memcpy}
function. It copies @var{size} bytes from the object beginning at
@code{from} into the object pointed to by @var{to}. But instead of
returning the value of @var{to} it returns a pointer to the byte
following the last written byte in the object beginning at @var{to}.
I.e., the value is @code{((void *) ((char *) @var{to} + @var{size}))}.
This function is useful in situations where a number of objects shall be
copied to consecutive memory positions.
@smallexample
void *
combine (void *o1, size_t s1, void *o2, size_t s2)
@{
void *result = malloc (s1 + s2);
if (result != NULL)
mempcpy (mempcpy (result, o1, s1), o2, s2);
return result;
@}
@end smallexample
This function is a GNU extension.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} wmempcpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wmempcpy} function is nearly identical to the @code{wmemcpy}
function. It copies @var{size} wide characters from the object
beginning at @code{wfrom} into the object pointed to by @var{wto}. But
instead of returning the value of @var{wto} it returns a pointer to the
wide character following the last written wide character in the object
beginning at @var{wto}. I.e., the value is @code{@var{wto} + @var{size}}.
This function is useful in situations where a number of objects shall be
copied to consecutive memory positions.
The following is a possible implementation of @code{wmemcpy} but there
are more optimizations possible.
@smallexample
wchar_t *
wmempcpy (wchar_t *restrict wto, const wchar_t *restrict wfrom,
size_t size)
@{
return (wchar_t *) mempcpy (wto, wfrom, size * sizeof (wchar_t));
@}
@end smallexample
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {void *} memmove (void *@var{to}, const void *@var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{memmove} copies the @var{size} bytes at @var{from} into the
@var{size} bytes at @var{to}, even if those two blocks of space
overlap. In the case of overlap, @code{memmove} is careful to copy the
original values of the bytes in the block at @var{from}, including those
bytes which also belong to the block at @var{to}.
The value returned by @code{memmove} is the value of @var{to}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wmemmove (wchar_t *@var{wto}, const wchar_t *@var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{wmemmove} copies the @var{size} wide characters at @var{wfrom}
into the @var{size} wide characters at @var{wto}, even if those two
blocks of space overlap. In the case of overlap, @code{memmove} is
careful to copy the original values of the wide characters in the block
at @var{wfrom}, including those wide characters which also belong to the
block at @var{wto}.
The following is a possible implementation of @code{wmemcpy} but there
are more optimizations possible.
@smallexample
wchar_t *
wmempcpy (wchar_t *restrict wto, const wchar_t *restrict wfrom,
size_t size)
@{
return (wchar_t *) mempcpy (wto, wfrom, size * sizeof (wchar_t));
@}
@end smallexample
The value returned by @code{wmemmove} is the value of @var{wto}.
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment SVID
@deftypefun {void *} memccpy (void *restrict @var{to}, const void *restrict @var{from}, int @var{c}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function copies no more than @var{size} bytes from @var{from} to
@var{to}, stopping if a byte matching @var{c} is found. The return
value is a pointer into @var{to} one byte past where @var{c} was copied,
or a null pointer if no byte matching @var{c} appeared in the first
@var{size} bytes of @var{from}.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {void *} memset (void *@var{block}, int @var{c}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function copies the value of @var{c} (converted to an
@code{unsigned char}) into each of the first @var{size} bytes of the
object beginning at @var{block}. It returns the value of @var{block}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wmemset (wchar_t *@var{block}, wchar_t @var{wc}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function copies the value of @var{wc} into each of the first
@var{size} wide characters of the object beginning at @var{block}. It
returns the value of @var{block}.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {char *} strcpy (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This copies characters from the string @var{from} (up to and including
the terminating null character) into the string @var{to}. Like
@code{memcpy}, this function has undefined results if the strings
overlap. The return value is the value of @var{to}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcscpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This copies wide characters from the string @var{wfrom} (up to and
including the terminating null wide character) into the string
@var{wto}. Like @code{wmemcpy}, this function has undefined results if
the strings overlap. The return value is the value of @var{wto}.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {char *} strncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{strcpy} but always copies exactly
@var{size} characters into @var{to}.
If the length of @var{from} is more than @var{size}, then @code{strncpy}
copies just the first @var{size} characters. Note that in this case
there is no null terminator written into @var{to}.
If the length of @var{from} is less than @var{size}, then @code{strncpy}
copies all of @var{from}, followed by enough null characters to add up
to @var{size} characters in all. This behavior is rarely useful, but it
is specified by the @w{ISO C} standard.
The behavior of @code{strncpy} is undefined if the strings overlap.
Using @code{strncpy} as opposed to @code{strcpy} is a way to avoid bugs
relating to writing past the end of the allocated space for @var{to}.
However, it can also make your program much slower in one common case:
copying a string which is probably small into a potentially large buffer.
In this case, @var{size} may be large, and when it is, @code{strncpy} will
waste a considerable amount of time copying null characters.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{wcscpy} but always copies exactly
@var{size} wide characters into @var{wto}.
If the length of @var{wfrom} is more than @var{size}, then
@code{wcsncpy} copies just the first @var{size} wide characters. Note
that in this case there is no null terminator written into @var{wto}.
If the length of @var{wfrom} is less than @var{size}, then
@code{wcsncpy} copies all of @var{wfrom}, followed by enough null wide
characters to add up to @var{size} wide characters in all. This
behavior is rarely useful, but it is specified by the @w{ISO C}
standard.
The behavior of @code{wcsncpy} is undefined if the strings overlap.
Using @code{wcsncpy} as opposed to @code{wcscpy} is a way to avoid bugs
relating to writing past the end of the allocated space for @var{wto}.
However, it can also make your program much slower in one common case:
copying a string which is probably small into a potentially large buffer.
In this case, @var{size} may be large, and when it is, @code{wcsncpy} will
waste a considerable amount of time copying null wide characters.
@end deftypefun
@comment string.h
@comment SVID
@deftypefun {char *} strdup (const char *@var{s})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function copies the null-terminated string @var{s} into a newly
allocated string. The string is allocated using @code{malloc}; see
@ref{Unconstrained Allocation}. If @code{malloc} cannot allocate space
for the new string, @code{strdup} returns a null pointer. Otherwise it
returns a pointer to the new string.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} wcsdup (const wchar_t *@var{ws})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function copies the null-terminated wide character string @var{ws}
into a newly allocated string. The string is allocated using
@code{malloc}; see @ref{Unconstrained Allocation}. If @code{malloc}
cannot allocate space for the new string, @code{wcsdup} returns a null
pointer. Otherwise it returns a pointer to the new wide character
string.
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {char *} strndup (const char *@var{s}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function is similar to @code{strdup} but always copies at most
@var{size} characters into the newly allocated string.
If the length of @var{s} is more than @var{size}, then @code{strndup}
copies just the first @var{size} characters and adds a closing null
terminator. Otherwise all characters are copied and the string is
terminated.
This function is different to @code{strncpy} in that it always
terminates the destination string.
@code{strndup} is a GNU extension.
@end deftypefun
@comment string.h
@comment Unknown origin
@deftypefun {char *} stpcpy (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{strcpy}, except that it returns a pointer to
the end of the string @var{to} (that is, the address of the terminating
null character @code{to + strlen (from)}) rather than the beginning.
For example, this program uses @code{stpcpy} to concatenate @samp{foo}
and @samp{bar} to produce @samp{foobar}, which it then prints.
@smallexample
@include stpcpy.c.texi
@end smallexample
This function is not part of the ISO or POSIX standards, and is not
customary on Unix systems, but we did not invent it either. Perhaps it
comes from MS-DOG.
Its behavior is undefined if the strings overlap. The function is
declared in @file{string.h}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} wcpcpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{wcscpy}, except that it returns a pointer to
the end of the string @var{wto} (that is, the address of the terminating
null character @code{wto + strlen (wfrom)}) rather than the beginning.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
The behavior of @code{wcpcpy} is undefined if the strings overlap.
@code{wcpcpy} is a GNU extension and is declared in @file{wchar.h}.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {char *} stpncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{stpcpy} but copies always exactly
@var{size} characters into @var{to}.
If the length of @var{from} is more than @var{size}, then @code{stpncpy}
copies just the first @var{size} characters and returns a pointer to the
character directly following the one which was copied last. Note that in
this case there is no null terminator written into @var{to}.
If the length of @var{from} is less than @var{size}, then @code{stpncpy}
copies all of @var{from}, followed by enough null characters to add up
to @var{size} characters in all. This behavior is rarely useful, but it
is implemented to be useful in contexts where this behavior of the
@code{strncpy} is used. @code{stpncpy} returns a pointer to the
@emph{first} written null character.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
Its behavior is undefined if the strings overlap. The function is
declared in @file{string.h}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} wcpncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{wcpcpy} but copies always exactly
@var{wsize} characters into @var{wto}.
If the length of @var{wfrom} is more than @var{size}, then
@code{wcpncpy} copies just the first @var{size} wide characters and
returns a pointer to the wide character directly following the last
non-null wide character which was copied last. Note that in this case
there is no null terminator written into @var{wto}.
If the length of @var{wfrom} is less than @var{size}, then @code{wcpncpy}
copies all of @var{wfrom}, followed by enough null characters to add up
to @var{size} characters in all. This behavior is rarely useful, but it
is implemented to be useful in contexts where this behavior of the
@code{wcsncpy} is used. @code{wcpncpy} returns a pointer to the
@emph{first} written null character.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
Its behavior is undefined if the strings overlap.
@code{wcpncpy} is a GNU extension and is declared in @file{wchar.h}.
@end deftypefun
@comment string.h
@comment GNU
@deftypefn {Macro} {char *} strdupa (const char *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro is similar to @code{strdup} but allocates the new string
using @code{alloca} instead of @code{malloc} (@pxref{Variable Size
Automatic}). This means of course the returned string has the same
limitations as any block of memory allocated using @code{alloca}.
For obvious reasons @code{strdupa} is implemented only as a macro;
you cannot get the address of this function. Despite this limitation
it is a useful function. The following code shows a situation where
using @code{malloc} would be a lot more expensive.
@smallexample
@include strdupa.c.texi
@end smallexample
Please note that calling @code{strtok} using @var{path} directly is
invalid. It is also not allowed to call @code{strdupa} in the argument
list of @code{strtok} since @code{strdupa} uses @code{alloca}
(@pxref{Variable Size Automatic}) can interfere with the parameter
passing.
This function is only available if GNU CC is used.
@end deftypefn
@comment string.h
@comment GNU
@deftypefn {Macro} {char *} strndupa (const char *@var{s}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{strndup} but like @code{strdupa} it
allocates the new string using @code{alloca}
@pxref{Variable Size Automatic}. The same advantages and limitations
of @code{strdupa} are valid for @code{strndupa}, too.
This function is implemented only as a macro, just like @code{strdupa}.
Just as @code{strdupa} this macro also must not be used inside the
parameter list in a function call.
@code{strndupa} is only available if GNU CC is used.
@end deftypefn
@comment string.h
@comment ISO
@deftypefun {char *} strcat (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcat} function is similar to @code{strcpy}, except that the
characters from @var{from} are concatenated or appended to the end of
@var{to}, instead of overwriting it. That is, the first character from
@var{from} overwrites the null character marking the end of @var{to}.
An equivalent definition for @code{strcat} would be:
@smallexample
char *
strcat (char *restrict to, const char *restrict from)
@{
strcpy (to + strlen (to), from);
return to;
@}
@end smallexample
This function has undefined results if the strings overlap.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcscat (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcscat} function is similar to @code{wcscpy}, except that the
characters from @var{wfrom} are concatenated or appended to the end of
@var{wto}, instead of overwriting it. That is, the first character from
@var{wfrom} overwrites the null character marking the end of @var{wto}.
An equivalent definition for @code{wcscat} would be:
@smallexample
wchar_t *
wcscat (wchar_t *wto, const wchar_t *wfrom)
@{
wcscpy (wto + wcslen (wto), wfrom);
return wto;
@}
@end smallexample
This function has undefined results if the strings overlap.
@end deftypefun
Programmers using the @code{strcat} or @code{wcscat} function (or the
following @code{strncat} or @code{wcsncar} functions for that matter)
can easily be recognized as lazy and reckless. In almost all situations
the lengths of the participating strings are known (it better should be
since how can one otherwise ensure the allocated size of the buffer is
sufficient?) Or at least, one could know them if one keeps track of the
results of the various function calls. But then it is very inefficient
to use @code{strcat}/@code{wcscat}. A lot of time is wasted finding the
end of the destination string so that the actual copying can start.
This is a common example:
@cindex va_copy
@smallexample
/* @r{This function concatenates arbitrarily many strings. The last}
@r{parameter must be @code{NULL}.} */
char *
concat (const char *str, @dots{})
@{
va_list ap, ap2;
size_t total = 1;
const char *s;
char *result;
va_start (ap, str);
va_copy (ap2, ap);
/* @r{Determine how much space we need.} */
for (s = str; s != NULL; s = va_arg (ap, const char *))
total += strlen (s);
va_end (ap);
result = (char *) malloc (total);
if (result != NULL)
@{
result[0] = '\0';
/* @r{Copy the strings.} */
for (s = str; s != NULL; s = va_arg (ap2, const char *))
strcat (result, s);
@}
va_end (ap2);
return result;
@}
@end smallexample
This looks quite simple, especially the second loop where the strings
are actually copied. But these innocent lines hide a major performance
penalty. Just imagine that ten strings of 100 bytes each have to be
concatenated. For the second string we search the already stored 100
bytes for the end of the string so that we can append the next string.
For all strings in total the comparisons necessary to find the end of
the intermediate results sums up to 5500! If we combine the copying
with the search for the allocation we can write this function more
efficient:
@smallexample
char *
concat (const char *str, @dots{})
@{
va_list ap;
size_t allocated = 100;
char *result = (char *) malloc (allocated);
if (result != NULL)
@{
char *newp;
char *wp;
const char *s;
va_start (ap, str);
wp = result;
for (s = str; s != NULL; s = va_arg (ap, const char *))
@{
size_t len = strlen (s);
/* @r{Resize the allocated memory if necessary.} */
if (wp + len + 1 > result + allocated)
@{
allocated = (allocated + len) * 2;
newp = (char *) realloc (result, allocated);
if (newp == NULL)
@{
free (result);
return NULL;
@}
wp = newp + (wp - result);
result = newp;
@}
wp = mempcpy (wp, s, len);
@}
/* @r{Terminate the result string.} */
*wp++ = '\0';
/* @r{Resize memory to the optimal size.} */
newp = realloc (result, wp - result);
if (newp != NULL)
result = newp;
va_end (ap);
@}
return result;
@}
@end smallexample
With a bit more knowledge about the input strings one could fine-tune
the memory allocation. The difference we are pointing to here is that
we don't use @code{strcat} anymore. We always keep track of the length
of the current intermediate result so we can safe us the search for the
end of the string and use @code{mempcpy}. Please note that we also
don't use @code{stpcpy} which might seem more natural since we handle
with strings. But this is not necessary since we already know the
length of the string and therefore can use the faster memory copying
function. The example would work for wide characters the same way.
Whenever a programmer feels the need to use @code{strcat} she or he
should think twice and look through the program whether the code cannot
be rewritten to take advantage of already calculated results. Again: it
is almost always unnecessary to use @code{strcat}.
@comment string.h
@comment ISO
@deftypefun {char *} strncat (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{strcat} except that not more than @var{size}
characters from @var{from} are appended to the end of @var{to}. A
single null character is also always appended to @var{to}, so the total
allocated size of @var{to} must be at least @code{@var{size} + 1} bytes
longer than its initial length.
The @code{strncat} function could be implemented like this:
@smallexample
@group
char *
strncat (char *to, const char *from, size_t size)
@{
memcpy (to + strlen (to), from, strnlen (from, size));
to[strlen (to) + strnlen (from, size)] = '\0';
return to;
@}
@end group
@end smallexample
The behavior of @code{strncat} is undefined if the strings overlap.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsncat (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{wcscat} except that not more than @var{size}
characters from @var{from} are appended to the end of @var{to}. A
single null character is also always appended to @var{to}, so the total
allocated size of @var{to} must be at least @code{@var{size} + 1} bytes
longer than its initial length.
The @code{wcsncat} function could be implemented like this:
@smallexample
@group
wchar_t *
wcsncat (wchar_t *restrict wto, const wchar_t *restrict wfrom,
size_t size)
@{
memcpy (wto + wcslen (wto), wfrom, wcsnlen (wfrom, size) * sizeof (wchar_t));
wto[wcslen (to) + wcsnlen (wfrom, size)] = '\0';
return wto;
@}
@end group
@end smallexample
The behavior of @code{wcsncat} is undefined if the strings overlap.
@end deftypefun
Here is an example showing the use of @code{strncpy} and @code{strncat}
(the wide character version is equivalent). Notice how, in the call to
@code{strncat}, the @var{size} parameter is computed to avoid
overflowing the character array @code{buffer}.
@smallexample
@include strncat.c.texi
@end smallexample
@noindent
The output produced by this program looks like:
@smallexample
hello
hello, wo
@end smallexample
@comment string.h
@comment BSD
@deftypefun void bcopy (const void *@var{from}, void *@var{to}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is a partially obsolete alternative for @code{memmove}, derived from
BSD. Note that it is not quite equivalent to @code{memmove}, because the
arguments are not in the same order and there is no return value.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun void bzero (void *@var{block}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is a partially obsolete alternative for @code{memset}, derived from
BSD. Note that it is not as general as @code{memset}, because the only
value it can store is zero.
@end deftypefun
@node String/Array Comparison
@section String/Array Comparison
@cindex comparing strings and arrays
@cindex string comparison functions
@cindex array comparison functions
@cindex predicates on strings
@cindex predicates on arrays
You can use the functions in this section to perform comparisons on the
contents of strings and arrays. As well as checking for equality, these
functions can also be used as the ordering functions for sorting
operations. @xref{Searching and Sorting}, for an example of this.
Unlike most comparison operations in C, the string comparison functions
return a nonzero value if the strings are @emph{not} equivalent rather
than if they are. The sign of the value indicates the relative ordering
of the first characters in the strings that are not equivalent: a
negative value indicates that the first string is ``less'' than the
second, while a positive value indicates that the first string is
``greater''.
The most common use of these functions is to check only for equality.
This is canonically done with an expression like @w{@samp{! strcmp (s1, s2)}}.
All of these functions are declared in the header file @file{string.h}.
@pindex string.h
@comment string.h
@comment ISO
@deftypefun int memcmp (const void *@var{a1}, const void *@var{a2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{memcmp} compares the @var{size} bytes of memory
beginning at @var{a1} against the @var{size} bytes of memory beginning
at @var{a2}. The value returned has the same sign as the difference
between the first differing pair of bytes (interpreted as @code{unsigned
char} objects, then promoted to @code{int}).
If the contents of the two blocks are equal, @code{memcmp} returns
@code{0}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wmemcmp (const wchar_t *@var{a1}, const wchar_t *@var{a2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{wmemcmp} compares the @var{size} wide characters
beginning at @var{a1} against the @var{size} wide characters beginning
at @var{a2}. The value returned is smaller than or larger than zero
depending on whether the first differing wide character is @var{a1} is
smaller or larger than the corresponding character in @var{a2}.
If the contents of the two blocks are equal, @code{wmemcmp} returns
@code{0}.
@end deftypefun
On arbitrary arrays, the @code{memcmp} function is mostly useful for
testing equality. It usually isn't meaningful to do byte-wise ordering
comparisons on arrays of things other than bytes. For example, a
byte-wise comparison on the bytes that make up floating-point numbers
isn't likely to tell you anything about the relationship between the
values of the floating-point numbers.
@code{wmemcmp} is really only useful to compare arrays of type
@code{wchar_t} since the function looks at @code{sizeof (wchar_t)} bytes
at a time and this number of bytes is system dependent.
You should also be careful about using @code{memcmp} to compare objects
that can contain ``holes'', such as the padding inserted into structure
objects to enforce alignment requirements, extra space at the end of
unions, and extra characters at the ends of strings whose length is less
than their allocated size. The contents of these ``holes'' are
indeterminate and may cause strange behavior when performing byte-wise
comparisons. For more predictable results, perform an explicit
component-wise comparison.
For example, given a structure type definition like:
@smallexample
struct foo
@{
unsigned char tag;
union
@{
double f;
long i;
char *p;
@} value;
@};
@end smallexample
@noindent
you are better off writing a specialized comparison function to compare
@code{struct foo} objects instead of comparing them with @code{memcmp}.
@comment string.h
@comment ISO
@deftypefun int strcmp (const char *@var{s1}, const char *@var{s2})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcmp} function compares the string @var{s1} against
@var{s2}, returning a value that has the same sign as the difference
between the first differing pair of characters (interpreted as
@code{unsigned char} objects, then promoted to @code{int}).
If the two strings are equal, @code{strcmp} returns @code{0}.
A consequence of the ordering used by @code{strcmp} is that if @var{s1}
is an initial substring of @var{s2}, then @var{s1} is considered to be
``less than'' @var{s2}.
@code{strcmp} does not take sorting conventions of the language the
strings are written in into account. To get that one has to use
@code{strcoll}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wcscmp (const wchar_t *@var{ws1}, const wchar_t *@var{ws2})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcscmp} function compares the wide character string @var{ws1}
against @var{ws2}. The value returned is smaller than or larger than zero
depending on whether the first differing wide character is @var{ws1} is
smaller or larger than the corresponding character in @var{ws2}.
If the two strings are equal, @code{wcscmp} returns @code{0}.
A consequence of the ordering used by @code{wcscmp} is that if @var{ws1}
is an initial substring of @var{ws2}, then @var{ws1} is considered to be
``less than'' @var{ws2}.
@code{wcscmp} does not take sorting conventions of the language the
strings are written in into account. To get that one has to use
@code{wcscoll}.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun int strcasecmp (const char *@var{s1}, const char *@var{s2})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Although this calls tolower multiple times, it's a macro, and
@c strcasecmp is optimized so that the locale pointer is read only once.
@c There are some asm implementations too, for which the single-read
@c from locale TLS pointers also applies.
This function is like @code{strcmp}, except that differences in case are
ignored. How uppercase and lowercase characters are related is
determined by the currently selected locale. In the standard @code{"C"}
locale the characters @"A and @"a do not match but in a locale which
regards these characters as parts of the alphabet they do match.
@noindent
@code{strcasecmp} is derived from BSD.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun int wcscasecmp (const wchar_t *@var{ws1}, const wchar_t *@var{ws2})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Since towlower is not a macro, the locale object may be read multiple
@c times.
This function is like @code{wcscmp}, except that differences in case are
ignored. How uppercase and lowercase characters are related is
determined by the currently selected locale. In the standard @code{"C"}
locale the characters @"A and @"a do not match but in a locale which
regards these characters as parts of the alphabet they do match.
@noindent
@code{wcscasecmp} is a GNU extension.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun int strncmp (const char *@var{s1}, const char *@var{s2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is the similar to @code{strcmp}, except that no more than
@var{size} characters are compared. In other words, if the two
strings are the same in their first @var{size} characters, the
return value is zero.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wcsncmp (const wchar_t *@var{ws1}, const wchar_t *@var{ws2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is the similar to @code{wcscmp}, except that no more than
@var{size} wide characters are compared. In other words, if the two
strings are the same in their first @var{size} wide characters, the
return value is zero.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun int strncasecmp (const char *@var{s1}, const char *@var{s2}, size_t @var{n})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is like @code{strncmp}, except that differences in case
are ignored. Like @code{strcasecmp}, it is locale dependent how
uppercase and lowercase characters are related.
@noindent
@code{strncasecmp} is a GNU extension.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun int wcsncasecmp (const wchar_t *@var{ws1}, const wchar_t *@var{s2}, size_t @var{n})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is like @code{wcsncmp}, except that differences in case
are ignored. Like @code{wcscasecmp}, it is locale dependent how
uppercase and lowercase characters are related.
@noindent
@code{wcsncasecmp} is a GNU extension.
@end deftypefun
Here are some examples showing the use of @code{strcmp} and
@code{strncmp} (equivalent examples can be constructed for the wide
character functions). These examples assume the use of the ASCII
character set. (If some other character set---say, EBCDIC---is used
instead, then the glyphs are associated with different numeric codes,
and the return values and ordering may differ.)
@smallexample
strcmp ("hello", "hello")
@result{} 0 /* @r{These two strings are the same.} */
strcmp ("hello", "Hello")
@result{} 32 /* @r{Comparisons are case-sensitive.} */
strcmp ("hello", "world")
@result{} -15 /* @r{The character @code{'h'} comes before @code{'w'}.} */
strcmp ("hello", "hello, world")
@result{} -44 /* @r{Comparing a null character against a comma.} */
strncmp ("hello", "hello, world", 5)
@result{} 0 /* @r{The initial 5 characters are the same.} */
strncmp ("hello, world", "hello, stupid world!!!", 5)
@result{} 0 /* @r{The initial 5 characters are the same.} */
@end smallexample
@comment string.h
@comment GNU
@deftypefun int strverscmp (const char *@var{s1}, const char *@var{s2})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Calls isdigit multiple times, locale may change in between.
The @code{strverscmp} function compares the string @var{s1} against
@var{s2}, considering them as holding indices/version numbers. The
return value follows the same conventions as found in the
@code{strcmp} function. In fact, if @var{s1} and @var{s2} contain no
digits, @code{strverscmp} behaves like @code{strcmp}.
Basically, we compare strings normally (character by character), until
we find a digit in each string - then we enter a special comparison
mode, where each sequence of digits is taken as a whole. If we reach the
end of these two parts without noticing a difference, we return to the
standard comparison mode. There are two types of numeric parts:
"integral" and "fractional" (those begin with a '0'). The types
of the numeric parts affect the way we sort them:
@itemize @bullet
@item
integral/integral: we compare values as you would expect.
@item
fractional/integral: the fractional part is less than the integral one.
Again, no surprise.
@item
fractional/fractional: the things become a bit more complex.
If the common prefix contains only leading zeroes, the longest part is less
than the other one; else the comparison behaves normally.
@end itemize
@smallexample
strverscmp ("no digit", "no digit")
@result{} 0 /* @r{same behavior as strcmp.} */
strverscmp ("item#99", "item#100")
@result{} <0 /* @r{same prefix, but 99 < 100.} */
strverscmp ("alpha1", "alpha001")
@result{} >0 /* @r{fractional part inferior to integral one.} */
strverscmp ("part1_f012", "part1_f01")
@result{} >0 /* @r{two fractional parts.} */
strverscmp ("foo.009", "foo.0")
@result{} <0 /* @r{idem, but with leading zeroes only.} */
@end smallexample
This function is especially useful when dealing with filename sorting,
because filenames frequently hold indices/version numbers.
@code{strverscmp} is a GNU extension.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun int bcmp (const void *@var{a1}, const void *@var{a2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is an obsolete alias for @code{memcmp}, derived from BSD.
@end deftypefun
@node Collation Functions
@section Collation Functions
@cindex collating strings
@cindex string collation functions
In some locales, the conventions for lexicographic ordering differ from
the strict numeric ordering of character codes. For example, in Spanish
most glyphs with diacritical marks such as accents are not considered
distinct letters for the purposes of collation. On the other hand, the
two-character sequence @samp{ll} is treated as a single letter that is
collated immediately after @samp{l}.
You can use the functions @code{strcoll} and @code{strxfrm} (declared in
the headers file @file{string.h}) and @code{wcscoll} and @code{wcsxfrm}
(declared in the headers file @file{wchar}) to compare strings using a
collation ordering appropriate for the current locale. The locale used
by these functions in particular can be specified by setting the locale
for the @code{LC_COLLATE} category; see @ref{Locales}.
@pindex string.h
@pindex wchar.h
In the standard C locale, the collation sequence for @code{strcoll} is
the same as that for @code{strcmp}. Similarly, @code{wcscoll} and
@code{wcscmp} are the same in this situation.
Effectively, the way these functions work is by applying a mapping to
transform the characters in a string to a byte sequence that represents
the string's position in the collating sequence of the current locale.
Comparing two such byte sequences in a simple fashion is equivalent to
comparing the strings with the locale's collating sequence.
The functions @code{strcoll} and @code{wcscoll} perform this translation
implicitly, in order to do one comparison. By contrast, @code{strxfrm}
and @code{wcsxfrm} perform the mapping explicitly. If you are making
multiple comparisons using the same string or set of strings, it is
likely to be more efficient to use @code{strxfrm} or @code{wcsxfrm} to
transform all the strings just once, and subsequently compare the
transformed strings with @code{strcmp} or @code{wcscmp}.
@comment string.h
@comment ISO
@deftypefun int strcoll (const char *@var{s1}, const char *@var{s2})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls strcoll_l with the current locale, which dereferences only the
@c LC_COLLATE data pointer.
The @code{strcoll} function is similar to @code{strcmp} but uses the
collating sequence of the current locale for collation (the
@code{LC_COLLATE} locale).
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wcscoll (const wchar_t *@var{ws1}, const wchar_t *@var{ws2})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Same as strcoll, but calling wcscoll_l.
The @code{wcscoll} function is similar to @code{wcscmp} but uses the
collating sequence of the current locale for collation (the
@code{LC_COLLATE} locale).
@end deftypefun
Here is an example of sorting an array of strings, using @code{strcoll}
to compare them. The actual sort algorithm is not written here; it
comes from @code{qsort} (@pxref{Array Sort Function}). The job of the
code shown here is to say how to compare the strings while sorting them.
(Later on in this section, we will show a way to do this more
efficiently using @code{strxfrm}.)
@smallexample
/* @r{This is the comparison function used with @code{qsort}.} */
int
compare_elements (const void *v1, const void *v2)
@{
char * const *p1 = v1;
char * const *p2 = v2;
return strcoll (*p1, *p2);
@}
/* @r{This is the entry point---the function to sort}
@r{strings using the locale's collating sequence.} */
void
sort_strings (char **array, int nstrings)
@{
/* @r{Sort @code{temp_array} by comparing the strings.} */
qsort (array, nstrings,
sizeof (char *), compare_elements);
@}
@end smallexample
@cindex converting string to collation order
@comment string.h
@comment ISO
@deftypefun size_t strxfrm (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The function @code{strxfrm} transforms the string @var{from} using the
collation transformation determined by the locale currently selected for
collation, and stores the transformed string in the array @var{to}. Up
to @var{size} characters (including a terminating null character) are
stored.
The behavior is undefined if the strings @var{to} and @var{from}
overlap; see @ref{Copying and Concatenation}.
The return value is the length of the entire transformed string. This
value is not affected by the value of @var{size}, but if it is greater
or equal than @var{size}, it means that the transformed string did not
entirely fit in the array @var{to}. In this case, only as much of the
string as actually fits was stored. To get the whole transformed
string, call @code{strxfrm} again with a bigger output array.
The transformed string may be longer than the original string, and it
may also be shorter.
If @var{size} is zero, no characters are stored in @var{to}. In this
case, @code{strxfrm} simply returns the number of characters that would
be the length of the transformed string. This is useful for determining
what size the allocated array should be. It does not matter what
@var{to} is if @var{size} is zero; @var{to} may even be a null pointer.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun size_t wcsxfrm (wchar_t *restrict @var{wto}, const wchar_t *@var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The function @code{wcsxfrm} transforms wide character string @var{wfrom}
using the collation transformation determined by the locale currently
selected for collation, and stores the transformed string in the array
@var{wto}. Up to @var{size} wide characters (including a terminating null
character) are stored.
The behavior is undefined if the strings @var{wto} and @var{wfrom}
overlap; see @ref{Copying and Concatenation}.
The return value is the length of the entire transformed wide character
string. This value is not affected by the value of @var{size}, but if
it is greater or equal than @var{size}, it means that the transformed
wide character string did not entirely fit in the array @var{wto}. In
this case, only as much of the wide character string as actually fits
was stored. To get the whole transformed wide character string, call
@code{wcsxfrm} again with a bigger output array.
The transformed wide character string may be longer than the original
wide character string, and it may also be shorter.
If @var{size} is zero, no characters are stored in @var{to}. In this
case, @code{wcsxfrm} simply returns the number of wide characters that
would be the length of the transformed wide character string. This is
useful for determining what size the allocated array should be (remember
to multiply with @code{sizeof (wchar_t)}). It does not matter what
@var{wto} is if @var{size} is zero; @var{wto} may even be a null pointer.
@end deftypefun
Here is an example of how you can use @code{strxfrm} when
you plan to do many comparisons. It does the same thing as the previous
example, but much faster, because it has to transform each string only
once, no matter how many times it is compared with other strings. Even
the time needed to allocate and free storage is much less than the time
we save, when there are many strings.
@smallexample
struct sorter @{ char *input; char *transformed; @};
/* @r{This is the comparison function used with @code{qsort}}
@r{to sort an array of @code{struct sorter}.} */
int
compare_elements (const void *v1, const void *v2)
@{
const struct sorter *p1 = v1;
const struct sorter *p2 = v2;
return strcmp (p1->transformed, p2->transformed);
@}
/* @r{This is the entry point---the function to sort}
@r{strings using the locale's collating sequence.} */
void
sort_strings_fast (char **array, int nstrings)
@{
struct sorter temp_array[nstrings];
int i;
/* @r{Set up @code{temp_array}. Each element contains}
@r{one input string and its transformed string.} */
for (i = 0; i < nstrings; i++)
@{
size_t length = strlen (array[i]) * 2;
char *transformed;
size_t transformed_length;
temp_array[i].input = array[i];
/* @r{First try a buffer perhaps big enough.} */
transformed = (char *) xmalloc (length);
/* @r{Transform @code{array[i]}.} */
transformed_length = strxfrm (transformed, array[i], length);
/* @r{If the buffer was not large enough, resize it}
@r{and try again.} */
if (transformed_length >= length)
@{
/* @r{Allocate the needed space. +1 for terminating}
@r{@code{NUL} character.} */
transformed = (char *) xrealloc (transformed,
transformed_length + 1);
/* @r{The return value is not interesting because we know}
@r{how long the transformed string is.} */
(void) strxfrm (transformed, array[i],
transformed_length + 1);
@}
temp_array[i].transformed = transformed;
@}
/* @r{Sort @code{temp_array} by comparing transformed strings.} */
qsort (temp_array, sizeof (struct sorter),
nstrings, compare_elements);
/* @r{Put the elements back in the permanent array}
@r{in their sorted order.} */
for (i = 0; i < nstrings; i++)
array[i] = temp_array[i].input;
/* @r{Free the strings we allocated.} */
for (i = 0; i < nstrings; i++)
free (temp_array[i].transformed);
@}
@end smallexample
The interesting part of this code for the wide character version would
look like this:
@smallexample
void
sort_strings_fast (wchar_t **array, int nstrings)
@{
@dots{}
/* @r{Transform @code{array[i]}.} */
transformed_length = wcsxfrm (transformed, array[i], length);
/* @r{If the buffer was not large enough, resize it}
@r{and try again.} */
if (transformed_length >= length)
@{
/* @r{Allocate the needed space. +1 for terminating}
@r{@code{NUL} character.} */
transformed = (wchar_t *) xrealloc (transformed,
(transformed_length + 1)
* sizeof (wchar_t));
/* @r{The return value is not interesting because we know}
@r{how long the transformed string is.} */
(void) wcsxfrm (transformed, array[i],
transformed_length + 1);
@}
@dots{}
@end smallexample
@noindent
Note the additional multiplication with @code{sizeof (wchar_t)} in the
@code{realloc} call.
@strong{Compatibility Note:} The string collation functions are a new
feature of @w{ISO C90}. Older C dialects have no equivalent feature.
The wide character versions were introduced in @w{Amendment 1} to @w{ISO
C90}.
@node Search Functions
@section Search Functions
This section describes library functions which perform various kinds
of searching operations on strings and arrays. These functions are
declared in the header file @file{string.h}.
@pindex string.h
@cindex search functions (for strings)
@cindex string search functions
@comment string.h
@comment ISO
@deftypefun {void *} memchr (const void *@var{block}, int @var{c}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function finds the first occurrence of the byte @var{c} (converted
to an @code{unsigned char}) in the initial @var{size} bytes of the
object beginning at @var{block}. The return value is a pointer to the
located byte, or a null pointer if no match was found.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wmemchr (const wchar_t *@var{block}, wchar_t @var{wc}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function finds the first occurrence of the wide character @var{wc}
in the initial @var{size} wide characters of the object beginning at
@var{block}. The return value is a pointer to the located wide
character, or a null pointer if no match was found.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {void *} rawmemchr (const void *@var{block}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Often the @code{memchr} function is used with the knowledge that the
byte @var{c} is available in the memory block specified by the
parameters. But this means that the @var{size} parameter is not really
needed and that the tests performed with it at runtime (to check whether
the end of the block is reached) are not needed.
The @code{rawmemchr} function exists for just this situation which is
surprisingly frequent. The interface is similar to @code{memchr} except
that the @var{size} parameter is missing. The function will look beyond
the end of the block pointed to by @var{block} in case the programmer
made an error in assuming that the byte @var{c} is present in the block.
In this case the result is unspecified. Otherwise the return value is a
pointer to the located byte.
This function is of special interest when looking for the end of a
string. Since all strings are terminated by a null byte a call like
@smallexample
rawmemchr (str, '\0')
@end smallexample
@noindent
will never go beyond the end of the string.
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {void *} memrchr (const void *@var{block}, int @var{c}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{memrchr} is like @code{memchr}, except that it searches
backwards from the end of the block defined by @var{block} and @var{size}
(instead of forwards from the front).
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {char *} strchr (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strchr} function finds the first occurrence of the character
@var{c} (converted to a @code{char}) in the null-terminated string
beginning at @var{string}. The return value is a pointer to the located
character, or a null pointer if no match was found.
For example,
@smallexample
strchr ("hello, world", 'l')
@result{} "llo, world"
strchr ("hello, world", '?')
@result{} NULL
@end smallexample
The terminating null character is considered to be part of the string,
so you can use this function get a pointer to the end of a string by
specifying a null character as the value of the @var{c} argument.
When @code{strchr} returns a null pointer, it does not let you know
the position of the terminating null character it has found. If you
need that information, it is better (but less portable) to use
@code{strchrnul} than to search for it a second time.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcschr (const wchar_t *@var{wstring}, int @var{wc})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcschr} function finds the first occurrence of the wide
character @var{wc} in the null-terminated wide character string
beginning at @var{wstring}. The return value is a pointer to the
located wide character, or a null pointer if no match was found.
The terminating null character is considered to be part of the wide
character string, so you can use this function get a pointer to the end
of a wide character string by specifying a null wude character as the
value of the @var{wc} argument. It would be better (but less portable)
to use @code{wcschrnul} in this case, though.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {char *} strchrnul (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{strchrnul} is the same as @code{strchr} except that if it does
not find the character, it returns a pointer to string's terminating
null character rather than a null pointer.
This function is a GNU extension.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} wcschrnul (const wchar_t *@var{wstring}, wchar_t @var{wc})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{wcschrnul} is the same as @code{wcschr} except that if it does not
find the wide character, it returns a pointer to wide character string's
terminating null wide character rather than a null pointer.
This function is a GNU extension.
@end deftypefun
One useful, but unusual, use of the @code{strchr}
function is when one wants to have a pointer pointing to the NUL byte
terminating a string. This is often written in this way:
@smallexample
s += strlen (s);
@end smallexample
@noindent
This is almost optimal but the addition operation duplicated a bit of
the work already done in the @code{strlen} function. A better solution
is this:
@smallexample
s = strchr (s, '\0');
@end smallexample
There is no restriction on the second parameter of @code{strchr} so it
could very well also be the NUL character. Those readers thinking very
hard about this might now point out that the @code{strchr} function is
more expensive than the @code{strlen} function since we have two abort
criteria. This is right. But in @theglibc{} the implementation of
@code{strchr} is optimized in a special way so that @code{strchr}
actually is faster.
@comment string.h
@comment ISO
@deftypefun {char *} strrchr (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{strrchr} is like @code{strchr}, except that it searches
backwards from the end of the string @var{string} (instead of forwards
from the front).
For example,
@smallexample
strrchr ("hello, world", 'l')
@result{} "ld"
@end smallexample
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsrchr (const wchar_t *@var{wstring}, wchar_t @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{wcsrchr} is like @code{wcschr}, except that it searches
backwards from the end of the string @var{wstring} (instead of forwards
from the front).
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {char *} strstr (const char *@var{haystack}, const char *@var{needle})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{strchr}, except that it searches @var{haystack} for a
substring @var{needle} rather than just a single character. It
returns a pointer into the string @var{haystack} that is the first
character of the substring, or a null pointer if no match was found. If
@var{needle} is an empty string, the function returns @var{haystack}.
For example,
@smallexample
strstr ("hello, world", "l")
@result{} "llo, world"
strstr ("hello, world", "wo")
@result{} "world"
@end smallexample
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsstr (const wchar_t *@var{haystack}, const wchar_t *@var{needle})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{wcschr}, except that it searches @var{haystack} for a
substring @var{needle} rather than just a single wide character. It
returns a pointer into the string @var{haystack} that is the first wide
character of the substring, or a null pointer if no match was found. If
@var{needle} is an empty string, the function returns @var{haystack}.
@end deftypefun
@comment wchar.h
@comment XPG
@deftypefun {wchar_t *} wcswcs (const wchar_t *@var{haystack}, const wchar_t *@var{needle})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{wcswcs} is a deprecated alias for @code{wcsstr}. This is the
name originally used in the X/Open Portability Guide before the
@w{Amendment 1} to @w{ISO C90} was published.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {char *} strcasestr (const char *@var{haystack}, const char *@var{needle})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c There may be multiple calls of strncasecmp, each accessing the locale
@c object independently.
This is like @code{strstr}, except that it ignores case in searching for
the substring. Like @code{strcasecmp}, it is locale dependent how
uppercase and lowercase characters are related.
For example,
@smallexample
strcasestr ("hello, world", "L")
@result{} "llo, world"
strcasestr ("hello, World", "wo")
@result{} "World"
@end smallexample
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {void *} memmem (const void *@var{haystack}, size_t @var{haystack-len},@*const void *@var{needle}, size_t @var{needle-len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{strstr}, but @var{needle} and @var{haystack} are byte
arrays rather than null-terminated strings. @var{needle-len} is the
length of @var{needle} and @var{haystack-len} is the length of
@var{haystack}.@refill
This function is a GNU extension.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun size_t strspn (const char *@var{string}, const char *@var{skipset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strspn} (``string span'') function returns the length of the
initial substring of @var{string} that consists entirely of characters that
are members of the set specified by the string @var{skipset}. The order
of the characters in @var{skipset} is not important.
For example,
@smallexample
strspn ("hello, world", "abcdefghijklmnopqrstuvwxyz")
@result{} 5
@end smallexample
Note that ``character'' is here used in the sense of byte. In a string
using a multibyte character encoding (abstract) character consisting of
more than one byte are not treated as an entity. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun size_t wcsspn (const wchar_t *@var{wstring}, const wchar_t *@var{skipset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcsspn} (``wide character string span'') function returns the
length of the initial substring of @var{wstring} that consists entirely
of wide characters that are members of the set specified by the string
@var{skipset}. The order of the wide characters in @var{skipset} is not
important.
@end deftypefun
@comment string.h
@comment ISO
@deftypefun size_t strcspn (const char *@var{string}, const char *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcspn} (``string complement span'') function returns the length
of the initial substring of @var{string} that consists entirely of characters
that are @emph{not} members of the set specified by the string @var{stopset}.
(In other words, it returns the offset of the first character in @var{string}
that is a member of the set @var{stopset}.)
For example,
@smallexample
strcspn ("hello, world", " \t\n,.;!?")
@result{} 5
@end smallexample
Note that ``character'' is here used in the sense of byte. In a string
using a multibyte character encoding (abstract) character consisting of
more than one byte are not treated as an entity. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun size_t wcscspn (const wchar_t *@var{wstring}, const wchar_t *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcscspn} (``wide character string complement span'') function
returns the length of the initial substring of @var{wstring} that
consists entirely of wide characters that are @emph{not} members of the
set specified by the string @var{stopset}. (In other words, it returns
the offset of the first character in @var{string} that is a member of
the set @var{stopset}.)
@end deftypefun
@comment string.h
@comment ISO
@deftypefun {char *} strpbrk (const char *@var{string}, const char *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strpbrk} (``string pointer break'') function is related to
@code{strcspn}, except that it returns a pointer to the first character
in @var{string} that is a member of the set @var{stopset} instead of the
length of the initial substring. It returns a null pointer if no such
character from @var{stopset} is found.
@c @group Invalid outside the example.
For example,
@smallexample
strpbrk ("hello, world", " \t\n,.;!?")
@result{} ", world"
@end smallexample
@c @end group
Note that ``character'' is here used in the sense of byte. In a string
using a multibyte character encoding (abstract) character consisting of
more than one byte are not treated as an entity. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcspbrk (const wchar_t *@var{wstring}, const wchar_t *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcspbrk} (``wide character string pointer break'') function is
related to @code{wcscspn}, except that it returns a pointer to the first
wide character in @var{wstring} that is a member of the set
@var{stopset} instead of the length of the initial substring. It
returns a null pointer if no such character from @var{stopset} is found.
@end deftypefun
@subsection Compatibility String Search Functions
@comment string.h
@comment BSD
@deftypefun {char *} index (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{index} is another name for @code{strchr}; they are exactly the same.
New code should always use @code{strchr} since this name is defined in
@w{ISO C} while @code{index} is a BSD invention which never was available
on @w{System V} derived systems.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun {char *} rindex (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{rindex} is another name for @code{strrchr}; they are exactly the same.
New code should always use @code{strrchr} since this name is defined in
@w{ISO C} while @code{rindex} is a BSD invention which never was available
on @w{System V} derived systems.
@end deftypefun
@node Finding Tokens in a String
@section Finding Tokens in a String
@cindex tokenizing strings
@cindex breaking a string into tokens
@cindex parsing tokens from a string
It's fairly common for programs to have a need to do some simple kinds
of lexical analysis and parsing, such as splitting a command string up
into tokens. You can do this with the @code{strtok} function, declared
in the header file @file{string.h}.
@pindex string.h
@comment string.h
@comment ISO
@deftypefun {char *} strtok (char *restrict @var{newstring}, const char *restrict @var{delimiters})
@safety{@prelim{}@mtunsafe{@mtasurace{:strtok}}@asunsafe{}@acsafe{}}
A string can be split into tokens by making a series of calls to the
function @code{strtok}.
The string to be split up is passed as the @var{newstring} argument on
the first call only. The @code{strtok} function uses this to set up
some internal state information. Subsequent calls to get additional
tokens from the same string are indicated by passing a null pointer as
the @var{newstring} argument. Calling @code{strtok} with another
non-null @var{newstring} argument reinitializes the state information.
It is guaranteed that no other library function ever calls @code{strtok}
behind your back (which would mess up this internal state information).
The @var{delimiters} argument is a string that specifies a set of delimiters
that may surround the token being extracted. All the initial characters
that are members of this set are discarded. The first character that is
@emph{not} a member of this set of delimiters marks the beginning of the
next token. The end of the token is found by looking for the next
character that is a member of the delimiter set. This character in the
original string @var{newstring} is overwritten by a null character, and the
pointer to the beginning of the token in @var{newstring} is returned.
On the next call to @code{strtok}, the searching begins at the next
character beyond the one that marked the end of the previous token.
Note that the set of delimiters @var{delimiters} do not have to be the
same on every call in a series of calls to @code{strtok}.
If the end of the string @var{newstring} is reached, or if the remainder of
string consists only of delimiter characters, @code{strtok} returns
a null pointer.
Note that ``character'' is here used in the sense of byte. In a string
using a multibyte character encoding (abstract) character consisting of
more than one byte are not treated as an entity. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcstok (wchar_t *@var{newstring}, const wchar_t *@var{delimiters}, wchar_t **@var{save_ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
A string can be split into tokens by making a series of calls to the
function @code{wcstok}.
The string to be split up is passed as the @var{newstring} argument on
the first call only. The @code{wcstok} function uses this to set up
some internal state information. Subsequent calls to get additional
tokens from the same wide character string are indicated by passing a
null pointer as the @var{newstring} argument, which causes the pointer
previously stored in @var{save_ptr} to be used instead.
The @var{delimiters} argument is a wide character string that specifies
a set of delimiters that may surround the token being extracted. All
the initial wide characters that are members of this set are discarded.
The first wide character that is @emph{not} a member of this set of
delimiters marks the beginning of the next token. The end of the token
is found by looking for the next wide character that is a member of the
delimiter set. This wide character in the original wide character
string @var{newstring} is overwritten by a null wide character, the
pointer past the overwritten wide character is saved in @var{save_ptr},
and the pointer to the beginning of the token in @var{newstring} is
returned.
On the next call to @code{wcstok}, the searching begins at the next
wide character beyond the one that marked the end of the previous token.
Note that the set of delimiters @var{delimiters} do not have to be the
same on every call in a series of calls to @code{wcstok}.
If the end of the wide character string @var{newstring} is reached, or
if the remainder of string consists only of delimiter wide characters,
@code{wcstok} returns a null pointer.
@end deftypefun
@strong{Warning:} Since @code{strtok} and @code{wcstok} alter the string
they is parsing, you should always copy the string to a temporary buffer
before parsing it with @code{strtok}/@code{wcstok} (@pxref{Copying and
Concatenation}). If you allow @code{strtok} or @code{wcstok} to modify
a string that came from another part of your program, you are asking for
trouble; that string might be used for other purposes after
@code{strtok} or @code{wcstok} has modified it, and it would not have
the expected value.
The string that you are operating on might even be a constant. Then
when @code{strtok} or @code{wcstok} tries to modify it, your program
will get a fatal signal for writing in read-only memory. @xref{Program
Error Signals}. Even if the operation of @code{strtok} or @code{wcstok}
would not require a modification of the string (e.g., if there is
exactly one token) the string can (and in the @glibcadj{} case will) be
modified.
This is a special case of a general principle: if a part of a program
does not have as its purpose the modification of a certain data
structure, then it is error-prone to modify the data structure
temporarily.
The function @code{strtok} is not reentrant, whereas @code{wcstok} is.
@xref{Nonreentrancy}, for a discussion of where and why reentrancy is
important.
Here is a simple example showing the use of @code{strtok}.
@comment Yes, this example has been tested.
@smallexample
#include
#include
@dots{}
const char string[] = "words separated by spaces -- and, punctuation!";
const char delimiters[] = " .,;:!-";
char *token, *cp;
@dots{}
cp = strdupa (string); /* Make writable copy. */
token = strtok (cp, delimiters); /* token => "words" */
token = strtok (NULL, delimiters); /* token => "separated" */
token = strtok (NULL, delimiters); /* token => "by" */
token = strtok (NULL, delimiters); /* token => "spaces" */
token = strtok (NULL, delimiters); /* token => "and" */
token = strtok (NULL, delimiters); /* token => "punctuation" */
token = strtok (NULL, delimiters); /* token => NULL */
@end smallexample
@Theglibc{} contains two more functions for tokenizing a string
which overcome the limitation of non-reentrancy. They are only
available for multibyte character strings.
@comment string.h
@comment POSIX
@deftypefun {char *} strtok_r (char *@var{newstring}, const char *@var{delimiters}, char **@var{save_ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Just like @code{strtok}, this function splits the string into several
tokens which can be accessed by successive calls to @code{strtok_r}.
The difference is that, as in @code{wcstok}, the information about the
next token is stored in the space pointed to by the third argument,
@var{save_ptr}, which is a pointer to a string pointer. Calling
@code{strtok_r} with a null pointer for @var{newstring} and leaving
@var{save_ptr} between the calls unchanged does the job without
hindering reentrancy.
This function is defined in POSIX.1 and can be found on many systems
which support multi-threading.
@end deftypefun
@comment string.h
@comment BSD
@deftypefun {char *} strsep (char **@var{string_ptr}, const char *@var{delimiter})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function has a similar functionality as @code{strtok_r} with the
@var{newstring} argument replaced by the @var{save_ptr} argument. The
initialization of the moving pointer has to be done by the user.
Successive calls to @code{strsep} move the pointer along the tokens
separated by @var{delimiter}, returning the address of the next token
and updating @var{string_ptr} to point to the beginning of the next
token.
One difference between @code{strsep} and @code{strtok_r} is that if the
input string contains more than one character from @var{delimiter} in a
row @code{strsep} returns an empty string for each pair of characters
from @var{delimiter}. This means that a program normally should test
for @code{strsep} returning an empty string before processing it.
This function was introduced in 4.3BSD and therefore is widely available.
@end deftypefun
Here is how the above example looks like when @code{strsep} is used.
@comment Yes, this example has been tested.
@smallexample
#include
#include
@dots{}
const char string[] = "words separated by spaces -- and, punctuation!";
const char delimiters[] = " .,;:!-";
char *running;
char *token;
@dots{}
running = strdupa (string);
token = strsep (&running, delimiters); /* token => "words" */
token = strsep (&running, delimiters); /* token => "separated" */
token = strsep (&running, delimiters); /* token => "by" */
token = strsep (&running, delimiters); /* token => "spaces" */
token = strsep (&running, delimiters); /* token => "" */
token = strsep (&running, delimiters); /* token => "" */
token = strsep (&running, delimiters); /* token => "" */
token = strsep (&running, delimiters); /* token => "and" */
token = strsep (&running, delimiters); /* token => "" */
token = strsep (&running, delimiters); /* token => "punctuation" */
token = strsep (&running, delimiters); /* token => "" */
token = strsep (&running, delimiters); /* token => NULL */
@end smallexample
@comment string.h
@comment GNU
@deftypefun {char *} basename (const char *@var{filename})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The GNU version of the @code{basename} function returns the last
component of the path in @var{filename}. This function is the preferred
usage, since it does not modify the argument, @var{filename}, and
respects trailing slashes. The prototype for @code{basename} can be
found in @file{string.h}. Note, this function is overriden by the XPG
version, if @file{libgen.h} is included.
Example of using GNU @code{basename}:
@smallexample
#include
int
main (int argc, char *argv[])
@{
char *prog = basename (argv[0]);
if (argc < 2)
@{
fprintf (stderr, "Usage %s \n", prog);
exit (1);
@}
@dots{}
@}
@end smallexample
@strong{Portability Note:} This function may produce different results
on different systems.
@end deftypefun
@comment libgen.h
@comment XPG
@deftypefun {char *} basename (const char *@var{path})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is the standard XPG defined @code{basename}. It is similar in
spirit to the GNU version, but may modify the @var{path} by removing
trailing '/' characters. If the @var{path} is made up entirely of '/'
characters, then "/" will be returned. Also, if @var{path} is
@code{NULL} or an empty string, then "." is returned. The prototype for
the XPG version can be found in @file{libgen.h}.
Example of using XPG @code{basename}:
@smallexample
#include
int
main (int argc, char *argv[])
@{
char *prog;
char *path = strdupa (argv[0]);
prog = basename (path);
if (argc < 2)
@{
fprintf (stderr, "Usage %s \n", prog);
exit (1);
@}
@dots{}
@}
@end smallexample
@end deftypefun
@comment libgen.h
@comment XPG
@deftypefun {char *} dirname (char *@var{path})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{dirname} function is the compliment to the XPG version of
@code{basename}. It returns the parent directory of the file specified
by @var{path}. If @var{path} is @code{NULL}, an empty string, or
contains no '/' characters, then "." is returned. The prototype for this
function can be found in @file{libgen.h}.
@end deftypefun
@node strfry
@section strfry
The function below addresses the perennial programming quandary: ``How do
I take good data in string form and painlessly turn it into garbage?''
This is actually a fairly simple task for C programmers who do not use
@theglibc{} string functions, but for programs based on @theglibc{},
the @code{strfry} function is the preferred method for
destroying string data.
The prototype for this function is in @file{string.h}.
@comment string.h
@comment GNU
@deftypefun {char *} strfry (char *@var{string})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Calls initstate_r, time, getpid, strlen, and random_r.
@code{strfry} creates a pseudorandom anagram of a string, replacing the
input with the anagram in place. For each position in the string,
@code{strfry} swaps it with a position in the string selected at random
(from a uniform distribution). The two positions may be the same.
The return value of @code{strfry} is always @var{string}.
@strong{Portability Note:} This function is unique to @theglibc{}.
@end deftypefun
@node Trivial Encryption
@section Trivial Encryption
@cindex encryption
The @code{memfrob} function converts an array of data to something
unrecognizable and back again. It is not encryption in its usual sense
since it is easy for someone to convert the encrypted data back to clear
text. The transformation is analogous to Usenet's ``Rot13'' encryption
method for obscuring offensive jokes from sensitive eyes and such.
Unlike Rot13, @code{memfrob} works on arbitrary binary data, not just
text.
@cindex Rot13
For true encryption, @xref{Cryptographic Functions}.
This function is declared in @file{string.h}.
@pindex string.h
@comment string.h
@comment GNU
@deftypefun {void *} memfrob (void *@var{mem}, size_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{memfrob} transforms (frobnicates) each byte of the data structure
at @var{mem}, which is @var{length} bytes long, by bitwise exclusive
oring it with binary 00101010. It does the transformation in place and
its return value is always @var{mem}.
Note that @code{memfrob} a second time on the same data structure
returns it to its original state.
This is a good function for hiding information from someone who doesn't
want to see it or doesn't want to see it very much. To really prevent
people from retrieving the information, use stronger encryption such as
that described in @xref{Cryptographic Functions}.
@strong{Portability Note:} This function is unique to @theglibc{}.
@end deftypefun
@node Encode Binary Data
@section Encode Binary Data
To store or transfer binary data in environments which only support text
one has to encode the binary data by mapping the input bytes to
characters in the range allowed for storing or transferring. SVID
systems (and nowadays XPG compliant systems) provide minimal support for
this task.
@comment stdlib.h
@comment XPG
@deftypefun {char *} l64a (long int @var{n})
@safety{@prelim{}@mtunsafe{@mtasurace{:l64a}}@asunsafe{}@acsafe{}}
This function encodes a 32-bit input value using characters from the
basic character set. It returns a pointer to a 7 character buffer which
contains an encoded version of @var{n}. To encode a series of bytes the
user must copy the returned string to a destination buffer. It returns
the empty string if @var{n} is zero, which is somewhat bizarre but
mandated by the standard.@*
@strong{Warning:} Since a static buffer is used this function should not
be used in multi-threaded programs. There is no thread-safe alternative
to this function in the C library.@*
@strong{Compatibility Note:} The XPG standard states that the return
value of @code{l64a} is undefined if @var{n} is negative. In the GNU
implementation, @code{l64a} treats its argument as unsigned, so it will
return a sensible encoding for any nonzero @var{n}; however, portable
programs should not rely on this.
To encode a large buffer @code{l64a} must be called in a loop, once for
each 32-bit word of the buffer. For example, one could do something
like this:
@smallexample
char *
encode (const void *buf, size_t len)
@{
/* @r{We know in advance how long the buffer has to be.} */
unsigned char *in = (unsigned char *) buf;
char *out = malloc (6 + ((len + 3) / 4) * 6 + 1);
char *cp = out, *p;
/* @r{Encode the length.} */
/* @r{Using `htonl' is necessary so that the data can be}
@r{decoded even on machines with different byte order.}
@r{`l64a' can return a string shorter than 6 bytes, so }
@r{we pad it with encoding of 0 (}'.'@r{) at the end by }
@r{hand.} */
p = stpcpy (cp, l64a (htonl (len)));
cp = mempcpy (p, "......", 6 - (p - cp));
while (len > 3)
@{
unsigned long int n = *in++;
n = (n << 8) | *in++;
n = (n << 8) | *in++;
n = (n << 8) | *in++;
len -= 4;
p = stpcpy (cp, l64a (htonl (n)));
cp = mempcpy (p, "......", 6 - (p - cp));
@}
if (len > 0)
@{
unsigned long int n = *in++;
if (--len > 0)
@{
n = (n << 8) | *in++;
if (--len > 0)
n = (n << 8) | *in;
@}
cp = stpcpy (cp, l64a (htonl (n)));
@}
*cp = '\0';
return out;
@}
@end smallexample
It is strange that the library does not provide the complete
functionality needed but so be it.
@end deftypefun
To decode data produced with @code{l64a} the following function should be
used.
@comment stdlib.h
@comment XPG
@deftypefun {long int} a64l (const char *@var{string})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The parameter @var{string} should contain a string which was produced by
a call to @code{l64a}. The function processes at least 6 characters of
this string, and decodes the characters it finds according to the table
below. It stops decoding when it finds a character not in the table,
rather like @code{atoi}; if you have a buffer which has been broken into
lines, you must be careful to skip over the end-of-line characters.
The decoded number is returned as a @code{long int} value.
@end deftypefun
The @code{l64a} and @code{a64l} functions use a base 64 encoding, in
which each character of an encoded string represents six bits of an
input word. These symbols are used for the base 64 digits:
@multitable {xxxxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx}
@item @tab 0 @tab 1 @tab 2 @tab 3 @tab 4 @tab 5 @tab 6 @tab 7
@item 0 @tab @code{.} @tab @code{/} @tab @code{0} @tab @code{1}
@tab @code{2} @tab @code{3} @tab @code{4} @tab @code{5}
@item 8 @tab @code{6} @tab @code{7} @tab @code{8} @tab @code{9}
@tab @code{A} @tab @code{B} @tab @code{C} @tab @code{D}
@item 16 @tab @code{E} @tab @code{F} @tab @code{G} @tab @code{H}
@tab @code{I} @tab @code{J} @tab @code{K} @tab @code{L}
@item 24 @tab @code{M} @tab @code{N} @tab @code{O} @tab @code{P}
@tab @code{Q} @tab @code{R} @tab @code{S} @tab @code{T}
@item 32 @tab @code{U} @tab @code{V} @tab @code{W} @tab @code{X}
@tab @code{Y} @tab @code{Z} @tab @code{a} @tab @code{b}
@item 40 @tab @code{c} @tab @code{d} @tab @code{e} @tab @code{f}
@tab @code{g} @tab @code{h} @tab @code{i} @tab @code{j}
@item 48 @tab @code{k} @tab @code{l} @tab @code{m} @tab @code{n}
@tab @code{o} @tab @code{p} @tab @code{q} @tab @code{r}
@item 56 @tab @code{s} @tab @code{t} @tab @code{u} @tab @code{v}
@tab @code{w} @tab @code{x} @tab @code{y} @tab @code{z}
@end multitable
This encoding scheme is not standard. There are some other encoding
methods which are much more widely used (UU encoding, MIME encoding).
Generally, it is better to use one of these encodings.
@node Argz and Envz Vectors
@section Argz and Envz Vectors
@cindex argz vectors (string vectors)
@cindex string vectors, null-character separated
@cindex argument vectors, null-character separated
@dfn{argz vectors} are vectors of strings in a contiguous block of
memory, each element separated from its neighbors by null-characters
(@code{'\0'}).
@cindex envz vectors (environment vectors)
@cindex environment vectors, null-character separated
@dfn{Envz vectors} are an extension of argz vectors where each element is a
name-value pair, separated by a @code{'='} character (as in a Unix
environment).
@menu
* Argz Functions:: Operations on argz vectors.
* Envz Functions:: Additional operations on environment vectors.
@end menu
@node Argz Functions, Envz Functions, , Argz and Envz Vectors
@subsection Argz Functions
Each argz vector is represented by a pointer to the first element, of
type @code{char *}, and a size, of type @code{size_t}, both of which can
be initialized to @code{0} to represent an empty argz vector. All argz
functions accept either a pointer and a size argument, or pointers to
them, if they will be modified.
The argz functions use @code{malloc}/@code{realloc} to allocate/grow
argz vectors, and so any argz vector creating using these functions may
be freed by using @code{free}; conversely, any argz function that may
grow a string expects that string to have been allocated using
@code{malloc} (those argz functions that only examine their arguments or
modify them in place will work on any sort of memory).
@xref{Unconstrained Allocation}.
All argz functions that do memory allocation have a return type of
@code{error_t}, and return @code{0} for success, and @code{ENOMEM} if an
allocation error occurs.
@pindex argz.h
These functions are declared in the standard include file @file{argz.h}.
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_create (char *const @var{argv}[], char **@var{argz}, size_t *@var{argz_len})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{argz_create} function converts the Unix-style argument vector
@var{argv} (a vector of pointers to normal C strings, terminated by
@code{(char *)0}; @pxref{Program Arguments}) into an argz vector with
the same elements, which is returned in @var{argz} and @var{argz_len}.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_create_sep (const char *@var{string}, int @var{sep}, char **@var{argz}, size_t *@var{argz_len})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{argz_create_sep} function converts the null-terminated string
@var{string} into an argz vector (returned in @var{argz} and
@var{argz_len}) by splitting it into elements at every occurrence of the
character @var{sep}.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {size_t} argz_count (const char *@var{argz}, size_t @var{arg_len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns the number of elements in the argz vector @var{argz} and
@var{argz_len}.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {void} argz_extract (const char *@var{argz}, size_t @var{argz_len}, char **@var{argv})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{argz_extract} function converts the argz vector @var{argz} and
@var{argz_len} into a Unix-style argument vector stored in @var{argv},
by putting pointers to every element in @var{argz} into successive
positions in @var{argv}, followed by a terminator of @code{0}.
@var{Argv} must be pre-allocated with enough space to hold all the
elements in @var{argz} plus the terminating @code{(char *)0}
(@code{(argz_count (@var{argz}, @var{argz_len}) + 1) * sizeof (char *)}
bytes should be enough). Note that the string pointers stored into
@var{argv} point into @var{argz}---they are not copies---and so
@var{argz} must be copied if it will be changed while @var{argv} is
still active. This function is useful for passing the elements in
@var{argz} to an exec function (@pxref{Executing a File}).
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {void} argz_stringify (char *@var{argz}, size_t @var{len}, int @var{sep})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{argz_stringify} converts @var{argz} into a normal string with
the elements separated by the character @var{sep}, by replacing each
@code{'\0'} inside @var{argz} (except the last one, which terminates the
string) with @var{sep}. This is handy for printing @var{argz} in a
readable manner.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_add (char **@var{argz}, size_t *@var{argz_len}, const char *@var{str})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls strlen and argz_append.
The @code{argz_add} function adds the string @var{str} to the end of the
argz vector @code{*@var{argz}}, and updates @code{*@var{argz}} and
@code{*@var{argz_len}} accordingly.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_add_sep (char **@var{argz}, size_t *@var{argz_len}, const char *@var{str}, int @var{delim})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{argz_add_sep} function is similar to @code{argz_add}, but
@var{str} is split into separate elements in the result at occurrences of
the character @var{delim}. This is useful, for instance, for
adding the components of a Unix search path to an argz vector, by using
a value of @code{':'} for @var{delim}.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_append (char **@var{argz}, size_t *@var{argz_len}, const char *@var{buf}, size_t @var{buf_len})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{argz_append} function appends @var{buf_len} bytes starting at
@var{buf} to the argz vector @code{*@var{argz}}, reallocating
@code{*@var{argz}} to accommodate it, and adding @var{buf_len} to
@code{*@var{argz_len}}.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {void} argz_delete (char **@var{argz}, size_t *@var{argz_len}, char *@var{entry})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls free if no argument is left.
If @var{entry} points to the beginning of one of the elements in the
argz vector @code{*@var{argz}}, the @code{argz_delete} function will
remove this entry and reallocate @code{*@var{argz}}, modifying
@code{*@var{argz}} and @code{*@var{argz_len}} accordingly. Note that as
destructive argz functions usually reallocate their argz argument,
pointers into argz vectors such as @var{entry} will then become invalid.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {error_t} argz_insert (char **@var{argz}, size_t *@var{argz_len}, char *@var{before}, const char *@var{entry})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls argz_add or realloc and memmove.
The @code{argz_insert} function inserts the string @var{entry} into the
argz vector @code{*@var{argz}} at a point just before the existing
element pointed to by @var{before}, reallocating @code{*@var{argz}} and
updating @code{*@var{argz}} and @code{*@var{argz_len}}. If @var{before}
is @code{0}, @var{entry} is added to the end instead (as if by
@code{argz_add}). Since the first element is in fact the same as
@code{*@var{argz}}, passing in @code{*@var{argz}} as the value of
@var{before} will result in @var{entry} being inserted at the beginning.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun {char *} argz_next (const char *@var{argz}, size_t @var{argz_len}, const char *@var{entry})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{argz_next} function provides a convenient way of iterating
over the elements in the argz vector @var{argz}. It returns a pointer
to the next element in @var{argz} after the element @var{entry}, or
@code{0} if there are no elements following @var{entry}. If @var{entry}
is @code{0}, the first element of @var{argz} is returned.
This behavior suggests two styles of iteration:
@smallexample
char *entry = 0;
while ((entry = argz_next (@var{argz}, @var{argz_len}, entry)))
@var{action};
@end smallexample
(the double parentheses are necessary to make some C compilers shut up
about what they consider a questionable @code{while}-test) and:
@smallexample
char *entry;
for (entry = @var{argz};
entry;
entry = argz_next (@var{argz}, @var{argz_len}, entry))
@var{action};
@end smallexample
Note that the latter depends on @var{argz} having a value of @code{0} if
it is empty (rather than a pointer to an empty block of memory); this
invariant is maintained for argz vectors created by the functions here.
@end deftypefun
@comment argz.h
@comment GNU
@deftypefun error_t argz_replace (@w{char **@var{argz}, size_t *@var{argz_len}}, @w{const char *@var{str}, const char *@var{with}}, @w{unsigned *@var{replace_count}})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
Replace any occurrences of the string @var{str} in @var{argz} with
@var{with}, reallocating @var{argz} as necessary. If
@var{replace_count} is non-zero, @code{*@var{replace_count}} will be
incremented by number of replacements performed.
@end deftypefun
@node Envz Functions, , Argz Functions, Argz and Envz Vectors
@subsection Envz Functions
Envz vectors are just argz vectors with additional constraints on the form
of each element; as such, argz functions can also be used on them, where it
makes sense.
Each element in an envz vector is a name-value pair, separated by a @code{'='}
character; if multiple @code{'='} characters are present in an element, those
after the first are considered part of the value, and treated like all other
non-@code{'\0'} characters.
If @emph{no} @code{'='} characters are present in an element, that element is
considered the name of a ``null'' entry, as distinct from an entry with an
empty value: @code{envz_get} will return @code{0} if given the name of null
entry, whereas an entry with an empty value would result in a value of
@code{""}; @code{envz_entry} will still find such entries, however. Null
entries can be removed with @code{envz_strip} function.
As with argz functions, envz functions that may allocate memory (and thus
fail) have a return type of @code{error_t}, and return either @code{0} or
@code{ENOMEM}.
@pindex envz.h
These functions are declared in the standard include file @file{envz.h}.
@comment envz.h
@comment GNU
@deftypefun {char *} envz_entry (const char *@var{envz}, size_t @var{envz_len}, const char *@var{name})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{envz_entry} function finds the entry in @var{envz} with the name
@var{name}, and returns a pointer to the whole entry---that is, the argz
element which begins with @var{name} followed by a @code{'='} character. If
there is no entry with that name, @code{0} is returned.
@end deftypefun
@comment envz.h
@comment GNU
@deftypefun {char *} envz_get (const char *@var{envz}, size_t @var{envz_len}, const char *@var{name})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{envz_get} function finds the entry in @var{envz} with the name
@var{name} (like @code{envz_entry}), and returns a pointer to the value
portion of that entry (following the @code{'='}). If there is no entry with
that name (or only a null entry), @code{0} is returned.
@end deftypefun
@comment envz.h
@comment GNU
@deftypefun {error_t} envz_add (char **@var{envz}, size_t *@var{envz_len}, const char *@var{name}, const char *@var{value})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls envz_remove, which calls enz_entry and argz_delete, and then
@c argz_add or equivalent code that reallocs and appends name=value.
The @code{envz_add} function adds an entry to @code{*@var{envz}}
(updating @code{*@var{envz}} and @code{*@var{envz_len}}) with the name
@var{name}, and value @var{value}. If an entry with the same name
already exists in @var{envz}, it is removed first. If @var{value} is
@code{0}, then the new entry will the special null type of entry
(mentioned above).
@end deftypefun
@comment envz.h
@comment GNU
@deftypefun {error_t} envz_merge (char **@var{envz}, size_t *@var{envz_len}, const char *@var{envz2}, size_t @var{envz2_len}, int @var{override})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{envz_merge} function adds each entry in @var{envz2} to @var{envz},
as if with @code{envz_add}, updating @code{*@var{envz}} and
@code{*@var{envz_len}}. If @var{override} is true, then values in @var{envz2}
will supersede those with the same name in @var{envz}, otherwise not.
Null entries are treated just like other entries in this respect, so a null
entry in @var{envz} can prevent an entry of the same name in @var{envz2} from
being added to @var{envz}, if @var{override} is false.
@end deftypefun
@comment envz.h
@comment GNU
@deftypefun {void} envz_strip (char **@var{envz}, size_t *@var{envz_len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{envz_strip} function removes any null entries from @var{envz},
updating @code{*@var{envz}} and @code{*@var{envz_len}}.
@end deftypefun
@c FIXME this are undocumented:
@c strcasecmp_l @safety{@mtsafe{}@assafe{}@acsafe{}} see strcasecmp
glibc-doc-reference-2.19.orig/manual/macros.texi 0000664 0001750 0001750 00000015715 12275120646 021747 0 ustar adconrad adconrad @c Define common macros used to keep phrasing consistent in the manual.
@ifclear MACROS
@set MACROS
@c Names used to refer to the library, as noun phrases at the start or
@c not at the start of a sentence.
@macro Theglibc
The GNU C Library
@end macro
@macro theglibc
the GNU C Library
@end macro
@c Name used to refer to the library as an adjective.
@macro glibcadj
GNU C Library
@end macro
@c Description applying to all GNU systems; that is, used in
@c describing a property of a system such that no system without that
@c property would be considered a variant of the GNU system.
@macro gnusystems
GNU systems
@end macro
@c Systems that are not GNU systems.
@macro nongnusystems
non-GNU systems
@end macro
@c Description applying to GNU/Linux and GNU/Hurd systems, but not
@c necessarily to other variants of the GNU system.
@macro gnulinuxhurdsystems
GNU/Linux and GNU/Hurd systems
@end macro
@c Description applying to GNU/Hurd systems; that is, systems using the
@c GNU Hurd with the GNU C Library.
@macro gnuhurdsystems
GNU/Hurd systems
@end macro
@c Description applying to GNU/Linux systems; that is, systems using
@c the Linux kernel with the GNU C Library.
@macro gnulinuxsystems
GNU/Linux systems
@end macro
@c Document the safety functions as preliminary. It does NOT expand its
@c comments.
@macro prelim {comments}
Preliminary:
@end macro
@c Document a function as thread safe.
@macro mtsafe {comments}
| MT-Safe \comments\
@end macro
@c Document a function as thread unsafe.
@macro mtunsafe {comments}
| MT-Unsafe \comments\
@end macro
@c Document a function as safe for use in asynchronous signal handlers.
@macro assafe {comments}
| AS-Safe \comments\
@end macro
@c Document a function as unsafe for use in asynchronous signal
@c handlers. This distinguishes unmarked functions, for which this
@c property has not been assessed, from those that have been analyzed.
@macro asunsafe {comments}
| AS-Unsafe \comments\
@end macro
@c Document a function as safe for use when asynchronous cancellation is
@c enabled.
@macro acsafe {comments}
| AC-Safe \comments\
@end macro
@c Document a function as unsafe for use when asynchronous cancellation
@c is enabled. This distinguishes unmarked functions, for which this
@c property has not been assessed, from those that have been analyzed.
@macro acunsafe {comments}
| AC-Unsafe \comments\
@end macro
@c Format safety properties without referencing the section of the
@c definitions. To be used in the definitions of the properties
@c themselves.
@macro sampsafety {notes}
@noindent
\notes\|
@end macro
@c Format the safety properties of a function.
@macro safety {notes}
\notes\| @xref{POSIX Safety Concepts}.
@end macro
@c Function is MT- and AS-Unsafe due to an internal race.
@macro mtasurace {comments}
race\comments\
@end macro
@c Function is AS-Unsafe due to an internal race.
@macro asurace {comments}
race\comments\
@end macro
@c Function is MT-Safe, but with potential race on user-supplied object
@c of opaque type.
@macro mtsrace {comments}
race\comments\
@end macro
@c Function is MT- and AS-Unsafe for modifying an object that is decreed
@c MT-constant due to MT-Unsafe accesses elsewhere.
@macro mtasuconst {comments}
const\comments\
@end macro
@c Function accesses the assumed-constant locale object.
@macro mtslocale {comments}
locale\comments\
@end macro
@c Function accesses the assumed-constant environment.
@macro mtsenv {comments}
env\comments\
@end macro
@c Function accesses the assumed-constant hostid.
@macro mtshostid {comments}
hostid\comments\
@end macro
@c Function accesses the assumed-constant _sigintr variable.
@macro mtssigintr {comments}
sigintr\comments\
@end macro
@c Function performs MT-Unsafe initialization at the first call.
@macro mtuinit {comments}
init\comments\
@end macro
@c Function performs libc_once AS-Unsafe initialization.
@macro asuinit {comments}
init\comments\
@end macro
@c Function performs libc_once AC-Unsafe initialization.
@macro acuinit {comments}
init\comments\
@end macro
@c Function is AS-Unsafe because it takes a non-recursive mutex that may
@c already be held by the function interrupted by the signal.
@macro asulock {comments}
lock\comments\
@end macro
@c Function is AC-Unsafe because it may fail to release a mutex.
@macro aculock {comments}
lock\comments\
@end macro
@c Function is AS-Unsafe because some data structure may be inconsistent
@c due to an ongoing updated interrupted by a signal.
@macro asucorrupt {comments}
corrupt\comments\
@end macro
@c Function is AC-Unsafe because some data structure may be left
@c inconsistent when cancelled.
@macro acucorrupt {comments}
corrupt\comments\
@end macro
@c Function is AS- and AC-Unsafe because of malloc/free.
@macro ascuheap {comments}
heap\comments\
@end macro
@c Function is AS-Unsafe because of malloc/free.
@macro asuheap {comments}
heap\comments\
@end macro
@c Function is AS- and AC-Unsafe because of dlopen/dlclose.
@macro ascudlopen {comments}
dlopen\comments\
@end macro
@c Function is AS- and AC-Unsafe because of unknown plugins.
@macro ascuplugin {comments}
plugin\comments\
@end macro
@c Function is AS- and AC-Unsafe because of i18n.
@macro ascuintl {comments}
i18n\comments\
@end macro
@c Function is AS--Unsafe because of i18n.
@macro asuintl {comments}
i18n\comments\
@end macro
@c Function may leak file descriptors if async-cancelled.
@macro acsfd {comments}
fd\comments\
@end macro
@c Function may leak memory if async-cancelled.
@macro acsmem {comments}
mem\comments\
@end macro
@c Function is unsafe due to temporary overriding a signal handler.
@macro mtascusig {comments}
sig\comments\
@end macro
@c Function is MT- and AS-Unsafe due to temporarily changing attributes
@c of the controlling terminal.
@macro mtasuterm {comments}
term\comments\
@end macro
@c Function is AC-Unsafe for failing to restore attributes of the
@c controlling terminal.
@macro acuterm {comments}
term\comments\
@end macro
@c Function sets timers atomically.
@macro mtstimer {comments}
timer\comments\
@end macro
@c Function sets and restores timers.
@macro mtascutimer {comments}
timer\comments\
@end macro
@c Function temporarily changes the current working directory.
@macro mtasscwd {comments}
cwd\comments\
@end macro
@c Function may fail to restore to the original current working
@c directory after temporarily changing it.
@macro acscwd {comments}
cwd\comments\
@end macro
@c Function is MT-Safe while POSIX says it needn't be MT-Safe.
@macro mtsposix {comments}
!posix\comments\
@end macro
@c Function is MT-Unsafe while POSIX says it should be MT-Safe.
@macro mtuposix {comments}
!posix\comments\
@end macro
@c Function is AS-Safe while POSIX says it needn't be AS-Safe.
@macro assposix {comments}
!posix\comments\
@end macro
@c Function is AS-Unsafe while POSIX says it should be AS-Safe.
@macro asuposix {comments}
!posix\comments\
@end macro
@c Function is AC-Safe while POSIX says it needn't be AC-Safe.
@macro acsposix {comments}
!posix\comments\
@end macro
@c Function is AC-Unsafe while POSIX says it should be AC-Safe.
@macro acuposix {comments}
!posix\comments\
@end macro
@end ifclear
glibc-doc-reference-2.19.orig/manual/contrib.texi 0000664 0001750 0001750 00000027376 12275120646 022131 0 ustar adconrad adconrad @node Contributors, Free Manuals, Platform, Top
@c %MENU% Who wrote what parts of the GNU C Library
@appendix Contributors to @theglibc{}
@Theglibc{} project would like to thank its many contributors.
Without them the project would not have been nearly as successful as
it has been. Any omissions in this list are accidental. Feel free to
file a bug in bugzilla if you have been left out or some of your
contributions are not listed. Please keep this list in alphabetical
order.
@itemize @bullet
@item
Ryan S. Arnold for his improvements for Linux on PowerPC and his direction
as FSF Project Steward for @theglibc{}.
@item
Miles Bader for writing the @code{argp} argument-parsing package, and the
@code{argz}/@code{envz} interfaces.
@item
Jeff Bailey for his maintainership of the HPPA architecture.
@item
Petr Baudis for bug fixes and testing.
@item
Stephen R. van den Berg for contributing a highly-optimized
@code{strstr} function.
@item
Ondrej Bilka for contributing optimized string routines for x64 and various
fixes.
@item
Eric Blake for adding O(n) implementations of @code{memmem},
@code{strstr} and @code{strcasestr}.
@item
Philip Blundell for the ports to Linux/ARM
(@code{arm-@var{ANYTHING}-linuxaout}) and ARM standalone
(@code{arm-@var{ANYTHING}-none}), as well as for parts of the IPv6
support code.
@item
Per Bothner for the implementation of the @code{libio} library which
is used to implement @code{stdio} functions.
@item
Mark Brown for his direction as part of @theglibc{} steering
committee.
@item
Thomas Bushnell for his contributions to Hurd.
@item
Liubov Dmitrieva for optimzed string and math functions on x86-64 and
x86.
@item
Ulrich Drepper for his many contributions in almost all parts of
@theglibc{}, including:
@itemize @bullet
@item internationalization support, including the @code{locale} and
@code{localedef} utilities.
@item Linux i386/ELF support
@item the @code{hsearch} and @code{drand48} families of functions,
reentrant @samp{@dots{}@code{_r}} versions of the @code{random}
family; System V shared memory and IPC support code
@item several highly-optimized string functions for i@var{x}86
processors
@item many math functions
@item the character conversion functions (@code{iconv})
@item the @code{ftw} and @code{nftw} functions
@item the floating-point printing function used by @code{printf} and friends
and the floating-point reading function used by @code{scanf},
@code{strtod} and friends
@item the @code{catgets} support and the entire suite of multi-byte
and wide-character support functions (@file{wctype.h}, @file{wchar.h}, etc.).
@item versioning of objects on the symbol level
@end itemize
@item
Paul Eggert for the @code{mktime} function and for his direction as
part of @theglibc{} steering committee.
@item
Steve Ellcey for various fixes.
@item
Tulio Magno Quites Machado Filho for adding a new class of installed
headers for low-level platform-specific functionality and one such for
PowerPC.
@item
Mike Frysinger for his maintaining of the IA64 architecture and for
testing and bug fixing.
@item
Michael Glad for the DES encryption function @code{crypt} and related
functions.
@item
Wolfram Gloger for contributing the memory allocation functions
functions @code{malloc}, @code{realloc} and @code{free} and related
code.
@item
Torbj@"orn Granlund for fast implementations of many of the string
functions (@code{memcpy}, @code{strlen}, etc.).
@item
Michael J. Haertel for writing the merge sort function @code{qsort}
and malloc checking functions like @code{mcheck}.
@item
Bruno Haible for his improvements to the @code{iconv} and locale
implementations.
@item
Richard Henderson for the port to Linux on Alpha
(@code{alpha-@var{anything}-linux}).
@item
David Holsgrove for the port to Linux on MicroBlaze.
@item
Daniel Jacobowitz for various fixes and enhancements.
@item
Andreas Jaeger for the port to Linux on x86-64
(@code{x86_64-@var{anything}-linux} and his work on Linux for MIPS
(@code{mips-@var{anything}-linux}), implementing the @file{ldconfig}
program, providing a test suite for the math library and for his
direction as part of @theglibc{} steering committee.
@item
Aurelien Jarno for various fixes.
@item
Jakub Jelinek for implementing a number of checking functions and for
his direction as part of @theglibc{} steering committee.
@item
Geoffrey Keating for the port to Linux on PowerPC
(@code{powerpc-@var{anything}-linux}).
@item
Brendan Kehoe for contributing the port to the MIPS DECStation running
Ultrix 4 (@code{mips-dec-ultrix4}) and the port to the DEC Alpha
running OSF/1 (@code{alpha-dec-osf1}).
@item
Mark Kettenis for implementing the @code{utmpx} interface and an utmp
daemon, and for a Hesiod NSS module.
@item
Andi Kleen for implementing pthreads lock elision with TSX.
@item
Kazumoto Kojima for the port of the Mach and Hurd code to the MIPS
architecture (@code{mips-@var{anything}-gnu}) and for his work on the
SH architecture.
@item
Andreas Krebbel for his work on Linux for s390 and s390x.
@item
Thorsten Kukuk for providing an implementation for NIS (YP) and NIS+,
securelevel 0, 1 and 2 and for the implementation for a caching daemon
for NSS (@file{nscd}).
@item
Jeff Law for various fixes.
@item
Doug Lea for contributing the memory allocation functions
functions @code{malloc}, @code{realloc} and @code{free} and related
code.
@item
Chris Leonard for various fixes and enhancements to localedata.
@item
Hongjiu Lu for providing the support for a Linux 32-bit runtime
environment under x86-64 (x32), for porting to Linux on IA64, for
improved string functions, a framework for testing IFUNC
implementations, and many bug fixes.
@item
Luis Machado for optimized functions on PowerPC.
@item
David J. MacKenzie for his contribution to the @code{getopt}
function and writing the @file{tar.h} header.
@item
Greg McGary for adding runtime support for bounds checking.
@item
Roland McGrath for writing most of @theglibc{} originally, for his
work on the Hurd port, his direction as part of @theglibc{} steering
committee and as FSF Project Steward for @theglibc{}, and for many bug
fixes and reviewing of contributions.
@item
Allan McRae for various fixes.
@item
Jason Merrill for the port to the Sequent Symmetry running Dynix
version 3 (@code{i386-sequent-bsd}).
@item
Chris Metcalf for the port to Linux/Tile
(@code{tilegx-@var{anything}-linux} and
@code{tilepro-@var{anything}-linux}).
@item
David Miller for contributing the port to Linux/Sparc
(@code{sparc*-@var{anything}-linux}).
@item
Alan Modra for his improvements for Linux on PowerPC.
@item
David Mosberger-Tang for contributing the port to Linux/Alpha
(@code{alpha-@var{anything}-linux}).
@item
Stephen Moshier for implementing some 128-bit long double format math
functions.
@item
Stephen Munroe for his port to Linux on PowerPC64
(@code{powerpc64-@var{anything}-linux}) and for adding optimized
implementations for PowerPC.
@item
Joseph S. Myers for numerous bug fixes for the libm functions, for
his maintainership of the ARM and MIPS architectures, improving
cross-compilation and cross-testing of @theglibc{}, expanded
coverage of conformtest, merging the ports/ subdirectory
into the @glibcadj{} main repository and his direction as FSF Project
Steward for @theglibc{}.
@item
Will Newton for contributing some optimized string functions and pointer
encryption support for ARM and various fixes.
@item
Carlos O'Donell for his maintainership of the HPPA architecture, for
maintaining @theglibc{} web pages and wiki, for his direction as FSF
Project Steward for @theglibc{} and various bug fixes.
@item
Alexandre Oliva for adding TLS descriptors for LD and GD on x86 and
x86-64, for the am33 port, for completing the MIPS n64/n32/o32 multilib
port, for thread-safety, async-signal safety and async-cancellation
safety documentation in the manual, for his direction as FSF Project
Maintainer and for various fixes.
@item
Paul Pluzhnikov for various fixes.
@item
Marek Polacek for various fixes.
@item
Siddhesh Poyarekar for various fixes and an implementation of a
framework for performance benchmarking of functions.
@item
Tom Quinn for contributing the startup code to support SunOS shared
libraries and the port to SGI machines running Irix 4
(@code{mips-sgi-irix4}).
@item
Pravin Satpute for writing sorting rules for some Indian languages.
@item
Douglas C. Schmidt for writing the quick sort function used as a
fallback by @code{qsort}.
@item
Will Schmidt for optimized string functions on PowerPC.
@item
Andreas Schwab for the port to Linux/m68k
(@code{m68k-@var{anything}-linux}) and for his direction as part of
@theglibc{} steering committee.
@item
Martin Schwidefsky for porting to Linux on s390
(@code{s390-@var{anything}-linux}) and s390x
(@code{s390x-@var{anything}-linux}).
@item
Thomas Schwinge for his contribution to Hurd and the SH architecture.
@item
Carlos Eduardo Seo for optimized functions on PowerPC.
@item
Marcus Shawcroft for contributing the AArch64 port.
@item
Franz Sirl for various fixes.
@item
Jes Sorensen for porting to Linux on IA64 (@code{ia64-@var{anything}-linux}).
@item
Richard Stallman for his contribution to the @code{getopt} function.
@item
Alfred M. Szmidt for various fixes.
@item
Ian Lance Taylor for contributing the port to the MIPS DECStation
running Ultrix 4 (@code{mips-dec-ultrix4}).
@item
Samuel Thibault for improving the Hurd port.
@item
Tim Waugh for the implementation of the POSIX.2 @code{wordexp}
function family.
@item
Eric Youngdale for implementing versioning of objects on the symbol level.
@item
Adhemerval Zanella for optimized functions on PowerPC.
@end itemize
Some code in @theglibc{} comes from other projects and might be under
a different license:
@itemize @bullet
@item
The timezone support code is derived from the public-domain timezone
package by Arthur David Olson and his many contributors.
@item
Some of the support code for Mach is taken from Mach 3.0 by CMU;
the file if_ppp.h is also copyright by CMU, but under a different license;
see the file @file{LICENSES} for the text of the licenses.
@item
The random number generation functions @code{random}, @code{srandom},
@code{setstate} and @code{initstate}, which are also the basis for the
@code{rand} and @code{srand} functions, were written by Earl T. Cohen
for the University of California at Berkeley and are copyrighted by the
Regents of the University of California. They have undergone minor
changes to fit into @theglibc{} and to fit the @w{ISO C} standard,
but the functional code is Berkeley's.@refill
@item
The Internet-related code (most of the @file{inet} subdirectory) and
several other miscellaneous functions and header files have been
included from 4.4 BSD with little or no modification. The copying
permission notice for this code can be found in the file @file{LICENSES}
in the source distribution.
@item
The @code{getaddrinfo} and @code{getnameinfo} functions and supporting
code were written by Craig Metz; see the file @file{LICENSES} for
details on their licensing.
@item
The DNS resolver code is taken directly from BIND 4.9.5, which
includes copyrighted code from UC Berkeley and from Digital Equipment
Corporation. See the file @file{LICENSES} for the text of the DEC license.
@item
The code to support Sun RPC is taken verbatim from Sun's
@w{@sc{rpcsrc-4.0}} distribution; see the file @file{LICENSES} for the
text of the license.
@item
The math functions are taken from @code{fdlibm-5.1} by Sun
Microsystems, as modified by J.T. Conklin, Ian Lance Taylor,
Ulrich Drepper, Andreas Schwab, and Roland McGrath.
@item
Many of the IEEE 64-bit double precision math functions
(in the @file{sysdeps/ieee754/dbl-64} subdirectory) come
from the IBM Accurate Mathematical Library, contributed by IBM.
@item
Many of the IA64 math functions are taken from a collection of
``Highly Optimized Mathematical Functions for Itanium'' that Intel
makes available under a free license; see the file @file{LICENSES} for
details.
@end itemize
glibc-doc-reference-2.19.orig/manual/charset.texi 0000664 0001750 0001750 00000400472 12275120646 022112 0 ustar adconrad adconrad @node Character Set Handling, Locales, String and Array Utilities, Top
@c %MENU% Support for extended character sets
@chapter Character Set Handling
@ifnottex
@macro cal{text}
\text\
@end macro
@end ifnottex
Character sets used in the early days of computing had only six, seven,
or eight bits for each character: there was never a case where more than
eight bits (one byte) were used to represent a single character. The
limitations of this approach became more apparent as more people
grappled with non-Roman character sets, where not all the characters
that make up a language's character set can be represented by @math{2^8}
choices. This chapter shows the functionality that was added to the C
library to support multiple character sets.
@menu
* Extended Char Intro:: Introduction to Extended Characters.
* Charset Function Overview:: Overview about Character Handling
Functions.
* Restartable multibyte conversion:: Restartable multibyte conversion
Functions.
* Non-reentrant Conversion:: Non-reentrant Conversion Function.
* Generic Charset Conversion:: Generic Charset Conversion.
@end menu
@node Extended Char Intro
@section Introduction to Extended Characters
A variety of solutions is available to overcome the differences between
character sets with a 1:1 relation between bytes and characters and
character sets with ratios of 2:1 or 4:1. The remainder of this
section gives a few examples to help understand the design decisions
made while developing the functionality of the @w{C library}.
@cindex internal representation
A distinction we have to make right away is between internal and
external representation. @dfn{Internal representation} means the
representation used by a program while keeping the text in memory.
External representations are used when text is stored or transmitted
through some communication channel. Examples of external
representations include files waiting in a directory to be
read and parsed.
Traditionally there has been no difference between the two representations.
It was equally comfortable and useful to use the same single-byte
representation internally and externally. This comfort level decreases
with more and larger character sets.
One of the problems to overcome with the internal representation is
handling text that is externally encoded using different character
sets. Assume a program that reads two texts and compares them using
some metric. The comparison can be usefully done only if the texts are
internally kept in a common format.
@cindex wide character
For such a common format (@math{=} character set) eight bits are certainly
no longer enough. So the smallest entity will have to grow: @dfn{wide
characters} will now be used. Instead of one byte per character, two or
four will be used instead. (Three are not good to address in memory and
more than four bytes seem not to be necessary).
@cindex Unicode
@cindex ISO 10646
As shown in some other part of this manual,
@c !!! Ahem, wide char string functions are not yet covered -- drepper
a completely new family has been created of functions that can handle wide
character texts in memory. The most commonly used character sets for such
internal wide character representations are Unicode and @w{ISO 10646}
(also known as UCS for Universal Character Set). Unicode was originally
planned as a 16-bit character set; whereas, @w{ISO 10646} was designed to
be a 31-bit large code space. The two standards are practically identical.
They have the same character repertoire and code table, but Unicode specifies
added semantics. At the moment, only characters in the first @code{0x10000}
code positions (the so-called Basic Multilingual Plane, BMP) have been
assigned, but the assignment of more specialized characters outside this
16-bit space is already in progress. A number of encodings have been
defined for Unicode and @w{ISO 10646} characters:
@cindex UCS-2
@cindex UCS-4
@cindex UTF-8
@cindex UTF-16
UCS-2 is a 16-bit word that can only represent characters
from the BMP, UCS-4 is a 32-bit word than can represent any Unicode
and @w{ISO 10646} character, UTF-8 is an ASCII compatible encoding where
ASCII characters are represented by ASCII bytes and non-ASCII characters
by sequences of 2-6 non-ASCII bytes, and finally UTF-16 is an extension
of UCS-2 in which pairs of certain UCS-2 words can be used to encode
non-BMP characters up to @code{0x10ffff}.
To represent wide characters the @code{char} type is not suitable. For
this reason the @w{ISO C} standard introduces a new type that is
designed to keep one character of a wide character string. To maintain
the similarity there is also a type corresponding to @code{int} for
those functions that take a single wide character.
@comment stddef.h
@comment ISO
@deftp {Data type} wchar_t
This data type is used as the base type for wide character strings.
In other words, arrays of objects of this type are the equivalent of
@code{char[]} for multibyte character strings. The type is defined in
@file{stddef.h}.
The @w{ISO C90} standard, where @code{wchar_t} was introduced, does not
say anything specific about the representation. It only requires that
this type is capable of storing all elements of the basic character set.
Therefore it would be legitimate to define @code{wchar_t} as @code{char},
which might make sense for embedded systems.
But in @theglibc{} @code{wchar_t} is always 32 bits wide and, therefore,
capable of representing all UCS-4 values and, therefore, covering all of
@w{ISO 10646}. Some Unix systems define @code{wchar_t} as a 16-bit type
and thereby follow Unicode very strictly. This definition is perfectly
fine with the standard, but it also means that to represent all
characters from Unicode and @w{ISO 10646} one has to use UTF-16 surrogate
characters, which is in fact a multi-wide-character encoding. But
resorting to multi-wide-character encoding contradicts the purpose of the
@code{wchar_t} type.
@end deftp
@comment wchar.h
@comment ISO
@deftp {Data type} wint_t
@code{wint_t} is a data type used for parameters and variables that
contain a single wide character. As the name suggests this type is the
equivalent of @code{int} when using the normal @code{char} strings. The
types @code{wchar_t} and @code{wint_t} often have the same
representation if their size is 32 bits wide but if @code{wchar_t} is
defined as @code{char} the type @code{wint_t} must be defined as
@code{int} due to the parameter promotion.
@pindex wchar.h
This type is defined in @file{wchar.h} and was introduced in
@w{Amendment 1} to @w{ISO C90}.
@end deftp
As there are for the @code{char} data type macros are available for
specifying the minimum and maximum value representable in an object of
type @code{wchar_t}.
@comment wchar.h
@comment ISO
@deftypevr Macro wint_t WCHAR_MIN
The macro @code{WCHAR_MIN} evaluates to the minimum value representable
by an object of type @code{wint_t}.
This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
@end deftypevr
@comment wchar.h
@comment ISO
@deftypevr Macro wint_t WCHAR_MAX
The macro @code{WCHAR_MAX} evaluates to the maximum value representable
by an object of type @code{wint_t}.
This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
@end deftypevr
Another special wide character value is the equivalent to @code{EOF}.
@comment wchar.h
@comment ISO
@deftypevr Macro wint_t WEOF
The macro @code{WEOF} evaluates to a constant expression of type
@code{wint_t} whose value is different from any member of the extended
character set.
@code{WEOF} need not be the same value as @code{EOF} and unlike
@code{EOF} it also need @emph{not} be negative. In other words, sloppy
code like
@smallexample
@{
int c;
@dots{}
while ((c = getc (fp)) < 0)
@dots{}
@}
@end smallexample
@noindent
has to be rewritten to use @code{WEOF} explicitly when wide characters
are used:
@smallexample
@{
wint_t c;
@dots{}
while ((c = wgetc (fp)) != WEOF)
@dots{}
@}
@end smallexample
@pindex wchar.h
This macro was introduced in @w{Amendment 1} to @w{ISO C90} and is
defined in @file{wchar.h}.
@end deftypevr
These internal representations present problems when it comes to storing
and transmittal. Because each single wide character consists of more
than one byte, they are affected by byte-ordering. Thus, machines with
different endianesses would see different values when accessing the same
data. This byte ordering concern also applies for communication protocols
that are all byte-based and therefore require that the sender has to
decide about splitting the wide character in bytes. A last (but not least
important) point is that wide characters often require more storage space
than a customized byte-oriented character set.
@cindex multibyte character
@cindex EBCDIC
For all the above reasons, an external encoding that is different from
the internal encoding is often used if the latter is UCS-2 or UCS-4.
The external encoding is byte-based and can be chosen appropriately for
the environment and for the texts to be handled. A variety of different
character sets can be used for this external encoding (information that
will not be exhaustively presented here--instead, a description of the
major groups will suffice). All of the ASCII-based character sets
fulfill one requirement: they are "filesystem safe." This means that
the character @code{'/'} is used in the encoding @emph{only} to
represent itself. Things are a bit different for character sets like
EBCDIC (Extended Binary Coded Decimal Interchange Code, a character set
family used by IBM), but if the operating system does not understand
EBCDIC directly the parameters-to-system calls have to be converted
first anyhow.
@itemize @bullet
@item
The simplest character sets are single-byte character sets. There can
be only up to 256 characters (for @w{8 bit} character sets), which is
not sufficient to cover all languages but might be sufficient to handle
a specific text. Handling of a @w{8 bit} character sets is simple. This
is not true for other kinds presented later, and therefore, the
application one uses might require the use of @w{8 bit} character sets.
@cindex ISO 2022
@item
The @w{ISO 2022} standard defines a mechanism for extended character
sets where one character @emph{can} be represented by more than one
byte. This is achieved by associating a state with the text.
Characters that can be used to change the state can be embedded in the
text. Each byte in the text might have a different interpretation in each
state. The state might even influence whether a given byte stands for a
character on its own or whether it has to be combined with some more
bytes.
@cindex EUC
@cindex Shift_JIS
@cindex SJIS
In most uses of @w{ISO 2022} the defined character sets do not allow
state changes that cover more than the next character. This has the
big advantage that whenever one can identify the beginning of the byte
sequence of a character one can interpret a text correctly. Examples of
character sets using this policy are the various EUC character sets
(used by Sun's operating systems, EUC-JP, EUC-KR, EUC-TW, and EUC-CN)
or Shift_JIS (SJIS, a Japanese encoding).
But there are also character sets using a state that is valid for more
than one character and has to be changed by another byte sequence.
Examples for this are ISO-2022-JP, ISO-2022-KR, and ISO-2022-CN.
@item
@cindex ISO 6937
Early attempts to fix 8 bit character sets for other languages using the
Roman alphabet lead to character sets like @w{ISO 6937}. Here bytes
representing characters like the acute accent do not produce output
themselves: one has to combine them with other characters to get the
desired result. For example, the byte sequence @code{0xc2 0x61}
(non-spacing acute accent, followed by lower-case `a') to get the ``small
a with acute'' character. To get the acute accent character on its own,
one has to write @code{0xc2 0x20} (the non-spacing acute followed by a
space).
Character sets like @w{ISO 6937} are used in some embedded systems such
as teletex.
@item
@cindex UTF-8
Instead of converting the Unicode or @w{ISO 10646} text used internally,
it is often also sufficient to simply use an encoding different than
UCS-2/UCS-4. The Unicode and @w{ISO 10646} standards even specify such an
encoding: UTF-8. This encoding is able to represent all of @w{ISO
10646} 31 bits in a byte string of length one to six.
@cindex UTF-7
There were a few other attempts to encode @w{ISO 10646} such as UTF-7,
but UTF-8 is today the only encoding that should be used. In fact, with
any luck UTF-8 will soon be the only external encoding that has to be
supported. It proves to be universally usable and its only disadvantage
is that it favors Roman languages by making the byte string
representation of other scripts (Cyrillic, Greek, Asian scripts) longer
than necessary if using a specific character set for these scripts.
Methods like the Unicode compression scheme can alleviate these
problems.
@end itemize
The question remaining is: how to select the character set or encoding
to use. The answer: you cannot decide about it yourself, it is decided
by the developers of the system or the majority of the users. Since the
goal is interoperability one has to use whatever the other people one
works with use. If there are no constraints, the selection is based on
the requirements the expected circle of users will have. In other words,
if a project is expected to be used in only, say, Russia it is fine to use
KOI8-R or a similar character set. But if at the same time people from,
say, Greece are participating one should use a character set that allows
all people to collaborate.
The most widely useful solution seems to be: go with the most general
character set, namely @w{ISO 10646}. Use UTF-8 as the external encoding
and problems about users not being able to use their own language
adequately are a thing of the past.
One final comment about the choice of the wide character representation
is necessary at this point. We have said above that the natural choice
is using Unicode or @w{ISO 10646}. This is not required, but at least
encouraged, by the @w{ISO C} standard. The standard defines at least a
macro @code{__STDC_ISO_10646__} that is only defined on systems where
the @code{wchar_t} type encodes @w{ISO 10646} characters. If this
symbol is not defined one should avoid making assumptions about the wide
character representation. If the programmer uses only the functions
provided by the C library to handle wide character strings there should
be no compatibility problems with other systems.
@node Charset Function Overview
@section Overview about Character Handling Functions
A Unix @w{C library} contains three different sets of functions in two
families to handle character set conversion. One of the function families
(the most commonly used) is specified in the @w{ISO C90} standard and,
therefore, is portable even beyond the Unix world. Unfortunately this
family is the least useful one. These functions should be avoided
whenever possible, especially when developing libraries (as opposed to
applications).
The second family of functions got introduced in the early Unix standards
(XPG2) and is still part of the latest and greatest Unix standard:
@w{Unix 98}. It is also the most powerful and useful set of functions.
But we will start with the functions defined in @w{Amendment 1} to
@w{ISO C90}.
@node Restartable multibyte conversion
@section Restartable Multibyte Conversion Functions
The @w{ISO C} standard defines functions to convert strings from a
multibyte representation to wide character strings. There are a number
of peculiarities:
@itemize @bullet
@item
The character set assumed for the multibyte encoding is not specified
as an argument to the functions. Instead the character set specified by
the @code{LC_CTYPE} category of the current locale is used; see
@ref{Locale Categories}.
@item
The functions handling more than one character at a time require NUL
terminated strings as the argument (i.e., converting blocks of text
does not work unless one can add a NUL byte at an appropriate place).
@Theglibc{} contains some extensions to the standard that allow
specifying a size, but basically they also expect terminated strings.
@end itemize
Despite these limitations the @w{ISO C} functions can be used in many
contexts. In graphical user interfaces, for instance, it is not
uncommon to have functions that require text to be displayed in a wide
character string if the text is not simple ASCII. The text itself might
come from a file with translations and the user should decide about the
current locale, which determines the translation and therefore also the
external encoding used. In such a situation (and many others) the
functions described here are perfect. If more freedom while performing
the conversion is necessary take a look at the @code{iconv} functions
(@pxref{Generic Charset Conversion}).
@menu
* Selecting the Conversion:: Selecting the conversion and its properties.
* Keeping the state:: Representing the state of the conversion.
* Converting a Character:: Converting Single Characters.
* Converting Strings:: Converting Multibyte and Wide Character
Strings.
* Multibyte Conversion Example:: A Complete Multibyte Conversion Example.
@end menu
@node Selecting the Conversion
@subsection Selecting the conversion and its properties
We already said above that the currently selected locale for the
@code{LC_CTYPE} category decides about the conversion that is performed
by the functions we are about to describe. Each locale uses its own
character set (given as an argument to @code{localedef}) and this is the
one assumed as the external multibyte encoding. The wide character
set is always UCS-4 in @theglibc{}.
A characteristic of each multibyte character set is the maximum number
of bytes that can be necessary to represent one character. This
information is quite important when writing code that uses the
conversion functions (as shown in the examples below).
The @w{ISO C} standard defines two macros that provide this information.
@comment limits.h
@comment ISO
@deftypevr Macro int MB_LEN_MAX
@code{MB_LEN_MAX} specifies the maximum number of bytes in the multibyte
sequence for a single character in any of the supported locales. It is
a compile-time constant and is defined in @file{limits.h}.
@pindex limits.h
@end deftypevr
@comment stdlib.h
@comment ISO
@deftypevr Macro int MB_CUR_MAX
@code{MB_CUR_MAX} expands into a positive integer expression that is the
maximum number of bytes in a multibyte character in the current locale.
The value is never greater than @code{MB_LEN_MAX}. Unlike
@code{MB_LEN_MAX} this macro need not be a compile-time constant, and in
@theglibc{} it is not.
@pindex stdlib.h
@code{MB_CUR_MAX} is defined in @file{stdlib.h}.
@end deftypevr
Two different macros are necessary since strictly @w{ISO C90} compilers
do not allow variable length array definitions, but still it is desirable
to avoid dynamic allocation. This incomplete piece of code shows the
problem:
@smallexample
@{
char buf[MB_LEN_MAX];
ssize_t len = 0;
while (! feof (fp))
@{
fread (&buf[len], 1, MB_CUR_MAX - len, fp);
/* @r{@dots{} process} buf */
len -= used;
@}
@}
@end smallexample
The code in the inner loop is expected to have always enough bytes in
the array @var{buf} to convert one multibyte character. The array
@var{buf} has to be sized statically since many compilers do not allow a
variable size. The @code{fread} call makes sure that @code{MB_CUR_MAX}
bytes are always available in @var{buf}. Note that it isn't
a problem if @code{MB_CUR_MAX} is not a compile-time constant.
@node Keeping the state
@subsection Representing the state of the conversion
@cindex stateful
In the introduction of this chapter it was said that certain character
sets use a @dfn{stateful} encoding. That is, the encoded values depend
in some way on the previous bytes in the text.
Since the conversion functions allow converting a text in more than one
step we must have a way to pass this information from one call of the
functions to another.
@comment wchar.h
@comment ISO
@deftp {Data type} mbstate_t
@cindex shift state
A variable of type @code{mbstate_t} can contain all the information
about the @dfn{shift state} needed from one call to a conversion
function to another.
@pindex wchar.h
@code{mbstate_t} is defined in @file{wchar.h}. It was introduced in
@w{Amendment 1} to @w{ISO C90}.
@end deftp
To use objects of type @code{mbstate_t} the programmer has to define such
objects (normally as local variables on the stack) and pass a pointer to
the object to the conversion functions. This way the conversion function
can update the object if the current multibyte character set is stateful.
There is no specific function or initializer to put the state object in
any specific state. The rules are that the object should always
represent the initial state before the first use, and this is achieved by
clearing the whole variable with code such as follows:
@smallexample
@{
mbstate_t state;
memset (&state, '\0', sizeof (state));
/* @r{from now on @var{state} can be used.} */
@dots{}
@}
@end smallexample
When using the conversion functions to generate output it is often
necessary to test whether the current state corresponds to the initial
state. This is necessary, for example, to decide whether to emit
escape sequences to set the state to the initial state at certain
sequence points. Communication protocols often require this.
@comment wchar.h
@comment ISO
@deftypefun int mbsinit (const mbstate_t *@var{ps})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c ps is dereferenced once, unguarded. This would call for @mtsrace:ps,
@c but since a single word-sized field is (atomically) accessed, any
@c race here would be harmless. Other functions that take an optional
@c mbstate_t* argument named ps are marked with @mtasurace:/!ps,
@c to indicate that the function uses a static buffer if ps is NULL.
@c These could also have been marked with @mtsrace:ps, but we'll omit
@c that for brevity, for it's somewhat redundant with the @mtasurace.
The @code{mbsinit} function determines whether the state object pointed
to by @var{ps} is in the initial state. If @var{ps} is a null pointer or
the object is in the initial state the return value is nonzero. Otherwise
it is zero.
@pindex wchar.h
@code{mbsinit} was introduced in @w{Amendment 1} to @w{ISO C90} and is
declared in @file{wchar.h}.
@end deftypefun
Code using @code{mbsinit} often looks similar to this:
@c Fix the example to explicitly say how to generate the escape sequence
@c to restore the initial state.
@smallexample
@{
mbstate_t state;
memset (&state, '\0', sizeof (state));
/* @r{Use @var{state}.} */
@dots{}
if (! mbsinit (&state))
@{
/* @r{Emit code to return to initial state.} */
const wchar_t empty[] = L"";
const wchar_t *srcp = empty;
wcsrtombs (outbuf, &srcp, outbuflen, &state);
@}
@dots{}
@}
@end smallexample
The code to emit the escape sequence to get back to the initial state is
interesting. The @code{wcsrtombs} function can be used to determine the
necessary output code (@pxref{Converting Strings}). Please note that with
@theglibc{} it is not necessary to perform this extra action for the
conversion from multibyte text to wide character text since the wide
character encoding is not stateful. But there is nothing mentioned in
any standard that prohibits making @code{wchar_t} using a stateful
encoding.
@node Converting a Character
@subsection Converting Single Characters
The most fundamental of the conversion functions are those dealing with
single characters. Please note that this does not always mean single
bytes. But since there is very often a subset of the multibyte
character set that consists of single byte sequences, there are
functions to help with converting bytes. Frequently, ASCII is a subpart
of the multibyte character set. In such a scenario, each ASCII character
stands for itself, and all other characters have at least a first byte
that is beyond the range @math{0} to @math{127}.
@comment wchar.h
@comment ISO
@deftypefun wint_t btowc (int @var{c})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Calls btowc_fct or __fct; reads from locale, and from the
@c get_gconv_fcts result multiple times. get_gconv_fcts calls
@c __wcsmbs_load_conv to initialize the ctype if it's null.
@c wcsmbs_load_conv takes a non-recursive wrlock before allocating
@c memory for the fcts structure, initializing it, and then storing it
@c in the locale object. The initialization involves dlopening and a
@c lot more.
The @code{btowc} function (``byte to wide character'') converts a valid
single byte character @var{c} in the initial shift state into the wide
character equivalent using the conversion rules from the currently
selected locale of the @code{LC_CTYPE} category.
If @code{(unsigned char) @var{c}} is no valid single byte multibyte
character or if @var{c} is @code{EOF}, the function returns @code{WEOF}.
Please note the restriction of @var{c} being tested for validity only in
the initial shift state. No @code{mbstate_t} object is used from
which the state information is taken, and the function also does not use
any static state.
@pindex wchar.h
The @code{btowc} function was introduced in @w{Amendment 1} to @w{ISO C90}
and is declared in @file{wchar.h}.
@end deftypefun
Despite the limitation that the single byte value is always interpreted
in the initial state, this function is actually useful most of the time.
Most characters are either entirely single-byte character sets or they
are extension to ASCII. But then it is possible to write code like this
(not that this specific example is very useful):
@smallexample
wchar_t *
itow (unsigned long int val)
@{
static wchar_t buf[30];
wchar_t *wcp = &buf[29];
*wcp = L'\0';
while (val != 0)
@{
*--wcp = btowc ('0' + val % 10);
val /= 10;
@}
if (wcp == &buf[29])
*--wcp = L'0';
return wcp;
@}
@end smallexample
Why is it necessary to use such a complicated implementation and not
simply cast @code{'0' + val % 10} to a wide character? The answer is
that there is no guarantee that one can perform this kind of arithmetic
on the character of the character set used for @code{wchar_t}
representation. In other situations the bytes are not constant at
compile time and so the compiler cannot do the work. In situations like
this, using @code{btowc} is required.
@noindent
There is also a function for the conversion in the other direction.
@comment wchar.h
@comment ISO
@deftypefun int wctob (wint_t @var{c})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{wctob} function (``wide character to byte'') takes as the
parameter a valid wide character. If the multibyte representation for
this character in the initial state is exactly one byte long, the return
value of this function is this character. Otherwise the return value is
@code{EOF}.
@pindex wchar.h
@code{wctob} was introduced in @w{Amendment 1} to @w{ISO C90} and
is declared in @file{wchar.h}.
@end deftypefun
There are more general functions to convert single character from
multibyte representation to wide characters and vice versa. These
functions pose no limit on the length of the multibyte representation
and they also do not require it to be in the initial state.
@comment wchar.h
@comment ISO
@deftypefun size_t mbrtowc (wchar_t *restrict @var{pwc}, const char *restrict @var{s}, size_t @var{n}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:mbrtowc/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@cindex stateful
The @code{mbrtowc} function (``multibyte restartable to wide
character'') converts the next multibyte character in the string pointed
to by @var{s} into a wide character and stores it in the wide character
string pointed to by @var{pwc}. The conversion is performed according
to the locale currently selected for the @code{LC_CTYPE} category. If
the conversion for the character set used in the locale requires a state,
the multibyte string is interpreted in the state represented by the
object pointed to by @var{ps}. If @var{ps} is a null pointer, a static,
internal state variable used only by the @code{mbrtowc} function is
used.
If the next multibyte character corresponds to the NUL wide character,
the return value of the function is @math{0} and the state object is
afterwards in the initial state. If the next @var{n} or fewer bytes
form a correct multibyte character, the return value is the number of
bytes starting from @var{s} that form the multibyte character. The
conversion state is updated according to the bytes consumed in the
conversion. In both cases the wide character (either the @code{L'\0'}
or the one found in the conversion) is stored in the string pointed to
by @var{pwc} if @var{pwc} is not null.
If the first @var{n} bytes of the multibyte string possibly form a valid
multibyte character but there are more than @var{n} bytes needed to
complete it, the return value of the function is @code{(size_t) -2} and
no value is stored. Please note that this can happen even if @var{n}
has a value greater than or equal to @code{MB_CUR_MAX} since the input
might contain redundant shift sequences.
If the first @code{n} bytes of the multibyte string cannot possibly form
a valid multibyte character, no value is stored, the global variable
@code{errno} is set to the value @code{EILSEQ}, and the function returns
@code{(size_t) -1}. The conversion state is afterwards undefined.
@pindex wchar.h
@code{mbrtowc} was introduced in @w{Amendment 1} to @w{ISO C90} and
is declared in @file{wchar.h}.
@end deftypefun
Use of @code{mbrtowc} is straightforward. A function that copies a
multibyte string into a wide character string while at the same time
converting all lowercase characters into uppercase could look like this
(this is not the final version, just an example; it has no error
checking, and sometimes leaks memory):
@smallexample
wchar_t *
mbstouwcs (const char *s)
@{
size_t len = strlen (s);
wchar_t *result = malloc ((len + 1) * sizeof (wchar_t));
wchar_t *wcp = result;
wchar_t tmp[1];
mbstate_t state;
size_t nbytes;
memset (&state, '\0', sizeof (state));
while ((nbytes = mbrtowc (tmp, s, len, &state)) > 0)
@{
if (nbytes >= (size_t) -2)
/* Invalid input string. */
return NULL;
*wcp++ = towupper (tmp[0]);
len -= nbytes;
s += nbytes;
@}
return result;
@}
@end smallexample
The use of @code{mbrtowc} should be clear. A single wide character is
stored in @code{@var{tmp}[0]}, and the number of consumed bytes is stored
in the variable @var{nbytes}. If the conversion is successful, the
uppercase variant of the wide character is stored in the @var{result}
array and the pointer to the input string and the number of available
bytes is adjusted.
The only non-obvious thing about @code{mbrtowc} might be the way memory
is allocated for the result. The above code uses the fact that there
can never be more wide characters in the converted results than there are
bytes in the multibyte input string. This method yields a pessimistic
guess about the size of the result, and if many wide character strings
have to be constructed this way or if the strings are long, the extra
memory required to be allocated because the input string contains
multibyte characters might be significant. The allocated memory block can
be resized to the correct size before returning it, but a better solution
might be to allocate just the right amount of space for the result right
away. Unfortunately there is no function to compute the length of the wide
character string directly from the multibyte string. There is, however, a
function that does part of the work.
@comment wchar.h
@comment ISO
@deftypefun size_t mbrlen (const char *restrict @var{s}, size_t @var{n}, mbstate_t *@var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:mbrlen/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{mbrlen} function (``multibyte restartable length'') computes
the number of at most @var{n} bytes starting at @var{s}, which form the
next valid and complete multibyte character.
If the next multibyte character corresponds to the NUL wide character,
the return value is @math{0}. If the next @var{n} bytes form a valid
multibyte character, the number of bytes belonging to this multibyte
character byte sequence is returned.
If the first @var{n} bytes possibly form a valid multibyte
character but the character is incomplete, the return value is
@code{(size_t) -2}. Otherwise the multibyte character sequence is invalid
and the return value is @code{(size_t) -1}.
The multibyte sequence is interpreted in the state represented by the
object pointed to by @var{ps}. If @var{ps} is a null pointer, a state
object local to @code{mbrlen} is used.
@pindex wchar.h
@code{mbrlen} was introduced in @w{Amendment 1} to @w{ISO C90} and
is declared in @file{wchar.h}.
@end deftypefun
The attentive reader now will note that @code{mbrlen} can be implemented
as
@smallexample
mbrtowc (NULL, s, n, ps != NULL ? ps : &internal)
@end smallexample
This is true and in fact is mentioned in the official specification.
How can this function be used to determine the length of the wide
character string created from a multibyte character string? It is not
directly usable, but we can define a function @code{mbslen} using it:
@smallexample
size_t
mbslen (const char *s)
@{
mbstate_t state;
size_t result = 0;
size_t nbytes;
memset (&state, '\0', sizeof (state));
while ((nbytes = mbrlen (s, MB_LEN_MAX, &state)) > 0)
@{
if (nbytes >= (size_t) -2)
/* @r{Something is wrong.} */
return (size_t) -1;
s += nbytes;
++result;
@}
return result;
@}
@end smallexample
This function simply calls @code{mbrlen} for each multibyte character
in the string and counts the number of function calls. Please note that
we here use @code{MB_LEN_MAX} as the size argument in the @code{mbrlen}
call. This is acceptable since a) this value is larger than the length of
the longest multibyte character sequence and b) we know that the string
@var{s} ends with a NUL byte, which cannot be part of any other multibyte
character sequence but the one representing the NUL wide character.
Therefore, the @code{mbrlen} function will never read invalid memory.
Now that this function is available (just to make this clear, this
function is @emph{not} part of @theglibc{}) we can compute the
number of wide character required to store the converted multibyte
character string @var{s} using
@smallexample
wcs_bytes = (mbslen (s) + 1) * sizeof (wchar_t);
@end smallexample
Please note that the @code{mbslen} function is quite inefficient. The
implementation of @code{mbstouwcs} with @code{mbslen} would have to
perform the conversion of the multibyte character input string twice, and
this conversion might be quite expensive. So it is necessary to think
about the consequences of using the easier but imprecise method before
doing the work twice.
@comment wchar.h
@comment ISO
@deftypefun size_t wcrtomb (char *restrict @var{s}, wchar_t @var{wc}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:wcrtomb/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c wcrtomb uses a static, non-thread-local unguarded state variable when
@c PS is NULL. When a state is passed in, and it's not used
@c concurrently in other threads, this function behaves safely as long
@c as gconv modules don't bring MT safety issues of their own.
@c Attempting to load gconv modules or to build conversion chains in
@c signal handlers may encounter gconv databases or caches in a
@c partially-updated state, and asynchronous cancellation may leave them
@c in such states, besides leaking the lock that guards them.
@c get_gconv_fcts ok
@c wcsmbs_load_conv ok
@c norm_add_slashes ok
@c wcsmbs_getfct ok
@c gconv_find_transform ok
@c gconv_read_conf (libc_once)
@c gconv_lookup_cache ok
@c find_module_idx ok
@c find_module ok
@c gconv_find_shlib (ok)
@c ->init_fct (assumed ok)
@c gconv_get_builtin_trans ok
@c gconv_release_step ok
@c do_lookup_alias ok
@c find_derivation ok
@c derivation_lookup ok
@c increment_counter ok
@c gconv_find_shlib ok
@c step->init_fct (assumed ok)
@c gen_steps ok
@c gconv_find_shlib ok
@c dlopen (presumed ok)
@c dlsym (presumed ok)
@c step->init_fct (assumed ok)
@c step->end_fct (assumed ok)
@c gconv_get_builtin_trans ok
@c gconv_release_step ok
@c add_derivation ok
@c gconv_close_transform ok
@c gconv_release_step ok
@c step->end_fct (assumed ok)
@c gconv_release_shlib ok
@c dlclose (presumed ok)
@c gconv_release_cache ok
@c ->tomb->__fct (assumed ok)
The @code{wcrtomb} function (``wide character restartable to
multibyte'') converts a single wide character into a multibyte string
corresponding to that wide character.
If @var{s} is a null pointer, the function resets the state stored in
the objects pointed to by @var{ps} (or the internal @code{mbstate_t}
object) to the initial state. This can also be achieved by a call like
this:
@smallexample
wcrtombs (temp_buf, L'\0', ps)
@end smallexample
@noindent
since, if @var{s} is a null pointer, @code{wcrtomb} performs as if it
writes into an internal buffer, which is guaranteed to be large enough.
If @var{wc} is the NUL wide character, @code{wcrtomb} emits, if
necessary, a shift sequence to get the state @var{ps} into the initial
state followed by a single NUL byte, which is stored in the string
@var{s}.
Otherwise a byte sequence (possibly including shift sequences) is written
into the string @var{s}. This only happens if @var{wc} is a valid wide
character (i.e., it has a multibyte representation in the character set
selected by locale of the @code{LC_CTYPE} category). If @var{wc} is no
valid wide character, nothing is stored in the strings @var{s},
@code{errno} is set to @code{EILSEQ}, the conversion state in @var{ps}
is undefined and the return value is @code{(size_t) -1}.
If no error occurred the function returns the number of bytes stored in
the string @var{s}. This includes all bytes representing shift
sequences.
One word about the interface of the function: there is no parameter
specifying the length of the array @var{s}. Instead the function
assumes that there are at least @code{MB_CUR_MAX} bytes available since
this is the maximum length of any byte sequence representing a single
character. So the caller has to make sure that there is enough space
available, otherwise buffer overruns can occur.
@pindex wchar.h
@code{wcrtomb} was introduced in @w{Amendment 1} to @w{ISO C90} and is
declared in @file{wchar.h}.
@end deftypefun
Using @code{wcrtomb} is as easy as using @code{mbrtowc}. The following
example appends a wide character string to a multibyte character string.
Again, the code is not really useful (or correct), it is simply here to
demonstrate the use and some problems.
@smallexample
char *
mbscatwcs (char *s, size_t len, const wchar_t *ws)
@{
mbstate_t state;
/* @r{Find the end of the existing string.} */
char *wp = strchr (s, '\0');
len -= wp - s;
memset (&state, '\0', sizeof (state));
do
@{
size_t nbytes;
if (len < MB_CUR_LEN)
@{
/* @r{We cannot guarantee that the next}
@r{character fits into the buffer, so}
@r{return an error.} */
errno = E2BIG;
return NULL;
@}
nbytes = wcrtomb (wp, *ws, &state);
if (nbytes == (size_t) -1)
/* @r{Error in the conversion.} */
return NULL;
len -= nbytes;
wp += nbytes;
@}
while (*ws++ != L'\0');
return s;
@}
@end smallexample
First the function has to find the end of the string currently in the
array @var{s}. The @code{strchr} call does this very efficiently since a
requirement for multibyte character representations is that the NUL byte
is never used except to represent itself (and in this context, the end
of the string).
After initializing the state object the loop is entered where the first
task is to make sure there is enough room in the array @var{s}. We
abort if there are not at least @code{MB_CUR_LEN} bytes available. This
is not always optimal but we have no other choice. We might have less
than @code{MB_CUR_LEN} bytes available but the next multibyte character
might also be only one byte long. At the time the @code{wcrtomb} call
returns it is too late to decide whether the buffer was large enough. If
this solution is unsuitable, there is a very slow but more accurate
solution.
@smallexample
@dots{}
if (len < MB_CUR_LEN)
@{
mbstate_t temp_state;
memcpy (&temp_state, &state, sizeof (state));
if (wcrtomb (NULL, *ws, &temp_state) > len)
@{
/* @r{We cannot guarantee that the next}
@r{character fits into the buffer, so}
@r{return an error.} */
errno = E2BIG;
return NULL;
@}
@}
@dots{}
@end smallexample
Here we perform the conversion that might overflow the buffer so that
we are afterwards in the position to make an exact decision about the
buffer size. Please note the @code{NULL} argument for the destination
buffer in the new @code{wcrtomb} call; since we are not interested in the
converted text at this point, this is a nice way to express this. The
most unusual thing about this piece of code certainly is the duplication
of the conversion state object, but if a change of the state is necessary
to emit the next multibyte character, we want to have the same shift state
change performed in the real conversion. Therefore, we have to preserve
the initial shift state information.
There are certainly many more and even better solutions to this problem.
This example is only provided for educational purposes.
@node Converting Strings
@subsection Converting Multibyte and Wide Character Strings
The functions described in the previous section only convert a single
character at a time. Most operations to be performed in real-world
programs include strings and therefore the @w{ISO C} standard also
defines conversions on entire strings. However, the defined set of
functions is quite limited; therefore, @theglibc{} contains a few
extensions that can help in some important situations.
@comment wchar.h
@comment ISO
@deftypefun size_t mbsrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:mbsrtowcs/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{mbsrtowcs} function (``multibyte string restartable to wide
character string'') converts a NUL-terminated multibyte character
string at @code{*@var{src}} into an equivalent wide character string,
including the NUL wide character at the end. The conversion is started
using the state information from the object pointed to by @var{ps} or
from an internal object of @code{mbsrtowcs} if @var{ps} is a null
pointer. Before returning, the state object is updated to match the state
after the last converted character. The state is the initial state if the
terminating NUL byte is reached and converted.
If @var{dst} is not a null pointer, the result is stored in the array
pointed to by @var{dst}; otherwise, the conversion result is not
available since it is stored in an internal buffer.
If @var{len} wide characters are stored in the array @var{dst} before
reaching the end of the input string, the conversion stops and @var{len}
is returned. If @var{dst} is a null pointer, @var{len} is never checked.
Another reason for a premature return from the function call is if the
input string contains an invalid multibyte sequence. In this case the
global variable @code{errno} is set to @code{EILSEQ} and the function
returns @code{(size_t) -1}.
@c XXX The ISO C9x draft seems to have a problem here. It says that PS
@c is not updated if DST is NULL. This is not said straightforward and
@c none of the other functions is described like this. It would make sense
@c to define the function this way but I don't think it is meant like this.
In all other cases the function returns the number of wide characters
converted during this call. If @var{dst} is not null, @code{mbsrtowcs}
stores in the pointer pointed to by @var{src} either a null pointer (if
the NUL byte in the input string was reached) or the address of the byte
following the last converted multibyte character.
@pindex wchar.h
@code{mbsrtowcs} was introduced in @w{Amendment 1} to @w{ISO C90} and is
declared in @file{wchar.h}.
@end deftypefun
The definition of the @code{mbsrtowcs} function has one important
limitation. The requirement that @var{dst} has to be a NUL-terminated
string provides problems if one wants to convert buffers with text. A
buffer is normally no collection of NUL-terminated strings but instead a
continuous collection of lines, separated by newline characters. Now
assume that a function to convert one line from a buffer is needed. Since
the line is not NUL-terminated, the source pointer cannot directly point
into the unmodified text buffer. This means, either one inserts the NUL
byte at the appropriate place for the time of the @code{mbsrtowcs}
function call (which is not doable for a read-only buffer or in a
multi-threaded application) or one copies the line in an extra buffer
where it can be terminated by a NUL byte. Note that it is not in general
possible to limit the number of characters to convert by setting the
parameter @var{len} to any specific value. Since it is not known how
many bytes each multibyte character sequence is in length, one can only
guess.
@cindex stateful
There is still a problem with the method of NUL-terminating a line right
after the newline character, which could lead to very strange results.
As said in the description of the @code{mbsrtowcs} function above the
conversion state is guaranteed to be in the initial shift state after
processing the NUL byte at the end of the input string. But this NUL
byte is not really part of the text (i.e., the conversion state after
the newline in the original text could be something different than the
initial shift state and therefore the first character of the next line
is encoded using this state). But the state in question is never
accessible to the user since the conversion stops after the NUL byte
(which resets the state). Most stateful character sets in use today
require that the shift state after a newline be the initial state--but
this is not a strict guarantee. Therefore, simply NUL-terminating a
piece of a running text is not always an adequate solution and,
therefore, should never be used in generally used code.
The generic conversion interface (@pxref{Generic Charset Conversion})
does not have this limitation (it simply works on buffers, not
strings), and @theglibc{} contains a set of functions that take
additional parameters specifying the maximal number of bytes that are
consumed from the input string. This way the problem of
@code{mbsrtowcs}'s example above could be solved by determining the line
length and passing this length to the function.
@comment wchar.h
@comment ISO
@deftypefun size_t wcsrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:wcsrtombs/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{wcsrtombs} function (``wide character string restartable to
multibyte string'') converts the NUL-terminated wide character string at
@code{*@var{src}} into an equivalent multibyte character string and
stores the result in the array pointed to by @var{dst}. The NUL wide
character is also converted. The conversion starts in the state
described in the object pointed to by @var{ps} or by a state object
locally to @code{wcsrtombs} in case @var{ps} is a null pointer. If
@var{dst} is a null pointer, the conversion is performed as usual but the
result is not available. If all characters of the input string were
successfully converted and if @var{dst} is not a null pointer, the
pointer pointed to by @var{src} gets assigned a null pointer.
If one of the wide characters in the input string has no valid multibyte
character equivalent, the conversion stops early, sets the global
variable @code{errno} to @code{EILSEQ}, and returns @code{(size_t) -1}.
Another reason for a premature stop is if @var{dst} is not a null
pointer and the next converted character would require more than
@var{len} bytes in total to the array @var{dst}. In this case (and if
@var{dest} is not a null pointer) the pointer pointed to by @var{src} is
assigned a value pointing to the wide character right after the last one
successfully converted.
Except in the case of an encoding error the return value of the
@code{wcsrtombs} function is the number of bytes in all the multibyte
character sequences stored in @var{dst}. Before returning the state in
the object pointed to by @var{ps} (or the internal object in case
@var{ps} is a null pointer) is updated to reflect the state after the
last conversion. The state is the initial shift state in case the
terminating NUL wide character was converted.
@pindex wchar.h
The @code{wcsrtombs} function was introduced in @w{Amendment 1} to
@w{ISO C90} and is declared in @file{wchar.h}.
@end deftypefun
The restriction mentioned above for the @code{mbsrtowcs} function applies
here also. There is no possibility of directly controlling the number of
input characters. One has to place the NUL wide character at the correct
place or control the consumed input indirectly via the available output
array size (the @var{len} parameter).
@comment wchar.h
@comment GNU
@deftypefun size_t mbsnrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{nmc}, size_t @var{len}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:mbsnrtowcs/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{mbsnrtowcs} function is very similar to the @code{mbsrtowcs}
function. All the parameters are the same except for @var{nmc}, which is
new. The return value is the same as for @code{mbsrtowcs}.
This new parameter specifies how many bytes at most can be used from the
multibyte character string. In other words, the multibyte character
string @code{*@var{src}} need not be NUL-terminated. But if a NUL byte
is found within the @var{nmc} first bytes of the string, the conversion
stops here.
This function is a GNU extension. It is meant to work around the
problems mentioned above. Now it is possible to convert a buffer with
multibyte character text piece for piece without having to care about
inserting NUL bytes and the effect of NUL bytes on the conversion state.
@end deftypefun
A function to convert a multibyte string into a wide character string
and display it could be written like this (this is not a really useful
example):
@smallexample
void
showmbs (const char *src, FILE *fp)
@{
mbstate_t state;
int cnt = 0;
memset (&state, '\0', sizeof (state));
while (1)
@{
wchar_t linebuf[100];
const char *endp = strchr (src, '\n');
size_t n;
/* @r{Exit if there is no more line.} */
if (endp == NULL)
break;
n = mbsnrtowcs (linebuf, &src, endp - src, 99, &state);
linebuf[n] = L'\0';
fprintf (fp, "line %d: \"%S\"\n", linebuf);
@}
@}
@end smallexample
There is no problem with the state after a call to @code{mbsnrtowcs}.
Since we don't insert characters in the strings that were not in there
right from the beginning and we use @var{state} only for the conversion
of the given buffer, there is no problem with altering the state.
@comment wchar.h
@comment GNU
@deftypefun size_t wcsnrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{nwc}, size_t @var{len}, mbstate_t *restrict @var{ps})
@safety{@prelim{}@mtunsafe{@mtasurace{:wcsnrtombs/!ps}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{wcsnrtombs} function implements the conversion from wide
character strings to multibyte character strings. It is similar to
@code{wcsrtombs} but, just like @code{mbsnrtowcs}, it takes an extra
parameter, which specifies the length of the input string.
No more than @var{nwc} wide characters from the input string
@code{*@var{src}} are converted. If the input string contains a NUL
wide character in the first @var{nwc} characters, the conversion stops at
this place.
The @code{wcsnrtombs} function is a GNU extension and just like
@code{mbsnrtowcs} helps in situations where no NUL-terminated input
strings are available.
@end deftypefun
@node Multibyte Conversion Example
@subsection A Complete Multibyte Conversion Example
The example programs given in the last sections are only brief and do
not contain all the error checking, etc. Presented here is a complete
and documented example. It features the @code{mbrtowc} function but it
should be easy to derive versions using the other functions.
@smallexample
int
file_mbsrtowcs (int input, int output)
@{
/* @r{Note the use of @code{MB_LEN_MAX}.}
@r{@code{MB_CUR_MAX} cannot portably be used here.} */
char buffer[BUFSIZ + MB_LEN_MAX];
mbstate_t state;
int filled = 0;
int eof = 0;
/* @r{Initialize the state.} */
memset (&state, '\0', sizeof (state));
while (!eof)
@{
ssize_t nread;
ssize_t nwrite;
char *inp = buffer;
wchar_t outbuf[BUFSIZ];
wchar_t *outp = outbuf;
/* @r{Fill up the buffer from the input file.} */
nread = read (input, buffer + filled, BUFSIZ);
if (nread < 0)
@{
perror ("read");
return 0;
@}
/* @r{If we reach end of file, make a note to read no more.} */
if (nread == 0)
eof = 1;
/* @r{@code{filled} is now the number of bytes in @code{buffer}.} */
filled += nread;
/* @r{Convert those bytes to wide characters--as many as we can.} */
while (1)
@{
size_t thislen = mbrtowc (outp, inp, filled, &state);
/* @r{Stop converting at invalid character;}
@r{this can mean we have read just the first part}
@r{of a valid character.} */
if (thislen == (size_t) -1)
break;
/* @r{We want to handle embedded NUL bytes}
@r{but the return value is 0. Correct this.} */
if (thislen == 0)
thislen = 1;
/* @r{Advance past this character.} */
inp += thislen;
filled -= thislen;
++outp;
@}
/* @r{Write the wide characters we just made.} */
nwrite = write (output, outbuf,
(outp - outbuf) * sizeof (wchar_t));
if (nwrite < 0)
@{
perror ("write");
return 0;
@}
/* @r{See if we have a @emph{real} invalid character.} */
if ((eof && filled > 0) || filled >= MB_CUR_MAX)
@{
error (0, 0, "invalid multibyte character");
return 0;
@}
/* @r{If any characters must be carried forward,}
@r{put them at the beginning of @code{buffer}.} */
if (filled > 0)
memmove (buffer, inp, filled);
@}
return 1;
@}
@end smallexample
@node Non-reentrant Conversion
@section Non-reentrant Conversion Function
The functions described in the previous chapter are defined in
@w{Amendment 1} to @w{ISO C90}, but the original @w{ISO C90} standard
also contained functions for character set conversion. The reason that
these original functions are not described first is that they are almost
entirely useless.
The problem is that all the conversion functions described in the
original @w{ISO C90} use a local state. Using a local state implies that
multiple conversions at the same time (not only when using threads)
cannot be done, and that you cannot first convert single characters and
then strings since you cannot tell the conversion functions which state
to use.
These original functions are therefore usable only in a very limited set
of situations. One must complete converting the entire string before
starting a new one, and each string/text must be converted with the same
function (there is no problem with the library itself; it is guaranteed
that no library function changes the state of any of these functions).
@strong{For the above reasons it is highly requested that the functions
described in the previous section be used in place of non-reentrant
conversion functions.}
@menu
* Non-reentrant Character Conversion:: Non-reentrant Conversion of Single
Characters.
* Non-reentrant String Conversion:: Non-reentrant Conversion of Strings.
* Shift State:: States in Non-reentrant Functions.
@end menu
@node Non-reentrant Character Conversion
@subsection Non-reentrant Conversion of Single Characters
@comment stdlib.h
@comment ISO
@deftypefun int mbtowc (wchar_t *restrict @var{result}, const char *restrict @var{string}, size_t @var{size})
@safety{@prelim{}@mtunsafe{@mtasurace{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{mbtowc} (``multibyte to wide character'') function when called
with non-null @var{string} converts the first multibyte character
beginning at @var{string} to its corresponding wide character code. It
stores the result in @code{*@var{result}}.
@code{mbtowc} never examines more than @var{size} bytes. (The idea is
to supply for @var{size} the number of bytes of data you have in hand.)
@code{mbtowc} with non-null @var{string} distinguishes three
possibilities: the first @var{size} bytes at @var{string} start with
valid multibyte characters, they start with an invalid byte sequence or
just part of a character, or @var{string} points to an empty string (a
null character).
For a valid multibyte character, @code{mbtowc} converts it to a wide
character and stores that in @code{*@var{result}}, and returns the
number of bytes in that character (always at least @math{1} and never
more than @var{size}).
For an invalid byte sequence, @code{mbtowc} returns @math{-1}. For an
empty string, it returns @math{0}, also storing @code{'\0'} in
@code{*@var{result}}.
If the multibyte character code uses shift characters, then
@code{mbtowc} maintains and updates a shift state as it scans. If you
call @code{mbtowc} with a null pointer for @var{string}, that
initializes the shift state to its standard initial value. It also
returns nonzero if the multibyte character code in use actually has a
shift state. @xref{Shift State}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun int wctomb (char *@var{string}, wchar_t @var{wchar})
@safety{@prelim{}@mtunsafe{@mtasurace{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{wctomb} (``wide character to multibyte'') function converts
the wide character code @var{wchar} to its corresponding multibyte
character sequence, and stores the result in bytes starting at
@var{string}. At most @code{MB_CUR_MAX} characters are stored.
@code{wctomb} with non-null @var{string} distinguishes three
possibilities for @var{wchar}: a valid wide character code (one that can
be translated to a multibyte character), an invalid code, and
@code{L'\0'}.
Given a valid code, @code{wctomb} converts it to a multibyte character,
storing the bytes starting at @var{string}. Then it returns the number
of bytes in that character (always at least @math{1} and never more
than @code{MB_CUR_MAX}).
If @var{wchar} is an invalid wide character code, @code{wctomb} returns
@math{-1}. If @var{wchar} is @code{L'\0'}, it returns @code{0}, also
storing @code{'\0'} in @code{*@var{string}}.
If the multibyte character code uses shift characters, then
@code{wctomb} maintains and updates a shift state as it scans. If you
call @code{wctomb} with a null pointer for @var{string}, that
initializes the shift state to its standard initial value. It also
returns nonzero if the multibyte character code in use actually has a
shift state. @xref{Shift State}.
Calling this function with a @var{wchar} argument of zero when
@var{string} is not null has the side-effect of reinitializing the
stored shift state @emph{as well as} storing the multibyte character
@code{'\0'} and returning @math{0}.
@end deftypefun
Similar to @code{mbrlen} there is also a non-reentrant function that
computes the length of a multibyte character. It can be defined in
terms of @code{mbtowc}.
@comment stdlib.h
@comment ISO
@deftypefun int mblen (const char *@var{string}, size_t @var{size})
@safety{@prelim{}@mtunsafe{@mtasurace{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{mblen} function with a non-null @var{string} argument returns
the number of bytes that make up the multibyte character beginning at
@var{string}, never examining more than @var{size} bytes. (The idea is
to supply for @var{size} the number of bytes of data you have in hand.)
The return value of @code{mblen} distinguishes three possibilities: the
first @var{size} bytes at @var{string} start with valid multibyte
characters, they start with an invalid byte sequence or just part of a
character, or @var{string} points to an empty string (a null character).
For a valid multibyte character, @code{mblen} returns the number of
bytes in that character (always at least @code{1} and never more than
@var{size}). For an invalid byte sequence, @code{mblen} returns
@math{-1}. For an empty string, it returns @math{0}.
If the multibyte character code uses shift characters, then @code{mblen}
maintains and updates a shift state as it scans. If you call
@code{mblen} with a null pointer for @var{string}, that initializes the
shift state to its standard initial value. It also returns a nonzero
value if the multibyte character code in use actually has a shift state.
@xref{Shift State}.
@pindex stdlib.h
The function @code{mblen} is declared in @file{stdlib.h}.
@end deftypefun
@node Non-reentrant String Conversion
@subsection Non-reentrant Conversion of Strings
For convenience the @w{ISO C90} standard also defines functions to
convert entire strings instead of single characters. These functions
suffer from the same problems as their reentrant counterparts from
@w{Amendment 1} to @w{ISO C90}; see @ref{Converting Strings}.
@comment stdlib.h
@comment ISO
@deftypefun size_t mbstowcs (wchar_t *@var{wstring}, const char *@var{string}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Odd... Although this was supposed to be non-reentrant, the internal
@c state is not a static buffer, but an automatic variable.
The @code{mbstowcs} (``multibyte string to wide character string'')
function converts the null-terminated string of multibyte characters
@var{string} to an array of wide character codes, storing not more than
@var{size} wide characters into the array beginning at @var{wstring}.
The terminating null character counts towards the size, so if @var{size}
is less than the actual number of wide characters resulting from
@var{string}, no terminating null character is stored.
The conversion of characters from @var{string} begins in the initial
shift state.
If an invalid multibyte character sequence is found, the @code{mbstowcs}
function returns a value of @math{-1}. Otherwise, it returns the number
of wide characters stored in the array @var{wstring}. This number does
not include the terminating null character, which is present if the
number is less than @var{size}.
Here is an example showing how to convert a string of multibyte
characters, allocating enough space for the result.
@smallexample
wchar_t *
mbstowcs_alloc (const char *string)
@{
size_t size = strlen (string) + 1;
wchar_t *buf = xmalloc (size * sizeof (wchar_t));
size = mbstowcs (buf, string, size);
if (size == (size_t) -1)
return NULL;
buf = xrealloc (buf, (size + 1) * sizeof (wchar_t));
return buf;
@}
@end smallexample
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun size_t wcstombs (char *@var{string}, const wchar_t *@var{wstring}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
The @code{wcstombs} (``wide character string to multibyte string'')
function converts the null-terminated wide character array @var{wstring}
into a string containing multibyte characters, storing not more than
@var{size} bytes starting at @var{string}, followed by a terminating
null character if there is room. The conversion of characters begins in
the initial shift state.
The terminating null character counts towards the size, so if @var{size}
is less than or equal to the number of bytes needed in @var{wstring}, no
terminating null character is stored.
If a code that does not correspond to a valid multibyte character is
found, the @code{wcstombs} function returns a value of @math{-1}.
Otherwise, the return value is the number of bytes stored in the array
@var{string}. This number does not include the terminating null character,
which is present if the number is less than @var{size}.
@end deftypefun
@node Shift State
@subsection States in Non-reentrant Functions
In some multibyte character codes, the @emph{meaning} of any particular
byte sequence is not fixed; it depends on what other sequences have come
earlier in the same string. Typically there are just a few sequences that
can change the meaning of other sequences; these few are called
@dfn{shift sequences} and we say that they set the @dfn{shift state} for
other sequences that follow.
To illustrate shift state and shift sequences, suppose we decide that
the sequence @code{0200} (just one byte) enters Japanese mode, in which
pairs of bytes in the range from @code{0240} to @code{0377} are single
characters, while @code{0201} enters Latin-1 mode, in which single bytes
in the range from @code{0240} to @code{0377} are characters, and
interpreted according to the ISO Latin-1 character set. This is a
multibyte code that has two alternative shift states (``Japanese mode''
and ``Latin-1 mode''), and two shift sequences that specify particular
shift states.
When the multibyte character code in use has shift states, then
@code{mblen}, @code{mbtowc}, and @code{wctomb} must maintain and update
the current shift state as they scan the string. To make this work
properly, you must follow these rules:
@itemize @bullet
@item
Before starting to scan a string, call the function with a null pointer
for the multibyte character address---for example, @code{mblen (NULL,
0)}. This initializes the shift state to its standard initial value.
@item
Scan the string one character at a time, in order. Do not ``back up''
and rescan characters already scanned, and do not intersperse the
processing of different strings.
@end itemize
Here is an example of using @code{mblen} following these rules:
@smallexample
void
scan_string (char *s)
@{
int length = strlen (s);
/* @r{Initialize shift state.} */
mblen (NULL, 0);
while (1)
@{
int thischar = mblen (s, length);
/* @r{Deal with end of string and invalid characters.} */
if (thischar == 0)
break;
if (thischar == -1)
@{
error ("invalid multibyte character");
break;
@}
/* @r{Advance past this character.} */
s += thischar;
length -= thischar;
@}
@}
@end smallexample
The functions @code{mblen}, @code{mbtowc} and @code{wctomb} are not
reentrant when using a multibyte code that uses a shift state. However,
no other library functions call these functions, so you don't have to
worry that the shift state will be changed mysteriously.
@node Generic Charset Conversion
@section Generic Charset Conversion
The conversion functions mentioned so far in this chapter all had in
common that they operate on character sets that are not directly
specified by the functions. The multibyte encoding used is specified by
the currently selected locale for the @code{LC_CTYPE} category. The
wide character set is fixed by the implementation (in the case of @theglibc{}
it is always UCS-4 encoded @w{ISO 10646}.
This has of course several problems when it comes to general character
conversion:
@itemize @bullet
@item
For every conversion where neither the source nor the destination
character set is the character set of the locale for the @code{LC_CTYPE}
category, one has to change the @code{LC_CTYPE} locale using
@code{setlocale}.
Changing the @code{LC_CTYPE} locale introduces major problems for the rest
of the programs since several more functions (e.g., the character
classification functions, @pxref{Classification of Characters}) use the
@code{LC_CTYPE} category.
@item
Parallel conversions to and from different character sets are not
possible since the @code{LC_CTYPE} selection is global and shared by all
threads.
@item
If neither the source nor the destination character set is the character
set used for @code{wchar_t} representation, there is at least a two-step
process necessary to convert a text using the functions above. One would
have to select the source character set as the multibyte encoding,
convert the text into a @code{wchar_t} text, select the destination
character set as the multibyte encoding, and convert the wide character
text to the multibyte (@math{=} destination) character set.
Even if this is possible (which is not guaranteed) it is a very tiring
work. Plus it suffers from the other two raised points even more due to
the steady changing of the locale.
@end itemize
The XPG2 standard defines a completely new set of functions, which has
none of these limitations. They are not at all coupled to the selected
locales, and they have no constraints on the character sets selected for
source and destination. Only the set of available conversions limits
them. The standard does not specify that any conversion at all must be
available. Such availability is a measure of the quality of the
implementation.
In the following text first the interface to @code{iconv} and then the
conversion function, will be described. Comparisons with other
implementations will show what obstacles stand in the way of portable
applications. Finally, the implementation is described in so far as might
interest the advanced user who wants to extend conversion capabilities.
@menu
* Generic Conversion Interface:: Generic Character Set Conversion Interface.
* iconv Examples:: A complete @code{iconv} example.
* Other iconv Implementations:: Some Details about other @code{iconv}
Implementations.
* glibc iconv Implementation:: The @code{iconv} Implementation in the GNU C
library.
@end menu
@node Generic Conversion Interface
@subsection Generic Character Set Conversion Interface
This set of functions follows the traditional cycle of using a resource:
open--use--close. The interface consists of three functions, each of
which implements one step.
Before the interfaces are described it is necessary to introduce a
data type. Just like other open--use--close interfaces the functions
introduced here work using handles and the @file{iconv.h} header
defines a special type for the handles used.
@comment iconv.h
@comment XPG2
@deftp {Data Type} iconv_t
This data type is an abstract type defined in @file{iconv.h}. The user
must not assume anything about the definition of this type; it must be
completely opaque.
Objects of this type can get assigned handles for the conversions using
the @code{iconv} functions. The objects themselves need not be freed, but
the conversions for which the handles stand for have to.
@end deftp
@noindent
The first step is the function to create a handle.
@comment iconv.h
@comment XPG2
@deftypefun iconv_t iconv_open (const char *@var{tocode}, const char *@var{fromcode})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Calls malloc if tocode and/or fromcode are too big for alloca. Calls
@c strip and upstr on both, then gconv_open. strip and upstr call
@c isalnum_l and toupper_l with the C locale. gconv_open may MT-safely
@c tokenize toset, replace unspecified codesets with the current locale
@c (possibly two different accesses), and finally it calls
@c gconv_find_transform and initializes the gconv_t result with all the
@c steps in the conversion sequence, running each one's initializer,
@c destructing and releasing them all if anything fails.
The @code{iconv_open} function has to be used before starting a
conversion. The two parameters this function takes determine the
source and destination character set for the conversion, and if the
implementation has the possibility to perform such a conversion, the
function returns a handle.
If the wanted conversion is not available, the @code{iconv_open} function
returns @code{(iconv_t) -1}. In this case the global variable
@code{errno} can have the following values:
@table @code
@item EMFILE
The process already has @code{OPEN_MAX} file descriptors open.
@item ENFILE
The system limit of open file is reached.
@item ENOMEM
Not enough memory to carry out the operation.
@item EINVAL
The conversion from @var{fromcode} to @var{tocode} is not supported.
@end table
It is not possible to use the same descriptor in different threads to
perform independent conversions. The data structures associated
with the descriptor include information about the conversion state.
This must not be messed up by using it in different conversions.
An @code{iconv} descriptor is like a file descriptor as for every use a
new descriptor must be created. The descriptor does not stand for all
of the conversions from @var{fromset} to @var{toset}.
The @glibcadj{} implementation of @code{iconv_open} has one
significant extension to other implementations. To ease the extension
of the set of available conversions, the implementation allows storing
the necessary files with data and code in an arbitrary number of
directories. How this extension must be written will be explained below
(@pxref{glibc iconv Implementation}). Here it is only important to say
that all directories mentioned in the @code{GCONV_PATH} environment
variable are considered only if they contain a file @file{gconv-modules}.
These directories need not necessarily be created by the system
administrator. In fact, this extension is introduced to help users
writing and using their own, new conversions. Of course, this does not
work for security reasons in SUID binaries; in this case only the system
directory is considered and this normally is
@file{@var{prefix}/lib/gconv}. The @code{GCONV_PATH} environment
variable is examined exactly once at the first call of the
@code{iconv_open} function. Later modifications of the variable have no
effect.
@pindex iconv.h
The @code{iconv_open} function was introduced early in the X/Open
Portability Guide, @w{version 2}. It is supported by all commercial
Unices as it is required for the Unix branding. However, the quality and
completeness of the implementation varies widely. The @code{iconv_open}
function is declared in @file{iconv.h}.
@end deftypefun
The @code{iconv} implementation can associate large data structure with
the handle returned by @code{iconv_open}. Therefore, it is crucial to
free all the resources once all conversions are carried out and the
conversion is not needed anymore.
@comment iconv.h
@comment XPG2
@deftypefun int iconv_close (iconv_t @var{cd})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Calls gconv_close to destruct and release each of the conversion
@c steps, release the gconv_t object, then call gconv_close_transform.
@c Access to the gconv_t object is not guarded, but calling iconv_close
@c concurrently with any other use is undefined.
The @code{iconv_close} function frees all resources associated with the
handle @var{cd}, which must have been returned by a successful call to
the @code{iconv_open} function.
If the function call was successful the return value is @math{0}.
Otherwise it is @math{-1} and @code{errno} is set appropriately.
Defined error are:
@table @code
@item EBADF
The conversion descriptor is invalid.
@end table
@pindex iconv.h
The @code{iconv_close} function was introduced together with the rest
of the @code{iconv} functions in XPG2 and is declared in @file{iconv.h}.
@end deftypefun
The standard defines only one actual conversion function. This has,
therefore, the most general interface: it allows conversion from one
buffer to another. Conversion from a file to a buffer, vice versa, or
even file to file can be implemented on top of it.
@comment iconv.h
@comment XPG2
@deftypefun size_t iconv (iconv_t @var{cd}, char **@var{inbuf}, size_t *@var{inbytesleft}, char **@var{outbuf}, size_t *@var{outbytesleft})
@safety{@prelim{}@mtsafe{@mtsrace{:cd}}@assafe{}@acunsafe{@acucorrupt{}}}
@c Without guarding access to the iconv_t object pointed to by cd, call
@c the conversion function to convert inbuf or flush the internal
@c conversion state.
@cindex stateful
The @code{iconv} function converts the text in the input buffer
according to the rules associated with the descriptor @var{cd} and
stores the result in the output buffer. It is possible to call the
function for the same text several times in a row since for stateful
character sets the necessary state information is kept in the data
structures associated with the descriptor.
The input buffer is specified by @code{*@var{inbuf}} and it contains
@code{*@var{inbytesleft}} bytes. The extra indirection is necessary for
communicating the used input back to the caller (see below). It is
important to note that the buffer pointer is of type @code{char} and the
length is measured in bytes even if the input text is encoded in wide
characters.
The output buffer is specified in a similar way. @code{*@var{outbuf}}
points to the beginning of the buffer with at least
@code{*@var{outbytesleft}} bytes room for the result. The buffer
pointer again is of type @code{char} and the length is measured in
bytes. If @var{outbuf} or @code{*@var{outbuf}} is a null pointer, the
conversion is performed but no output is available.
If @var{inbuf} is a null pointer, the @code{iconv} function performs the
necessary action to put the state of the conversion into the initial
state. This is obviously a no-op for non-stateful encodings, but if the
encoding has a state, such a function call might put some byte sequences
in the output buffer, which perform the necessary state changes. The
next call with @var{inbuf} not being a null pointer then simply goes on
from the initial state. It is important that the programmer never makes
any assumption as to whether the conversion has to deal with states.
Even if the input and output character sets are not stateful, the
implementation might still have to keep states. This is due to the
implementation chosen for @theglibc{} as it is described below.
Therefore an @code{iconv} call to reset the state should always be
performed if some protocol requires this for the output text.
The conversion stops for one of three reasons. The first is that all
characters from the input buffer are converted. This actually can mean
two things: either all bytes from the input buffer are consumed or
there are some bytes at the end of the buffer that possibly can form a
complete character but the input is incomplete. The second reason for a
stop is that the output buffer is full. And the third reason is that
the input contains invalid characters.
In all of these cases the buffer pointers after the last successful
conversion, for input and output buffer, are stored in @var{inbuf} and
@var{outbuf}, and the available room in each buffer is stored in
@var{inbytesleft} and @var{outbytesleft}.
Since the character sets selected in the @code{iconv_open} call can be
almost arbitrary, there can be situations where the input buffer contains
valid characters, which have no identical representation in the output
character set. The behavior in this situation is undefined. The
@emph{current} behavior of @theglibc{} in this situation is to
return with an error immediately. This certainly is not the most
desirable solution; therefore, future versions will provide better ones,
but they are not yet finished.
If all input from the input buffer is successfully converted and stored
in the output buffer, the function returns the number of non-reversible
conversions performed. In all other cases the return value is
@code{(size_t) -1} and @code{errno} is set appropriately. In such cases
the value pointed to by @var{inbytesleft} is nonzero.
@table @code
@item EILSEQ
The conversion stopped because of an invalid byte sequence in the input.
After the call, @code{*@var{inbuf}} points at the first byte of the
invalid byte sequence.
@item E2BIG
The conversion stopped because it ran out of space in the output buffer.
@item EINVAL
The conversion stopped because of an incomplete byte sequence at the end
of the input buffer.
@item EBADF
The @var{cd} argument is invalid.
@end table
@pindex iconv.h
The @code{iconv} function was introduced in the XPG2 standard and is
declared in the @file{iconv.h} header.
@end deftypefun
The definition of the @code{iconv} function is quite good overall. It
provides quite flexible functionality. The only problems lie in the
boundary cases, which are incomplete byte sequences at the end of the
input buffer and invalid input. A third problem, which is not really
a design problem, is the way conversions are selected. The standard
does not say anything about the legitimate names, a minimal set of
available conversions. We will see how this negatively impacts other
implementations, as demonstrated below.
@node iconv Examples
@subsection A complete @code{iconv} example
The example below features a solution for a common problem. Given that
one knows the internal encoding used by the system for @code{wchar_t}
strings, one often is in the position to read text from a file and store
it in wide character buffers. One can do this using @code{mbsrtowcs},
but then we run into the problems discussed above.
@smallexample
int
file2wcs (int fd, const char *charset, wchar_t *outbuf, size_t avail)
@{
char inbuf[BUFSIZ];
size_t insize = 0;
char *wrptr = (char *) outbuf;
int result = 0;
iconv_t cd;
cd = iconv_open ("WCHAR_T", charset);
if (cd == (iconv_t) -1)
@{
/* @r{Something went wrong.} */
if (errno == EINVAL)
error (0, 0, "conversion from '%s' to wchar_t not available",
charset);
else
perror ("iconv_open");
/* @r{Terminate the output string.} */
*outbuf = L'\0';
return -1;
@}
while (avail > 0)
@{
size_t nread;
size_t nconv;
char *inptr = inbuf;
/* @r{Read more input.} */
nread = read (fd, inbuf + insize, sizeof (inbuf) - insize);
if (nread == 0)
@{
/* @r{When we come here the file is completely read.}
@r{This still could mean there are some unused}
@r{characters in the @code{inbuf}. Put them back.} */
if (lseek (fd, -insize, SEEK_CUR) == -1)
result = -1;
/* @r{Now write out the byte sequence to get into the}
@r{initial state if this is necessary.} */
iconv (cd, NULL, NULL, &wrptr, &avail);
break;
@}
insize += nread;
/* @r{Do the conversion.} */
nconv = iconv (cd, &inptr, &insize, &wrptr, &avail);
if (nconv == (size_t) -1)
@{
/* @r{Not everything went right. It might only be}
@r{an unfinished byte sequence at the end of the}
@r{buffer. Or it is a real problem.} */
if (errno == EINVAL)
/* @r{This is harmless. Simply move the unused}
@r{bytes to the beginning of the buffer so that}
@r{they can be used in the next round.} */
memmove (inbuf, inptr, insize);
else
@{
/* @r{It is a real problem. Maybe we ran out of}
@r{space in the output buffer or we have invalid}
@r{input. In any case back the file pointer to}
@r{the position of the last processed byte.} */
lseek (fd, -insize, SEEK_CUR);
result = -1;
break;
@}
@}
@}
/* @r{Terminate the output string.} */
if (avail >= sizeof (wchar_t))
*((wchar_t *) wrptr) = L'\0';
if (iconv_close (cd) != 0)
perror ("iconv_close");
return (wchar_t *) wrptr - outbuf;
@}
@end smallexample
@cindex stateful
This example shows the most important aspects of using the @code{iconv}
functions. It shows how successive calls to @code{iconv} can be used to
convert large amounts of text. The user does not have to care about
stateful encodings as the functions take care of everything.
An interesting point is the case where @code{iconv} returns an error and
@code{errno} is set to @code{EINVAL}. This is not really an error in the
transformation. It can happen whenever the input character set contains
byte sequences of more than one byte for some character and texts are not
processed in one piece. In this case there is a chance that a multibyte
sequence is cut. The caller can then simply read the remainder of the
takes and feed the offending bytes together with new character from the
input to @code{iconv} and continue the work. The internal state kept in
the descriptor is @emph{not} unspecified after such an event as is the
case with the conversion functions from the @w{ISO C} standard.
The example also shows the problem of using wide character strings with
@code{iconv}. As explained in the description of the @code{iconv}
function above, the function always takes a pointer to a @code{char}
array and the available space is measured in bytes. In the example, the
output buffer is a wide character buffer; therefore, we use a local
variable @var{wrptr} of type @code{char *}, which is used in the
@code{iconv} calls.
This looks rather innocent but can lead to problems on platforms that
have tight restriction on alignment. Therefore the caller of @code{iconv}
has to make sure that the pointers passed are suitable for access of
characters from the appropriate character set. Since, in the
above case, the input parameter to the function is a @code{wchar_t}
pointer, this is the case (unless the user violates alignment when
computing the parameter). But in other situations, especially when
writing generic functions where one does not know what type of character
set one uses and, therefore, treats text as a sequence of bytes, it might
become tricky.
@node Other iconv Implementations
@subsection Some Details about other @code{iconv} Implementations
This is not really the place to discuss the @code{iconv} implementation
of other systems but it is necessary to know a bit about them to write
portable programs. The above mentioned problems with the specification
of the @code{iconv} functions can lead to portability issues.
The first thing to notice is that, due to the large number of character
sets in use, it is certainly not practical to encode the conversions
directly in the C library. Therefore, the conversion information must
come from files outside the C library. This is usually done in one or
both of the following ways:
@itemize @bullet
@item
The C library contains a set of generic conversion functions that can
read the needed conversion tables and other information from data files.
These files get loaded when necessary.
This solution is problematic as it requires a great deal of effort to
apply to all character sets (potentially an infinite set). The
differences in the structure of the different character sets is so large
that many different variants of the table-processing functions must be
developed. In addition, the generic nature of these functions make them
slower than specifically implemented functions.
@item
The C library only contains a framework that can dynamically load
object files and execute the conversion functions contained therein.
This solution provides much more flexibility. The C library itself
contains only very little code and therefore reduces the general memory
footprint. Also, with a documented interface between the C library and
the loadable modules it is possible for third parties to extend the set
of available conversion modules. A drawback of this solution is that
dynamic loading must be available.
@end itemize
Some implementations in commercial Unices implement a mixture of these
possibilities; the majority implement only the second solution. Using
loadable modules moves the code out of the library itself and keeps
the door open for extensions and improvements, but this design is also
limiting on some platforms since not many platforms support dynamic
loading in statically linked programs. On platforms without this
capability it is therefore not possible to use this interface in
statically linked programs. @Theglibc{} has, on ELF platforms, no
problems with dynamic loading in these situations; therefore, this
point is moot. The danger is that one gets acquainted with this
situation and forgets about the restrictions on other systems.
A second thing to know about other @code{iconv} implementations is that
the number of available conversions is often very limited. Some
implementations provide, in the standard release (not special
international or developer releases), at most 100 to 200 conversion
possibilities. This does not mean 200 different character sets are
supported; for example, conversions from one character set to a set of 10
others might count as 10 conversions. Together with the other direction
this makes 20 conversion possibilities used up by one character set. One
can imagine the thin coverage these platform provide. Some Unix vendors
even provide only a handful of conversions, which renders them useless for
almost all uses.
This directly leads to a third and probably the most problematic point.
The way the @code{iconv} conversion functions are implemented on all
known Unix systems and the availability of the conversion functions from
character set @math{@cal{A}} to @math{@cal{B}} and the conversion from
@math{@cal{B}} to @math{@cal{C}} does @emph{not} imply that the
conversion from @math{@cal{A}} to @math{@cal{C}} is available.
This might not seem unreasonable and problematic at first, but it is a
quite big problem as one will notice shortly after hitting it. To show
the problem we assume to write a program that has to convert from
@math{@cal{A}} to @math{@cal{C}}. A call like
@smallexample
cd = iconv_open ("@math{@cal{C}}", "@math{@cal{A}}");
@end smallexample
@noindent
fails according to the assumption above. But what does the program
do now? The conversion is necessary; therefore, simply giving up is not
an option.
This is a nuisance. The @code{iconv} function should take care of this.
But how should the program proceed from here on? If it tries to convert
to character set @math{@cal{B}}, first the two @code{iconv_open}
calls
@smallexample
cd1 = iconv_open ("@math{@cal{B}}", "@math{@cal{A}}");
@end smallexample
@noindent
and
@smallexample
cd2 = iconv_open ("@math{@cal{C}}", "@math{@cal{B}}");
@end smallexample
@noindent
will succeed, but how to find @math{@cal{B}}?
Unfortunately, the answer is: there is no general solution. On some
systems guessing might help. On those systems most character sets can
convert to and from UTF-8 encoded @w{ISO 10646} or Unicode text. Beside
this only some very system-specific methods can help. Since the
conversion functions come from loadable modules and these modules must
be stored somewhere in the filesystem, one @emph{could} try to find them
and determine from the available file which conversions are available
and whether there is an indirect route from @math{@cal{A}} to
@math{@cal{C}}.
This example shows one of the design errors of @code{iconv} mentioned
above. It should at least be possible to determine the list of available
conversion programmatically so that if @code{iconv_open} says there is no
such conversion, one could make sure this also is true for indirect
routes.
@node glibc iconv Implementation
@subsection The @code{iconv} Implementation in @theglibc{}
After reading about the problems of @code{iconv} implementations in the
last section it is certainly good to note that the implementation in
@theglibc{} has none of the problems mentioned above. What
follows is a step-by-step analysis of the points raised above. The
evaluation is based on the current state of the development (as of
January 1999). The development of the @code{iconv} functions is not
complete, but basic functionality has solidified.
@Theglibc{}'s @code{iconv} implementation uses shared loadable
modules to implement the conversions. A very small number of
conversions are built into the library itself but these are only rather
trivial conversions.
All the benefits of loadable modules are available in the @glibcadj{}
implementation. This is especially appealing since the interface is
well documented (see below), and it, therefore, is easy to write new
conversion modules. The drawback of using loadable objects is not a
problem in @theglibc{}, at least on ELF systems. Since the
library is able to load shared objects even in statically linked
binaries, static linking need not be forbidden in case one wants to use
@code{iconv}.
The second mentioned problem is the number of supported conversions.
Currently, @theglibc{} supports more than 150 character sets. The
way the implementation is designed the number of supported conversions
is greater than 22350 (@math{150} times @math{149}). If any conversion
from or to a character set is missing, it can be added easily.
Particularly impressive as it may be, this high number is due to the
fact that the @glibcadj{} implementation of @code{iconv} does not have
the third problem mentioned above (i.e., whenever there is a conversion
from a character set @math{@cal{A}} to @math{@cal{B}} and from
@math{@cal{B}} to @math{@cal{C}} it is always possible to convert from
@math{@cal{A}} to @math{@cal{C}} directly). If the @code{iconv_open}
returns an error and sets @code{errno} to @code{EINVAL}, there is no
known way, directly or indirectly, to perform the wanted conversion.
@cindex triangulation
Triangulation is achieved by providing for each character set a
conversion from and to UCS-4 encoded @w{ISO 10646}. Using @w{ISO 10646}
as an intermediate representation it is possible to @dfn{triangulate}
(i.e., convert with an intermediate representation).
There is no inherent requirement to provide a conversion to @w{ISO
10646} for a new character set, and it is also possible to provide other
conversions where neither source nor destination character set is @w{ISO
10646}. The existing set of conversions is simply meant to cover all
conversions that might be of interest.
@cindex ISO-2022-JP
@cindex EUC-JP
All currently available conversions use the triangulation method above,
making conversion run unnecessarily slow. If, for example, somebody
often needs the conversion from ISO-2022-JP to EUC-JP, a quicker solution
would involve direct conversion between the two character sets, skipping
the input to @w{ISO 10646} first. The two character sets of interest
are much more similar to each other than to @w{ISO 10646}.
In such a situation one easily can write a new conversion and provide it
as a better alternative. The @glibcadj{} @code{iconv} implementation
would automatically use the module implementing the conversion if it is
specified to be more efficient.
@subsubsection Format of @file{gconv-modules} files
All information about the available conversions comes from a file named
@file{gconv-modules}, which can be found in any of the directories along
the @code{GCONV_PATH}. The @file{gconv-modules} files are line-oriented
text files, where each of the lines has one of the following formats:
@itemize @bullet
@item
If the first non-whitespace character is a @kbd{#} the line contains only
comments and is ignored.
@item
Lines starting with @code{alias} define an alias name for a character
set. Two more words are expected on the line. The first word
defines the alias name, and the second defines the original name of the
character set. The effect is that it is possible to use the alias name
in the @var{fromset} or @var{toset} parameters of @code{iconv_open} and
achieve the same result as when using the real character set name.
This is quite important as a character set has often many different
names. There is normally an official name but this need not correspond to
the most popular name. Beside this many character sets have special
names that are somehow constructed. For example, all character sets
specified by the ISO have an alias of the form @code{ISO-IR-@var{nnn}}
where @var{nnn} is the registration number. This allows programs that
know about the registration number to construct character set names and
use them in @code{iconv_open} calls. More on the available names and
aliases follows below.
@item
Lines starting with @code{module} introduce an available conversion
module. These lines must contain three or four more words.
The first word specifies the source character set, the second word the
destination character set of conversion implemented in this module, and
the third word is the name of the loadable module. The filename is
constructed by appending the usual shared object suffix (normally
@file{.so}) and this file is then supposed to be found in the same
directory the @file{gconv-modules} file is in. The last word on the line,
which is optional, is a numeric value representing the cost of the
conversion. If this word is missing, a cost of @math{1} is assumed. The
numeric value itself does not matter that much; what counts are the
relative values of the sums of costs for all possible conversion paths.
Below is a more precise description of the use of the cost value.
@end itemize
Returning to the example above where one has written a module to directly
convert from ISO-2022-JP to EUC-JP and back. All that has to be done is
to put the new module, let its name be ISO2022JP-EUCJP.so, in a directory
and add a file @file{gconv-modules} with the following content in the
same directory:
@smallexample
module ISO-2022-JP// EUC-JP// ISO2022JP-EUCJP 1
module EUC-JP// ISO-2022-JP// ISO2022JP-EUCJP 1
@end smallexample
To see why this is sufficient, it is necessary to understand how the
conversion used by @code{iconv} (and described in the descriptor) is
selected. The approach to this problem is quite simple.
At the first call of the @code{iconv_open} function the program reads
all available @file{gconv-modules} files and builds up two tables: one
containing all the known aliases and another that contains the
information about the conversions and which shared object implements
them.
@subsubsection Finding the conversion path in @code{iconv}
The set of available conversions form a directed graph with weighted
edges. The weights on the edges are the costs specified in the
@file{gconv-modules} files. The @code{iconv_open} function uses an
algorithm suitable for search for the best path in such a graph and so
constructs a list of conversions that must be performed in succession
to get the transformation from the source to the destination character
set.
Explaining why the above @file{gconv-modules} files allows the
@code{iconv} implementation to resolve the specific ISO-2022-JP to
EUC-JP conversion module instead of the conversion coming with the
library itself is straightforward. Since the latter conversion takes two
steps (from ISO-2022-JP to @w{ISO 10646} and then from @w{ISO 10646} to
EUC-JP), the cost is @math{1+1 = 2}. The above @file{gconv-modules}
file, however, specifies that the new conversion modules can perform this
conversion with only the cost of @math{1}.
A mysterious item about the @file{gconv-modules} file above (and also
the file coming with @theglibc{}) are the names of the character
sets specified in the @code{module} lines. Why do almost all the names
end in @code{//}? And this is not all: the names can actually be
regular expressions. At this point in time this mystery should not be
revealed, unless you have the relevant spell-casting materials: ashes
from an original @w{DOS 6.2} boot disk burnt in effigy, a crucifix
blessed by St.@: Emacs, assorted herbal roots from Central America, sand
from Cebu, etc. Sorry! @strong{The part of the implementation where
this is used is not yet finished. For now please simply follow the
existing examples. It'll become clearer once it is. --drepper}
A last remark about the @file{gconv-modules} is about the names not
ending with @code{//}. A character set named @code{INTERNAL} is often
mentioned. From the discussion above and the chosen name it should have
become clear that this is the name for the representation used in the
intermediate step of the triangulation. We have said that this is UCS-4
but actually that is not quite right. The UCS-4 specification also
includes the specification of the byte ordering used. Since a UCS-4 value
consists of four bytes, a stored value is affected by byte ordering. The
internal representation is @emph{not} the same as UCS-4 in case the byte
ordering of the processor (or at least the running process) is not the
same as the one required for UCS-4. This is done for performance reasons
as one does not want to perform unnecessary byte-swapping operations if
one is not interested in actually seeing the result in UCS-4. To avoid
trouble with endianness, the internal representation consistently is named
@code{INTERNAL} even on big-endian systems where the representations are
identical.
@subsubsection @code{iconv} module data structures
So far this section has described how modules are located and considered
to be used. What remains to be described is the interface of the modules
so that one can write new ones. This section describes the interface as
it is in use in January 1999. The interface will change a bit in the
future but, with luck, only in an upwardly compatible way.
The definitions necessary to write new modules are publicly available
in the non-standard header @file{gconv.h}. The following text,
therefore, describes the definitions from this header file. First,
however, it is necessary to get an overview.
From the perspective of the user of @code{iconv} the interface is quite
simple: the @code{iconv_open} function returns a handle that can be used
in calls to @code{iconv}, and finally the handle is freed with a call to
@code{iconv_close}. The problem is that the handle has to be able to
represent the possibly long sequences of conversion steps and also the
state of each conversion since the handle is all that is passed to the
@code{iconv} function. Therefore, the data structures are really the
elements necessary to understanding the implementation.
We need two different kinds of data structures. The first describes the
conversion and the second describes the state etc. There are really two
type definitions like this in @file{gconv.h}.
@pindex gconv.h
@comment gconv.h
@comment GNU
@deftp {Data type} {struct __gconv_step}
This data structure describes one conversion a module can perform. For
each function in a loaded module with conversion functions there is
exactly one object of this type. This object is shared by all users of
the conversion (i.e., this object does not contain any information
corresponding to an actual conversion; it only describes the conversion
itself).
@table @code
@item struct __gconv_loaded_object *__shlib_handle
@itemx const char *__modname
@itemx int __counter
All these elements of the structure are used internally in the C library
to coordinate loading and unloading the shared. One must not expect any
of the other elements to be available or initialized.
@item const char *__from_name
@itemx const char *__to_name
@code{__from_name} and @code{__to_name} contain the names of the source and
destination character sets. They can be used to identify the actual
conversion to be carried out since one module might implement conversions
for more than one character set and/or direction.
@item gconv_fct __fct
@itemx gconv_init_fct __init_fct
@itemx gconv_end_fct __end_fct
These elements contain pointers to the functions in the loadable module.
The interface will be explained below.
@item int __min_needed_from
@itemx int __max_needed_from
@itemx int __min_needed_to
@itemx int __max_needed_to;
These values have to be supplied in the init function of the module. The
@code{__min_needed_from} value specifies how many bytes a character of
the source character set at least needs. The @code{__max_needed_from}
specifies the maximum value that also includes possible shift sequences.
The @code{__min_needed_to} and @code{__max_needed_to} values serve the
same purpose as @code{__min_needed_from} and @code{__max_needed_from} but
this time for the destination character set.
It is crucial that these values be accurate since otherwise the
conversion functions will have problems or not work at all.
@item int __stateful
This element must also be initialized by the init function.
@code{int __stateful} is nonzero if the source character set is stateful.
Otherwise it is zero.
@item void *__data
This element can be used freely by the conversion functions in the
module. @code{void *__data} can be used to communicate extra information
from one call to another. @code{void *__data} need not be initialized if
not needed at all. If @code{void *__data} element is assigned a pointer
to dynamically allocated memory (presumably in the init function) it has
to be made sure that the end function deallocates the memory. Otherwise
the application will leak memory.
It is important to be aware that this data structure is shared by all
users of this specification conversion and therefore the @code{__data}
element must not contain data specific to one specific use of the
conversion function.
@end table
@end deftp
@comment gconv.h
@comment GNU
@deftp {Data type} {struct __gconv_step_data}
This is the data structure that contains the information specific to
each use of the conversion functions.
@table @code
@item char *__outbuf
@itemx char *__outbufend
These elements specify the output buffer for the conversion step. The
@code{__outbuf} element points to the beginning of the buffer, and
@code{__outbufend} points to the byte following the last byte in the
buffer. The conversion function must not assume anything about the size
of the buffer but it can be safely assumed the there is room for at
least one complete character in the output buffer.
Once the conversion is finished, if the conversion is the last step, the
@code{__outbuf} element must be modified to point after the last byte
written into the buffer to signal how much output is available. If this
conversion step is not the last one, the element must not be modified.
The @code{__outbufend} element must not be modified.
@item int __is_last
This element is nonzero if this conversion step is the last one. This
information is necessary for the recursion. See the description of the
conversion function internals below. This element must never be
modified.
@item int __invocation_counter
The conversion function can use this element to see how many calls of
the conversion function already happened. Some character sets require a
certain prolog when generating output, and by comparing this value with
zero, one can find out whether it is the first call and whether,
therefore, the prolog should be emitted. This element must never be
modified.
@item int __internal_use
This element is another one rarely used but needed in certain
situations. It is assigned a nonzero value in case the conversion
functions are used to implement @code{mbsrtowcs} et.al.@: (i.e., the
function is not used directly through the @code{iconv} interface).
This sometimes makes a difference as it is expected that the
@code{iconv} functions are used to translate entire texts while the
@code{mbsrtowcs} functions are normally used only to convert single
strings and might be used multiple times to convert entire texts.
But in this situation we would have problem complying with some rules of
the character set specification. Some character sets require a prolog,
which must appear exactly once for an entire text. If a number of
@code{mbsrtowcs} calls are used to convert the text, only the first call
must add the prolog. However, because there is no communication between the
different calls of @code{mbsrtowcs}, the conversion functions have no
possibility to find this out. The situation is different for sequences
of @code{iconv} calls since the handle allows access to the needed
information.
The @code{int __internal_use} element is mostly used together with
@code{__invocation_counter} as follows:
@smallexample
if (!data->__internal_use
&& data->__invocation_counter == 0)
/* @r{Emit prolog.} */
@dots{}
@end smallexample
This element must never be modified.
@item mbstate_t *__statep
The @code{__statep} element points to an object of type @code{mbstate_t}
(@pxref{Keeping the state}). The conversion of a stateful character
set must use the object pointed to by @code{__statep} to store
information about the conversion state. The @code{__statep} element
itself must never be modified.
@item mbstate_t __state
This element must @emph{never} be used directly. It is only part of
this structure to have the needed space allocated.
@end table
@end deftp
@subsubsection @code{iconv} module interfaces
With the knowledge about the data structures we now can describe the
conversion function itself. To understand the interface a bit of
knowledge is necessary about the functionality in the C library that
loads the objects with the conversions.
It is often the case that one conversion is used more than once (i.e.,
there are several @code{iconv_open} calls for the same set of character
sets during one program run). The @code{mbsrtowcs} et.al.@: functions in
@theglibc{} also use the @code{iconv} functionality, which
increases the number of uses of the same functions even more.
Because of this multiple use of conversions, the modules do not get
loaded exclusively for one conversion. Instead a module once loaded can
be used by an arbitrary number of @code{iconv} or @code{mbsrtowcs} calls
at the same time. The splitting of the information between conversion-
function-specific information and conversion data makes this possible.
The last section showed the two data structures used to do this.
This is of course also reflected in the interface and semantics of the
functions that the modules must provide. There are three functions that
must have the following names:
@table @code
@item gconv_init
The @code{gconv_init} function initializes the conversion function
specific data structure. This very same object is shared by all
conversions that use this conversion and, therefore, no state information
about the conversion itself must be stored in here. If a module
implements more than one conversion, the @code{gconv_init} function will
be called multiple times.
@item gconv_end
The @code{gconv_end} function is responsible for freeing all resources
allocated by the @code{gconv_init} function. If there is nothing to do,
this function can be missing. Special care must be taken if the module
implements more than one conversion and the @code{gconv_init} function
does not allocate the same resources for all conversions.
@item gconv
This is the actual conversion function. It is called to convert one
block of text. It gets passed the conversion step information
initialized by @code{gconv_init} and the conversion data, specific to
this use of the conversion functions.
@end table
There are three data types defined for the three module interface
functions and these define the interface.
@comment gconv.h
@comment GNU
@deftypevr {Data type} int {(*__gconv_init_fct)} (struct __gconv_step *)
This specifies the interface of the initialization function of the
module. It is called exactly once for each conversion the module
implements.
As explained in the description of the @code{struct __gconv_step} data
structure above the initialization function has to initialize parts of
it.
@table @code
@item __min_needed_from
@itemx __max_needed_from
@itemx __min_needed_to
@itemx __max_needed_to
These elements must be initialized to the exact numbers of the minimum
and maximum number of bytes used by one character in the source and
destination character sets, respectively. If the characters all have the
same size, the minimum and maximum values are the same.
@item __stateful
This element must be initialized to a nonzero value if the source
character set is stateful. Otherwise it must be zero.
@end table
If the initialization function needs to communicate some information
to the conversion function, this communication can happen using the
@code{__data} element of the @code{__gconv_step} structure. But since
this data is shared by all the conversions, it must not be modified by
the conversion function. The example below shows how this can be used.
@smallexample
#define MIN_NEEDED_FROM 1
#define MAX_NEEDED_FROM 4
#define MIN_NEEDED_TO 4
#define MAX_NEEDED_TO 4
int
gconv_init (struct __gconv_step *step)
@{
/* @r{Determine which direction.} */
struct iso2022jp_data *new_data;
enum direction dir = illegal_dir;
enum variant var = illegal_var;
int result;
if (__strcasecmp (step->__from_name, "ISO-2022-JP//") == 0)
@{
dir = from_iso2022jp;
var = iso2022jp;
@}
else if (__strcasecmp (step->__to_name, "ISO-2022-JP//") == 0)
@{
dir = to_iso2022jp;
var = iso2022jp;
@}
else if (__strcasecmp (step->__from_name, "ISO-2022-JP-2//") == 0)
@{
dir = from_iso2022jp;
var = iso2022jp2;
@}
else if (__strcasecmp (step->__to_name, "ISO-2022-JP-2//") == 0)
@{
dir = to_iso2022jp;
var = iso2022jp2;
@}
result = __GCONV_NOCONV;
if (dir != illegal_dir)
@{
new_data = (struct iso2022jp_data *)
malloc (sizeof (struct iso2022jp_data));
result = __GCONV_NOMEM;
if (new_data != NULL)
@{
new_data->dir = dir;
new_data->var = var;
step->__data = new_data;
if (dir == from_iso2022jp)
@{
step->__min_needed_from = MIN_NEEDED_FROM;
step->__max_needed_from = MAX_NEEDED_FROM;
step->__min_needed_to = MIN_NEEDED_TO;
step->__max_needed_to = MAX_NEEDED_TO;
@}
else
@{
step->__min_needed_from = MIN_NEEDED_TO;
step->__max_needed_from = MAX_NEEDED_TO;
step->__min_needed_to = MIN_NEEDED_FROM;
step->__max_needed_to = MAX_NEEDED_FROM + 2;
@}
/* @r{Yes, this is a stateful encoding.} */
step->__stateful = 1;
result = __GCONV_OK;
@}
@}
return result;
@}
@end smallexample
The function first checks which conversion is wanted. The module from
which this function is taken implements four different conversions;
which one is selected can be determined by comparing the names. The
comparison should always be done without paying attention to the case.
Next, a data structure, which contains the necessary information about
which conversion is selected, is allocated. The data structure
@code{struct iso2022jp_data} is locally defined since, outside the
module, this data is not used at all. Please note that if all four
conversions this modules supports are requested there are four data
blocks.
One interesting thing is the initialization of the @code{__min_} and
@code{__max_} elements of the step data object. A single ISO-2022-JP
character can consist of one to four bytes. Therefore the
@code{MIN_NEEDED_FROM} and @code{MAX_NEEDED_FROM} macros are defined
this way. The output is always the @code{INTERNAL} character set (aka
UCS-4) and therefore each character consists of exactly four bytes. For
the conversion from @code{INTERNAL} to ISO-2022-JP we have to take into
account that escape sequences might be necessary to switch the character
sets. Therefore the @code{__max_needed_to} element for this direction
gets assigned @code{MAX_NEEDED_FROM + 2}. This takes into account the
two bytes needed for the escape sequences to single the switching. The
asymmetry in the maximum values for the two directions can be explained
easily: when reading ISO-2022-JP text, escape sequences can be handled
alone (i.e., it is not necessary to process a real character since the
effect of the escape sequence can be recorded in the state information).
The situation is different for the other direction. Since it is in
general not known which character comes next, one cannot emit escape
sequences to change the state in advance. This means the escape
sequences that have to be emitted together with the next character.
Therefore one needs more room than only for the character itself.
The possible return values of the initialization function are:
@table @code
@item __GCONV_OK
The initialization succeeded
@item __GCONV_NOCONV
The requested conversion is not supported in the module. This can
happen if the @file{gconv-modules} file has errors.
@item __GCONV_NOMEM
Memory required to store additional information could not be allocated.
@end table
@end deftypevr
The function called before the module is unloaded is significantly
easier. It often has nothing at all to do; in which case it can be left
out completely.
@comment gconv.h
@comment GNU
@deftypevr {Data type} void {(*__gconv_end_fct)} (struct gconv_step *)
The task of this function is to free all resources allocated in the
initialization function. Therefore only the @code{__data} element of
the object pointed to by the argument is of interest. Continuing the
example from the initialization function, the finalization function
looks like this:
@smallexample
void
gconv_end (struct __gconv_step *data)
@{
free (data->__data);
@}
@end smallexample
@end deftypevr
The most important function is the conversion function itself, which can
get quite complicated for complex character sets. But since this is not
of interest here, we will only describe a possible skeleton for the
conversion function.
@comment gconv.h
@comment GNU
@deftypevr {Data type} int {(*__gconv_fct)} (struct __gconv_step *, struct __gconv_step_data *, const char **, const char *, size_t *, int)
The conversion function can be called for two basic reason: to convert
text or to reset the state. From the description of the @code{iconv}
function it can be seen why the flushing mode is necessary. What mode
is selected is determined by the sixth argument, an integer. This
argument being nonzero means that flushing is selected.
Common to both modes is where the output buffer can be found. The
information about this buffer is stored in the conversion step data. A
pointer to this information is passed as the second argument to this
function. The description of the @code{struct __gconv_step_data}
structure has more information on the conversion step data.
@cindex stateful
What has to be done for flushing depends on the source character set.
If the source character set is not stateful, nothing has to be done.
Otherwise the function has to emit a byte sequence to bring the state
object into the initial state. Once this all happened the other
conversion modules in the chain of conversions have to get the same
chance. Whether another step follows can be determined from the
@code{__is_last} element of the step data structure to which the first
parameter points.
The more interesting mode is when actual text has to be converted. The
first step in this case is to convert as much text as possible from the
input buffer and store the result in the output buffer. The start of the
input buffer is determined by the third argument, which is a pointer to a
pointer variable referencing the beginning of the buffer. The fourth
argument is a pointer to the byte right after the last byte in the buffer.
The conversion has to be performed according to the current state if the
character set is stateful. The state is stored in an object pointed to
by the @code{__statep} element of the step data (second argument). Once
either the input buffer is empty or the output buffer is full the
conversion stops. At this point, the pointer variable referenced by the
third parameter must point to the byte following the last processed
byte (i.e., if all of the input is consumed, this pointer and the fourth
parameter have the same value).
What now happens depends on whether this step is the last one. If it is
the last step, the only thing that has to be done is to update the
@code{__outbuf} element of the step data structure to point after the
last written byte. This update gives the caller the information on how
much text is available in the output buffer. In addition, the variable
pointed to by the fifth parameter, which is of type @code{size_t}, must
be incremented by the number of characters (@emph{not bytes}) that were
converted in a non-reversible way. Then, the function can return.
In case the step is not the last one, the later conversion functions have
to get a chance to do their work. Therefore, the appropriate conversion
function has to be called. The information about the functions is
stored in the conversion data structures, passed as the first parameter.
This information and the step data are stored in arrays, so the next
element in both cases can be found by simple pointer arithmetic:
@smallexample
int
gconv (struct __gconv_step *step, struct __gconv_step_data *data,
const char **inbuf, const char *inbufend, size_t *written,
int do_flush)
@{
struct __gconv_step *next_step = step + 1;
struct __gconv_step_data *next_data = data + 1;
@dots{}
@end smallexample
The @code{next_step} pointer references the next step information and
@code{next_data} the next data record. The call of the next function
therefore will look similar to this:
@smallexample
next_step->__fct (next_step, next_data, &outerr, outbuf,
written, 0)
@end smallexample
But this is not yet all. Once the function call returns the conversion
function might have some more to do. If the return value of the function
is @code{__GCONV_EMPTY_INPUT}, more room is available in the output
buffer. Unless the input buffer is empty the conversion, functions start
all over again and process the rest of the input buffer. If the return
value is not @code{__GCONV_EMPTY_INPUT}, something went wrong and we have
to recover from this.
A requirement for the conversion function is that the input buffer
pointer (the third argument) always point to the last character that
was put in converted form into the output buffer. This is trivially
true after the conversion performed in the current step, but if the
conversion functions deeper downstream stop prematurely, not all
characters from the output buffer are consumed and, therefore, the input
buffer pointers must be backed off to the right position.
Correcting the input buffers is easy to do if the input and output
character sets have a fixed width for all characters. In this situation
we can compute how many characters are left in the output buffer and,
therefore, can correct the input buffer pointer appropriately with a
similar computation. Things are getting tricky if either character set
has characters represented with variable length byte sequences, and it
gets even more complicated if the conversion has to take care of the
state. In these cases the conversion has to be performed once again, from
the known state before the initial conversion (i.e., if necessary the
state of the conversion has to be reset and the conversion loop has to be
executed again). The difference now is that it is known how much input
must be created, and the conversion can stop before converting the first
unused character. Once this is done the input buffer pointers must be
updated again and the function can return.
One final thing should be mentioned. If it is necessary for the
conversion to know whether it is the first invocation (in case a prolog
has to be emitted), the conversion function should increment the
@code{__invocation_counter} element of the step data structure just
before returning to the caller. See the description of the @code{struct
__gconv_step_data} structure above for more information on how this can
be used.
The return value must be one of the following values:
@table @code
@item __GCONV_EMPTY_INPUT
All input was consumed and there is room left in the output buffer.
@item __GCONV_FULL_OUTPUT
No more room in the output buffer. In case this is not the last step
this value is propagated down from the call of the next conversion
function in the chain.
@item __GCONV_INCOMPLETE_INPUT
The input buffer is not entirely empty since it contains an incomplete
character sequence.
@end table
The following example provides a framework for a conversion function.
In case a new conversion has to be written the holes in this
implementation have to be filled and that is it.
@smallexample
int
gconv (struct __gconv_step *step, struct __gconv_step_data *data,
const char **inbuf, const char *inbufend, size_t *written,
int do_flush)
@{
struct __gconv_step *next_step = step + 1;
struct __gconv_step_data *next_data = data + 1;
gconv_fct fct = next_step->__fct;
int status;
/* @r{If the function is called with no input this means we have}
@r{to reset to the initial state. The possibly partly}
@r{converted input is dropped.} */
if (do_flush)
@{
status = __GCONV_OK;
/* @r{Possible emit a byte sequence which put the state object}
@r{into the initial state.} */
/* @r{Call the steps down the chain if there are any but only}
@r{if we successfully emitted the escape sequence.} */
if (status == __GCONV_OK && ! data->__is_last)
status = fct (next_step, next_data, NULL, NULL,
written, 1);
@}
else
@{
/* @r{We preserve the initial values of the pointer variables.} */
const char *inptr = *inbuf;
char *outbuf = data->__outbuf;
char *outend = data->__outbufend;
char *outptr;
do
@{
/* @r{Remember the start value for this round.} */
inptr = *inbuf;
/* @r{The outbuf buffer is empty.} */
outptr = outbuf;
/* @r{For stateful encodings the state must be safe here.} */
/* @r{Run the conversion loop. @code{status} is set}
@r{appropriately afterwards.} */
/* @r{If this is the last step, leave the loop. There is}
@r{nothing we can do.} */
if (data->__is_last)
@{
/* @r{Store information about how many bytes are}
@r{available.} */
data->__outbuf = outbuf;
/* @r{If any non-reversible conversions were performed,}
@r{add the number to @code{*written}.} */
break;
@}
/* @r{Write out all output that was produced.} */
if (outbuf > outptr)
@{
const char *outerr = data->__outbuf;
int result;
result = fct (next_step, next_data, &outerr,
outbuf, written, 0);
if (result != __GCONV_EMPTY_INPUT)
@{
if (outerr != outbuf)
@{
/* @r{Reset the input buffer pointer. We}
@r{document here the complex case.} */
size_t nstatus;
/* @r{Reload the pointers.} */
*inbuf = inptr;
outbuf = outptr;
/* @r{Possibly reset the state.} */
/* @r{Redo the conversion, but this time}
@r{the end of the output buffer is at}
@r{@code{outerr}.} */
@}
/* @r{Change the status.} */
status = result;
@}
else
/* @r{All the output is consumed, we can make}
@r{ another run if everything was ok.} */
if (status == __GCONV_FULL_OUTPUT)
status = __GCONV_OK;
@}
@}
while (status == __GCONV_OK);
/* @r{We finished one use of this step.} */
++data->__invocation_counter;
@}
return status;
@}
@end smallexample
@end deftypevr
This information should be sufficient to write new modules. Anybody
doing so should also take a look at the available source code in the
@glibcadj{} sources. It contains many examples of working and optimized
modules.
@c File charset.texi edited October 2001 by Dennis Grace, IBM Corporation
glibc-doc-reference-2.19.orig/manual/crypt.texi 0000664 0001750 0001750 00000044244 12275120646 021623 0 ustar adconrad adconrad @c This node must have no pointers.
@node Cryptographic Functions
@c @node Cryptographic Functions, Debugging Support, System Configuration, Top
@chapter DES Encryption and Password Handling
@c %MENU% DES encryption and password handling
On many systems, it is unnecessary to have any kind of user
authentication; for instance, a workstation which is not connected to a
network probably does not need any user authentication, because to use
the machine an intruder must have physical access.
Sometimes, however, it is necessary to be sure that a user is authorized
to use some service a machine provides---for instance, to log in as a
particular user id (@pxref{Users and Groups}). One traditional way of
doing this is for each user to choose a secret @dfn{password}; then, the
system can ask someone claiming to be a user what the user's password
is, and if the person gives the correct password then the system can
grant the appropriate privileges.
If all the passwords are just stored in a file somewhere, then this file
has to be very carefully protected. To avoid this, passwords are run
through a @dfn{one-way function}, a function which makes it difficult to
work out what its input was by looking at its output, before storing in
the file.
@Theglibc{} provides a one-way function that is compatible with
the behavior of the @code{crypt} function introduced in FreeBSD 2.0.
It supports two one-way algorithms: one based on the MD5
message-digest algorithm that is compatible with modern BSD systems,
and the other based on the Data Encryption Standard (DES) that is
compatible with Unix systems.
@vindex AUTH_DES
@cindex FIPS 140-2
It also provides support for Secure RPC, and some library functions that
can be used to perform normal DES encryption. The @code{AUTH_DES}
authentication flavor in Secure RPC, as provided by @theglibc{},
uses DES and does not comply with FIPS 140-2 nor does any other use of DES
within @theglibc{}. It is recommended that Secure RPC should not be used
for systems that need to comply with FIPS 140-2 since all flavors of
encrypted authentication use normal DES.
@menu
* Legal Problems:: This software can get you locked up, or worse.
* getpass:: Prompting the user for a password.
* crypt:: A one-way function for passwords.
* DES Encryption:: Routines for DES encryption.
@end menu
@node Legal Problems
@section Legal Problems
Because of the continuously changing state of the law, it's not possible
to provide a definitive survey of the laws affecting cryptography.
Instead, this section warns you of some of the known trouble spots; this
may help you when you try to find out what the laws of your country are.
Some countries require that you have a licence to use, possess, or import
cryptography. These countries are believed to include Byelorussia,
Burma, India, Indonesia, Israel, Kazakhstan, Pakistan, Russia, and Saudi
Arabia.
Some countries restrict the transmission of encrypted messages by radio;
some telecommunications carriers restrict the transmission of encrypted
messages over their network.
Many countries have some form of export control for encryption software.
The Wassenaar Arrangement is a multilateral agreement between 33
countries (Argentina, Australia, Austria, Belgium, Bulgaria, Canada, the
Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary,
Ireland, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway,
Poland, Portugal, the Republic of Korea, Romania, the Russian
Federation, the Slovak Republic, Spain, Sweden, Switzerland, Turkey,
Ukraine, the United Kingdom and the United States) which restricts some
kinds of encryption exports. Different countries apply the arrangement
in different ways; some do not allow the exception for certain kinds of
``public domain'' software (which would include this library), some
only restrict the export of software in tangible form, and others impose
significant additional restrictions.
The United States has additional rules. This software would generally
be exportable under 15 CFR 740.13(e), which permits exports of
``encryption source code'' which is ``publicly available'' and which is
``not subject to an express agreement for the payment of a licensing fee or
royalty for commercial production or sale of any product developed with
the source code'' to most countries.
The rules in this area are continuously changing. If you know of any
information in this manual that is out-of-date, please report it to
the bug database. @xref{Reporting Bugs}.
@node getpass
@section Reading Passwords
When reading in a password, it is desirable to avoid displaying it on
the screen, to help keep it secret. The following function handles this
in a convenient way.
@comment unistd.h
@comment BSD
@deftypefun {char *} getpass (const char *@var{prompt})
@safety{@prelim{}@mtunsafe{@mtasuterm{}}@asunsafe{@ascuheap{} @asulock{} @asucorrupt{}}@acunsafe{@acuterm{} @aculock{} @acucorrupt{}}}
@c This function will attempt to create a stream for terminal I/O, but
@c will fallback to stdio/stderr. It attempts to change the terminal
@c mode in a thread-unsafe way, write out the prompt, read the password,
@c then restore the terminal mode. It has a cleanup to close the stream
@c in case of (synchronous) cancellation, but not to restore the
@c terminal mode.
@code{getpass} outputs @var{prompt}, then reads a string in from the
terminal without echoing it. It tries to connect to the real terminal,
@file{/dev/tty}, if possible, to encourage users not to put plaintext
passwords in files; otherwise, it uses @code{stdin} and @code{stderr}.
@code{getpass} also disables the INTR, QUIT, and SUSP characters on the
terminal using the @code{ISIG} terminal attribute (@pxref{Local Modes}).
The terminal is flushed before and after @code{getpass}, so that
characters of a mistyped password are not accidentally visible.
In other C libraries, @code{getpass} may only return the first
@code{PASS_MAX} bytes of a password. @Theglibc{} has no limit, so
@code{PASS_MAX} is undefined.
The prototype for this function is in @file{unistd.h}. @code{PASS_MAX}
would be defined in @file{limits.h}.
@end deftypefun
This precise set of operations may not suit all possible situations. In
this case, it is recommended that users write their own @code{getpass}
substitute. For instance, a very simple substitute is as follows:
@smallexample
@include mygetpass.c.texi
@end smallexample
The substitute takes the same parameters as @code{getline}
(@pxref{Line Input}); the user must print any prompt desired.
@node crypt
@section Encrypting Passwords
@comment crypt.h
@comment BSD, SVID
@deftypefun {char *} crypt (const char *@var{key}, const char *@var{salt})
@safety{@prelim{}@mtunsafe{@mtasurace{:crypt}}@asunsafe{@asucorrupt{} @asulock{} @ascuheap{} @ascudlopen{}}@acunsafe{@aculock{} @acsmem{}}}
@c Besides the obvious problem of returning a pointer into static
@c storage, the DES initializer takes an internal lock with the usual
@c set of problems for AS- and AC-Safety. The FIPS mode checker and the
@c NSS implementations of may leak file descriptors if canceled. The
@c The MD5, SHA256 and SHA512 implementations will malloc on long keys,
@c and NSS relies on dlopening, which brings about another can of worms.
The @code{crypt} function takes a password, @var{key}, as a string, and
a @var{salt} character array which is described below, and returns a
printable ASCII string which starts with another salt. It is believed
that, given the output of the function, the best way to find a @var{key}
that will produce that output is to guess values of @var{key} until the
original value of @var{key} is found.
The @var{salt} parameter does two things. Firstly, it selects which
algorithm is used, the MD5-based one or the DES-based one. Secondly, it
makes life harder for someone trying to guess passwords against a file
containing many passwords; without a @var{salt}, an intruder can make a
guess, run @code{crypt} on it once, and compare the result with all the
passwords. With a @var{salt}, the intruder must run @code{crypt} once
for each different salt.
For the MD5-based algorithm, the @var{salt} should consist of the string
@code{$1$}, followed by up to 8 characters, terminated by either
another @code{$} or the end of the string. The result of @code{crypt}
will be the @var{salt}, followed by a @code{$} if the salt didn't end
with one, followed by 22 characters from the alphabet
@code{./0-9A-Za-z}, up to 34 characters total. Every character in the
@var{key} is significant.
For the DES-based algorithm, the @var{salt} should consist of two
characters from the alphabet @code{./0-9A-Za-z}, and the result of
@code{crypt} will be those two characters followed by 11 more from the
same alphabet, 13 in total. Only the first 8 characters in the
@var{key} are significant.
The MD5-based algorithm has no limit on the useful length of the
password used, and is slightly more secure. It is therefore preferred
over the DES-based algorithm.
When the user enters their password for the first time, the @var{salt}
should be set to a new string which is reasonably random. To verify a
password against the result of a previous call to @code{crypt}, pass
the result of the previous call as the @var{salt}.
@end deftypefun
The following short program is an example of how to use @code{crypt} the
first time a password is entered. Note that the @var{salt} generation
is just barely acceptable; in particular, it is not unique between
machines, and in many applications it would not be acceptable to let an
attacker know what time the user's password was last set.
@smallexample
@include genpass.c.texi
@end smallexample
The next program shows how to verify a password. It prompts the user
for a password and prints ``Access granted.'' if the user types
@code{GNU libc manual}.
@smallexample
@include testpass.c.texi
@end smallexample
@comment crypt.h
@comment GNU
@deftypefun {char *} crypt_r (const char *@var{key}, const char *@var{salt}, {struct crypt_data *} @var{data})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{} @ascuheap{} @ascudlopen{}}@acunsafe{@aculock{} @acsmem{}}}
@c Compared with crypt, this function fixes the @mtasurace:crypt
@c problem, but nothing else.
The @code{crypt_r} function does the same thing as @code{crypt}, but
takes an extra parameter which includes space for its result (among
other things), so it can be reentrant. @code{data@w{->}initialized} must be
cleared to zero before the first time @code{crypt_r} is called.
The @code{crypt_r} function is a GNU extension.
@end deftypefun
The @code{crypt} and @code{crypt_r} functions are prototyped in the
header @file{crypt.h}.
@node DES Encryption
@section DES Encryption
@cindex FIPS 46-3
The Data Encryption Standard is described in the US Government Federal
Information Processing Standards (FIPS) 46-3 published by the National
Institute of Standards and Technology. The DES has been very thoroughly
analyzed since it was developed in the late 1970s, and no new
significant flaws have been found.
However, the DES uses only a 56-bit key (plus 8 parity bits), and a
machine has been built in 1998 which can search through all possible
keys in about 6 days, which cost about US$200000; faster searches would
be possible with more money. This makes simple DES insecure for most
purposes, and NIST no longer permits new US government systems
to use simple DES.
For serious encryption functionality, it is recommended that one of the
many free encryption libraries be used instead of these routines.
The DES is a reversible operation which takes a 64-bit block and a
64-bit key, and produces another 64-bit block. Usually the bits are
numbered so that the most-significant bit, the first bit, of each block
is numbered 1.
Under that numbering, every 8th bit of the key (the 8th, 16th, and so
on) is not used by the encryption algorithm itself. But the key must
have odd parity; that is, out of bits 1 through 8, and 9 through 16, and
so on, there must be an odd number of `1' bits, and this completely
specifies the unused bits.
@comment crypt.h
@comment BSD, SVID
@deftypefun void setkey (const char *@var{key})
@safety{@prelim{}@mtunsafe{@mtasurace{:crypt}}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@aculock{}}}
@c The static buffer stores the key, making it fundamentally
@c thread-unsafe. The locking issues are only in the initialization
@c path; cancelling the initialization will leave the lock held, it
@c would otherwise repeat the initialization on the next call.
The @code{setkey} function sets an internal data structure to be an
expanded form of @var{key}. @var{key} is specified as an array of 64
bits each stored in a @code{char}, the first bit is @code{key[0]} and
the 64th bit is @code{key[63]}. The @var{key} should have the correct
parity.
@end deftypefun
@comment crypt.h
@comment BSD, SVID
@deftypefun void encrypt (char *@var{block}, int @var{edflag})
@safety{@prelim{}@mtunsafe{@mtasurace{:crypt}}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@aculock{}}}
@c Same issues as setkey.
The @code{encrypt} function encrypts @var{block} if
@var{edflag} is 0, otherwise it decrypts @var{block}, using a key
previously set by @code{setkey}. The result is
placed in @var{block}.
Like @code{setkey}, @var{block} is specified as an array of 64 bits each
stored in a @code{char}, but there are no parity bits in @var{block}.
@end deftypefun
@comment crypt.h
@comment GNU
@deftypefun void setkey_r (const char *@var{key}, {struct crypt_data *} @var{data})
@c @safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@aculock{}}}
@comment crypt.h
@comment GNU
@deftypefunx void encrypt_r (char *@var{block}, int @var{edflag}, {struct crypt_data *} @var{data})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@aculock{}}}
These are reentrant versions of @code{setkey} and @code{encrypt}. The
only difference is the extra parameter, which stores the expanded
version of @var{key}. Before calling @code{setkey_r} the first time,
@code{data->initialized} must be cleared to zero.
@end deftypefun
The @code{setkey_r} and @code{encrypt_r} functions are GNU extensions.
@code{setkey}, @code{encrypt}, @code{setkey_r}, and @code{encrypt_r} are
defined in @file{crypt.h}.
@comment rpc/des_crypt.h
@comment SUNRPC
@deftypefun int ecb_crypt (char *@var{key}, char *@var{blocks}, unsigned @var{len}, unsigned @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{ecb_crypt} encrypts or decrypts one or more blocks
using DES. Each block is encrypted independently.
The @var{blocks} and the @var{key} are stored packed in 8-bit bytes, so
that the first bit of the key is the most-significant bit of
@code{key[0]} and the 63rd bit of the key is stored as the
least-significant bit of @code{key[7]}. The @var{key} should have the
correct parity.
@var{len} is the number of bytes in @var{blocks}. It should be a
multiple of 8 (so that there is a whole number of blocks to encrypt).
@var{len} is limited to a maximum of @code{DES_MAXDATA} bytes.
The result of the encryption replaces the input in @var{blocks}.
The @var{mode} parameter is the bitwise OR of two of the following:
@vtable @code
@comment rpc/des_crypt.h
@comment SUNRPC
@item DES_ENCRYPT
This constant, used in the @var{mode} parameter, specifies that
@var{blocks} is to be encrypted.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DES_DECRYPT
This constant, used in the @var{mode} parameter, specifies that
@var{blocks} is to be decrypted.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DES_HW
This constant, used in the @var{mode} parameter, asks to use a hardware
device. If no hardware device is available, encryption happens anyway,
but in software.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DES_SW
This constant, used in the @var{mode} parameter, specifies that no
hardware device is to be used.
@end vtable
The result of the function will be one of these values:
@vtable @code
@comment rpc/des_crypt.h
@comment SUNRPC
@item DESERR_NONE
The encryption succeeded.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DESERR_NOHWDEVICE
The encryption succeeded, but there was no hardware device available.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DESERR_HWERROR
The encryption failed because of a hardware problem.
@comment rpc/des_crypt.h
@comment SUNRPC
@item DESERR_BADPARAM
The encryption failed because of a bad parameter, for instance @var{len}
is not a multiple of 8 or @var{len} is larger than @code{DES_MAXDATA}.
@end vtable
@end deftypefun
@comment rpc/des_crypt.h
@comment SUNRPC
@deftypefun int DES_FAILED (int @var{err})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns 1 if @var{err} is a `success' result code from
@code{ecb_crypt} or @code{cbc_crypt}, and 0 otherwise.
@end deftypefun
@comment rpc/des_crypt.h
@comment SUNRPC
@deftypefun int cbc_crypt (char *@var{key}, char *@var{blocks}, unsigned @var{len}, unsigned @var{mode}, char *@var{ivec})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{cbc_crypt} encrypts or decrypts one or more blocks
using DES in Cipher Block Chaining mode.
For encryption in CBC mode, each block is exclusive-ored with @var{ivec}
before being encrypted, then @var{ivec} is replaced with the result of
the encryption, then the next block is processed. Decryption is the
reverse of this process.
This has the advantage that blocks which are the same before being
encrypted are very unlikely to be the same after being encrypted, making
it much harder to detect patterns in the data.
Usually, @var{ivec} is set to 8 random bytes before encryption starts.
Then the 8 random bytes are transmitted along with the encrypted data
(without themselves being encrypted), and passed back in as @var{ivec}
for decryption. Another possibility is to set @var{ivec} to 8 zeroes
initially, and have the first the block encrypted consist of 8 random
bytes.
Otherwise, all the parameters are similar to those for @code{ecb_crypt}.
@end deftypefun
@comment rpc/des_crypt.h
@comment SUNRPC
@deftypefun void des_setparity (char *@var{key})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{des_setparity} changes the 64-bit @var{key}, stored
packed in 8-bit bytes, to have odd parity by altering the low bits of
each byte.
@end deftypefun
The @code{ecb_crypt}, @code{cbc_crypt}, and @code{des_setparity}
functions and their accompanying macros are all defined in the header
@file{rpc/des_crypt.h}.
glibc-doc-reference-2.19.orig/manual/xtract-typefun.awk 0000664 0001750 0001750 00000001544 12275120646 023264 0 ustar adconrad adconrad #! /usr/local/bin/gawk -f
BEGIN {
last_node="";
}
/^@node/ {
name = $0;
sub(/^@node +/, "", name);
sub(/[@,].*$/, "", name);
last_node = name;
}
/^@deftype(fn|vr)/ {
# The string we want is $4, except that if there were brace blocks
# before that point then it gets shifted to the right, since awk
# doesn't know from brace blocks.
id = 4; check = 2; squig = 0;
while(check < id)
{
if($check ~ /{/) squig++;
if($check ~ /}/) squig--;
if(squig) id++;
check++;
}
gsub(/[(){}*]/, "", $id);
printf ("* %s: (libc)%s.\n", $id, last_node);
}
/^@deftypefun/ {
# Likewise, except it's $3 theoretically.
id = 3; check = 2; squig = 0;
while(check < id)
{
if($check ~ /{/) squig++;
if($check ~ /}/) squig--;
if(squig) id++;
check++;
}
gsub(/[(){}*]/, "", $id);
printf ("* %s: (libc)%s.\n", $id, last_node);
}
glibc-doc-reference-2.19.orig/manual/install.texi 0000664 0001750 0001750 00000057231 12275120646 022130 0 ustar adconrad adconrad @include macros.texi
@include pkgvers.texi
@ifclear plain
@node Installation, Maintenance, Library Summary, Top
@end ifclear
@c %MENU% How to install the GNU C Library
@appendix Installing @theglibc{}
Before you do anything else, you should read the FAQ at
@url{http://sourceware.org/glibc/wiki/FAQ}. It answers common
questions and describes problems you may experience with compilation
and installation.
Features can be added to @theglibc{} via @dfn{add-on} bundles. These are
separate tar files, which you unpack into the top level of the source
tree. Then you give @code{configure} the @samp{--enable-add-ons} option
to activate them, and they will be compiled into the library.
You will need recent versions of several GNU tools: definitely GCC and
GNU Make, and possibly others. @xref{Tools for Compilation}, below.
@ifclear plain
@menu
* Configuring and compiling:: How to compile and test GNU libc.
* Running make install:: How to install it once you've got it
compiled.
* Tools for Compilation:: You'll need these first.
* Linux:: Specific advice for GNU/Linux systems.
* Reporting Bugs:: So they'll get fixed.
@end menu
@end ifclear
@node Configuring and compiling
@appendixsec Configuring and compiling @theglibc{}
@cindex configuring
@cindex compiling
@Theglibc{} cannot be compiled in the source directory. You must build
it in a separate build directory. For example, if you have unpacked
the @glibcadj{} sources in @file{/src/gnu/glibc-@var{version}},
create a directory
@file{/src/gnu/glibc-build} to put the object files in. This allows
removing the whole build directory in case an error occurs, which is
the safest way to get a fresh start and should always be done.
From your object directory, run the shell script @file{configure} located
at the top level of the source tree. In the scenario above, you'd type
@smallexample
$ ../glibc-@var{version}/configure @var{args@dots{}}
@end smallexample
Please note that even though you're building in a separate build
directory, the compilation may need to create or modify files and
directories in the source directory.
@noindent
@code{configure} takes many options, but the only one that is usually
mandatory is @samp{--prefix}. This option tells @code{configure}
where you want @theglibc{} installed. This defaults to @file{/usr/local},
but the normal setting to install as the standard system library is
@samp{--prefix=/usr} for @gnulinuxsystems{} and @samp{--prefix=} (an
empty prefix) for @gnuhurdsystems{}.
It may also be useful to set the @var{CC} and @var{CFLAGS} variables in
the environment when running @code{configure}. @var{CC} selects the C
compiler that will be used, and @var{CFLAGS} sets optimization options
for the compiler.
The following list describes all of the available options for
@code{configure}:
@table @samp
@item --prefix=@var{directory}
Install machine-independent data files in subdirectories of
@file{@var{directory}}. The default is to install in @file{/usr/local}.
@item --exec-prefix=@var{directory}
Install the library and other machine-dependent files in subdirectories
of @file{@var{directory}}. The default is to the @samp{--prefix}
directory if that option is specified, or @file{/usr/local} otherwise.
@item --with-headers=@var{directory}
Look for kernel header files in @var{directory}, not
@file{/usr/include}. @Theglibc{} needs information from the kernel's header
files describing the interface to the kernel. @Theglibc{} will normally
look in @file{/usr/include} for them,
but if you specify this option, it will look in @var{DIRECTORY} instead.
This option is primarily of use on a system where the headers in
@file{/usr/include} come from an older version of @theglibc{}. Conflicts can
occasionally happen in this case. You can also use this option if you want to
compile @theglibc{} with a newer set of kernel headers than the ones found in
@file{/usr/include}.
@item --enable-add-ons[=@var{list}]
Specify add-on packages to include in the build. If this option is
specified with no list, it enables all the add-on packages it finds in
the main source directory; this is the default behavior. You may
specify an explicit list of add-ons to use in @var{list}, separated by
spaces or commas (if you use spaces, remember to quote them from the
shell). Each add-on in @var{list} can be an absolute directory name
or can be a directory name relative to the main source directory, or
relative to the build directory (that is, the current working directory).
For example, @samp{--enable-add-ons=nptl,../glibc-libidn-@var{version}}.
@item --enable-kernel=@var{version}
This option is currently only useful on @gnulinuxsystems{}. The
@var{version} parameter should have the form X.Y.Z and describes the
smallest version of the Linux kernel the generated library is expected
to support. The higher the @var{version} number is, the less
compatibility code is added, and the faster the code gets.
@item --with-binutils=@var{directory}
Use the binutils (assembler and linker) in @file{@var{directory}}, not
the ones the C compiler would default to. You can use this option if
the default binutils on your system cannot deal with all the constructs
in @theglibc{}. In that case, @code{configure} will detect the
problem and suppress these constructs, so that the library will still be
usable, but functionality may be lost---for example, you can't build a
shared libc with old binutils.
@item --without-fp
Use this option if your computer lacks hardware floating-point support
and your operating system does not emulate an FPU.
@c disable static doesn't work currently
@c @item --disable-static
@c Don't build static libraries. Static libraries aren't that useful these
@c days, but we recommend you build them in case you need them.
@item --disable-shared
Don't build shared libraries even if it is possible. Not all systems
support shared libraries; you need ELF support and (currently) the GNU
linker.
@item --disable-profile
Don't build libraries with profiling information. You may want to use
this option if you don't plan to do profiling.
@item --enable-static-nss
Compile static versions of the NSS (Name Service Switch) libraries.
This is not recommended because it defeats the purpose of NSS; a program
linked statically with the NSS libraries cannot be dynamically
reconfigured to use a different name database.
@item --without-tls
By default the C library is built with support for thread-local storage
if the used tools support it. By using @samp{--without-tls} this can be
prevented though there generally is no reason since it creates
compatibility problems.
@item --enable-hardcoded-path-in-tests
By default, dynamic tests are linked to run with the installed C library.
This option hardcodes the newly built C library path in dynamic tests
so that they can be invoked directly.
@item --enable-lock-elision=yes
Enable lock elision for pthread mutexes by default.
@pindex pt_chown
@findex grantpt
@item --enable-pt_chown
The file @file{pt_chown} is a helper binary for @code{grantpt}
(@pxref{Allocation, Pseudo-Terminals}) that is installed setuid root to
fix up pseudo-terminal ownership. It is not built by default because
systems using the Linux kernel are commonly built with the @code{devpts}
filesystem enabled and mounted at @file{/dev/pts}, which manages
pseudo-terminal ownership automatically. By using
@samp{--enable-pt_chown}, you may build @file{pt_chown} and install it
setuid and owned by @code{root}. The use of @file{pt_chown} introduces
additional security risks to the system and you should enable it only if
you understand and accept those risks.
@item --build=@var{build-system}
@itemx --host=@var{host-system}
These options are for cross-compiling. If you specify both options and
@var{build-system} is different from @var{host-system}, @code{configure}
will prepare to cross-compile @theglibc{} from @var{build-system} to be used
on @var{host-system}. You'll probably need the @samp{--with-headers}
option too, and you may have to override @var{configure}'s selection of
the compiler and/or binutils.
If you only specify @samp{--host}, @code{configure} will prepare for a
native compile but use what you specify instead of guessing what your
system is. This is most useful to change the CPU submodel. For example,
if @code{configure} guesses your machine as @code{i686-pc-linux-gnu} but
you want to compile a library for 586es, give
@samp{--host=i586-pc-linux-gnu} or just @samp{--host=i586-linux} and add
the appropriate compiler flags (@samp{-mcpu=i586} will do the trick) to
@var{CFLAGS}.
If you specify just @samp{--build}, @code{configure} will get confused.
@item --with-pkgversion=@var{version}
Specify a description, possibly including a build number or build
date, of the binaries being built, to be included in
@option{--version} output from programs installed with @theglibc{}.
For example, @option{--with-pkgversion='FooBar GNU/Linux glibc build
123'}. The default value is @samp{GNU libc}.
@item --with-bugurl=@var{url}
Specify the URL that users should visit if they wish to report a bug,
to be included in @option{--help} output from programs installed with
@theglibc{}. The default value refers to the main bug-reporting
information for @theglibc{}.
@end table
To build the library and related programs, type @code{make}. This will
produce a lot of output, some of which may look like errors from
@code{make} but isn't. Look for error messages from @code{make}
containing @samp{***}. Those indicate that something is seriously wrong.
The compilation process can take a long time, depending on the
configuration and the speed of your machine. Some complex modules may
take a very long time to compile, as much as several minutes on slower
machines. Do not panic if the compiler appears to hang.
If you want to run a parallel make, simply pass the @samp{-j} option
with an appropriate numeric parameter to @code{make}. You need a recent
GNU @code{make} version, though.
To build and run test programs which exercise some of the library
facilities, type @code{make check}. If it does not complete
successfully, do not use the built library, and report a bug after
verifying that the problem is not already known. @xref{Reporting Bugs},
for instructions on reporting bugs. Note that some of the tests assume
they are not being run by @code{root}. We recommend you compile and
test @theglibc{} as an unprivileged user.
Before reporting bugs make sure there is no problem with your system.
The tests (and later installation) use some pre-existing files of the
system such as @file{/etc/passwd}, @file{/etc/nsswitch.conf} and others.
These files must all contain correct and sensible content.
To format the @cite{GNU C Library Reference Manual} for printing, type
@w{@code{make dvi}}. You need a working @TeX{} installation to do
this. The distribution builds the on-line formatted version of the
manual, as Info files, as part of the build process. You can build
them manually with @w{@code{make info}}.
The library has a number of special-purpose configuration parameters
which you can find in @file{Makeconfig}. These can be overwritten with
the file @file{configparms}. To change them, create a
@file{configparms} in your build directory and add values as appropriate
for your system. The file is included and parsed by @code{make} and has
to follow the conventions for makefiles.
It is easy to configure @theglibc{} for cross-compilation by
setting a few variables in @file{configparms}. Set @code{CC} to the
cross-compiler for the target you configured the library for; it is
important to use this same @code{CC} value when running
@code{configure}, like this: @samp{CC=@var{target}-gcc configure
@var{target}}. Set @code{BUILD_CC} to the compiler to use for programs
run on the build system as part of compiling the library. You may need to
set @code{AR} to cross-compiling versions of @code{ar}
if the native tools are not configured to work with
object files for the target you configured for. When cross-compiling
@theglibc{}, it may be tested using @samp{make check
test-wrapper="@var{srcdir}/scripts/cross-test-ssh.sh @var{hostname}"},
where @var{srcdir} is the absolute directory name for the main source
directory and @var{hostname} is the host name of a system that can run
the newly built binaries of @theglibc{}. The source and build
directories must be visible at the same locations on both the build
system and @var{hostname}.
In general, when testing @theglibc{}, @samp{test-wrapper} may be set
to the name and arguments of any program to run newly built binaries.
This program must preserve the arguments to the binary being run, its
working directory, all environment variables set as part of testing
and the standard input, output and error file descriptors. If
@samp{@var{test-wrapper} env} will not work to run a program with
environment variables set, then @samp{test-wrapper-env} must be set to
a program that runs a newly built program with environment variable
assignments in effect, those assignments being specified as
@samp{@var{var}=@var{value}} before the name of the program to be run.
@node Running make install
@appendixsec Installing the C Library
@cindex installing
To install the library and its header files, and the Info files of the
manual, type @code{env LANGUAGE=C LC_ALL=C make install}. This will
build things, if necessary, before installing them; however, you should
still compile everything first. If you are installing @theglibc{} as your
primary C library, we recommend that you shut the system down to
single-user mode first, and reboot afterward. This minimizes the risk
of breaking things when the library changes out from underneath.
@samp{make install} will do the entire job of upgrading from a
previous installation of @theglibc{} version 2.x. There may sometimes
be headers
left behind from the previous installation, but those are generally
harmless. If you want to avoid leaving headers behind you can do
things in the following order.
You must first build the library (@samp{make}), optionally check it
(@samp{make check}), switch the include directories and then install
(@samp{make install}). The steps must be done in this order. Not moving
the directory before install will result in an unusable mixture of header
files from both libraries, but configuring, building, and checking the
library requires the ability to compile and run programs against the old
library. The new @file{/usr/include}, after switching the include
directories and before installing the library should contain the Linux
headers, but nothing else. If you do this, you will need to restore
any headers from libraries other than @theglibc{} yourself after installing the
library.
You can install @theglibc{} somewhere other than where you configured it to go
by setting the @code{install_root} variable on the command line for
@samp{make install}. The value of this variable is prepended to all the
paths for installation. This is useful when setting up a chroot
environment or preparing a binary distribution. The directory should be
specified with an absolute file name.
@Theglibc{} includes a daemon called @code{nscd}, which you
may or may not want to run. @code{nscd} caches name service lookups; it
can dramatically improve performance with NIS+, and may help with DNS as
well.
One auxiliary program, @file{/usr/libexec/pt_chown}, is installed setuid
@code{root} if the @samp{--enable-pt_chown} configuration option is used.
This program is invoked by the @code{grantpt} function; it sets the
permissions on a pseudoterminal so it can be used by the calling process.
If you are using a Linux kernel with the @code{devpts} filesystem enabled
and mounted at @file{/dev/pts}, you don't need this program.
After installation you might want to configure the timezone and locale
installation of your system. @Theglibc{} comes with a locale
database which gets configured with @code{localedef}. For example, to
set up a German locale with name @code{de_DE}, simply issue the command
@samp{localedef -i de_DE -f ISO-8859-1 de_DE}. To configure all locales
that are supported by @theglibc{}, you can issue from your build directory the
command @samp{make localedata/install-locales}.
To configure the locally used timezone, set the @code{TZ} environment
variable. The script @code{tzselect} helps you to select the right value.
As an example, for Germany, @code{tzselect} would tell you to use
@samp{TZ='Europe/Berlin'}. For a system wide installation (the given
paths are for an installation with @samp{--prefix=/usr}), link the
timezone file which is in @file{/usr/share/zoneinfo} to the file
@file{/etc/localtime}. For Germany, you might execute @samp{ln -s
/usr/share/zoneinfo/Europe/Berlin /etc/localtime}.
@node Tools for Compilation
@appendixsec Recommended Tools for Compilation
@cindex installation tools
@cindex tools, for installing library
We recommend installing the following GNU tools before attempting to
build @theglibc{}:
@itemize @bullet
@item
GNU @code{make} 3.79 or newer
You need the latest version of GNU @code{make}. Modifying @theglibc{}
to work with other @code{make} programs would be so difficult that
we recommend you port GNU @code{make} instead. @strong{Really.} We
recommend GNU @code{make} version 3.79. All earlier versions have severe
bugs or lack features.
@item
GCC 4.4 or newer, GCC 4.6 recommended
GCC 4.4 or higher is required; as of this writing, GCC 4.6 is the
compiler we advise to use to build @theglibc{}.
You can use whatever compiler you like to compile programs that use
@theglibc{}.
Check the FAQ for any special compiler issues on particular platforms.
@item
GNU @code{binutils} 2.20 or later
You must use GNU @code{binutils} (as and ld) to build @theglibc{}.
No other assembler or linker has the necessary functionality at the
moment.
@item
GNU @code{texinfo} 4.5 or later
To correctly translate and install the Texinfo documentation you need
this version of the @code{texinfo} package. Earlier versions do not
understand all the tags used in the document, and the installation
mechanism for the info files is not present or works differently.
@item
GNU @code{awk} 3.1.2, or higher
@code{awk} is used in several places to generate files.
Some @code{gawk} extensions are used, including the @code{asorti}
function, which was introduced in version 3.1.2 of @code{gawk}.
@item
Perl 5
Perl is not required, but it is used if present to test the
installation. We may decide to use it elsewhere in the future.
@item
GNU @code{sed} 3.02 or newer
@code{Sed} is used in several places to generate files. Most scripts work
with any version of @code{sed}. The known exception is the script
@code{po2test.sed} in the @code{intl} subdirectory which is used to
generate @code{msgs.h} for the test suite. This script works correctly
only with GNU @code{sed} 3.02. If you like to run the test suite, you
should definitely upgrade @code{sed}.
@end itemize
@noindent
If you change any of the @file{configure.ac} files you will also need
@itemize @bullet
@item
GNU @code{autoconf} 2.53 or higher
@end itemize
@noindent
and if you change any of the message translation files you will need
@itemize @bullet
@item
GNU @code{gettext} 0.10.36 or later
@end itemize
@noindent
You may also need these packages if you upgrade your source tree using
patches, although we try to avoid this.
@node Linux
@appendixsec Specific advice for @gnulinuxsystems{}
@cindex kernel header files
If you are installing @theglibc{} on @gnulinuxsystems{}, you need to have
the header files from a 2.6.19.1 or newer kernel around for reference.
These headers must be installed using @samp{make headers_install}; the
headers present in the kernel source directory are not suitable for
direct use by @theglibc{}. You do not need to use that kernel, just have
its headers installed where @theglibc{} can access them, referred to here as
@var{install-directory}. The easiest way to do this is to unpack it
in a directory such as @file{/usr/src/linux-@var{version}}. In that
directory, run @samp{make headers_install
INSTALL_HDR_PATH=@var{install-directory}}. Finally, configure @theglibc{}
with the option @samp{--with-headers=@var{install-directory}/include}.
Use the most recent kernel you can get your hands on. (If you are
cross-compiling @theglibc{}, you need to specify
@samp{ARCH=@var{architecture}} in the @samp{make headers_install}
command, where @var{architecture} is the architecture name used by the
Linux kernel, such as @samp{x86} or @samp{powerpc}.)
After installing @theglibc{}, you may need to remove or rename
directories such as @file{/usr/include/linux} and
@file{/usr/include/asm}, and replace them with copies of directories
such as @file{linux} and @file{asm} from
@file{@var{install-directory}/include}. All directories present in
@file{@var{install-directory}/include} should be copied, except that
@theglibc{} provides its own version of @file{/usr/include/scsi}; the
files provided by the kernel should be copied without replacing those
provided by @theglibc{}. The @file{linux}, @file{asm} and
@file{asm-generic} directories are required to compile programs using
@theglibc{}; the other directories describe interfaces to the kernel but
are not required if not compiling programs using those interfaces.
You do not need to copy kernel headers if you did not specify an
alternate kernel header source using @samp{--with-headers}.
The Filesystem Hierarchy Standard for @gnulinuxsystems{} expects some
components of the @glibcadj{} installation to be in
@file{/lib} and some in @file{/usr/lib}. This is handled automatically
if you configure @theglibc{} with @samp{--prefix=/usr}. If you set some other
prefix or allow it to default to @file{/usr/local}, then all the
components are installed there.
@node Reporting Bugs
@appendixsec Reporting Bugs
@cindex reporting bugs
@cindex bugs, reporting
There are probably bugs in @theglibc{}. There are certainly
errors and omissions in this manual. If you report them, they will get
fixed. If you don't, no one will ever know about them and they will
remain unfixed for all eternity, if not longer.
It is a good idea to verify that the problem has not already been
reported. Bugs are documented in two places: The file @file{BUGS}
describes a number of well known bugs and the central @glibcadj{}
bug tracking system has a
WWW interface at
@url{http://sourceware.org/bugzilla/}. The WWW
interface gives you access to open and closed reports. A closed report
normally includes a patch or a hint on solving the problem.
To report a bug, first you must find it. With any luck, this will be the
hard part. Once you've found a bug, make sure it's really a bug. A
good way to do this is to see if @theglibc{} behaves the same way
some other C library does. If so, probably you are wrong and the
libraries are right (but not necessarily). If not, one of the libraries
is probably wrong. It might not be @theglibc{}. Many historical
Unix C libraries permit things that we don't, such as closing a file
twice.
If you think you have found some way in which @theglibc{} does not
conform to the ISO and POSIX standards (@pxref{Standards and
Portability}), that is definitely a bug. Report it!
Once you're sure you've found a bug, try to narrow it down to the
smallest test case that reproduces the problem. In the case of a C
library, you really only need to narrow it down to one library
function call, if possible. This should not be too difficult.
The final step when you have a simple test case is to report the bug.
Do this at @value{REPORT_BUGS_TO}.
If you are not sure how a function should behave, and this manual
doesn't tell you, that's a bug in the manual. Report that too! If the
function's behavior disagrees with the manual, then either the library
or the manual has a bug, so report the disagreement. If you find any
errors or omissions in this manual, please report them to the
bug database. If you refer to specific
sections of the manual, please include the section names for easier
identification.
glibc-doc-reference-2.19.orig/manual/freemanuals.texi 0000664 0001750 0001750 00000011477 12275120646 022766 0 ustar adconrad adconrad @c freemanuals.texi - blurb for free documentation.
@c This file is intended to be included within another document,
@c hence no sectioning command or @node.
@cindex free documentation
The biggest deficiency in the free software community today is not in
the software---it is the lack of good free documentation that we can
include with the free software. Many of our most important
programs do not come with free reference manuals and free introductory
texts. Documentation is an essential part of any software package;
when an important free software package does not come with a free
manual and a free tutorial, that is a major gap. We have many such
gaps today.
Consider Perl, for instance. The tutorial manuals that people
normally use are non-free. How did this come about? Because the
authors of those manuals published them with restrictive terms---no
copying, no modification, source files not available---which exclude
them from the free software world.
That wasn't the first time this sort of thing happened, and it was far
from the last. Many times we have heard a GNU user eagerly describe a
manual that he is writing, his intended contribution to the community,
only to learn that he had ruined everything by signing a publication
contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not
price. The problem with the non-free manual is not that publishers
charge a price for printed copies---that in itself is fine. (The Free
Software Foundation sells printed copies of manuals, too.) The
problem is the restrictions on the use of the manual. Free manuals
are available in source code form, and give you permission to copy and
modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for
free software. Redistribution (including the normal kinds of
commercial redistribution) must be permitted, so that the manual can
accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too.
When people modify the software, adding or changing features, if they
are conscientious they will change the manual too---so they can
provide accurate and clear documentation for the modified program. A
manual that leaves you no choice but to write a new manual to document
a changed version of the program is not really available to our
community.
Some kinds of limits on the way modification is handled are
acceptable. For example, requirements to preserve the original
author's copyright notice, the distribution terms, or the list of
authors, are ok. It is also no problem to require modified versions
to include notice that they were modified. Even entire sections that
may not be deleted or changed are acceptable, as long as they deal
with nontechnical topics (like this one). These kinds of restrictions
are acceptable because they don't obstruct the community's normal use
of the manual.
However, it must be possible to modify all the @emph{technical}
content of the manual, and then distribute the result in all the usual
media, through all the usual channels. Otherwise, the restrictions
obstruct the use of the manual, it is not free, and we need another
manual to replace it.
Please spread the word about this issue. Our community continues to
lose manuals to proprietary publishing. If we spread the word that
free software needs free reference manuals and free tutorials, perhaps
the next person who wants to contribute by writing documentation will
realize, before it is too late, that only free manuals contribute to
the free software community.
If you are writing documentation, please insist on publishing it under
the GNU Free Documentation License or another free documentation
license. Remember that this decision requires your approval---you
don't have to let the publisher decide. Some commercial publishers
will use a free license if you insist, but they will not propose the
option; it is up to you to raise the issue and say firmly that this is
what you want. If the publisher you are dealing with refuses, please
try other publishers. If you're not sure whether a proposed license
is free, write to @email{licensing@@gnu.org}.
You can encourage commercial publishers to sell more free, copylefted
manuals and tutorials by buying them, and particularly by buying
copies from the publishers that paid for their writing or for major
improvements. Meanwhile, try to avoid buying non-free documentation
at all. Check the distribution terms of a manual before you buy it,
and insist that whoever seeks your business must respect your freedom.
Check the history of the book, and try reward the publishers that have
paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation
published by other publishers, at
@url{http://www.fsf.org/doc/other-free-books.html}.
glibc-doc-reference-2.19.orig/manual/llio.texi 0000664 0001750 0001750 00000463543 12275120646 021430 0 ustar adconrad adconrad @node Low-Level I/O, File System Interface, I/O on Streams, Top
@c %MENU% Low-level, less portable I/O
@chapter Low-Level Input/Output
This chapter describes functions for performing low-level input/output
operations on file descriptors. These functions include the primitives
for the higher-level I/O functions described in @ref{I/O on Streams}, as
well as functions for performing low-level control operations for which
there are no equivalents on streams.
Stream-level I/O is more flexible and usually more convenient;
therefore, programmers generally use the descriptor-level functions only
when necessary. These are some of the usual reasons:
@itemize @bullet
@item
For reading binary files in large chunks.
@item
For reading an entire file into core before parsing it.
@item
To perform operations other than data transfer, which can only be done
with a descriptor. (You can use @code{fileno} to get the descriptor
corresponding to a stream.)
@item
To pass descriptors to a child process. (The child can create its own
stream to use a descriptor that it inherits, but cannot inherit a stream
directly.)
@end itemize
@menu
* Opening and Closing Files:: How to open and close file
descriptors.
* I/O Primitives:: Reading and writing data.
* File Position Primitive:: Setting a descriptor's file
position.
* Descriptors and Streams:: Converting descriptor to stream
or vice-versa.
* Stream/Descriptor Precautions:: Precautions needed if you use both
descriptors and streams.
* Scatter-Gather:: Fast I/O to discontinuous buffers.
* Memory-mapped I/O:: Using files like memory.
* Waiting for I/O:: How to check for input or output
on multiple file descriptors.
* Synchronizing I/O:: Making sure all I/O actions completed.
* Asynchronous I/O:: Perform I/O in parallel.
* Control Operations:: Various other operations on file
descriptors.
* Duplicating Descriptors:: Fcntl commands for duplicating
file descriptors.
* Descriptor Flags:: Fcntl commands for manipulating
flags associated with file
descriptors.
* File Status Flags:: Fcntl commands for manipulating
flags associated with open files.
* File Locks:: Fcntl commands for implementing
file locking.
* Interrupt Input:: Getting an asynchronous signal when
input arrives.
* IOCTLs:: Generic I/O Control operations.
@end menu
@node Opening and Closing Files
@section Opening and Closing Files
@cindex opening a file descriptor
@cindex closing a file descriptor
This section describes the primitives for opening and closing files
using file descriptors. The @code{open} and @code{creat} functions are
declared in the header file @file{fcntl.h}, while @code{close} is
declared in @file{unistd.h}.
@pindex unistd.h
@pindex fcntl.h
@comment fcntl.h
@comment POSIX.1
@deftypefun int open (const char *@var{filename}, int @var{flags}[, mode_t @var{mode}])
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
The @code{open} function creates and returns a new file descriptor for
the file named by @var{filename}. Initially, the file position
indicator for the file is at the beginning of the file. The argument
@var{mode} (@pxref{Permission Bits}) is used only when a file is
created, but it doesn't hurt to supply the argument in any case.
The @var{flags} argument controls how the file is to be opened. This is
a bit mask; you create the value by the bitwise OR of the appropriate
parameters (using the @samp{|} operator in C).
@xref{File Status Flags}, for the parameters available.
The normal return value from @code{open} is a non-negative integer file
descriptor. In the case of an error, a value of @math{-1} is returned
instead. In addition to the usual file name errors (@pxref{File
Name Errors}), the following @code{errno} error conditions are defined
for this function:
@table @code
@item EACCES
The file exists but is not readable/writable as requested by the @var{flags}
argument, the file does not exist and the directory is unwritable so
it cannot be created.
@item EEXIST
Both @code{O_CREAT} and @code{O_EXCL} are set, and the named file already
exists.
@item EINTR
The @code{open} operation was interrupted by a signal.
@xref{Interrupted Primitives}.
@item EISDIR
The @var{flags} argument specified write access, and the file is a directory.
@item EMFILE
The process has too many files open.
The maximum number of file descriptors is controlled by the
@code{RLIMIT_NOFILE} resource limit; @pxref{Limits on Resources}.
@item ENFILE
The entire system, or perhaps the file system which contains the
directory, cannot support any additional open files at the moment.
(This problem cannot happen on @gnuhurdsystems{}.)
@item ENOENT
The named file does not exist, and @code{O_CREAT} is not specified.
@item ENOSPC
The directory or file system that would contain the new file cannot be
extended, because there is no disk space left.
@item ENXIO
@code{O_NONBLOCK} and @code{O_WRONLY} are both set in the @var{flags}
argument, the file named by @var{filename} is a FIFO (@pxref{Pipes and
FIFOs}), and no process has the file open for reading.
@item EROFS
The file resides on a read-only file system and any of @w{@code{O_WRONLY}},
@code{O_RDWR}, and @code{O_TRUNC} are set in the @var{flags} argument,
or @code{O_CREAT} is set and the file does not already exist.
@end table
@c !!! umask
If on a 32 bit machine the sources are translated with
@code{_FILE_OFFSET_BITS == 64} the function @code{open} returns a file
descriptor opened in the large file mode which enables the file handling
functions to use files up to @math{2^63} bytes in size and offset from
@math{-2^63} to @math{2^63}. This happens transparently for the user
since all of the lowlevel file handling functions are equally replaced.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{open} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{open} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{open} function is the underlying primitive for the @code{fopen}
and @code{freopen} functions, that create streams.
@end deftypefun
@comment fcntl.h
@comment Unix98
@deftypefun int open64 (const char *@var{filename}, int @var{flags}[, mode_t @var{mode}])
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function is similar to @code{open}. It returns a file descriptor
which can be used to access the file named by @var{filename}. The only
difference is that on 32 bit systems the file is opened in the
large file mode. I.e., file length and file offsets can exceed 31 bits.
When the sources are translated with @code{_FILE_OFFSET_BITS == 64} this
function is actually available under the name @code{open}. I.e., the
new, extended API using 64 bit file sizes and offsets transparently
replaces the old API.
@end deftypefun
@comment fcntl.h
@comment POSIX.1
@deftypefn {Obsolete function} int creat (const char *@var{filename}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function is obsolete. The call:
@smallexample
creat (@var{filename}, @var{mode})
@end smallexample
@noindent
is equivalent to:
@smallexample
open (@var{filename}, O_WRONLY | O_CREAT | O_TRUNC, @var{mode})
@end smallexample
If on a 32 bit machine the sources are translated with
@code{_FILE_OFFSET_BITS == 64} the function @code{creat} returns a file
descriptor opened in the large file mode which enables the file handling
functions to use files up to @math{2^63} in size and offset from
@math{-2^63} to @math{2^63}. This happens transparently for the user
since all of the lowlevel file handling functions are equally replaced.
@end deftypefn
@comment fcntl.h
@comment Unix98
@deftypefn {Obsolete function} int creat64 (const char *@var{filename}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function is similar to @code{creat}. It returns a file descriptor
which can be used to access the file named by @var{filename}. The only
the difference is that on 32 bit systems the file is opened in the
large file mode. I.e., file length and file offsets can exceed 31 bits.
To use this file descriptor one must not use the normal operations but
instead the counterparts named @code{*64}, e.g., @code{read64}.
When the sources are translated with @code{_FILE_OFFSET_BITS == 64} this
function is actually available under the name @code{open}. I.e., the
new, extended API using 64 bit file sizes and offsets transparently
replaces the old API.
@end deftypefn
@comment unistd.h
@comment POSIX.1
@deftypefun int close (int @var{filedes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
The function @code{close} closes the file descriptor @var{filedes}.
Closing a file has the following consequences:
@itemize @bullet
@item
The file descriptor is deallocated.
@item
Any record locks owned by the process on the file are unlocked.
@item
When all file descriptors associated with a pipe or FIFO have been closed,
any unread data is discarded.
@end itemize
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{close} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this, calls to @code{close} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The normal return value from @code{close} is @math{0}; a value of @math{-1}
is returned in case of failure. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINTR
The @code{close} call was interrupted by a signal.
@xref{Interrupted Primitives}.
Here is an example of how to handle @code{EINTR} properly:
@smallexample
TEMP_FAILURE_RETRY (close (desc));
@end smallexample
@item ENOSPC
@itemx EIO
@itemx EDQUOT
When the file is accessed by NFS, these errors from @code{write} can sometimes
not be detected until @code{close}. @xref{I/O Primitives}, for details
on their meaning.
@end table
Please note that there is @emph{no} separate @code{close64} function.
This is not necessary since this function does not determine nor depend
on the mode of the file. The kernel which performs the @code{close}
operation knows which mode the descriptor is used for and can handle
this situation.
@end deftypefun
To close a stream, call @code{fclose} (@pxref{Closing Streams}) instead
of trying to close its underlying file descriptor with @code{close}.
This flushes any buffered output and updates the stream object to
indicate that it is closed.
@node I/O Primitives
@section Input and Output Primitives
This section describes the functions for performing primitive input and
output operations on file descriptors: @code{read}, @code{write}, and
@code{lseek}. These functions are declared in the header file
@file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftp {Data Type} ssize_t
This data type is used to represent the sizes of blocks that can be
read or written in a single operation. It is similar to @code{size_t},
but must be a signed type.
@end deftp
@cindex reading from a file descriptor
@comment unistd.h
@comment POSIX.1
@deftypefun ssize_t read (int @var{filedes}, void *@var{buffer}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{read} function reads up to @var{size} bytes from the file
with descriptor @var{filedes}, storing the results in the @var{buffer}.
(This is not necessarily a character string, and no terminating null
character is added.)
@cindex end-of-file, on a file descriptor
The return value is the number of bytes actually read. This might be
less than @var{size}; for example, if there aren't that many bytes left
in the file or if there aren't that many bytes immediately available.
The exact behavior depends on what kind of file it is. Note that
reading less than @var{size} bytes is not an error.
A value of zero indicates end-of-file (except if the value of the
@var{size} argument is also zero). This is not considered an error.
If you keep calling @code{read} while at end-of-file, it will keep
returning zero and doing nothing else.
If @code{read} returns at least one character, there is no way you can
tell whether end-of-file was reached. But if you did reach the end, the
next read will return zero.
In case of an error, @code{read} returns @math{-1}. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EAGAIN
Normally, when no input is immediately available, @code{read} waits for
some input. But if the @code{O_NONBLOCK} flag is set for the file
(@pxref{File Status Flags}), @code{read} returns immediately without
reading any data, and reports this error.
@strong{Compatibility Note:} Most versions of BSD Unix use a different
error code for this: @code{EWOULDBLOCK}. In @theglibc{},
@code{EWOULDBLOCK} is an alias for @code{EAGAIN}, so it doesn't matter
which name you use.
On some systems, reading a large amount of data from a character special
file can also fail with @code{EAGAIN} if the kernel cannot find enough
physical memory to lock down the user's pages. This is limited to
devices that transfer with direct memory access into the user's memory,
which means it does not include terminals, since they always use
separate buffers inside the kernel. This problem never happens on
@gnuhurdsystems{}.
Any condition that could result in @code{EAGAIN} can instead result in a
successful @code{read} which returns fewer bytes than requested.
Calling @code{read} again immediately would result in @code{EAGAIN}.
@item EBADF
The @var{filedes} argument is not a valid file descriptor,
or is not open for reading.
@item EINTR
@code{read} was interrupted by a signal while it was waiting for input.
@xref{Interrupted Primitives}. A signal will not necessary cause
@code{read} to return @code{EINTR}; it may instead result in a
successful @code{read} which returns fewer bytes than requested.
@item EIO
For many devices, and for disk files, this error code indicates
a hardware error.
@code{EIO} also occurs when a background process tries to read from the
controlling terminal, and the normal action of stopping the process by
sending it a @code{SIGTTIN} signal isn't working. This might happen if
the signal is being blocked or ignored, or because the process group is
orphaned. @xref{Job Control}, for more information about job control,
and @ref{Signal Handling}, for information about signals.
@item EINVAL
In some systems, when reading from a character or block device, position
and size offsets must be aligned to a particular block size. This error
indicates that the offsets were not properly aligned.
@end table
Please note that there is no function named @code{read64}. This is not
necessary since this function does not directly modify or handle the
possibly wide file offset. Since the kernel handles this state
internally, the @code{read} function can be used for all cases.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{read} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this, calls to @code{read} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{read} function is the underlying primitive for all of the
functions that read from streams, such as @code{fgetc}.
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun ssize_t pread (int @var{filedes}, void *@var{buffer}, size_t @var{size}, off_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is usually a safe syscall. The sysdeps/posix fallback emulation
@c is not MT-Safe because it uses lseek, read and lseek back, but is it
@c used anywhere?
The @code{pread} function is similar to the @code{read} function. The
first three arguments are identical, and the return values and error
codes also correspond.
The difference is the fourth argument and its handling. The data block
is not read from the current position of the file descriptor
@code{filedes}. Instead the data is read from the file starting at
position @var{offset}. The position of the file descriptor itself is
not affected by the operation. The value is the same as before the call.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{pread} function is in fact @code{pread64} and the type
@code{off_t} has 64 bits, which makes it possible to handle files up to
@math{2^63} bytes in length.
The return value of @code{pread} describes the number of bytes read.
In the error case it returns @math{-1} like @code{read} does and the
error codes are also the same, with these additions:
@table @code
@item EINVAL
The value given for @var{offset} is negative and therefore illegal.
@item ESPIPE
The file descriptor @var{filedes} is associate with a pipe or a FIFO and
this device does not allow positioning of the file pointer.
@end table
The function is an extension defined in the Unix Single Specification
version 2.
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun ssize_t pread64 (int @var{filedes}, void *@var{buffer}, size_t @var{size}, off64_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is usually a safe syscall. The sysdeps/posix fallback emulation
@c is not MT-Safe because it uses lseek64, read and lseek64 back, but is
@c it used anywhere?
This function is similar to the @code{pread} function. The difference
is that the @var{offset} parameter is of type @code{off64_t} instead of
@code{off_t} which makes it possible on 32 bit machines to address
files larger than @math{2^31} bytes and up to @math{2^63} bytes. The
file descriptor @code{filedes} must be opened using @code{open64} since
otherwise the large offsets possible with @code{off64_t} will lead to
errors with a descriptor in small file mode.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is actually available under the name
@code{pread} and so transparently replaces the 32 bit interface.
@end deftypefun
@cindex writing to a file descriptor
@comment unistd.h
@comment POSIX.1
@deftypefun ssize_t write (int @var{filedes}, const void *@var{buffer}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{write} function writes up to @var{size} bytes from
@var{buffer} to the file with descriptor @var{filedes}. The data in
@var{buffer} is not necessarily a character string and a null character is
output like any other character.
The return value is the number of bytes actually written. This may be
@var{size}, but can always be smaller. Your program should always call
@code{write} in a loop, iterating until all the data is written.
Once @code{write} returns, the data is enqueued to be written and can be
read back right away, but it is not necessarily written out to permanent
storage immediately. You can use @code{fsync} when you need to be sure
your data has been permanently stored before continuing. (It is more
efficient for the system to batch up consecutive writes and do them all
at once when convenient. Normally they will always be written to disk
within a minute or less.) Modern systems provide another function
@code{fdatasync} which guarantees integrity only for the file data and
is therefore faster.
@c !!! xref fsync, fdatasync
You can use the @code{O_FSYNC} open mode to make @code{write} always
store the data to disk before returning; @pxref{Operating Modes}.
In the case of an error, @code{write} returns @math{-1}. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EAGAIN
Normally, @code{write} blocks until the write operation is complete.
But if the @code{O_NONBLOCK} flag is set for the file (@pxref{Control
Operations}), it returns immediately without writing any data and
reports this error. An example of a situation that might cause the
process to block on output is writing to a terminal device that supports
flow control, where output has been suspended by receipt of a STOP
character.
@strong{Compatibility Note:} Most versions of BSD Unix use a different
error code for this: @code{EWOULDBLOCK}. In @theglibc{},
@code{EWOULDBLOCK} is an alias for @code{EAGAIN}, so it doesn't matter
which name you use.
On some systems, writing a large amount of data from a character special
file can also fail with @code{EAGAIN} if the kernel cannot find enough
physical memory to lock down the user's pages. This is limited to
devices that transfer with direct memory access into the user's memory,
which means it does not include terminals, since they always use
separate buffers inside the kernel. This problem does not arise on
@gnuhurdsystems{}.
@item EBADF
The @var{filedes} argument is not a valid file descriptor,
or is not open for writing.
@item EFBIG
The size of the file would become larger than the implementation can support.
@item EINTR
The @code{write} operation was interrupted by a signal while it was
blocked waiting for completion. A signal will not necessarily cause
@code{write} to return @code{EINTR}; it may instead result in a
successful @code{write} which writes fewer bytes than requested.
@xref{Interrupted Primitives}.
@item EIO
For many devices, and for disk files, this error code indicates
a hardware error.
@item ENOSPC
The device containing the file is full.
@item EPIPE
This error is returned when you try to write to a pipe or FIFO that
isn't open for reading by any process. When this happens, a @code{SIGPIPE}
signal is also sent to the process; see @ref{Signal Handling}.
@item EINVAL
In some systems, when writing to a character or block device, position
and size offsets must be aligned to a particular block size. This error
indicates that the offsets were not properly aligned.
@end table
Unless you have arranged to prevent @code{EINTR} failures, you should
check @code{errno} after each failing call to @code{write}, and if the
error was @code{EINTR}, you should simply repeat the call.
@xref{Interrupted Primitives}. The easy way to do this is with the
macro @code{TEMP_FAILURE_RETRY}, as follows:
@smallexample
nbytes = TEMP_FAILURE_RETRY (write (desc, buffer, count));
@end smallexample
Please note that there is no function named @code{write64}. This is not
necessary since this function does not directly modify or handle the
possibly wide file offset. Since the kernel handles this state
internally the @code{write} function can be used for all cases.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{write} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this, calls to @code{write} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{write} function is the underlying primitive for all of the
functions that write to streams, such as @code{fputc}.
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun ssize_t pwrite (int @var{filedes}, const void *@var{buffer}, size_t @var{size}, off_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is usually a safe syscall. The sysdeps/posix fallback emulation
@c is not MT-Safe because it uses lseek, write and lseek back, but is it
@c used anywhere?
The @code{pwrite} function is similar to the @code{write} function. The
first three arguments are identical, and the return values and error codes
also correspond.
The difference is the fourth argument and its handling. The data block
is not written to the current position of the file descriptor
@code{filedes}. Instead the data is written to the file starting at
position @var{offset}. The position of the file descriptor itself is
not affected by the operation. The value is the same as before the call.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{pwrite} function is in fact @code{pwrite64} and the type
@code{off_t} has 64 bits, which makes it possible to handle files up to
@math{2^63} bytes in length.
The return value of @code{pwrite} describes the number of written bytes.
In the error case it returns @math{-1} like @code{write} does and the
error codes are also the same, with these additions:
@table @code
@item EINVAL
The value given for @var{offset} is negative and therefore illegal.
@item ESPIPE
The file descriptor @var{filedes} is associated with a pipe or a FIFO and
this device does not allow positioning of the file pointer.
@end table
The function is an extension defined in the Unix Single Specification
version 2.
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun ssize_t pwrite64 (int @var{filedes}, const void *@var{buffer}, size_t @var{size}, off64_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is usually a safe syscall. The sysdeps/posix fallback emulation
@c is not MT-Safe because it uses lseek64, write and lseek64 back, but
@c is it used anywhere?
This function is similar to the @code{pwrite} function. The difference
is that the @var{offset} parameter is of type @code{off64_t} instead of
@code{off_t} which makes it possible on 32 bit machines to address
files larger than @math{2^31} bytes and up to @math{2^63} bytes. The
file descriptor @code{filedes} must be opened using @code{open64} since
otherwise the large offsets possible with @code{off64_t} will lead to
errors with a descriptor in small file mode.
When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is actually available under the name
@code{pwrite} and so transparently replaces the 32 bit interface.
@end deftypefun
@node File Position Primitive
@section Setting the File Position of a Descriptor
Just as you can set the file position of a stream with @code{fseek}, you
can set the file position of a descriptor with @code{lseek}. This
specifies the position in the file for the next @code{read} or
@code{write} operation. @xref{File Positioning}, for more information
on the file position and what it means.
To read the current file position value from a descriptor, use
@code{lseek (@var{desc}, 0, SEEK_CUR)}.
@cindex file positioning on a file descriptor
@cindex positioning a file descriptor
@cindex seeking on a file descriptor
@comment unistd.h
@comment POSIX.1
@deftypefun off_t lseek (int @var{filedes}, off_t @var{offset}, int @var{whence})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{lseek} function is used to change the file position of the
file with descriptor @var{filedes}.
The @var{whence} argument specifies how the @var{offset} should be
interpreted, in the same way as for the @code{fseek} function, and it must
be one of the symbolic constants @code{SEEK_SET}, @code{SEEK_CUR}, or
@code{SEEK_END}.
@table @code
@item SEEK_SET
Specifies that @var{offset} is a count of characters from the beginning
of the file.
@item SEEK_CUR
Specifies that @var{offset} is a count of characters from the current
file position. This count may be positive or negative.
@item SEEK_END
Specifies that @var{offset} is a count of characters from the end of
the file. A negative count specifies a position within the current
extent of the file; a positive count specifies a position past the
current end. If you set the position past the current end, and
actually write data, you will extend the file with zeros up to that
position.
@end table
The return value from @code{lseek} is normally the resulting file
position, measured in bytes from the beginning of the file.
You can use this feature together with @code{SEEK_CUR} to read the
current file position.
If you want to append to the file, setting the file position to the
current end of file with @code{SEEK_END} is not sufficient. Another
process may write more data after you seek but before you write,
extending the file so the position you write onto clobbers their data.
Instead, use the @code{O_APPEND} operating mode; @pxref{Operating Modes}.
You can set the file position past the current end of the file. This
does not by itself make the file longer; @code{lseek} never changes the
file. But subsequent output at that position will extend the file.
Characters between the previous end of file and the new position are
filled with zeros. Extending the file in this way can create a
``hole'': the blocks of zeros are not actually allocated on disk, so the
file takes up less space than it appears to; it is then called a
``sparse file''.
@cindex sparse files
@cindex holes in files
If the file position cannot be changed, or the operation is in some way
invalid, @code{lseek} returns a value of @math{-1}. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} is not a valid file descriptor.
@item EINVAL
The @var{whence} argument value is not valid, or the resulting
file offset is not valid. A file offset is invalid.
@item ESPIPE
The @var{filedes} corresponds to an object that cannot be positioned,
such as a pipe, FIFO or terminal device. (POSIX.1 specifies this error
only for pipes and FIFOs, but on @gnusystems{}, you always get
@code{ESPIPE} if the object is not seekable.)
@end table
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{lseek} function is in fact @code{lseek64} and the type
@code{off_t} has 64 bits which makes it possible to handle files up to
@math{2^63} bytes in length.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{lseek} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{lseek} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The @code{lseek} function is the underlying primitive for the
@code{fseek}, @code{fseeko}, @code{ftell}, @code{ftello} and
@code{rewind} functions, which operate on streams instead of file
descriptors.
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun off64_t lseek64 (int @var{filedes}, off64_t @var{offset}, int @var{whence})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to the @code{lseek} function. The difference
is that the @var{offset} parameter is of type @code{off64_t} instead of
@code{off_t} which makes it possible on 32 bit machines to address
files larger than @math{2^31} bytes and up to @math{2^63} bytes. The
file descriptor @code{filedes} must be opened using @code{open64} since
otherwise the large offsets possible with @code{off64_t} will lead to
errors with a descriptor in small file mode.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bits machine this function is actually available under the name
@code{lseek} and so transparently replaces the 32 bit interface.
@end deftypefun
You can have multiple descriptors for the same file if you open the file
more than once, or if you duplicate a descriptor with @code{dup}.
Descriptors that come from separate calls to @code{open} have independent
file positions; using @code{lseek} on one descriptor has no effect on the
other. For example,
@smallexample
@group
@{
int d1, d2;
char buf[4];
d1 = open ("foo", O_RDONLY);
d2 = open ("foo", O_RDONLY);
lseek (d1, 1024, SEEK_SET);
read (d2, buf, 4);
@}
@end group
@end smallexample
@noindent
will read the first four characters of the file @file{foo}. (The
error-checking code necessary for a real program has been omitted here
for brevity.)
By contrast, descriptors made by duplication share a common file
position with the original descriptor that was duplicated. Anything
which alters the file position of one of the duplicates, including
reading or writing data, affects all of them alike. Thus, for example,
@smallexample
@{
int d1, d2, d3;
char buf1[4], buf2[4];
d1 = open ("foo", O_RDONLY);
d2 = dup (d1);
d3 = dup (d2);
lseek (d3, 1024, SEEK_SET);
read (d1, buf1, 4);
read (d2, buf2, 4);
@}
@end smallexample
@noindent
will read four characters starting with the 1024'th character of
@file{foo}, and then four more characters starting with the 1028'th
character.
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} off_t
This is a signed integer type used to represent file sizes. In
@theglibc{}, this type is no narrower than @code{int}.
If the source is compiled with @code{_FILE_OFFSET_BITS == 64} this type
is transparently replaced by @code{off64_t}.
@end deftp
@comment sys/types.h
@comment Unix98
@deftp {Data Type} off64_t
This type is used similar to @code{off_t}. The difference is that even
on 32 bit machines, where the @code{off_t} type would have 32 bits,
@code{off64_t} has 64 bits and so is able to address files up to
@math{2^63} bytes in length.
When compiling with @code{_FILE_OFFSET_BITS == 64} this type is
available under the name @code{off_t}.
@end deftp
These aliases for the @samp{SEEK_@dots{}} constants exist for the sake
of compatibility with older BSD systems. They are defined in two
different header files: @file{fcntl.h} and @file{sys/file.h}.
@table @code
@item L_SET
An alias for @code{SEEK_SET}.
@item L_INCR
An alias for @code{SEEK_CUR}.
@item L_XTND
An alias for @code{SEEK_END}.
@end table
@node Descriptors and Streams
@section Descriptors and Streams
@cindex streams, and file descriptors
@cindex converting file descriptor to stream
@cindex extracting file descriptor from stream
Given an open file descriptor, you can create a stream for it with the
@code{fdopen} function. You can get the underlying file descriptor for
an existing stream with the @code{fileno} function. These functions are
declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment POSIX.1
@deftypefun {FILE *} fdopen (int @var{filedes}, const char *@var{opentype})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @aculock{}}}
The @code{fdopen} function returns a new stream for the file descriptor
@var{filedes}.
The @var{opentype} argument is interpreted in the same way as for the
@code{fopen} function (@pxref{Opening Streams}), except that
the @samp{b} option is not permitted; this is because @gnusystems{} make no
distinction between text and binary files. Also, @code{"w"} and
@code{"w+"} do not cause truncation of the file; these have an effect only
when opening a file, and in this case the file has already been opened.
You must make sure that the @var{opentype} argument matches the actual
mode of the open file descriptor.
The return value is the new stream. If the stream cannot be created
(for example, if the modes for the file indicated by the file descriptor
do not permit the access specified by the @var{opentype} argument), a
null pointer is returned instead.
In some other systems, @code{fdopen} may fail to detect that the modes
for file descriptor do not permit the access specified by
@code{opentype}. @Theglibc{} always checks for this.
@end deftypefun
For an example showing the use of the @code{fdopen} function,
see @ref{Creating a Pipe}.
@comment stdio.h
@comment POSIX.1
@deftypefun int fileno (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns the file descriptor associated with the stream
@var{stream}. If an error is detected (for example, if the @var{stream}
is not valid) or if @var{stream} does not do I/O to a file,
@code{fileno} returns @math{-1}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int fileno_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fileno_unlocked} function is equivalent to the @code{fileno}
function except that it does not implicitly lock the stream if the state
is @code{FSETLOCKING_INTERNAL}.
This function is a GNU extension.
@end deftypefun
@cindex standard file descriptors
@cindex file descriptors, standard
There are also symbolic constants defined in @file{unistd.h} for the
file descriptors belonging to the standard streams @code{stdin},
@code{stdout}, and @code{stderr}; see @ref{Standard Streams}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@table @code
@item STDIN_FILENO
@vindex STDIN_FILENO
This macro has value @code{0}, which is the file descriptor for
standard input.
@cindex standard input file descriptor
@comment unistd.h
@comment POSIX.1
@item STDOUT_FILENO
@vindex STDOUT_FILENO
This macro has value @code{1}, which is the file descriptor for
standard output.
@cindex standard output file descriptor
@comment unistd.h
@comment POSIX.1
@item STDERR_FILENO
@vindex STDERR_FILENO
This macro has value @code{2}, which is the file descriptor for
standard error output.
@end table
@cindex standard error file descriptor
@node Stream/Descriptor Precautions
@section Dangers of Mixing Streams and Descriptors
@cindex channels
@cindex streams and descriptors
@cindex descriptors and streams
@cindex mixing descriptors and streams
You can have multiple file descriptors and streams (let's call both
streams and descriptors ``channels'' for short) connected to the same
file, but you must take care to avoid confusion between channels. There
are two cases to consider: @dfn{linked} channels that share a single
file position value, and @dfn{independent} channels that have their own
file positions.
It's best to use just one channel in your program for actual data
transfer to any given file, except when all the access is for input.
For example, if you open a pipe (something you can only do at the file
descriptor level), either do all I/O with the descriptor, or construct a
stream from the descriptor with @code{fdopen} and then do all I/O with
the stream.
@menu
* Linked Channels:: Dealing with channels sharing a file position.
* Independent Channels:: Dealing with separately opened, unlinked channels.
* Cleaning Streams:: Cleaning a stream makes it safe to use
another channel.
@end menu
@node Linked Channels
@subsection Linked Channels
@cindex linked channels
Channels that come from a single opening share the same file position;
we call them @dfn{linked} channels. Linked channels result when you
make a stream from a descriptor using @code{fdopen}, when you get a
descriptor from a stream with @code{fileno}, when you copy a descriptor
with @code{dup} or @code{dup2}, and when descriptors are inherited
during @code{fork}. For files that don't support random access, such as
terminals and pipes, @emph{all} channels are effectively linked. On
random-access files, all append-type output streams are effectively
linked to each other.
@cindex cleaning up a stream
If you have been using a stream for I/O (or have just opened the stream),
and you want to do I/O using
another channel (either a stream or a descriptor) that is linked to it,
you must first @dfn{clean up} the stream that you have been using.
@xref{Cleaning Streams}.
Terminating a process, or executing a new program in the process,
destroys all the streams in the process. If descriptors linked to these
streams persist in other processes, their file positions become
undefined as a result. To prevent this, you must clean up the streams
before destroying them.
@node Independent Channels
@subsection Independent Channels
@cindex independent channels
When you open channels (streams or descriptors) separately on a seekable
file, each channel has its own file position. These are called
@dfn{independent channels}.
The system handles each channel independently. Most of the time, this
is quite predictable and natural (especially for input): each channel
can read or write sequentially at its own place in the file. However,
if some of the channels are streams, you must take these precautions:
@itemize @bullet
@item
You should clean an output stream after use, before doing anything else
that might read or write from the same part of the file.
@item
You should clean an input stream before reading data that may have been
modified using an independent channel. Otherwise, you might read
obsolete data that had been in the stream's buffer.
@end itemize
If you do output to one channel at the end of the file, this will
certainly leave the other independent channels positioned somewhere
before the new end. You cannot reliably set their file positions to the
new end of file before writing, because the file can always be extended
by another process between when you set the file position and when you
write the data. Instead, use an append-type descriptor or stream; they
always output at the current end of the file. In order to make the
end-of-file position accurate, you must clean the output channel you
were using, if it is a stream.
It's impossible for two channels to have separate file pointers for a
file that doesn't support random access. Thus, channels for reading or
writing such files are always linked, never independent. Append-type
channels are also always linked. For these channels, follow the rules
for linked channels; see @ref{Linked Channels}.
@node Cleaning Streams
@subsection Cleaning Streams
You can use @code{fflush} to clean a stream in most
cases.
You can skip the @code{fflush} if you know the stream
is already clean. A stream is clean whenever its buffer is empty. For
example, an unbuffered stream is always clean. An input stream that is
at end-of-file is clean. A line-buffered stream is clean when the last
character output was a newline. However, a just-opened input stream
might not be clean, as its input buffer might not be empty.
There is one case in which cleaning a stream is impossible on most
systems. This is when the stream is doing input from a file that is not
random-access. Such streams typically read ahead, and when the file is
not random access, there is no way to give back the excess data already
read. When an input stream reads from a random-access file,
@code{fflush} does clean the stream, but leaves the file pointer at an
unpredictable place; you must set the file pointer before doing any
further I/O.
Closing an output-only stream also does @code{fflush}, so this is a
valid way of cleaning an output stream.
You need not clean a stream before using its descriptor for control
operations such as setting terminal modes; these operations don't affect
the file position and are not affected by it. You can use any
descriptor for these operations, and all channels are affected
simultaneously. However, text already ``output'' to a stream but still
buffered by the stream will be subject to the new terminal modes when
subsequently flushed. To make sure ``past'' output is covered by the
terminal settings that were in effect at the time, flush the output
streams for that terminal before setting the modes. @xref{Terminal
Modes}.
@node Scatter-Gather
@section Fast Scatter-Gather I/O
@cindex scatter-gather
Some applications may need to read or write data to multiple buffers,
which are separated in memory. Although this can be done easily enough
with multiple calls to @code{read} and @code{write}, it is inefficient
because there is overhead associated with each kernel call.
Instead, many platforms provide special high-speed primitives to perform
these @dfn{scatter-gather} operations in a single kernel call. @Theglibc{}
will provide an emulation on any system that lacks these
primitives, so they are not a portability threat. They are defined in
@code{sys/uio.h}.
These functions are controlled with arrays of @code{iovec} structures,
which describe the location and size of each buffer.
@comment sys/uio.h
@comment BSD
@deftp {Data Type} {struct iovec}
The @code{iovec} structure describes a buffer. It contains two fields:
@table @code
@item void *iov_base
Contains the address of a buffer.
@item size_t iov_len
Contains the length of the buffer.
@end table
@end deftp
@comment sys/uio.h
@comment BSD
@deftypefun ssize_t readv (int @var{filedes}, const struct iovec *@var{vector}, int @var{count})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c The fallback sysdeps/posix implementation, used even on GNU/Linux
@c with old kernels that lack a full readv/writev implementation, may
@c malloc the buffer into which data is read, if the total read size is
@c too large for alloca.
The @code{readv} function reads data from @var{filedes} and scatters it
into the buffers described in @var{vector}, which is taken to be
@var{count} structures long. As each buffer is filled, data is sent to the
next.
Note that @code{readv} is not guaranteed to fill all the buffers.
It may stop at any point, for the same reasons @code{read} would.
The return value is a count of bytes (@emph{not} buffers) read, @math{0}
indicating end-of-file, or @math{-1} indicating an error. The possible
errors are the same as in @code{read}.
@end deftypefun
@comment sys/uio.h
@comment BSD
@deftypefun ssize_t writev (int @var{filedes}, const struct iovec *@var{vector}, int @var{count})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c The fallback sysdeps/posix implementation, used even on GNU/Linux
@c with old kernels that lack a full readv/writev implementation, may
@c malloc the buffer from which data is written, if the total write size
@c is too large for alloca.
The @code{writev} function gathers data from the buffers described in
@var{vector}, which is taken to be @var{count} structures long, and writes
them to @code{filedes}. As each buffer is written, it moves on to the
next.
Like @code{readv}, @code{writev} may stop midstream under the same
conditions @code{write} would.
The return value is a count of bytes written, or @math{-1} indicating an
error. The possible errors are the same as in @code{write}.
@end deftypefun
@c Note - I haven't read this anywhere. I surmised it from my knowledge
@c of computer science. Thus, there could be subtleties I'm missing.
Note that if the buffers are small (under about 1kB), high-level streams
may be easier to use than these functions. However, @code{readv} and
@code{writev} are more efficient when the individual buffers themselves
(as opposed to the total output), are large. In that case, a high-level
stream would not be able to cache the data effectively.
@node Memory-mapped I/O
@section Memory-mapped I/O
On modern operating systems, it is possible to @dfn{mmap} (pronounced
``em-map'') a file to a region of memory. When this is done, the file can
be accessed just like an array in the program.
This is more efficient than @code{read} or @code{write}, as only the regions
of the file that a program actually accesses are loaded. Accesses to
not-yet-loaded parts of the mmapped region are handled in the same way as
swapped out pages.
Since mmapped pages can be stored back to their file when physical
memory is low, it is possible to mmap files orders of magnitude larger
than both the physical memory @emph{and} swap space. The only limit is
address space. The theoretical limit is 4GB on a 32-bit machine -
however, the actual limit will be smaller since some areas will be
reserved for other purposes. If the LFS interface is used the file size
on 32-bit systems is not limited to 2GB (offsets are signed which
reduces the addressable area of 4GB by half); the full 64-bit are
available.
Memory mapping only works on entire pages of memory. Thus, addresses
for mapping must be page-aligned, and length values will be rounded up.
To determine the size of a page the machine uses one should use
@vindex _SC_PAGESIZE
@smallexample
size_t page_size = (size_t) sysconf (_SC_PAGESIZE);
@end smallexample
@noindent
These functions are declared in @file{sys/mman.h}.
@comment sys/mman.h
@comment POSIX
@deftypefun {void *} mmap (void *@var{address}, size_t @var{length}, int @var{protect}, int @var{flags}, int @var{filedes}, off_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{mmap} function creates a new mapping, connected to bytes
(@var{offset}) to (@var{offset} + @var{length} - 1) in the file open on
@var{filedes}. A new reference for the file specified by @var{filedes}
is created, which is not removed by closing the file.
@var{address} gives a preferred starting address for the mapping.
@code{NULL} expresses no preference. Any previous mapping at that
address is automatically removed. The address you give may still be
changed, unless you use the @code{MAP_FIXED} flag.
@vindex PROT_READ
@vindex PROT_WRITE
@vindex PROT_EXEC
@var{protect} contains flags that control what kind of access is
permitted. They include @code{PROT_READ}, @code{PROT_WRITE}, and
@code{PROT_EXEC}, which permit reading, writing, and execution,
respectively. Inappropriate access will cause a segfault (@pxref{Program
Error Signals}).
Note that most hardware designs cannot support write permission without
read permission, and many do not distinguish read and execute permission.
Thus, you may receive wider permissions than you ask for, and mappings of
write-only files may be denied even if you do not use @code{PROT_READ}.
@var{flags} contains flags that control the nature of the map.
One of @code{MAP_SHARED} or @code{MAP_PRIVATE} must be specified.
They include:
@vtable @code
@item MAP_PRIVATE
This specifies that writes to the region should never be written back
to the attached file. Instead, a copy is made for the process, and the
region will be swapped normally if memory runs low. No other process will
see the changes.
Since private mappings effectively revert to ordinary memory
when written to, you must have enough virtual memory for a copy of
the entire mmapped region if you use this mode with @code{PROT_WRITE}.
@item MAP_SHARED
This specifies that writes to the region will be written back to the
file. Changes made will be shared immediately with other processes
mmaping the same file.
Note that actual writing may take place at any time. You need to use
@code{msync}, described below, if it is important that other processes
using conventional I/O get a consistent view of the file.
@item MAP_FIXED
This forces the system to use the exact mapping address specified in
@var{address} and fail if it can't.
@c One of these is official - the other is obviously an obsolete synonym
@c Which is which?
@item MAP_ANONYMOUS
@itemx MAP_ANON
This flag tells the system to create an anonymous mapping, not connected
to a file. @var{filedes} and @var{off} are ignored, and the region is
initialized with zeros.
Anonymous maps are used as the basic primitive to extend the heap on some
systems. They are also useful to share data between multiple tasks
without creating a file.
On some systems using private anonymous mmaps is more efficient than using
@code{malloc} for large blocks. This is not an issue with @theglibc{},
as the included @code{malloc} automatically uses @code{mmap} where appropriate.
@c Linux has some other MAP_ options, which I have not discussed here.
@c MAP_DENYWRITE, MAP_EXECUTABLE and MAP_GROWSDOWN don't seem applicable to
@c user programs (and I don't understand the last two). MAP_LOCKED does
@c not appear to be implemented.
@end vtable
@code{mmap} returns the address of the new mapping, or
@code{MAP_FAILED} for an error.
Possible errors include:
@table @code
@item EINVAL
Either @var{address} was unusable, or inconsistent @var{flags} were
given.
@item EACCES
@var{filedes} was not open for the type of access specified in @var{protect}.
@item ENOMEM
Either there is not enough memory for the operation, or the process is
out of address space.
@item ENODEV
This file is of a type that doesn't support mapping.
@item ENOEXEC
The file is on a filesystem that doesn't support mapping.
@c On Linux, EAGAIN will appear if the file has a conflicting mandatory lock.
@c However mandatory locks are not discussed in this manual.
@c
@c Similarly, ETXTBSY will occur if the MAP_DENYWRITE flag (not documented
@c here) is used and the file is already open for writing.
@end table
@end deftypefun
@comment sys/mman.h
@comment LFS
@deftypefun {void *} mmap64 (void *@var{address}, size_t @var{length}, int @var{protect}, int @var{flags}, int @var{filedes}, off64_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c The page_shift auto detection when MMAP2_PAGE_SHIFT is -1 (it never
@c is) would be thread-unsafe.
The @code{mmap64} function is equivalent to the @code{mmap} function but
the @var{offset} parameter is of type @code{off64_t}. On 32-bit systems
this allows the file associated with the @var{filedes} descriptor to be
larger than 2GB. @var{filedes} must be a descriptor returned from a
call to @code{open64} or @code{fopen64} and @code{freopen64} where the
descriptor is retrieved with @code{fileno}.
When the sources are translated with @code{_FILE_OFFSET_BITS == 64} this
function is actually available under the name @code{mmap}. I.e., the
new, extended API using 64 bit file sizes and offsets transparently
replaces the old API.
@end deftypefun
@comment sys/mman.h
@comment POSIX
@deftypefun int munmap (void *@var{addr}, size_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{munmap} removes any memory maps from (@var{addr}) to (@var{addr} +
@var{length}). @var{length} should be the length of the mapping.
It is safe to unmap multiple mappings in one command, or include unmapped
space in the range. It is also possible to unmap only part of an existing
mapping. However, only entire pages can be removed. If @var{length} is not
an even number of pages, it will be rounded up.
It returns @math{0} for success and @math{-1} for an error.
One error is possible:
@table @code
@item EINVAL
The memory range given was outside the user mmap range or wasn't page
aligned.
@end table
@end deftypefun
@comment sys/mman.h
@comment POSIX
@deftypefun int msync (void *@var{address}, size_t @var{length}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
When using shared mappings, the kernel can write the file at any time
before the mapping is removed. To be certain data has actually been
written to the file and will be accessible to non-memory-mapped I/O, it
is necessary to use this function.
It operates on the region @var{address} to (@var{address} + @var{length}).
It may be used on part of a mapping or multiple mappings, however the
region given should not contain any unmapped space.
@var{flags} can contain some options:
@vtable @code
@item MS_SYNC
This flag makes sure the data is actually written @emph{to disk}.
Normally @code{msync} only makes sure that accesses to a file with
conventional I/O reflect the recent changes.
@item MS_ASYNC
This tells @code{msync} to begin the synchronization, but not to wait for
it to complete.
@c Linux also has MS_INVALIDATE, which I don't understand.
@end vtable
@code{msync} returns @math{0} for success and @math{-1} for
error. Errors include:
@table @code
@item EINVAL
An invalid region was given, or the @var{flags} were invalid.
@item EFAULT
There is no existing mapping in at least part of the given region.
@end table
@end deftypefun
@comment sys/mman.h
@comment GNU
@deftypefun {void *} mremap (void *@var{address}, size_t @var{length}, size_t @var{new_length}, int @var{flag})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function can be used to change the size of an existing memory
area. @var{address} and @var{length} must cover a region entirely mapped
in the same @code{mmap} statement. A new mapping with the same
characteristics will be returned with the length @var{new_length}.
One option is possible, @code{MREMAP_MAYMOVE}. If it is given in
@var{flags}, the system may remove the existing mapping and create a new
one of the desired length in another location.
The address of the resulting mapping is returned, or @math{-1}. Possible
error codes include:
@table @code
@item EFAULT
There is no existing mapping in at least part of the original region, or
the region covers two or more distinct mappings.
@item EINVAL
The address given is misaligned or inappropriate.
@item EAGAIN
The region has pages locked, and if extended it would exceed the
process's resource limit for locked pages. @xref{Limits on Resources}.
@item ENOMEM
The region is private writable, and insufficient virtual memory is
available to extend it. Also, this error will occur if
@code{MREMAP_MAYMOVE} is not given and the extension would collide with
another mapped region.
@end table
@end deftypefun
This function is only available on a few systems. Except for performing
optional optimizations one should not rely on this function.
Not all file descriptors may be mapped. Sockets, pipes, and most devices
only allow sequential access and do not fit into the mapping abstraction.
In addition, some regular files may not be mmapable, and older kernels may
not support mapping at all. Thus, programs using @code{mmap} should
have a fallback method to use should it fail. @xref{Mmap,,,standards,GNU
Coding Standards}.
@comment sys/mman.h
@comment POSIX
@deftypefun int madvise (void *@var{addr}, size_t @var{length}, int @var{advice})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function can be used to provide the system with @var{advice} about
the intended usage patterns of the memory region starting at @var{addr}
and extending @var{length} bytes.
The valid BSD values for @var{advice} are:
@table @code
@item MADV_NORMAL
The region should receive no further special treatment.
@item MADV_RANDOM
The region will be accessed via random page references. The kernel
should page-in the minimal number of pages for each page fault.
@item MADV_SEQUENTIAL
The region will be accessed via sequential page references. This
may cause the kernel to aggressively read-ahead, expecting further
sequential references after any page fault within this region.
@item MADV_WILLNEED
The region will be needed. The pages within this region may
be pre-faulted in by the kernel.
@item MADV_DONTNEED
The region is no longer needed. The kernel may free these pages,
causing any changes to the pages to be lost, as well as swapped
out pages to be discarded.
@end table
The POSIX names are slightly different, but with the same meanings:
@table @code
@item POSIX_MADV_NORMAL
This corresponds with BSD's @code{MADV_NORMAL}.
@item POSIX_MADV_RANDOM
This corresponds with BSD's @code{MADV_RANDOM}.
@item POSIX_MADV_SEQUENTIAL
This corresponds with BSD's @code{MADV_SEQUENTIAL}.
@item POSIX_MADV_WILLNEED
This corresponds with BSD's @code{MADV_WILLNEED}.
@item POSIX_MADV_DONTNEED
This corresponds with BSD's @code{MADV_DONTNEED}.
@end table
@code{madvise} returns @math{0} for success and @math{-1} for
error. Errors include:
@table @code
@item EINVAL
An invalid region was given, or the @var{advice} was invalid.
@item EFAULT
There is no existing mapping in at least part of the given region.
@end table
@end deftypefun
@comment sys/mman.h
@comment POSIX
@deftypefn Function int shm_open (const char *@var{name}, int @var{oflag}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asuinit{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c shm_open @mtslocale @asuinit @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_once(where_is_shmfs) @mtslocale @asuinit @ascuheap @asulock @aculock @acsmem @acsfd
@c where_is_shmfs @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c statfs dup ok
@c setmntent dup @ascuheap @asulock @acsmem @acsfd @aculock
@c getmntent_r dup @mtslocale @ascuheap @aculock @acsmem [no @asucorrupt @acucorrupt; exclusive stream]
@c strcmp dup ok
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c mempcpy dup ok
@c endmntent dup @ascuheap @asulock @aculock @acsmem @acsfd
@c strlen dup ok
@c strchr dup ok
@c mempcpy dup ok
@c open dup @acsfd
@c fcntl dup ok
@c close dup @acsfd
This function returns a file descriptor that can be used to allocate shared
memory via mmap. Unrelated processes can use same @var{name} to create or
open existing shared memory objects.
A @var{name} argument specifies the shared memory object to be opened.
In @theglibc{} it must be a string smaller than @code{NAME_MAX} bytes starting
with an optional slash but containing no other slashes.
The semantics of @var{oflag} and @var{mode} arguments is same as in @code{open}.
@code{shm_open} returns the file descriptor on success or @math{-1} on error.
On failure @code{errno} is set.
@end deftypefn
@deftypefn Function int shm_unlink (const char *@var{name})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asuinit{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c shm_unlink @mtslocale @asuinit @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_once(where_is_shmfs) dup @mtslocale @asuinit @ascuheap @asulock @aculock @acsmem @acsfd
@c strlen dup ok
@c strchr dup ok
@c mempcpy dup ok
@c unlink dup ok
This function is inverse of @code{shm_open} and removes the object with
the given @var{name} previously created by @code{shm_open}.
@code{shm_unlink} returns @math{0} on success or @math{-1} on error.
On failure @code{errno} is set.
@end deftypefn
@node Waiting for I/O
@section Waiting for Input or Output
@cindex waiting for input or output
@cindex multiplexing input
@cindex input from multiple files
Sometimes a program needs to accept input on multiple input channels
whenever input arrives. For example, some workstations may have devices
such as a digitizing tablet, function button box, or dial box that are
connected via normal asynchronous serial interfaces; good user interface
style requires responding immediately to input on any device. Another
example is a program that acts as a server to several other processes
via pipes or sockets.
You cannot normally use @code{read} for this purpose, because this
blocks the program until input is available on one particular file
descriptor; input on other channels won't wake it up. You could set
nonblocking mode and poll each file descriptor in turn, but this is very
inefficient.
A better solution is to use the @code{select} function. This blocks the
program until input or output is ready on a specified set of file
descriptors, or until a timer expires, whichever comes first. This
facility is declared in the header file @file{sys/types.h}.
@pindex sys/types.h
In the case of a server socket (@pxref{Listening}), we say that
``input'' is available when there are pending connections that could be
accepted (@pxref{Accepting Connections}). @code{accept} for server
sockets blocks and interacts with @code{select} just as @code{read} does
for normal input.
@cindex file descriptor sets, for @code{select}
The file descriptor sets for the @code{select} function are specified
as @code{fd_set} objects. Here is the description of the data type
and some macros for manipulating these objects.
@comment sys/types.h
@comment BSD
@deftp {Data Type} fd_set
The @code{fd_set} data type represents file descriptor sets for the
@code{select} function. It is actually a bit array.
@end deftp
@comment sys/types.h
@comment BSD
@deftypevr Macro int FD_SETSIZE
The value of this macro is the maximum number of file descriptors that a
@code{fd_set} object can hold information about. On systems with a
fixed maximum number, @code{FD_SETSIZE} is at least that number. On
some systems, including GNU, there is no absolute limit on the number of
descriptors open, but this macro still has a constant value which
controls the number of bits in an @code{fd_set}; if you get a file
descriptor with a value as high as @code{FD_SETSIZE}, you cannot put
that descriptor into an @code{fd_set}.
@end deftypevr
@comment sys/types.h
@comment BSD
@deftypefn Macro void FD_ZERO (fd_set *@var{set})
@safety{@prelim{}@mtsafe{@mtsrace{:set}}@assafe{}@acsafe{}}
This macro initializes the file descriptor set @var{set} to be the
empty set.
@end deftypefn
@comment sys/types.h
@comment BSD
@deftypefn Macro void FD_SET (int @var{filedes}, fd_set *@var{set})
@safety{@prelim{}@mtsafe{@mtsrace{:set}}@assafe{}@acsafe{}}
@c Setting a bit isn't necessarily atomic, so there's a potential race
@c here if set is not used exclusively.
This macro adds @var{filedes} to the file descriptor set @var{set}.
The @var{filedes} parameter must not have side effects since it is
evaluated more than once.
@end deftypefn
@comment sys/types.h
@comment BSD
@deftypefn Macro void FD_CLR (int @var{filedes}, fd_set *@var{set})
@safety{@prelim{}@mtsafe{@mtsrace{:set}}@assafe{}@acsafe{}}
@c Setting a bit isn't necessarily atomic, so there's a potential race
@c here if set is not used exclusively.
This macro removes @var{filedes} from the file descriptor set @var{set}.
The @var{filedes} parameter must not have side effects since it is
evaluated more than once.
@end deftypefn
@comment sys/types.h
@comment BSD
@deftypefn Macro int FD_ISSET (int @var{filedes}, const fd_set *@var{set})
@safety{@prelim{}@mtsafe{@mtsrace{:set}}@assafe{}@acsafe{}}
This macro returns a nonzero value (true) if @var{filedes} is a member
of the file descriptor set @var{set}, and zero (false) otherwise.
The @var{filedes} parameter must not have side effects since it is
evaluated more than once.
@end deftypefn
Next, here is the description of the @code{select} function itself.
@comment sys/types.h
@comment BSD
@deftypefun int select (int @var{nfds}, fd_set *@var{read-fds}, fd_set *@var{write-fds}, fd_set *@var{except-fds}, struct timeval *@var{timeout})
@safety{@prelim{}@mtsafe{@mtsrace{:read-fds} @mtsrace{:write-fds} @mtsrace{:except-fds}}@assafe{}@acsafe{}}
@c The select syscall is preferred, but pselect6 may be used instead,
@c which requires converting timeout to a timespec and back. The
@c conversions are not atomic.
The @code{select} function blocks the calling process until there is
activity on any of the specified sets of file descriptors, or until the
timeout period has expired.
The file descriptors specified by the @var{read-fds} argument are
checked to see if they are ready for reading; the @var{write-fds} file
descriptors are checked to see if they are ready for writing; and the
@var{except-fds} file descriptors are checked for exceptional
conditions. You can pass a null pointer for any of these arguments if
you are not interested in checking for that kind of condition.
A file descriptor is considered ready for reading if a @code{read}
call will not block. This usually includes the read offset being at
the end of the file or there is an error to report. A server socket
is considered ready for reading if there is a pending connection which
can be accepted with @code{accept}; @pxref{Accepting Connections}. A
client socket is ready for writing when its connection is fully
established; @pxref{Connecting}.
``Exceptional conditions'' does not mean errors---errors are reported
immediately when an erroneous system call is executed, and do not
constitute a state of the descriptor. Rather, they include conditions
such as the presence of an urgent message on a socket. (@xref{Sockets},
for information on urgent messages.)
The @code{select} function checks only the first @var{nfds} file
descriptors. The usual thing is to pass @code{FD_SETSIZE} as the value
of this argument.
The @var{timeout} specifies the maximum time to wait. If you pass a
null pointer for this argument, it means to block indefinitely until one
of the file descriptors is ready. Otherwise, you should provide the
time in @code{struct timeval} format; see @ref{High-Resolution
Calendar}. Specify zero as the time (a @code{struct timeval} containing
all zeros) if you want to find out which descriptors are ready without
waiting if none are ready.
The normal return value from @code{select} is the total number of ready file
descriptors in all of the sets. Each of the argument sets is overwritten
with information about the descriptors that are ready for the corresponding
operation. Thus, to see if a particular descriptor @var{desc} has input,
use @code{FD_ISSET (@var{desc}, @var{read-fds})} after @code{select} returns.
If @code{select} returns because the timeout period expires, it returns
a value of zero.
Any signal will cause @code{select} to return immediately. So if your
program uses signals, you can't rely on @code{select} to keep waiting
for the full time specified. If you want to be sure of waiting for a
particular amount of time, you must check for @code{EINTR} and repeat
the @code{select} with a newly calculated timeout based on the current
time. See the example below. See also @ref{Interrupted Primitives}.
If an error occurs, @code{select} returns @code{-1} and does not modify
the argument file descriptor sets. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EBADF
One of the file descriptor sets specified an invalid file descriptor.
@item EINTR
The operation was interrupted by a signal. @xref{Interrupted Primitives}.
@item EINVAL
The @var{timeout} argument is invalid; one of the components is negative
or too large.
@end table
@end deftypefun
@strong{Portability Note:} The @code{select} function is a BSD Unix
feature.
Here is an example showing how you can use @code{select} to establish a
timeout period for reading from a file descriptor. The @code{input_timeout}
function blocks the calling process until input is available on the
file descriptor, or until the timeout period expires.
@smallexample
@include select.c.texi
@end smallexample
There is another example showing the use of @code{select} to multiplex
input from multiple sockets in @ref{Server Example}.
@node Synchronizing I/O
@section Synchronizing I/O operations
@cindex synchronizing
In most modern operating systems, the normal I/O operations are not
executed synchronously. I.e., even if a @code{write} system call
returns, this does not mean the data is actually written to the media,
e.g., the disk.
In situations where synchronization points are necessary, you can use
special functions which ensure that all operations finish before
they return.
@comment unistd.h
@comment X/Open
@deftypefun void sync (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
A call to this function will not return as long as there is data which
has not been written to the device. All dirty buffers in the kernel will
be written and so an overall consistent system can be achieved (if no
other process in parallel writes data).
A prototype for @code{sync} can be found in @file{unistd.h}.
@end deftypefun
Programs more often want to ensure that data written to a given file is
committed, rather than all data in the system. For this, @code{sync} is overkill.
@comment unistd.h
@comment POSIX
@deftypefun int fsync (int @var{fildes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fsync} function can be used to make sure all data associated with
the open file @var{fildes} is written to the device associated with the
descriptor. The function call does not return unless all actions have
finished.
A prototype for @code{fsync} can be found in @file{unistd.h}.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{fsync} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this, calls to @code{fsync} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The return value of the function is zero if no error occurred. Otherwise
it is @math{-1} and the global variable @var{errno} is set to the
following values:
@table @code
@item EBADF
The descriptor @var{fildes} is not valid.
@item EINVAL
No synchronization is possible since the system does not implement this.
@end table
@end deftypefun
Sometimes it is not even necessary to write all data associated with a
file descriptor. E.g., in database files which do not change in size it
is enough to write all the file content data to the device.
Meta-information, like the modification time etc., are not that important
and leaving such information uncommitted does not prevent a successful
recovering of the file in case of a problem.
@comment unistd.h
@comment POSIX
@deftypefun int fdatasync (int @var{fildes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
When a call to the @code{fdatasync} function returns, it is ensured
that all of the file data is written to the device. For all pending I/O
operations, the parts guaranteeing data integrity finished.
Not all systems implement the @code{fdatasync} operation. On systems
missing this functionality @code{fdatasync} is emulated by a call to
@code{fsync} since the performed actions are a superset of those
required by @code{fdatasync}.
The prototype for @code{fdatasync} is in @file{unistd.h}.
The return value of the function is zero if no error occurred. Otherwise
it is @math{-1} and the global variable @var{errno} is set to the
following values:
@table @code
@item EBADF
The descriptor @var{fildes} is not valid.
@item EINVAL
No synchronization is possible since the system does not implement this.
@end table
@end deftypefun
@node Asynchronous I/O
@section Perform I/O Operations in Parallel
The POSIX.1b standard defines a new set of I/O operations which can
significantly reduce the time an application spends waiting at I/O. The
new functions allow a program to initiate one or more I/O operations and
then immediately resume normal work while the I/O operations are
executed in parallel. This functionality is available if the
@file{unistd.h} file defines the symbol @code{_POSIX_ASYNCHRONOUS_IO}.
These functions are part of the library with realtime functions named
@file{librt}. They are not actually part of the @file{libc} binary.
The implementation of these functions can be done using support in the
kernel (if available) or using an implementation based on threads at
userlevel. In the latter case it might be necessary to link applications
with the thread library @file{libpthread} in addition to @file{librt}.
All AIO operations operate on files which were opened previously. There
might be arbitrarily many operations running for one file. The
asynchronous I/O operations are controlled using a data structure named
@code{struct aiocb} (@dfn{AIO control block}). It is defined in
@file{aio.h} as follows.
@comment aio.h
@comment POSIX.1b
@deftp {Data Type} {struct aiocb}
The POSIX.1b standard mandates that the @code{struct aiocb} structure
contains at least the members described in the following table. There
might be more elements which are used by the implementation, but
depending upon these elements is not portable and is highly deprecated.
@table @code
@item int aio_fildes
This element specifies the file descriptor to be used for the
operation. It must be a legal descriptor, otherwise the operation will
fail.
The device on which the file is opened must allow the seek operation.
I.e., it is not possible to use any of the AIO operations on devices
like terminals where an @code{lseek} call would lead to an error.
@item off_t aio_offset
This element specifies the offset in the file at which the operation (input
or output) is performed. Since the operations are carried out in arbitrary
order and more than one operation for one file descriptor can be
started, one cannot expect a current read/write position of the file
descriptor.
@item volatile void *aio_buf
This is a pointer to the buffer with the data to be written or the place
where the read data is stored.
@item size_t aio_nbytes
This element specifies the length of the buffer pointed to by @code{aio_buf}.
@item int aio_reqprio
If the platform has defined @code{_POSIX_PRIORITIZED_IO} and
@code{_POSIX_PRIORITY_SCHEDULING}, the AIO requests are
processed based on the current scheduling priority. The
@code{aio_reqprio} element can then be used to lower the priority of the
AIO operation.
@item struct sigevent aio_sigevent
This element specifies how the calling process is notified once the
operation terminates. If the @code{sigev_notify} element is
@code{SIGEV_NONE}, no notification is sent. If it is @code{SIGEV_SIGNAL},
the signal determined by @code{sigev_signo} is sent. Otherwise,
@code{sigev_notify} must be @code{SIGEV_THREAD}. In this case, a thread
is created which starts executing the function pointed to by
@code{sigev_notify_function}.
@item int aio_lio_opcode
This element is only used by the @code{lio_listio} and
@code{lio_listio64} functions. Since these functions allow an
arbitrary number of operations to start at once, and each operation can be
input or output (or nothing), the information must be stored in the
control block. The possible values are:
@vtable @code
@item LIO_READ
Start a read operation. Read from the file at position
@code{aio_offset} and store the next @code{aio_nbytes} bytes in the
buffer pointed to by @code{aio_buf}.
@item LIO_WRITE
Start a write operation. Write @code{aio_nbytes} bytes starting at
@code{aio_buf} into the file starting at position @code{aio_offset}.
@item LIO_NOP
Do nothing for this control block. This value is useful sometimes when
an array of @code{struct aiocb} values contains holes, i.e., some of the
values must not be handled although the whole array is presented to the
@code{lio_listio} function.
@end vtable
@end table
When the sources are compiled using @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine, this type is in fact @code{struct aiocb64}, since the LFS
interface transparently replaces the @code{struct aiocb} definition.
@end deftp
For use with the AIO functions defined in the LFS, there is a similar type
defined which replaces the types of the appropriate members with larger
types but otherwise is equivalent to @code{struct aiocb}. Particularly,
all member names are the same.
@comment aio.h
@comment POSIX.1b
@deftp {Data Type} {struct aiocb64}
@table @code
@item int aio_fildes
This element specifies the file descriptor which is used for the
operation. It must be a legal descriptor since otherwise the operation
fails for obvious reasons.
The device on which the file is opened must allow the seek operation.
I.e., it is not possible to use any of the AIO operations on devices
like terminals where an @code{lseek} call would lead to an error.
@item off64_t aio_offset
This element specifies at which offset in the file the operation (input
or output) is performed. Since the operation are carried in arbitrary
order and more than one operation for one file descriptor can be
started, one cannot expect a current read/write position of the file
descriptor.
@item volatile void *aio_buf
This is a pointer to the buffer with the data to be written or the place
where the read data is stored.
@item size_t aio_nbytes
This element specifies the length of the buffer pointed to by @code{aio_buf}.
@item int aio_reqprio
If for the platform @code{_POSIX_PRIORITIZED_IO} and
@code{_POSIX_PRIORITY_SCHEDULING} are defined the AIO requests are
processed based on the current scheduling priority. The
@code{aio_reqprio} element can then be used to lower the priority of the
AIO operation.
@item struct sigevent aio_sigevent
This element specifies how the calling process is notified once the
operation terminates. If the @code{sigev_notify}, element is
@code{SIGEV_NONE} no notification is sent. If it is @code{SIGEV_SIGNAL},
the signal determined by @code{sigev_signo} is sent. Otherwise,
@code{sigev_notify} must be @code{SIGEV_THREAD} in which case a thread
which starts executing the function pointed to by
@code{sigev_notify_function}.
@item int aio_lio_opcode
This element is only used by the @code{lio_listio} and
@code{[lio_listio64} functions. Since these functions allow an
arbitrary number of operations to start at once, and since each operation can be
input or output (or nothing), the information must be stored in the
control block. See the description of @code{struct aiocb} for a description
of the possible values.
@end table
When the sources are compiled using @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine, this type is available under the name @code{struct
aiocb64}, since the LFS transparently replaces the old interface.
@end deftp
@menu
* Asynchronous Reads/Writes:: Asynchronous Read and Write Operations.
* Status of AIO Operations:: Getting the Status of AIO Operations.
* Synchronizing AIO Operations:: Getting into a consistent state.
* Cancel AIO Operations:: Cancellation of AIO Operations.
* Configuration of AIO:: How to optimize the AIO implementation.
@end menu
@node Asynchronous Reads/Writes
@subsection Asynchronous Read and Write Operations
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_read (struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c Calls aio_enqueue_request.
@c aio_enqueue_request @asulock @ascuheap @aculock @acsmem
@c pthread_self ok
@c pthread_getschedparam @asulock @aculock
@c lll_lock (pthread descriptor's lock) @asulock @aculock
@c sched_getparam ok
@c sched_getscheduler ok
@c lll_unlock @aculock
@c pthread_mutex_lock (aio_requests_mutex) @asulock @aculock
@c get_elem @ascuheap @acsmem [@asucorrupt @acucorrupt]
@c realloc @ascuheap @acsmem
@c calloc @ascuheap @acsmem
@c aio_create_helper_thread @asulock @ascuheap @aculock @acsmem
@c pthread_attr_init ok
@c pthread_attr_setdetachstate ok
@c pthread_get_minstack ok
@c pthread_attr_setstacksize ok
@c sigfillset ok
@c memset ok
@c sigdelset ok
@c SYSCALL rt_sigprocmask ok
@c pthread_create @asulock @ascuheap @aculock @acsmem
@c lll_lock (default_pthread_attr_lock) @asulock @aculock
@c alloca/malloc @ascuheap @acsmem
@c lll_unlock @aculock
@c allocate_stack @asulock @ascuheap @aculock @acsmem
@c getpagesize dup
@c lll_lock (default_pthread_attr_lock) @asulock @aculock
@c lll_unlock @aculock
@c _dl_allocate_tls @ascuheap @acsmem
@c _dl_allocate_tls_storage @ascuheap @acsmem
@c memalign @ascuheap @acsmem
@c memset ok
@c allocate_dtv dup
@c free @ascuheap @acsmem
@c allocate_dtv @ascuheap @acsmem
@c calloc @ascuheap @acsmem
@c INSTALL_DTV ok
@c list_add dup
@c get_cached_stack
@c lll_lock (stack_cache_lock) @asulock @aculock
@c list_for_each ok
@c list_entry dup
@c FREE_P dup
@c stack_list_del dup
@c stack_list_add dup
@c lll_unlock @aculock
@c _dl_allocate_tls_init ok
@c GET_DTV ok
@c mmap ok
@c atomic_increment_val ok
@c munmap ok
@c change_stack_perm ok
@c mprotect ok
@c mprotect ok
@c stack_list_del dup
@c _dl_deallocate_tls dup
@c munmap ok
@c THREAD_COPY_STACK_GUARD ok
@c THREAD_COPY_POINTER_GUARD ok
@c atomic_exchange_acq ok
@c lll_futex_wake ok
@c deallocate_stack @asulock @ascuheap @aculock @acsmem
@c lll_lock (state_cache_lock) @asulock @aculock
@c stack_list_del ok
@c atomic_write_barrier ok
@c list_del ok
@c atomic_write_barrier ok
@c queue_stack @ascuheap @acsmem
@c stack_list_add ok
@c atomic_write_barrier ok
@c list_add ok
@c atomic_write_barrier ok
@c free_stacks @ascuheap @acsmem
@c list_for_each_prev_safe ok
@c list_entry ok
@c FREE_P ok
@c stack_list_del dup
@c _dl_deallocate_tls dup
@c munmap ok
@c _dl_deallocate_tls @ascuheap @acsmem
@c free @ascuheap @acsmem
@c lll_unlock @aculock
@c create_thread @asulock @ascuheap @aculock @acsmem
@c td_eventword
@c td_eventmask
@c do_clone @asulock @ascuheap @aculock @acsmem
@c PREPARE_CREATE ok
@c lll_lock (pd->lock) @asulock @aculock
@c atomic_increment ok
@c clone ok
@c atomic_decrement ok
@c atomic_exchange_acq ok
@c lll_futex_wake ok
@c deallocate_stack dup
@c sched_setaffinity ok
@c tgkill ok
@c sched_setscheduler ok
@c atomic_compare_and_exchange_bool_acq ok
@c nptl_create_event ok
@c lll_unlock (pd->lock) @aculock
@c free @ascuheap @acsmem
@c pthread_attr_destroy ok (cpuset won't be set, so free isn't called)
@c add_request_to_runlist ok
@c pthread_cond_signal ok
@c aio_free_request ok
@c pthread_mutex_unlock @aculock
@c (in the new thread, initiated with clone)
@c start_thread ok
@c HP_TIMING_NOW ok
@c ctype_init @mtslocale
@c atomic_exchange_acq ok
@c lll_futex_wake ok
@c sigemptyset ok
@c sigaddset ok
@c setjmp ok
@c CANCEL_ASYNC -> pthread_enable_asynccancel ok
@c do_cancel ok
@c pthread_unwind ok
@c Unwind_ForcedUnwind or longjmp ok [@ascuheap @acsmem?]
@c lll_lock @asulock @aculock
@c lll_unlock @asulock @aculock
@c CANCEL_RESET -> pthread_disable_asynccancel ok
@c lll_futex_wait ok
@c ->start_routine ok -----
@c call_tls_dtors @asulock @ascuheap @aculock @acsmem
@c user-supplied dtor
@c rtld_lock_lock_recursive (dl_load_lock) @asulock @aculock
@c rtld_lock_unlock_recursive @aculock
@c free @ascuheap @acsmem
@c nptl_deallocate_tsd @ascuheap @acsmem
@c tsd user-supplied dtors ok
@c free @ascuheap @acsmem
@c libc_thread_freeres
@c libc_thread_subfreeres ok
@c atomic_decrement_and_test ok
@c td_eventword ok
@c td_eventmask ok
@c atomic_compare_exchange_bool_acq ok
@c nptl_death_event ok
@c lll_robust_dead ok
@c getpagesize ok
@c madvise ok
@c free_tcb @asulock @ascuheap @aculock @acsmem
@c free @ascuheap @acsmem
@c deallocate_stack @asulock @ascuheap @aculock @acsmem
@c lll_futex_wait ok
@c exit_thread_inline ok
@c syscall(exit) ok
This function initiates an asynchronous read operation. It
immediately returns after the operation was enqueued or when an
error was encountered.
The first @code{aiocbp->aio_nbytes} bytes of the file for which
@code{aiocbp->aio_fildes} is a descriptor are written to the buffer
starting at @code{aiocbp->aio_buf}. Reading starts at the absolute
position @code{aiocbp->aio_offset} in the file.
If prioritized I/O is supported by the platform the
@code{aiocbp->aio_reqprio} value is used to adjust the priority before
the request is actually enqueued.
The calling process is notified about the termination of the read
request according to the @code{aiocbp->aio_sigevent} value.
When @code{aio_read} returns, the return value is zero if no error
occurred that can be found before the process is enqueued. If such an
early error is found, the function returns @math{-1} and sets
@code{errno} to one of the following values:
@table @code
@item EAGAIN
The request was not enqueued due to (temporarily) exceeded resource
limitations.
@item ENOSYS
The @code{aio_read} function is not implemented.
@item EBADF
The @code{aiocbp->aio_fildes} descriptor is not valid. This condition
need not be recognized before enqueueing the request and so this error
might also be signaled asynchronously.
@item EINVAL
The @code{aiocbp->aio_offset} or @code{aiocbp->aio_reqpiro} value is
invalid. This condition need not be recognized before enqueueing the
request and so this error might also be signaled asynchronously.
@end table
If @code{aio_read} returns zero, the current status of the request
can be queried using @code{aio_error} and @code{aio_return} functions.
As long as the value returned by @code{aio_error} is @code{EINPROGRESS}
the operation has not yet completed. If @code{aio_error} returns zero,
the operation successfully terminated, otherwise the value is to be
interpreted as an error code. If the function terminated, the result of
the operation can be obtained using a call to @code{aio_return}. The
returned value is the same as an equivalent call to @code{read} would
have returned. Possible error codes returned by @code{aio_error} are:
@table @code
@item EBADF
The @code{aiocbp->aio_fildes} descriptor is not valid.
@item ECANCELED
The operation was canceled before the operation was finished
(@pxref{Cancel AIO Operations})
@item EINVAL
The @code{aiocbp->aio_offset} value is invalid.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{aio_read64} since the LFS interface transparently
replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_read64 (struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function is similar to the @code{aio_read} function. The only
difference is that on @w{32 bit} machines, the file descriptor should
be opened in the large file mode. Internally, @code{aio_read64} uses
functionality equivalent to @code{lseek64} (@pxref{File Position
Primitive}) to position the file descriptor correctly for the reading,
as opposed to @code{lseek} functionality used in @code{aio_read}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is available under the name @code{aio_read} and so transparently
replaces the interface for small files on 32 bit machines.
@end deftypefun
To write data asynchronously to a file, there exists an equivalent pair
of functions with a very similar interface.
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_write (struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function initiates an asynchronous write operation. The function
call immediately returns after the operation was enqueued or if before
this happens an error was encountered.
The first @code{aiocbp->aio_nbytes} bytes from the buffer starting at
@code{aiocbp->aio_buf} are written to the file for which
@code{aiocbp->aio_fildes} is a descriptor, starting at the absolute
position @code{aiocbp->aio_offset} in the file.
If prioritized I/O is supported by the platform, the
@code{aiocbp->aio_reqprio} value is used to adjust the priority before
the request is actually enqueued.
The calling process is notified about the termination of the read
request according to the @code{aiocbp->aio_sigevent} value.
When @code{aio_write} returns, the return value is zero if no error
occurred that can be found before the process is enqueued. If such an
early error is found the function returns @math{-1} and sets
@code{errno} to one of the following values.
@table @code
@item EAGAIN
The request was not enqueued due to (temporarily) exceeded resource
limitations.
@item ENOSYS
The @code{aio_write} function is not implemented.
@item EBADF
The @code{aiocbp->aio_fildes} descriptor is not valid. This condition
may not be recognized before enqueueing the request, and so this error
might also be signaled asynchronously.
@item EINVAL
The @code{aiocbp->aio_offset} or @code{aiocbp->aio_reqprio} value is
invalid. This condition may not be recognized before enqueueing the
request and so this error might also be signaled asynchronously.
@end table
In the case @code{aio_write} returns zero, the current status of the
request can be queried using @code{aio_error} and @code{aio_return}
functions. As long as the value returned by @code{aio_error} is
@code{EINPROGRESS} the operation has not yet completed. If
@code{aio_error} returns zero, the operation successfully terminated,
otherwise the value is to be interpreted as an error code. If the
function terminated, the result of the operation can be get using a call
to @code{aio_return}. The returned value is the same as an equivalent
call to @code{read} would have returned. Possible error codes returned
by @code{aio_error} are:
@table @code
@item EBADF
The @code{aiocbp->aio_fildes} descriptor is not valid.
@item ECANCELED
The operation was canceled before the operation was finished.
(@pxref{Cancel AIO Operations})
@item EINVAL
The @code{aiocbp->aio_offset} value is invalid.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is in fact @code{aio_write64} since the LFS interface transparently
replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_write64 (struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function is similar to the @code{aio_write} function. The only
difference is that on @w{32 bit} machines the file descriptor should
be opened in the large file mode. Internally @code{aio_write64} uses
functionality equivalent to @code{lseek64} (@pxref{File Position
Primitive}) to position the file descriptor correctly for the writing,
as opposed to @code{lseek} functionality used in @code{aio_write}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is available under the name @code{aio_write} and so transparently
replaces the interface for small files on 32 bit machines.
@end deftypefun
Besides these functions with the more or less traditional interface,
POSIX.1b also defines a function which can initiate more than one
operation at a time, and which can handle freely mixed read and write
operations. It is therefore similar to a combination of @code{readv} and
@code{writev}.
@comment aio.h
@comment POSIX.1b
@deftypefun int lio_listio (int @var{mode}, struct aiocb *const @var{list}[], int @var{nent}, struct sigevent *@var{sig})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c Call lio_listio_internal, that takes the aio_requests_mutex lock and
@c enqueues each request. Then, it waits for notification or prepares
@c for it before releasing the lock. Even though it performs memory
@c allocation and locking of its own, it doesn't add any classes of
@c safety issues that aren't already covered by aio_enqueue_request.
The @code{lio_listio} function can be used to enqueue an arbitrary
number of read and write requests at one time. The requests can all be
meant for the same file, all for different files or every solution in
between.
@code{lio_listio} gets the @var{nent} requests from the array pointed to
by @var{list}. The operation to be performed is determined by the
@code{aio_lio_opcode} member in each element of @var{list}. If this
field is @code{LIO_READ} a read operation is enqueued, similar to a call
of @code{aio_read} for this element of the array (except that the way
the termination is signalled is different, as we will see below). If
the @code{aio_lio_opcode} member is @code{LIO_WRITE} a write operation
is enqueued. Otherwise the @code{aio_lio_opcode} must be @code{LIO_NOP}
in which case this element of @var{list} is simply ignored. This
``operation'' is useful in situations where one has a fixed array of
@code{struct aiocb} elements from which only a few need to be handled at
a time. Another situation is where the @code{lio_listio} call was
canceled before all requests are processed (@pxref{Cancel AIO
Operations}) and the remaining requests have to be reissued.
The other members of each element of the array pointed to by
@code{list} must have values suitable for the operation as described in
the documentation for @code{aio_read} and @code{aio_write} above.
The @var{mode} argument determines how @code{lio_listio} behaves after
having enqueued all the requests. If @var{mode} is @code{LIO_WAIT} it
waits until all requests terminated. Otherwise @var{mode} must be
@code{LIO_NOWAIT} and in this case the function returns immediately after
having enqueued all the requests. In this case the caller gets a
notification of the termination of all requests according to the
@var{sig} parameter. If @var{sig} is @code{NULL} no notification is
send. Otherwise a signal is sent or a thread is started, just as
described in the description for @code{aio_read} or @code{aio_write}.
If @var{mode} is @code{LIO_WAIT}, the return value of @code{lio_listio}
is @math{0} when all requests completed successfully. Otherwise the
function return @math{-1} and @code{errno} is set accordingly. To find
out which request or requests failed one has to use the @code{aio_error}
function on all the elements of the array @var{list}.
In case @var{mode} is @code{LIO_NOWAIT}, the function returns @math{0} if
all requests were enqueued correctly. The current state of the requests
can be found using @code{aio_error} and @code{aio_return} as described
above. If @code{lio_listio} returns @math{-1} in this mode, the
global variable @code{errno} is set accordingly. If a request did not
yet terminate, a call to @code{aio_error} returns @code{EINPROGRESS}. If
the value is different, the request is finished and the error value (or
@math{0}) is returned and the result of the operation can be retrieved
using @code{aio_return}.
Possible values for @code{errno} are:
@table @code
@item EAGAIN
The resources necessary to queue all the requests are not available at
the moment. The error status for each element of @var{list} must be
checked to determine which request failed.
Another reason could be that the system wide limit of AIO requests is
exceeded. This cannot be the case for the implementation on @gnusystems{}
since no arbitrary limits exist.
@item EINVAL
The @var{mode} parameter is invalid or @var{nent} is larger than
@code{AIO_LISTIO_MAX}.
@item EIO
One or more of the request's I/O operations failed. The error status of
each request should be checked to determine which one failed.
@item ENOSYS
The @code{lio_listio} function is not supported.
@end table
If the @var{mode} parameter is @code{LIO_NOWAIT} and the caller cancels
a request, the error status for this request returned by
@code{aio_error} is @code{ECANCELED}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is in fact @code{lio_listio64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int lio_listio64 (int @var{mode}, struct aiocb64 *const @var{list}[], int @var{nent}, struct sigevent *@var{sig})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function is similar to the @code{lio_listio} function. The only
difference is that on @w{32 bit} machines, the file descriptor should
be opened in the large file mode. Internally, @code{lio_listio64} uses
functionality equivalent to @code{lseek64} (@pxref{File Position
Primitive}) to position the file descriptor correctly for the reading or
writing, as opposed to @code{lseek} functionality used in
@code{lio_listio}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is available under the name @code{lio_listio} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
@node Status of AIO Operations
@subsection Getting the Status of AIO Operations
As already described in the documentation of the functions in the last
section, it must be possible to get information about the status of an I/O
request. When the operation is performed truly asynchronously (as with
@code{aio_read} and @code{aio_write} and with @code{lio_listio} when the
mode is @code{LIO_NOWAIT}), one sometimes needs to know whether a
specific request already terminated and if so, what the result was.
The following two functions allow you to get this kind of information.
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_error (const struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function determines the error state of the request described by the
@code{struct aiocb} variable pointed to by @var{aiocbp}. If the
request has not yet terminated the value returned is always
@code{EINPROGRESS}. Once the request has terminated the value
@code{aio_error} returns is either @math{0} if the request completed
successfully or it returns the value which would be stored in the
@code{errno} variable if the request would have been done using
@code{read}, @code{write}, or @code{fsync}.
The function can return @code{ENOSYS} if it is not implemented. It
could also return @code{EINVAL} if the @var{aiocbp} parameter does not
refer to an asynchronous operation whose return status is not yet known.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{aio_error64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_error64 (const struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{aio_error} with the only difference
that the argument is a reference to a variable of type @code{struct
aiocb64}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{aio_error} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
@comment aio.h
@comment POSIX.1b
@deftypefun ssize_t aio_return (struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function can be used to retrieve the return status of the operation
carried out by the request described in the variable pointed to by
@var{aiocbp}. As long as the error status of this request as returned
by @code{aio_error} is @code{EINPROGRESS} the return of this function is
undefined.
Once the request is finished this function can be used exactly once to
retrieve the return value. Following calls might lead to undefined
behavior. The return value itself is the value which would have been
returned by the @code{read}, @code{write}, or @code{fsync} call.
The function can return @code{ENOSYS} if it is not implemented. It
could also return @code{EINVAL} if the @var{aiocbp} parameter does not
refer to an asynchronous operation whose return status is not yet known.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{aio_return64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun ssize_t aio_return64 (struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{aio_return} with the only difference
that the argument is a reference to a variable of type @code{struct
aiocb64}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{aio_return} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
@node Synchronizing AIO Operations
@subsection Getting into a Consistent State
When dealing with asynchronous operations it is sometimes necessary to
get into a consistent state. This would mean for AIO that one wants to
know whether a certain request or a group of request were processed.
This could be done by waiting for the notification sent by the system
after the operation terminated, but this sometimes would mean wasting
resources (mainly computation time). Instead POSIX.1b defines two
functions which will help with most kinds of consistency.
The @code{aio_fsync} and @code{aio_fsync64} functions are only available
if the symbol @code{_POSIX_SYNCHRONIZED_IO} is defined in @file{unistd.h}.
@cindex synchronizing
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_fsync (int @var{op}, struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c After fcntl to check that the FD is open, it calls
@c aio_enqueue_request.
Calling this function forces all I/O operations operating queued at the
time of the function call operating on the file descriptor
@code{aiocbp->aio_fildes} into the synchronized I/O completion state
(@pxref{Synchronizing I/O}). The @code{aio_fsync} function returns
immediately but the notification through the method described in
@code{aiocbp->aio_sigevent} will happen only after all requests for this
file descriptor have terminated and the file is synchronized. This also
means that requests for this very same file descriptor which are queued
after the synchronization request are not affected.
If @var{op} is @code{O_DSYNC} the synchronization happens as with a call
to @code{fdatasync}. Otherwise @var{op} should be @code{O_SYNC} and
the synchronization happens as with @code{fsync}.
As long as the synchronization has not happened, a call to
@code{aio_error} with the reference to the object pointed to by
@var{aiocbp} returns @code{EINPROGRESS}. Once the synchronization is
done @code{aio_error} return @math{0} if the synchronization was not
successful. Otherwise the value returned is the value to which the
@code{fsync} or @code{fdatasync} function would have set the
@code{errno} variable. In this case nothing can be assumed about the
consistency for the data written to this file descriptor.
The return value of this function is @math{0} if the request was
successfully enqueued. Otherwise the return value is @math{-1} and
@code{errno} is set to one of the following values:
@table @code
@item EAGAIN
The request could not be enqueued due to temporary lack of resources.
@item EBADF
The file descriptor @code{@var{aiocbp}->aio_fildes} is not valid.
@item EINVAL
The implementation does not support I/O synchronization or the @var{op}
parameter is other than @code{O_DSYNC} and @code{O_SYNC}.
@item ENOSYS
This function is not implemented.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{aio_fsync64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_fsync64 (int @var{op}, struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function is similar to @code{aio_fsync} with the only difference
that the argument is a reference to a variable of type @code{struct
aiocb64}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{aio_fsync} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
Another method of synchronization is to wait until one or more requests of a
specific set terminated. This could be achieved by the @code{aio_*}
functions to notify the initiating process about the termination but in
some situations this is not the ideal solution. In a program which
constantly updates clients somehow connected to the server it is not
always the best solution to go round robin since some connections might
be slow. On the other hand letting the @code{aio_*} function notify the
caller might also be not the best solution since whenever the process
works on preparing data for on client it makes no sense to be
interrupted by a notification since the new client will not be handled
before the current client is served. For situations like this
@code{aio_suspend} should be used.
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_suspend (const struct aiocb *const @var{list}[], int @var{nent}, const struct timespec *@var{timeout})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Take aio_requests_mutex, set up waitlist and requestlist, wait
@c for completion or timeout, and release the mutex.
When calling this function, the calling thread is suspended until at
least one of the requests pointed to by the @var{nent} elements of the
array @var{list} has completed. If any of the requests has already
completed at the time @code{aio_suspend} is called, the function returns
immediately. Whether a request has terminated or not is determined by
comparing the error status of the request with @code{EINPROGRESS}. If
an element of @var{list} is @code{NULL}, the entry is simply ignored.
If no request has finished, the calling process is suspended. If
@var{timeout} is @code{NULL}, the process is not woken until a request
has finished. If @var{timeout} is not @code{NULL}, the process remains
suspended at least as long as specified in @var{timeout}. In this case,
@code{aio_suspend} returns with an error.
The return value of the function is @math{0} if one or more requests
from the @var{list} have terminated. Otherwise the function returns
@math{-1} and @code{errno} is set to one of the following values:
@table @code
@item EAGAIN
None of the requests from the @var{list} completed in the time specified
by @var{timeout}.
@item EINTR
A signal interrupted the @code{aio_suspend} function. This signal might
also be sent by the AIO implementation while signalling the termination
of one of the requests.
@item ENOSYS
The @code{aio_suspend} function is not implemented.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{aio_suspend64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_suspend64 (const struct aiocb64 *const @var{list}[], int @var{nent}, const struct timespec *@var{timeout})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
This function is similar to @code{aio_suspend} with the only difference
that the argument is a reference to a variable of type @code{struct
aiocb64}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{aio_suspend} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
@node Cancel AIO Operations
@subsection Cancellation of AIO Operations
When one or more requests are asynchronously processed, it might be
useful in some situations to cancel a selected operation, e.g., if it
becomes obvious that the written data is no longer accurate and would
have to be overwritten soon. As an example, assume an application, which
writes data in files in a situation where new incoming data would have
to be written in a file which will be updated by an enqueued request.
The POSIX AIO implementation provides such a function, but this function
is not capable of forcing the cancellation of the request. It is up to the
implementation to decide whether it is possible to cancel the operation
or not. Therefore using this function is merely a hint.
@comment aio.h
@comment POSIX.1b
@deftypefun int aio_cancel (int @var{fildes}, struct aiocb *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c After fcntl to check the fd is open, hold aio_requests_mutex, call
@c aio_find_req_fd, aio_remove_request, then aio_notify and
@c aio_free_request each request before releasing the lock.
@c aio_notify calls aio_notify_only and free, besides cond signal or
@c similar. aio_notify_only calls pthread_attr_init,
@c pthread_attr_setdetachstate, malloc, pthread_create,
@c notify_func_wrapper, aio_sigqueue, getpid, raise.
@c notify_func_wraper calls aio_start_notify_thread, free and then the
@c notifier function.
The @code{aio_cancel} function can be used to cancel one or more
outstanding requests. If the @var{aiocbp} parameter is @code{NULL}, the
function tries to cancel all of the outstanding requests which would process
the file descriptor @var{fildes} (i.e., whose @code{aio_fildes} member
is @var{fildes}). If @var{aiocbp} is not @code{NULL}, @code{aio_cancel}
attempts to cancel the specific request pointed to by @var{aiocbp}.
For requests which were successfully canceled, the normal notification
about the termination of the request should take place. I.e., depending
on the @code{struct sigevent} object which controls this, nothing
happens, a signal is sent or a thread is started. If the request cannot
be canceled, it terminates the usual way after performing the operation.
After a request is successfully canceled, a call to @code{aio_error} with
a reference to this request as the parameter will return
@code{ECANCELED} and a call to @code{aio_return} will return @math{-1}.
If the request wasn't canceled and is still running the error status is
still @code{EINPROGRESS}.
The return value of the function is @code{AIO_CANCELED} if there were
requests which haven't terminated and which were successfully canceled.
If there is one or more requests left which couldn't be canceled, the
return value is @code{AIO_NOTCANCELED}. In this case @code{aio_error}
must be used to find out which of the, perhaps multiple, requests (in
@var{aiocbp} is @code{NULL}) weren't successfully canceled. If all
requests already terminated at the time @code{aio_cancel} is called the
return value is @code{AIO_ALLDONE}.
If an error occurred during the execution of @code{aio_cancel} the
function returns @math{-1} and sets @code{errno} to one of the following
values.
@table @code
@item EBADF
The file descriptor @var{fildes} is not valid.
@item ENOSYS
@code{aio_cancel} is not implemented.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is in fact @code{aio_cancel64} since the LFS interface
transparently replaces the normal implementation.
@end deftypefun
@comment aio.h
@comment Unix98
@deftypefun int aio_cancel64 (int @var{fildes}, struct aiocb64 *@var{aiocbp})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
This function is similar to @code{aio_cancel} with the only difference
that the argument is a reference to a variable of type @code{struct
aiocb64}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64}, this
function is available under the name @code{aio_cancel} and so
transparently replaces the interface for small files on 32 bit
machines.
@end deftypefun
@node Configuration of AIO
@subsection How to optimize the AIO implementation
The POSIX standard does not specify how the AIO functions are
implemented. They could be system calls, but it is also possible to
emulate them at userlevel.
At the point of this writing, the available implementation is a userlevel
implementation which uses threads for handling the enqueued requests.
While this implementation requires making some decisions about
limitations, hard limitations are something which is best avoided
in @theglibc{}. Therefore, @theglibc{} provides a means
for tuning the AIO implementation according to the individual use.
@comment aio.h
@comment GNU
@deftp {Data Type} {struct aioinit}
This data type is used to pass the configuration or tunable parameters
to the implementation. The program has to initialize the members of
this struct and pass it to the implementation using the @code{aio_init}
function.
@table @code
@item int aio_threads
This member specifies the maximal number of threads which may be used
at any one time.
@item int aio_num
This number provides an estimate on the maximal number of simultaneously
enqueued requests.
@item int aio_locks
Unused.
@item int aio_usedba
Unused.
@item int aio_debug
Unused.
@item int aio_numusers
Unused.
@item int aio_reserved[2]
Unused.
@end table
@end deftp
@comment aio.h
@comment GNU
@deftypefun void aio_init (const struct aioinit *@var{init})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c All changes to global objects are guarded by aio_requests_mutex.
This function must be called before any other AIO function. Calling it
is completely voluntary, as it is only meant to help the AIO
implementation perform better.
Before calling the @code{aio_init}, function the members of a variable of
type @code{struct aioinit} must be initialized. Then a reference to
this variable is passed as the parameter to @code{aio_init} which itself
may or may not pay attention to the hints.
The function has no return value and no error cases are defined. It is
a extension which follows a proposal from the SGI implementation in
@w{Irix 6}. It is not covered by POSIX.1b or Unix98.
@end deftypefun
@node Control Operations
@section Control Operations on Files
@cindex control operations on files
@cindex @code{fcntl} function
This section describes how you can perform various other operations on
file descriptors, such as inquiring about or setting flags describing
the status of the file descriptor, manipulating record locks, and the
like. All of these operations are performed by the function @code{fcntl}.
The second argument to the @code{fcntl} function is a command that
specifies which operation to perform. The function and macros that name
various flags that are used with it are declared in the header file
@file{fcntl.h}. Many of these flags are also used by the @code{open}
function; see @ref{Opening and Closing Files}.
@pindex fcntl.h
@comment fcntl.h
@comment POSIX.1
@deftypefun int fcntl (int @var{filedes}, int @var{command}, @dots{})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fcntl} function performs the operation specified by
@var{command} on the file descriptor @var{filedes}. Some commands
require additional arguments to be supplied. These additional arguments
and the return value and error conditions are given in the detailed
descriptions of the individual commands.
Briefly, here is a list of what the various commands are.
@table @code
@item F_DUPFD
Duplicate the file descriptor (return another file descriptor pointing
to the same open file). @xref{Duplicating Descriptors}.
@item F_GETFD
Get flags associated with the file descriptor. @xref{Descriptor Flags}.
@item F_SETFD
Set flags associated with the file descriptor. @xref{Descriptor Flags}.
@item F_GETFL
Get flags associated with the open file. @xref{File Status Flags}.
@item F_SETFL
Set flags associated with the open file. @xref{File Status Flags}.
@item F_GETLK
Get a file lock. @xref{File Locks}.
@item F_SETLK
Set or clear a file lock. @xref{File Locks}.
@item F_SETLKW
Like @code{F_SETLK}, but wait for completion. @xref{File Locks}.
@item F_GETOWN
Get process or process group ID to receive @code{SIGIO} signals.
@xref{Interrupt Input}.
@item F_SETOWN
Set process or process group ID to receive @code{SIGIO} signals.
@xref{Interrupt Input}.
@end table
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{fcntl} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{fcntl} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
@end deftypefun
@node Duplicating Descriptors
@section Duplicating Descriptors
@cindex duplicating file descriptors
@cindex redirecting input and output
You can @dfn{duplicate} a file descriptor, or allocate another file
descriptor that refers to the same open file as the original. Duplicate
descriptors share one file position and one set of file status flags
(@pxref{File Status Flags}), but each has its own set of file descriptor
flags (@pxref{Descriptor Flags}).
The major use of duplicating a file descriptor is to implement
@dfn{redirection} of input or output: that is, to change the
file or pipe that a particular file descriptor corresponds to.
You can perform this operation using the @code{fcntl} function with the
@code{F_DUPFD} command, but there are also convenient functions
@code{dup} and @code{dup2} for duplicating descriptors.
@pindex unistd.h
@pindex fcntl.h
The @code{fcntl} function and flags are declared in @file{fcntl.h},
while prototypes for @code{dup} and @code{dup2} are in the header file
@file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun int dup (int @var{old})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function copies descriptor @var{old} to the first available
descriptor number (the first number not currently open). It is
equivalent to @code{fcntl (@var{old}, F_DUPFD, 0)}.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int dup2 (int @var{old}, int @var{new})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function copies the descriptor @var{old} to descriptor number
@var{new}.
If @var{old} is an invalid descriptor, then @code{dup2} does nothing; it
does not close @var{new}. Otherwise, the new duplicate of @var{old}
replaces any previous meaning of descriptor @var{new}, as if @var{new}
were closed first.
If @var{old} and @var{new} are different numbers, and @var{old} is a
valid descriptor number, then @code{dup2} is equivalent to:
@smallexample
close (@var{new});
fcntl (@var{old}, F_DUPFD, @var{new})
@end smallexample
However, @code{dup2} does this atomically; there is no instant in the
middle of calling @code{dup2} at which @var{new} is closed and not yet a
duplicate of @var{old}.
@end deftypefun
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_DUPFD
This macro is used as the @var{command} argument to @code{fcntl}, to
copy the file descriptor given as the first argument.
The form of the call in this case is:
@smallexample
fcntl (@var{old}, F_DUPFD, @var{next-filedes})
@end smallexample
The @var{next-filedes} argument is of type @code{int} and specifies that
the file descriptor returned should be the next available one greater
than or equal to this value.
The return value from @code{fcntl} with this command is normally the value
of the new file descriptor. A return value of @math{-1} indicates an
error. The following @code{errno} error conditions are defined for
this command:
@table @code
@item EBADF
The @var{old} argument is invalid.
@item EINVAL
The @var{next-filedes} argument is invalid.
@item EMFILE
There are no more file descriptors available---your program is already
using the maximum. In BSD and GNU, the maximum is controlled by a
resource limit that can be changed; @pxref{Limits on Resources}, for
more information about the @code{RLIMIT_NOFILE} limit.
@end table
@code{ENFILE} is not a possible error code for @code{dup2} because
@code{dup2} does not create a new opening of a file; duplicate
descriptors do not count toward the limit which @code{ENFILE}
indicates. @code{EMFILE} is possible because it refers to the limit on
distinct descriptor numbers in use in one process.
@end deftypevr
Here is an example showing how to use @code{dup2} to do redirection.
Typically, redirection of the standard streams (like @code{stdin}) is
done by a shell or shell-like program before calling one of the
@code{exec} functions (@pxref{Executing a File}) to execute a new
program in a child process. When the new program is executed, it
creates and initializes the standard streams to point to the
corresponding file descriptors, before its @code{main} function is
invoked.
So, to redirect standard input to a file, the shell could do something
like:
@smallexample
pid = fork ();
if (pid == 0)
@{
char *filename;
char *program;
int file;
@dots{}
file = TEMP_FAILURE_RETRY (open (filename, O_RDONLY));
dup2 (file, STDIN_FILENO);
TEMP_FAILURE_RETRY (close (file));
execv (program, NULL);
@}
@end smallexample
There is also a more detailed example showing how to implement redirection
in the context of a pipeline of processes in @ref{Launching Jobs}.
@node Descriptor Flags
@section File Descriptor Flags
@cindex file descriptor flags
@dfn{File descriptor flags} are miscellaneous attributes of a file
descriptor. These flags are associated with particular file
descriptors, so that if you have created duplicate file descriptors
from a single opening of a file, each descriptor has its own set of flags.
Currently there is just one file descriptor flag: @code{FD_CLOEXEC},
which causes the descriptor to be closed if you use any of the
@code{exec@dots{}} functions (@pxref{Executing a File}).
The symbols in this section are defined in the header file
@file{fcntl.h}.
@pindex fcntl.h
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_GETFD
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should return the file descriptor flags associated
with the @var{filedes} argument.
The normal return value from @code{fcntl} with this command is a
nonnegative number which can be interpreted as the bitwise OR of the
individual flags (except that currently there is only one flag to use).
In case of an error, @code{fcntl} returns @math{-1}. The following
@code{errno} error conditions are defined for this command:
@table @code
@item EBADF
The @var{filedes} argument is invalid.
@end table
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_SETFD
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should set the file descriptor flags associated with the
@var{filedes} argument. This requires a third @code{int} argument to
specify the new flags, so the form of the call is:
@smallexample
fcntl (@var{filedes}, F_SETFD, @var{new-flags})
@end smallexample
The normal return value from @code{fcntl} with this command is an
unspecified value other than @math{-1}, which indicates an error.
The flags and error conditions are the same as for the @code{F_GETFD}
command.
@end deftypevr
The following macro is defined for use as a file descriptor flag with
the @code{fcntl} function. The value is an integer constant usable
as a bit mask value.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int FD_CLOEXEC
@cindex close-on-exec (file descriptor flag)
This flag specifies that the file descriptor should be closed when
an @code{exec} function is invoked; see @ref{Executing a File}. When
a file descriptor is allocated (as with @code{open} or @code{dup}),
this bit is initially cleared on the new file descriptor, meaning that
descriptor will survive into the new program after @code{exec}.
@end deftypevr
If you want to modify the file descriptor flags, you should get the
current flags with @code{F_GETFD} and modify the value. Don't assume
that the flags listed here are the only ones that are implemented; your
program may be run years from now and more flags may exist then. For
example, here is a function to set or clear the flag @code{FD_CLOEXEC}
without altering any other flags:
@smallexample
/* @r{Set the @code{FD_CLOEXEC} flag of @var{desc} if @var{value} is nonzero,}
@r{or clear the flag if @var{value} is 0.}
@r{Return 0 on success, or -1 on error with @code{errno} set.} */
int
set_cloexec_flag (int desc, int value)
@{
int oldflags = fcntl (desc, F_GETFD, 0);
/* @r{If reading the flags failed, return error indication now.} */
if (oldflags < 0)
return oldflags;
/* @r{Set just the flag we want to set.} */
if (value != 0)
oldflags |= FD_CLOEXEC;
else
oldflags &= ~FD_CLOEXEC;
/* @r{Store modified flag word in the descriptor.} */
return fcntl (desc, F_SETFD, oldflags);
@}
@end smallexample
@node File Status Flags
@section File Status Flags
@cindex file status flags
@dfn{File status flags} are used to specify attributes of the opening of a
file. Unlike the file descriptor flags discussed in @ref{Descriptor
Flags}, the file status flags are shared by duplicated file descriptors
resulting from a single opening of the file. The file status flags are
specified with the @var{flags} argument to @code{open};
@pxref{Opening and Closing Files}.
File status flags fall into three categories, which are described in the
following sections.
@itemize @bullet
@item
@ref{Access Modes}, specify what type of access is allowed to the
file: reading, writing, or both. They are set by @code{open} and are
returned by @code{fcntl}, but cannot be changed.
@item
@ref{Open-time Flags}, control details of what @code{open} will do.
These flags are not preserved after the @code{open} call.
@item
@ref{Operating Modes}, affect how operations such as @code{read} and
@code{write} are done. They are set by @code{open}, and can be fetched or
changed with @code{fcntl}.
@end itemize
The symbols in this section are defined in the header file
@file{fcntl.h}.
@pindex fcntl.h
@menu
* Access Modes:: Whether the descriptor can read or write.
* Open-time Flags:: Details of @code{open}.
* Operating Modes:: Special modes to control I/O operations.
* Getting File Status Flags:: Fetching and changing these flags.
@end menu
@node Access Modes
@subsection File Access Modes
The file access modes allow a file descriptor to be used for reading,
writing, or both. (On @gnuhurdsystems{}, they can also allow none of these,
and allow execution of the file as a program.) The access modes are chosen
when the file is opened, and never change.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_RDONLY
Open the file for read access.
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_WRONLY
Open the file for write access.
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_RDWR
Open the file for both reading and writing.
@end deftypevr
On @gnuhurdsystems{} (and not on other systems), @code{O_RDONLY} and
@code{O_WRONLY} are independent bits that can be bitwise-ORed together,
and it is valid for either bit to be set or clear. This means that
@code{O_RDWR} is the same as @code{O_RDONLY|O_WRONLY}. A file access
mode of zero is permissible; it allows no operations that do input or
output to the file, but does allow other operations such as
@code{fchmod}. On @gnuhurdsystems{}, since ``read-only'' or ``write-only''
is a misnomer, @file{fcntl.h} defines additional names for the file
access modes. These names are preferred when writing GNU-specific code.
But most programs will want to be portable to other POSIX.1 systems and
should use the POSIX.1 names above instead.
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_READ
Open the file for reading. Same as @code{O_RDONLY}; only defined on GNU.
@end deftypevr
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_WRITE
Open the file for writing. Same as @code{O_WRONLY}; only defined on GNU.
@end deftypevr
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_EXEC
Open the file for executing. Only defined on GNU.
@end deftypevr
To determine the file access mode with @code{fcntl}, you must extract
the access mode bits from the retrieved file status flags. On
@gnuhurdsystems{},
you can just test the @code{O_READ} and @code{O_WRITE} bits in
the flags word. But in other POSIX.1 systems, reading and writing
access modes are not stored as distinct bit flags. The portable way to
extract the file access mode bits is with @code{O_ACCMODE}.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_ACCMODE
This macro stands for a mask that can be bitwise-ANDed with the file
status flag value to produce a value representing the file access mode.
The mode will be @code{O_RDONLY}, @code{O_WRONLY}, or @code{O_RDWR}.
(On @gnuhurdsystems{} it could also be zero, and it never includes the
@code{O_EXEC} bit.)
@end deftypevr
@node Open-time Flags
@subsection Open-time Flags
The open-time flags specify options affecting how @code{open} will behave.
These options are not preserved once the file is open. The exception to
this is @code{O_NONBLOCK}, which is also an I/O operating mode and so it
@emph{is} saved. @xref{Opening and Closing Files}, for how to call
@code{open}.
There are two sorts of options specified by open-time flags.
@itemize @bullet
@item
@dfn{File name translation flags} affect how @code{open} looks up the
file name to locate the file, and whether the file can be created.
@cindex file name translation flags
@cindex flags, file name translation
@item
@dfn{Open-time action flags} specify extra operations that @code{open} will
perform on the file once it is open.
@cindex open-time action flags
@cindex flags, open-time action
@end itemize
Here are the file name translation flags.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_CREAT
If set, the file will be created if it doesn't already exist.
@c !!! mode arg, umask
@cindex create on open (file status flag)
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_EXCL
If both @code{O_CREAT} and @code{O_EXCL} are set, then @code{open} fails
if the specified file already exists. This is guaranteed to never
clobber an existing file.
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_NONBLOCK
@cindex non-blocking open
This prevents @code{open} from blocking for a ``long time'' to open the
file. This is only meaningful for some kinds of files, usually devices
such as serial ports; when it is not meaningful, it is harmless and
ignored. Often opening a port to a modem blocks until the modem reports
carrier detection; if @code{O_NONBLOCK} is specified, @code{open} will
return immediately without a carrier.
Note that the @code{O_NONBLOCK} flag is overloaded as both an I/O operating
mode and a file name translation flag. This means that specifying
@code{O_NONBLOCK} in @code{open} also sets nonblocking I/O mode;
@pxref{Operating Modes}. To open the file without blocking but do normal
I/O that blocks, you must call @code{open} with @code{O_NONBLOCK} set and
then call @code{fcntl} to turn the bit off.
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_NOCTTY
If the named file is a terminal device, don't make it the controlling
terminal for the process. @xref{Job Control}, for information about
what it means to be the controlling terminal.
On @gnuhurdsystems{} and 4.4 BSD, opening a file never makes it the
controlling terminal and @code{O_NOCTTY} is zero. However, @gnulinuxsystems{}
and some other systems use a nonzero value for @code{O_NOCTTY} and set the
controlling terminal when you open a file that is a terminal device; so
to be portable, use @code{O_NOCTTY} when it is important to avoid this.
@cindex controlling terminal, setting
@end deftypevr
The following three file name translation flags exist only on
@gnuhurdsystems{}.
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_IGNORE_CTTY
Do not recognize the named file as the controlling terminal, even if it
refers to the process's existing controlling terminal device. Operations
on the new file descriptor will never induce job control signals.
@xref{Job Control}.
@end deftypevr
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_NOLINK
If the named file is a symbolic link, open the link itself instead of
the file it refers to. (@code{fstat} on the new file descriptor will
return the information returned by @code{lstat} on the link's name.)
@cindex symbolic link, opening
@end deftypevr
@comment fcntl.h (optional)
@comment GNU
@deftypevr Macro int O_NOTRANS
If the named file is specially translated, do not invoke the translator.
Open the bare file the translator itself sees.
@end deftypevr
The open-time action flags tell @code{open} to do additional operations
which are not really related to opening the file. The reason to do them
as part of @code{open} instead of in separate calls is that @code{open}
can do them @i{atomically}.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_TRUNC
Truncate the file to zero length. This option is only useful for
regular files, not special files such as directories or FIFOs. POSIX.1
requires that you open the file for writing to use @code{O_TRUNC}. In
BSD and GNU you must have permission to write the file to truncate it,
but you need not open for write access.
This is the only open-time action flag specified by POSIX.1. There is
no good reason for truncation to be done by @code{open}, instead of by
calling @code{ftruncate} afterwards. The @code{O_TRUNC} flag existed in
Unix before @code{ftruncate} was invented, and is retained for backward
compatibility.
@end deftypevr
The remaining operating modes are BSD extensions. They exist only
on some systems. On other systems, these macros are not defined.
@comment fcntl.h (optional)
@comment BSD
@deftypevr Macro int O_SHLOCK
Acquire a shared lock on the file, as with @code{flock}.
@xref{File Locks}.
If @code{O_CREAT} is specified, the locking is done atomically when
creating the file. You are guaranteed that no other process will get
the lock on the new file first.
@end deftypevr
@comment fcntl.h (optional)
@comment BSD
@deftypevr Macro int O_EXLOCK
Acquire an exclusive lock on the file, as with @code{flock}.
@xref{File Locks}. This is atomic like @code{O_SHLOCK}.
@end deftypevr
@node Operating Modes
@subsection I/O Operating Modes
The operating modes affect how input and output operations using a file
descriptor work. These flags are set by @code{open} and can be fetched
and changed with @code{fcntl}.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_APPEND
The bit that enables append mode for the file. If set, then all
@code{write} operations write the data at the end of the file, extending
it, regardless of the current file position. This is the only reliable
way to append to a file. In append mode, you are guaranteed that the
data you write will always go to the current end of the file, regardless
of other processes writing to the file. Conversely, if you simply set
the file position to the end of file and write, then another process can
extend the file after you set the file position but before you write,
resulting in your data appearing someplace before the real end of file.
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int O_NONBLOCK
The bit that enables nonblocking mode for the file. If this bit is set,
@code{read} requests on the file can return immediately with a failure
status if there is no input immediately available, instead of blocking.
Likewise, @code{write} requests can also return immediately with a
failure status if the output can't be written immediately.
Note that the @code{O_NONBLOCK} flag is overloaded as both an I/O
operating mode and a file name translation flag; @pxref{Open-time Flags}.
@end deftypevr
@comment fcntl.h
@comment BSD
@deftypevr Macro int O_NDELAY
This is an obsolete name for @code{O_NONBLOCK}, provided for
compatibility with BSD. It is not defined by the POSIX.1 standard.
@end deftypevr
The remaining operating modes are BSD and GNU extensions. They exist only
on some systems. On other systems, these macros are not defined.
@comment fcntl.h
@comment BSD
@deftypevr Macro int O_ASYNC
The bit that enables asynchronous input mode. If set, then @code{SIGIO}
signals will be generated when input is available. @xref{Interrupt Input}.
Asynchronous input mode is a BSD feature.
@end deftypevr
@comment fcntl.h
@comment BSD
@deftypevr Macro int O_FSYNC
The bit that enables synchronous writing for the file. If set, each
@code{write} call will make sure the data is reliably stored on disk before
returning. @c !!! xref fsync
Synchronous writing is a BSD feature.
@end deftypevr
@comment fcntl.h
@comment BSD
@deftypevr Macro int O_SYNC
This is another name for @code{O_FSYNC}. They have the same value.
@end deftypevr
@comment fcntl.h
@comment GNU
@deftypevr Macro int O_NOATIME
If this bit is set, @code{read} will not update the access time of the
file. @xref{File Times}. This is used by programs that do backups, so
that backing a file up does not count as reading it.
Only the owner of the file or the superuser may use this bit.
This is a GNU extension.
@end deftypevr
@node Getting File Status Flags
@subsection Getting and Setting File Status Flags
The @code{fcntl} function can fetch or change file status flags.
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_GETFL
This macro is used as the @var{command} argument to @code{fcntl}, to
read the file status flags for the open file with descriptor
@var{filedes}.
The normal return value from @code{fcntl} with this command is a
nonnegative number which can be interpreted as the bitwise OR of the
individual flags. Since the file access modes are not single-bit values,
you can mask off other bits in the returned flags with @code{O_ACCMODE}
to compare them.
In case of an error, @code{fcntl} returns @math{-1}. The following
@code{errno} error conditions are defined for this command:
@table @code
@item EBADF
The @var{filedes} argument is invalid.
@end table
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_SETFL
This macro is used as the @var{command} argument to @code{fcntl}, to set
the file status flags for the open file corresponding to the
@var{filedes} argument. This command requires a third @code{int}
argument to specify the new flags, so the call looks like this:
@smallexample
fcntl (@var{filedes}, F_SETFL, @var{new-flags})
@end smallexample
You can't change the access mode for the file in this way; that is,
whether the file descriptor was opened for reading or writing.
The normal return value from @code{fcntl} with this command is an
unspecified value other than @math{-1}, which indicates an error. The
error conditions are the same as for the @code{F_GETFL} command.
@end deftypevr
If you want to modify the file status flags, you should get the current
flags with @code{F_GETFL} and modify the value. Don't assume that the
flags listed here are the only ones that are implemented; your program
may be run years from now and more flags may exist then. For example,
here is a function to set or clear the flag @code{O_NONBLOCK} without
altering any other flags:
@smallexample
@group
/* @r{Set the @code{O_NONBLOCK} flag of @var{desc} if @var{value} is nonzero,}
@r{or clear the flag if @var{value} is 0.}
@r{Return 0 on success, or -1 on error with @code{errno} set.} */
int
set_nonblock_flag (int desc, int value)
@{
int oldflags = fcntl (desc, F_GETFL, 0);
/* @r{If reading the flags failed, return error indication now.} */
if (oldflags == -1)
return -1;
/* @r{Set just the flag we want to set.} */
if (value != 0)
oldflags |= O_NONBLOCK;
else
oldflags &= ~O_NONBLOCK;
/* @r{Store modified flag word in the descriptor.} */
return fcntl (desc, F_SETFL, oldflags);
@}
@end group
@end smallexample
@node File Locks
@section File Locks
@cindex file locks
@cindex record locking
The remaining @code{fcntl} commands are used to support @dfn{record
locking}, which permits multiple cooperating programs to prevent each
other from simultaneously accessing parts of a file in error-prone
ways.
@cindex exclusive lock
@cindex write lock
An @dfn{exclusive} or @dfn{write} lock gives a process exclusive access
for writing to the specified part of the file. While a write lock is in
place, no other process can lock that part of the file.
@cindex shared lock
@cindex read lock
A @dfn{shared} or @dfn{read} lock prohibits any other process from
requesting a write lock on the specified part of the file. However,
other processes can request read locks.
The @code{read} and @code{write} functions do not actually check to see
whether there are any locks in place. If you want to implement a
locking protocol for a file shared by multiple processes, your application
must do explicit @code{fcntl} calls to request and clear locks at the
appropriate points.
Locks are associated with processes. A process can only have one kind
of lock set for each byte of a given file. When any file descriptor for
that file is closed by the process, all of the locks that process holds
on that file are released, even if the locks were made using other
descriptors that remain open. Likewise, locks are released when a
process exits, and are not inherited by child processes created using
@code{fork} (@pxref{Creating a Process}).
When making a lock, use a @code{struct flock} to specify what kind of
lock and where. This data type and the associated macros for the
@code{fcntl} function are declared in the header file @file{fcntl.h}.
@pindex fcntl.h
@comment fcntl.h
@comment POSIX.1
@deftp {Data Type} {struct flock}
This structure is used with the @code{fcntl} function to describe a file
lock. It has these members:
@table @code
@item short int l_type
Specifies the type of the lock; one of @code{F_RDLCK}, @code{F_WRLCK}, or
@code{F_UNLCK}.
@item short int l_whence
This corresponds to the @var{whence} argument to @code{fseek} or
@code{lseek}, and specifies what the offset is relative to. Its value
can be one of @code{SEEK_SET}, @code{SEEK_CUR}, or @code{SEEK_END}.
@item off_t l_start
This specifies the offset of the start of the region to which the lock
applies, and is given in bytes relative to the point specified by
@code{l_whence} member.
@item off_t l_len
This specifies the length of the region to be locked. A value of
@code{0} is treated specially; it means the region extends to the end of
the file.
@item pid_t l_pid
This field is the process ID (@pxref{Process Creation Concepts}) of the
process holding the lock. It is filled in by calling @code{fcntl} with
the @code{F_GETLK} command, but is ignored when making a lock.
@end table
@end deftp
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_GETLK
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should get information about a lock. This command
requires a third argument of type @w{@code{struct flock *}} to be passed
to @code{fcntl}, so that the form of the call is:
@smallexample
fcntl (@var{filedes}, F_GETLK, @var{lockp})
@end smallexample
If there is a lock already in place that would block the lock described
by the @var{lockp} argument, information about that lock overwrites
@code{*@var{lockp}}. Existing locks are not reported if they are
compatible with making a new lock as specified. Thus, you should
specify a lock type of @code{F_WRLCK} if you want to find out about both
read and write locks, or @code{F_RDLCK} if you want to find out about
write locks only.
There might be more than one lock affecting the region specified by the
@var{lockp} argument, but @code{fcntl} only returns information about
one of them. The @code{l_whence} member of the @var{lockp} structure is
set to @code{SEEK_SET} and the @code{l_start} and @code{l_len} fields
set to identify the locked region.
If no lock applies, the only change to the @var{lockp} structure is to
update the @code{l_type} to a value of @code{F_UNLCK}.
The normal return value from @code{fcntl} with this command is an
unspecified value other than @math{-1}, which is reserved to indicate an
error. The following @code{errno} error conditions are defined for
this command:
@table @code
@item EBADF
The @var{filedes} argument is invalid.
@item EINVAL
Either the @var{lockp} argument doesn't specify valid lock information,
or the file associated with @var{filedes} doesn't support locks.
@end table
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_SETLK
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should set or clear a lock. This command requires a
third argument of type @w{@code{struct flock *}} to be passed to
@code{fcntl}, so that the form of the call is:
@smallexample
fcntl (@var{filedes}, F_SETLK, @var{lockp})
@end smallexample
If the process already has a lock on any part of the region, the old lock
on that part is replaced with the new lock. You can remove a lock
by specifying a lock type of @code{F_UNLCK}.
If the lock cannot be set, @code{fcntl} returns immediately with a value
of @math{-1}. This function does not block waiting for other processes
to release locks. If @code{fcntl} succeeds, it return a value other
than @math{-1}.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EAGAIN
@itemx EACCES
The lock cannot be set because it is blocked by an existing lock on the
file. Some systems use @code{EAGAIN} in this case, and other systems
use @code{EACCES}; your program should treat them alike, after
@code{F_SETLK}. (@gnulinuxhurdsystems{} always use @code{EAGAIN}.)
@item EBADF
Either: the @var{filedes} argument is invalid; you requested a read lock
but the @var{filedes} is not open for read access; or, you requested a
write lock but the @var{filedes} is not open for write access.
@item EINVAL
Either the @var{lockp} argument doesn't specify valid lock information,
or the file associated with @var{filedes} doesn't support locks.
@item ENOLCK
The system has run out of file lock resources; there are already too
many file locks in place.
Well-designed file systems never report this error, because they have no
limitation on the number of locks. However, you must still take account
of the possibility of this error, as it could result from network access
to a file system on another machine.
@end table
@end deftypevr
@comment fcntl.h
@comment POSIX.1
@deftypevr Macro int F_SETLKW
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should set or clear a lock. It is just like the
@code{F_SETLK} command, but causes the process to block (or wait)
until the request can be specified.
This command requires a third argument of type @code{struct flock *}, as
for the @code{F_SETLK} command.
The @code{fcntl} return values and errors are the same as for the
@code{F_SETLK} command, but these additional @code{errno} error conditions
are defined for this command:
@table @code
@item EINTR
The function was interrupted by a signal while it was waiting.
@xref{Interrupted Primitives}.
@item EDEADLK
The specified region is being locked by another process. But that
process is waiting to lock a region which the current process has
locked, so waiting for the lock would result in deadlock. The system
does not guarantee that it will detect all such conditions, but it lets
you know if it notices one.
@end table
@end deftypevr
The following macros are defined for use as values for the @code{l_type}
member of the @code{flock} structure. The values are integer constants.
@table @code
@comment fcntl.h
@comment POSIX.1
@vindex F_RDLCK
@item F_RDLCK
This macro is used to specify a read (or shared) lock.
@comment fcntl.h
@comment POSIX.1
@vindex F_WRLCK
@item F_WRLCK
This macro is used to specify a write (or exclusive) lock.
@comment fcntl.h
@comment POSIX.1
@vindex F_UNLCK
@item F_UNLCK
This macro is used to specify that the region is unlocked.
@end table
As an example of a situation where file locking is useful, consider a
program that can be run simultaneously by several different users, that
logs status information to a common file. One example of such a program
might be a game that uses a file to keep track of high scores. Another
example might be a program that records usage or accounting information
for billing purposes.
Having multiple copies of the program simultaneously writing to the
file could cause the contents of the file to become mixed up. But
you can prevent this kind of problem by setting a write lock on the
file before actually writing to the file.
If the program also needs to read the file and wants to make sure that
the contents of the file are in a consistent state, then it can also use
a read lock. While the read lock is set, no other process can lock
that part of the file for writing.
@c ??? This section could use an example program.
Remember that file locks are only a @emph{voluntary} protocol for
controlling access to a file. There is still potential for access to
the file by programs that don't use the lock protocol.
@node Interrupt Input
@section Interrupt-Driven Input
@cindex interrupt-driven input
If you set the @code{O_ASYNC} status flag on a file descriptor
(@pxref{File Status Flags}), a @code{SIGIO} signal is sent whenever
input or output becomes possible on that file descriptor. The process
or process group to receive the signal can be selected by using the
@code{F_SETOWN} command to the @code{fcntl} function. If the file
descriptor is a socket, this also selects the recipient of @code{SIGURG}
signals that are delivered when out-of-band data arrives on that socket;
see @ref{Out-of-Band Data}. (@code{SIGURG} is sent in any situation
where @code{select} would report the socket as having an ``exceptional
condition''. @xref{Waiting for I/O}.)
If the file descriptor corresponds to a terminal device, then @code{SIGIO}
signals are sent to the foreground process group of the terminal.
@xref{Job Control}.
@pindex fcntl.h
The symbols in this section are defined in the header file
@file{fcntl.h}.
@comment fcntl.h
@comment BSD
@deftypevr Macro int F_GETOWN
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should get information about the process or process
group to which @code{SIGIO} signals are sent. (For a terminal, this is
actually the foreground process group ID, which you can get using
@code{tcgetpgrp}; see @ref{Terminal Access Functions}.)
The return value is interpreted as a process ID; if negative, its
absolute value is the process group ID.
The following @code{errno} error condition is defined for this command:
@table @code
@item EBADF
The @var{filedes} argument is invalid.
@end table
@end deftypevr
@comment fcntl.h
@comment BSD
@deftypevr Macro int F_SETOWN
This macro is used as the @var{command} argument to @code{fcntl}, to
specify that it should set the process or process group to which
@code{SIGIO} signals are sent. This command requires a third argument
of type @code{pid_t} to be passed to @code{fcntl}, so that the form of
the call is:
@smallexample
fcntl (@var{filedes}, F_SETOWN, @var{pid})
@end smallexample
The @var{pid} argument should be a process ID. You can also pass a
negative number whose absolute value is a process group ID.
The return value from @code{fcntl} with this command is @math{-1}
in case of error and some other value if successful. The following
@code{errno} error conditions are defined for this command:
@table @code
@item EBADF
The @var{filedes} argument is invalid.
@item ESRCH
There is no process or process group corresponding to @var{pid}.
@end table
@end deftypevr
@c ??? This section could use an example program.
@node IOCTLs
@section Generic I/O Control operations
@cindex generic i/o control operations
@cindex IOCTLs
@gnusystems{} can handle most input/output operations on many different
devices and objects in terms of a few file primitives - @code{read},
@code{write} and @code{lseek}. However, most devices also have a few
peculiar operations which do not fit into this model. Such as:
@itemize @bullet
@item
Changing the character font used on a terminal.
@item
Telling a magnetic tape system to rewind or fast forward. (Since they
cannot move in byte increments, @code{lseek} is inapplicable).
@item
Ejecting a disk from a drive.
@item
Playing an audio track from a CD-ROM drive.
@item
Maintaining routing tables for a network.
@end itemize
Although some such objects such as sockets and terminals
@footnote{Actually, the terminal-specific functions are implemented with
IOCTLs on many platforms.} have special functions of their own, it would
not be practical to create functions for all these cases.
Instead these minor operations, known as @dfn{IOCTL}s, are assigned code
numbers and multiplexed through the @code{ioctl} function, defined in
@code{sys/ioctl.h}. The code numbers themselves are defined in many
different headers.
@comment sys/ioctl.h
@comment BSD
@deftypefun int ioctl (int @var{filedes}, int @var{command}, @dots{})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{ioctl} function performs the generic I/O operation
@var{command} on @var{filedes}.
A third argument is usually present, either a single number or a pointer
to a structure. The meaning of this argument, the returned value, and
any error codes depends upon the command used. Often @math{-1} is
returned for a failure.
@end deftypefun
On some systems, IOCTLs used by different devices share the same numbers.
Thus, although use of an inappropriate IOCTL @emph{usually} only produces
an error, you should not attempt to use device-specific IOCTLs on an
unknown device.
Most IOCTLs are OS-specific and/or only used in special system utilities,
and are thus beyond the scope of this document. For an example of the use
of an IOCTL, see @ref{Out-of-Band Data}.
@c FIXME this is undocumented:
@c dup3
glibc-doc-reference-2.19.orig/manual/filesys.texi 0000664 0001750 0001750 00000414345 12275120646 022143 0 ustar adconrad adconrad @node File System Interface, Pipes and FIFOs, Low-Level I/O, Top
@c %MENU% Functions for manipulating files
@chapter File System Interface
This chapter describes @theglibc{}'s functions for manipulating
files. Unlike the input and output functions (@pxref{I/O on Streams};
@pxref{Low-Level I/O}), these functions are concerned with operating
on the files themselves rather than on their contents.
Among the facilities described in this chapter are functions for
examining or modifying directories, functions for renaming and deleting
files, and functions for examining and setting file attributes such as
access permissions and modification times.
@menu
* Working Directory:: This is used to resolve relative
file names.
* Accessing Directories:: Finding out what files a directory
contains.
* Working with Directory Trees:: Apply actions to all files or a selectable
subset of a directory hierarchy.
* Hard Links:: Adding alternate names to a file.
* Symbolic Links:: A file that ``points to'' a file name.
* Deleting Files:: How to delete a file, and what that means.
* Renaming Files:: Changing a file's name.
* Creating Directories:: A system call just for creating a directory.
* File Attributes:: Attributes of individual files.
* Making Special Files:: How to create special files.
* Temporary Files:: Naming and creating temporary files.
@end menu
@node Working Directory
@section Working Directory
@cindex current working directory
@cindex working directory
@cindex change working directory
Each process has associated with it a directory, called its @dfn{current
working directory} or simply @dfn{working directory}, that is used in
the resolution of relative file names (@pxref{File Name Resolution}).
When you log in and begin a new session, your working directory is
initially set to the home directory associated with your login account
in the system user database. You can find any user's home directory
using the @code{getpwuid} or @code{getpwnam} functions; see @ref{User
Database}.
Users can change the working directory using shell commands like
@code{cd}. The functions described in this section are the primitives
used by those commands and by other programs for examining and changing
the working directory.
@pindex cd
Prototypes for these functions are declared in the header file
@file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun {char *} getcwd (char *@var{buffer}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c If buffer is NULL, this function calls malloc and realloc, and, in
@c case of error, free. Linux offers a getcwd syscall that we use on
@c GNU/Linux systems, but it may fail if the pathname is too long. As a
@c fallback, and on other systems, the generic implementation opens each
@c parent directory with opendir, which allocates memory for the
@c directory stream with malloc. If a fstatat64 syscall is not
@c available, very deep directory trees may also have to malloc to build
@c longer sequences of ../../../... than those supported by a global
@c const read-only string.
@c linux/__getcwd
@c posix/__getcwd
@c malloc/realloc/free if buffer is NULL, or if dir is too deep
@c lstat64 -> see its own entry
@c fstatat64
@c direct syscall if possible, alloca+snprintf+*stat64 otherwise
@c openat64_not_cancel_3, close_not_cancel_no_status
@c __fdopendir, __opendir, __readdir, rewinddir
The @code{getcwd} function returns an absolute file name representing
the current working directory, storing it in the character array
@var{buffer} that you provide. The @var{size} argument is how you tell
the system the allocation size of @var{buffer}.
The @glibcadj{} version of this function also permits you to specify a
null pointer for the @var{buffer} argument. Then @code{getcwd}
allocates a buffer automatically, as with @code{malloc}
(@pxref{Unconstrained Allocation}). If the @var{size} is greater than
zero, then the buffer is that large; otherwise, the buffer is as large
as necessary to hold the result.
The return value is @var{buffer} on success and a null pointer on failure.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The @var{size} argument is zero and @var{buffer} is not a null pointer.
@item ERANGE
The @var{size} argument is less than the length of the working directory
name. You need to allocate a bigger array and try again.
@item EACCES
Permission to read or search a component of the file name was denied.
@end table
@end deftypefun
You could implement the behavior of GNU's @w{@code{getcwd (NULL, 0)}}
using only the standard behavior of @code{getcwd}:
@smallexample
char *
gnu_getcwd ()
@{
size_t size = 100;
while (1)
@{
char *buffer = (char *) xmalloc (size);
if (getcwd (buffer, size) == buffer)
return buffer;
free (buffer);
if (errno != ERANGE)
return 0;
size *= 2;
@}
@}
@end smallexample
@noindent
@xref{Malloc Examples}, for information about @code{xmalloc}, which is
not a library function but is a customary name used in most GNU
software.
@comment unistd.h
@comment BSD
@deftypefn {Deprecated Function} {char *} getwd (char *@var{buffer})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @ascuintl{}}@acunsafe{@acsmem{} @acsfd{}}}
@c Besides the getcwd safety issues, it calls strerror_r on error, which
@c brings in all of the i18n issues.
This is similar to @code{getcwd}, but has no way to specify the size of
the buffer. @Theglibc{} provides @code{getwd} only
for backwards compatibility with BSD.
The @var{buffer} argument should be a pointer to an array at least
@code{PATH_MAX} bytes long (@pxref{Limits for Files}). On @gnuhurdsystems{}
there is no limit to the size of a file name, so this is not
necessarily enough space to contain the directory name. That is why
this function is deprecated.
@end deftypefn
@comment unistd.h
@comment GNU
@deftypefun {char *} get_current_dir_name (void)
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c Besides getcwd, which this function calls as a fallback, it calls
@c getenv, with the potential thread-safety issues that brings about.
@vindex PWD
This @code{get_current_dir_name} function is basically equivalent to
@w{@code{getcwd (NULL, 0)}}. The only difference is that the value of
the @code{PWD} variable is returned if this value is correct. This is a
subtle difference which is visible if the path described by the
@code{PWD} value is using one or more symbol links in which case the
value returned by @code{getcwd} can resolve the symbol links and
therefore yield a different result.
This function is a GNU extension.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int chdir (const char *@var{filename})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is used to set the process's working directory to
@var{filename}.
The normal, successful return value from @code{chdir} is @code{0}. A
value of @code{-1} is returned to indicate an error. The @code{errno}
error conditions defined for this function are the usual file name
syntax errors (@pxref{File Name Errors}), plus @code{ENOTDIR} if the
file @var{filename} is not a directory.
@end deftypefun
@comment unistd.h
@comment XPG
@deftypefun int fchdir (int @var{filedes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is used to set the process's working directory to
directory associated with the file descriptor @var{filedes}.
The normal, successful return value from @code{fchdir} is @code{0}. A
value of @code{-1} is returned to indicate an error. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EACCES
Read permission is denied for the directory named by @code{dirname}.
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOTDIR
The file descriptor @var{filedes} is not associated with a directory.
@item EINTR
The function call was interrupt by a signal.
@item EIO
An I/O error occurred.
@end table
@end deftypefun
@node Accessing Directories
@section Accessing Directories
@cindex accessing directories
@cindex reading from a directory
@cindex directories, accessing
The facilities described in this section let you read the contents of a
directory file. This is useful if you want your program to list all the
files in a directory, perhaps as part of a menu.
@cindex directory stream
The @code{opendir} function opens a @dfn{directory stream} whose
elements are directory entries. Alternatively @code{fdopendir} can be
used which can have advantages if the program needs to have more
control over the way the directory is opened for reading. This
allows, for instance, to pass the @code{O_NOATIME} flag to
@code{open}.
You use the @code{readdir} function on the directory stream to
retrieve these entries, represented as @w{@code{struct dirent}}
objects. The name of the file for each entry is stored in the
@code{d_name} member of this structure. There are obvious parallels
here to the stream facilities for ordinary files, described in
@ref{I/O on Streams}.
@menu
* Directory Entries:: Format of one directory entry.
* Opening a Directory:: How to open a directory stream.
* Reading/Closing Directory:: How to read directory entries from the stream.
* Simple Directory Lister:: A very simple directory listing program.
* Random Access Directory:: Rereading part of the directory
already read with the same stream.
* Scanning Directory Content:: Get entries for user selected subset of
contents in given directory.
* Simple Directory Lister Mark II:: Revised version of the program.
@end menu
@node Directory Entries
@subsection Format of a Directory Entry
@pindex dirent.h
This section describes what you find in a single directory entry, as you
might obtain it from a directory stream. All the symbols are declared
in the header file @file{dirent.h}.
@comment dirent.h
@comment POSIX.1
@deftp {Data Type} {struct dirent}
This is a structure type used to return information about directory
entries. It contains the following fields:
@table @code
@item char d_name[]
This is the null-terminated file name component. This is the only
field you can count on in all POSIX systems.
@item ino_t d_fileno
This is the file serial number. For BSD compatibility, you can also
refer to this member as @code{d_ino}. On @gnulinuxhurdsystems{} and most POSIX
systems, for most files this the same as the @code{st_ino} member that
@code{stat} will return for the file. @xref{File Attributes}.
@item unsigned char d_namlen
This is the length of the file name, not including the terminating
null character. Its type is @code{unsigned char} because that is the
integer type of the appropriate size. This member is a BSD extension.
The symbol @code{_DIRENT_HAVE_D_NAMLEN} is defined if this member is
available.
@item unsigned char d_type
This is the type of the file, possibly unknown. The following constants
are defined for its value:
@vtable @code
@item DT_UNKNOWN
The type is unknown. Only some filesystems have full support to
return the type of the file, others might always return this value.
@item DT_REG
A regular file.
@item DT_DIR
A directory.
@item DT_FIFO
A named pipe, or FIFO. @xref{FIFO Special Files}.
@item DT_SOCK
A local-domain socket. @c !!! @xref{Local Domain}.
@item DT_CHR
A character device.
@item DT_BLK
A block device.
@item DT_LNK
A symbolic link.
@end vtable
This member is a BSD extension. The symbol @code{_DIRENT_HAVE_D_TYPE}
is defined if this member is available. On systems where it is used, it
corresponds to the file type bits in the @code{st_mode} member of
@code{struct stat}. If the value cannot be determine the member
value is DT_UNKNOWN. These two macros convert between @code{d_type}
values and @code{st_mode} values:
@comment dirent.h
@comment BSD
@deftypefun int IFTODT (mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This returns the @code{d_type} value corresponding to @var{mode}.
@end deftypefun
@comment dirent.h
@comment BSD
@deftypefun mode_t DTTOIF (int @var{dtype})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This returns the @code{st_mode} value corresponding to @var{dtype}.
@end deftypefun
@end table
This structure may contain additional members in the future. Their
availability is always announced in the compilation environment by a
macro names @code{_DIRENT_HAVE_D_@var{xxx}} where @var{xxx} is replaced
by the name of the new member. For instance, the member @code{d_reclen}
available on some systems is announced through the macro
@code{_DIRENT_HAVE_D_RECLEN}.
When a file has multiple names, each name has its own directory entry.
The only way you can tell that the directory entries belong to a
single file is that they have the same value for the @code{d_fileno}
field.
File attributes such as size, modification times etc., are part of the
file itself, not of any particular directory entry. @xref{File
Attributes}.
@end deftp
@node Opening a Directory
@subsection Opening a Directory Stream
@pindex dirent.h
This section describes how to open a directory stream. All the symbols
are declared in the header file @file{dirent.h}.
@comment dirent.h
@comment POSIX.1
@deftp {Data Type} DIR
The @code{DIR} data type represents a directory stream.
@end deftp
You shouldn't ever allocate objects of the @code{struct dirent} or
@code{DIR} data types, since the directory access functions do that for
you. Instead, you refer to these objects using the pointers returned by
the following functions.
@comment dirent.h
@comment POSIX.1
@deftypefun {DIR *} opendir (const char *@var{dirname})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c Besides the safe syscall, we have to allocate the DIR object with
@c __alloc_dir, that calls malloc.
The @code{opendir} function opens and returns a directory stream for
reading the directory whose file name is @var{dirname}. The stream has
type @code{DIR *}.
If unsuccessful, @code{opendir} returns a null pointer. In addition to
the usual file name errors (@pxref{File Name Errors}), the
following @code{errno} error conditions are defined for this function:
@table @code
@item EACCES
Read permission is denied for the directory named by @code{dirname}.
@item EMFILE
The process has too many files open.
@item ENFILE
The entire system, or perhaps the file system which contains the
directory, cannot support any additional open files at the moment.
(This problem cannot happen on @gnuhurdsystems{}.)
@item ENOMEM
Not enough memory available.
@end table
The @code{DIR} type is typically implemented using a file descriptor,
and the @code{opendir} function in terms of the @code{open} function.
@xref{Low-Level I/O}. Directory streams and the underlying
file descriptors are closed on @code{exec} (@pxref{Executing a File}).
@end deftypefun
The directory which is opened for reading by @code{opendir} is
identified by the name. In some situations this is not sufficient.
Or the way @code{opendir} implicitly creates a file descriptor for the
directory is not the way a program might want it. In these cases an
alternative interface can be used.
@comment dirent.h
@comment GNU
@deftypefun {DIR *} fdopendir (int @var{fd})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c The DIR object is allocated with __alloc_dir, that calls malloc.
The @code{fdopendir} function works just like @code{opendir} but
instead of taking a file name and opening a file descriptor for the
directory the caller is required to provide a file descriptor. This
file descriptor is then used in subsequent uses of the returned
directory stream object.
The caller must make sure the file descriptor is associated with a
directory and it allows reading.
If the @code{fdopendir} call returns successfully the file descriptor
is now under the control of the system. It can be used in the same
way the descriptor implicitly created by @code{opendir} can be used
but the program must not close the descriptor.
In case the function is unsuccessful it returns a null pointer and the
file descriptor remains to be usable by the program. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The file descriptor is not valid.
@item ENOTDIR
The file descriptor is not associated with a directory.
@item EINVAL
The descriptor does not allow reading the directory content.
@item ENOMEM
Not enough memory available.
@end table
@end deftypefun
In some situations it can be desirable to get hold of the file
descriptor which is created by the @code{opendir} call. For instance,
to switch the current working directory to the directory just read the
@code{fchdir} function could be used. Historically the @code{DIR} type
was exposed and programs could access the fields. This does not happen
in @theglibc{}. Instead a separate function is provided to allow
access.
@comment dirent.h
@comment GNU
@deftypefun int dirfd (DIR *@var{dirstream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{dirfd} returns the file descriptor associated with
the directory stream @var{dirstream}. This descriptor can be used until
the directory is closed with @code{closedir}. If the directory stream
implementation is not using file descriptors the return value is
@code{-1}.
@end deftypefun
@node Reading/Closing Directory
@subsection Reading and Closing a Directory Stream
@pindex dirent.h
This section describes how to read directory entries from a directory
stream, and how to close the stream when you are done with it. All the
symbols are declared in the header file @file{dirent.h}.
@comment dirent.h
@comment POSIX.1
@deftypefun {struct dirent *} readdir (DIR *@var{dirstream})
@safety{@prelim{}@mtunsafe{@mtasurace{:dirstream}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c This function holds dirstream's non-recursive lock, which brings
@c about the usual issues with locks and async signals and cancellation,
@c but the lock taking is not enough to make the returned value safe to
@c use, since it points to a stream's internal buffer that can be
@c overwritten by subsequent calls or even released by closedir.
This function reads the next entry from the directory. It normally
returns a pointer to a structure containing information about the
file. This structure is associated with the @var{dirstream} handle
and can be rewritten by a subsequent call.
@strong{Portability Note:} On some systems @code{readdir} may not
return entries for @file{.} and @file{..}, even though these are always
valid file names in any directory. @xref{File Name Resolution}.
If there are no more entries in the directory or an error is detected,
@code{readdir} returns a null pointer. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EBADF
The @var{dirstream} argument is not valid.
@end table
To distinguish between an end-of-directory condition or an error, you
must set @code{errno} to zero before calling @code{readdir}. To avoid
entering an infinite loop, you should stop reading from the directory
after the first error.
In POSIX.1-2008, @code{readdir} is not thread-safe. In @theglibc{}
implementation, it is safe to call @code{readdir} concurrently on
different @var{dirstream}s, but multiple threads accessing the same
@var{dirstream} result in undefined behavior. @code{readdir_r} is a
fully thread-safe alternative, but suffers from poor portability (see
below). It is recommended that you use @code{readdir}, with external
locking if multiple threads access the same @var{dirstream}.
@end deftypefun
@comment dirent.h
@comment GNU
@deftypefun int readdir_r (DIR *@var{dirstream}, struct dirent *@var{entry}, struct dirent **@var{result})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
This function is a version of @code{readdir} which performs internal
locking. Like @code{readdir} it returns the next entry from the
directory. To prevent conflicts between simultaneously running
threads the result is stored inside the @var{entry} object.
@strong{Portability Note:} It is recommended to use @code{readdir}
instead of @code{readdir_r} for the following reasons:
@itemize @bullet
@item
On systems which do not define @code{NAME_MAX}, it may not be possible
to use @code{readdir_r} safely because the caller does not specify the
length of the buffer for the directory entry.
@item
On some systems, @code{readdir_r} cannot read directory entries with
very long names. If such a name is encountered, @theglibc{}
implementation of @code{readdir_r} returns with an error code of
@code{ENAMETOOLONG} after the final directory entry has been read. On
other systems, @code{readdir_r} may return successfully, but the
@code{d_name} member may not be NUL-terminated or may be truncated.
@item
POSIX-1.2008 does not guarantee that @code{readdir} is thread-safe,
even when access to the same @var{dirstream} is serialized. But in
current implementations (including @theglibc{}), it is safe to call
@code{readdir} concurrently on different @var{dirstream}s, so there is
no need to use @code{readdir_r} in most multi-threaded programs. In
the rare case that multiple threads need to read from the same
@var{dirstream}, it is still better to use @code{readdir} and external
synchronization.
@item
It is expected that future versions of POSIX will obsolete
@code{readdir_r} and mandate the level of thread safety for
@code{readdir} which is provided by @theglibc{} and other
implementations today.
@end itemize
Normally @code{readdir_r} returns zero and sets @code{*@var{result}}
to @var{entry}. If there are no more entries in the directory or an
error is detected, @code{readdir_r} sets @code{*@var{result}} to a
null pointer and returns a nonzero error code, also stored in
@code{errno}, as described for @code{readdir}.
It is also important to look at the definition of the @code{struct
dirent} type. Simply passing a pointer to an object of this type for
the second parameter of @code{readdir_r} might not be enough. Some
systems don't define the @code{d_name} element sufficiently long. In
this case the user has to provide additional space. There must be room
for at least @code{NAME_MAX + 1} characters in the @code{d_name} array.
Code to call @code{readdir_r} could look like this:
@smallexample
union
@{
struct dirent d;
char b[offsetof (struct dirent, d_name) + NAME_MAX + 1];
@} u;
if (readdir_r (dir, &u.d, &res) == 0)
@dots{}
@end smallexample
@end deftypefun
To support large filesystems on 32-bit machines there are LFS variants
of the last two functions.
@comment dirent.h
@comment LFS
@deftypefun {struct dirent64 *} readdir64 (DIR *@var{dirstream})
@safety{@prelim{}@mtunsafe{@mtasurace{:dirstream}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
The @code{readdir64} function is just like the @code{readdir} function
except that it returns a pointer to a record of type @code{struct
dirent64}. Some of the members of this data type (notably @code{d_ino})
might have a different size to allow large filesystems.
In all other aspects this function is equivalent to @code{readdir}.
@end deftypefun
@comment dirent.h
@comment LFS
@deftypefun int readdir64_r (DIR *@var{dirstream}, struct dirent64 *@var{entry}, struct dirent64 **@var{result})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
The @code{readdir64_r} function is equivalent to the @code{readdir_r}
function except that it takes parameters of base type @code{struct
dirent64} instead of @code{struct dirent} in the second and third
position. The same precautions mentioned in the documentation of
@code{readdir_r} also apply here.
@end deftypefun
@comment dirent.h
@comment POSIX.1
@deftypefun int closedir (DIR *@var{dirstream})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{/hurd}}@acunsafe{@acsmem{} @acsfd{} @aculock{/hurd}}}
@c No synchronization in the posix implementation, only in the hurd
@c one. This is regarded as safe because it is undefined behavior if
@c other threads could still be using the dir stream while it's closed.
This function closes the directory stream @var{dirstream}. It returns
@code{0} on success and @code{-1} on failure.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EBADF
The @var{dirstream} argument is not valid.
@end table
@end deftypefun
@node Simple Directory Lister
@subsection Simple Program to List a Directory
Here's a simple program that prints the names of the files in
the current working directory:
@smallexample
@include dir.c.texi
@end smallexample
The order in which files appear in a directory tends to be fairly
random. A more useful program would sort the entries (perhaps by
alphabetizing them) before printing them; see
@ref{Scanning Directory Content}, and @ref{Array Sort Function}.
@node Random Access Directory
@subsection Random Access in a Directory Stream
@pindex dirent.h
This section describes how to reread parts of a directory that you have
already read from an open directory stream. All the symbols are
declared in the header file @file{dirent.h}.
@comment dirent.h
@comment POSIX.1
@deftypefun void rewinddir (DIR *@var{dirstream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
The @code{rewinddir} function is used to reinitialize the directory
stream @var{dirstream}, so that if you call @code{readdir} it
returns information about the first entry in the directory again. This
function also notices if files have been added or removed to the
directory since it was opened with @code{opendir}. (Entries for these
files might or might not be returned by @code{readdir} if they were
added or removed since you last called @code{opendir} or
@code{rewinddir}.)
@end deftypefun
@comment dirent.h
@comment BSD
@deftypefun {long int} telldir (DIR *@var{dirstream})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{/bsd} @asulock{/bsd}}@acunsafe{@acsmem{/bsd} @aculock{/bsd}}}
@c The implementation is safe on most platforms, but on BSD it uses
@c cookies, buckets and records, and the global array of pointers to
@c dynamically allocated records is guarded by a non-recursive lock.
The @code{telldir} function returns the file position of the directory
stream @var{dirstream}. You can use this value with @code{seekdir} to
restore the directory stream to that position.
@end deftypefun
@comment dirent.h
@comment BSD
@deftypefun void seekdir (DIR *@var{dirstream}, long int @var{pos})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{/bsd} @asulock{/bsd}}@acunsafe{@acsmem{/bsd} @aculock{/bsd}}}
@c The implementation is safe on most platforms, but on BSD it uses
@c cookies, buckets and records, and the global array of pointers to
@c dynamically allocated records is guarded by a non-recursive lock.
The @code{seekdir} function sets the file position of the directory
stream @var{dirstream} to @var{pos}. The value @var{pos} must be the
result of a previous call to @code{telldir} on this particular stream;
closing and reopening the directory can invalidate values returned by
@code{telldir}.
@end deftypefun
@node Scanning Directory Content
@subsection Scanning the Content of a Directory
A higher-level interface to the directory handling functions is the
@code{scandir} function. With its help one can select a subset of the
entries in a directory, possibly sort them and get a list of names as
the result.
@comment dirent.h
@comment BSD/SVID
@deftypefun int scandir (const char *@var{dir}, struct dirent ***@var{namelist}, int (*@var{selector}) (const struct dirent *), int (*@var{cmp}) (const struct dirent **, const struct dirent **))
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c The scandir function calls __opendirat, __readdir, and __closedir to
@c go over the named dir; malloc and realloc to allocate the namelist
@c and copies of each selected dirent, besides the selector, if given,
@c and qsort and the cmp functions if the latter is given. In spite of
@c the cleanup handler that releases memory and the file descriptor in
@c case of synchronous cancellation, an asynchronous cancellation may
@c still leak memory and a file descriptor. Although readdir is unsafe
@c in general, the use of an internal dir stream for sequential scanning
@c of the directory with copying of dirents before subsequent calls
@c makes the use safe, and the fact that the dir stream is private to
@c each scandir call does away with the lock issues in readdir and
@c closedir.
The @code{scandir} function scans the contents of the directory selected
by @var{dir}. The result in *@var{namelist} is an array of pointers to
structure of type @code{struct dirent} which describe all selected
directory entries and which is allocated using @code{malloc}. Instead
of always getting all directory entries returned, the user supplied
function @var{selector} can be used to decide which entries are in the
result. Only the entries for which @var{selector} returns a non-zero
value are selected.
Finally the entries in *@var{namelist} are sorted using the
user-supplied function @var{cmp}. The arguments passed to the @var{cmp}
function are of type @code{struct dirent **}, therefore one cannot
directly use the @code{strcmp} or @code{strcoll} functions; instead see
the functions @code{alphasort} and @code{versionsort} below.
The return value of the function is the number of entries placed in
*@var{namelist}. If it is @code{-1} an error occurred (either the
directory could not be opened for reading or the malloc call failed) and
the global variable @code{errno} contains more information on the error.
@end deftypefun
As described above the fourth argument to the @code{scandir} function
must be a pointer to a sorting function. For the convenience of the
programmer @theglibc{} contains implementations of functions which
are very helpful for this purpose.
@comment dirent.h
@comment BSD/SVID
@deftypefun int alphasort (const void *@var{a}, const void *@var{b})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c Calls strcoll.
The @code{alphasort} function behaves like the @code{strcoll} function
(@pxref{String/Array Comparison}). The difference is that the arguments
are not string pointers but instead they are of type
@code{struct dirent **}.
The return value of @code{alphasort} is less than, equal to, or greater
than zero depending on the order of the two entries @var{a} and @var{b}.
@end deftypefun
@comment dirent.h
@comment GNU
@deftypefun int versionsort (const void *@var{a}, const void *@var{b})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Calls strverscmp, which will accesses the locale object multiple
@c times.
The @code{versionsort} function is like @code{alphasort} except that it
uses the @code{strverscmp} function internally.
@end deftypefun
If the filesystem supports large files we cannot use the @code{scandir}
anymore since the @code{dirent} structure might not able to contain all
the information. The LFS provides the new type @w{@code{struct
dirent64}}. To use this we need a new function.
@comment dirent.h
@comment GNU
@deftypefun int scandir64 (const char *@var{dir}, struct dirent64 ***@var{namelist}, int (*@var{selector}) (const struct dirent64 *), int (*@var{cmp}) (const struct dirent64 **, const struct dirent64 **))
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c See scandir.
The @code{scandir64} function works like the @code{scandir} function
except that the directory entries it returns are described by elements
of type @w{@code{struct dirent64}}. The function pointed to by
@var{selector} is again used to select the desired entries, except that
@var{selector} now must point to a function which takes a
@w{@code{struct dirent64 *}} parameter.
Similarly the @var{cmp} function should expect its two arguments to be
of type @code{struct dirent64 **}.
@end deftypefun
As @var{cmp} is now a function of a different type, the functions
@code{alphasort} and @code{versionsort} cannot be supplied for that
argument. Instead we provide the two replacement functions below.
@comment dirent.h
@comment GNU
@deftypefun int alphasort64 (const void *@var{a}, const void *@var{b})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c See alphasort.
The @code{alphasort64} function behaves like the @code{strcoll} function
(@pxref{String/Array Comparison}). The difference is that the arguments
are not string pointers but instead they are of type
@code{struct dirent64 **}.
Return value of @code{alphasort64} is less than, equal to, or greater
than zero depending on the order of the two entries @var{a} and @var{b}.
@end deftypefun
@comment dirent.h
@comment GNU
@deftypefun int versionsort64 (const void *@var{a}, const void *@var{b})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c See versionsort.
The @code{versionsort64} function is like @code{alphasort64}, excepted that it
uses the @code{strverscmp} function internally.
@end deftypefun
It is important not to mix the use of @code{scandir} and the 64-bit
comparison functions or vice versa. There are systems on which this
works but on others it will fail miserably.
@node Simple Directory Lister Mark II
@subsection Simple Program to List a Directory, Mark II
Here is a revised version of the directory lister found above
(@pxref{Simple Directory Lister}). Using the @code{scandir} function we
can avoid the functions which work directly with the directory contents.
After the call the returned entries are available for direct use.
@smallexample
@include dir2.c.texi
@end smallexample
Note the simple selector function in this example. Since we want to see
all directory entries we always return @code{1}.
@node Working with Directory Trees
@section Working with Directory Trees
@cindex directory hierarchy
@cindex hierarchy, directory
@cindex tree, directory
The functions described so far for handling the files in a directory
have allowed you to either retrieve the information bit by bit, or to
process all the files as a group (see @code{scandir}). Sometimes it is
useful to process whole hierarchies of directories and their contained
files. The X/Open specification defines two functions to do this. The
simpler form is derived from an early definition in @w{System V} systems
and therefore this function is available on SVID-derived systems. The
prototypes and required definitions can be found in the @file{ftw.h}
header.
There are four functions in this family: @code{ftw}, @code{nftw} and
their 64-bit counterparts @code{ftw64} and @code{nftw64}. These
functions take as one of their arguments a pointer to a callback
function of the appropriate type.
@comment ftw.h
@comment GNU
@deftp {Data Type} __ftw_func_t
@smallexample
int (*) (const char *, const struct stat *, int)
@end smallexample
The type of callback functions given to the @code{ftw} function. The
first parameter points to the file name, the second parameter to an
object of type @code{struct stat} which is filled in for the file named
in the first parameter.
@noindent
The last parameter is a flag giving more information about the current
file. It can have the following values:
@vtable @code
@item FTW_F
The item is either a normal file or a file which does not fit into one
of the following categories. This could be special files, sockets etc.
@item FTW_D
The item is a directory.
@item FTW_NS
The @code{stat} call failed and so the information pointed to by the
second paramater is invalid.
@item FTW_DNR
The item is a directory which cannot be read.
@item FTW_SL
The item is a symbolic link. Since symbolic links are normally followed
seeing this value in a @code{ftw} callback function means the referenced
file does not exist. The situation for @code{nftw} is different.
This value is only available if the program is compiled with
@code{_BSD_SOURCE} or @code{_XOPEN_EXTENDED} defined before including
the first header. The original SVID systems do not have symbolic links.
@end vtable
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
type is in fact @code{__ftw64_func_t} since this mode changes
@code{struct stat} to be @code{struct stat64}.
@end deftp
For the LFS interface and for use in the function @code{ftw64}, the
header @file{ftw.h} defines another function type.
@comment ftw.h
@comment GNU
@deftp {Data Type} __ftw64_func_t
@smallexample
int (*) (const char *, const struct stat64 *, int)
@end smallexample
This type is used just like @code{__ftw_func_t} for the callback
function, but this time is called from @code{ftw64}. The second
parameter to the function is a pointer to a variable of type
@code{struct stat64} which is able to represent the larger values.
@end deftp
@comment ftw.h
@comment GNU
@deftp {Data Type} __nftw_func_t
@smallexample
int (*) (const char *, const struct stat *, int, struct FTW *)
@end smallexample
@vindex FTW_DP
@vindex FTW_SLN
The first three arguments are the same as for the @code{__ftw_func_t}
type. However for the third argument some additional values are defined
to allow finer differentiation:
@table @code
@item FTW_DP
The current item is a directory and all subdirectories have already been
visited and reported. This flag is returned instead of @code{FTW_D} if
the @code{FTW_DEPTH} flag is passed to @code{nftw} (see below).
@item FTW_SLN
The current item is a stale symbolic link. The file it points to does
not exist.
@end table
The last parameter of the callback function is a pointer to a structure
with some extra information as described below.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
type is in fact @code{__nftw64_func_t} since this mode changes
@code{struct stat} to be @code{struct stat64}.
@end deftp
For the LFS interface there is also a variant of this data type
available which has to be used with the @code{nftw64} function.
@comment ftw.h
@comment GNU
@deftp {Data Type} __nftw64_func_t
@smallexample
int (*) (const char *, const struct stat64 *, int, struct FTW *)
@end smallexample
This type is used just like @code{__nftw_func_t} for the callback
function, but this time is called from @code{nftw64}. The second
parameter to the function is this time a pointer to a variable of type
@code{struct stat64} which is able to represent the larger values.
@end deftp
@comment ftw.h
@comment XPG4.2
@deftp {Data Type} {struct FTW}
The information contained in this structure helps in interpreting the
name parameter and gives some information about the current state of the
traversal of the directory hierarchy.
@table @code
@item int base
The value is the offset into the string passed in the first parameter to
the callback function of the beginning of the file name. The rest of
the string is the path of the file. This information is especially
important if the @code{FTW_CHDIR} flag was set in calling @code{nftw}
since then the current directory is the one the current item is found
in.
@item int level
Whilst processing, the code tracks how many directories down it has gone
to find the current file. This nesting level starts at @math{0} for
files in the initial directory (or is zero for the initial file if a
file was passed).
@end table
@end deftp
@comment ftw.h
@comment SVID
@deftypefun int ftw (const char *@var{filename}, __ftw_func_t @var{func}, int @var{descriptors})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c see nftw for safety details
The @code{ftw} function calls the callback function given in the
parameter @var{func} for every item which is found in the directory
specified by @var{filename} and all directories below. The function
follows symbolic links if necessary but does not process an item twice.
If @var{filename} is not a directory then it itself is the only object
returned to the callback function.
The file name passed to the callback function is constructed by taking
the @var{filename} parameter and appending the names of all passed
directories and then the local file name. So the callback function can
use this parameter to access the file. @code{ftw} also calls
@code{stat} for the file and passes that information on to the callback
function. If this @code{stat} call was not successful the failure is
indicated by setting the third argument of the callback function to
@code{FTW_NS}. Otherwise it is set according to the description given
in the account of @code{__ftw_func_t} above.
The callback function is expected to return @math{0} to indicate that no
error occurred and that processing should continue. If an error
occurred in the callback function or it wants @code{ftw} to return
immediately, the callback function can return a value other than
@math{0}. This is the only correct way to stop the function. The
program must not use @code{setjmp} or similar techniques to continue
from another place. This would leave resources allocated by the
@code{ftw} function unfreed.
The @var{descriptors} parameter to @code{ftw} specifies how many file
descriptors it is allowed to consume. The function runs faster the more
descriptors it can use. For each level in the directory hierarchy at
most one descriptor is used, but for very deep ones any limit on open
file descriptors for the process or the system may be exceeded.
Moreover, file descriptor limits in a multi-threaded program apply to
all the threads as a group, and therefore it is a good idea to supply a
reasonable limit to the number of open descriptors.
The return value of the @code{ftw} function is @math{0} if all callback
function calls returned @math{0} and all actions performed by the
@code{ftw} succeeded. If a function call failed (other than calling
@code{stat} on an item) the function returns @math{-1}. If a callback
function returns a value other than @math{0} this value is returned as
the return value of @code{ftw}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{ftw64}, i.e., the LFS
interface transparently replaces the old interface.
@end deftypefun
@comment ftw.h
@comment Unix98
@deftypefun int ftw64 (const char *@var{filename}, __ftw64_func_t @var{func}, int @var{descriptors})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
This function is similar to @code{ftw} but it can work on filesystems
with large files. File information is reported using a variable of type
@code{struct stat64} which is passed by reference to the callback
function.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is available under the name @code{ftw} and
transparently replaces the old implementation.
@end deftypefun
@comment ftw.h
@comment XPG4.2
@deftypefun int nftw (const char *@var{filename}, __nftw_func_t @var{func}, int @var{descriptors}, int @var{flag})
@safety{@prelim{}@mtsafe{@mtasscwd{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{} @acscwd{}}}
@c ftw_startup calls alloca, malloc, free, xstat/lxstat, tdestroy, and ftw_dir
@c if FTW_CHDIR, call open, and fchdir, or chdir and getcwd
@c ftw_dir calls open_dir_stream, readdir64, process_entry, closedir
@c if FTW_CHDIR, also calls fchdir
@c open_dir_stream calls malloc, realloc, readdir64, free, closedir,
@c then openat64_not_cancel_3 and fdopendir or opendir, then dirfd.
@c process_entry may cal realloc, fxstatat/lxstat/xstat, ftw_dir, and
@c find_object (tsearch) and add_object (tfind).
@c Since each invocation of *ftw uses its own private search tree, none
@c of the search tree concurrency issues apply.
The @code{nftw} function works like the @code{ftw} functions. They call
the callback function @var{func} for all items found in the directory
@var{filename} and below. At most @var{descriptors} file descriptors
are consumed during the @code{nftw} call.
One difference is that the callback function is of a different type. It
is of type @w{@code{struct FTW *}} and provides the callback function
with the extra information described above.
A second difference is that @code{nftw} takes a fourth argument, which
is @math{0} or a bitwise-OR combination of any of the following values.
@vtable @code
@item FTW_PHYS
While traversing the directory symbolic links are not followed. Instead
symbolic links are reported using the @code{FTW_SL} value for the type
parameter to the callback function. If the file referenced by a
symbolic link does not exist @code{FTW_SLN} is returned instead.
@item FTW_MOUNT
The callback function is only called for items which are on the same
mounted filesystem as the directory given by the @var{filename}
parameter to @code{nftw}.
@item FTW_CHDIR
If this flag is given the current working directory is changed to the
directory of the reported object before the callback function is called.
When @code{ntfw} finally returns the current directory is restored to
its original value.
@item FTW_DEPTH
If this option is specified then all subdirectories and files within
them are processed before processing the top directory itself
(depth-first processing). This also means the type flag given to the
callback function is @code{FTW_DP} and not @code{FTW_D}.
@item FTW_ACTIONRETVAL
If this option is specified then return values from callbacks
are handled differently. If the callback returns @code{FTW_CONTINUE},
walking continues normally. @code{FTW_STOP} means walking stops
and @code{FTW_STOP} is returned to the caller. If @code{FTW_SKIP_SUBTREE}
is returned by the callback with @code{FTW_D} argument, the subtree
is skipped and walking continues with next sibling of the directory.
If @code{FTW_SKIP_SIBLINGS} is returned by the callback, all siblings
of the current entry are skipped and walking continues in its parent.
No other return values should be returned from the callbacks if
this option is set. This option is a GNU extension.
@end vtable
The return value is computed in the same way as for @code{ftw}.
@code{nftw} returns @math{0} if no failures occurred and all callback
functions returned @math{0}. In case of internal errors, such as memory
problems, the return value is @math{-1} and @var{errno} is set
accordingly. If the return value of a callback invocation was non-zero
then that value is returned.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{nftw64}, i.e., the LFS
interface transparently replaces the old interface.
@end deftypefun
@comment ftw.h
@comment Unix98
@deftypefun int nftw64 (const char *@var{filename}, __nftw64_func_t @var{func}, int @var{descriptors}, int @var{flag})
@safety{@prelim{}@mtsafe{@mtasscwd{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{} @acscwd{}}}
This function is similar to @code{nftw} but it can work on filesystems
with large files. File information is reported using a variable of type
@code{struct stat64} which is passed by reference to the callback
function.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is available under the name @code{nftw} and
transparently replaces the old implementation.
@end deftypefun
@node Hard Links
@section Hard Links
@cindex hard link
@cindex link, hard
@cindex multiple names for one file
@cindex file names, multiple
In POSIX systems, one file can have many names at the same time. All of
the names are equally real, and no one of them is preferred to the
others.
To add a name to a file, use the @code{link} function. (The new name is
also called a @dfn{hard link} to the file.) Creating a new link to a
file does not copy the contents of the file; it simply makes a new name
by which the file can be known, in addition to the file's existing name
or names.
One file can have names in several directories, so the organization
of the file system is not a strict hierarchy or tree.
In most implementations, it is not possible to have hard links to the
same file in multiple file systems. @code{link} reports an error if you
try to make a hard link to the file from another file system when this
cannot be done.
The prototype for the @code{link} function is declared in the header
file @file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun int link (const char *@var{oldname}, const char *@var{newname})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{link} function makes a new link to the existing file named by
@var{oldname}, under the new name @var{newname}.
This function returns a value of @code{0} if it is successful and
@code{-1} on failure. In addition to the usual file name errors
(@pxref{File Name Errors}) for both @var{oldname} and @var{newname}, the
following @code{errno} error conditions are defined for this function:
@table @code
@item EACCES
You are not allowed to write to the directory in which the new link is
to be written.
@ignore
Some implementations also require that the existing file be accessible
by the caller, and use this error to report failure for that reason.
@end ignore
@item EEXIST
There is already a file named @var{newname}. If you want to replace
this link with a new link, you must remove the old link explicitly first.
@item EMLINK
There are already too many links to the file named by @var{oldname}.
(The maximum number of links to a file is @w{@code{LINK_MAX}}; see
@ref{Limits for Files}.)
@item ENOENT
The file named by @var{oldname} doesn't exist. You can't make a link to
a file that doesn't exist.
@item ENOSPC
The directory or file system that would contain the new link is full
and cannot be extended.
@item EPERM
On @gnulinuxhurdsystems{} and some others, you cannot make links to
directories.
Many systems allow only privileged users to do so. This error
is used to report the problem.
@item EROFS
The directory containing the new link can't be modified because it's on
a read-only file system.
@item EXDEV
The directory specified in @var{newname} is on a different file system
than the existing file.
@item EIO
A hardware error occurred while trying to read or write the to filesystem.
@end table
@end deftypefun
@node Symbolic Links
@section Symbolic Links
@cindex soft link
@cindex link, soft
@cindex symbolic link
@cindex link, symbolic
@gnusystems{} support @dfn{soft links} or @dfn{symbolic links}. This
is a kind of ``file'' that is essentially a pointer to another file
name. Unlike hard links, symbolic links can be made to directories or
across file systems with no restrictions. You can also make a symbolic
link to a name which is not the name of any file. (Opening this link
will fail until a file by that name is created.) Likewise, if the
symbolic link points to an existing file which is later deleted, the
symbolic link continues to point to the same file name even though the
name no longer names any file.
The reason symbolic links work the way they do is that special things
happen when you try to open the link. The @code{open} function realizes
you have specified the name of a link, reads the file name contained in
the link, and opens that file name instead. The @code{stat} function
likewise operates on the file that the symbolic link points to, instead
of on the link itself.
By contrast, other operations such as deleting or renaming the file
operate on the link itself. The functions @code{readlink} and
@code{lstat} also refrain from following symbolic links, because their
purpose is to obtain information about the link. @code{link}, the
function that makes a hard link, does too. It makes a hard link to the
symbolic link, which one rarely wants.
Some systems have for some functions operating on files have a limit on
how many symbolic links are followed when resolving a path name. The
limit if it exists is published in the @file{sys/param.h} header file.
@comment sys/param.h
@comment BSD
@deftypevr Macro int MAXSYMLINKS
The macro @code{MAXSYMLINKS} specifies how many symlinks some function
will follow before returning @code{ELOOP}. Not all functions behave the
same and this value is not the same a that returned for
@code{_SC_SYMLOOP} by @code{sysconf}. In fact, the @code{sysconf}
result can indicate that there is no fixed limit although
@code{MAXSYMLINKS} exists and has a finite value.
@end deftypevr
Prototypes for most of the functions listed in this section are in
@file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment BSD
@deftypefun int symlink (const char *@var{oldname}, const char *@var{newname})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{symlink} function makes a symbolic link to @var{oldname} named
@var{newname}.
The normal return value from @code{symlink} is @code{0}. A return value
of @code{-1} indicates an error. In addition to the usual file name
syntax errors (@pxref{File Name Errors}), the following @code{errno}
error conditions are defined for this function:
@table @code
@item EEXIST
There is already an existing file named @var{newname}.
@item EROFS
The file @var{newname} would exist on a read-only file system.
@item ENOSPC
The directory or file system cannot be extended to make the new link.
@item EIO
A hardware error occurred while reading or writing data on the disk.
@ignore
@comment not sure about these
@item ELOOP
There are too many levels of indirection. This can be the result of
circular symbolic links to directories.
@item EDQUOT
The new link can't be created because the user's disk quota has been
exceeded.
@end ignore
@end table
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun ssize_t readlink (const char *@var{filename}, char *@var{buffer}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{readlink} function gets the value of the symbolic link
@var{filename}. The file name that the link points to is copied into
@var{buffer}. This file name string is @emph{not} null-terminated;
@code{readlink} normally returns the number of characters copied. The
@var{size} argument specifies the maximum number of characters to copy,
usually the allocation size of @var{buffer}.
If the return value equals @var{size}, you cannot tell whether or not
there was room to return the entire name. So make a bigger buffer and
call @code{readlink} again. Here is an example:
@smallexample
char *
readlink_malloc (const char *filename)
@{
int size = 100;
char *buffer = NULL;
while (1)
@{
buffer = (char *) xrealloc (buffer, size);
int nchars = readlink (filename, buffer, size);
if (nchars < 0)
@{
free (buffer);
return NULL;
@}
if (nchars < size)
return buffer;
size *= 2;
@}
@}
@end smallexample
@c @group Invalid outside example.
A value of @code{-1} is returned in case of error. In addition to the
usual file name errors (@pxref{File Name Errors}), the following
@code{errno} error conditions are defined for this function:
@table @code
@item EINVAL
The named file is not a symbolic link.
@item EIO
A hardware error occurred while reading or writing data on the disk.
@end table
@c @end group
@end deftypefun
In some situations it is desirable to resolve all the
symbolic links to get the real
name of a file where no prefix names a symbolic link which is followed
and no filename in the path is @code{.} or @code{..}. This is for
instance desirable if files have to be compare in which case different
names can refer to the same inode.
@comment stdlib.h
@comment GNU
@deftypefun {char *} canonicalize_file_name (const char *@var{name})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c Calls realpath.
The @code{canonicalize_file_name} function returns the absolute name of
the file named by @var{name} which contains no @code{.}, @code{..}
components nor any repeated path separators (@code{/}) or symlinks. The
result is passed back as the return value of the function in a block of
memory allocated with @code{malloc}. If the result is not used anymore
the memory should be freed with a call to @code{free}.
If any of the path components is missing the function returns a NULL
pointer. This is also what is returned if the length of the path
reaches or exceeds @code{PATH_MAX} characters. In any case
@code{errno} is set accordingly.
@table @code
@item ENAMETOOLONG
The resulting path is too long. This error only occurs on systems which
have a limit on the file name length.
@item EACCES
At least one of the path components is not readable.
@item ENOENT
The input file name is empty.
@item ENOENT
At least one of the path components does not exist.
@item ELOOP
More than @code{MAXSYMLINKS} many symlinks have been followed.
@end table
This function is a GNU extension and is declared in @file{stdlib.h}.
@end deftypefun
The Unix standard includes a similar function which differs from
@code{canonicalize_file_name} in that the user has to provide the buffer
where the result is placed in.
@comment stdlib.h
@comment XPG
@deftypefun {char *} realpath (const char *restrict @var{name}, char *restrict @var{resolved})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c Calls malloc, realloc, getcwd, lxstat64, readlink, alloca.
A call to @code{realpath} where the @var{resolved} parameter is
@code{NULL} behaves exactly like @code{canonicalize_file_name}. The
function allocates a buffer for the file name and returns a pointer to
it. If @var{resolved} is not @code{NULL} it points to a buffer into
which the result is copied. It is the callers responsibility to
allocate a buffer which is large enough. On systems which define
@code{PATH_MAX} this means the buffer must be large enough for a
pathname of this size. For systems without limitations on the pathname
length the requirement cannot be met and programs should not call
@code{realpath} with anything but @code{NULL} for the second parameter.
One other difference is that the buffer @var{resolved} (if nonzero) will
contain the part of the path component which does not exist or is not
readable if the function returns @code{NULL} and @code{errno} is set to
@code{EACCES} or @code{ENOENT}.
This function is declared in @file{stdlib.h}.
@end deftypefun
The advantage of using this function is that it is more widely
available. The drawback is that it reports failures for long path on
systems which have no limits on the file name length.
@node Deleting Files
@section Deleting Files
@cindex deleting a file
@cindex removing a file
@cindex unlinking a file
You can delete a file with @code{unlink} or @code{remove}.
Deletion actually deletes a file name. If this is the file's only name,
then the file is deleted as well. If the file has other remaining names
(@pxref{Hard Links}), it remains accessible under those names.
@comment unistd.h
@comment POSIX.1
@deftypefun int unlink (const char *@var{filename})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{unlink} function deletes the file name @var{filename}. If
this is a file's sole name, the file itself is also deleted. (Actually,
if any process has the file open when this happens, deletion is
postponed until all processes have closed the file.)
@pindex unistd.h
The function @code{unlink} is declared in the header file @file{unistd.h}.
This function returns @code{0} on successful completion, and @code{-1}
on error. In addition to the usual file name errors
(@pxref{File Name Errors}), the following @code{errno} error conditions are
defined for this function:
@table @code
@item EACCES
Write permission is denied for the directory from which the file is to be
removed, or the directory has the sticky bit set and you do not own the file.
@item EBUSY
This error indicates that the file is being used by the system in such a
way that it can't be unlinked. For example, you might see this error if
the file name specifies the root directory or a mount point for a file
system.
@item ENOENT
The file name to be deleted doesn't exist.
@item EPERM
On some systems @code{unlink} cannot be used to delete the name of a
directory, or at least can only be used this way by a privileged user.
To avoid such problems, use @code{rmdir} to delete directories. (On
@gnulinuxhurdsystems{} @code{unlink} can never delete the name of a directory.)
@item EROFS
The directory containing the file name to be deleted is on a read-only
file system and can't be modified.
@end table
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int rmdir (const char *@var{filename})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@cindex directories, deleting
@cindex deleting a directory
The @code{rmdir} function deletes a directory. The directory must be
empty before it can be removed; in other words, it can only contain
entries for @file{.} and @file{..}.
In most other respects, @code{rmdir} behaves like @code{unlink}. There
are two additional @code{errno} error conditions defined for
@code{rmdir}:
@table @code
@item ENOTEMPTY
@itemx EEXIST
The directory to be deleted is not empty.
@end table
These two error codes are synonymous; some systems use one, and some use
the other. @gnulinuxhurdsystems{} always use @code{ENOTEMPTY}.
The prototype for this function is declared in the header file
@file{unistd.h}.
@pindex unistd.h
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int remove (const char *@var{filename})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Calls unlink and rmdir.
This is the @w{ISO C} function to remove a file. It works like
@code{unlink} for files and like @code{rmdir} for directories.
@code{remove} is declared in @file{stdio.h}.
@pindex stdio.h
@end deftypefun
@node Renaming Files
@section Renaming Files
The @code{rename} function is used to change a file's name.
@cindex renaming a file
@comment stdio.h
@comment ISO
@deftypefun int rename (const char *@var{oldname}, const char *@var{newname})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a rename syscall, there's an emulation with link
@c and unlink, but it's racy, even more so if newname exists and is
@c unlinked first.
The @code{rename} function renames the file @var{oldname} to
@var{newname}. The file formerly accessible under the name
@var{oldname} is afterwards accessible as @var{newname} instead. (If
the file had any other names aside from @var{oldname}, it continues to
have those names.)
The directory containing the name @var{newname} must be on the same file
system as the directory containing the name @var{oldname}.
One special case for @code{rename} is when @var{oldname} and
@var{newname} are two names for the same file. The consistent way to
handle this case is to delete @var{oldname}. However, in this case
POSIX requires that @code{rename} do nothing and report success---which
is inconsistent. We don't know what your operating system will do.
If @var{oldname} is not a directory, then any existing file named
@var{newname} is removed during the renaming operation. However, if
@var{newname} is the name of a directory, @code{rename} fails in this
case.
If @var{oldname} is a directory, then either @var{newname} must not
exist or it must name a directory that is empty. In the latter case,
the existing directory named @var{newname} is deleted first. The name
@var{newname} must not specify a subdirectory of the directory
@code{oldname} which is being renamed.
One useful feature of @code{rename} is that the meaning of @var{newname}
changes ``atomically'' from any previously existing file by that name to
its new meaning (i.e., the file that was called @var{oldname}). There is
no instant at which @var{newname} is non-existent ``in between'' the old
meaning and the new meaning. If there is a system crash during the
operation, it is possible for both names to still exist; but
@var{newname} will always be intact if it exists at all.
If @code{rename} fails, it returns @code{-1}. In addition to the usual
file name errors (@pxref{File Name Errors}), the following
@code{errno} error conditions are defined for this function:
@table @code
@item EACCES
One of the directories containing @var{newname} or @var{oldname}
refuses write permission; or @var{newname} and @var{oldname} are
directories and write permission is refused for one of them.
@item EBUSY
A directory named by @var{oldname} or @var{newname} is being used by
the system in a way that prevents the renaming from working. This includes
directories that are mount points for filesystems, and directories
that are the current working directories of processes.
@item ENOTEMPTY
@itemx EEXIST
The directory @var{newname} isn't empty. @gnulinuxhurdsystems{} always return
@code{ENOTEMPTY} for this, but some other systems return @code{EEXIST}.
@item EINVAL
@var{oldname} is a directory that contains @var{newname}.
@item EISDIR
@var{newname} is a directory but the @var{oldname} isn't.
@item EMLINK
The parent directory of @var{newname} would have too many links
(entries).
@item ENOENT
The file @var{oldname} doesn't exist.
@item ENOSPC
The directory that would contain @var{newname} has no room for another
entry, and there is no space left in the file system to expand it.
@item EROFS
The operation would involve writing to a directory on a read-only file
system.
@item EXDEV
The two file names @var{newname} and @var{oldname} are on different
file systems.
@end table
@end deftypefun
@node Creating Directories
@section Creating Directories
@cindex creating a directory
@cindex directories, creating
@pindex mkdir
Directories are created with the @code{mkdir} function. (There is also
a shell command @code{mkdir} which does the same thing.)
@c !!! umask
@comment sys/stat.h
@comment POSIX.1
@deftypefun int mkdir (const char *@var{filename}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{mkdir} function creates a new, empty directory with name
@var{filename}.
The argument @var{mode} specifies the file permissions for the new
directory file. @xref{Permission Bits}, for more information about
this.
A return value of @code{0} indicates successful completion, and
@code{-1} indicates failure. In addition to the usual file name syntax
errors (@pxref{File Name Errors}), the following @code{errno} error
conditions are defined for this function:
@table @code
@item EACCES
Write permission is denied for the parent directory in which the new
directory is to be added.
@item EEXIST
A file named @var{filename} already exists.
@item EMLINK
The parent directory has too many links (entries).
Well-designed file systems never report this error, because they permit
more links than your disk could possibly hold. However, you must still
take account of the possibility of this error, as it could result from
network access to a file system on another machine.
@item ENOSPC
The file system doesn't have enough room to create the new directory.
@item EROFS
The parent directory of the directory being created is on a read-only
file system and cannot be modified.
@end table
To use this function, your program should include the header file
@file{sys/stat.h}.
@pindex sys/stat.h
@end deftypefun
@node File Attributes
@section File Attributes
@pindex ls
When you issue an @samp{ls -l} shell command on a file, it gives you
information about the size of the file, who owns it, when it was last
modified, etc. These are called the @dfn{file attributes}, and are
associated with the file itself and not a particular one of its names.
This section contains information about how you can inquire about and
modify the attributes of a file.
@menu
* Attribute Meanings:: The names of the file attributes,
and what their values mean.
* Reading Attributes:: How to read the attributes of a file.
* Testing File Type:: Distinguishing ordinary files,
directories, links@dots{}
* File Owner:: How ownership for new files is determined,
and how to change it.
* Permission Bits:: How information about a file's access
mode is stored.
* Access Permission:: How the system decides who can access a file.
* Setting Permissions:: How permissions for new files are assigned,
and how to change them.
* Testing File Access:: How to find out if your process can
access a file.
* File Times:: About the time attributes of a file.
* File Size:: Manually changing the size of a file.
@end menu
@node Attribute Meanings
@subsection The meaning of the File Attributes
@cindex status of a file
@cindex attributes of a file
@cindex file attributes
When you read the attributes of a file, they come back in a structure
called @code{struct stat}. This section describes the names of the
attributes, their data types, and what they mean. For the functions
to read the attributes of a file, see @ref{Reading Attributes}.
The header file @file{sys/stat.h} declares all the symbols defined
in this section.
@pindex sys/stat.h
@comment sys/stat.h
@comment POSIX.1
@deftp {Data Type} {struct stat}
The @code{stat} structure type is used to return information about the
attributes of a file. It contains at least the following members:
@table @code
@item mode_t st_mode
Specifies the mode of the file. This includes file type information
(@pxref{Testing File Type}) and the file permission bits
(@pxref{Permission Bits}).
@item ino_t st_ino
The file serial number, which distinguishes this file from all other
files on the same device.
@item dev_t st_dev
Identifies the device containing the file. The @code{st_ino} and
@code{st_dev}, taken together, uniquely identify the file. The
@code{st_dev} value is not necessarily consistent across reboots or
system crashes, however.
@item nlink_t st_nlink
The number of hard links to the file. This count keeps track of how
many directories have entries for this file. If the count is ever
decremented to zero, then the file itself is discarded as soon as no
process still holds it open. Symbolic links are not counted in the
total.
@item uid_t st_uid
The user ID of the file's owner. @xref{File Owner}.
@item gid_t st_gid
The group ID of the file. @xref{File Owner}.
@item off_t st_size
This specifies the size of a regular file in bytes. For files that are
really devices this field isn't usually meaningful. For symbolic links
this specifies the length of the file name the link refers to.
@item time_t st_atime
This is the last access time for the file. @xref{File Times}.
@item unsigned long int st_atime_usec
This is the fractional part of the last access time for the file.
@xref{File Times}.
@item time_t st_mtime
This is the time of the last modification to the contents of the file.
@xref{File Times}.
@item unsigned long int st_mtime_usec
This is the fractional part of the time of the last modification to the
contents of the file. @xref{File Times}.
@item time_t st_ctime
This is the time of the last modification to the attributes of the file.
@xref{File Times}.
@item unsigned long int st_ctime_usec
This is the fractional part of the time of the last modification to the
attributes of the file. @xref{File Times}.
@c !!! st_rdev
@item blkcnt_t st_blocks
This is the amount of disk space that the file occupies, measured in
units of 512-byte blocks.
The number of disk blocks is not strictly proportional to the size of
the file, for two reasons: the file system may use some blocks for
internal record keeping; and the file may be sparse---it may have
``holes'' which contain zeros but do not actually take up space on the
disk.
You can tell (approximately) whether a file is sparse by comparing this
value with @code{st_size}, like this:
@smallexample
(st.st_blocks * 512 < st.st_size)
@end smallexample
This test is not perfect because a file that is just slightly sparse
might not be detected as sparse at all. For practical applications,
this is not a problem.
@item unsigned int st_blksize
The optimal block size for reading of writing this file, in bytes. You
might use this size for allocating the buffer space for reading of
writing the file. (This is unrelated to @code{st_blocks}.)
@end table
@end deftp
The extensions for the Large File Support (LFS) require, even on 32-bit
machines, types which can handle file sizes up to @math{2^63}.
Therefore a new definition of @code{struct stat} is necessary.
@comment sys/stat.h
@comment LFS
@deftp {Data Type} {struct stat64}
The members of this type are the same and have the same names as those
in @code{struct stat}. The only difference is that the members
@code{st_ino}, @code{st_size}, and @code{st_blocks} have a different
type to support larger values.
@table @code
@item mode_t st_mode
Specifies the mode of the file. This includes file type information
(@pxref{Testing File Type}) and the file permission bits
(@pxref{Permission Bits}).
@item ino64_t st_ino
The file serial number, which distinguishes this file from all other
files on the same device.
@item dev_t st_dev
Identifies the device containing the file. The @code{st_ino} and
@code{st_dev}, taken together, uniquely identify the file. The
@code{st_dev} value is not necessarily consistent across reboots or
system crashes, however.
@item nlink_t st_nlink
The number of hard links to the file. This count keeps track of how
many directories have entries for this file. If the count is ever
decremented to zero, then the file itself is discarded as soon as no
process still holds it open. Symbolic links are not counted in the
total.
@item uid_t st_uid
The user ID of the file's owner. @xref{File Owner}.
@item gid_t st_gid
The group ID of the file. @xref{File Owner}.
@item off64_t st_size
This specifies the size of a regular file in bytes. For files that are
really devices this field isn't usually meaningful. For symbolic links
this specifies the length of the file name the link refers to.
@item time_t st_atime
This is the last access time for the file. @xref{File Times}.
@item unsigned long int st_atime_usec
This is the fractional part of the last access time for the file.
@xref{File Times}.
@item time_t st_mtime
This is the time of the last modification to the contents of the file.
@xref{File Times}.
@item unsigned long int st_mtime_usec
This is the fractional part of the time of the last modification to the
contents of the file. @xref{File Times}.
@item time_t st_ctime
This is the time of the last modification to the attributes of the file.
@xref{File Times}.
@item unsigned long int st_ctime_usec
This is the fractional part of the time of the last modification to the
attributes of the file. @xref{File Times}.
@c !!! st_rdev
@item blkcnt64_t st_blocks
This is the amount of disk space that the file occupies, measured in
units of 512-byte blocks.
@item unsigned int st_blksize
The optimal block size for reading of writing this file, in bytes. You
might use this size for allocating the buffer space for reading of
writing the file. (This is unrelated to @code{st_blocks}.)
@end table
@end deftp
Some of the file attributes have special data type names which exist
specifically for those attributes. (They are all aliases for well-known
integer types that you know and love.) These typedef names are defined
in the header file @file{sys/types.h} as well as in @file{sys/stat.h}.
Here is a list of them.
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} mode_t
This is an integer data type used to represent file modes. In
@theglibc{}, this is an unsigned type no narrower than @code{unsigned
int}.
@end deftp
@cindex inode number
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} ino_t
This is an unsigned integer type used to represent file serial numbers.
(In Unix jargon, these are sometimes called @dfn{inode numbers}.)
In @theglibc{}, this type is no narrower than @code{unsigned int}.
If the source is compiled with @code{_FILE_OFFSET_BITS == 64} this type
is transparently replaced by @code{ino64_t}.
@end deftp
@comment sys/types.h
@comment Unix98
@deftp {Data Type} ino64_t
This is an unsigned integer type used to represent file serial numbers
for the use in LFS. In @theglibc{}, this type is no narrower than
@code{unsigned int}.
When compiling with @code{_FILE_OFFSET_BITS == 64} this type is
available under the name @code{ino_t}.
@end deftp
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} dev_t
This is an arithmetic data type used to represent file device numbers.
In @theglibc{}, this is an integer type no narrower than @code{int}.
@end deftp
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} nlink_t
This is an integer type used to represent file link counts.
@end deftp
@comment sys/types.h
@comment Unix98
@deftp {Data Type} blkcnt_t
This is a signed integer type used to represent block counts.
In @theglibc{}, this type is no narrower than @code{int}.
If the source is compiled with @code{_FILE_OFFSET_BITS == 64} this type
is transparently replaced by @code{blkcnt64_t}.
@end deftp
@comment sys/types.h
@comment Unix98
@deftp {Data Type} blkcnt64_t
This is a signed integer type used to represent block counts for the
use in LFS. In @theglibc{}, this type is no narrower than @code{int}.
When compiling with @code{_FILE_OFFSET_BITS == 64} this type is
available under the name @code{blkcnt_t}.
@end deftp
@node Reading Attributes
@subsection Reading the Attributes of a File
To examine the attributes of files, use the functions @code{stat},
@code{fstat} and @code{lstat}. They return the attribute information in
a @code{struct stat} object. All three functions are declared in the
header file @file{sys/stat.h}.
@comment sys/stat.h
@comment POSIX.1
@deftypefun int stat (const char *@var{filename}, struct stat *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{stat} function returns information about the attributes of the
file named by @w{@var{filename}} in the structure pointed to by @var{buf}.
If @var{filename} is the name of a symbolic link, the attributes you get
describe the file that the link points to. If the link points to a
nonexistent file name, then @code{stat} fails reporting a nonexistent
file.
The return value is @code{0} if the operation is successful, or
@code{-1} on failure. In addition to the usual file name errors
(@pxref{File Name Errors}, the following @code{errno} error conditions
are defined for this function:
@table @code
@item ENOENT
The file named by @var{filename} doesn't exist.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{stat64} since the LFS interface transparently
replaces the normal implementation.
@end deftypefun
@comment sys/stat.h
@comment Unix98
@deftypefun int stat64 (const char *@var{filename}, struct stat64 *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{stat} but it is also able to work on
files larger than @math{2^31} bytes on 32-bit systems. To be able to do
this the result is stored in a variable of type @code{struct stat64} to
which @var{buf} must point.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{stat} and so transparently
replaces the interface for small files on 32-bit machines.
@end deftypefun
@comment sys/stat.h
@comment POSIX.1
@deftypefun int fstat (int @var{filedes}, struct stat *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{fstat} function is like @code{stat}, except that it takes an
open file descriptor as an argument instead of a file name.
@xref{Low-Level I/O}.
Like @code{stat}, @code{fstat} returns @code{0} on success and @code{-1}
on failure. The following @code{errno} error conditions are defined for
@code{fstat}:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@end table
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{fstat64} since the LFS interface transparently
replaces the normal implementation.
@end deftypefun
@comment sys/stat.h
@comment Unix98
@deftypefun int fstat64 (int @var{filedes}, struct stat64 *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{fstat} but is able to work on large
files on 32-bit platforms. For large files the file descriptor
@var{filedes} should be obtained by @code{open64} or @code{creat64}.
The @var{buf} pointer points to a variable of type @code{struct stat64}
which is able to represent the larger values.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{fstat} and so transparently
replaces the interface for small files on 32-bit machines.
@end deftypefun
@c fstatat will call alloca and snprintf if the syscall is not
@c available.
@c @safety{@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@comment sys/stat.h
@comment BSD
@deftypefun int lstat (const char *@var{filename}, struct stat *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct system call through lxstat, sometimes with an xstat conv call
@c afterwards.
The @code{lstat} function is like @code{stat}, except that it does not
follow symbolic links. If @var{filename} is the name of a symbolic
link, @code{lstat} returns information about the link itself; otherwise
@code{lstat} works like @code{stat}. @xref{Symbolic Links}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is in fact @code{lstat64} since the LFS interface transparently
replaces the normal implementation.
@end deftypefun
@comment sys/stat.h
@comment Unix98
@deftypefun int lstat64 (const char *@var{filename}, struct stat64 *@var{buf})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct system call through lxstat64, sometimes with an xstat conv
@c call afterwards.
This function is similar to @code{lstat} but it is also able to work on
files larger than @math{2^31} bytes on 32-bit systems. To be able to do
this the result is stored in a variable of type @code{struct stat64} to
which @var{buf} must point.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
function is available under the name @code{lstat} and so transparently
replaces the interface for small files on 32-bit machines.
@end deftypefun
@node Testing File Type
@subsection Testing the Type of a File
The @dfn{file mode}, stored in the @code{st_mode} field of the file
attributes, contains two kinds of information: the file type code, and
the access permission bits. This section discusses only the type code,
which you can use to tell whether the file is a directory, socket,
symbolic link, and so on. For details about access permissions see
@ref{Permission Bits}.
There are two ways you can access the file type information in a file
mode. Firstly, for each file type there is a @dfn{predicate macro}
which examines a given file mode and returns whether it is of that type
or not. Secondly, you can mask out the rest of the file mode to leave
just the file type code, and compare this against constants for each of
the supported file types.
All of the symbols listed in this section are defined in the header file
@file{sys/stat.h}.
@pindex sys/stat.h
The following predicate macros test the type of a file, given the value
@var{m} which is the @code{st_mode} field returned by @code{stat} on
that file:
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_ISDIR (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a directory.
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_ISCHR (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a character special file (a
device like a terminal).
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_ISBLK (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a block special file (a device
like a disk).
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_ISREG (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a regular file.
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_ISFIFO (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a FIFO special file, or a
pipe. @xref{Pipes and FIFOs}.
@end deftypefn
@comment sys/stat.h
@comment GNU
@deftypefn Macro int S_ISLNK (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a symbolic link.
@xref{Symbolic Links}.
@end deftypefn
@comment sys/stat.h
@comment GNU
@deftypefn Macro int S_ISSOCK (mode_t @var{m})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns non-zero if the file is a socket. @xref{Sockets}.
@end deftypefn
An alternate non-POSIX method of testing the file type is supported for
compatibility with BSD. The mode can be bitwise AND-ed with
@code{S_IFMT} to extract the file type code, and compared to the
appropriate constant. For example,
@smallexample
S_ISCHR (@var{mode})
@end smallexample
@noindent
is equivalent to:
@smallexample
((@var{mode} & S_IFMT) == S_IFCHR)
@end smallexample
@comment sys/stat.h
@comment BSD
@deftypevr Macro int S_IFMT
This is a bit mask used to extract the file type code from a mode value.
@end deftypevr
These are the symbolic names for the different file type codes:
@table @code
@comment sys/stat.h
@comment BSD
@item S_IFDIR
@vindex S_IFDIR
This is the file type constant of a directory file.
@comment sys/stat.h
@comment BSD
@item S_IFCHR
@vindex S_IFCHR
This is the file type constant of a character-oriented device file.
@comment sys/stat.h
@comment BSD
@item S_IFBLK
@vindex S_IFBLK
This is the file type constant of a block-oriented device file.
@comment sys/stat.h
@comment BSD
@item S_IFREG
@vindex S_IFREG
This is the file type constant of a regular file.
@comment sys/stat.h
@comment BSD
@item S_IFLNK
@vindex S_IFLNK
This is the file type constant of a symbolic link.
@comment sys/stat.h
@comment BSD
@item S_IFSOCK
@vindex S_IFSOCK
This is the file type constant of a socket.
@comment sys/stat.h
@comment BSD
@item S_IFIFO
@vindex S_IFIFO
This is the file type constant of a FIFO or pipe.
@end table
The POSIX.1b standard introduced a few more objects which possibly can
be implemented as object in the filesystem. These are message queues,
semaphores, and shared memory objects. To allow differentiating these
objects from other files the POSIX standard introduces three new test
macros. But unlike the other macros it does not take the value of the
@code{st_mode} field as the parameter. Instead they expect a pointer to
the whole @code{struct stat} structure.
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_TYPEISMQ (struct stat *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If the system implement POSIX message queues as distinct objects and the
file is a message queue object, this macro returns a non-zero value.
In all other cases the result is zero.
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_TYPEISSEM (struct stat *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If the system implement POSIX semaphores as distinct objects and the
file is a semaphore object, this macro returns a non-zero value.
In all other cases the result is zero.
@end deftypefn
@comment sys/stat.h
@comment POSIX
@deftypefn Macro int S_TYPEISSHM (struct stat *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If the system implement POSIX shared memory objects as distinct objects
and the file is a shared memory object, this macro returns a non-zero
value. In all other cases the result is zero.
@end deftypefn
@node File Owner
@subsection File Owner
@cindex file owner
@cindex owner of a file
@cindex group owner of a file
Every file has an @dfn{owner} which is one of the registered user names
defined on the system. Each file also has a @dfn{group} which is one of
the defined groups. The file owner can often be useful for showing you
who edited the file (especially when you edit with GNU Emacs), but its
main purpose is for access control.
The file owner and group play a role in determining access because the
file has one set of access permission bits for the owner, another set
that applies to users who belong to the file's group, and a third set of
bits that applies to everyone else. @xref{Access Permission}, for the
details of how access is decided based on this data.
When a file is created, its owner is set to the effective user ID of the
process that creates it (@pxref{Process Persona}). The file's group ID
may be set to either the effective group ID of the process, or the group
ID of the directory that contains the file, depending on the system
where the file is stored. When you access a remote file system, it
behaves according to its own rules, not according to the system your
program is running on. Thus, your program must be prepared to encounter
either kind of behavior no matter what kind of system you run it on.
@pindex chown
@pindex chgrp
You can change the owner and/or group owner of an existing file using
the @code{chown} function. This is the primitive for the @code{chown}
and @code{chgrp} shell commands.
@pindex unistd.h
The prototype for this function is declared in @file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun int chown (const char *@var{filename}, uid_t @var{owner}, gid_t @var{group})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{chown} function changes the owner of the file @var{filename} to
@var{owner}, and its group owner to @var{group}.
Changing the owner of the file on certain systems clears the set-user-ID
and set-group-ID permission bits. (This is because those bits may not
be appropriate for the new owner.) Other file permission bits are not
changed.
The return value is @code{0} on success and @code{-1} on failure.
In addition to the usual file name errors (@pxref{File Name Errors}),
the following @code{errno} error conditions are defined for this function:
@table @code
@item EPERM
This process lacks permission to make the requested change.
Only privileged users or the file's owner can change the file's group.
On most file systems, only privileged users can change the file owner;
some file systems allow you to change the owner if you are currently the
owner. When you access a remote file system, the behavior you encounter
is determined by the system that actually holds the file, not by the
system your program is running on.
@xref{Options for Files}, for information about the
@code{_POSIX_CHOWN_RESTRICTED} macro.
@item EROFS
The file is on a read-only file system.
@end table
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int fchown (int @var{filedes}, uid_t @var{owner}, gid_t @var{group})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{chown}, except that it changes the owner of the open
file with descriptor @var{filedes}.
The return value from @code{fchown} is @code{0} on success and @code{-1}
on failure. The following @code{errno} error codes are defined for this
function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The @var{filedes} argument corresponds to a pipe or socket, not an ordinary
file.
@item EPERM
This process lacks permission to make the requested change. For details
see @code{chmod} above.
@item EROFS
The file resides on a read-only file system.
@end table
@end deftypefun
@node Permission Bits
@subsection The Mode Bits for Access Permission
The @dfn{file mode}, stored in the @code{st_mode} field of the file
attributes, contains two kinds of information: the file type code, and
the access permission bits. This section discusses only the access
permission bits, which control who can read or write the file.
@xref{Testing File Type}, for information about the file type code.
All of the symbols listed in this section are defined in the header file
@file{sys/stat.h}.
@pindex sys/stat.h
@cindex file permission bits
These symbolic constants are defined for the file mode bits that control
access permission for the file:
@table @code
@comment sys/stat.h
@comment POSIX.1
@item S_IRUSR
@vindex S_IRUSR
@comment sys/stat.h
@comment BSD
@itemx S_IREAD
@vindex S_IREAD
Read permission bit for the owner of the file. On many systems this bit
is 0400. @code{S_IREAD} is an obsolete synonym provided for BSD
compatibility.
@comment sys/stat.h
@comment POSIX.1
@item S_IWUSR
@vindex S_IWUSR
@comment sys/stat.h
@comment BSD
@itemx S_IWRITE
@vindex S_IWRITE
Write permission bit for the owner of the file. Usually 0200.
@w{@code{S_IWRITE}} is an obsolete synonym provided for BSD compatibility.
@comment sys/stat.h
@comment POSIX.1
@item S_IXUSR
@vindex S_IXUSR
@comment sys/stat.h
@comment BSD
@itemx S_IEXEC
@vindex S_IEXEC
Execute (for ordinary files) or search (for directories) permission bit
for the owner of the file. Usually 0100. @code{S_IEXEC} is an obsolete
synonym provided for BSD compatibility.
@comment sys/stat.h
@comment POSIX.1
@item S_IRWXU
@vindex S_IRWXU
This is equivalent to @samp{(S_IRUSR | S_IWUSR | S_IXUSR)}.
@comment sys/stat.h
@comment POSIX.1
@item S_IRGRP
@vindex S_IRGRP
Read permission bit for the group owner of the file. Usually 040.
@comment sys/stat.h
@comment POSIX.1
@item S_IWGRP
@vindex S_IWGRP
Write permission bit for the group owner of the file. Usually 020.
@comment sys/stat.h
@comment POSIX.1
@item S_IXGRP
@vindex S_IXGRP
Execute or search permission bit for the group owner of the file.
Usually 010.
@comment sys/stat.h
@comment POSIX.1
@item S_IRWXG
@vindex S_IRWXG
This is equivalent to @samp{(S_IRGRP | S_IWGRP | S_IXGRP)}.
@comment sys/stat.h
@comment POSIX.1
@item S_IROTH
@vindex S_IROTH
Read permission bit for other users. Usually 04.
@comment sys/stat.h
@comment POSIX.1
@item S_IWOTH
@vindex S_IWOTH
Write permission bit for other users. Usually 02.
@comment sys/stat.h
@comment POSIX.1
@item S_IXOTH
@vindex S_IXOTH
Execute or search permission bit for other users. Usually 01.
@comment sys/stat.h
@comment POSIX.1
@item S_IRWXO
@vindex S_IRWXO
This is equivalent to @samp{(S_IROTH | S_IWOTH | S_IXOTH)}.
@comment sys/stat.h
@comment POSIX
@item S_ISUID
@vindex S_ISUID
This is the set-user-ID on execute bit, usually 04000.
@xref{How Change Persona}.
@comment sys/stat.h
@comment POSIX
@item S_ISGID
@vindex S_ISGID
This is the set-group-ID on execute bit, usually 02000.
@xref{How Change Persona}.
@cindex sticky bit
@comment sys/stat.h
@comment BSD
@item S_ISVTX
@vindex S_ISVTX
This is the @dfn{sticky} bit, usually 01000.
For a directory it gives permission to delete a file in that directory
only if you own that file. Ordinarily, a user can either delete all the
files in a directory or cannot delete any of them (based on whether the
user has write permission for the directory). The same restriction
applies---you must have both write permission for the directory and own
the file you want to delete. The one exception is that the owner of the
directory can delete any file in the directory, no matter who owns it
(provided the owner has given himself write permission for the
directory). This is commonly used for the @file{/tmp} directory, where
anyone may create files but not delete files created by other users.
Originally the sticky bit on an executable file modified the swapping
policies of the system. Normally, when a program terminated, its pages
in core were immediately freed and reused. If the sticky bit was set on
the executable file, the system kept the pages in core for a while as if
the program were still running. This was advantageous for a program
likely to be run many times in succession. This usage is obsolete in
modern systems. When a program terminates, its pages always remain in
core as long as there is no shortage of memory in the system. When the
program is next run, its pages will still be in core if no shortage
arose since the last run.
On some modern systems where the sticky bit has no useful meaning for an
executable file, you cannot set the bit at all for a non-directory.
If you try, @code{chmod} fails with @code{EFTYPE};
@pxref{Setting Permissions}.
Some systems (particularly SunOS) have yet another use for the sticky
bit. If the sticky bit is set on a file that is @emph{not} executable,
it means the opposite: never cache the pages of this file at all. The
main use of this is for the files on an NFS server machine which are
used as the swap area of diskless client machines. The idea is that the
pages of the file will be cached in the client's memory, so it is a
waste of the server's memory to cache them a second time. With this
usage the sticky bit also implies that the filesystem may fail to record
the file's modification time onto disk reliably (the idea being that
no-one cares for a swap file).
This bit is only available on BSD systems (and those derived from
them). Therefore one has to use the @code{_BSD_SOURCE} feature select
macro to get the definition (@pxref{Feature Test Macros}).
@end table
The actual bit values of the symbols are listed in the table above
so you can decode file mode values when debugging your programs.
These bit values are correct for most systems, but they are not
guaranteed.
@strong{Warning:} Writing explicit numbers for file permissions is bad
practice. Not only is it not portable, it also requires everyone who
reads your program to remember what the bits mean. To make your program
clean use the symbolic names.
@node Access Permission
@subsection How Your Access to a File is Decided
@cindex permission to access a file
@cindex access permission for a file
@cindex file access permission
Recall that the operating system normally decides access permission for
a file based on the effective user and group IDs of the process and its
supplementary group IDs, together with the file's owner, group and
permission bits. These concepts are discussed in detail in @ref{Process
Persona}.
If the effective user ID of the process matches the owner user ID of the
file, then permissions for read, write, and execute/search are
controlled by the corresponding ``user'' (or ``owner'') bits. Likewise,
if any of the effective group ID or supplementary group IDs of the
process matches the group owner ID of the file, then permissions are
controlled by the ``group'' bits. Otherwise, permissions are controlled
by the ``other'' bits.
Privileged users, like @samp{root}, can access any file regardless of
its permission bits. As a special case, for a file to be executable
even by a privileged user, at least one of its execute bits must be set.
@node Setting Permissions
@subsection Assigning File Permissions
@cindex file creation mask
@cindex umask
The primitive functions for creating files (for example, @code{open} or
@code{mkdir}) take a @var{mode} argument, which specifies the file
permissions to give the newly created file. This mode is modified by
the process's @dfn{file creation mask}, or @dfn{umask}, before it is
used.
The bits that are set in the file creation mask identify permissions
that are always to be disabled for newly created files. For example, if
you set all the ``other'' access bits in the mask, then newly created
files are not accessible at all to processes in the ``other'' category,
even if the @var{mode} argument passed to the create function would
permit such access. In other words, the file creation mask is the
complement of the ordinary access permissions you want to grant.
Programs that create files typically specify a @var{mode} argument that
includes all the permissions that make sense for the particular file.
For an ordinary file, this is typically read and write permission for
all classes of users. These permissions are then restricted as
specified by the individual user's own file creation mask.
@findex chmod
To change the permission of an existing file given its name, call
@code{chmod}. This function uses the specified permission bits and
ignores the file creation mask.
@pindex umask
In normal use, the file creation mask is initialized by the user's login
shell (using the @code{umask} shell command), and inherited by all
subprocesses. Application programs normally don't need to worry about
the file creation mask. It will automatically do what it is supposed to
do.
When your program needs to create a file and bypass the umask for its
access permissions, the easiest way to do this is to use @code{fchmod}
after opening the file, rather than changing the umask. In fact,
changing the umask is usually done only by shells. They use the
@code{umask} function.
The functions in this section are declared in @file{sys/stat.h}.
@pindex sys/stat.h
@comment sys/stat.h
@comment POSIX.1
@deftypefun mode_t umask (mode_t @var{mask})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{umask} function sets the file creation mask of the current
process to @var{mask}, and returns the previous value of the file
creation mask.
Here is an example showing how to read the mask with @code{umask}
without changing it permanently:
@smallexample
mode_t
read_umask (void)
@{
mode_t mask = umask (0);
umask (mask);
return mask;
@}
@end smallexample
@noindent
However, on @gnuhurdsystems{} it is better to use @code{getumask} if
you just want to read the mask value, because it is reentrant.
@end deftypefun
@comment sys/stat.h
@comment GNU
@deftypefun mode_t getumask (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Return the current value of the file creation mask for the current
process. This function is a GNU extension and is only available on
@gnuhurdsystems{}.
@end deftypefun
@comment sys/stat.h
@comment POSIX.1
@deftypefun int chmod (const char *@var{filename}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{chmod} function sets the access permission bits for the file
named by @var{filename} to @var{mode}.
If @var{filename} is a symbolic link, @code{chmod} changes the
permissions of the file pointed to by the link, not those of the link
itself.
This function returns @code{0} if successful and @code{-1} if not. In
addition to the usual file name errors (@pxref{File Name
Errors}), the following @code{errno} error conditions are defined for
this function:
@table @code
@item ENOENT
The named file doesn't exist.
@item EPERM
This process does not have permission to change the access permissions
of this file. Only the file's owner (as judged by the effective user ID
of the process) or a privileged user can change them.
@item EROFS
The file resides on a read-only file system.
@item EFTYPE
@var{mode} has the @code{S_ISVTX} bit (the ``sticky bit'') set,
and the named file is not a directory. Some systems do not allow setting the
sticky bit on non-directory files, and some do (and only some of those
assign a useful meaning to the bit for non-directory files).
You only get @code{EFTYPE} on systems where the sticky bit has no useful
meaning for non-directory files, so it is always safe to just clear the
bit in @var{mode} and call @code{chmod} again. @xref{Permission Bits},
for full details on the sticky bit.
@end table
@end deftypefun
@comment sys/stat.h
@comment BSD
@deftypefun int fchmod (int @var{filedes}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{chmod}, except that it changes the permissions of the
currently open file given by @var{filedes}.
The return value from @code{fchmod} is @code{0} on success and @code{-1}
on failure. The following @code{errno} error codes are defined for this
function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The @var{filedes} argument corresponds to a pipe or socket, or something
else that doesn't really have access permissions.
@item EPERM
This process does not have permission to change the access permissions
of this file. Only the file's owner (as judged by the effective user ID
of the process) or a privileged user can change them.
@item EROFS
The file resides on a read-only file system.
@end table
@end deftypefun
@node Testing File Access
@subsection Testing Permission to Access a File
@cindex testing access permission
@cindex access, testing for
@cindex setuid programs and file access
In some situations it is desirable to allow programs to access files or
devices even if this is not possible with the permissions granted to the
user. One possible solution is to set the setuid-bit of the program
file. If such a program is started the @emph{effective} user ID of the
process is changed to that of the owner of the program file. So to
allow write access to files like @file{/etc/passwd}, which normally can
be written only by the super-user, the modifying program will have to be
owned by @code{root} and the setuid-bit must be set.
But beside the files the program is intended to change the user should
not be allowed to access any file to which s/he would not have access
anyway. The program therefore must explicitly check whether @emph{the
user} would have the necessary access to a file, before it reads or
writes the file.
To do this, use the function @code{access}, which checks for access
permission based on the process's @emph{real} user ID rather than the
effective user ID. (The setuid feature does not alter the real user ID,
so it reflects the user who actually ran the program.)
There is another way you could check this access, which is easy to
describe, but very hard to use. This is to examine the file mode bits
and mimic the system's own access computation. This method is
undesirable because many systems have additional access control
features; your program cannot portably mimic them, and you would not
want to try to keep track of the diverse features that different systems
have. Using @code{access} is simple and automatically does whatever is
appropriate for the system you are using.
@code{access} is @emph{only} only appropriate to use in setuid programs.
A non-setuid program will always use the effective ID rather than the
real ID.
@pindex unistd.h
The symbols in this section are declared in @file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun int access (const char *@var{filename}, int @var{how})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{access} function checks to see whether the file named by
@var{filename} can be accessed in the way specified by the @var{how}
argument. The @var{how} argument either can be the bitwise OR of the
flags @code{R_OK}, @code{W_OK}, @code{X_OK}, or the existence test
@code{F_OK}.
This function uses the @emph{real} user and group IDs of the calling
process, rather than the @emph{effective} IDs, to check for access
permission. As a result, if you use the function from a @code{setuid}
or @code{setgid} program (@pxref{How Change Persona}), it gives
information relative to the user who actually ran the program.
The return value is @code{0} if the access is permitted, and @code{-1}
otherwise. (In other words, treated as a predicate function,
@code{access} returns true if the requested access is @emph{denied}.)
In addition to the usual file name errors (@pxref{File Name
Errors}), the following @code{errno} error conditions are defined for
this function:
@table @code
@item EACCES
The access specified by @var{how} is denied.
@item ENOENT
The file doesn't exist.
@item EROFS
Write permission was requested for a file on a read-only file system.
@end table
@end deftypefun
These macros are defined in the header file @file{unistd.h} for use
as the @var{how} argument to the @code{access} function. The values
are integer constants.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int R_OK
Flag meaning test for read permission.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int W_OK
Flag meaning test for write permission.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int X_OK
Flag meaning test for execute/search permission.
@end deftypevr
@comment unistd.h
@comment POSIX.1
@deftypevr Macro int F_OK
Flag meaning test for existence of the file.
@end deftypevr
@node File Times
@subsection File Times
@cindex file access time
@cindex file modification time
@cindex file attribute modification time
Each file has three time stamps associated with it: its access time,
its modification time, and its attribute modification time. These
correspond to the @code{st_atime}, @code{st_mtime}, and @code{st_ctime}
members of the @code{stat} structure; see @ref{File Attributes}.
All of these times are represented in calendar time format, as
@code{time_t} objects. This data type is defined in @file{time.h}.
For more information about representation and manipulation of time
values, see @ref{Calendar Time}.
@pindex time.h
Reading from a file updates its access time attribute, and writing
updates its modification time. When a file is created, all three
time stamps for that file are set to the current time. In addition, the
attribute change time and modification time fields of the directory that
contains the new entry are updated.
Adding a new name for a file with the @code{link} function updates the
attribute change time field of the file being linked, and both the
attribute change time and modification time fields of the directory
containing the new name. These same fields are affected if a file name
is deleted with @code{unlink}, @code{remove} or @code{rmdir}. Renaming
a file with @code{rename} affects only the attribute change time and
modification time fields of the two parent directories involved, and not
the times for the file being renamed.
Changing the attributes of a file (for example, with @code{chmod})
updates its attribute change time field.
You can also change some of the time stamps of a file explicitly using
the @code{utime} function---all except the attribute change time. You
need to include the header file @file{utime.h} to use this facility.
@pindex utime.h
@comment utime.h
@comment POSIX.1
@deftp {Data Type} {struct utimbuf}
The @code{utimbuf} structure is used with the @code{utime} function to
specify new access and modification times for a file. It contains the
following members:
@table @code
@item time_t actime
This is the access time for the file.
@item time_t modtime
This is the modification time for the file.
@end table
@end deftp
@comment utime.h
@comment POSIX.1
@deftypefun int utime (const char *@var{filename}, const struct utimbuf *@var{times})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a utime syscall, it non-atomically converts times
@c to a struct timeval and calls utimes.
This function is used to modify the file times associated with the file
named @var{filename}.
If @var{times} is a null pointer, then the access and modification times
of the file are set to the current time. Otherwise, they are set to the
values from the @code{actime} and @code{modtime} members (respectively)
of the @code{utimbuf} structure pointed to by @var{times}.
The attribute modification time for the file is set to the current time
in either case (since changing the time stamps is itself a modification
of the file attributes).
The @code{utime} function returns @code{0} if successful and @code{-1}
on failure. In addition to the usual file name errors
(@pxref{File Name Errors}), the following @code{errno} error conditions
are defined for this function:
@table @code
@item EACCES
There is a permission problem in the case where a null pointer was
passed as the @var{times} argument. In order to update the time stamp on
the file, you must either be the owner of the file, have write
permission for the file, or be a privileged user.
@item ENOENT
The file doesn't exist.
@item EPERM
If the @var{times} argument is not a null pointer, you must either be
the owner of the file or be a privileged user.
@item EROFS
The file lives on a read-only file system.
@end table
@end deftypefun
Each of the three time stamps has a corresponding microsecond part,
which extends its resolution. These fields are called
@code{st_atime_usec}, @code{st_mtime_usec}, and @code{st_ctime_usec};
each has a value between 0 and 999,999, which indicates the time in
microseconds. They correspond to the @code{tv_usec} field of a
@code{timeval} structure; see @ref{High-Resolution Calendar}.
The @code{utimes} function is like @code{utime}, but also lets you specify
the fractional part of the file times. The prototype for this function is
in the header file @file{sys/time.h}.
@pindex sys/time.h
@comment sys/time.h
@comment BSD
@deftypefun int utimes (const char *@var{filename}, const struct timeval @var{tvp}@t{[2]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a utimes syscall, it non-atomically converts tvp
@c to struct timespec array and issues a utimensat syscall, or to
@c struct utimbuf and calls utime.
This function sets the file access and modification times of the file
@var{filename}. The new file access time is specified by
@code{@var{tvp}[0]}, and the new modification time by
@code{@var{tvp}[1]}. Similar to @code{utime}, if @var{tvp} is a null
pointer then the access and modification times of the file are set to
the current time. This function comes from BSD.
The return values and error conditions are the same as for the @code{utime}
function.
@end deftypefun
@comment sys/time.h
@comment BSD
@deftypefun int lutimes (const char *@var{filename}, const struct timeval @var{tvp}@t{[2]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Since there's no lutimes syscall, it non-atomically converts tvp
@c to struct timespec array and issues a utimensat syscall.
This function is like @code{utimes}, except that it does not follow
symbolic links. If @var{filename} is the name of a symbolic link,
@code{lutimes} sets the file access and modification times of the
symbolic link special file itself (as seen by @code{lstat};
@pxref{Symbolic Links}) while @code{utimes} sets the file access and
modification times of the file the symbolic link refers to. This
function comes from FreeBSD, and is not available on all platforms (if
not available, it will fail with @code{ENOSYS}).
The return values and error conditions are the same as for the @code{utime}
function.
@end deftypefun
@comment sys/time.h
@comment BSD
@deftypefun int futimes (int @var{fd}, const struct timeval @var{tvp}@t{[2]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Since there's no futimes syscall, it non-atomically converts tvp
@c to struct timespec array and issues a utimensat syscall, falling back
@c to utimes on a /proc/self/fd symlink.
This function is like @code{utimes}, except that it takes an open file
descriptor as an argument instead of a file name. @xref{Low-Level
I/O}. This function comes from FreeBSD, and is not available on all
platforms (if not available, it will fail with @code{ENOSYS}).
Like @code{utimes}, @code{futimes} returns @code{0} on success and @code{-1}
on failure. The following @code{errno} error conditions are defined for
@code{futimes}:
@table @code
@item EACCES
There is a permission problem in the case where a null pointer was
passed as the @var{times} argument. In order to update the time stamp on
the file, you must either be the owner of the file, have write
permission for the file, or be a privileged user.
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EPERM
If the @var{times} argument is not a null pointer, you must either be
the owner of the file or be a privileged user.
@item EROFS
The file lives on a read-only file system.
@end table
@end deftypefun
@node File Size
@subsection File Size
Normally file sizes are maintained automatically. A file begins with a
size of @math{0} and is automatically extended when data is written past
its end. It is also possible to empty a file completely by an
@code{open} or @code{fopen} call.
However, sometimes it is necessary to @emph{reduce} the size of a file.
This can be done with the @code{truncate} and @code{ftruncate} functions.
They were introduced in BSD Unix. @code{ftruncate} was later added to
POSIX.1.
Some systems allow you to extend a file (creating holes) with these
functions. This is useful when using memory-mapped I/O
(@pxref{Memory-mapped I/O}), where files are not automatically extended.
However, it is not portable but must be implemented if @code{mmap}
allows mapping of files (i.e., @code{_POSIX_MAPPED_FILES} is defined).
Using these functions on anything other than a regular file gives
@emph{undefined} results. On many systems, such a call will appear to
succeed, without actually accomplishing anything.
@comment unistd.h
@comment X/Open
@deftypefun int truncate (const char *@var{filename}, off_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a truncate syscall, we use open and ftruncate.
The @code{truncate} function changes the size of @var{filename} to
@var{length}. If @var{length} is shorter than the previous length, data
at the end will be lost. The file must be writable by the user to
perform this operation.
If @var{length} is longer, holes will be added to the end. However, some
systems do not support this feature and will leave the file unchanged.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{truncate} function is in fact @code{truncate64} and the type
@code{off_t} has 64 bits which makes it possible to handle files up to
@math{2^63} bytes in length.
The return value is @math{0} for success, or @math{-1} for an error. In
addition to the usual file name errors, the following errors may occur:
@table @code
@item EACCES
The file is a directory or not writable.
@item EINVAL
@var{length} is negative.
@item EFBIG
The operation would extend the file beyond the limits of the operating system.
@item EIO
A hardware I/O error occurred.
@item EPERM
The file is "append-only" or "immutable".
@item EINTR
The operation was interrupted by a signal.
@end table
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun int truncate64 (const char *@var{name}, off64_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a syscall, try truncate if length fits.
This function is similar to the @code{truncate} function. The
difference is that the @var{length} argument is 64 bits wide even on 32
bits machines, which allows the handling of files with sizes up to
@math{2^63} bytes.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bits machine this function is actually available under the name
@code{truncate} and so transparently replaces the 32 bits interface.
@end deftypefun
@comment unistd.h
@comment POSIX
@deftypefun int ftruncate (int @var{fd}, off_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{truncate}, but it works on a file descriptor @var{fd}
for an opened file instead of a file name to identify the object. The
file must be opened for writing to successfully carry out the operation.
The POSIX standard leaves it implementation defined what happens if the
specified new @var{length} of the file is bigger than the original size.
The @code{ftruncate} function might simply leave the file alone and do
nothing or it can increase the size to the desired size. In this later
case the extended area should be zero-filled. So using @code{ftruncate}
is no reliable way to increase the file size but if it is possible it is
probably the fastest way. The function also operates on POSIX shared
memory segments if these are implemented by the system.
@code{ftruncate} is especially useful in combination with @code{mmap}.
Since the mapped region must have a fixed size one cannot enlarge the
file by writing something beyond the last mapped page. Instead one has
to enlarge the file itself and then remap the file with the new size.
The example below shows how this works.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{ftruncate} function is in fact @code{ftruncate64} and the type
@code{off_t} has 64 bits which makes it possible to handle files up to
@math{2^63} bytes in length.
The return value is @math{0} for success, or @math{-1} for an error. The
following errors may occur:
@table @code
@item EBADF
@var{fd} does not correspond to an open file.
@item EACCES
@var{fd} is a directory or not open for writing.
@item EINVAL
@var{length} is negative.
@item EFBIG
The operation would extend the file beyond the limits of the operating system.
@c or the open() call -- with the not-yet-discussed feature of opening
@c files with extra-large offsets.
@item EIO
A hardware I/O error occurred.
@item EPERM
The file is "append-only" or "immutable".
@item EINTR
The operation was interrupted by a signal.
@c ENOENT is also possible on Linux --- however it only occurs if the file
@c descriptor has a `file' structure but no `inode' structure. I'm not
@c sure how such an fd could be created. Perhaps it's a bug.
@end table
@end deftypefun
@comment unistd.h
@comment Unix98
@deftypefun int ftruncate64 (int @var{id}, off64_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c In the absence of a syscall, try ftruncate if length fits.
This function is similar to the @code{ftruncate} function. The
difference is that the @var{length} argument is 64 bits wide even on 32
bits machines which allows the handling of files with sizes up to
@math{2^63} bytes.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bits machine this function is actually available under the name
@code{ftruncate} and so transparently replaces the 32 bits interface.
@end deftypefun
As announced here is a little example of how to use @code{ftruncate} in
combination with @code{mmap}:
@smallexample
int fd;
void *start;
size_t len;
int
add (off_t at, void *block, size_t size)
@{
if (at + size > len)
@{
/* Resize the file and remap. */
size_t ps = sysconf (_SC_PAGESIZE);
size_t ns = (at + size + ps - 1) & ~(ps - 1);
void *np;
if (ftruncate (fd, ns) < 0)
return -1;
np = mmap (NULL, ns, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (np == MAP_FAILED)
return -1;
start = np;
len = ns;
@}
memcpy ((char *) start + at, block, size);
return 0;
@}
@end smallexample
The function @code{add} writes a block of memory at an arbitrary
position in the file. If the current size of the file is too small it
is extended. Note the it is extended by a round number of pages. This
is a requirement of @code{mmap}. The program has to keep track of the
real size, and when it has finished a final @code{ftruncate} call should
set the real size of the file.
@node Making Special Files
@section Making Special Files
@cindex creating special files
@cindex special files
The @code{mknod} function is the primitive for making special files,
such as files that correspond to devices. @Theglibc{} includes
this function for compatibility with BSD.
The prototype for @code{mknod} is declared in @file{sys/stat.h}.
@pindex sys/stat.h
@comment sys/stat.h
@comment BSD
@deftypefun int mknod (const char *@var{filename}, mode_t @var{mode}, dev_t @var{dev})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Instead of issuing the syscall directly, we go through xmknod.
@c Although the internal xmknod takes a dev_t*, that could lead to
@c @mtsrace races, it's passed a pointer to mknod's dev.
The @code{mknod} function makes a special file with name @var{filename}.
The @var{mode} specifies the mode of the file, and may include the various
special file bits, such as @code{S_IFCHR} (for a character special file)
or @code{S_IFBLK} (for a block special file). @xref{Testing File Type}.
The @var{dev} argument specifies which device the special file refers to.
Its exact interpretation depends on the kind of special file being created.
The return value is @code{0} on success and @code{-1} on error. In addition
to the usual file name errors (@pxref{File Name Errors}), the
following @code{errno} error conditions are defined for this function:
@table @code
@item EPERM
The calling process is not privileged. Only the superuser can create
special files.
@item ENOSPC
The directory or file system that would contain the new file is full
and cannot be extended.
@item EROFS
The directory containing the new file can't be modified because it's on
a read-only file system.
@item EEXIST
There is already a file named @var{filename}. If you want to replace
this file, you must remove the old file explicitly first.
@end table
@end deftypefun
@node Temporary Files
@section Temporary Files
If you need to use a temporary file in your program, you can use the
@code{tmpfile} function to open it. Or you can use the @code{tmpnam}
(better: @code{tmpnam_r}) function to provide a name for a temporary
file and then you can open it in the usual way with @code{fopen}.
The @code{tempnam} function is like @code{tmpnam} but lets you choose
what directory temporary files will go in, and something about what
their file names will look like. Important for multi-threaded programs
is that @code{tempnam} is reentrant, while @code{tmpnam} is not since it
returns a pointer to a static buffer.
These facilities are declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun {FILE *} tmpfile (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @acsfd{} @aculock{}}}
@c The unsafety issues are those of fdopen, plus @acsfd because of the
@c open.
@c __path_search (internal buf, !dir, const pfx, !try_tmpdir) ok
@c libc_secure_genenv only if try_tmpdir
@c xstat64, strlen, strcmp, sprintf
@c __gen_tempname (internal tmpl, __GT_FILE) ok
@c strlen, memcmp, getpid, open/mkdir/lxstat64 ok
@c HP_TIMING_NOW if available ok
@c gettimeofday (!tz) first time, or every time if no HP_TIMING_NOW ok
@c static value is used and modified without synchronization ok
@c but the use is as a source of non-cryptographic randomness
@c with retries in case of collision, so it should be safe
@c unlink, fdopen
This function creates a temporary binary file for update mode, as if by
calling @code{fopen} with mode @code{"wb+"}. The file is deleted
automatically when it is closed or when the program terminates. (On
some other @w{ISO C} systems the file may fail to be deleted if the program
terminates abnormally).
This function is reentrant.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{tmpfile64}, i.e., the LFS
interface transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun {FILE *} tmpfile64 (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @acsfd{} @aculock{}}}
This function is similar to @code{tmpfile}, but the stream it returns a
pointer to was opened using @code{tmpfile64}. Therefore this stream can
be used for files larger than @math{2^31} bytes on 32-bit machines.
Please note that the return type is still @code{FILE *}. There is no
special @code{FILE} type for the LFS interface.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{tmpfile}
and so transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun {char *} tmpnam (char *@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:tmpnam/!result}}@asunsafe{}@acsafe{}}
@c The passed-in buffer should not be modified concurrently with the
@c call.
@c __path_search (static or passed-in buf, !dir, !pfx, !try_tmpdir) ok
@c __gen_tempname (internal tmpl, __GT_NOCREATE) ok
This function constructs and returns a valid file name that does not
refer to any existing file. If the @var{result} argument is a null
pointer, the return value is a pointer to an internal static string,
which might be modified by subsequent calls and therefore makes this
function non-reentrant. Otherwise, the @var{result} argument should be
a pointer to an array of at least @code{L_tmpnam} characters, and the
result is written into that array.
It is possible for @code{tmpnam} to fail if you call it too many times
without removing previously-created files. This is because the limited
length of the temporary file names gives room for only a finite number
of different names. If @code{tmpnam} fails it returns a null pointer.
@strong{Warning:} Between the time the pathname is constructed and the
file is created another process might have created a file with the same
name using @code{tmpnam}, leading to a possible security hole. The
implementation generates names which can hardly be predicted, but when
opening the file you should use the @code{O_EXCL} flag. Using
@code{tmpfile} or @code{mkstemp} is a safe way to avoid this problem.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun {char *} tmpnam_r (char *@var{result})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is nearly identical to the @code{tmpnam} function, except
that if @var{result} is a null pointer it returns a null pointer.
This guarantees reentrancy because the non-reentrant situation of
@code{tmpnam} cannot happen here.
@strong{Warning}: This function has the same security problems as
@code{tmpnam}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypevr Macro int L_tmpnam
The value of this macro is an integer constant expression that
represents the minimum size of a string large enough to hold a file name
generated by the @code{tmpnam} function.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int TMP_MAX
The macro @code{TMP_MAX} is a lower bound for how many temporary names
you can create with @code{tmpnam}. You can rely on being able to call
@code{tmpnam} at least this many times before it might fail saying you
have made too many temporary file names.
With @theglibc{}, you can create a very large number of temporary
file names. If you actually created the files, you would probably run
out of disk space before you ran out of names. Some other systems have
a fixed, small limit on the number of temporary files. The limit is
never less than @code{25}.
@end deftypevr
@comment stdio.h
@comment SVID
@deftypefun {char *} tempnam (const char *@var{dir}, const char *@var{prefix})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c There's no way (short of being setuid) to avoid getenv("TMPDIR"),
@c even with a non-NULL dir.
@c
@c __path_search (internal buf, dir, pfx, try_tmpdir) unsafe getenv
@c __gen_tempname (internal tmpl, __GT_NOCREATE) ok
@c strdup
This function generates a unique temporary file name. If @var{prefix}
is not a null pointer, up to five characters of this string are used as
a prefix for the file name. The return value is a string newly
allocated with @code{malloc}, so you should release its storage with
@code{free} when it is no longer needed.
Because the string is dynamically allocated this function is reentrant.
The directory prefix for the temporary file name is determined by
testing each of the following in sequence. The directory must exist and
be writable.
@itemize @bullet
@item
The environment variable @code{TMPDIR}, if it is defined. For security
reasons this only happens if the program is not SUID or SGID enabled.
@item
The @var{dir} argument, if it is not a null pointer.
@item
The value of the @code{P_tmpdir} macro.
@item
The directory @file{/tmp}.
@end itemize
This function is defined for SVID compatibility.
@strong{Warning:} Between the time the pathname is constructed and the
file is created another process might have created a file with the same
name using @code{tempnam}, leading to a possible security hole. The
implementation generates names which can hardly be predicted, but when
opening the file you should use the @code{O_EXCL} flag. Using
@code{tmpfile} or @code{mkstemp} is a safe way to avoid this problem.
@end deftypefun
@cindex TMPDIR environment variable
@comment stdio.h
@comment SVID
@c !!! are we putting SVID/GNU/POSIX.1/BSD in here or not??
@deftypevr {SVID Macro} {char *} P_tmpdir
This macro is the name of the default directory for temporary files.
@end deftypevr
Older Unix systems did not have the functions just described. Instead
they used @code{mktemp} and @code{mkstemp}. Both of these functions
work by modifying a file name template string you pass. The last six
characters of this string must be @samp{XXXXXX}. These six @samp{X}s
are replaced with six characters which make the whole string a unique
file name. Usually the template string is something like
@samp{/tmp/@var{prefix}XXXXXX}, and each program uses a unique @var{prefix}.
@strong{NB:} Because @code{mktemp} and @code{mkstemp} modify the
template string, you @emph{must not} pass string constants to them.
String constants are normally in read-only storage, so your program
would crash when @code{mktemp} or @code{mkstemp} tried to modify the
string. These functions are declared in the header file @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment Unix
@deftypefun {char *} mktemp (char *@var{template})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c __gen_tempname (caller tmpl, __GT_NOCREATE) ok
The @code{mktemp} function generates a unique file name by modifying
@var{template} as described above. If successful, it returns
@var{template} as modified. If @code{mktemp} cannot find a unique file
name, it makes @var{template} an empty string and returns that. If
@var{template} does not end with @samp{XXXXXX}, @code{mktemp} returns a
null pointer.
@strong{Warning:} Between the time the pathname is constructed and the
file is created another process might have created a file with the same
name using @code{mktemp}, leading to a possible security hole. The
implementation generates names which can hardly be predicted, but when
opening the file you should use the @code{O_EXCL} flag. Using
@code{mkstemp} is a safe way to avoid this problem.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun int mkstemp (char *@var{template})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
@c __gen_tempname (caller tmpl, __GT_FILE) ok
The @code{mkstemp} function generates a unique file name just as
@code{mktemp} does, but it also opens the file for you with @code{open}
(@pxref{Opening and Closing Files}). If successful, it modifies
@var{template} in place and returns a file descriptor for that file open
for reading and writing. If @code{mkstemp} cannot create a
uniquely-named file, it returns @code{-1}. If @var{template} does not
end with @samp{XXXXXX}, @code{mkstemp} returns @code{-1} and does not
modify @var{template}.
The file is opened using mode @code{0600}. If the file is meant to be
used by other users this mode must be changed explicitly.
@end deftypefun
Unlike @code{mktemp}, @code{mkstemp} is actually guaranteed to create a
unique file that cannot possibly clash with any other program trying to
create a temporary file. This is because it works by calling
@code{open} with the @code{O_EXCL} flag, which says you want to create a
new file and get an error if the file already exists.
@comment stdlib.h
@comment BSD
@deftypefun {char *} mkdtemp (char *@var{template})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c __gen_tempname (caller tmpl, __GT_DIR) ok
The @code{mkdtemp} function creates a directory with a unique name. If
it succeeds, it overwrites @var{template} with the name of the
directory, and returns @var{template}. As with @code{mktemp} and
@code{mkstemp}, @var{template} should be a string ending with
@samp{XXXXXX}.
If @code{mkdtemp} cannot create an uniquely named directory, it returns
@code{NULL} and sets @var{errno} appropriately. If @var{template} does
not end with @samp{XXXXXX}, @code{mkdtemp} returns @code{NULL} and does
not modify @var{template}. @var{errno} will be set to @code{EINVAL} in
this case.
The directory is created using mode @code{0700}.
@end deftypefun
The directory created by @code{mkdtemp} cannot clash with temporary
files or directories created by other users. This is because directory
creation always works like @code{open} with @code{O_EXCL}.
@xref{Creating Directories}.
The @code{mkdtemp} function comes from OpenBSD.
@c FIXME these are undocumented:
@c faccessat
@c fchmodat
@c fchownat
@c futimesat
@c fstatat (there's a commented-out safety assessment for this one)
@c linkat
@c mkdirat
@c mkfifoat
@c name_to_handle_at
@c openat
@c open_by_handle_at
@c readlinkat
@c renameat
@c scandirat
@c symlinkat
@c unlinkat
@c utimensat
@c mknodat
glibc-doc-reference-2.19.orig/manual/Makefile 0000664 0001750 0001750 00000015505 12275120646 021225 0 ustar adconrad adconrad # Copyright (C) 1992-2014 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# .
# Makefile for the GNU C Library manual.
subdir := manual
# Allow override
INSTALL_INFO = install-info
.PHONY: dvi pdf info html
# Get glibc's configuration info.
include ../Makeconfig
dvi: $(objpfx)libc.dvi
pdf: $(objpfx)libc.pdf
TEXI2DVI = texi2dvi
TEXI2PDF = texi2dvi --pdf
ifneq ($(strip $(MAKEINFO)),:)
info: $(objpfx)libc.info
endif
chapters = $(addsuffix .texi, \
intro errno memory ctype string charset locale \
message search pattern io stdio llio filesys \
pipe socket terminal syslog math arith time \
resource setjmp signal startup process job nss \
users sysinfo conf crypt debug threads probes)
add-chapters = $(wildcard $(foreach d, $(add-ons), ../$d/$d.texi))
appendices = lang.texi header.texi install.texi maint.texi platform.texi \
contrib.texi
licenses = freemanuals.texi lgpl-2.1.texi fdl-1.3.texi
-include $(objpfx)texis
$(objpfx)texis: texis.awk $(chapters) $(add-chapters) $(appendices) $(licenses)
$(make-target-directory)
$(AWK) -f $^ > $@.T
mv -f $@.T $@
nonexamples = $(filter-out $(add-chapters) %.c.texi, $(texis))
examples = $(filter-out $(foreach d, $(add-ons), ../$d/%.c.texi), \
$(filter %.c.texi, $(texis)))
# Generated files directly included from libc.texinfo.
libc-texi-generated = chapters.texi top-menu.texi dir-add.texi \
libm-err.texi version.texi pkgvers.texi
# Add path to build dir for generated files
texis-path := $(filter-out $(libc-texi-generated) summary.texi $(examples), \
$(texis)) \
$(addprefix $(objpfx),$(filter $(libc-texi-generated) summary.texi \
$(examples), $(texis)))
# Kludge: implicit rule so Make knows the one command does it all.
chapters.% top-menu.%: libc-texinfo.sh $(texis-path) Makefile
AWK=$(AWK) $(SHELL) $< $(objpfx) \
'$(chapters)' \
'$(add-chapters)' \
'$(appendices) $(licenses)'
$(objpfx)libc.dvi $(objpfx)libc.pdf $(objpfx)libc.info: \
$(addprefix $(objpfx),$(libc-texi-generated))
$(objpfx)libc.dvi $(objpfx)libc.pdf: texinfo.tex
html: $(objpfx)libc/index.html
$(objpfx)libc/index.html: $(addprefix $(objpfx),$(libc-texi-generated))
$(MAKEINFO) -P $(objpfx) -o $(objpfx)libc --html libc.texinfo
# Generate the summary from the Texinfo source files for each chapter.
$(objpfx)summary.texi: $(objpfx)stamp-summary ;
$(objpfx)stamp-summary: summary.awk $(filter-out $(objpfx)summary.texi, \
$(texis-path))
-$(SHELL) ./check-safety.sh $(filter-out $(objpfx)%, $(texis-path))
$(AWK) -f $^ | sort -t' ' -df -k 1,1 | tr '\014' '\012' \
> $(objpfx)summary-tmp
$(move-if-change) $(objpfx)summary-tmp $(objpfx)summary.texi
touch $@
# Generate a file which can be added to the `dir' content to provide direct
# access to the documentation of the function, variables, and other
# definitions.
$(objpfx)dir-add.texi: xtract-typefun.awk $(texis-path)
(echo "@dircategory GNU C library functions and macros"; \
echo "@direntry"; \
$(AWK) -f $^ | sort; \
echo "@end direntry") > $@.new
mv -f $@.new $@
# The table with the math errors is generated.
$(objpfx)libm-err.texi: $(objpfx)stamp-libm-err
$(objpfx)stamp-libm-err: libm-err-tab.pl $(wildcard $(foreach dir,$(sysdirs),\
$(dir)/libm-test-ulps))
pwd=`pwd`; \
$(PERL) $< $$pwd/.. > $(objpfx)libm-err-tmp
$(move-if-change) $(objpfx)libm-err-tmp $(objpfx)libm-err.texi
touch $@
# Package version and bug reporting URL.
$(objpfx)pkgvers.texi: $(objpfx)stamp-pkgvers ;
$(objpfx)stamp-pkgvers: $(common-objpfx)config.make
echo "@ifclear PKGVERS" > $(objpfx)pkgvers-tmp
echo "@set PKGVERS" >> $(objpfx)pkgvers-tmp
echo "@set PKGVERSION $(PKGVERSION_TEXI)" >> $(objpfx)pkgvers-tmp
if [ "$(PKGVERSION_TEXI)" = "(GNU libc) " ]; then \
echo "@set PKGVERSION_DEFAULT" >> $(objpfx)pkgvers-tmp; \
fi
echo "@set REPORT_BUGS_TO $(REPORT_BUGS_TEXI)" >> $(objpfx)pkgvers-tmp
echo "@end ifclear" >> $(objpfx)pkgvers-tmp
$(move-if-change) $(objpfx)pkgvers-tmp $(objpfx)pkgvers.texi
touch $@
# Generate a file with the version number.
$(objpfx)version.texi: $(objpfx)stamp-version ;
$(objpfx)stamp-version: $(common-objpfx)config.make
echo "@set VERSION $(version)" > $(objpfx)version-tmp
$(move-if-change) $(objpfx)version-tmp $(objpfx)version.texi
touch $@
# Generate Texinfo files from the C source for the example programs.
$(objpfx)%.c.texi: examples/%.c
sed -e '1,/^\*\/$$/d' \
-e 's,[{}],@&,g' \
-e 's,/\*\(@.*\)\*/,\1,g' \
-e 's,/\* *,/* @r{,g' -e 's, *\*/,} */,' \
-e 's/\(@[a-z][a-z]*\)@{\([^}]*\)@}/\1{\2}/g'\
$< | expand > $@.new
mv -f $@.new $@
$(objpfx)%.info: %.texinfo
LANGUAGE=C LC_ALL=C $(MAKEINFO) -P $(objpfx) --output=$@ $<
$(objpfx)%.dvi: %.texinfo
cd $(objpfx);$(TEXI2DVI) -I $(shell cd $(/dev/null 2>&1; then \
test -f $(inst_infodir)/dir || $(INSTALL_DATA) dir $(inst_infodir);\
$(INSTALL_INFO) --info-dir=$(inst_infodir) $(inst_infodir)/libc.info;\
else : ; fi
endif
# Catchall implicit rule for other installation targets from the parent.
install-%: ;
$(inst_infodir)/libc.info: $(objpfx)libc.info
$(make-target-directory)
for file in $<*; do \
$(INSTALL_DATA) $$file $(@D)/; \
done
TAGS: $(minimal-dist)
$(ETAGS) -o $@ $^
glibc-doc-reference-2.19.orig/manual/threads.texi 0000664 0001750 0001750 00000017331 12275120646 022111 0 ustar adconrad adconrad @node POSIX Threads
@c @node POSIX Threads, Internal Probes, Cryptographic Functions, Top
@chapter POSIX Threads
@c %MENU% POSIX Threads
@cindex pthreads
This chapter describes the @glibcadj{} POSIX Thread implementation.
@menu
* Thread-specific Data:: Support for creating and
managing thread-specific data
* Non-POSIX Extensions:: Additional functions to extend
POSIX Thread functionality
@end menu
@node Thread-specific Data
@section Thread-specific Data
The @glibcadj{} implements functions to allow users to create and manage
data specific to a thread. Such data may be destroyed at thread exit,
if a destructor is provided. The following functions are defined:
@deftypefun int pthread_key_create (pthread_key_t *@var{key}, void (*@var{destructor})(void*))
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c pthread_key_create ok
@c KEY_UNUSED ok
@c KEY_USABLE ok
Create a thread-specific data key for the calling thread, referenced by
@var{key}.
Objects declared with the C++11 @code{thread_local} keyword are destroyed
before thread-specific data, so they should not be used in thread-specific
data destructors or even as members of the thread-specific data, since the
latter is passed as an argument to the destructor function.
@end deftypefun
@deftypefun int pthread_key_delete (pthread_key_t @var{key})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c pthread_key_delete ok
@c This uses atomic compare and exchange to increment the seq number
@c after testing it's not a KEY_UNUSED seq number.
@c KEY_UNUSED dup ok
Destroy the thread-specific data @var{key} in the calling thread. The
destructor for the thread-specific data is not called during destruction, nor
is it called during thread exit.
@end deftypefun
@deftypefun void *pthread_getspecific (pthread_key_t @var{key})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c pthread_getspecific ok
Return the thread-specific data associated with @var{key} in the calling
thread.
@end deftypefun
@deftypefun int pthread_setspecific (pthread_key_t @var{key}, const void *@var{value})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c pthread_setspecific @asucorrupt @ascuheap @acucorrupt @acsmem
@c a level2 block may be allocated by a signal handler after
@c another call already made a decision to allocate it, thus losing
@c the allocated value. the seq number is updated before the
@c value, which might cause an earlier-generation value to seem
@c current if setspecific is cancelled or interrupted by a signal
@c KEY_UNUSED ok
@c calloc dup @ascuheap @acsmem
Associate the thread-specific @var{value} with @var{key} in the calling thread.
@end deftypefun
@node Non-POSIX Extensions
@section Non-POSIX Extensions
In addition to implementing the POSIX API for threads, @theglibc{} provides
additional functions and interfaces to provide functionality not specified in
the standard.
@menu
* Default Thread Attributes:: Setting default attributes for
threads in a process.
@end menu
@node Default Thread Attributes
@subsection Setting Process-wide defaults for thread attributes
@Theglibc{} provides non-standard API functions to set and get the default
attributes used in the creation of threads in a process.
@deftypefun int pthread_getattr_default_np (pthread_attr_t *@var{attr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c Takes lock around read from default_pthread_attr.
Get the default attribute values and set @var{attr} to match. This
function returns @math{0} on success and a non-zero error code on
failure.
@end deftypefun
@deftypefun int pthread_setattr_default_np (pthread_attr_t *@var{attr})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
@c pthread_setattr_default_np @ascuheap @asulock @aculock @acsmem
@c check_sched_policy_attr ok
@c check_sched_priority_attr ok
@c sched_get_priority_min dup ok
@c sched_get_priority_max dup ok
@c check_cpuset_attr ok
@c determine_cpumask_size ok
@c check_stacksize_attr ok
@c lll_lock @asulock @aculock
@c free dup @ascuheap @acsmem
@c realloc dup @ascuheap @acsmem
@c memcpy dup ok
@c lll_unlock @asulock @aculock
Set the default attribute values to match the values in @var{attr}. The
function returns @math{0} on success and a non-zero error code on failure.
The following error codes are defined for this function:
@table @code
@item EINVAL
At least one of the values in @var{attr} does not qualify as valid for the
attributes or the stack address is set in the attribute.
@item ENOMEM
The system does not have sufficient memory.
@end table
@end deftypefun
@c FIXME these are undocumented:
@c pthread_atfork
@c pthread_attr_destroy
@c pthread_attr_getaffinity_np
@c pthread_attr_getdetachstate
@c pthread_attr_getguardsize
@c pthread_attr_getinheritsched
@c pthread_attr_getschedparam
@c pthread_attr_getschedpolicy
@c pthread_attr_getscope
@c pthread_attr_getstack
@c pthread_attr_getstackaddr
@c pthread_attr_getstacksize
@c pthread_attr_init
@c pthread_attr_setaffinity_np
@c pthread_attr_setdetachstate
@c pthread_attr_setguardsize
@c pthread_attr_setinheritsched
@c pthread_attr_setschedparam
@c pthread_attr_setschedpolicy
@c pthread_attr_setscope
@c pthread_attr_setstack
@c pthread_attr_setstackaddr
@c pthread_attr_setstacksize
@c pthread_barrierattr_destroy
@c pthread_barrierattr_getpshared
@c pthread_barrierattr_init
@c pthread_barrierattr_setpshared
@c pthread_barrier_destroy
@c pthread_barrier_init
@c pthread_barrier_wait
@c pthread_cancel
@c pthread_cleanup_push
@c pthread_cleanup_pop
@c pthread_condattr_destroy
@c pthread_condattr_getclock
@c pthread_condattr_getpshared
@c pthread_condattr_init
@c pthread_condattr_setclock
@c pthread_condattr_setpshared
@c pthread_cond_broadcast
@c pthread_cond_destroy
@c pthread_cond_init
@c pthread_cond_signal
@c pthread_cond_timedwait
@c pthread_cond_wait
@c pthread_create
@c pthread_detach
@c pthread_equal
@c pthread_exit
@c pthread_getaffinity_np
@c pthread_getattr_np
@c pthread_getconcurrency
@c pthread_getcpuclockid
@c pthread_getname_np
@c pthread_getschedparam
@c pthread_join
@c pthread_kill
@c pthread_kill_other_threads_np
@c pthread_mutexattr_destroy
@c pthread_mutexattr_getkind_np
@c pthread_mutexattr_getprioceiling
@c pthread_mutexattr_getprotocol
@c pthread_mutexattr_getpshared
@c pthread_mutexattr_getrobust
@c pthread_mutexattr_getrobust_np
@c pthread_mutexattr_gettype
@c pthread_mutexattr_init
@c pthread_mutexattr_setkind_np
@c pthread_mutexattr_setprioceiling
@c pthread_mutexattr_setprotocol
@c pthread_mutexattr_setpshared
@c pthread_mutexattr_setrobust
@c pthread_mutexattr_setrobust_np
@c pthread_mutexattr_settype
@c pthread_mutex_consistent
@c pthread_mutex_consistent_np
@c pthread_mutex_destroy
@c pthread_mutex_getprioceiling
@c pthread_mutex_init
@c pthread_mutex_lock
@c pthread_mutex_setprioceiling
@c pthread_mutex_timedlock
@c pthread_mutex_trylock
@c pthread_mutex_unlock
@c pthread_once
@c pthread_rwlockattr_destroy
@c pthread_rwlockattr_getkind_np
@c pthread_rwlockattr_getpshared
@c pthread_rwlockattr_init
@c pthread_rwlockattr_setkind_np
@c pthread_rwlockattr_setpshared
@c pthread_rwlock_destroy
@c pthread_rwlock_init
@c pthread_rwlock_rdlock
@c pthread_rwlock_timedrdlock
@c pthread_rwlock_timedwrlock
@c pthread_rwlock_tryrdlock
@c pthread_rwlock_trywrlock
@c pthread_rwlock_unlock
@c pthread_rwlock_wrlock
@c pthread_self
@c pthread_setaffinity_np
@c pthread_setcancelstate
@c pthread_setcanceltype
@c pthread_setconcurrency
@c pthread_setname_np
@c pthread_setschedparam
@c pthread_setschedprio
@c pthread_sigmask
@c pthread_sigqueue
@c pthread_spin_destroy
@c pthread_spin_init
@c pthread_spin_lock
@c pthread_spin_trylock
@c pthread_spin_unlock
@c pthread_testcancel
@c pthread_timedjoin_np
@c pthread_tryjoin_np
@c pthread_yield
glibc-doc-reference-2.19.orig/manual/stdio.texi 0000664 0001750 0001750 00000704117 12275120646 021606 0 ustar adconrad adconrad @node I/O on Streams, Low-Level I/O, I/O Overview, Top
@c %MENU% High-level, portable I/O facilities
@chapter Input/Output on Streams
@c fix an overfull:
@tex
\hyphenation{which-ever}
@end tex
This chapter describes the functions for creating streams and performing
input and output operations on them. As discussed in @ref{I/O
Overview}, a stream is a fairly abstract, high-level concept
representing a communications channel to a file, device, or process.
@menu
* Streams:: About the data type representing a stream.
* Standard Streams:: Streams to the standard input and output
devices are created for you.
* Opening Streams:: How to create a stream to talk to a file.
* Closing Streams:: Close a stream when you are finished with it.
* Streams and Threads:: Issues with streams in threaded programs.
* Streams and I18N:: Streams in internationalized applications.
* Simple Output:: Unformatted output by characters and lines.
* Character Input:: Unformatted input by characters and words.
* Line Input:: Reading a line or a record from a stream.
* Unreading:: Peeking ahead/pushing back input just read.
* Block Input/Output:: Input and output operations on blocks of data.
* Formatted Output:: @code{printf} and related functions.
* Customizing Printf:: You can define new conversion specifiers for
@code{printf} and friends.
* Formatted Input:: @code{scanf} and related functions.
* EOF and Errors:: How you can tell if an I/O error happens.
* Error Recovery:: What you can do about errors.
* Binary Streams:: Some systems distinguish between text files
and binary files.
* File Positioning:: About random-access streams.
* Portable Positioning:: Random access on peculiar ISO C systems.
* Stream Buffering:: How to control buffering of streams.
* Other Kinds of Streams:: Streams that do not necessarily correspond
to an open file.
* Formatted Messages:: Print strictly formatted messages.
@end menu
@node Streams
@section Streams
For historical reasons, the type of the C data structure that represents
a stream is called @code{FILE} rather than ``stream''. Since most of
the library functions deal with objects of type @code{FILE *}, sometimes
the term @dfn{file pointer} is also used to mean ``stream''. This leads
to unfortunate confusion over terminology in many books on C. This
manual, however, is careful to use the terms ``file'' and ``stream''
only in the technical sense.
@cindex file pointer
@pindex stdio.h
The @code{FILE} type is declared in the header file @file{stdio.h}.
@comment stdio.h
@comment ISO
@deftp {Data Type} FILE
This is the data type used to represent stream objects. A @code{FILE}
object holds all of the internal state information about the connection
to the associated file, including such things as the file position
indicator and buffering information. Each stream also has error and
end-of-file status indicators that can be tested with the @code{ferror}
and @code{feof} functions; see @ref{EOF and Errors}.
@end deftp
@code{FILE} objects are allocated and managed internally by the
input/output library functions. Don't try to create your own objects of
type @code{FILE}; let the library do it. Your programs should
deal only with pointers to these objects (that is, @code{FILE *} values)
rather than the objects themselves.
@c !!! should say that FILE's have "No user-serviceable parts inside."
@node Standard Streams
@section Standard Streams
@cindex standard streams
@cindex streams, standard
When the @code{main} function of your program is invoked, it already has
three predefined streams open and available for use. These represent
the ``standard'' input and output channels that have been established
for the process.
These streams are declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypevar {FILE *} stdin
The @dfn{standard input} stream, which is the normal source of input for the
program.
@end deftypevar
@cindex standard input stream
@comment stdio.h
@comment ISO
@deftypevar {FILE *} stdout
The @dfn{standard output} stream, which is used for normal output from
the program.
@end deftypevar
@cindex standard output stream
@comment stdio.h
@comment ISO
@deftypevar {FILE *} stderr
The @dfn{standard error} stream, which is used for error messages and
diagnostics issued by the program.
@end deftypevar
@cindex standard error stream
On @gnusystems{}, you can specify what files or processes correspond to
these streams using the pipe and redirection facilities provided by the
shell. (The primitives shells use to implement these facilities are
described in @ref{File System Interface}.) Most other operating systems
provide similar mechanisms, but the details of how to use them can vary.
In @theglibc{}, @code{stdin}, @code{stdout}, and @code{stderr} are
normal variables which you can set just like any others. For example,
to redirect the standard output to a file, you could do:
@smallexample
fclose (stdout);
stdout = fopen ("standard-output-file", "w");
@end smallexample
Note however, that in other systems @code{stdin}, @code{stdout}, and
@code{stderr} are macros that you cannot assign to in the normal way.
But you can use @code{freopen} to get the effect of closing one and
reopening it. @xref{Opening Streams}.
The three streams @code{stdin}, @code{stdout}, and @code{stderr} are not
unoriented at program start (@pxref{Streams and I18N}).
@node Opening Streams
@section Opening Streams
@cindex opening a stream
Opening a file with the @code{fopen} function creates a new stream and
establishes a connection between the stream and a file. This may
involve creating a new file.
@pindex stdio.h
Everything described in this section is declared in the header file
@file{stdio.h}.
@comment stdio.h
@comment ISO
@deftypefun {FILE *} fopen (const char *@var{filename}, const char *@var{opentype})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @acsfd{} @aculock{}}}
@c fopen may leak the list lock if cancelled within _IO_link_in.
The @code{fopen} function opens a stream for I/O to the file
@var{filename}, and returns a pointer to the stream.
The @var{opentype} argument is a string that controls how the file is
opened and specifies attributes of the resulting stream. It must begin
with one of the following sequences of characters:
@table @samp
@item r
Open an existing file for reading only.
@item w
Open the file for writing only. If the file already exists, it is
truncated to zero length. Otherwise a new file is created.
@item a
Open a file for append access; that is, writing at the end of file only.
If the file already exists, its initial contents are unchanged and
output to the stream is appended to the end of the file.
Otherwise, a new, empty file is created.
@item r+
Open an existing file for both reading and writing. The initial contents
of the file are unchanged and the initial file position is at the
beginning of the file.
@item w+
Open a file for both reading and writing. If the file already exists, it
is truncated to zero length. Otherwise, a new file is created.
@item a+
Open or create file for both reading and appending. If the file exists,
its initial contents are unchanged. Otherwise, a new file is created.
The initial file position for reading is at the beginning of the file,
but output is always appended to the end of the file.
@end table
As you can see, @samp{+} requests a stream that can do both input and
output. When using such a stream, you must call @code{fflush}
(@pxref{Stream Buffering}) or a file positioning function such as
@code{fseek} (@pxref{File Positioning}) when switching from reading
to writing or vice versa. Otherwise, internal buffers might not be
emptied properly.
Additional characters may appear after these to specify flags for the
call. Always put the mode (@samp{r}, @samp{w+}, etc.) first; that is
the only part you are guaranteed will be understood by all systems.
@Theglibc{} defines additional characters for use in @var{opentype}:
@table @samp
@item c
The file is opened with cancellation in the I/O functions disabled.
@item e
The underlying file descriptor will be closed if you use any of the
@code{exec@dots{}} functions (@pxref{Executing a File}). (This is
equivalent to having set @code{FD_CLOEXEC} on that descriptor.
@xref{Descriptor Flags}.)
@item m
The file is opened and accessed using @code{mmap}. This is only
supported with files opened for reading.
@item x
Insist on creating a new file---if a file @var{filename} already
exists, @code{fopen} fails rather than opening it. If you use
@samp{x} you are guaranteed that you will not clobber an existing
file. This is equivalent to the @code{O_EXCL} option to the
@code{open} function (@pxref{Opening and Closing Files}).
The @samp{x} modifier is part of @w{ISO C11}.
@end table
The character @samp{b} in @var{opentype} has a standard meaning; it
requests a binary stream rather than a text stream. But this makes no
difference in POSIX systems (including @gnusystems{}). If both
@samp{+} and @samp{b} are specified, they can appear in either order.
@xref{Binary Streams}.
@cindex stream orientation
@cindex orientation, stream
If the @var{opentype} string contains the sequence
@code{,ccs=@var{STRING}} then @var{STRING} is taken as the name of a
coded character set and @code{fopen} will mark the stream as
wide-oriented with appropriate conversion functions in place to convert
from and to the character set @var{STRING}. Any other stream
is opened initially unoriented and the orientation is decided with the
first file operation. If the first operation is a wide character
operation, the stream is not only marked as wide-oriented, also the
conversion functions to convert to the coded character set used for the
current locale are loaded. This will not change anymore from this point
on even if the locale selected for the @code{LC_CTYPE} category is
changed.
Any other characters in @var{opentype} are simply ignored. They may be
meaningful in other systems.
If the open fails, @code{fopen} returns a null pointer.
When the sources are compiling with @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is in fact @code{fopen64} since the LFS
interface replaces transparently the old interface.
@end deftypefun
You can have multiple streams (or file descriptors) pointing to the same
file open at the same time. If you do only input, this works
straightforwardly, but you must be careful if any output streams are
included. @xref{Stream/Descriptor Precautions}. This is equally true
whether the streams are in one program (not usual) or in several
programs (which can easily happen). It may be advantageous to use the
file locking facilities to avoid simultaneous access. @xref{File
Locks}.
@comment stdio.h
@comment Unix98
@deftypefun {FILE *} fopen64 (const char *@var{filename}, const char *@var{opentype})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @acsfd{} @aculock{}}}
This function is similar to @code{fopen} but the stream it returns a
pointer for is opened using @code{open64}. Therefore this stream can be
used even on files larger than @math{2^31} bytes on 32 bit machines.
Please note that the return type is still @code{FILE *}. There is no
special @code{FILE} type for the LFS interface.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{fopen}
and so transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypevr Macro int FOPEN_MAX
The value of this macro is an integer constant expression that
represents the minimum number of streams that the implementation
guarantees can be open simultaneously. You might be able to open more
than this many streams, but that is not guaranteed. The value of this
constant is at least eight, which includes the three standard streams
@code{stdin}, @code{stdout}, and @code{stderr}. In POSIX.1 systems this
value is determined by the @code{OPEN_MAX} parameter; @pxref{General
Limits}. In BSD and GNU, it is controlled by the @code{RLIMIT_NOFILE}
resource limit; @pxref{Limits on Resources}.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypefun {FILE *} freopen (const char *@var{filename}, const char *@var{opentype}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @acsfd{}}}
@c Like most I/O operations, this one is guarded by a recursive lock,
@c released even upon cancellation, but cancellation may leak file
@c descriptors and leave the stream in an inconsistent state (e.g.,
@c still bound to the closed descriptor). Also, if the stream is
@c part-way through a significant update (say running freopen) when a
@c signal handler calls freopen again on the same stream, the result is
@c likely to be an inconsistent stream, and the possibility of closing
@c twice file descriptor number that the stream used to use, the second
@c time when it might have already been reused by another thread.
This function is like a combination of @code{fclose} and @code{fopen}.
It first closes the stream referred to by @var{stream}, ignoring any
errors that are detected in the process. (Because errors are ignored,
you should not use @code{freopen} on an output stream if you have
actually done any output using the stream.) Then the file named by
@var{filename} is opened with mode @var{opentype} as for @code{fopen},
and associated with the same stream object @var{stream}.
If the operation fails, a null pointer is returned; otherwise,
@code{freopen} returns @var{stream}.
@code{freopen} has traditionally been used to connect a standard stream
such as @code{stdin} with a file of your own choice. This is useful in
programs in which use of a standard stream for certain purposes is
hard-coded. In @theglibc{}, you can simply close the standard
streams and open new ones with @code{fopen}. But other systems lack
this ability, so using @code{freopen} is more portable.
When the sources are compiling with @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is in fact @code{freopen64} since the LFS
interface replaces transparently the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun {FILE *} freopen64 (const char *@var{filename}, const char *@var{opentype}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @acsfd{}}}
This function is similar to @code{freopen}. The only difference is that
on 32 bit machine the stream returned is able to read beyond the
@math{2^31} bytes limits imposed by the normal interface. It should be
noted that the stream pointed to by @var{stream} need not be opened
using @code{fopen64} or @code{freopen64} since its mode is not important
for this function.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{freopen}
and so transparently replaces the old interface.
@end deftypefun
In some situations it is useful to know whether a given stream is
available for reading or writing. This information is normally not
available and would have to be remembered separately. Solaris
introduced a few functions to get this information from the stream
descriptor and these functions are also available in @theglibc{}.
@comment stdio_ext.h
@comment GNU
@deftypefun int __freadable (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{__freadable} function determines whether the stream
@var{stream} was opened to allow reading. In this case the return value
is nonzero. For write-only streams the function returns zero.
This function is declared in @file{stdio_ext.h}.
@end deftypefun
@comment stdio_ext.h
@comment GNU
@deftypefun int __fwritable (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{__fwritable} function determines whether the stream
@var{stream} was opened to allow writing. In this case the return value
is nonzero. For read-only streams the function returns zero.
This function is declared in @file{stdio_ext.h}.
@end deftypefun
For slightly different kind of problems there are two more functions.
They provide even finer-grained information.
@comment stdio_ext.h
@comment GNU
@deftypefun int __freading (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{__freading} function determines whether the stream
@var{stream} was last read from or whether it is opened read-only. In
this case the return value is nonzero, otherwise it is zero.
Determining whether a stream opened for reading and writing was last
used for writing allows to draw conclusions about the content about the
buffer, among other things.
This function is declared in @file{stdio_ext.h}.
@end deftypefun
@comment stdio_ext.h
@comment GNU
@deftypefun int __fwriting (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{__fwriting} function determines whether the stream
@var{stream} was last written to or whether it is opened write-only. In
this case the return value is nonzero, otherwise it is zero.
This function is declared in @file{stdio_ext.h}.
@end deftypefun
@node Closing Streams
@section Closing Streams
@cindex closing a stream
When a stream is closed with @code{fclose}, the connection between the
stream and the file is canceled. After you have closed a stream, you
cannot perform any additional operations on it.
@comment stdio.h
@comment ISO
@deftypefun int fclose (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c After fclose, it is undefined behavior to use the stream it points
@c to. Therefore, one must only call fclose when the stream is
@c otherwise unused. Concurrent uses started before will complete
@c successfully because of the lock, which makes it MT-Safe. Calling it
@c from a signal handler is perfectly safe if the stream is known to be
@c no longer used, which is a precondition for fclose to be safe in the
@c first place; since this is no further requirement, fclose is safe for
@c use in async signals too. After calling fclose, you can no longer
@c use the stream, not even to fclose it again, so its memory and file
@c descriptor may leak if fclose is canceled before @c releasing them.
@c That the stream must be unused and it becomes unused after the call
@c is what would enable fclose to be AS- and AC-Safe while freopen
@c isn't. However, because of the possibility of leaving __gconv_lock
@c taken upon cancellation, AC-Safety is lost.
This function causes @var{stream} to be closed and the connection to
the corresponding file to be broken. Any buffered output is written
and any buffered input is discarded. The @code{fclose} function returns
a value of @code{0} if the file was closed successfully, and @code{EOF}
if an error was detected.
It is important to check for errors when you call @code{fclose} to close
an output stream, because real, everyday errors can be detected at this
time. For example, when @code{fclose} writes the remaining buffered
output, it might get an error because the disk is full. Even if you
know the buffer is empty, errors can still occur when closing a file if
you are using NFS.
The function @code{fclose} is declared in @file{stdio.h}.
@end deftypefun
To close all streams currently available @theglibc{} provides
another function.
@comment stdio.h
@comment GNU
@deftypefun int fcloseall (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:streams}}@asunsafe{}@acsafe{}}
@c Like fclose, using any previously-opened streams after fcloseall is
@c undefined. However, the implementation of fcloseall isn't equivalent
@c to calling fclose for all streams: it just flushes and unbuffers all
@c streams, without any locking. It's the flushing without locking that
@c makes it unsafe.
This function causes all open streams of the process to be closed and
the connection to corresponding files to be broken. All buffered data
is written and any buffered input is discarded. The @code{fcloseall}
function returns a value of @code{0} if all the files were closed
successfully, and @code{EOF} if an error was detected.
This function should be used only in special situations, e.g., when an
error occurred and the program must be aborted. Normally each single
stream should be closed separately so that problems with individual
streams can be identified. It is also problematic since the standard
streams (@pxref{Standard Streams}) will also be closed.
The function @code{fcloseall} is declared in @file{stdio.h}.
@end deftypefun
If the @code{main} function to your program returns, or if you call the
@code{exit} function (@pxref{Normal Termination}), all open streams are
automatically closed properly. If your program terminates in any other
manner, such as by calling the @code{abort} function (@pxref{Aborting a
Program}) or from a fatal signal (@pxref{Signal Handling}), open streams
might not be closed properly. Buffered output might not be flushed and
files may be incomplete. For more information on buffering of streams,
see @ref{Stream Buffering}.
@node Streams and Threads
@section Streams and Threads
@cindex threads
@cindex multi-threaded application
Streams can be used in multi-threaded applications in the same way they
are used in single-threaded applications. But the programmer must be
aware of the possible complications. It is important to know about
these also if the program one writes never use threads since the design
and implementation of many stream functions is heavily influenced by the
requirements added by multi-threaded programming.
The POSIX standard requires that by default the stream operations are
atomic. I.e., issuing two stream operations for the same stream in two
threads at the same time will cause the operations to be executed as if
they were issued sequentially. The buffer operations performed while
reading or writing are protected from other uses of the same stream. To
do this each stream has an internal lock object which has to be
(implicitly) acquired before any work can be done.
But there are situations where this is not enough and there are also
situations where this is not wanted. The implicit locking is not enough
if the program requires more than one stream function call to happen
atomically. One example would be if an output line a program wants to
generate is created by several function calls. The functions by
themselves would ensure only atomicity of their own operation, but not
atomicity over all the function calls. For this it is necessary to
perform the stream locking in the application code.
@comment stdio.h
@comment POSIX
@deftypefun void flockfile (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
@c There's no way to tell whether the lock was acquired before or after
@c cancellation so as to unlock only when appropriate.
The @code{flockfile} function acquires the internal locking object
associated with the stream @var{stream}. This ensures that no other
thread can explicitly through @code{flockfile}/@code{ftrylockfile} or
implicit through a call of a stream function lock the stream. The
thread will block until the lock is acquired. An explicit call to
@code{funlockfile} has to be used to release the lock.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int ftrylockfile (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
The @code{ftrylockfile} function tries to acquire the internal locking
object associated with the stream @var{stream} just like
@code{flockfile}. But unlike @code{flockfile} this function does not
block if the lock is not available. @code{ftrylockfile} returns zero if
the lock was successfully acquired. Otherwise the stream is locked by
another thread.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun void funlockfile (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
The @code{funlockfile} function releases the internal locking object of
the stream @var{stream}. The stream must have been locked before by a
call to @code{flockfile} or a successful call of @code{ftrylockfile}.
The implicit locking performed by the stream operations do not count.
The @code{funlockfile} function does not return an error status and the
behavior of a call for a stream which is not locked by the current
thread is undefined.
@end deftypefun
The following example shows how the functions above can be used to
generate an output line atomically even in multi-threaded applications
(yes, the same job could be done with one @code{fprintf} call but it is
sometimes not possible):
@smallexample
FILE *fp;
@{
@dots{}
flockfile (fp);
fputs ("This is test number ", fp);
fprintf (fp, "%d\n", test);
funlockfile (fp)
@}
@end smallexample
Without the explicit locking it would be possible for another thread to
use the stream @var{fp} after the @code{fputs} call return and before
@code{fprintf} was called with the result that the number does not
follow the word @samp{number}.
From this description it might already be clear that the locking objects
in streams are no simple mutexes. Since locking the same stream twice
in the same thread is allowed the locking objects must be equivalent to
recursive mutexes. These mutexes keep track of the owner and the number
of times the lock is acquired. The same number of @code{funlockfile}
calls by the same threads is necessary to unlock the stream completely.
For instance:
@smallexample
void
foo (FILE *fp)
@{
ftrylockfile (fp);
fputs ("in foo\n", fp);
/* @r{This is very wrong!!!} */
funlockfile (fp);
@}
@end smallexample
It is important here that the @code{funlockfile} function is only called
if the @code{ftrylockfile} function succeeded in locking the stream. It
is therefore always wrong to ignore the result of @code{ftrylockfile}.
And it makes no sense since otherwise one would use @code{flockfile}.
The result of code like that above is that either @code{funlockfile}
tries to free a stream that hasn't been locked by the current thread or it
frees the stream prematurely. The code should look like this:
@smallexample
void
foo (FILE *fp)
@{
if (ftrylockfile (fp) == 0)
@{
fputs ("in foo\n", fp);
funlockfile (fp);
@}
@}
@end smallexample
Now that we covered why it is necessary to have these locking it is
necessary to talk about situations when locking is unwanted and what can
be done. The locking operations (explicit or implicit) don't come for
free. Even if a lock is not taken the cost is not zero. The operations
which have to be performed require memory operations that are safe in
multi-processor environments. With the many local caches involved in
such systems this is quite costly. So it is best to avoid the locking
completely if it is not needed -- because the code in question is never
used in a context where two or more threads may use a stream at a time.
This can be determined most of the time for application code; for
library code which can be used in many contexts one should default to be
conservative and use locking.
There are two basic mechanisms to avoid locking. The first is to use
the @code{_unlocked} variants of the stream operations. The POSIX
standard defines quite a few of those and @theglibc{} adds a few
more. These variants of the functions behave just like the functions
with the name without the suffix except that they do not lock the
stream. Using these functions is very desirable since they are
potentially much faster. This is not only because the locking
operation itself is avoided. More importantly, functions like
@code{putc} and @code{getc} are very simple and traditionally (before the
introduction of threads) were implemented as macros which are very fast
if the buffer is not empty. With the addition of locking requirements
these functions are no longer implemented as macros since they would
expand to too much code.
But these macros are still available with the same functionality under the new
names @code{putc_unlocked} and @code{getc_unlocked}. This possibly huge
difference of speed also suggests the use of the @code{_unlocked}
functions even if locking is required. The difference is that the
locking then has to be performed in the program:
@smallexample
void
foo (FILE *fp, char *buf)
@{
flockfile (fp);
while (*buf != '/')
putc_unlocked (*buf++, fp);
funlockfile (fp);
@}
@end smallexample
If in this example the @code{putc} function would be used and the
explicit locking would be missing the @code{putc} function would have to
acquire the lock in every call, potentially many times depending on when
the loop terminates. Writing it the way illustrated above allows the
@code{putc_unlocked} macro to be used which means no locking and direct
manipulation of the buffer of the stream.
A second way to avoid locking is by using a non-standard function which
was introduced in Solaris and is available in @theglibc{} as well.
@comment stdio_ext.h
@comment GNU
@deftypefun int __fsetlocking (FILE *@var{stream}, int @var{type})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asulock{}}@acsafe{}}
@c Changing the implicit-locking status of a stream while it's in use by
@c another thread may cause a lock to be implicitly acquired and not
@c released, or vice-versa. This function should probably hold the lock
@c while changing this setting, to make sure we don't change it while
@c there are any concurrent uses. Meanwhile, callers should acquire the
@c lock themselves to be safe, and even concurrent uses with external
@c locking will be fine, as long as functions that require external
@c locking are not called without holding locks.
The @code{__fsetlocking} function can be used to select whether the
stream operations will implicitly acquire the locking object of the
stream @var{stream}. By default this is done but it can be disabled and
reinstated using this function. There are three values defined for the
@var{type} parameter.
@vtable @code
@item FSETLOCKING_INTERNAL
The stream @code{stream} will from now on use the default internal
locking. Every stream operation with exception of the @code{_unlocked}
variants will implicitly lock the stream.
@item FSETLOCKING_BYCALLER
After the @code{__fsetlocking} function returns the user is responsible
for locking the stream. None of the stream operations will implicitly
do this anymore until the state is set back to
@code{FSETLOCKING_INTERNAL}.
@item FSETLOCKING_QUERY
@code{__fsetlocking} only queries the current locking state of the
stream. The return value will be @code{FSETLOCKING_INTERNAL} or
@code{FSETLOCKING_BYCALLER} depending on the state.
@end vtable
The return value of @code{__fsetlocking} is either
@code{FSETLOCKING_INTERNAL} or @code{FSETLOCKING_BYCALLER} depending on
the state of the stream before the call.
This function and the values for the @var{type} parameter are declared
in @file{stdio_ext.h}.
@end deftypefun
This function is especially useful when program code has to be used
which is written without knowledge about the @code{_unlocked} functions
(or if the programmer was too lazy to use them).
@node Streams and I18N
@section Streams in Internationalized Applications
@w{ISO C90} introduced the new type @code{wchar_t} to allow handling
larger character sets. What was missing was a possibility to output
strings of @code{wchar_t} directly. One had to convert them into
multibyte strings using @code{mbstowcs} (there was no @code{mbsrtowcs}
yet) and then use the normal stream functions. While this is doable it
is very cumbersome since performing the conversions is not trivial and
greatly increases program complexity and size.
The Unix standard early on (I think in XPG4.2) introduced two additional
format specifiers for the @code{printf} and @code{scanf} families of
functions. Printing and reading of single wide characters was made
possible using the @code{%C} specifier and wide character strings can be
handled with @code{%S}. These modifiers behave just like @code{%c} and
@code{%s} only that they expect the corresponding argument to have the
wide character type and that the wide character and string are
transformed into/from multibyte strings before being used.
This was a beginning but it is still not good enough. Not always is it
desirable to use @code{printf} and @code{scanf}. The other, smaller and
faster functions cannot handle wide characters. Second, it is not
possible to have a format string for @code{printf} and @code{scanf}
consisting of wide characters. The result is that format strings would
have to be generated if they have to contain non-basic characters.
@cindex C++ streams
@cindex streams, C++
In the @w{Amendment 1} to @w{ISO C90} a whole new set of functions was
added to solve the problem. Most of the stream functions got a
counterpart which take a wide character or wide character string instead
of a character or string respectively. The new functions operate on the
same streams (like @code{stdout}). This is different from the model of
the C++ runtime library where separate streams for wide and normal I/O
are used.
@cindex orientation, stream
@cindex stream orientation
Being able to use the same stream for wide and normal operations comes
with a restriction: a stream can be used either for wide operations or
for normal operations. Once it is decided there is no way back. Only a
call to @code{freopen} or @code{freopen64} can reset the
@dfn{orientation}. The orientation can be decided in three ways:
@itemize @bullet
@item
If any of the normal character functions is used (this includes the
@code{fread} and @code{fwrite} functions) the stream is marked as not
wide oriented.
@item
If any of the wide character functions is used the stream is marked as
wide oriented.
@item
The @code{fwide} function can be used to set the orientation either way.
@end itemize
It is important to never mix the use of wide and not wide operations on
a stream. There are no diagnostics issued. The application behavior
will simply be strange or the application will simply crash. The
@code{fwide} function can help avoiding this.
@comment wchar.h
@comment ISO
@deftypefun int fwide (FILE *@var{stream}, int @var{mode})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{}}}
@c Querying is always safe, but changing the stream when it's in use
@c upthread may be problematic. Like most lock-acquiring functions,
@c this one may leak the lock if canceled.
The @code{fwide} function can be used to set and query the state of the
orientation of the stream @var{stream}. If the @var{mode} parameter has
a positive value the streams get wide oriented, for negative values
narrow oriented. It is not possible to overwrite previous orientations
with @code{fwide}. I.e., if the stream @var{stream} was already
oriented before the call nothing is done.
If @var{mode} is zero the current orientation state is queried and
nothing is changed.
The @code{fwide} function returns a negative value, zero, or a positive
value if the stream is narrow, not at all, or wide oriented
respectively.
This function was introduced in @w{Amendment 1} to @w{ISO C90} and is
declared in @file{wchar.h}.
@end deftypefun
It is generally a good idea to orient a stream as early as possible.
This can prevent surprise especially for the standard streams
@code{stdin}, @code{stdout}, and @code{stderr}. If some library
function in some situations uses one of these streams and this use
orients the stream in a different way the rest of the application
expects it one might end up with hard to reproduce errors. Remember
that no errors are signal if the streams are used incorrectly. Leaving
a stream unoriented after creation is normally only necessary for
library functions which create streams which can be used in different
contexts.
When writing code which uses streams and which can be used in different
contexts it is important to query the orientation of the stream before
using it (unless the rules of the library interface demand a specific
orientation). The following little, silly function illustrates this.
@smallexample
void
print_f (FILE *fp)
@{
if (fwide (fp, 0) > 0)
/* @r{Positive return value means wide orientation.} */
fputwc (L'f', fp);
else
fputc ('f', fp);
@}
@end smallexample
Note that in this case the function @code{print_f} decides about the
orientation of the stream if it was unoriented before (will not happen
if the advise above is followed).
The encoding used for the @code{wchar_t} values is unspecified and the
user must not make any assumptions about it. For I/O of @code{wchar_t}
values this means that it is impossible to write these values directly
to the stream. This is not what follows from the @w{ISO C} locale model
either. What happens instead is that the bytes read from or written to
the underlying media are first converted into the internal encoding
chosen by the implementation for @code{wchar_t}. The external encoding
is determined by the @code{LC_CTYPE} category of the current locale or
by the @samp{ccs} part of the mode specification given to @code{fopen},
@code{fopen64}, @code{freopen}, or @code{freopen64}. How and when the
conversion happens is unspecified and it happens invisible to the user.
Since a stream is created in the unoriented state it has at that point
no conversion associated with it. The conversion which will be used is
determined by the @code{LC_CTYPE} category selected at the time the
stream is oriented. If the locales are changed at the runtime this
might produce surprising results unless one pays attention. This is
just another good reason to orient the stream explicitly as soon as
possible, perhaps with a call to @code{fwide}.
@node Simple Output
@section Simple Output by Characters or Lines
@cindex writing to a stream, by characters
This section describes functions for performing character- and
line-oriented output.
These narrow streams functions are declared in the header file
@file{stdio.h} and the wide stream functions in @file{wchar.h}.
@pindex stdio.h
@pindex wchar.h
@comment stdio.h
@comment ISO
@deftypefun int fputc (int @var{c}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c If the stream is in use when interrupted by a signal, the recursive
@c lock won't help ensure the stream is consistent; indeed, if fputc
@c gets a signal precisely before the post-incremented _IO_write_ptr
@c value is stored, we may overwrite the interrupted write. Conversely,
@c depending on compiler optimizations, the incremented _IO_write_ptr
@c may be stored before the character is stored in the buffer,
@c corrupting the stream if async cancel hits between the two stores.
@c There may be other reasons for AS- and AC-unsafety in the overflow
@c cases.
The @code{fputc} function converts the character @var{c} to type
@code{unsigned char}, and writes it to the stream @var{stream}.
@code{EOF} is returned if a write error occurs; otherwise the
character @var{c} is returned.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t fputwc (wchar_t @var{wc}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
The @code{fputwc} function writes the wide character @var{wc} to the
stream @var{stream}. @code{WEOF} is returned if a write error occurs;
otherwise the character @var{wc} is returned.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int fputc_unlocked (int @var{c}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c The unlocked functions can't possibly satisfy the MT-Safety
@c requirements on their own, because they require external locking for
@c safety.
The @code{fputc_unlocked} function is equivalent to the @code{fputc}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment POSIX
@deftypefun wint_t fputwc_unlocked (wchar_t @var{wc}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fputwc_unlocked} function is equivalent to the @code{fputwc}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int putc (int @var{c}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
This is just like @code{fputc}, except that most systems implement it as
a macro, making it faster. One consequence is that it may evaluate the
@var{stream} argument more than once, which is an exception to the
general rule for macros. @code{putc} is usually the best function to
use for writing a single character.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t putwc (wchar_t @var{wc}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
This is just like @code{fputwc}, except that it can be implement as
a macro, making it faster. One consequence is that it may evaluate the
@var{stream} argument more than once, which is an exception to the
general rule for macros. @code{putwc} is usually the best function to
use for writing a single wide character.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int putc_unlocked (int @var{c}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{putc_unlocked} function is equivalent to the @code{putc}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun wint_t putwc_unlocked (wchar_t @var{wc}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{putwc_unlocked} function is equivalent to the @code{putwc}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int putchar (int @var{c})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
The @code{putchar} function is equivalent to @code{putc} with
@code{stdout} as the value of the @var{stream} argument.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t putwchar (wchar_t @var{wc})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
The @code{putwchar} function is equivalent to @code{putwc} with
@code{stdout} as the value of the @var{stream} argument.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int putchar_unlocked (int @var{c})
@safety{@prelim{}@mtunsafe{@mtasurace{:stdout}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{putchar_unlocked} function is equivalent to the @code{putchar}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun wint_t putwchar_unlocked (wchar_t @var{wc})
@safety{@prelim{}@mtunsafe{@mtasurace{:stdout}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{putwchar_unlocked} function is equivalent to the @code{putwchar}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int fputs (const char *@var{s}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
The function @code{fputs} writes the string @var{s} to the stream
@var{stream}. The terminating null character is not written.
This function does @emph{not} add a newline character, either.
It outputs only the characters in the string.
This function returns @code{EOF} if a write error occurs, and otherwise
a non-negative value.
For example:
@smallexample
fputs ("Are ", stdout);
fputs ("you ", stdout);
fputs ("hungry?\n", stdout);
@end smallexample
@noindent
outputs the text @samp{Are you hungry?} followed by a newline.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int fputws (const wchar_t *@var{ws}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
The function @code{fputws} writes the wide character string @var{ws} to
the stream @var{stream}. The terminating null character is not written.
This function does @emph{not} add a newline character, either. It
outputs only the characters in the string.
This function returns @code{WEOF} if a write error occurs, and otherwise
a non-negative value.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int fputs_unlocked (const char *@var{s}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fputs_unlocked} function is equivalent to the @code{fputs}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun int fputws_unlocked (const wchar_t *@var{ws}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fputws_unlocked} function is equivalent to the @code{fputws}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int puts (const char *@var{s})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{puts} function writes the string @var{s} to the stream
@code{stdout} followed by a newline. The terminating null character of
the string is not written. (Note that @code{fputs} does @emph{not}
write a newline as this function does.)
@code{puts} is the most convenient function for printing simple
messages. For example:
@smallexample
puts ("This is a message.");
@end smallexample
@noindent
outputs the text @samp{This is a message.} followed by a newline.
@end deftypefun
@comment stdio.h
@comment SVID
@deftypefun int putw (int @var{w}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function writes the word @var{w} (that is, an @code{int}) to
@var{stream}. It is provided for compatibility with SVID, but we
recommend you use @code{fwrite} instead (@pxref{Block Input/Output}).
@end deftypefun
@node Character Input
@section Character Input
@cindex reading from a stream, by characters
This section describes functions for performing character-oriented
input. These narrow streams functions are declared in the header file
@file{stdio.h} and the wide character functions are declared in
@file{wchar.h}.
@pindex stdio.h
@pindex wchar.h
These functions return an @code{int} or @code{wint_t} value (for narrow
and wide stream functions respectively) that is either a character of
input, or the special value @code{EOF}/@code{WEOF} (usually -1). For
the narrow stream functions it is important to store the result of these
functions in a variable of type @code{int} instead of @code{char}, even
when you plan to use it only as a character. Storing @code{EOF} in a
@code{char} variable truncates its value to the size of a character, so
that it is no longer distinguishable from the valid character
@samp{(char) -1}. So always use an @code{int} for the result of
@code{getc} and friends, and check for @code{EOF} after the call; once
you've verified that the result is not @code{EOF}, you can be sure that
it will fit in a @samp{char} variable without loss of information.
@comment stdio.h
@comment ISO
@deftypefun int fgetc (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
@c Same caveats as fputc, but instead of losing a write in case of async
@c signals, we may read the same character more than once, and the
@c stream may be left in odd states due to cancellation in the underflow
@c cases.
This function reads the next character as an @code{unsigned char} from
the stream @var{stream} and returns its value, converted to an
@code{int}. If an end-of-file condition or read error occurs,
@code{EOF} is returned instead.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t fgetwc (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function reads the next wide character from the stream @var{stream}
and returns its value. If an end-of-file condition or read error
occurs, @code{WEOF} is returned instead.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int fgetc_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fgetc_unlocked} function is equivalent to the @code{fgetc}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun wint_t fgetwc_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fgetwc_unlocked} function is equivalent to the @code{fgetwc}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int getc (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This is just like @code{fgetc}, except that it is permissible (and
typical) for it to be implemented as a macro that evaluates the
@var{stream} argument more than once. @code{getc} is often highly
optimized, so it is usually the best function to use to read a single
character.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t getwc (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This is just like @code{fgetwc}, except that it is permissible for it to
be implemented as a macro that evaluates the @var{stream} argument more
than once. @code{getwc} can be highly optimized, so it is usually the
best function to use to read a single wide character.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int getc_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{getc_unlocked} function is equivalent to the @code{getc}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun wint_t getwc_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{getwc_unlocked} function is equivalent to the @code{getwc}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int getchar (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{getchar} function is equivalent to @code{getc} with @code{stdin}
as the value of the @var{stream} argument.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t getwchar (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{getwchar} function is equivalent to @code{getwc} with @code{stdin}
as the value of the @var{stream} argument.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int getchar_unlocked (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:stdin}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{getchar_unlocked} function is equivalent to the @code{getchar}
function except that it does not implicitly lock the stream.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun wint_t getwchar_unlocked (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:stdin}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{getwchar_unlocked} function is equivalent to the @code{getwchar}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
Here is an example of a function that does input using @code{fgetc}. It
would work just as well using @code{getc} instead, or using
@code{getchar ()} instead of @w{@code{fgetc (stdin)}}. The code would
also work the same for the wide character stream functions.
@smallexample
int
y_or_n_p (const char *question)
@{
fputs (question, stdout);
while (1)
@{
int c, answer;
/* @r{Write a space to separate answer from question.} */
fputc (' ', stdout);
/* @r{Read the first character of the line.}
@r{This should be the answer character, but might not be.} */
c = tolower (fgetc (stdin));
answer = c;
/* @r{Discard rest of input line.} */
while (c != '\n' && c != EOF)
c = fgetc (stdin);
/* @r{Obey the answer if it was valid.} */
if (answer == 'y')
return 1;
if (answer == 'n')
return 0;
/* @r{Answer was invalid: ask for valid answer.} */
fputs ("Please answer y or n:", stdout);
@}
@}
@end smallexample
@comment stdio.h
@comment SVID
@deftypefun int getw (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function reads a word (that is, an @code{int}) from @var{stream}.
It's provided for compatibility with SVID. We recommend you use
@code{fread} instead (@pxref{Block Input/Output}). Unlike @code{getc},
any @code{int} value could be a valid result. @code{getw} returns
@code{EOF} when it encounters end-of-file or an error, but there is no
way to distinguish this from an input word with value -1.
@end deftypefun
@node Line Input
@section Line-Oriented Input
Since many programs interpret input on the basis of lines, it is
convenient to have functions to read a line of text from a stream.
Standard C has functions to do this, but they aren't very safe: null
characters and even (for @code{gets}) long lines can confuse them. So
@theglibc{} provides the nonstandard @code{getline} function that
makes it easy to read lines reliably.
Another GNU extension, @code{getdelim}, generalizes @code{getline}. It
reads a delimited record, defined as everything through the next
occurrence of a specified delimiter character.
All these functions are declared in @file{stdio.h}.
@comment stdio.h
@comment GNU
@deftypefun ssize_t getline (char **@var{lineptr}, size_t *@var{n}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{}}}
@c Besides the usual possibility of getting an inconsistent stream in a
@c signal handler or leaving it inconsistent in case of cancellation,
@c the possibility of leaving a dangling pointer upon cancellation
@c between reallocing the buffer at *lineptr and updating the pointer
@c brings about another case of @acucorrupt.
This function reads an entire line from @var{stream}, storing the text
(including the newline and a terminating null character) in a buffer
and storing the buffer address in @code{*@var{lineptr}}.
Before calling @code{getline}, you should place in @code{*@var{lineptr}}
the address of a buffer @code{*@var{n}} bytes long, allocated with
@code{malloc}. If this buffer is long enough to hold the line,
@code{getline} stores the line in this buffer. Otherwise,
@code{getline} makes the buffer bigger using @code{realloc}, storing the
new buffer address back in @code{*@var{lineptr}} and the increased size
back in @code{*@var{n}}.
@xref{Unconstrained Allocation}.
If you set @code{*@var{lineptr}} to a null pointer, and @code{*@var{n}}
to zero, before the call, then @code{getline} allocates the initial
buffer for you by calling @code{malloc}.
In either case, when @code{getline} returns, @code{*@var{lineptr}} is
a @code{char *} which points to the text of the line.
When @code{getline} is successful, it returns the number of characters
read (including the newline, but not including the terminating null).
This value enables you to distinguish null characters that are part of
the line from the null character inserted as a terminator.
This function is a GNU extension, but it is the recommended way to read
lines from a stream. The alternative standard functions are unreliable.
If an error occurs or end of file is reached without any bytes read,
@code{getline} returns @code{-1}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun ssize_t getdelim (char **@var{lineptr}, size_t *@var{n}, int @var{delimiter}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{}}}
@c See the getline @acucorrupt note.
This function is like @code{getline} except that the character which
tells it to stop reading is not necessarily newline. The argument
@var{delimiter} specifies the delimiter character; @code{getdelim} keeps
reading until it sees that character (or end of file).
The text is stored in @var{lineptr}, including the delimiter character
and a terminating null. Like @code{getline}, @code{getdelim} makes
@var{lineptr} bigger if it isn't big enough.
@code{getline} is in fact implemented in terms of @code{getdelim}, just
like this:
@smallexample
ssize_t
getline (char **lineptr, size_t *n, FILE *stream)
@{
return getdelim (lineptr, n, '\n', stream);
@}
@end smallexample
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun {char *} fgets (char *@var{s}, int @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{fgets} function reads characters from the stream @var{stream}
up to and including a newline character and stores them in the string
@var{s}, adding a null character to mark the end of the string. You
must supply @var{count} characters worth of space in @var{s}, but the
number of characters read is at most @var{count} @minus{} 1. The extra
character space is used to hold the null character at the end of the
string.
If the system is already at end of file when you call @code{fgets}, then
the contents of the array @var{s} are unchanged and a null pointer is
returned. A null pointer is also returned if a read error occurs.
Otherwise, the return value is the pointer @var{s}.
@strong{Warning:} If the input data has a null character, you can't tell.
So don't use @code{fgets} unless you know the data cannot contain a null.
Don't use it to read files edited by the user because, if the user inserts
a null character, you should either handle it properly or print a clear
error message. We recommend using @code{getline} instead of @code{fgets}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} fgetws (wchar_t *@var{ws}, int @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{fgetws} function reads wide characters from the stream
@var{stream} up to and including a newline character and stores them in
the string @var{ws}, adding a null wide character to mark the end of the
string. You must supply @var{count} wide characters worth of space in
@var{ws}, but the number of characters read is at most @var{count}
@minus{} 1. The extra character space is used to hold the null wide
character at the end of the string.
If the system is already at end of file when you call @code{fgetws}, then
the contents of the array @var{ws} are unchanged and a null pointer is
returned. A null pointer is also returned if a read error occurs.
Otherwise, the return value is the pointer @var{ws}.
@strong{Warning:} If the input data has a null wide character (which are
null bytes in the input stream), you can't tell. So don't use
@code{fgetws} unless you know the data cannot contain a null. Don't use
it to read files edited by the user because, if the user inserts a null
character, you should either handle it properly or print a clear error
message.
@comment XXX We need getwline!!!
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun {char *} fgets_unlocked (char *@var{s}, int @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fgets_unlocked} function is equivalent to the @code{fgets}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun {wchar_t *} fgetws_unlocked (wchar_t *@var{ws}, int @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fgetws_unlocked} function is equivalent to the @code{fgetws}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefn {Deprecated function} {char *} gets (char *@var{s})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The function @code{gets} reads characters from the stream @code{stdin}
up to the next newline character, and stores them in the string @var{s}.
The newline character is discarded (note that this differs from the
behavior of @code{fgets}, which copies the newline character into the
string). If @code{gets} encounters a read error or end-of-file, it
returns a null pointer; otherwise it returns @var{s}.
@strong{Warning:} The @code{gets} function is @strong{very dangerous}
because it provides no protection against overflowing the string
@var{s}. @Theglibc{} includes it for compatibility only. You
should @strong{always} use @code{fgets} or @code{getline} instead. To
remind you of this, the linker (if using GNU @code{ld}) will issue a
warning whenever you use @code{gets}.
@end deftypefn
@node Unreading
@section Unreading
@cindex peeking at input
@cindex unreading characters
@cindex pushing input back
In parser programs it is often useful to examine the next character in
the input stream without removing it from the stream. This is called
``peeking ahead'' at the input because your program gets a glimpse of
the input it will read next.
Using stream I/O, you can peek ahead at input by first reading it and
then @dfn{unreading} it (also called @dfn{pushing it back} on the stream).
Unreading a character makes it available to be input again from the stream,
by the next call to @code{fgetc} or other input function on that stream.
@menu
* Unreading Idea:: An explanation of unreading with pictures.
* How Unread:: How to call @code{ungetc} to do unreading.
@end menu
@node Unreading Idea
@subsection What Unreading Means
Here is a pictorial explanation of unreading. Suppose you have a
stream reading a file that contains just six characters, the letters
@samp{foobar}. Suppose you have read three characters so far. The
situation looks like this:
@smallexample
f o o b a r
^
@end smallexample
@noindent
so the next input character will be @samp{b}.
@c @group Invalid outside @example
If instead of reading @samp{b} you unread the letter @samp{o}, you get a
situation like this:
@smallexample
f o o b a r
|
o--
^
@end smallexample
@noindent
so that the next input characters will be @samp{o} and @samp{b}.
@c @end group
@c @group
If you unread @samp{9} instead of @samp{o}, you get this situation:
@smallexample
f o o b a r
|
9--
^
@end smallexample
@noindent
so that the next input characters will be @samp{9} and @samp{b}.
@c @end group
@node How Unread
@subsection Using @code{ungetc} To Do Unreading
The function to unread a character is called @code{ungetc}, because it
reverses the action of @code{getc}.
@comment stdio.h
@comment ISO
@deftypefun int ungetc (int @var{c}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{ungetc} function pushes back the character @var{c} onto the
input stream @var{stream}. So the next input from @var{stream} will
read @var{c} before anything else.
If @var{c} is @code{EOF}, @code{ungetc} does nothing and just returns
@code{EOF}. This lets you call @code{ungetc} with the return value of
@code{getc} without needing to check for an error from @code{getc}.
The character that you push back doesn't have to be the same as the last
character that was actually read from the stream. In fact, it isn't
necessary to actually read any characters from the stream before
unreading them with @code{ungetc}! But that is a strange way to write a
program; usually @code{ungetc} is used only to unread a character that
was just read from the same stream. @Theglibc{} supports this
even on files opened in binary mode, but other systems might not.
@Theglibc{} only supports one character of pushback---in other
words, it does not work to call @code{ungetc} twice without doing input
in between. Other systems might let you push back multiple characters;
then reading from the stream retrieves the characters in the reverse
order that they were pushed.
Pushing back characters doesn't alter the file; only the internal
buffering for the stream is affected. If a file positioning function
(such as @code{fseek}, @code{fseeko} or @code{rewind}; @pxref{File
Positioning}) is called, any pending pushed-back characters are
discarded.
Unreading a character on a stream that is at end of file clears the
end-of-file indicator for the stream, because it makes the character of
input available. After you read that character, trying to read again
will encounter end of file.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun wint_t ungetwc (wint_t @var{wc}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{ungetwc} function behaves just like @code{ungetc} just that it
pushes back a wide character.
@end deftypefun
Here is an example showing the use of @code{getc} and @code{ungetc} to
skip over whitespace characters. When this function reaches a
non-whitespace character, it unreads that character to be seen again on
the next read operation on the stream.
@smallexample
#include
#include
void
skip_whitespace (FILE *stream)
@{
int c;
do
/* @r{No need to check for @code{EOF} because it is not}
@r{@code{isspace}, and @code{ungetc} ignores @code{EOF}.} */
c = getc (stream);
while (isspace (c));
ungetc (c, stream);
@}
@end smallexample
@node Block Input/Output
@section Block Input/Output
This section describes how to do input and output operations on blocks
of data. You can use these functions to read and write binary data, as
well as to read and write text in fixed-size blocks instead of by
characters or lines.
@cindex binary I/O to a stream
@cindex block I/O to a stream
@cindex reading from a stream, by blocks
@cindex writing to a stream, by blocks
Binary files are typically used to read and write blocks of data in the
same format as is used to represent the data in a running program. In
other words, arbitrary blocks of memory---not just character or string
objects---can be written to a binary file, and meaningfully read in
again by the same program.
Storing data in binary form is often considerably more efficient than
using the formatted I/O functions. Also, for floating-point numbers,
the binary form avoids possible loss of precision in the conversion
process. On the other hand, binary files can't be examined or modified
easily using many standard file utilities (such as text editors), and
are not portable between different implementations of the language, or
different kinds of computers.
These functions are declared in @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun size_t fread (void *@var{data}, size_t @var{size}, size_t @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function reads up to @var{count} objects of size @var{size} into
the array @var{data}, from the stream @var{stream}. It returns the
number of objects actually read, which might be less than @var{count} if
a read error occurs or the end of the file is reached. This function
returns a value of zero (and doesn't read anything) if either @var{size}
or @var{count} is zero.
If @code{fread} encounters end of file in the middle of an object, it
returns the number of complete objects read, and discards the partial
object. Therefore, the stream remains at the actual end of the file.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun size_t fread_unlocked (void *@var{data}, size_t @var{size}, size_t @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fread_unlocked} function is equivalent to the @code{fread}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun size_t fwrite (const void *@var{data}, size_t @var{size}, size_t @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function writes up to @var{count} objects of size @var{size} from
the array @var{data}, to the stream @var{stream}. The return value is
normally @var{count}, if the call succeeds. Any other value indicates
some sort of error, such as running out of space.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun size_t fwrite_unlocked (const void *@var{data}, size_t @var{size}, size_t @var{count}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fwrite_unlocked} function is equivalent to the @code{fwrite}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
@node Formatted Output
@section Formatted Output
@cindex format string, for @code{printf}
@cindex template, for @code{printf}
@cindex formatted output to a stream
@cindex writing to a stream, formatted
The functions described in this section (@code{printf} and related
functions) provide a convenient way to perform formatted output. You
call @code{printf} with a @dfn{format string} or @dfn{template string}
that specifies how to format the values of the remaining arguments.
Unless your program is a filter that specifically performs line- or
character-oriented processing, using @code{printf} or one of the other
related functions described in this section is usually the easiest and
most concise way to perform output. These functions are especially
useful for printing error messages, tables of data, and the like.
@menu
* Formatted Output Basics:: Some examples to get you started.
* Output Conversion Syntax:: General syntax of conversion
specifications.
* Table of Output Conversions:: Summary of output conversions and
what they do.
* Integer Conversions:: Details about formatting of integers.
* Floating-Point Conversions:: Details about formatting of
floating-point numbers.
* Other Output Conversions:: Details about formatting of strings,
characters, pointers, and the like.
* Formatted Output Functions:: Descriptions of the actual functions.
* Dynamic Output:: Functions that allocate memory for the output.
* Variable Arguments Output:: @code{vprintf} and friends.
* Parsing a Template String:: What kinds of args does a given template
call for?
* Example of Parsing:: Sample program using @code{parse_printf_format}.
@end menu
@node Formatted Output Basics
@subsection Formatted Output Basics
The @code{printf} function can be used to print any number of arguments.
The template string argument you supply in a call provides
information not only about the number of additional arguments, but also
about their types and what style should be used for printing them.
Ordinary characters in the template string are simply written to the
output stream as-is, while @dfn{conversion specifications} introduced by
a @samp{%} character in the template cause subsequent arguments to be
formatted and written to the output stream. For example,
@cindex conversion specifications (@code{printf})
@smallexample
int pct = 37;
char filename[] = "foo.txt";
printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n",
filename, pct);
@end smallexample
@noindent
produces output like
@smallexample
Processing of `foo.txt' is 37% finished.
Please be patient.
@end smallexample
This example shows the use of the @samp{%d} conversion to specify that
an @code{int} argument should be printed in decimal notation, the
@samp{%s} conversion to specify printing of a string argument, and
the @samp{%%} conversion to print a literal @samp{%} character.
There are also conversions for printing an integer argument as an
unsigned value in octal, decimal, or hexadecimal radix (@samp{%o},
@samp{%u}, or @samp{%x}, respectively); or as a character value
(@samp{%c}).
Floating-point numbers can be printed in normal, fixed-point notation
using the @samp{%f} conversion or in exponential notation using the
@samp{%e} conversion. The @samp{%g} conversion uses either @samp{%e}
or @samp{%f} format, depending on what is more appropriate for the
magnitude of the particular number.
You can control formatting more precisely by writing @dfn{modifiers}
between the @samp{%} and the character that indicates which conversion
to apply. These slightly alter the ordinary behavior of the conversion.
For example, most conversion specifications permit you to specify a
minimum field width and a flag indicating whether you want the result
left- or right-justified within the field.
The specific flags and modifiers that are permitted and their
interpretation vary depending on the particular conversion. They're all
described in more detail in the following sections. Don't worry if this
all seems excessively complicated at first; you can almost always get
reasonable free-format output without using any of the modifiers at all.
The modifiers are mostly used to make the output look ``prettier'' in
tables.
@node Output Conversion Syntax
@subsection Output Conversion Syntax
This section provides details about the precise syntax of conversion
specifications that can appear in a @code{printf} template
string.
Characters in the template string that are not part of a conversion
specification are printed as-is to the output stream. Multibyte
character sequences (@pxref{Character Set Handling}) are permitted in a
template string.
The conversion specifications in a @code{printf} template string have
the general form:
@smallexample
% @r{[} @var{param-no} @r{$]} @var{flags} @var{width} @r{[} . @var{precision} @r{]} @var{type} @var{conversion}
@end smallexample
@noindent
or
@smallexample
% @r{[} @var{param-no} @r{$]} @var{flags} @var{width} . @r{*} @r{[} @var{param-no} @r{$]} @var{type} @var{conversion}
@end smallexample
For example, in the conversion specifier @samp{%-10.8ld}, the @samp{-}
is a flag, @samp{10} specifies the field width, the precision is
@samp{8}, the letter @samp{l} is a type modifier, and @samp{d} specifies
the conversion style. (This particular type specifier says to
print a @code{long int} argument in decimal notation, with a minimum of
8 digits left-justified in a field at least 10 characters wide.)
In more detail, output conversion specifications consist of an
initial @samp{%} character followed in sequence by:
@itemize @bullet
@item
An optional specification of the parameter used for this format.
Normally the parameters to the @code{printf} function are assigned to the
formats in the order of appearance in the format string. But in some
situations (such as message translation) this is not desirable and this
extension allows an explicit parameter to be specified.
The @var{param-no} parts of the format must be integers in the range of
1 to the maximum number of arguments present to the function call. Some
implementations limit this number to a certainly upper bound. The exact
limit can be retrieved by the following constant.
@defvr Macro NL_ARGMAX
The value of @code{NL_ARGMAX} is the maximum value allowed for the
specification of a positional parameter in a @code{printf} call. The
actual value in effect at runtime can be retrieved by using
@code{sysconf} using the @code{_SC_NL_ARGMAX} parameter @pxref{Sysconf
Definition}.
Some system have a quite low limit such as @math{9} for @w{System V}
systems. @Theglibc{} has no real limit.
@end defvr
If any of the formats has a specification for the parameter position all
of them in the format string shall have one. Otherwise the behavior is
undefined.
@item
Zero or more @dfn{flag characters} that modify the normal behavior of
the conversion specification.
@cindex flag character (@code{printf})
@item
An optional decimal integer specifying the @dfn{minimum field width}.
If the normal conversion produces fewer characters than this, the field
is padded with spaces to the specified width. This is a @emph{minimum}
value; if the normal conversion produces more characters than this, the
field is @emph{not} truncated. Normally, the output is right-justified
within the field.
@cindex minimum field width (@code{printf})
You can also specify a field width of @samp{*}. This means that the
next argument in the argument list (before the actual value to be
printed) is used as the field width. The value must be an @code{int}.
If the value is negative, this means to set the @samp{-} flag (see
below) and to use the absolute value as the field width.
@item
An optional @dfn{precision} to specify the number of digits to be
written for the numeric conversions. If the precision is specified, it
consists of a period (@samp{.}) followed optionally by a decimal integer
(which defaults to zero if omitted).
@cindex precision (@code{printf})
You can also specify a precision of @samp{*}. This means that the next
argument in the argument list (before the actual value to be printed) is
used as the precision. The value must be an @code{int}, and is ignored
if it is negative. If you specify @samp{*} for both the field width and
precision, the field width argument precedes the precision argument.
Other C library versions may not recognize this syntax.
@item
An optional @dfn{type modifier character}, which is used to specify the
data type of the corresponding argument if it differs from the default
type. (For example, the integer conversions assume a type of @code{int},
but you can specify @samp{h}, @samp{l}, or @samp{L} for other integer
types.)
@cindex type modifier character (@code{printf})
@item
A character that specifies the conversion to be applied.
@end itemize
The exact options that are permitted and how they are interpreted vary
between the different conversion specifiers. See the descriptions of the
individual conversions for information about the particular options that
they use.
With the @samp{-Wformat} option, the GNU C compiler checks calls to
@code{printf} and related functions. It examines the format string and
verifies that the correct number and types of arguments are supplied.
There is also a GNU C syntax to tell the compiler that a function you
write uses a @code{printf}-style format string.
@xref{Function Attributes, , Declaring Attributes of Functions,
gcc.info, Using GNU CC}, for more information.
@node Table of Output Conversions
@subsection Table of Output Conversions
@cindex output conversions, for @code{printf}
Here is a table summarizing what all the different conversions do:
@table @asis
@item @samp{%d}, @samp{%i}
Print an integer as a signed decimal number. @xref{Integer
Conversions}, for details. @samp{%d} and @samp{%i} are synonymous for
output, but are different when used with @code{scanf} for input
(@pxref{Table of Input Conversions}).
@item @samp{%o}
Print an integer as an unsigned octal number. @xref{Integer
Conversions}, for details.
@item @samp{%u}
Print an integer as an unsigned decimal number. @xref{Integer
Conversions}, for details.
@item @samp{%x}, @samp{%X}
Print an integer as an unsigned hexadecimal number. @samp{%x} uses
lower-case letters and @samp{%X} uses upper-case. @xref{Integer
Conversions}, for details.
@item @samp{%f}
Print a floating-point number in normal (fixed-point) notation.
@xref{Floating-Point Conversions}, for details.
@item @samp{%e}, @samp{%E}
Print a floating-point number in exponential notation. @samp{%e} uses
lower-case letters and @samp{%E} uses upper-case. @xref{Floating-Point
Conversions}, for details.
@item @samp{%g}, @samp{%G}
Print a floating-point number in either normal or exponential notation,
whichever is more appropriate for its magnitude. @samp{%g} uses
lower-case letters and @samp{%G} uses upper-case. @xref{Floating-Point
Conversions}, for details.
@item @samp{%a}, @samp{%A}
Print a floating-point number in a hexadecimal fractional notation which
the exponent to base 2 represented in decimal digits. @samp{%a} uses
lower-case letters and @samp{%A} uses upper-case. @xref{Floating-Point
Conversions}, for details.
@item @samp{%c}
Print a single character. @xref{Other Output Conversions}.
@item @samp{%C}
This is an alias for @samp{%lc} which is supported for compatibility
with the Unix standard.
@item @samp{%s}
Print a string. @xref{Other Output Conversions}.
@item @samp{%S}
This is an alias for @samp{%ls} which is supported for compatibility
with the Unix standard.
@item @samp{%p}
Print the value of a pointer. @xref{Other Output Conversions}.
@item @samp{%n}
Get the number of characters printed so far. @xref{Other Output Conversions}.
Note that this conversion specification never produces any output.
@item @samp{%m}
Print the string corresponding to the value of @code{errno}.
(This is a GNU extension.)
@xref{Other Output Conversions}.
@item @samp{%%}
Print a literal @samp{%} character. @xref{Other Output Conversions}.
@end table
If the syntax of a conversion specification is invalid, unpredictable
things will happen, so don't do this. If there aren't enough function
arguments provided to supply values for all the conversion
specifications in the template string, or if the arguments are not of
the correct types, the results are unpredictable. If you supply more
arguments than conversion specifications, the extra argument values are
simply ignored; this is sometimes useful.
@node Integer Conversions
@subsection Integer Conversions
This section describes the options for the @samp{%d}, @samp{%i},
@samp{%o}, @samp{%u}, @samp{%x}, and @samp{%X} conversion
specifications. These conversions print integers in various formats.
The @samp{%d} and @samp{%i} conversion specifications both print an
@code{int} argument as a signed decimal number; while @samp{%o},
@samp{%u}, and @samp{%x} print the argument as an unsigned octal,
decimal, or hexadecimal number (respectively). The @samp{%X} conversion
specification is just like @samp{%x} except that it uses the characters
@samp{ABCDEF} as digits instead of @samp{abcdef}.
The following flags are meaningful:
@table @asis
@item @samp{-}
Left-justify the result in the field (instead of the normal
right-justification).
@item @samp{+}
For the signed @samp{%d} and @samp{%i} conversions, print a
plus sign if the value is positive.
@item @samp{ }
For the signed @samp{%d} and @samp{%i} conversions, if the result
doesn't start with a plus or minus sign, prefix it with a space
character instead. Since the @samp{+} flag ensures that the result
includes a sign, this flag is ignored if you supply both of them.
@item @samp{#}
For the @samp{%o} conversion, this forces the leading digit to be
@samp{0}, as if by increasing the precision. For @samp{%x} or
@samp{%X}, this prefixes a leading @samp{0x} or @samp{0X} (respectively)
to the result. This doesn't do anything useful for the @samp{%d},
@samp{%i}, or @samp{%u} conversions. Using this flag produces output
which can be parsed by the @code{strtoul} function (@pxref{Parsing of
Integers}) and @code{scanf} with the @samp{%i} conversion
(@pxref{Numeric Input Conversions}).
@item @samp{'}
Separate the digits into groups as specified by the locale specified for
the @code{LC_NUMERIC} category; @pxref{General Numeric}. This flag is a
GNU extension.
@item @samp{0}
Pad the field with zeros instead of spaces. The zeros are placed after
any indication of sign or base. This flag is ignored if the @samp{-}
flag is also specified, or if a precision is specified.
@end table
If a precision is supplied, it specifies the minimum number of digits to
appear; leading zeros are produced if necessary. If you don't specify a
precision, the number is printed with as many digits as it needs. If
you convert a value of zero with an explicit precision of zero, then no
characters at all are produced.
Without a type modifier, the corresponding argument is treated as an
@code{int} (for the signed conversions @samp{%i} and @samp{%d}) or
@code{unsigned int} (for the unsigned conversions @samp{%o}, @samp{%u},
@samp{%x}, and @samp{%X}). Recall that since @code{printf} and friends
are variadic, any @code{char} and @code{short} arguments are
automatically converted to @code{int} by the default argument
promotions. For arguments of other integer types, you can use these
modifiers:
@table @samp
@item hh
Specifies that the argument is a @code{signed char} or @code{unsigned
char}, as appropriate. A @code{char} argument is converted to an
@code{int} or @code{unsigned int} by the default argument promotions
anyway, but the @samp{h} modifier says to convert it back to a
@code{char} again.
This modifier was introduced in @w{ISO C99}.
@item h
Specifies that the argument is a @code{short int} or @code{unsigned
short int}, as appropriate. A @code{short} argument is converted to an
@code{int} or @code{unsigned int} by the default argument promotions
anyway, but the @samp{h} modifier says to convert it back to a
@code{short} again.
@item j
Specifies that the argument is a @code{intmax_t} or @code{uintmax_t}, as
appropriate.
This modifier was introduced in @w{ISO C99}.
@item l
Specifies that the argument is a @code{long int} or @code{unsigned long
int}, as appropriate. Two @samp{l} characters is like the @samp{L}
modifier, below.
If used with @samp{%c} or @samp{%s} the corresponding parameter is
considered as a wide character or wide character string respectively.
This use of @samp{l} was introduced in @w{Amendment 1} to @w{ISO C90}.
@item L
@itemx ll
@itemx q
Specifies that the argument is a @code{long long int}. (This type is
an extension supported by the GNU C compiler. On systems that don't
support extra-long integers, this is the same as @code{long int}.)
The @samp{q} modifier is another name for the same thing, which comes
from 4.4 BSD; a @w{@code{long long int}} is sometimes called a ``quad''
@code{int}.
@item t
Specifies that the argument is a @code{ptrdiff_t}.
This modifier was introduced in @w{ISO C99}.
@item z
@itemx Z
Specifies that the argument is a @code{size_t}.
@samp{z} was introduced in @w{ISO C99}. @samp{Z} is a GNU extension
predating this addition and should not be used in new code.
@end table
Here is an example. Using the template string:
@smallexample
"|%5d|%-5d|%+5d|%+-5d|% 5d|%05d|%5.0d|%5.2d|%d|\n"
@end smallexample
@noindent
to print numbers using the different options for the @samp{%d}
conversion gives results like:
@smallexample
| 0|0 | +0|+0 | 0|00000| | 00|0|
| 1|1 | +1|+1 | 1|00001| 1| 01|1|
| -1|-1 | -1|-1 | -1|-0001| -1| -01|-1|
|100000|100000|+100000|+100000| 100000|100000|100000|100000|100000|
@end smallexample
In particular, notice what happens in the last case where the number
is too large to fit in the minimum field width specified.
Here are some more examples showing how unsigned integers print under
various format options, using the template string:
@smallexample
"|%5u|%5o|%5x|%5X|%#5o|%#5x|%#5X|%#10.8x|\n"
@end smallexample
@smallexample
| 0| 0| 0| 0| 0| 0| 0| 00000000|
| 1| 1| 1| 1| 01| 0x1| 0X1|0x00000001|
|100000|303240|186a0|186A0|0303240|0x186a0|0X186A0|0x000186a0|
@end smallexample
@node Floating-Point Conversions
@subsection Floating-Point Conversions
This section discusses the conversion specifications for floating-point
numbers: the @samp{%f}, @samp{%e}, @samp{%E}, @samp{%g}, and @samp{%G}
conversions.
The @samp{%f} conversion prints its argument in fixed-point notation,
producing output of the form
@w{[@code{-}]@var{ddd}@code{.}@var{ddd}},
where the number of digits following the decimal point is controlled
by the precision you specify.
The @samp{%e} conversion prints its argument in exponential notation,
producing output of the form
@w{[@code{-}]@var{d}@code{.}@var{ddd}@code{e}[@code{+}|@code{-}]@var{dd}}.
Again, the number of digits following the decimal point is controlled by
the precision. The exponent always contains at least two digits. The
@samp{%E} conversion is similar but the exponent is marked with the letter
@samp{E} instead of @samp{e}.
The @samp{%g} and @samp{%G} conversions print the argument in the style
of @samp{%e} or @samp{%E} (respectively) if the exponent would be less
than -4 or greater than or equal to the precision; otherwise they use
the @samp{%f} style. A precision of @code{0}, is taken as 1.
Trailing zeros are removed from the fractional portion of the result and
a decimal-point character appears only if it is followed by a digit.
The @samp{%a} and @samp{%A} conversions are meant for representing
floating-point numbers exactly in textual form so that they can be
exchanged as texts between different programs and/or machines. The
numbers are represented is the form
@w{[@code{-}]@code{0x}@var{h}@code{.}@var{hhh}@code{p}[@code{+}|@code{-}]@var{dd}}.
At the left of the decimal-point character exactly one digit is print.
This character is only @code{0} if the number is denormalized.
Otherwise the value is unspecified; it is implementation dependent how many
bits are used. The number of hexadecimal digits on the right side of
the decimal-point character is equal to the precision. If the precision
is zero it is determined to be large enough to provide an exact
representation of the number (or it is large enough to distinguish two
adjacent values if the @code{FLT_RADIX} is not a power of 2,
@pxref{Floating Point Parameters}). For the @samp{%a} conversion
lower-case characters are used to represent the hexadecimal number and
the prefix and exponent sign are printed as @code{0x} and @code{p}
respectively. Otherwise upper-case characters are used and @code{0X}
and @code{P} are used for the representation of prefix and exponent
string. The exponent to the base of two is printed as a decimal number
using at least one digit but at most as many digits as necessary to
represent the value exactly.
If the value to be printed represents infinity or a NaN, the output is
@w{[@code{-}]@code{inf}} or @code{nan} respectively if the conversion
specifier is @samp{%a}, @samp{%e}, @samp{%f}, or @samp{%g} and it is
@w{[@code{-}]@code{INF}} or @code{NAN} respectively if the conversion is
@samp{%A}, @samp{%E}, or @samp{%G}.
The following flags can be used to modify the behavior:
@comment We use @asis instead of @samp so we can have ` ' as an item.
@table @asis
@item @samp{-}
Left-justify the result in the field. Normally the result is
right-justified.
@item @samp{+}
Always include a plus or minus sign in the result.
@item @samp{ }
If the result doesn't start with a plus or minus sign, prefix it with a
space instead. Since the @samp{+} flag ensures that the result includes
a sign, this flag is ignored if you supply both of them.
@item @samp{#}
Specifies that the result should always include a decimal point, even
if no digits follow it. For the @samp{%g} and @samp{%G} conversions,
this also forces trailing zeros after the decimal point to be left
in place where they would otherwise be removed.
@item @samp{'}
Separate the digits of the integer part of the result into groups as
specified by the locale specified for the @code{LC_NUMERIC} category;
@pxref{General Numeric}. This flag is a GNU extension.
@item @samp{0}
Pad the field with zeros instead of spaces; the zeros are placed
after any sign. This flag is ignored if the @samp{-} flag is also
specified.
@end table
The precision specifies how many digits follow the decimal-point
character for the @samp{%f}, @samp{%e}, and @samp{%E} conversions. For
these conversions, the default precision is @code{6}. If the precision
is explicitly @code{0}, this suppresses the decimal point character
entirely. For the @samp{%g} and @samp{%G} conversions, the precision
specifies how many significant digits to print. Significant digits are
the first digit before the decimal point, and all the digits after it.
If the precision is @code{0} or not specified for @samp{%g} or @samp{%G},
it is treated like a value of @code{1}. If the value being printed
cannot be expressed accurately in the specified number of digits, the
value is rounded to the nearest number that fits.
Without a type modifier, the floating-point conversions use an argument
of type @code{double}. (By the default argument promotions, any
@code{float} arguments are automatically converted to @code{double}.)
The following type modifier is supported:
@table @samp
@item L
An uppercase @samp{L} specifies that the argument is a @code{long
double}.
@end table
Here are some examples showing how numbers print using the various
floating-point conversions. All of the numbers were printed using
this template string:
@smallexample
"|%13.4a|%13.4f|%13.4e|%13.4g|\n"
@end smallexample
Here is the output:
@smallexample
| 0x0.0000p+0| 0.0000| 0.0000e+00| 0|
| 0x1.0000p-1| 0.5000| 5.0000e-01| 0.5|
| 0x1.0000p+0| 1.0000| 1.0000e+00| 1|
| -0x1.0000p+0| -1.0000| -1.0000e+00| -1|
| 0x1.9000p+6| 100.0000| 1.0000e+02| 100|
| 0x1.f400p+9| 1000.0000| 1.0000e+03| 1000|
| 0x1.3880p+13| 10000.0000| 1.0000e+04| 1e+04|
| 0x1.81c8p+13| 12345.0000| 1.2345e+04| 1.234e+04|
| 0x1.86a0p+16| 100000.0000| 1.0000e+05| 1e+05|
| 0x1.e240p+16| 123456.0000| 1.2346e+05| 1.235e+05|
@end smallexample
Notice how the @samp{%g} conversion drops trailing zeros.
@node Other Output Conversions
@subsection Other Output Conversions
This section describes miscellaneous conversions for @code{printf}.
The @samp{%c} conversion prints a single character. In case there is no
@samp{l} modifier the @code{int} argument is first converted to an
@code{unsigned char}. Then, if used in a wide stream function, the
character is converted into the corresponding wide character. The
@samp{-} flag can be used to specify left-justification in the field,
but no other flags are defined, and no precision or type modifier can be
given. For example:
@smallexample
printf ("%c%c%c%c%c", 'h', 'e', 'l', 'l', 'o');
@end smallexample
@noindent
prints @samp{hello}.
If there is a @samp{l} modifier present the argument is expected to be
of type @code{wint_t}. If used in a multibyte function the wide
character is converted into a multibyte character before being added to
the output. In this case more than one output byte can be produced.
The @samp{%s} conversion prints a string. If no @samp{l} modifier is
present the corresponding argument must be of type @code{char *} (or
@code{const char *}). If used in a wide stream function the string is
first converted in a wide character string. A precision can be
specified to indicate the maximum number of characters to write;
otherwise characters in the string up to but not including the
terminating null character are written to the output stream. The
@samp{-} flag can be used to specify left-justification in the field,
but no other flags or type modifiers are defined for this conversion.
For example:
@smallexample
printf ("%3s%-6s", "no", "where");
@end smallexample
@noindent
prints @samp{ nowhere }.
If there is a @samp{l} modifier present the argument is expected to be of type @code{wchar_t} (or @code{const wchar_t *}).
If you accidentally pass a null pointer as the argument for a @samp{%s}
conversion, @theglibc{} prints it as @samp{(null)}. We think this
is more useful than crashing. But it's not good practice to pass a null
argument intentionally.
The @samp{%m} conversion prints the string corresponding to the error
code in @code{errno}. @xref{Error Messages}. Thus:
@smallexample
fprintf (stderr, "can't open `%s': %m\n", filename);
@end smallexample
@noindent
is equivalent to:
@smallexample
fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));
@end smallexample
@noindent
The @samp{%m} conversion is a @glibcadj{} extension.
The @samp{%p} conversion prints a pointer value. The corresponding
argument must be of type @code{void *}. In practice, you can use any
type of pointer.
In @theglibc{}, non-null pointers are printed as unsigned integers,
as if a @samp{%#x} conversion were used. Null pointers print as
@samp{(nil)}. (Pointers might print differently in other systems.)
For example:
@smallexample
printf ("%p", "testing");
@end smallexample
@noindent
prints @samp{0x} followed by a hexadecimal number---the address of the
string constant @code{"testing"}. It does not print the word
@samp{testing}.
You can supply the @samp{-} flag with the @samp{%p} conversion to
specify left-justification, but no other flags, precision, or type
modifiers are defined.
The @samp{%n} conversion is unlike any of the other output conversions.
It uses an argument which must be a pointer to an @code{int}, but
instead of printing anything it stores the number of characters printed
so far by this call at that location. The @samp{h} and @samp{l} type
modifiers are permitted to specify that the argument is of type
@code{short int *} or @code{long int *} instead of @code{int *}, but no
flags, field width, or precision are permitted.
For example,
@smallexample
int nchar;
printf ("%d %s%n\n", 3, "bears", &nchar);
@end smallexample
@noindent
prints:
@smallexample
3 bears
@end smallexample
@noindent
and sets @code{nchar} to @code{7}, because @samp{3 bears} is seven
characters.
The @samp{%%} conversion prints a literal @samp{%} character. This
conversion doesn't use an argument, and no flags, field width,
precision, or type modifiers are permitted.
@node Formatted Output Functions
@subsection Formatted Output Functions
This section describes how to call @code{printf} and related functions.
Prototypes for these functions are in the header file @file{stdio.h}.
Because these functions take a variable number of arguments, you
@emph{must} declare prototypes for them before using them. Of course,
the easiest way to make sure you have all the right prototypes is to
just include @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun int printf (const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
The @code{printf} function prints the optional arguments under the
control of the template string @var{template} to the stream
@code{stdout}. It returns the number of characters printed, or a
negative value if there was an output error.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wprintf (const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
The @code{wprintf} function prints the optional arguments under the
control of the wide template string @var{template} to the stream
@code{stdout}. It returns the number of wide characters printed, or a
negative value if there was an output error.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int fprintf (FILE *@var{stream}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is just like @code{printf}, except that the output is
written to the stream @var{stream} instead of @code{stdout}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int fwprintf (FILE *@var{stream}, const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is just like @code{wprintf}, except that the output is
written to the stream @var{stream} instead of @code{stdout}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int sprintf (char *@var{s}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is like @code{printf}, except that the output is stored in the character
array @var{s} instead of written to a stream. A null character is written
to mark the end of the string.
The @code{sprintf} function returns the number of characters stored in
the array @var{s}, not including the terminating null character.
The behavior of this function is undefined if copying takes place
between objects that overlap---for example, if @var{s} is also given
as an argument to be printed under control of the @samp{%s} conversion.
@xref{Copying and Concatenation}.
@strong{Warning:} The @code{sprintf} function can be @strong{dangerous}
because it can potentially output more characters than can fit in the
allocation size of the string @var{s}. Remember that the field width
given in a conversion specification is only a @emph{minimum} value.
To avoid this problem, you can use @code{snprintf} or @code{asprintf},
described below.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun int swprintf (wchar_t *@var{s}, size_t @var{size}, const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is like @code{wprintf}, except that the output is stored in the
wide character array @var{ws} instead of written to a stream. A null
wide character is written to mark the end of the string. The @var{size}
argument specifies the maximum number of characters to produce. The
trailing null character is counted towards this limit, so you should
allocate at least @var{size} wide characters for the string @var{ws}.
The return value is the number of characters generated for the given
input, excluding the trailing null. If not all output fits into the
provided buffer a negative value is returned. You should try again with
a bigger output string. @emph{Note:} this is different from how
@code{snprintf} handles this situation.
Note that the corresponding narrow stream function takes fewer
parameters. @code{swprintf} in fact corresponds to the @code{snprintf}
function. Since the @code{sprintf} function can be dangerous and should
be avoided the @w{ISO C} committee refused to make the same mistake
again and decided to not define a function exactly corresponding to
@code{sprintf}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int snprintf (char *@var{s}, size_t @var{size}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{snprintf} function is similar to @code{sprintf}, except that
the @var{size} argument specifies the maximum number of characters to
produce. The trailing null character is counted towards this limit, so
you should allocate at least @var{size} characters for the string @var{s}.
If @var{size} is zero, nothing, not even the null byte, shall be written and
@var{s} may be a null pointer.
The return value is the number of characters which would be generated
for the given input, excluding the trailing null. If this value is
greater or equal to @var{size}, not all characters from the result have
been stored in @var{s}. You should try again with a bigger output
string. Here is an example of doing this:
@smallexample
@group
/* @r{Construct a message describing the value of a variable}
@r{whose name is @var{name} and whose value is @var{value}.} */
char *
make_message (char *name, char *value)
@{
/* @r{Guess we need no more than 100 chars of space.} */
int size = 100;
char *buffer = (char *) xmalloc (size);
int nchars;
@end group
@group
if (buffer == NULL)
return NULL;
/* @r{Try to print in the allocated space.} */
nchars = snprintf (buffer, size, "value of %s is %s",
name, value);
@end group
@group
if (nchars >= size)
@{
/* @r{Reallocate buffer now that we know
how much space is needed.} */
size = nchars + 1;
buffer = (char *) xrealloc (buffer, size);
if (buffer != NULL)
/* @r{Try again.} */
snprintf (buffer, size, "value of %s is %s",
name, value);
@}
/* @r{The last call worked, return the string.} */
return buffer;
@}
@end group
@end smallexample
In practice, it is often easier just to use @code{asprintf}, below.
@strong{Attention:} In versions of @theglibc{} prior to 2.1 the
return value is the number of characters stored, not including the
terminating null; unless there was not enough space in @var{s} to
store the result in which case @code{-1} is returned. This was
changed in order to comply with the @w{ISO C99} standard.
@end deftypefun
@node Dynamic Output
@subsection Dynamically Allocating Formatted Output
The functions in this section do formatted output and place the results
in dynamically allocated memory.
@comment stdio.h
@comment GNU
@deftypefun int asprintf (char **@var{ptr}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function is similar to @code{sprintf}, except that it dynamically
allocates a string (as with @code{malloc}; @pxref{Unconstrained
Allocation}) to hold the output, instead of putting the output in a
buffer you allocate in advance. The @var{ptr} argument should be the
address of a @code{char *} object, and a successful call to
@code{asprintf} stores a pointer to the newly allocated string at that
location.
The return value is the number of characters allocated for the buffer, or
less than zero if an error occurred. Usually this means that the buffer
could not be allocated.
Here is how to use @code{asprintf} to get the same result as the
@code{snprintf} example, but more easily:
@smallexample
/* @r{Construct a message describing the value of a variable}
@r{whose name is @var{name} and whose value is @var{value}.} */
char *
make_message (char *name, char *value)
@{
char *result;
if (asprintf (&result, "value of %s is %s", name, value) < 0)
return NULL;
return result;
@}
@end smallexample
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int obstack_printf (struct obstack *@var{obstack}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
This function is similar to @code{asprintf}, except that it uses the
obstack @var{obstack} to allocate the space. @xref{Obstacks}.
The characters are written onto the end of the current object.
To get at them, you must finish the object with @code{obstack_finish}
(@pxref{Growing Objects}).@refill
@end deftypefun
@node Variable Arguments Output
@subsection Variable Arguments Output Functions
The functions @code{vprintf} and friends are provided so that you can
define your own variadic @code{printf}-like functions that make use of
the same internals as the built-in formatted output functions.
The most natural way to define such functions would be to use a language
construct to say, ``Call @code{printf} and pass this template plus all
of my arguments after the first five.'' But there is no way to do this
in C, and it would be hard to provide a way, since at the C language
level there is no way to tell how many arguments your function received.
Since that method is impossible, we provide alternative functions, the
@code{vprintf} series, which lets you pass a @code{va_list} to describe
``all of my arguments after the first five.''
When it is sufficient to define a macro rather than a real function,
the GNU C compiler provides a way to do this much more easily with macros.
For example:
@smallexample
#define myprintf(a, b, c, d, e, rest...) \
printf (mytemplate , ## rest)
@end smallexample
@noindent
@xref{Variadic Macros,,, cpp, The C preprocessor}, for details.
But this is limited to macros, and does not apply to real functions at all.
Before calling @code{vprintf} or the other functions listed in this
section, you @emph{must} call @code{va_start} (@pxref{Variadic
Functions}) to initialize a pointer to the variable arguments. Then you
can call @code{va_arg} to fetch the arguments that you want to handle
yourself. This advances the pointer past those arguments.
Once your @code{va_list} pointer is pointing at the argument of your
choice, you are ready to call @code{vprintf}. That argument and all
subsequent arguments that were passed to your function are used by
@code{vprintf} along with the template that you specified separately.
In some other systems, the @code{va_list} pointer may become invalid
after the call to @code{vprintf}, so you must not use @code{va_arg}
after you call @code{vprintf}. Instead, you should call @code{va_end}
to retire the pointer from service. However, you can safely call
@code{va_start} on another pointer variable and begin fetching the
arguments again through that pointer. Calling @code{vprintf} does not
destroy the argument list of your function, merely the particular
pointer that you passed to it.
GNU C does not have such restrictions. You can safely continue to fetch
arguments from a @code{va_list} pointer after passing it to
@code{vprintf}, and @code{va_end} is a no-op. (Note, however, that
subsequent @code{va_arg} calls will fetch the same arguments which
@code{vprintf} previously used.)
Prototypes for these functions are declared in @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun int vprintf (const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is similar to @code{printf} except that, instead of taking
a variable number of arguments directly, it takes an argument list
pointer @var{ap}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int vwprintf (const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is similar to @code{wprintf} except that, instead of taking
a variable number of arguments directly, it takes an argument list
pointer @var{ap}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int vfprintf (FILE *@var{stream}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c Although vfprintf sets up a cleanup region to release the lock on the
@c output stream, it doesn't use it to release args_value or string in
@c case of cancellation. This doesn't make it unsafe, but cancelling it
@c may leak memory. The unguarded use of __printf_function_table is
@c also of concern for all callers.
@c _itoa ok
@c _udiv_qrnnd_preinv ok
@c group_number ok
@c _i18n_number_rewrite
@c __wctrans ok
@c __towctrans @mtslocale
@c __wcrtomb ok? dup below
@c outdigit_value ok
@c outdigitwc_value ok
@c outchar ok
@c outstring ok
@c PAD ok
@c __printf_fp @mtslocale @ascuheap @acsmem
@c __printf_fphex @mtslocale
@c __readonly_area
@c [GNU/Linux] fopen, strtoul, free
@c __strerror_r ok if no translation, check otherwise
@c __btowc ? gconv-modules
@c __wcrtomb ok (not using internal state) gconv-modules
@c ARGCHECK
@c UNBUFFERED_P (tested before taking the stream lock)
@c buffered_vfprintf ok
@c __find_spec(wc|mb)
@c read_int
@c __libc_use_alloca
@c process_arg
@c process_string_arg
@c extend_alloca
@c __parse_one_spec(wc|mb)
@c *__printf_arginfo_table unguarded
@c __printf_va_arg_table-> unguarded
@c *__printf_function_table unguarded
@c done_add
@c printf_unknown
@c outchar
@c _itoa_word
This is the equivalent of @code{fprintf} with the variable argument list
specified directly as for @code{vprintf}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int vfwprintf (FILE *@var{stream}, const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This is the equivalent of @code{fwprintf} with the variable argument list
specified directly as for @code{vwprintf}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int vsprintf (char *@var{s}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is the equivalent of @code{sprintf} with the variable argument list
specified directly as for @code{vprintf}.
@end deftypefun
@comment wchar.h
@comment GNU
@deftypefun int vswprintf (wchar_t *@var{s}, size_t @var{size}, const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is the equivalent of @code{swprintf} with the variable argument list
specified directly as for @code{vwprintf}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int vsnprintf (char *@var{s}, size_t @var{size}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is the equivalent of @code{snprintf} with the variable argument list
specified directly as for @code{vprintf}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int vasprintf (char **@var{ptr}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{vasprintf} function is the equivalent of @code{asprintf} with the
variable argument list specified directly as for @code{vprintf}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int obstack_vprintf (struct obstack *@var{obstack}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c The obstack is not guarded by mutexes, it might be at an inconsistent
@c state within a signal handler, and it could be left at an
@c inconsistent state in case of cancellation.
The @code{obstack_vprintf} function is the equivalent of
@code{obstack_printf} with the variable argument list specified directly
as for @code{vprintf}.@refill
@end deftypefun
Here's an example showing how you might use @code{vfprintf}. This is a
function that prints error messages to the stream @code{stderr}, along
with a prefix indicating the name of the program
(@pxref{Error Messages}, for a description of
@code{program_invocation_short_name}).
@smallexample
@group
#include
#include
void
eprintf (const char *template, ...)
@{
va_list ap;
extern char *program_invocation_short_name;
fprintf (stderr, "%s: ", program_invocation_short_name);
va_start (ap, template);
vfprintf (stderr, template, ap);
va_end (ap);
@}
@end group
@end smallexample
@noindent
You could call @code{eprintf} like this:
@smallexample
eprintf ("file `%s' does not exist\n", filename);
@end smallexample
In GNU C, there is a special construct you can use to let the compiler
know that a function uses a @code{printf}-style format string. Then it
can check the number and types of arguments in each call to the
function, and warn you when they do not match the format string.
For example, take this declaration of @code{eprintf}:
@smallexample
void eprintf (const char *template, ...)
__attribute__ ((format (printf, 1, 2)));
@end smallexample
@noindent
This tells the compiler that @code{eprintf} uses a format string like
@code{printf} (as opposed to @code{scanf}; @pxref{Formatted Input});
the format string appears as the first argument;
and the arguments to satisfy the format begin with the second.
@xref{Function Attributes, , Declaring Attributes of Functions,
gcc.info, Using GNU CC}, for more information.
@node Parsing a Template String
@subsection Parsing a Template String
@cindex parsing a template string
You can use the function @code{parse_printf_format} to obtain
information about the number and types of arguments that are expected by
a given template string. This function permits interpreters that
provide interfaces to @code{printf} to avoid passing along invalid
arguments from the user's program, which could cause a crash.
All the symbols described in this section are declared in the header
file @file{printf.h}.
@comment printf.h
@comment GNU
@deftypefun size_t parse_printf_format (const char *@var{template}, size_t @var{n}, int *@var{argtypes})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function returns information about the number and types of
arguments expected by the @code{printf} template string @var{template}.
The information is stored in the array @var{argtypes}; each element of
this array describes one argument. This information is encoded using
the various @samp{PA_} macros, listed below.
The argument @var{n} specifies the number of elements in the array
@var{argtypes}. This is the maximum number of elements that
@code{parse_printf_format} will try to write.
@code{parse_printf_format} returns the total number of arguments required
by @var{template}. If this number is greater than @var{n}, then the
information returned describes only the first @var{n} arguments. If you
want information about additional arguments, allocate a bigger
array and call @code{parse_printf_format} again.
@end deftypefun
The argument types are encoded as a combination of a basic type and
modifier flag bits.
@comment printf.h
@comment GNU
@deftypevr Macro int PA_FLAG_MASK
This macro is a bitmask for the type modifier flag bits. You can write
the expression @code{(argtypes[i] & PA_FLAG_MASK)} to extract just the
flag bits for an argument, or @code{(argtypes[i] & ~PA_FLAG_MASK)} to
extract just the basic type code.
@end deftypevr
Here are symbolic constants that represent the basic types; they stand
for integer values.
@vtable @code
@comment printf.h
@comment GNU
@item PA_INT
This specifies that the base type is @code{int}.
@comment printf.h
@comment GNU
@item PA_CHAR
This specifies that the base type is @code{int}, cast to @code{char}.
@comment printf.h
@comment GNU
@item PA_STRING
This specifies that the base type is @code{char *}, a null-terminated string.
@comment printf.h
@comment GNU
@item PA_POINTER
This specifies that the base type is @code{void *}, an arbitrary pointer.
@comment printf.h
@comment GNU
@item PA_FLOAT
This specifies that the base type is @code{float}.
@comment printf.h
@comment GNU
@item PA_DOUBLE
This specifies that the base type is @code{double}.
@comment printf.h
@comment GNU
@item PA_LAST
You can define additional base types for your own programs as offsets
from @code{PA_LAST}. For example, if you have data types @samp{foo}
and @samp{bar} with their own specialized @code{printf} conversions,
you could define encodings for these types as:
@smallexample
#define PA_FOO PA_LAST
#define PA_BAR (PA_LAST + 1)
@end smallexample
@end vtable
Here are the flag bits that modify a basic type. They are combined with
the code for the basic type using inclusive-or.
@vtable @code
@comment printf.h
@comment GNU
@item PA_FLAG_PTR
If this bit is set, it indicates that the encoded type is a pointer to
the base type, rather than an immediate value.
For example, @samp{PA_INT|PA_FLAG_PTR} represents the type @samp{int *}.
@comment printf.h
@comment GNU
@item PA_FLAG_SHORT
If this bit is set, it indicates that the base type is modified with
@code{short}. (This corresponds to the @samp{h} type modifier.)
@comment printf.h
@comment GNU
@item PA_FLAG_LONG
If this bit is set, it indicates that the base type is modified with
@code{long}. (This corresponds to the @samp{l} type modifier.)
@comment printf.h
@comment GNU
@item PA_FLAG_LONG_LONG
If this bit is set, it indicates that the base type is modified with
@code{long long}. (This corresponds to the @samp{L} type modifier.)
@comment printf.h
@comment GNU
@item PA_FLAG_LONG_DOUBLE
This is a synonym for @code{PA_FLAG_LONG_LONG}, used by convention with
a base type of @code{PA_DOUBLE} to indicate a type of @code{long double}.
@end vtable
@ifinfo
For an example of using these facilities, see @ref{Example of Parsing}.
@end ifinfo
@node Example of Parsing
@subsection Example of Parsing a Template String
Here is an example of decoding argument types for a format string. We
assume this is part of an interpreter which contains arguments of type
@code{NUMBER}, @code{CHAR}, @code{STRING} and @code{STRUCTURE} (and
perhaps others which are not valid here).
@smallexample
/* @r{Test whether the @var{nargs} specified objects}
@r{in the vector @var{args} are valid}
@r{for the format string @var{format}:}
@r{if so, return 1.}
@r{If not, return 0 after printing an error message.} */
int
validate_args (char *format, int nargs, OBJECT *args)
@{
int *argtypes;
int nwanted;
/* @r{Get the information about the arguments.}
@r{Each conversion specification must be at least two characters}
@r{long, so there cannot be more specifications than half the}
@r{length of the string.} */
argtypes = (int *) alloca (strlen (format) / 2 * sizeof (int));
nwanted = parse_printf_format (string, nelts, argtypes);
/* @r{Check the number of arguments.} */
if (nwanted > nargs)
@{
error ("too few arguments (at least %d required)", nwanted);
return 0;
@}
/* @r{Check the C type wanted for each argument}
@r{and see if the object given is suitable.} */
for (i = 0; i < nwanted; i++)
@{
int wanted;
if (argtypes[i] & PA_FLAG_PTR)
wanted = STRUCTURE;
else
switch (argtypes[i] & ~PA_FLAG_MASK)
@{
case PA_INT:
case PA_FLOAT:
case PA_DOUBLE:
wanted = NUMBER;
break;
case PA_CHAR:
wanted = CHAR;
break;
case PA_STRING:
wanted = STRING;
break;
case PA_POINTER:
wanted = STRUCTURE;
break;
@}
if (TYPE (args[i]) != wanted)
@{
error ("type mismatch for arg number %d", i);
return 0;
@}
@}
return 1;
@}
@end smallexample
@node Customizing Printf
@section Customizing @code{printf}
@cindex customizing @code{printf}
@cindex defining new @code{printf} conversions
@cindex extending @code{printf}
@Theglibc{} lets you define your own custom conversion specifiers
for @code{printf} template strings, to teach @code{printf} clever ways
to print the important data structures of your program.
The way you do this is by registering the conversion with the function
@code{register_printf_function}; see @ref{Registering New Conversions}.
One of the arguments you pass to this function is a pointer to a handler
function that produces the actual output; see @ref{Defining the Output
Handler}, for information on how to write this function.
You can also install a function that just returns information about the
number and type of arguments expected by the conversion specifier.
@xref{Parsing a Template String}, for information about this.
The facilities of this section are declared in the header file
@file{printf.h}.
@menu
* Registering New Conversions:: Using @code{register_printf_function}
to register a new output conversion.
* Conversion Specifier Options:: The handler must be able to get
the options specified in the
template when it is called.
* Defining the Output Handler:: Defining the handler and arginfo
functions that are passed as arguments
to @code{register_printf_function}.
* Printf Extension Example:: How to define a @code{printf}
handler function.
* Predefined Printf Handlers:: Predefined @code{printf} handlers.
@end menu
@strong{Portability Note:} The ability to extend the syntax of
@code{printf} template strings is a GNU extension. ISO standard C has
nothing similar.
@node Registering New Conversions
@subsection Registering New Conversions
The function to register a new output conversion is
@code{register_printf_function}, declared in @file{printf.h}.
@pindex printf.h
@comment printf.h
@comment GNU
@deftypefun int register_printf_function (int @var{spec}, printf_function @var{handler-function}, printf_arginfo_function @var{arginfo-function})
@safety{@prelim{}@mtunsafe{@mtasuconst{:printfext}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @aculock{}}}
@c This function is guarded by the global non-recursive libc lock, but
@c users of the variables it sets aren't, and those should be MT-Safe,
@c so we're ruling out the use of this extension with threads. Calling
@c it from a signal handler may self-deadlock, and cancellation may
@c leave the lock held, besides leaking allocated memory.
This function defines the conversion specifier character @var{spec}.
Thus, if @var{spec} is @code{'Y'}, it defines the conversion @samp{%Y}.
You can redefine the built-in conversions like @samp{%s}, but flag
characters like @samp{#} and type modifiers like @samp{l} can never be
used as conversions; calling @code{register_printf_function} for those
characters has no effect. It is advisable not to use lowercase letters,
since the ISO C standard warns that additional lowercase letters may be
standardized in future editions of the standard.
The @var{handler-function} is the function called by @code{printf} and
friends when this conversion appears in a template string.
@xref{Defining the Output Handler}, for information about how to define
a function to pass as this argument. If you specify a null pointer, any
existing handler function for @var{spec} is removed.
The @var{arginfo-function} is the function called by
@code{parse_printf_format} when this conversion appears in a
template string. @xref{Parsing a Template String}, for information
about this.
@c The following is not true anymore. The `parse_printf_format' function
@c is now also called from `vfprintf' via `parse_one_spec'.
@c --drepper@gnu, 1996/11/14
@c
@c Normally, you install both functions for a conversion at the same time,
@c but if you are never going to call @code{parse_printf_format}, you do
@c not need to define an arginfo function.
@strong{Attention:} In @theglibc{} versions before 2.0 the
@var{arginfo-function} function did not need to be installed unless
the user used the @code{parse_printf_format} function. This has changed.
Now a call to any of the @code{printf} functions will call this
function when this format specifier appears in the format string.
The return value is @code{0} on success, and @code{-1} on failure
(which occurs if @var{spec} is out of range).
You can redefine the standard output conversions, but this is probably
not a good idea because of the potential for confusion. Library routines
written by other people could break if you do this.
@end deftypefun
@node Conversion Specifier Options
@subsection Conversion Specifier Options
If you define a meaning for @samp{%A}, what if the template contains
@samp{%+23A} or @samp{%-#A}? To implement a sensible meaning for these,
the handler when called needs to be able to get the options specified in
the template.
Both the @var{handler-function} and @var{arginfo-function} accept an
argument that points to a @code{struct printf_info}, which contains
information about the options appearing in an instance of the conversion
specifier. This data type is declared in the header file
@file{printf.h}.
@pindex printf.h
@comment printf.h
@comment GNU
@deftp {Type} {struct printf_info}
This structure is used to pass information about the options appearing
in an instance of a conversion specifier in a @code{printf} template
string to the handler and arginfo functions for that specifier. It
contains the following members:
@table @code
@item int prec
This is the precision specified. The value is @code{-1} if no precision
was specified. If the precision was given as @samp{*}, the
@code{printf_info} structure passed to the handler function contains the
actual value retrieved from the argument list. But the structure passed
to the arginfo function contains a value of @code{INT_MIN}, since the
actual value is not known.
@item int width
This is the minimum field width specified. The value is @code{0} if no
width was specified. If the field width was given as @samp{*}, the
@code{printf_info} structure passed to the handler function contains the
actual value retrieved from the argument list. But the structure passed
to the arginfo function contains a value of @code{INT_MIN}, since the
actual value is not known.
@item wchar_t spec
This is the conversion specifier character specified. It's stored in
the structure so that you can register the same handler function for
multiple characters, but still have a way to tell them apart when the
handler function is called.
@item unsigned int is_long_double
This is a boolean that is true if the @samp{L}, @samp{ll}, or @samp{q}
type modifier was specified. For integer conversions, this indicates
@code{long long int}, as opposed to @code{long double} for floating
point conversions.
@item unsigned int is_char
This is a boolean that is true if the @samp{hh} type modifier was specified.
@item unsigned int is_short
This is a boolean that is true if the @samp{h} type modifier was specified.
@item unsigned int is_long
This is a boolean that is true if the @samp{l} type modifier was specified.
@item unsigned int alt
This is a boolean that is true if the @samp{#} flag was specified.
@item unsigned int space
This is a boolean that is true if the @samp{ } flag was specified.
@item unsigned int left
This is a boolean that is true if the @samp{-} flag was specified.
@item unsigned int showsign
This is a boolean that is true if the @samp{+} flag was specified.
@item unsigned int group
This is a boolean that is true if the @samp{'} flag was specified.
@item unsigned int extra
This flag has a special meaning depending on the context. It could
be used freely by the user-defined handlers but when called from
the @code{printf} function this variable always contains the value
@code{0}.
@item unsigned int wide
This flag is set if the stream is wide oriented.
@item wchar_t pad
This is the character to use for padding the output to the minimum field
width. The value is @code{'0'} if the @samp{0} flag was specified, and
@code{' '} otherwise.
@end table
@end deftp
@node Defining the Output Handler
@subsection Defining the Output Handler
Now let's look at how to define the handler and arginfo functions
which are passed as arguments to @code{register_printf_function}.
@strong{Compatibility Note:} The interface changed in @theglibc{}
version 2.0. Previously the third argument was of type
@code{va_list *}.
You should define your handler functions with a prototype like:
@smallexample
int @var{function} (FILE *stream, const struct printf_info *info,
const void *const *args)
@end smallexample
The @var{stream} argument passed to the handler function is the stream to
which it should write output.
The @var{info} argument is a pointer to a structure that contains
information about the various options that were included with the
conversion in the template string. You should not modify this structure
inside your handler function. @xref{Conversion Specifier Options}, for
a description of this data structure.
@c The following changes some time back. --drepper@gnu, 1996/11/14
@c
@c The @code{ap_pointer} argument is used to pass the tail of the variable
@c argument list containing the values to be printed to your handler.
@c Unlike most other functions that can be passed an explicit variable
@c argument list, this is a @emph{pointer} to a @code{va_list}, rather than
@c the @code{va_list} itself. Thus, you should fetch arguments by
@c means of @code{va_arg (*ap_pointer, @var{type})}.
@c
@c (Passing a pointer here allows the function that calls your handler
@c function to update its own @code{va_list} variable to account for the
@c arguments that your handler processes. @xref{Variadic Functions}.)
The @var{args} is a vector of pointers to the arguments data.
The number of arguments was determined by calling the argument
information function provided by the user.
Your handler function should return a value just like @code{printf}
does: it should return the number of characters it has written, or a
negative value to indicate an error.
@comment printf.h
@comment GNU
@deftp {Data Type} printf_function
This is the data type that a handler function should have.
@end deftp
If you are going to use @w{@code{parse_printf_format}} in your
application, you must also define a function to pass as the
@var{arginfo-function} argument for each new conversion you install with
@code{register_printf_function}.
You have to define these functions with a prototype like:
@smallexample
int @var{function} (const struct printf_info *info,
size_t n, int *argtypes)
@end smallexample
The return value from the function should be the number of arguments the
conversion expects. The function should also fill in no more than
@var{n} elements of the @var{argtypes} array with information about the
types of each of these arguments. This information is encoded using the
various @samp{PA_} macros. (You will notice that this is the same
calling convention @code{parse_printf_format} itself uses.)
@comment printf.h
@comment GNU
@deftp {Data Type} printf_arginfo_function
This type is used to describe functions that return information about
the number and type of arguments used by a conversion specifier.
@end deftp
@node Printf Extension Example
@subsection @code{printf} Extension Example
Here is an example showing how to define a @code{printf} handler function.
This program defines a data structure called a @code{Widget} and
defines the @samp{%W} conversion to print information about @w{@code{Widget *}}
arguments, including the pointer value and the name stored in the data
structure. The @samp{%W} conversion supports the minimum field width and
left-justification options, but ignores everything else.
@smallexample
@include rprintf.c.texi
@end smallexample
The output produced by this program looks like:
@smallexample
||
| |
| |
@end smallexample
@node Predefined Printf Handlers
@subsection Predefined @code{printf} Handlers
@Theglibc{} also contains a concrete and useful application of the
@code{printf} handler extension. There are two functions available
which implement a special way to print floating-point numbers.
@comment printf.h
@comment GNU
@deftypefun int printf_size (FILE *@var{fp}, const struct printf_info *@var{info}, const void *const *@var{args})
@safety{@prelim{}@mtsafe{@mtsrace{:fp} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @acucorrupt{}}}
@c This is meant to be called by vfprintf, that should hold the lock on
@c the stream, but if this function is called directly, output will be
@c racy, besides the uses of the global locale object while other
@c threads may be changing it and the possbility of leaving the stream
@c object in an inconsistent state in case of cancellation.
Print a given floating point number as for the format @code{%f} except
that there is a postfix character indicating the divisor for the
number to make this less than 1000. There are two possible divisors:
powers of 1024 or powers of 1000. Which one is used depends on the
format character specified while registered this handler. If the
character is of lower case, 1024 is used. For upper case characters,
1000 is used.
The postfix tag corresponds to bytes, kilobytes, megabytes, gigabytes,
etc. The full table is:
@ifinfo
@multitable {' '} {2^10 (1024)} {zetta} {Upper} {10^24 (1000)}
@item low @tab Multiplier @tab From @tab Upper @tab Multiplier
@item ' ' @tab 1 @tab @tab ' ' @tab 1
@item k @tab 2^10 (1024) @tab kilo @tab K @tab 10^3 (1000)
@item m @tab 2^20 @tab mega @tab M @tab 10^6
@item g @tab 2^30 @tab giga @tab G @tab 10^9
@item t @tab 2^40 @tab tera @tab T @tab 10^12
@item p @tab 2^50 @tab peta @tab P @tab 10^15
@item e @tab 2^60 @tab exa @tab E @tab 10^18
@item z @tab 2^70 @tab zetta @tab Z @tab 10^21
@item y @tab 2^80 @tab yotta @tab Y @tab 10^24
@end multitable
@end ifinfo
@iftex
@tex
\hbox to\hsize{\hfil\vbox{\offinterlineskip
\hrule
\halign{\strut#& \vrule#\tabskip=1em plus2em& {\tt#}\hfil& \vrule#& #\hfil& \vrule#& #\hfil& \vrule#& {\tt#}\hfil& \vrule#& #\hfil& \vrule#\tabskip=0pt\cr
\noalign{\hrule}
\omit&height2pt&\omit&&\omit&&\omit&&\omit&&\omit&\cr
&& \omit low && Multiplier && From && \omit Upper && Multiplier &\cr
\omit&height2pt&\omit&&\omit&&\omit&&\omit&&\omit&\cr
\noalign{\hrule}
&& {\tt\char32} && 1 && && {\tt\char32} && 1 &\cr
&& k && $2^{10} = 1024$ && kilo && K && $10^3 = 1000$ &\cr
&& m && $2^{20}$ && mega && M && $10^6$ &\cr
&& g && $2^{30}$ && giga && G && $10^9$ &\cr
&& t && $2^{40}$ && tera && T && $10^{12}$ &\cr
&& p && $2^{50}$ && peta && P && $10^{15}$ &\cr
&& e && $2^{60}$ && exa && E && $10^{18}$ &\cr
&& z && $2^{70}$ && zetta && Z && $10^{21}$ &\cr
&& y && $2^{80}$ && yotta && Y && $10^{24}$ &\cr
\noalign{\hrule}}}\hfil}
@end tex
@end iftex
The default precision is 3, i.e., 1024 is printed with a lower-case
format character as if it were @code{%.3fk} and will yield @code{1.000k}.
@end deftypefun
Due to the requirements of @code{register_printf_function} we must also
provide the function which returns information about the arguments.
@comment printf.h
@comment GNU
@deftypefun int printf_size_info (const struct printf_info *@var{info}, size_t @var{n}, int *@var{argtypes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function will return in @var{argtypes} the information about the
used parameters in the way the @code{vfprintf} implementation expects
it. The format always takes one argument.
@end deftypefun
To use these functions both functions must be registered with a call like
@smallexample
register_printf_function ('B', printf_size, printf_size_info);
@end smallexample
Here we register the functions to print numbers as powers of 1000 since
the format character @code{'B'} is an upper-case character. If we
would additionally use @code{'b'} in a line like
@smallexample
register_printf_function ('b', printf_size, printf_size_info);
@end smallexample
@noindent
we could also print using a power of 1024. Please note that all that is
different in these two lines is the format specifier. The
@code{printf_size} function knows about the difference between lower and upper
case format specifiers.
The use of @code{'B'} and @code{'b'} is no coincidence. Rather it is
the preferred way to use this functionality since it is available on
some other systems which also use format specifiers.
@node Formatted Input
@section Formatted Input
@cindex formatted input from a stream
@cindex reading from a stream, formatted
@cindex format string, for @code{scanf}
@cindex template, for @code{scanf}
The functions described in this section (@code{scanf} and related
functions) provide facilities for formatted input analogous to the
formatted output facilities. These functions provide a mechanism for
reading arbitrary values under the control of a @dfn{format string} or
@dfn{template string}.
@menu
* Formatted Input Basics:: Some basics to get you started.
* Input Conversion Syntax:: Syntax of conversion specifications.
* Table of Input Conversions:: Summary of input conversions and what they do.
* Numeric Input Conversions:: Details of conversions for reading numbers.
* String Input Conversions:: Details of conversions for reading strings.
* Dynamic String Input:: String conversions that @code{malloc} the buffer.
* Other Input Conversions:: Details of miscellaneous other conversions.
* Formatted Input Functions:: Descriptions of the actual functions.
* Variable Arguments Input:: @code{vscanf} and friends.
@end menu
@node Formatted Input Basics
@subsection Formatted Input Basics
Calls to @code{scanf} are superficially similar to calls to
@code{printf} in that arbitrary arguments are read under the control of
a template string. While the syntax of the conversion specifications in
the template is very similar to that for @code{printf}, the
interpretation of the template is oriented more towards free-format
input and simple pattern matching, rather than fixed-field formatting.
For example, most @code{scanf} conversions skip over any amount of
``white space'' (including spaces, tabs, and newlines) in the input
file, and there is no concept of precision for the numeric input
conversions as there is for the corresponding output conversions.
Ordinarily, non-whitespace characters in the template are expected to
match characters in the input stream exactly, but a matching failure is
distinct from an input error on the stream.
@cindex conversion specifications (@code{scanf})
Another area of difference between @code{scanf} and @code{printf} is
that you must remember to supply pointers rather than immediate values
as the optional arguments to @code{scanf}; the values that are read are
stored in the objects that the pointers point to. Even experienced
programmers tend to forget this occasionally, so if your program is
getting strange errors that seem to be related to @code{scanf}, you
might want to double-check this.
When a @dfn{matching failure} occurs, @code{scanf} returns immediately,
leaving the first non-matching character as the next character to be
read from the stream. The normal return value from @code{scanf} is the
number of values that were assigned, so you can use this to determine if
a matching error happened before all the expected values were read.
@cindex matching failure, in @code{scanf}
The @code{scanf} function is typically used for things like reading in
the contents of tables. For example, here is a function that uses
@code{scanf} to initialize an array of @code{double}:
@smallexample
void
readarray (double *array, int n)
@{
int i;
for (i=0; i scanf ("%a[a-zA-Z0-9] = %a[^\n]\n",
&variable, &value))
@{
invalid_input_error ();
return 0;
@}
@dots{}
@}
@end smallexample
@node Other Input Conversions
@subsection Other Input Conversions
This section describes the miscellaneous input conversions.
The @samp{%p} conversion is used to read a pointer value. It recognizes
the same syntax used by the @samp{%p} output conversion for
@code{printf} (@pxref{Other Output Conversions}); that is, a hexadecimal
number just as the @samp{%x} conversion accepts. The corresponding
argument should be of type @code{void **}; that is, the address of a
place to store a pointer.
The resulting pointer value is not guaranteed to be valid if it was not
originally written during the same program execution that reads it in.
The @samp{%n} conversion produces the number of characters read so far
by this call. The corresponding argument should be of type @code{int *}.
This conversion works in the same way as the @samp{%n} conversion for
@code{printf}; see @ref{Other Output Conversions}, for an example.
The @samp{%n} conversion is the only mechanism for determining the
success of literal matches or conversions with suppressed assignments.
If the @samp{%n} follows the locus of a matching failure, then no value
is stored for it since @code{scanf} returns before processing the
@samp{%n}. If you store @code{-1} in that argument slot before calling
@code{scanf}, the presence of @code{-1} after @code{scanf} indicates an
error occurred before the @samp{%n} was reached.
Finally, the @samp{%%} conversion matches a literal @samp{%} character
in the input stream, without using an argument. This conversion does
not permit any flags, field width, or type modifier to be specified.
@node Formatted Input Functions
@subsection Formatted Input Functions
Here are the descriptions of the functions for performing formatted
input.
Prototypes for these functions are in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun int scanf (const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
The @code{scanf} function reads formatted input from the stream
@code{stdin} under the control of the template string @var{template}.
The optional arguments are pointers to the places which receive the
resulting values.
The return value is normally the number of successful assignments. If
an end-of-file condition is detected before any matches are performed,
including matches against whitespace and literal characters in the
template, then @code{EOF} is returned.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int wscanf (const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
The @code{wscanf} function reads formatted input from the stream
@code{stdin} under the control of the template string @var{template}.
The optional arguments are pointers to the places which receive the
resulting values.
The return value is normally the number of successful assignments. If
an end-of-file condition is detected before any matches are performed,
including matches against whitespace and literal characters in the
template, then @code{WEOF} is returned.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int fscanf (FILE *@var{stream}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is just like @code{scanf}, except that the input is read
from the stream @var{stream} instead of @code{stdin}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int fwscanf (FILE *@var{stream}, const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is just like @code{wscanf}, except that the input is read
from the stream @var{stream} instead of @code{stdin}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int sscanf (const char *@var{s}, const char *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is like @code{scanf}, except that the characters are taken from the
null-terminated string @var{s} instead of from a stream. Reaching the
end of the string is treated as an end-of-file condition.
The behavior of this function is undefined if copying takes place
between objects that overlap---for example, if @var{s} is also given
as an argument to receive a string read under control of the @samp{%s},
@samp{%S}, or @samp{%[} conversion.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int swscanf (const wchar_t *@var{ws}, const wchar_t *@var{template}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is like @code{wscanf}, except that the characters are taken from the
null-terminated string @var{ws} instead of from a stream. Reaching the
end of the string is treated as an end-of-file condition.
The behavior of this function is undefined if copying takes place
between objects that overlap---for example, if @var{ws} is also given as
an argument to receive a string read under control of the @samp{%s},
@samp{%S}, or @samp{%[} conversion.
@end deftypefun
@node Variable Arguments Input
@subsection Variable Arguments Input Functions
The functions @code{vscanf} and friends are provided so that you can
define your own variadic @code{scanf}-like functions that make use of
the same internals as the built-in formatted output functions.
These functions are analogous to the @code{vprintf} series of output
functions. @xref{Variable Arguments Output}, for important
information on how to use them.
@strong{Portability Note:} The functions listed in this section were
introduced in @w{ISO C99} and were before available as GNU extensions.
@comment stdio.h
@comment ISO
@deftypefun int vscanf (const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is similar to @code{scanf}, but instead of taking
a variable number of arguments directly, it takes an argument list
pointer @var{ap} of type @code{va_list} (@pxref{Variadic Functions}).
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int vwscanf (const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This function is similar to @code{wscanf}, but instead of taking
a variable number of arguments directly, it takes an argument list
pointer @var{ap} of type @code{va_list} (@pxref{Variadic Functions}).
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int vfscanf (FILE *@var{stream}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This is the equivalent of @code{fscanf} with the variable argument list
specified directly as for @code{vscanf}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int vfwscanf (FILE *@var{stream}, const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
This is the equivalent of @code{fwscanf} with the variable argument list
specified directly as for @code{vwscanf}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int vsscanf (const char *@var{s}, const char *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is the equivalent of @code{sscanf} with the variable argument list
specified directly as for @code{vscanf}.
@end deftypefun
@comment wchar.h
@comment ISO
@deftypefun int vswscanf (const wchar_t *@var{s}, const wchar_t *@var{template}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is the equivalent of @code{swscanf} with the variable argument list
specified directly as for @code{vwscanf}.
@end deftypefun
In GNU C, there is a special construct you can use to let the compiler
know that a function uses a @code{scanf}-style format string. Then it
can check the number and types of arguments in each call to the
function, and warn you when they do not match the format string.
For details, see @ref{Function Attributes, , Declaring Attributes of Functions,
gcc.info, Using GNU CC}.
@node EOF and Errors
@section End-Of-File and Errors
@cindex end of file, on a stream
Many of the functions described in this chapter return the value of the
macro @code{EOF} to indicate unsuccessful completion of the operation.
Since @code{EOF} is used to report both end of file and random errors,
it's often better to use the @code{feof} function to check explicitly
for end of file and @code{ferror} to check for errors. These functions
check indicators that are part of the internal state of the stream
object, indicators set if the appropriate condition was detected by a
previous I/O operation on that stream.
@comment stdio.h
@comment ISO
@deftypevr Macro int EOF
This macro is an integer value that is returned by a number of narrow
stream functions to indicate an end-of-file condition, or some other
error situation. With @theglibc{}, @code{EOF} is @code{-1}. In
other libraries, its value may be some other negative number.
This symbol is declared in @file{stdio.h}.
@end deftypevr
@comment wchar.h
@comment ISO
@deftypevr Macro int WEOF
This macro is an integer value that is returned by a number of wide
stream functions to indicate an end-of-file condition, or some other
error situation. With @theglibc{}, @code{WEOF} is @code{-1}. In
other libraries, its value may be some other negative number.
This symbol is declared in @file{wchar.h}.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypefun int feof (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
The @code{feof} function returns nonzero if and only if the end-of-file
indicator for the stream @var{stream} is set.
This symbol is declared in @file{stdio.h}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int feof_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c There isn't much of a thread unsafety risk in reading a flag word and
@c testing a bit in it.
The @code{feof_unlocked} function is equivalent to the @code{feof}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
This symbol is declared in @file{stdio.h}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int ferror (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
The @code{ferror} function returns nonzero if and only if the error
indicator for the stream @var{stream} is set, indicating that an error
has occurred on a previous operation on the stream.
This symbol is declared in @file{stdio.h}.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun int ferror_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{ferror_unlocked} function is equivalent to the @code{ferror}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
This symbol is declared in @file{stdio.h}.
@end deftypefun
In addition to setting the error indicator associated with the stream,
the functions that operate on streams also set @code{errno} in the same
way as the corresponding low-level functions that operate on file
descriptors. For example, all of the functions that perform output to a
stream---such as @code{fputc}, @code{printf}, and @code{fflush}---are
implemented in terms of @code{write}, and all of the @code{errno} error
conditions defined for @code{write} are meaningful for these functions.
For more information about the descriptor-level I/O functions, see
@ref{Low-Level I/O}.
@node Error Recovery
@section Recovering from errors
You may explicitly clear the error and EOF flags with the @code{clearerr}
function.
@comment stdio.h
@comment ISO
@deftypefun void clearerr (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
This function clears the end-of-file and error indicators for the
stream @var{stream}.
The file positioning functions (@pxref{File Positioning}) also clear the
end-of-file indicator for the stream.
@end deftypefun
@comment stdio.h
@comment GNU
@deftypefun void clearerr_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@assafe{}@acsafe{}}
The @code{clearerr_unlocked} function is equivalent to the @code{clearerr}
function except that it does not implicitly lock the stream.
This function is a GNU extension.
@end deftypefun
Note that it is @emph{not} correct to just clear the error flag and retry
a failed stream operation. After a failed write, any number of
characters since the last buffer flush may have been committed to the
file, while some buffered data may have been discarded. Merely retrying
can thus cause lost or repeated data.
A failed read may leave the file pointer in an inappropriate position for
a second try. In both cases, you should seek to a known position before
retrying.
Most errors that can happen are not recoverable --- a second try will
always fail again in the same way. So usually it is best to give up and
report the error to the user, rather than install complicated recovery
logic.
One important exception is @code{EINTR} (@pxref{Interrupted Primitives}).
Many stream I/O implementations will treat it as an ordinary error, which
can be quite inconvenient. You can avoid this hassle by installing all
signals with the @code{SA_RESTART} flag.
For similar reasons, setting nonblocking I/O on a stream's file
descriptor is not usually advisable.
@node Binary Streams
@section Text and Binary Streams
@gnusystems{} and other POSIX-compatible operating systems organize all
files as uniform sequences of characters. However, some other systems
make a distinction between files containing text and files containing
binary data, and the input and output facilities of @w{ISO C} provide for
this distinction. This section tells you how to write programs portable
to such systems.
@cindex text stream
@cindex binary stream
When you open a stream, you can specify either a @dfn{text stream} or a
@dfn{binary stream}. You indicate that you want a binary stream by
specifying the @samp{b} modifier in the @var{opentype} argument to
@code{fopen}; see @ref{Opening Streams}. Without this
option, @code{fopen} opens the file as a text stream.
Text and binary streams differ in several ways:
@itemize @bullet
@item
The data read from a text stream is divided into @dfn{lines} which are
terminated by newline (@code{'\n'}) characters, while a binary stream is
simply a long series of characters. A text stream might on some systems
fail to handle lines more than 254 characters long (including the
terminating newline character).
@cindex lines (in a text file)
@item
On some systems, text files can contain only printing characters,
horizontal tab characters, and newlines, and so text streams may not
support other characters. However, binary streams can handle any
character value.
@item
Space characters that are written immediately preceding a newline
character in a text stream may disappear when the file is read in again.
@item
More generally, there need not be a one-to-one mapping between
characters that are read from or written to a text stream, and the
characters in the actual file.
@end itemize
Since a binary stream is always more capable and more predictable than a
text stream, you might wonder what purpose text streams serve. Why not
simply always use binary streams? The answer is that on these operating
systems, text and binary streams use different file formats, and the
only way to read or write ``an ordinary file of text'' that can work
with other text-oriented programs is through a text stream.
In @theglibc{}, and on all POSIX systems, there is no difference
between text streams and binary streams. When you open a stream, you
get the same kind of stream regardless of whether you ask for binary.
This stream can handle any file content, and has none of the
restrictions that text streams sometimes have.
@node File Positioning
@section File Positioning
@cindex file positioning on a stream
@cindex positioning a stream
@cindex seeking on a stream
The @dfn{file position} of a stream describes where in the file the
stream is currently reading or writing. I/O on the stream advances the
file position through the file. On @gnusystems{}, the file position is
represented as an integer, which counts the number of bytes from the
beginning of the file. @xref{File Position}.
During I/O to an ordinary disk file, you can change the file position
whenever you wish, so as to read or write any portion of the file. Some
other kinds of files may also permit this. Files which support changing
the file position are sometimes referred to as @dfn{random-access}
files.
You can use the functions in this section to examine or modify the file
position indicator associated with a stream. The symbols listed below
are declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun {long int} ftell (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function returns the current file position of the stream
@var{stream}.
This function can fail if the stream doesn't support file positioning,
or if the file position can't be represented in a @code{long int}, and
possibly for other reasons as well. If a failure occurs, a value of
@code{-1} is returned.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun off_t ftello (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{ftello} function is similar to @code{ftell}, except that it
returns a value of type @code{off_t}. Systems which support this type
use it to describe all file positions, unlike the POSIX specification
which uses a long int. The two are not necessarily the same size.
Therefore, using ftell can lead to problems if the implementation is
written on top of a POSIX compliant low-level I/O implementation, and using
@code{ftello} is preferable whenever it is available.
If this function fails it returns @code{(off_t) -1}. This can happen due
to missing support for file positioning or internal errors. Otherwise
the return value is the current file position.
The function is an extension defined in the Unix Single Specification
version 2.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bit system this function is in fact @code{ftello64}. I.e., the
LFS interface transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun off64_t ftello64 (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is similar to @code{ftello} with the only difference that
the return value is of type @code{off64_t}. This also requires that the
stream @var{stream} was opened using either @code{fopen64},
@code{freopen64}, or @code{tmpfile64} since otherwise the underlying
file operations to position the file pointer beyond the @math{2^31}
bytes limit might fail.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{ftello}
and so transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int fseek (FILE *@var{stream}, long int @var{offset}, int @var{whence})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{fseek} function is used to change the file position of the
stream @var{stream}. The value of @var{whence} must be one of the
constants @code{SEEK_SET}, @code{SEEK_CUR}, or @code{SEEK_END}, to
indicate whether the @var{offset} is relative to the beginning of the
file, the current file position, or the end of the file, respectively.
This function returns a value of zero if the operation was successful,
and a nonzero value to indicate failure. A successful call also clears
the end-of-file indicator of @var{stream} and discards any characters
that were ``pushed back'' by the use of @code{ungetc}.
@code{fseek} either flushes any buffered output before setting the file
position or else remembers it so it will be written later in its proper
place in the file.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun int fseeko (FILE *@var{stream}, off_t @var{offset}, int @var{whence})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is similar to @code{fseek} but it corrects a problem with
@code{fseek} in a system with POSIX types. Using a value of type
@code{long int} for the offset is not compatible with POSIX.
@code{fseeko} uses the correct type @code{off_t} for the @var{offset}
parameter.
For this reason it is a good idea to prefer @code{ftello} whenever it is
available since its functionality is (if different at all) closer the
underlying definition.
The functionality and return value is the same as for @code{fseek}.
The function is an extension defined in the Unix Single Specification
version 2.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bit system this function is in fact @code{fseeko64}. I.e., the
LFS interface transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun int fseeko64 (FILE *@var{stream}, off64_t @var{offset}, int @var{whence})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is similar to @code{fseeko} with the only difference that
the @var{offset} parameter is of type @code{off64_t}. This also
requires that the stream @var{stream} was opened using either
@code{fopen64}, @code{freopen64}, or @code{tmpfile64} since otherwise
the underlying file operations to position the file pointer beyond the
@math{2^31} bytes limit might fail.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{fseeko}
and so transparently replaces the old interface.
@end deftypefun
@strong{Portability Note:} In non-POSIX systems, @code{ftell},
@code{ftello}, @code{fseek} and @code{fseeko} might work reliably only
on binary streams. @xref{Binary Streams}.
The following symbolic constants are defined for use as the @var{whence}
argument to @code{fseek}. They are also used with the @code{lseek}
function (@pxref{I/O Primitives}) and to specify offsets for file locks
(@pxref{Control Operations}).
@comment stdio.h
@comment ISO
@deftypevr Macro int SEEK_SET
This is an integer constant which, when used as the @var{whence}
argument to the @code{fseek} or @code{fseeko} function, specifies that
the offset provided is relative to the beginning of the file.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int SEEK_CUR
This is an integer constant which, when used as the @var{whence}
argument to the @code{fseek} or @code{fseeko} function, specifies that
the offset provided is relative to the current file position.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int SEEK_END
This is an integer constant which, when used as the @var{whence}
argument to the @code{fseek} or @code{fseeko} function, specifies that
the offset provided is relative to the end of the file.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypefun void rewind (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{rewind} function positions the stream @var{stream} at the
beginning of the file. It is equivalent to calling @code{fseek} or
@code{fseeko} on the @var{stream} with an @var{offset} argument of
@code{0L} and a @var{whence} argument of @code{SEEK_SET}, except that
the return value is discarded and the error indicator for the stream is
reset.
@end deftypefun
These three aliases for the @samp{SEEK_@dots{}} constants exist for the
sake of compatibility with older BSD systems. They are defined in two
different header files: @file{fcntl.h} and @file{sys/file.h}.
@table @code
@comment sys/file.h
@comment BSD
@item L_SET
@vindex L_SET
An alias for @code{SEEK_SET}.
@comment sys/file.h
@comment BSD
@item L_INCR
@vindex L_INCR
An alias for @code{SEEK_CUR}.
@comment sys/file.h
@comment BSD
@item L_XTND
@vindex L_XTND
An alias for @code{SEEK_END}.
@end table
@node Portable Positioning
@section Portable File-Position Functions
On @gnusystems{}, the file position is truly a character count. You
can specify any character count value as an argument to @code{fseek} or
@code{fseeko} and get reliable results for any random access file.
However, some @w{ISO C} systems do not represent file positions in this
way.
On some systems where text streams truly differ from binary streams, it
is impossible to represent the file position of a text stream as a count
of characters from the beginning of the file. For example, the file
position on some systems must encode both a record offset within the
file, and a character offset within the record.
As a consequence, if you want your programs to be portable to these
systems, you must observe certain rules:
@itemize @bullet
@item
The value returned from @code{ftell} on a text stream has no predictable
relationship to the number of characters you have read so far. The only
thing you can rely on is that you can use it subsequently as the
@var{offset} argument to @code{fseek} or @code{fseeko} to move back to
the same file position.
@item
In a call to @code{fseek} or @code{fseeko} on a text stream, either the
@var{offset} must be zero, or @var{whence} must be @code{SEEK_SET} and
the @var{offset} must be the result of an earlier call to @code{ftell}
on the same stream.
@item
The value of the file position indicator of a text stream is undefined
while there are characters that have been pushed back with @code{ungetc}
that haven't been read or discarded. @xref{Unreading}.
@end itemize
But even if you observe these rules, you may still have trouble for long
files, because @code{ftell} and @code{fseek} use a @code{long int} value
to represent the file position. This type may not have room to encode
all the file positions in a large file. Using the @code{ftello} and
@code{fseeko} functions might help here since the @code{off_t} type is
expected to be able to hold all file position values but this still does
not help to handle additional information which must be associated with
a file position.
So if you do want to support systems with peculiar encodings for the
file positions, it is better to use the functions @code{fgetpos} and
@code{fsetpos} instead. These functions represent the file position
using the data type @code{fpos_t}, whose internal representation varies
from system to system.
These symbols are declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftp {Data Type} fpos_t
This is the type of an object that can encode information about the
file position of a stream, for use by the functions @code{fgetpos} and
@code{fsetpos}.
In @theglibc{}, @code{fpos_t} is an opaque data structure that
contains internal data to represent file offset and conversion state
information. In other systems, it might have a different internal
representation.
When compiling with @code{_FILE_OFFSET_BITS == 64} on a 32 bit machine
this type is in fact equivalent to @code{fpos64_t} since the LFS
interface transparently replaces the old interface.
@end deftp
@comment stdio.h
@comment Unix98
@deftp {Data Type} fpos64_t
This is the type of an object that can encode information about the
file position of a stream, for use by the functions @code{fgetpos64} and
@code{fsetpos64}.
In @theglibc{}, @code{fpos64_t} is an opaque data structure that
contains internal data to represent file offset and conversion state
information. In other systems, it might have a different internal
representation.
@end deftp
@comment stdio.h
@comment ISO
@deftypefun int fgetpos (FILE *@var{stream}, fpos_t *@var{position})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function stores the value of the file position indicator for the
stream @var{stream} in the @code{fpos_t} object pointed to by
@var{position}. If successful, @code{fgetpos} returns zero; otherwise
it returns a nonzero value and stores an implementation-defined positive
value in @code{errno}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bit system the function is in fact @code{fgetpos64}. I.e., the LFS
interface transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun int fgetpos64 (FILE *@var{stream}, fpos64_t *@var{position})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is similar to @code{fgetpos} but the file position is
returned in a variable of type @code{fpos64_t} to which @var{position}
points.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{fgetpos}
and so transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun int fsetpos (FILE *@var{stream}, const fpos_t *@var{position})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function sets the file position indicator for the stream @var{stream}
to the position @var{position}, which must have been set by a previous
call to @code{fgetpos} on the same stream. If successful, @code{fsetpos}
clears the end-of-file indicator on the stream, discards any characters
that were ``pushed back'' by the use of @code{ungetc}, and returns a value
of zero. Otherwise, @code{fsetpos} returns a nonzero value and stores
an implementation-defined positive value in @code{errno}.
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32 bit system the function is in fact @code{fsetpos64}. I.e., the LFS
interface transparently replaces the old interface.
@end deftypefun
@comment stdio.h
@comment Unix98
@deftypefun int fsetpos64 (FILE *@var{stream}, const fpos64_t *@var{position})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is similar to @code{fsetpos} but the file position used
for positioning is provided in a variable of type @code{fpos64_t} to
which @var{position} points.
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
bits machine this function is available under the name @code{fsetpos}
and so transparently replaces the old interface.
@end deftypefun
@node Stream Buffering
@section Stream Buffering
@cindex buffering of streams
Characters that are written to a stream are normally accumulated and
transmitted asynchronously to the file in a block, instead of appearing
as soon as they are output by the application program. Similarly,
streams often retrieve input from the host environment in blocks rather
than on a character-by-character basis. This is called @dfn{buffering}.
If you are writing programs that do interactive input and output using
streams, you need to understand how buffering works when you design the
user interface to your program. Otherwise, you might find that output
(such as progress or prompt messages) doesn't appear when you intended
it to, or displays some other unexpected behavior.
This section deals only with controlling when characters are transmitted
between the stream and the file or device, and @emph{not} with how
things like echoing, flow control, and the like are handled on specific
classes of devices. For information on common control operations on
terminal devices, see @ref{Low-Level Terminal Interface}.
You can bypass the stream buffering facilities altogether by using the
low-level input and output functions that operate on file descriptors
instead. @xref{Low-Level I/O}.
@menu
* Buffering Concepts:: Terminology is defined here.
* Flushing Buffers:: How to ensure that output buffers are flushed.
* Controlling Buffering:: How to specify what kind of buffering to use.
@end menu
@node Buffering Concepts
@subsection Buffering Concepts
There are three different kinds of buffering strategies:
@itemize @bullet
@item
Characters written to or read from an @dfn{unbuffered} stream are
transmitted individually to or from the file as soon as possible.
@cindex unbuffered stream
@item
Characters written to a @dfn{line buffered} stream are transmitted to
the file in blocks when a newline character is encountered.
@cindex line buffered stream
@item
Characters written to or read from a @dfn{fully buffered} stream are
transmitted to or from the file in blocks of arbitrary size.
@cindex fully buffered stream
@end itemize
Newly opened streams are normally fully buffered, with one exception: a
stream connected to an interactive device such as a terminal is
initially line buffered. @xref{Controlling Buffering}, for information
on how to select a different kind of buffering. Usually the automatic
selection gives you the most convenient kind of buffering for the file
or device you open.
The use of line buffering for interactive devices implies that output
messages ending in a newline will appear immediately---which is usually
what you want. Output that doesn't end in a newline might or might not
show up immediately, so if you want them to appear immediately, you
should flush buffered output explicitly with @code{fflush}, as described
in @ref{Flushing Buffers}.
@node Flushing Buffers
@subsection Flushing Buffers
@cindex flushing a stream
@dfn{Flushing} output on a buffered stream means transmitting all
accumulated characters to the file. There are many circumstances when
buffered output on a stream is flushed automatically:
@itemize @bullet
@item
When you try to do output and the output buffer is full.
@item
When the stream is closed. @xref{Closing Streams}.
@item
When the program terminates by calling @code{exit}.
@xref{Normal Termination}.
@item
When a newline is written, if the stream is line buffered.
@item
Whenever an input operation on @emph{any} stream actually reads data
from its file.
@end itemize
If you want to flush the buffered output at another time, call
@code{fflush}, which is declared in the header file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun int fflush (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function causes any buffered output on @var{stream} to be delivered
to the file. If @var{stream} is a null pointer, then
@code{fflush} causes buffered output on @emph{all} open output streams
to be flushed.
This function returns @code{EOF} if a write error occurs, or zero
otherwise.
@end deftypefun
@comment stdio.h
@comment POSIX
@deftypefun int fflush_unlocked (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{fflush_unlocked} function is equivalent to the @code{fflush}
function except that it does not implicitly lock the stream.
@end deftypefun
The @code{fflush} function can be used to flush all streams currently
opened. While this is useful in some situations it does often more than
necessary since it might be done in situations when terminal input is
required and the program wants to be sure that all output is visible on
the terminal. But this means that only line buffered streams have to be
flushed. Solaris introduced a function especially for this. It was
always available in @theglibc{} in some form but never officially
exported.
@comment stdio_ext.h
@comment GNU
@deftypefun void _flushlbf (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
The @code{_flushlbf} function flushes all line buffered streams
currently opened.
This function is declared in the @file{stdio_ext.h} header.
@end deftypefun
@strong{Compatibility Note:} Some brain-damaged operating systems have
been known to be so thoroughly fixated on line-oriented input and output
that flushing a line buffered stream causes a newline to be written!
Fortunately, this ``feature'' seems to be becoming less common. You do
not need to worry about this with @theglibc{}.
In some situations it might be useful to not flush the output pending
for a stream but instead simply forget it. If transmission is costly
and the output is not needed anymore this is valid reasoning. In this
situation a non-standard function introduced in Solaris and available in
@theglibc{} can be used.
@comment stdio_ext.h
@comment GNU
@deftypefun void __fpurge (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
The @code{__fpurge} function causes the buffer of the stream
@var{stream} to be emptied. If the stream is currently in read mode all
input in the buffer is lost. If the stream is in output mode the
buffered output is not written to the device (or whatever other
underlying storage) and the buffer the cleared.
This function is declared in @file{stdio_ext.h}.
@end deftypefun
@node Controlling Buffering
@subsection Controlling Which Kind of Buffering
After opening a stream (but before any other operations have been
performed on it), you can explicitly specify what kind of buffering you
want it to have using the @code{setvbuf} function.
@cindex buffering, controlling
The facilities listed in this section are declared in the header
file @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment ISO
@deftypefun int setvbuf (FILE *@var{stream}, char *@var{buf}, int @var{mode}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function is used to specify that the stream @var{stream} should
have the buffering mode @var{mode}, which can be either @code{_IOFBF}
(for full buffering), @code{_IOLBF} (for line buffering), or
@code{_IONBF} (for unbuffered input/output).
If you specify a null pointer as the @var{buf} argument, then @code{setvbuf}
allocates a buffer itself using @code{malloc}. This buffer will be freed
when you close the stream.
Otherwise, @var{buf} should be a character array that can hold at least
@var{size} characters. You should not free the space for this array as
long as the stream remains open and this array remains its buffer. You
should usually either allocate it statically, or @code{malloc}
(@pxref{Unconstrained Allocation}) the buffer. Using an automatic array
is not a good idea unless you close the file before exiting the block
that declares the array.
While the array remains a stream buffer, the stream I/O functions will
use the buffer for their internal purposes. You shouldn't try to access
the values in the array directly while the stream is using it for
buffering.
The @code{setvbuf} function returns zero on success, or a nonzero value
if the value of @var{mode} is not valid or if the request could not
be honored.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypevr Macro int _IOFBF
The value of this macro is an integer constant expression that can be
used as the @var{mode} argument to the @code{setvbuf} function to
specify that the stream should be fully buffered.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int _IOLBF
The value of this macro is an integer constant expression that can be
used as the @var{mode} argument to the @code{setvbuf} function to
specify that the stream should be line buffered.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int _IONBF
The value of this macro is an integer constant expression that can be
used as the @var{mode} argument to the @code{setvbuf} function to
specify that the stream should be unbuffered.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypevr Macro int BUFSIZ
The value of this macro is an integer constant expression that is good
to use for the @var{size} argument to @code{setvbuf}. This value is
guaranteed to be at least @code{256}.
The value of @code{BUFSIZ} is chosen on each system so as to make stream
I/O efficient. So it is a good idea to use @code{BUFSIZ} as the size
for the buffer when you call @code{setvbuf}.
Actually, you can get an even better value to use for the buffer size
by means of the @code{fstat} system call: it is found in the
@code{st_blksize} field of the file attributes. @xref{Attribute Meanings}.
Sometimes people also use @code{BUFSIZ} as the allocation size of
buffers used for related purposes, such as strings used to receive a
line of input with @code{fgets} (@pxref{Character Input}). There is no
particular reason to use @code{BUFSIZ} for this instead of any other
integer, except that it might lead to doing I/O in chunks of an
efficient size.
@end deftypevr
@comment stdio.h
@comment ISO
@deftypefun void setbuf (FILE *@var{stream}, char *@var{buf})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
If @var{buf} is a null pointer, the effect of this function is
equivalent to calling @code{setvbuf} with a @var{mode} argument of
@code{_IONBF}. Otherwise, it is equivalent to calling @code{setvbuf}
with @var{buf}, and a @var{mode} of @code{_IOFBF} and a @var{size}
argument of @code{BUFSIZ}.
The @code{setbuf} function is provided for compatibility with old code;
use @code{setvbuf} in all new programs.
@end deftypefun
@comment stdio.h
@comment BSD
@deftypefun void setbuffer (FILE *@var{stream}, char *@var{buf}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
If @var{buf} is a null pointer, this function makes @var{stream} unbuffered.
Otherwise, it makes @var{stream} fully buffered using @var{buf} as the
buffer. The @var{size} argument specifies the length of @var{buf}.
This function is provided for compatibility with old BSD code. Use
@code{setvbuf} instead.
@end deftypefun
@comment stdio.h
@comment BSD
@deftypefun void setlinebuf (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
This function makes @var{stream} be line buffered, and allocates the
buffer for you.
This function is provided for compatibility with old BSD code. Use
@code{setvbuf} instead.
@end deftypefun
It is possible to query whether a given stream is line buffered or not
using a non-standard function introduced in Solaris and available in
@theglibc{}.
@comment stdio_ext.h
@comment GNU
@deftypefun int __flbf (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{__flbf} function will return a nonzero value in case the
stream @var{stream} is line buffered. Otherwise the return value is
zero.
This function is declared in the @file{stdio_ext.h} header.
@end deftypefun
Two more extensions allow to determine the size of the buffer and how
much of it is used. These functions were also introduced in Solaris.
@comment stdio_ext.h
@comment GNU
@deftypefun size_t __fbufsize (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acsafe{}}
The @code{__fbufsize} function return the size of the buffer in the
stream @var{stream}. This value can be used to optimize the use of the
stream.
This function is declared in the @file{stdio_ext.h} header.
@end deftypefun
@comment stdio_ext.h
@comment GNU
@deftypefun size_t __fpending (FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtsrace{:stream}}@asunsafe{@asucorrupt{}}@acsafe{}}
The @code{__fpending}
function returns the number of bytes currently in the output buffer.
For wide-oriented stream the measuring unit is wide characters. This
function should not be used on buffers in read mode or opened read-only.
This function is declared in the @file{stdio_ext.h} header.
@end deftypefun
@node Other Kinds of Streams
@section Other Kinds of Streams
@Theglibc{} provides ways for you to define additional kinds of
streams that do not necessarily correspond to an open file.
One such type of stream takes input from or writes output to a string.
These kinds of streams are used internally to implement the
@code{sprintf} and @code{sscanf} functions. You can also create such a
stream explicitly, using the functions described in @ref{String Streams}.
More generally, you can define streams that do input/output to arbitrary
objects using functions supplied by your program. This protocol is
discussed in @ref{Custom Streams}.
@strong{Portability Note:} The facilities described in this section are
specific to GNU. Other systems or C implementations might or might not
provide equivalent functionality.
@menu
* String Streams:: Streams that get data from or put data in
a string or memory buffer.
* Custom Streams:: Defining your own streams with an arbitrary
input data source and/or output data sink.
@end menu
@node String Streams
@subsection String Streams
@cindex stream, for I/O to a string
@cindex string stream
The @code{fmemopen} and @code{open_memstream} functions allow you to do
I/O to a string or memory buffer. These facilities are declared in
@file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment GNU
@deftypefun {FILE *} fmemopen (void *@var{buf}, size_t @var{size}, const char *@var{opentype})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @aculock{}}}
@c Unlike open_memstream, fmemopen does (indirectly) call _IO_link_in,
@c bringing with it additional potential for async trouble with
@c list_all_lock.
This function opens a stream that allows the access specified by the
@var{opentype} argument, that reads from or writes to the buffer specified
by the argument @var{buf}. This array must be at least @var{size} bytes long.
If you specify a null pointer as the @var{buf} argument, @code{fmemopen}
dynamically allocates an array @var{size} bytes long (as with @code{malloc};
@pxref{Unconstrained Allocation}). This is really only useful
if you are going to write things to the buffer and then read them back
in again, because you have no way of actually getting a pointer to the
buffer (for this, try @code{open_memstream}, below). The buffer is
freed when the stream is closed.
The argument @var{opentype} is the same as in @code{fopen}
(@pxref{Opening Streams}). If the @var{opentype} specifies
append mode, then the initial file position is set to the first null
character in the buffer. Otherwise the initial file position is at the
beginning of the buffer.
When a stream open for writing is flushed or closed, a null character
(zero byte) is written at the end of the buffer if it fits. You
should add an extra byte to the @var{size} argument to account for this.
Attempts to write more than @var{size} bytes to the buffer result
in an error.
For a stream open for reading, null characters (zero bytes) in the
buffer do not count as ``end of file''. Read operations indicate end of
file only when the file position advances past @var{size} bytes. So, if
you want to read characters from a null-terminated string, you should
supply the length of the string as the @var{size} argument.
@end deftypefun
Here is an example of using @code{fmemopen} to create a stream for
reading from a string:
@smallexample
@include memopen.c.texi
@end smallexample
This program produces the following output:
@smallexample
Got f
Got o
Got o
Got b
Got a
Got r
@end smallexample
@comment stdio.h
@comment GNU
@deftypefun {FILE *} open_memstream (char **@var{ptr}, size_t *@var{sizeloc})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function opens a stream for writing to a buffer. The buffer is
allocated dynamically and grown as necessary, using @code{malloc}.
After you've closed the stream, this buffer is your responsibility to
clean up using @code{free} or @code{realloc}. @xref{Unconstrained Allocation}.
When the stream is closed with @code{fclose} or flushed with
@code{fflush}, the locations @var{ptr} and @var{sizeloc} are updated to
contain the pointer to the buffer and its size. The values thus stored
remain valid only as long as no further output on the stream takes
place. If you do more output, you must flush the stream again to store
new values before you use them again.
A null character is written at the end of the buffer. This null character
is @emph{not} included in the size value stored at @var{sizeloc}.
You can move the stream's file position with @code{fseek} or
@code{fseeko} (@pxref{File Positioning}). Moving the file position past
the end of the data already written fills the intervening space with
zeroes.
@end deftypefun
Here is an example of using @code{open_memstream}:
@smallexample
@include memstrm.c.texi
@end smallexample
This program produces the following output:
@smallexample
buf = `hello', size = 5
buf = `hello, world', size = 12
@end smallexample
@node Custom Streams
@subsection Programming Your Own Custom Streams
@cindex custom streams
@cindex programming your own streams
This section describes how you can make a stream that gets input from an
arbitrary data source or writes output to an arbitrary data sink
programmed by you. We call these @dfn{custom streams}. The functions
and types described here are all GNU extensions.
@c !!! this does not talk at all about the higher-level hooks
@menu
* Streams and Cookies:: The @dfn{cookie} records where to fetch or
store data that is read or written.
* Hook Functions:: How you should define the four @dfn{hook
functions} that a custom stream needs.
@end menu
@node Streams and Cookies
@subsubsection Custom Streams and Cookies
@cindex cookie, for custom stream
Inside every custom stream is a special object called the @dfn{cookie}.
This is an object supplied by you which records where to fetch or store
the data read or written. It is up to you to define a data type to use
for the cookie. The stream functions in the library never refer
directly to its contents, and they don't even know what the type is;
they record its address with type @code{void *}.
To implement a custom stream, you must specify @emph{how} to fetch or
store the data in the specified place. You do this by defining
@dfn{hook functions} to read, write, change ``file position'', and close
the stream. All four of these functions will be passed the stream's
cookie so they can tell where to fetch or store the data. The library
functions don't know what's inside the cookie, but your functions will
know.
When you create a custom stream, you must specify the cookie pointer,
and also the four hook functions stored in a structure of type
@code{cookie_io_functions_t}.
These facilities are declared in @file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment GNU
@deftp {Data Type} {cookie_io_functions_t}
This is a structure type that holds the functions that define the
communications protocol between the stream and its cookie. It has
the following members:
@table @code
@item cookie_read_function_t *read
This is the function that reads data from the cookie. If the value is a
null pointer instead of a function, then read operations on this stream
always return @code{EOF}.
@item cookie_write_function_t *write
This is the function that writes data to the cookie. If the value is a
null pointer instead of a function, then data written to the stream is
discarded.
@item cookie_seek_function_t *seek
This is the function that performs the equivalent of file positioning on
the cookie. If the value is a null pointer instead of a function, calls
to @code{fseek} or @code{fseeko} on this stream can only seek to
locations within the buffer; any attempt to seek outside the buffer will
return an @code{ESPIPE} error.
@item cookie_close_function_t *close
This function performs any appropriate cleanup on the cookie when
closing the stream. If the value is a null pointer instead of a
function, nothing special is done to close the cookie when the stream is
closed.
@end table
@end deftp
@comment stdio.h
@comment GNU
@deftypefun {FILE *} fopencookie (void *@var{cookie}, const char *@var{opentype}, cookie_io_functions_t @var{io-functions})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acsmem{} @aculock{}}}
This function actually creates the stream for communicating with the
@var{cookie} using the functions in the @var{io-functions} argument.
The @var{opentype} argument is interpreted as for @code{fopen};
see @ref{Opening Streams}. (But note that the ``truncate on
open'' option is ignored.) The new stream is fully buffered.
The @code{fopencookie} function returns the newly created stream, or a null
pointer in case of an error.
@end deftypefun
@node Hook Functions
@subsubsection Custom Stream Hook Functions
@cindex hook functions (of custom streams)
Here are more details on how you should define the four hook functions
that a custom stream needs.
You should define the function to read data from the cookie as:
@smallexample
ssize_t @var{reader} (void *@var{cookie}, char *@var{buffer}, size_t @var{size})
@end smallexample
This is very similar to the @code{read} function; see @ref{I/O
Primitives}. Your function should transfer up to @var{size} bytes into
the @var{buffer}, and return the number of bytes read, or zero to
indicate end-of-file. You can return a value of @code{-1} to indicate
an error.
You should define the function to write data to the cookie as:
@smallexample
ssize_t @var{writer} (void *@var{cookie}, const char *@var{buffer}, size_t @var{size})
@end smallexample
This is very similar to the @code{write} function; see @ref{I/O
Primitives}. Your function should transfer up to @var{size} bytes from
the buffer, and return the number of bytes written. You can return a
value of @code{0} to indicate an error. You must not return any
negative value.
You should define the function to perform seek operations on the cookie
as:
@smallexample
int @var{seeker} (void *@var{cookie}, off64_t *@var{position}, int @var{whence})
@end smallexample
For this function, the @var{position} and @var{whence} arguments are
interpreted as for @code{fgetpos}; see @ref{Portable Positioning}.
After doing the seek operation, your function should store the resulting
file position relative to the beginning of the file in @var{position}.
Your function should return a value of @code{0} on success and @code{-1}
to indicate an error.
You should define the function to do cleanup operations on the cookie
appropriate for closing the stream as:
@smallexample
int @var{cleaner} (void *@var{cookie})
@end smallexample
Your function should return @code{-1} to indicate an error, and @code{0}
otherwise.
@comment stdio.h
@comment GNU
@deftp {Data Type} cookie_read_function
This is the data type that the read function for a custom stream should have.
If you declare the function as shown above, this is the type it will have.
@end deftp
@comment stdio.h
@comment GNU
@deftp {Data Type} cookie_write_function
The data type of the write function for a custom stream.
@end deftp
@comment stdio.h
@comment GNU
@deftp {Data Type} cookie_seek_function
The data type of the seek function for a custom stream.
@end deftp
@comment stdio.h
@comment GNU
@deftp {Data Type} cookie_close_function
The data type of the close function for a custom stream.
@end deftp
@ignore
Roland says:
@quotation
There is another set of functions one can give a stream, the
input-room and output-room functions. These functions must
understand stdio internals. To describe how to use these
functions, you also need to document lots of how stdio works
internally (which isn't relevant for other uses of stdio).
Perhaps I can write an interface spec from which you can write
good documentation. But it's pretty complex and deals with lots
of nitty-gritty details. I think it might be better to let this
wait until the rest of the manual is more done and polished.
@end quotation
@end ignore
@c ??? This section could use an example.
@node Formatted Messages
@section Formatted Messages
@cindex formatted messages
On systems which are based on System V messages of programs (especially
the system tools) are printed in a strict form using the @code{fmtmsg}
function. The uniformity sometimes helps the user to interpret messages
and the strictness tests of the @code{fmtmsg} function ensure that the
programmer follows some minimal requirements.
@menu
* Printing Formatted Messages:: The @code{fmtmsg} function.
* Adding Severity Classes:: Add more severity classes.
* Example:: How to use @code{fmtmsg} and @code{addseverity}.
@end menu
@node Printing Formatted Messages
@subsection Printing Formatted Messages
Messages can be printed to standard error and/or to the console. To
select the destination the programmer can use the following two values,
bitwise OR combined if wanted, for the @var{classification} parameter of
@code{fmtmsg}:
@vtable @code
@item MM_PRINT
Display the message in standard error.
@item MM_CONSOLE
Display the message on the system console.
@end vtable
The erroneous piece of the system can be signalled by exactly one of the
following values which also is bitwise ORed with the
@var{classification} parameter to @code{fmtmsg}:
@vtable @code
@item MM_HARD
The source of the condition is some hardware.
@item MM_SOFT
The source of the condition is some software.
@item MM_FIRM
The source of the condition is some firmware.
@end vtable
A third component of the @var{classification} parameter to @code{fmtmsg}
can describe the part of the system which detects the problem. This is
done by using exactly one of the following values:
@vtable @code
@item MM_APPL
The erroneous condition is detected by the application.
@item MM_UTIL
The erroneous condition is detected by a utility.
@item MM_OPSYS
The erroneous condition is detected by the operating system.
@end vtable
A last component of @var{classification} can signal the results of this
message. Exactly one of the following values can be used:
@vtable @code
@item MM_RECOVER
It is a recoverable error.
@item MM_NRECOV
It is a non-recoverable error.
@end vtable
@comment fmtmsg.h
@comment XPG
@deftypefun int fmtmsg (long int @var{classification}, const char *@var{label}, int @var{severity}, const char *@var{text}, const char *@var{action}, const char *@var{tag})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acsafe{}}
Display a message described by its parameters on the device(s) specified
in the @var{classification} parameter. The @var{label} parameter
identifies the source of the message. The string should consist of two
colon separated parts where the first part has not more than 10 and the
second part not more than 14 characters. The @var{text} parameter
describes the condition of the error, the @var{action} parameter possible
steps to recover from the error and the @var{tag} parameter is a
reference to the online documentation where more information can be
found. It should contain the @var{label} value and a unique
identification number.
Each of the parameters can be a special value which means this value
is to be omitted. The symbolic names for these values are:
@vtable @code
@item MM_NULLLBL
Ignore @var{label} parameter.
@item MM_NULLSEV
Ignore @var{severity} parameter.
@item MM_NULLMC
Ignore @var{classification} parameter. This implies that nothing is
actually printed.
@item MM_NULLTXT
Ignore @var{text} parameter.
@item MM_NULLACT
Ignore @var{action} parameter.
@item MM_NULLTAG
Ignore @var{tag} parameter.
@end vtable
There is another way certain fields can be omitted from the output to
standard error. This is described below in the description of
environment variables influencing the behavior.
The @var{severity} parameter can have one of the values in the following
table:
@cindex severity class
@vtable @code
@item MM_NOSEV
Nothing is printed, this value is the same as @code{MM_NULLSEV}.
@item MM_HALT
This value is printed as @code{HALT}.
@item MM_ERROR
This value is printed as @code{ERROR}.
@item MM_WARNING
This value is printed as @code{WARNING}.
@item MM_INFO
This value is printed as @code{INFO}.
@end vtable
The numeric value of these five macros are between @code{0} and
@code{4}. Using the environment variable @code{SEV_LEVEL} or using the
@code{addseverity} function one can add more severity levels with their
corresponding string to print. This is described below
(@pxref{Adding Severity Classes}).
@noindent
If no parameter is ignored the output looks like this:
@smallexample
@var{label}: @var{severity-string}: @var{text}
TO FIX: @var{action} @var{tag}
@end smallexample
The colons, new line characters and the @code{TO FIX} string are
inserted if necessary, i.e., if the corresponding parameter is not
ignored.
This function is specified in the X/Open Portability Guide. It is also
available on all systems derived from System V.
The function returns the value @code{MM_OK} if no error occurred. If
only the printing to standard error failed, it returns @code{MM_NOMSG}.
If printing to the console fails, it returns @code{MM_NOCON}. If
nothing is printed @code{MM_NOTOK} is returned. Among situations where
all outputs fail this last value is also returned if a parameter value
is incorrect.
@end deftypefun
There are two environment variables which influence the behavior of
@code{fmtmsg}. The first is @code{MSGVERB}. It is used to control the
output actually happening on standard error (@emph{not} the console
output). Each of the five fields can explicitly be enabled. To do
this the user has to put the @code{MSGVERB} variable with a format like
the following in the environment before calling the @code{fmtmsg} function
the first time:
@smallexample
MSGVERB=@var{keyword}[:@var{keyword}[:@dots{}]]
@end smallexample
Valid @var{keyword}s are @code{label}, @code{severity}, @code{text},
@code{action}, and @code{tag}. If the environment variable is not given
or is the empty string, a not supported keyword is given or the value is
somehow else invalid, no part of the message is masked out.
The second environment variable which influences the behavior of
@code{fmtmsg} is @code{SEV_LEVEL}. This variable and the change in the
behavior of @code{fmtmsg} is not specified in the X/Open Portability
Guide. It is available in System V systems, though. It can be used to
introduce new severity levels. By default, only the five severity levels
described above are available. Any other numeric value would make
@code{fmtmsg} print nothing.
If the user puts @code{SEV_LEVEL} with a format like
@smallexample
SEV_LEVEL=[@var{description}[:@var{description}[:@dots{}]]]
@end smallexample
@noindent
in the environment of the process before the first call to
@code{fmtmsg}, where @var{description} has a value of the form
@smallexample
@var{severity-keyword},@var{level},@var{printstring}
@end smallexample
The @var{severity-keyword} part is not used by @code{fmtmsg} but it has
to be present. The @var{level} part is a string representation of a
number. The numeric value must be a number greater than 4. This value
must be used in the @var{severity} parameter of @code{fmtmsg} to select
this class. It is not possible to overwrite any of the predefined
classes. The @var{printstring} is the string printed when a message of
this class is processed by @code{fmtmsg} (see above, @code{fmtsmg} does
not print the numeric value but instead the string representation).
@node Adding Severity Classes
@subsection Adding Severity Classes
@cindex severity class
There is another possibility to introduce severity classes besides using
the environment variable @code{SEV_LEVEL}. This simplifies the task of
introducing new classes in a running program. One could use the
@code{setenv} or @code{putenv} function to set the environment variable,
but this is toilsome.
@deftypefun int addseverity (int @var{severity}, const char *@var{string})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
This function allows the introduction of new severity classes which can be
addressed by the @var{severity} parameter of the @code{fmtmsg} function.
The @var{severity} parameter of @code{addseverity} must match the value
for the parameter with the same name of @code{fmtmsg}, and @var{string}
is the string printed in the actual messages instead of the numeric
value.
If @var{string} is @code{NULL} the severity class with the numeric value
according to @var{severity} is removed.
It is not possible to overwrite or remove one of the default severity
classes. All calls to @code{addseverity} with @var{severity} set to one
of the values for the default classes will fail.
The return value is @code{MM_OK} if the task was successfully performed.
If the return value is @code{MM_NOTOK} something went wrong. This could
mean that no more memory is available or a class is not available when
it has to be removed.
This function is not specified in the X/Open Portability Guide although
the @code{fmtsmg} function is. It is available on System V systems.
@end deftypefun
@node Example
@subsection How to use @code{fmtmsg} and @code{addseverity}
Here is a simple example program to illustrate the use of the both
functions described in this section.
@smallexample
@include fmtmsgexpl.c.texi
@end smallexample
The second call to @code{fmtmsg} illustrates a use of this function as
it usually occurs on System V systems, which heavily use this function.
It seems worthwhile to give a short explanation here of how this system
works on System V. The value of the
@var{label} field (@code{UX:cat}) says that the error occurred in the
Unix program @code{cat}. The explanation of the error follows and the
value for the @var{action} parameter is @code{"refer to manual"}. One
could be more specific here, if necessary. The @var{tag} field contains,
as proposed above, the value of the string given for the @var{label}
parameter, and additionally a unique ID (@code{001} in this case). For
a GNU environment this string could contain a reference to the
corresponding node in the Info page for the program.
@noindent
Running this program without specifying the @code{MSGVERB} and
@code{SEV_LEVEL} function produces the following output:
@smallexample
UX:cat: NOTE2: invalid syntax
TO FIX: refer to manual UX:cat:001
@end smallexample
We see the different fields of the message and how the extra glue (the
colons and the @code{TO FIX} string) are printed. But only one of the
three calls to @code{fmtmsg} produced output. The first call does not
print anything because the @var{label} parameter is not in the correct
form. The string must contain two fields, separated by a colon
(@pxref{Printing Formatted Messages}). The third @code{fmtmsg} call
produced no output since the class with the numeric value @code{6} is
not defined. Although a class with numeric value @code{5} is also not
defined by default, the call to @code{addseverity} introduces it and
the second call to @code{fmtmsg} produces the above output.
When we change the environment of the program to contain
@code{SEV_LEVEL=XXX,6,NOTE} when running it we get a different result:
@smallexample
UX:cat: NOTE2: invalid syntax
TO FIX: refer to manual UX:cat:001
label:foo: NOTE: text
TO FIX: action tag
@end smallexample
Now the third call to @code{fmtmsg} produced some output and we see how
the string @code{NOTE} from the environment variable appears in the
message.
Now we can reduce the output by specifying which fields we are
interested in. If we additionally set the environment variable
@code{MSGVERB} to the value @code{severity:label:action} we get the
following output:
@smallexample
UX:cat: NOTE2
TO FIX: refer to manual
label:foo: NOTE
TO FIX: action
@end smallexample
@noindent
I.e., the output produced by the @var{text} and the @var{tag} parameters
to @code{fmtmsg} vanished. Please also note that now there is no colon
after the @code{NOTE} and @code{NOTE2} strings in the output. This is
not necessary since there is no more output on this line because the text
is missing.
glibc-doc-reference-2.19.orig/manual/dir 0000664 0001750 0001750 00000001040 12275120646 020253 0 ustar adconrad adconrad This is the file .../info/dir, which contains the topmost node of the
Info hierarchy. The first time you invoke Info you start off
looking at that node, which is (dir)Top.
File: dir Node: Top This is the top of the INFO tree
This (the Directory node) gives a menu of major topics.
Typing "q" exits, "?" lists all Info commands, "d" returns here,
"h" gives a primer for first-timers,
"mEmacs" visits the Emacs topic, etc.
In Emacs, you can click mouse button 2 on a menu item or cross reference
to select it.
* Menu:
glibc-doc-reference-2.19.orig/manual/probes.texi 0000664 0001750 0001750 00000044100 12275120646 021743 0 ustar adconrad adconrad @node Internal Probes
@c @node Internal Probes, , POSIX Threads, Top
@c %MENU% Probes to monitor libc internal behavior
@chapter Internal probes
In order to aid in debugging and monitoring internal behavior,
@theglibc{} exposes nearly-zero-overhead SystemTap probes marked with
the @code{libc} provider.
These probes are not part of the @glibcadj{} stable ABI, and they are
subject to change or removal across releases. Our only promise with
regard to them is that, if we find a need to remove or modify the
arguments of a probe, the modified probe will have a different name, so
that program monitors relying on the old probe will not get unexpected
arguments.
@menu
* Memory Allocation Probes:: Probes in the memory allocation subsystem
* Mathematical Function Probes:: Probes in mathematical functions
@end menu
@node Memory Allocation Probes
@section Memory Allocation Probes
These probes are designed to signal relatively unusual situations within
the virtual memory subsystem of @theglibc{}.
@deftp Probe memory_sbrk_more (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered after the main arena is extended by calling
@code{sbrk}. Argument @var{$arg1} is the additional size requested to
@code{sbrk}, and @var{$arg2} is the pointer that marks the end of the
@code{sbrk} area, returned in response to the request.
@end deftp
@deftp Probe memory_sbrk_less (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered after the size of the main arena is decreased by
calling @code{sbrk}. Argument @var{$arg1} is the size released by
@code{sbrk} (the positive value, rather than the negative value passed
to @code{sbrk}), and @var{$arg2} is the pointer that marks the end of
the @code{sbrk} area, returned in response to the request.
@end deftp
@deftp Probe memory_heap_new (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered after a new heap is @code{mmap}ed. Argument
@var{$arg1} is a pointer to the base of the memory area, where the
@code{heap_info} data structure is held, and @var{$arg2} is the size of
the heap.
@end deftp
@deftp Probe memory_heap_free (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered @emph{before} (unlike the other sbrk and heap
probes) a heap is completely removed via @code{munmap}. Argument
@var{$arg1} is a pointer to the heap, and @var{$arg2} is the size of the
heap.
@end deftp
@deftp Probe memory_heap_more (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered after a trailing portion of an @code{mmap}ed
heap is extended. Argument @var{$arg1} is a pointer to the heap, and
@var{$arg2} is the new size of the heap.
@end deftp
@deftp Probe memory_heap_less (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered after a trailing portion of an @code{mmap}ed
heap is released. Argument @var{$arg1} is a pointer to the heap, and
@var{$arg2} is the new size of the heap.
@end deftp
@deftp Probe memory_malloc_retry (size_t @var{$arg1})
@deftpx Probe memory_realloc_retry (size_t @var{$arg1}, void *@var{$arg2})
@deftpx Probe memory_memalign_retry (size_t @var{$arg1}, size_t @var{$arg2})
@deftpx Probe memory_calloc_retry (size_t @var{$arg1})
These probes are triggered when the corresponding functions fail to
obtain the requested amount of memory from the arena in use, before they
call @code{arena_get_retry} to select an alternate arena in which to
retry the allocation. Argument @var{$arg1} is the amount of memory
requested by the user; in the @code{calloc} case, that is the total size
computed from both function arguments. In the @code{realloc} case,
@var{$arg2} is the pointer to the memory area being resized. In the
@code{memalign} case, @var{$arg2} is the alignment to be used for the
request, which may be stricter than the value passed to the
@code{memalign} function. A @code{memalign} probe is also used by functions
@code{posix_memalign, valloc} and @code{pvalloc}.
Note that the argument order does @emph{not} match that of the
corresponding two-argument functions, so that in all of these probes the
user-requested allocation size is in @var{$arg1}.
@end deftp
@deftp Probe memory_arena_retry (size_t @var{$arg1}, void *@var{$arg2})
This probe is triggered within @code{arena_get_retry} (the function
called to select the alternate arena in which to retry an allocation
that failed on the first attempt), before the selection of an alternate
arena. This probe is redundant, but much easier to use when it's not
important to determine which of the various memory allocation functions
is failing to allocate on the first try. Argument @var{$arg1} is the
same as in the function-specific probes, except for extra room for
padding introduced by functions that have to ensure stricter alignment.
Argument @var{$arg2} is the arena in which allocation failed.
@end deftp
@deftp Probe memory_arena_new (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered when @code{malloc} allocates and initializes an
additional arena (not the main arena), but before the arena is assigned
to the running thread or inserted into the internal linked list of
arenas. The arena's @code{malloc_state} internal data structure is
located at @var{$arg1}, within a newly-allocated heap big enough to hold
at least @var{$arg2} bytes.
@end deftp
@deftp Probe memory_arena_reuse (void *@var{$arg1}, void *@var{$arg2})
This probe is triggered when @code{malloc} has just selected an existing
arena to reuse, and (temporarily) reserved it for exclusive use.
Argument @var{$arg1} is a pointer to the newly-selected arena, and
@var{$arg2} is a pointer to the arena previously used by that thread.
This occurs within
@code{reused_arena}, right after the mutex mentioned in probe
@code{memory_arena_reuse_wait} is acquired; argument @var{$arg1} will
point to the same arena. In this configuration, this will usually only
occur once per thread. The exception is when a thread first selected
the main arena, but a subsequent allocation from it fails: then, and
only then, may we switch to another arena to retry that allocations, and
for further allocations within that thread.
@end deftp
@deftp Probe memory_arena_reuse_wait (void *@var{$arg1}, void *@var{$arg2}, void *@var{$arg3})
This probe is triggered when @code{malloc} is about to wait for an arena
to become available for reuse. Argument @var{$arg1} holds a pointer to
the mutex the thread is going to wait on, @var{$arg2} is a pointer to a
newly-chosen arena to be reused, and @var{$arg3} is a pointer to the
arena previously used by that thread.
This occurs within
@code{reused_arena}, when a thread first tries to allocate memory or
needs a retry after a failure to allocate from the main arena, there
isn't any free arena, the maximum number of arenas has been reached, and
an existing arena was chosen for reuse, but its mutex could not be
immediately acquired. The mutex in @var{$arg1} is the mutex of the
selected arena.
@end deftp
@deftp Probe memory_arena_reuse_free_list (void *@var{$arg1})
This probe is triggered when @code{malloc} has chosen an arena that is
in the free list for use by a thread, within the @code{get_free_list}
function. The argument @var{$arg1} holds a pointer to the selected arena.
@end deftp
@deftp Probe memory_mallopt (int @var{$arg1}, int @var{$arg2})
This probe is triggered when function @code{mallopt} is called to change
@code{malloc} internal configuration parameters, before any change to
the parameters is made. The arguments @var{$arg1} and @var{$arg2} are
the ones passed to the @code{mallopt} function.
@end deftp
@deftp Probe memory_mallopt_mxfast (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MXFAST}, and the requested
value is in an acceptable range. Argument @var{$arg1} is the requested
value, and @var{$arg2} is the previous value of this @code{malloc}
parameter.
@end deftp
@deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggere shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_TRIM_THRESHOLD}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_TOP_PAD}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MMAP_THRESHOLD}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, @var{$arg2} is the previous value of this @code{malloc}
parameter, and @var{$arg3} is nonzero if dynamic threshold adjustment
was already disabled.
@end deftp
@deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MMAP_MAX}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_check_action (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_CHECK_ACTION}. Argument
@var{$arg1} is the requested value, and @var{$arg2} is the previous
value of this @code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_perturb (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_PERTURB}. Argument
@var{$arg1} is the requested value, and @var{$arg2} is the previous
value of this @code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_arena_test (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_ARENA_TEST}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, and @var{$arg2} is the previous value of this
@code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_arena_max (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_ARENA_MAX}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, and @var{$arg2} is the previous value of this
@code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_free_dyn_thresholds (int @var{$arg1}, int @var{$arg2})
This probe is triggered when function @code{free} decides to adjust the
dynamic brk/mmap thresholds. Argument @var{$arg1} and @var{$arg2} are
the adjusted mmap and trim thresholds, respectively.
@end deftp
@node Mathematical Function Probes
@section Mathematical Function Probes
Some mathematical functions fall back to multiple precision arithmetic for
some inputs to get last bit precision for their return values. This multiple
precision fallback is much slower than the default algorithms and may have a
significant impact on application performance. The systemtap probe markers
described in this section may help you determine if your application calls
mathematical functions with inputs that may result in multiple-precision
arithmetic.
Unless explicitly mentioned otherwise, a precision of 1 implies 24 bits of
precision in the mantissa of the multiple precision number. Hence, a precision
level of 32 implies 768 bits of precision in the mantissa.
@deftp Probe slowexp_p6 (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{exp} function is called with an input that
results in multiple precision computation with precision 6. Argument
@var{$arg1} is the input value and @var{$arg2} is the computed output.
@end deftp
@deftp Probe slowexp_p32 (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{exp} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input value and @var{$arg2} is the computed output.
@end deftp
@deftp Probe slowpow_p10 (double @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
This probe is hit when the @code{pow} function is called with inputs that
result in multiple precision computation with precision 10. Arguments
@var{$arg1} and @var{$arg2} are the input values, @code{$arg3} is the value
computed in the fast phase of the algorithm and @code{$arg4} is the final
accurate value.
@end deftp
@deftp Probe slowpow_p32 (double @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
This probe is hit when the @code{pow} function is called with an input that
results in multiple precision computation with precision 32. Arguments
@var{$arg1} and @var{$arg2} are the input values, @code{$arg3} is the value
computed in the fast phase of the algorithm and @code{$arg4} is the final
accurate value.
@end deftp
@deftp Probe slowlog (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{log} function is called with an input that
results in multiple precision computation. Argument @var{$arg1} is the
precision with which the computation succeeded. Argument @var{$arg2} is the
input and @var{$arg3} is the computed output.
@end deftp
@deftp Probe slowlog_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{log} function is called with an input that
results in multiple precision computation and none of the multiple precision
computations result in an accurate result. Argument @var{$arg1} is the maximum
precision with which computations were performed. Argument @var{$arg2} is the
input and @var{$arg3} is the computed output.
@end deftp
@deftp Probe slowatan2 (int @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
This probe is hit when the @code{atan2} function is called with an input that
results in multiple precision computation. Argument @var{$arg1} is the
precision with which computation succeeded. Arguments @var{$arg2} and
@var{$arg3} are inputs to the @code{atan2} function and @var{$arg4} is the
computed result.
@end deftp
@deftp Probe slowatan2_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
This probe is hit when the @code{atan} function is called with an input that
results in multiple precision computation and none of the multiple precision
computations result in an accurate result. Argument @var{$arg1} is the maximum
precision with which computations were performed. Arguments @var{$arg2} and
@var{$arg3} are inputs to the @code{atan2} function and @var{$arg4} is the
computed result.
@end deftp
@deftp Probe slowatan (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{atan} function is called with an input that
results in multiple precision computation. Argument @var{$arg1} is the
precision with which computation succeeded. Argument @var{$arg2} is the
input to the @code{atan} function and @var{$arg3} is the computed result.
@end deftp
@deftp Probe slowatan_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{atan} function is called with an input that
results in multiple precision computation and none of the multiple precision
computations result in an accurate result. Argument @var{$arg1} is the maximum
precision with which computations were performed. Argument @var{$arg2} is the
input to the @code{atan} function and @var{$arg3} is the computed result.
@end deftp
@deftp Probe slowtan (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{tan} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function and @var{$arg2} is the computed
result.
@end deftp
@deftp Probe slowasin (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{asin} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function and @var{$arg2} is the computed
result.
@end deftp
@deftp Probe slowacos (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{acos} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function and @var{$arg2} is the computed
result.
@end deftp
@deftp Probe slowsin (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{sin} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function and @var{$arg2} is the computed
result.
@end deftp
@deftp Probe slowcos (double @var{$arg1}, double @var{$arg2})
This probe is hit when the @code{cos} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function and @var{$arg2} is the computed
result.
@end deftp
@deftp Probe slowsin_dx (double @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{sin} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function, @var{$arg2} is the error bound of
@var{$arg1} and @var{$arg3} is the computed result.
@end deftp
@deftp Probe slowcos_dx (double @var{$arg1}, double @var{$arg2}, double @var{$arg3})
This probe is hit when the @code{cos} function is called with an input that
results in multiple precision computation with precision 32. Argument
@var{$arg1} is the input to the function, @var{$arg2} is the error bound of
@var{$arg1} and @var{$arg3} is the computed result.
@end deftp
glibc-doc-reference-2.19.orig/manual/texinfo.tex 0000664 0001750 0001750 00001174247 12275120646 021775 0 ustar adconrad adconrad % texinfo.tex -- TeX macros to handle Texinfo files.
%
% Load plain if necessary, i.e., if running under initex.
\expandafter\ifx\csname fmtname\endcsname\relax\input plain\fi
%
\def\texinfoversion{2013-11-26.10}
%
% Copyright 1985, 1986, 1988, 1990, 1991, 1992, 1993, 1994, 1995,
% 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
% 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
%
% This texinfo.tex file is free software: you can redistribute it and/or
% modify it under the terms of the GNU General Public License as
% published by the Free Software Foundation, either version 3 of the
% License, or (at your option) any later version.
%
% This texinfo.tex file is distributed in the hope that it will be
% useful, but WITHOUT ANY WARRANTY; without even the implied warranty
% of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
% General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program. If not, see .
%
% As a special exception, when this file is read by TeX when processing
% a Texinfo source document, you may use the result without
% restriction. This Exception is an additional permission under section 7
% of the GNU General Public License, version 3 ("GPLv3").
%
% Please try the latest version of texinfo.tex before submitting bug
% reports; you can get the latest version from:
% http://ftp.gnu.org/gnu/texinfo/ (the Texinfo release area), or
% http://ftpmirror.gnu.org/texinfo/ (same, via a mirror), or
% http://www.gnu.org/software/texinfo/ (the Texinfo home page)
% The texinfo.tex in any given distribution could well be out
% of date, so if that's what you're using, please check.
%
% Send bug reports to bug-texinfo@gnu.org. Please include including a
% complete document in each bug report with which we can reproduce the
% problem. Patches are, of course, greatly appreciated.
%
% To process a Texinfo manual with TeX, it's most reliable to use the
% texi2dvi shell script that comes with the distribution. For a simple
% manual foo.texi, however, you can get away with this:
% tex foo.texi
% texindex foo.??
% tex foo.texi
% tex foo.texi
% dvips foo.dvi -o # or whatever; this makes foo.ps.
% The extra TeX runs get the cross-reference information correct.
% Sometimes one run after texindex suffices, and sometimes you need more
% than two; texi2dvi does it as many times as necessary.
%
% It is possible to adapt texinfo.tex for other languages, to some
% extent. You can get the existing language-specific files from the
% full Texinfo distribution.
%
% The GNU Texinfo home page is http://www.gnu.org/software/texinfo.
\message{Loading texinfo [version \texinfoversion]:}
% If in a .fmt file, print the version number
% and turn on active characters that we couldn't do earlier because
% they might have appeared in the input file name.
\everyjob{\message{[Texinfo version \texinfoversion]}%
\catcode`+=\active \catcode`\_=\active}
\chardef\other=12
% We never want plain's \outer definition of \+ in Texinfo.
% For @tex, we can use \tabalign.
\let\+ = \relax
% Save some plain tex macros whose names we will redefine.
\let\ptexb=\b
\let\ptexbullet=\bullet
\let\ptexc=\c
\let\ptexcomma=\,
\let\ptexdot=\.
\let\ptexdots=\dots
\let\ptexend=\end
\let\ptexequiv=\equiv
\let\ptexexclam=\!
\let\ptexfootnote=\footnote
\let\ptexgtr=>
\let\ptexhat=^
\let\ptexi=\i
\let\ptexindent=\indent
\let\ptexinsert=\insert
\let\ptexlbrace=\{
\let\ptexless=<
\let\ptexnewwrite\newwrite
\let\ptexnoindent=\noindent
\let\ptexplus=+
\let\ptexraggedright=\raggedright
\let\ptexrbrace=\}
\let\ptexslash=\/
\let\ptexstar=\*
\let\ptext=\t
\let\ptextop=\top
{\catcode`\'=\active \global\let\ptexquoteright'}% active in plain's math mode
% If this character appears in an error message or help string, it
% starts a new line in the output.
\newlinechar = `^^J
% Use TeX 3.0's \inputlineno to get the line number, for better error
% messages, but if we're using an old version of TeX, don't do anything.
%
\ifx\inputlineno\thisisundefined
\let\linenumber = \empty % Pre-3.0.
\else
\def\linenumber{l.\the\inputlineno:\space}
\fi
% Set up fixed words for English if not already set.
\ifx\putwordAppendix\undefined \gdef\putwordAppendix{Appendix}\fi
\ifx\putwordChapter\undefined \gdef\putwordChapter{Chapter}\fi
\ifx\putworderror\undefined \gdef\putworderror{error}\fi
\ifx\putwordfile\undefined \gdef\putwordfile{file}\fi
\ifx\putwordin\undefined \gdef\putwordin{in}\fi
\ifx\putwordIndexIsEmpty\undefined \gdef\putwordIndexIsEmpty{(Index is empty)}\fi
\ifx\putwordIndexNonexistent\undefined \gdef\putwordIndexNonexistent{(Index is nonexistent)}\fi
\ifx\putwordInfo\undefined \gdef\putwordInfo{Info}\fi
\ifx\putwordInstanceVariableof\undefined \gdef\putwordInstanceVariableof{Instance Variable of}\fi
\ifx\putwordMethodon\undefined \gdef\putwordMethodon{Method on}\fi
\ifx\putwordNoTitle\undefined \gdef\putwordNoTitle{No Title}\fi
\ifx\putwordof\undefined \gdef\putwordof{of}\fi
\ifx\putwordon\undefined \gdef\putwordon{on}\fi
\ifx\putwordpage\undefined \gdef\putwordpage{page}\fi
\ifx\putwordsection\undefined \gdef\putwordsection{section}\fi
\ifx\putwordSection\undefined \gdef\putwordSection{Section}\fi
\ifx\putwordsee\undefined \gdef\putwordsee{see}\fi
\ifx\putwordSee\undefined \gdef\putwordSee{See}\fi
\ifx\putwordShortTOC\undefined \gdef\putwordShortTOC{Short Contents}\fi
\ifx\putwordTOC\undefined \gdef\putwordTOC{Table of Contents}\fi
%
\ifx\putwordMJan\undefined \gdef\putwordMJan{January}\fi
\ifx\putwordMFeb\undefined \gdef\putwordMFeb{February}\fi
\ifx\putwordMMar\undefined \gdef\putwordMMar{March}\fi
\ifx\putwordMApr\undefined \gdef\putwordMApr{April}\fi
\ifx\putwordMMay\undefined \gdef\putwordMMay{May}\fi
\ifx\putwordMJun\undefined \gdef\putwordMJun{June}\fi
\ifx\putwordMJul\undefined \gdef\putwordMJul{July}\fi
\ifx\putwordMAug\undefined \gdef\putwordMAug{August}\fi
\ifx\putwordMSep\undefined \gdef\putwordMSep{September}\fi
\ifx\putwordMOct\undefined \gdef\putwordMOct{October}\fi
\ifx\putwordMNov\undefined \gdef\putwordMNov{November}\fi
\ifx\putwordMDec\undefined \gdef\putwordMDec{December}\fi
%
\ifx\putwordDefmac\undefined \gdef\putwordDefmac{Macro}\fi
\ifx\putwordDefspec\undefined \gdef\putwordDefspec{Special Form}\fi
\ifx\putwordDefvar\undefined \gdef\putwordDefvar{Variable}\fi
\ifx\putwordDefopt\undefined \gdef\putwordDefopt{User Option}\fi
\ifx\putwordDeffunc\undefined \gdef\putwordDeffunc{Function}\fi
% Since the category of space is not known, we have to be careful.
\chardef\spacecat = 10
\def\spaceisspace{\catcode`\ =\spacecat}
% sometimes characters are active, so we need control sequences.
\chardef\ampChar = `\&
\chardef\colonChar = `\:
\chardef\commaChar = `\,
\chardef\dashChar = `\-
\chardef\dotChar = `\.
\chardef\exclamChar= `\!
\chardef\hashChar = `\#
\chardef\lquoteChar= `\`
\chardef\questChar = `\?
\chardef\rquoteChar= `\'
\chardef\semiChar = `\;
\chardef\slashChar = `\/
\chardef\underChar = `\_
% Ignore a token.
%
\def\gobble#1{}
% The following is used inside several \edef's.
\def\makecsname#1{\expandafter\noexpand\csname#1\endcsname}
% Hyphenation fixes.
\hyphenation{
Flor-i-da Ghost-script Ghost-view Mac-OS Post-Script
ap-pen-dix bit-map bit-maps
data-base data-bases eshell fall-ing half-way long-est man-u-script
man-u-scripts mini-buf-fer mini-buf-fers over-view par-a-digm
par-a-digms rath-er rec-tan-gu-lar ro-bot-ics se-vere-ly set-up spa-ces
spell-ing spell-ings
stand-alone strong-est time-stamp time-stamps which-ever white-space
wide-spread wrap-around
}
% Margin to add to right of even pages, to left of odd pages.
\newdimen\bindingoffset
\newdimen\normaloffset
\newdimen\pagewidth \newdimen\pageheight
% For a final copy, take out the rectangles
% that mark overfull boxes (in case you have decided
% that the text looks ok even though it passes the margin).
%
\def\finalout{\overfullrule=0pt }
% Sometimes it is convenient to have everything in the transcript file
% and nothing on the terminal. We don't just call \tracingall here,
% since that produces some useless output on the terminal. We also make
% some effort to order the tracing commands to reduce output in the log
% file; cf. trace.sty in LaTeX.
%
\def\gloggingall{\begingroup \globaldefs = 1 \loggingall \endgroup}%
\def\loggingall{%
\tracingstats2
\tracingpages1
\tracinglostchars2 % 2 gives us more in etex
\tracingparagraphs1
\tracingoutput1
\tracingmacros2
\tracingrestores1
\showboxbreadth\maxdimen \showboxdepth\maxdimen
\ifx\eTeXversion\thisisundefined\else % etex gives us more logging
\tracingscantokens1
\tracingifs1
\tracinggroups1
\tracingnesting2
\tracingassigns1
\fi
\tracingcommands3 % 3 gives us more in etex
\errorcontextlines16
}%
% @errormsg{MSG}. Do the index-like expansions on MSG, but if things
% aren't perfect, it's not the end of the world, being an error message,
% after all.
%
\def\errormsg{\begingroup \indexnofonts \doerrormsg}
\def\doerrormsg#1{\errmessage{#1}}
% add check for \lastpenalty to plain's definitions. If the last thing
% we did was a \nobreak, we don't want to insert more space.
%
\def\smallbreak{\ifnum\lastpenalty<10000\par\ifdim\lastskip<\smallskipamount
\removelastskip\penalty-50\smallskip\fi\fi}
\def\medbreak{\ifnum\lastpenalty<10000\par\ifdim\lastskip<\medskipamount
\removelastskip\penalty-100\medskip\fi\fi}
\def\bigbreak{\ifnum\lastpenalty<10000\par\ifdim\lastskip<\bigskipamount
\removelastskip\penalty-200\bigskip\fi\fi}
% Do @cropmarks to get crop marks.
%
\newif\ifcropmarks
\let\cropmarks = \cropmarkstrue
%
% Dimensions to add cropmarks at corners.
% Added by P. A. MacKay, 12 Nov. 1986
%
\newdimen\outerhsize \newdimen\outervsize % set by the paper size routines
\newdimen\cornerlong \cornerlong=1pc
\newdimen\cornerthick \cornerthick=.3pt
\newdimen\topandbottommargin \topandbottommargin=.75in
% Output a mark which sets \thischapter, \thissection and \thiscolor.
% We dump everything together because we only have one kind of mark.
% This works because we only use \botmark / \topmark, not \firstmark.
%
% A mark contains a subexpression of the \ifcase ... \fi construct.
% \get*marks macros below extract the needed part using \ifcase.
%
% Another complication is to let the user choose whether \thischapter
% (\thissection) refers to the chapter (section) in effect at the top
% of a page, or that at the bottom of a page. The solution is
% described on page 260 of The TeXbook. It involves outputting two
% marks for the sectioning macros, one before the section break, and
% one after. I won't pretend I can describe this better than DEK...
\def\domark{%
\toks0=\expandafter{\lastchapterdefs}%
\toks2=\expandafter{\lastsectiondefs}%
\toks4=\expandafter{\prevchapterdefs}%
\toks6=\expandafter{\prevsectiondefs}%
\toks8=\expandafter{\lastcolordefs}%
\mark{%
\the\toks0 \the\toks2 % 0: top marks (\last...)
\noexpand\or \the\toks4 \the\toks6 % 1: bottom marks (default, \prev...)
\noexpand\else \the\toks8 % 2: color marks
}%
}
% \topmark doesn't work for the very first chapter (after the title
% page or the contents), so we use \firstmark there -- this gets us
% the mark with the chapter defs, unless the user sneaks in, e.g.,
% @setcolor (or @url, or @link, etc.) between @contents and the very
% first @chapter.
\def\gettopheadingmarks{%
\ifcase0\topmark\fi
\ifx\thischapter\empty \ifcase0\firstmark\fi \fi
}
\def\getbottomheadingmarks{\ifcase1\botmark\fi}
\def\getcolormarks{\ifcase2\topmark\fi}
% Avoid "undefined control sequence" errors.
\def\lastchapterdefs{}
\def\lastsectiondefs{}
\def\prevchapterdefs{}
\def\prevsectiondefs{}
\def\lastcolordefs{}
% Main output routine.
\chardef\PAGE = 255
\output = {\onepageout{\pagecontents\PAGE}}
\newbox\headlinebox
\newbox\footlinebox
% \onepageout takes a vbox as an argument. Note that \pagecontents
% does insertions, but you have to call it yourself.
\def\onepageout#1{%
\ifcropmarks \hoffset=0pt \else \hoffset=\normaloffset \fi
%
\ifodd\pageno \advance\hoffset by \bindingoffset
\else \advance\hoffset by -\bindingoffset\fi
%
% Do this outside of the \shipout so @code etc. will be expanded in
% the headline as they should be, not taken literally (outputting ''code).
\def\commmonheadfootline{\let\hsize=\pagewidth \texinfochars}
%
\ifodd\pageno \getoddheadingmarks \else \getevenheadingmarks \fi
\global\setbox\headlinebox = \vbox{\commmonheadfootline \makeheadline}%
%
\ifodd\pageno \getoddfootingmarks \else \getevenfootingmarks \fi
\global\setbox\footlinebox = \vbox{\commmonheadfootline \makefootline}%
%
{%
% Have to do this stuff outside the \shipout because we want it to
% take effect in \write's, yet the group defined by the \vbox ends
% before the \shipout runs.
%
\indexdummies % don't expand commands in the output.
\normalturnoffactive % \ in index entries must not stay \, e.g., if
% the page break happens to be in the middle of an example.
% We don't want .vr (or whatever) entries like this:
% \entry{{\tt \indexbackslash }acronym}{32}{\code {\acronym}}
% "\acronym" won't work when it's read back in;
% it needs to be
% {\code {{\tt \backslashcurfont }acronym}
\shipout\vbox{%
% Do this early so pdf references go to the beginning of the page.
\ifpdfmakepagedest \pdfdest name{\the\pageno} xyz\fi
%
\ifcropmarks \vbox to \outervsize\bgroup
\hsize = \outerhsize
\vskip-\topandbottommargin
\vtop to0pt{%
\line{\ewtop\hfil\ewtop}%
\nointerlineskip
\line{%
\vbox{\moveleft\cornerthick\nstop}%
\hfill
\vbox{\moveright\cornerthick\nstop}%
}%
\vss}%
\vskip\topandbottommargin
\line\bgroup
\hfil % center the page within the outer (page) hsize.
\ifodd\pageno\hskip\bindingoffset\fi
\vbox\bgroup
\fi
%
\unvbox\headlinebox
\pagebody{#1}%
\ifdim\ht\footlinebox > 0pt
% Only leave this space if the footline is nonempty.
% (We lessened \vsize for it in \oddfootingyyy.)
% The \baselineskip=24pt in plain's \makefootline has no effect.
\vskip 24pt
\unvbox\footlinebox
\fi
%
\ifcropmarks
\egroup % end of \vbox\bgroup
\hfil\egroup % end of (centering) \line\bgroup
\vskip\topandbottommargin plus1fill minus1fill
\boxmaxdepth = \cornerthick
\vbox to0pt{\vss
\line{%
\vbox{\moveleft\cornerthick\nsbot}%
\hfill
\vbox{\moveright\cornerthick\nsbot}%
}%
\nointerlineskip
\line{\ewbot\hfil\ewbot}%
}%
\egroup % \vbox from first cropmarks clause
\fi
}% end of \shipout\vbox
}% end of group with \indexdummies
\advancepageno
\ifnum\outputpenalty>-20000 \else\dosupereject\fi
}
\newinsert\margin \dimen\margin=\maxdimen
\def\pagebody#1{\vbox to\pageheight{\boxmaxdepth=\maxdepth #1}}
{\catcode`\@ =11
\gdef\pagecontents#1{\ifvoid\topins\else\unvbox\topins\fi
% marginal hacks, juha@viisa.uucp (Juha Takala)
\ifvoid\margin\else % marginal info is present
\rlap{\kern\hsize\vbox to\z@{\kern1pt\box\margin \vss}}\fi
\dimen@=\dp#1\relax \unvbox#1\relax
\ifvoid\footins\else\vskip\skip\footins\footnoterule \unvbox\footins\fi
\ifr@ggedbottom \kern-\dimen@ \vfil \fi}
}
% Here are the rules for the cropmarks. Note that they are
% offset so that the space between them is truly \outerhsize or \outervsize
% (P. A. MacKay, 12 November, 1986)
%
\def\ewtop{\vrule height\cornerthick depth0pt width\cornerlong}
\def\nstop{\vbox
{\hrule height\cornerthick depth\cornerlong width\cornerthick}}
\def\ewbot{\vrule height0pt depth\cornerthick width\cornerlong}
\def\nsbot{\vbox
{\hrule height\cornerlong depth\cornerthick width\cornerthick}}
% Parse an argument, then pass it to #1. The argument is the rest of
% the input line (except we remove a trailing comment). #1 should be a
% macro which expects an ordinary undelimited TeX argument.
%
\def\parsearg{\parseargusing{}}
\def\parseargusing#1#2{%
\def\argtorun{#2}%
\begingroup
\obeylines
\spaceisspace
#1%
\parseargline\empty% Insert the \empty token, see \finishparsearg below.
}
{\obeylines %
\gdef\parseargline#1^^M{%
\endgroup % End of the group started in \parsearg.
\argremovecomment #1\comment\ArgTerm%
}%
}
% First remove any @comment, then any @c comment.
\def\argremovecomment#1\comment#2\ArgTerm{\argremovec #1\c\ArgTerm}
\def\argremovec#1\c#2\ArgTerm{\argcheckspaces#1\^^M\ArgTerm}
% Each occurrence of `\^^M' or `\^^M' is replaced by a single space.
%
% \argremovec might leave us with trailing space, e.g.,
% @end itemize @c foo
% This space token undergoes the same procedure and is eventually removed
% by \finishparsearg.
%
\def\argcheckspaces#1\^^M{\argcheckspacesX#1\^^M \^^M}
\def\argcheckspacesX#1 \^^M{\argcheckspacesY#1\^^M}
\def\argcheckspacesY#1\^^M#2\^^M#3\ArgTerm{%
\def\temp{#3}%
\ifx\temp\empty
% Do not use \next, perhaps the caller of \parsearg uses it; reuse \temp:
\let\temp\finishparsearg
\else
\let\temp\argcheckspaces
\fi
% Put the space token in:
\temp#1 #3\ArgTerm
}
% If a _delimited_ argument is enclosed in braces, they get stripped; so
% to get _exactly_ the rest of the line, we had to prevent such situation.
% We prepended an \empty token at the very beginning and we expand it now,
% just before passing the control to \argtorun.
% (Similarly, we have to think about #3 of \argcheckspacesY above: it is
% either the null string, or it ends with \^^M---thus there is no danger
% that a pair of braces would be stripped.
%
% But first, we have to remove the trailing space token.
%
\def\finishparsearg#1 \ArgTerm{\expandafter\argtorun\expandafter{#1}}
% \parseargdef\foo{...}
% is roughly equivalent to
% \def\foo{\parsearg\Xfoo}
% \def\Xfoo#1{...}
%
% Actually, I use \csname\string\foo\endcsname, ie. \\foo, as it is my
% favourite TeX trick. --kasal, 16nov03
\def\parseargdef#1{%
\expandafter \doparseargdef \csname\string#1\endcsname #1%
}
\def\doparseargdef#1#2{%
\def#2{\parsearg#1}%
\def#1##1%
}
% Several utility definitions with active space:
{
\obeyspaces
\gdef\obeyedspace{ }
% Make each space character in the input produce a normal interword
% space in the output. Don't allow a line break at this space, as this
% is used only in environments like @example, where each line of input
% should produce a line of output anyway.
%
\gdef\sepspaces{\obeyspaces\let =\tie}
% If an index command is used in an @example environment, any spaces
% therein should become regular spaces in the raw index file, not the
% expansion of \tie (\leavevmode \penalty \@M \ ).
\gdef\unsepspaces{\let =\space}
}
\def\flushcr{\ifx\par\lisppar \def\next##1{}\else \let\next=\relax \fi \next}
% Define the framework for environments in texinfo.tex. It's used like this:
%
% \envdef\foo{...}
% \def\Efoo{...}
%
% It's the responsibility of \envdef to insert \begingroup before the
% actual body; @end closes the group after calling \Efoo. \envdef also
% defines \thisenv, so the current environment is known; @end checks
% whether the environment name matches. The \checkenv macro can also be
% used to check whether the current environment is the one expected.
%
% Non-false conditionals (@iftex, @ifset) don't fit into this, so they
% are not treated as environments; they don't open a group. (The
% implementation of @end takes care not to call \endgroup in this
% special case.)
% At run-time, environments start with this:
\def\startenvironment#1{\begingroup\def\thisenv{#1}}
% initialize
\let\thisenv\empty
% ... but they get defined via ``\envdef\foo{...}'':
\long\def\envdef#1#2{\def#1{\startenvironment#1#2}}
\def\envparseargdef#1#2{\parseargdef#1{\startenvironment#1#2}}
% Check whether we're in the right environment:
\def\checkenv#1{%
\def\temp{#1}%
\ifx\thisenv\temp
\else
\badenverr
\fi
}
% Environment mismatch, #1 expected:
\def\badenverr{%
\errhelp = \EMsimple
\errmessage{This command can appear only \inenvironment\temp,
not \inenvironment\thisenv}%
}
\def\inenvironment#1{%
\ifx#1\empty
outside of any environment%
\else
in environment \expandafter\string#1%
\fi
}
% @end foo executes the definition of \Efoo.
% But first, it executes a specialized version of \checkenv
%
\parseargdef\end{%
\if 1\csname iscond.#1\endcsname
\else
% The general wording of \badenverr may not be ideal.
\expandafter\checkenv\csname#1\endcsname
\csname E#1\endcsname
\endgroup
\fi
}
\newhelp\EMsimple{Press RETURN to continue.}
% Be sure we're in horizontal mode when doing a tie, since we make space
% equivalent to this in @example-like environments. Otherwise, a space
% at the beginning of a line will start with \penalty -- and
% since \penalty is valid in vertical mode, we'd end up putting the
% penalty on the vertical list instead of in the new paragraph.
{\catcode`@ = 11
% Avoid using \@M directly, because that causes trouble
% if the definition is written into an index file.
\global\let\tiepenalty = \@M
\gdef\tie{\leavevmode\penalty\tiepenalty\ }
}
% @: forces normal size whitespace following.
\def\:{\spacefactor=1000 }
% @* forces a line break.
\def\*{\unskip\hfil\break\hbox{}\ignorespaces}
% @/ allows a line break.
\let\/=\allowbreak
% @. is an end-of-sentence period.
\def\.{.\spacefactor=\endofsentencespacefactor\space}
% @! is an end-of-sentence bang.
\def\!{!\spacefactor=\endofsentencespacefactor\space}
% @? is an end-of-sentence query.
\def\?{?\spacefactor=\endofsentencespacefactor\space}
% @frenchspacing on|off says whether to put extra space after punctuation.
%
\def\onword{on}
\def\offword{off}
%
\parseargdef\frenchspacing{%
\def\temp{#1}%
\ifx\temp\onword \plainfrenchspacing
\else\ifx\temp\offword \plainnonfrenchspacing
\else
\errhelp = \EMsimple
\errmessage{Unknown @frenchspacing option `\temp', must be on|off}%
\fi\fi
}
% @w prevents a word break. Without the \leavevmode, @w at the
% beginning of a paragraph, when TeX is still in vertical mode, would
% produce a whole line of output instead of starting the paragraph.
\def\w#1{\leavevmode\hbox{#1}}
% @group ... @end group forces ... to be all on one page, by enclosing
% it in a TeX vbox. We use \vtop instead of \vbox to construct the box
% to keep its height that of a normal line. According to the rules for
% \topskip (p.114 of the TeXbook), the glue inserted is
% max (\topskip - \ht (first item), 0). If that height is large,
% therefore, no glue is inserted, and the space between the headline and
% the text is small, which looks bad.
%
% Another complication is that the group might be very large. This can
% cause the glue on the previous page to be unduly stretched, because it
% does not have much material. In this case, it's better to add an
% explicit \vfill so that the extra space is at the bottom. The
% threshold for doing this is if the group is more than \vfilllimit
% percent of a page (\vfilllimit can be changed inside of @tex).
%
\newbox\groupbox
\def\vfilllimit{0.7}
%
\envdef\group{%
\ifnum\catcode`\^^M=\active \else
\errhelp = \groupinvalidhelp
\errmessage{@group invalid in context where filling is enabled}%
\fi
\startsavinginserts
%
\setbox\groupbox = \vtop\bgroup
% Do @comment since we are called inside an environment such as
% @example, where each end-of-line in the input causes an
% end-of-line in the output. We don't want the end-of-line after
% the `@group' to put extra space in the output. Since @group
% should appear on a line by itself (according to the Texinfo
% manual), we don't worry about eating any user text.
\comment
}
%
% The \vtop produces a box with normal height and large depth; thus, TeX puts
% \baselineskip glue before it, and (when the next line of text is done)
% \lineskip glue after it. Thus, space below is not quite equal to space
% above. But it's pretty close.
\def\Egroup{%
% To get correct interline space between the last line of the group
% and the first line afterwards, we have to propagate \prevdepth.
\endgraf % Not \par, as it may have been set to \lisppar.
\global\dimen1 = \prevdepth
\egroup % End the \vtop.
% \dimen0 is the vertical size of the group's box.
\dimen0 = \ht\groupbox \advance\dimen0 by \dp\groupbox
% \dimen2 is how much space is left on the page (more or less).
\dimen2 = \pageheight \advance\dimen2 by -\pagetotal
% if the group doesn't fit on the current page, and it's a big big
% group, force a page break.
\ifdim \dimen0 > \dimen2
\ifdim \pagetotal < \vfilllimit\pageheight
\page
\fi
\fi
\box\groupbox
\prevdepth = \dimen1
\checkinserts
}
%
% TeX puts in an \escapechar (i.e., `@') at the beginning of the help
% message, so this ends up printing `@group can only ...'.
%
\newhelp\groupinvalidhelp{%
group can only be used in environments such as @example,^^J%
where each line of input produces a line of output.}
% @need space-in-mils
% forces a page break if there is not space-in-mils remaining.
\newdimen\mil \mil=0.001in
\parseargdef\need{%
% Ensure vertical mode, so we don't make a big box in the middle of a
% paragraph.
\par
%
% If the @need value is less than one line space, it's useless.
\dimen0 = #1\mil
\dimen2 = \ht\strutbox
\advance\dimen2 by \dp\strutbox
\ifdim\dimen0 > \dimen2
%
% Do a \strut just to make the height of this box be normal, so the
% normal leading is inserted relative to the preceding line.
% And a page break here is fine.
\vtop to #1\mil{\strut\vfil}%
%
% TeX does not even consider page breaks if a penalty added to the
% main vertical list is 10000 or more. But in order to see if the
% empty box we just added fits on the page, we must make it consider
% page breaks. On the other hand, we don't want to actually break the
% page after the empty box. So we use a penalty of 9999.
%
% There is an extremely small chance that TeX will actually break the
% page at this \penalty, if there are no other feasible breakpoints in
% sight. (If the user is using lots of big @group commands, which
% almost-but-not-quite fill up a page, TeX will have a hard time doing
% good page breaking, for example.) However, I could not construct an
% example where a page broke at this \penalty; if it happens in a real
% document, then we can reconsider our strategy.
\penalty9999
%
% Back up by the size of the box, whether we did a page break or not.
\kern -#1\mil
%
% Do not allow a page break right after this kern.
\nobreak
\fi
}
% @br forces paragraph break (and is undocumented).
\let\br = \par
% @page forces the start of a new page.
%
\def\page{\par\vfill\supereject}
% @exdent text....
% outputs text on separate line in roman font, starting at standard page margin
% This records the amount of indent in the innermost environment.
% That's how much \exdent should take out.
\newskip\exdentamount
% This defn is used inside fill environments such as @defun.
\parseargdef\exdent{\hfil\break\hbox{\kern -\exdentamount{\rm#1}}\hfil\break}
% This defn is used inside nofill environments such as @example.
\parseargdef\nofillexdent{{\advance \leftskip by -\exdentamount
\leftline{\hskip\leftskip{\rm#1}}}}
% @inmargin{WHICH}{TEXT} puts TEXT in the WHICH margin next to the current
% paragraph. For more general purposes, use the \margin insertion
% class. WHICH is `l' or `r'. Not documented, written for gawk manual.
%
\newskip\inmarginspacing \inmarginspacing=1cm
\def\strutdepth{\dp\strutbox}
%
\def\doinmargin#1#2{\strut\vadjust{%
\nobreak
\kern-\strutdepth
\vtop to \strutdepth{%
\baselineskip=\strutdepth
\vss
% if you have multiple lines of stuff to put here, you'll need to
% make the vbox yourself of the appropriate size.
\ifx#1l%
\llap{\ignorespaces #2\hskip\inmarginspacing}%
\else
\rlap{\hskip\hsize \hskip\inmarginspacing \ignorespaces #2}%
\fi
\null
}%
}}
\def\inleftmargin{\doinmargin l}
\def\inrightmargin{\doinmargin r}
%
% @inmargin{TEXT [, RIGHT-TEXT]}
% (if RIGHT-TEXT is given, use TEXT for left page, RIGHT-TEXT for right;
% else use TEXT for both).
%
\def\inmargin#1{\parseinmargin #1,,\finish}
\def\parseinmargin#1,#2,#3\finish{% not perfect, but better than nothing.
\setbox0 = \hbox{\ignorespaces #2}%
\ifdim\wd0 > 0pt
\def\lefttext{#1}% have both texts
\def\righttext{#2}%
\else
\def\lefttext{#1}% have only one text
\def\righttext{#1}%
\fi
%
\ifodd\pageno
\def\temp{\inrightmargin\righttext}% odd page -> outside is right margin
\else
\def\temp{\inleftmargin\lefttext}%
\fi
\temp
}
% @| inserts a changebar to the left of the current line. It should
% surround any changed text. This approach does *not* work if the
% change spans more than two lines of output. To handle that, we would
% have adopt a much more difficult approach (putting marks into the main
% vertical list for the beginning and end of each change). This command
% is not documented, not supported, and doesn't work.
%
\def\|{%
% \vadjust can only be used in horizontal mode.
\leavevmode
%
% Append this vertical mode material after the current line in the output.
\vadjust{%
% We want to insert a rule with the height and depth of the current
% leading; that is exactly what \strutbox is supposed to record.
\vskip-\baselineskip
%
% \vadjust-items are inserted at the left edge of the type. So
% the \llap here moves out into the left-hand margin.
\llap{%
%
% For a thicker or thinner bar, change the `1pt'.
\vrule height\baselineskip width1pt
%
% This is the space between the bar and the text.
\hskip 12pt
}%
}%
}
% @include FILE -- \input text of FILE.
%
\def\include{\parseargusing\filenamecatcodes\includezzz}
\def\includezzz#1{%
\pushthisfilestack
\def\thisfile{#1}%
{%
\makevalueexpandable % we want to expand any @value in FILE.
\turnoffactive % and allow special characters in the expansion
\indexnofonts % Allow `@@' and other weird things in file names.
\wlog{texinfo.tex: doing @include of #1^^J}%
\edef\temp{\noexpand\input #1 }%
%
% This trickery is to read FILE outside of a group, in case it makes
% definitions, etc.
\expandafter
}\temp
\popthisfilestack
}
\def\filenamecatcodes{%
\catcode`\\=\other
\catcode`~=\other
\catcode`^=\other
\catcode`_=\other
\catcode`|=\other
\catcode`<=\other
\catcode`>=\other
\catcode`+=\other
\catcode`-=\other
\catcode`\`=\other
\catcode`\'=\other
}
\def\pushthisfilestack{%
\expandafter\pushthisfilestackX\popthisfilestack\StackTerm
}
\def\pushthisfilestackX{%
\expandafter\pushthisfilestackY\thisfile\StackTerm
}
\def\pushthisfilestackY #1\StackTerm #2\StackTerm {%
\gdef\popthisfilestack{\gdef\thisfile{#1}\gdef\popthisfilestack{#2}}%
}
\def\popthisfilestack{\errthisfilestackempty}
\def\errthisfilestackempty{\errmessage{Internal error:
the stack of filenames is empty.}}
%
\def\thisfile{}
% @center line
% outputs that line, centered.
%
\parseargdef\center{%
\ifhmode
\let\centersub\centerH
\else
\let\centersub\centerV
\fi
\centersub{\hfil \ignorespaces#1\unskip \hfil}%
\let\centersub\relax % don't let the definition persist, just in case
}
\def\centerH#1{{%
\hfil\break
\advance\hsize by -\leftskip
\advance\hsize by -\rightskip
\line{#1}%
\break
}}
%
\newcount\centerpenalty
\def\centerV#1{%
% The idea here is the same as in \startdefun, \cartouche, etc.: if
% @center is the first thing after a section heading, we need to wipe
% out the negative parskip inserted by \sectionheading, but still
% prevent a page break here.
\centerpenalty = \lastpenalty
\ifnum\centerpenalty>10000 \vskip\parskip \fi
\ifnum\centerpenalty>9999 \penalty\centerpenalty \fi
\line{\kern\leftskip #1\kern\rightskip}%
}
% @sp n outputs n lines of vertical space
%
\parseargdef\sp{\vskip #1\baselineskip}
% @comment ...line which is ignored...
% @c is the same as @comment
% @ignore ... @end ignore is another way to write a comment
%
\def\comment{\begingroup \catcode`\^^M=\other%
\catcode`\@=\other \catcode`\{=\other \catcode`\}=\other%
\commentxxx}
{\catcode`\^^M=\other \gdef\commentxxx#1^^M{\endgroup}}
%
\let\c=\comment
% @paragraphindent NCHARS
% We'll use ems for NCHARS, close enough.
% NCHARS can also be the word `asis' or `none'.
% We cannot feasibly implement @paragraphindent asis, though.
%
\def\asisword{asis} % no translation, these are keywords
\def\noneword{none}
%
\parseargdef\paragraphindent{%
\def\temp{#1}%
\ifx\temp\asisword
\else
\ifx\temp\noneword
\defaultparindent = 0pt
\else
\defaultparindent = #1em
\fi
\fi
\parindent = \defaultparindent
}
% @exampleindent NCHARS
% We'll use ems for NCHARS like @paragraphindent.
% It seems @exampleindent asis isn't necessary, but
% I preserve it to make it similar to @paragraphindent.
\parseargdef\exampleindent{%
\def\temp{#1}%
\ifx\temp\asisword
\else
\ifx\temp\noneword
\lispnarrowing = 0pt
\else
\lispnarrowing = #1em
\fi
\fi
}
% @firstparagraphindent WORD
% If WORD is `none', then suppress indentation of the first paragraph
% after a section heading. If WORD is `insert', then do indent at such
% paragraphs.
%
% The paragraph indentation is suppressed or not by calling
% \suppressfirstparagraphindent, which the sectioning commands do.
% We switch the definition of this back and forth according to WORD.
% By default, we suppress indentation.
%
\def\suppressfirstparagraphindent{\dosuppressfirstparagraphindent}
\def\insertword{insert}
%
\parseargdef\firstparagraphindent{%
\def\temp{#1}%
\ifx\temp\noneword
\let\suppressfirstparagraphindent = \dosuppressfirstparagraphindent
\else\ifx\temp\insertword
\let\suppressfirstparagraphindent = \relax
\else
\errhelp = \EMsimple
\errmessage{Unknown @firstparagraphindent option `\temp'}%
\fi\fi
}
% Here is how we actually suppress indentation. Redefine \everypar to
% \kern backwards by \parindent, and then reset itself to empty.
%
% We also make \indent itself not actually do anything until the next
% paragraph.
%
\gdef\dosuppressfirstparagraphindent{%
\gdef\indent{%
\restorefirstparagraphindent
\indent
}%
\gdef\noindent{%
\restorefirstparagraphindent
\noindent
}%
\global\everypar = {%
\kern -\parindent
\restorefirstparagraphindent
}%
}
\gdef\restorefirstparagraphindent{%
\global \let \indent = \ptexindent
\global \let \noindent = \ptexnoindent
\global \everypar = {}%
}
% @refill is a no-op.
\let\refill=\relax
% If working on a large document in chapters, it is convenient to
% be able to disable indexing, cross-referencing, and contents, for test runs.
% This is done with @novalidate (before @setfilename).
%
\newif\iflinks \linkstrue % by default we want the aux files.
\let\novalidate = \linksfalse
% @setfilename is done at the beginning of every texinfo file.
% So open here the files we need to have open while reading the input.
% This makes it possible to make a .fmt file for texinfo.
\def\setfilename{%
\fixbackslash % Turn off hack to swallow `\input texinfo'.
\iflinks
\tryauxfile
% Open the new aux file. TeX will close it automatically at exit.
\immediate\openout\auxfile=\jobname.aux
\fi % \openindices needs to do some work in any case.
\openindices
\let\setfilename=\comment % Ignore extra @setfilename cmds.
%
% If texinfo.cnf is present on the system, read it.
% Useful for site-wide @afourpaper, etc.
\openin 1 texinfo.cnf
\ifeof 1 \else \input texinfo.cnf \fi
\closein 1
%
\comment % Ignore the actual filename.
}
% Called from \setfilename.
%
\def\openindices{%
\newindex{cp}%
\newcodeindex{fn}%
\newcodeindex{vr}%
\newcodeindex{tp}%
\newcodeindex{ky}%
\newcodeindex{pg}%
}
% @bye.
\outer\def\bye{\pagealignmacro\tracingstats=1\ptexend}
\message{pdf,}
% adobe `portable' document format
\newcount\tempnum
\newcount\lnkcount
\newtoks\filename
\newcount\filenamelength
\newcount\pgn
\newtoks\toksA
\newtoks\toksB
\newtoks\toksC
\newtoks\toksD
\newbox\boxA
\newcount\countA
\newif\ifpdf
\newif\ifpdfmakepagedest
% when pdftex is run in dvi mode, \pdfoutput is defined (so \pdfoutput=1
% can be set). So we test for \relax and 0 as well as being undefined.
\ifx\pdfoutput\thisisundefined
\else
\ifx\pdfoutput\relax
\else
\ifcase\pdfoutput
\else
\pdftrue
\fi
\fi
\fi
% PDF uses PostScript string constants for the names of xref targets,
% for display in the outlines, and in other places. Thus, we have to
% double any backslashes. Otherwise, a name like "\node" will be
% interpreted as a newline (\n), followed by o, d, e. Not good.
%
% See http://www.ntg.nl/pipermail/ntg-pdftex/2004-July/000654.html and
% related messages. The final outcome is that it is up to the TeX user
% to double the backslashes and otherwise make the string valid, so
% that's what we do. pdftex 1.30.0 (ca.2005) introduced a primitive to
% do this reliably, so we use it.
% #1 is a control sequence in which to do the replacements,
% which we \xdef.
\def\txiescapepdf#1{%
\ifx\pdfescapestring\thisisundefined
% No primitive available; should we give a warning or log?
% Many times it won't matter.
\else
% The expandable \pdfescapestring primitive escapes parentheses,
% backslashes, and other special chars.
\xdef#1{\pdfescapestring{#1}}%
\fi
}
\newhelp\nopdfimagehelp{Texinfo supports .png, .jpg, .jpeg, and .pdf images
with PDF output, and none of those formats could be found. (.eps cannot
be supported due to the design of the PDF format; use regular TeX (DVI
output) for that.)}
\ifpdf
%
% Color manipulation macros based on pdfcolor.tex,
% except using rgb instead of cmyk; the latter is said to render as a
% very dark gray on-screen and a very dark halftone in print, instead
% of actual black. The dark red here is dark enough to print on paper as
% nearly black, but still distinguishable for online viewing. We use
% black by default, though.
\def\rgbDarkRed{0.50 0.09 0.12}
\def\rgbBlack{0 0 0}
%
% k sets the color for filling (usual text, etc.);
% K sets the color for stroking (thin rules, e.g., normal _'s).
\def\pdfsetcolor#1{\pdfliteral{#1 rg #1 RG}}
%
% Set color, and create a mark which defines \thiscolor accordingly,
% so that \makeheadline knows which color to restore.
\def\setcolor#1{%
\xdef\lastcolordefs{\gdef\noexpand\thiscolor{#1}}%
\domark
\pdfsetcolor{#1}%
}
%
\def\maincolor{\rgbBlack}
\pdfsetcolor{\maincolor}
\edef\thiscolor{\maincolor}
\def\lastcolordefs{}
%
\def\makefootline{%
\baselineskip24pt
\line{\pdfsetcolor{\maincolor}\the\footline}%
}
%
\def\makeheadline{%
\vbox to 0pt{%
\vskip-22.5pt
\line{%
\vbox to8.5pt{}%
% Extract \thiscolor definition from the marks.
\getcolormarks
% Typeset the headline with \maincolor, then restore the color.
\pdfsetcolor{\maincolor}\the\headline\pdfsetcolor{\thiscolor}%
}%
\vss
}%
\nointerlineskip
}
%
%
\pdfcatalog{/PageMode /UseOutlines}
%
% #1 is image name, #2 width (might be empty/whitespace), #3 height (ditto).
\def\dopdfimage#1#2#3{%
\def\pdfimagewidth{#2}\setbox0 = \hbox{\ignorespaces #2}%
\def\pdfimageheight{#3}\setbox2 = \hbox{\ignorespaces #3}%
%
% pdftex (and the PDF format) support .pdf, .png, .jpg (among
% others). Let's try in that order, PDF first since if
% someone has a scalable image, presumably better to use that than a
% bitmap.
\let\pdfimgext=\empty
\begingroup
\openin 1 #1.pdf \ifeof 1
\openin 1 #1.PDF \ifeof 1
\openin 1 #1.png \ifeof 1
\openin 1 #1.jpg \ifeof 1
\openin 1 #1.jpeg \ifeof 1
\openin 1 #1.JPG \ifeof 1
\errhelp = \nopdfimagehelp
\errmessage{Could not find image file #1 for pdf}%
\else \gdef\pdfimgext{JPG}%
\fi
\else \gdef\pdfimgext{jpeg}%
\fi
\else \gdef\pdfimgext{jpg}%
\fi
\else \gdef\pdfimgext{png}%
\fi
\else \gdef\pdfimgext{PDF}%
\fi
\else \gdef\pdfimgext{pdf}%
\fi
\closein 1
\endgroup
%
% without \immediate, ancient pdftex seg faults when the same image is
% included twice. (Version 3.14159-pre-1.0-unofficial-20010704.)
\ifnum\pdftexversion < 14
\immediate\pdfimage
\else
\immediate\pdfximage
\fi
\ifdim \wd0 >0pt width \pdfimagewidth \fi
\ifdim \wd2 >0pt height \pdfimageheight \fi
\ifnum\pdftexversion<13
#1.\pdfimgext
\else
{#1.\pdfimgext}%
\fi
\ifnum\pdftexversion < 14 \else
\pdfrefximage \pdflastximage
\fi}
%
\def\pdfmkdest#1{{%
% We have to set dummies so commands such as @code, and characters
% such as \, aren't expanded when present in a section title.
\indexnofonts
\turnoffactive
\makevalueexpandable
\def\pdfdestname{#1}%
\txiescapepdf\pdfdestname
\safewhatsit{\pdfdest name{\pdfdestname} xyz}%
}}
%
% used to mark target names; must be expandable.
\def\pdfmkpgn#1{#1}
%
% by default, use black for everything.
\def\urlcolor{\rgbBlack}
\def\linkcolor{\rgbBlack}
\def\endlink{\setcolor{\maincolor}\pdfendlink}
%
% Adding outlines to PDF; macros for calculating structure of outlines
% come from Petr Olsak
\def\expnumber#1{\expandafter\ifx\csname#1\endcsname\relax 0%
\else \csname#1\endcsname \fi}
\def\advancenumber#1{\tempnum=\expnumber{#1}\relax
\advance\tempnum by 1
\expandafter\xdef\csname#1\endcsname{\the\tempnum}}
%
% #1 is the section text, which is what will be displayed in the
% outline by the pdf viewer. #2 is the pdf expression for the number
% of subentries (or empty, for subsubsections). #3 is the node text,
% which might be empty if this toc entry had no corresponding node.
% #4 is the page number
%
\def\dopdfoutline#1#2#3#4{%
% Generate a link to the node text if that exists; else, use the
% page number. We could generate a destination for the section
% text in the case where a section has no node, but it doesn't
% seem worth the trouble, since most documents are normally structured.
\edef\pdfoutlinedest{#3}%
\ifx\pdfoutlinedest\empty
\def\pdfoutlinedest{#4}%
\else
\txiescapepdf\pdfoutlinedest
\fi
%
% Also escape PDF chars in the display string.
\edef\pdfoutlinetext{#1}%
\txiescapepdf\pdfoutlinetext
%
\pdfoutline goto name{\pdfmkpgn{\pdfoutlinedest}}#2{\pdfoutlinetext}%
}
%
\def\pdfmakeoutlines{%
\begingroup
% Read toc silently, to get counts of subentries for \pdfoutline.
\def\partentry##1##2##3##4{}% ignore parts in the outlines
\def\numchapentry##1##2##3##4{%
\def\thischapnum{##2}%
\def\thissecnum{0}%
\def\thissubsecnum{0}%
}%
\def\numsecentry##1##2##3##4{%
\advancenumber{chap\thischapnum}%
\def\thissecnum{##2}%
\def\thissubsecnum{0}%
}%
\def\numsubsecentry##1##2##3##4{%
\advancenumber{sec\thissecnum}%
\def\thissubsecnum{##2}%
}%
\def\numsubsubsecentry##1##2##3##4{%
\advancenumber{subsec\thissubsecnum}%
}%
\def\thischapnum{0}%
\def\thissecnum{0}%
\def\thissubsecnum{0}%
%
% use \def rather than \let here because we redefine \chapentry et
% al. a second time, below.
\def\appentry{\numchapentry}%
\def\appsecentry{\numsecentry}%
\def\appsubsecentry{\numsubsecentry}%
\def\appsubsubsecentry{\numsubsubsecentry}%
\def\unnchapentry{\numchapentry}%
\def\unnsecentry{\numsecentry}%
\def\unnsubsecentry{\numsubsecentry}%
\def\unnsubsubsecentry{\numsubsubsecentry}%
\readdatafile{toc}%
%
% Read toc second time, this time actually producing the outlines.
% The `-' means take the \expnumber as the absolute number of
% subentries, which we calculated on our first read of the .toc above.
%
% We use the node names as the destinations.
\def\numchapentry##1##2##3##4{%
\dopdfoutline{##1}{count-\expnumber{chap##2}}{##3}{##4}}%
\def\numsecentry##1##2##3##4{%
\dopdfoutline{##1}{count-\expnumber{sec##2}}{##3}{##4}}%
\def\numsubsecentry##1##2##3##4{%
\dopdfoutline{##1}{count-\expnumber{subsec##2}}{##3}{##4}}%
\def\numsubsubsecentry##1##2##3##4{% count is always zero
\dopdfoutline{##1}{}{##3}{##4}}%
%
% PDF outlines are displayed using system fonts, instead of
% document fonts. Therefore we cannot use special characters,
% since the encoding is unknown. For example, the eogonek from
% Latin 2 (0xea) gets translated to a | character. Info from
% Staszek Wawrykiewicz, 19 Jan 2004 04:09:24 +0100.
%
% TODO this right, we have to translate 8-bit characters to
% their "best" equivalent, based on the @documentencoding. Too
% much work for too little return. Just use the ASCII equivalents
% we use for the index sort strings.
%
\indexnofonts
\setupdatafile
% We can have normal brace characters in the PDF outlines, unlike
% Texinfo index files. So set that up.
\def\{{\lbracecharliteral}%
\def\}{\rbracecharliteral}%
\catcode`\\=\active \otherbackslash
\input \tocreadfilename
\endgroup
}
{\catcode`[=1 \catcode`]=2
\catcode`{=\other \catcode`}=\other
\gdef\lbracecharliteral[{]%
\gdef\rbracecharliteral[}]%
]
%
\def\skipspaces#1{\def\PP{#1}\def\D{|}%
\ifx\PP\D\let\nextsp\relax
\else\let\nextsp\skipspaces
\addtokens{\filename}{\PP}%
\advance\filenamelength by 1
\fi
\nextsp}
\def\getfilename#1{%
\filenamelength=0
% If we don't expand the argument now, \skipspaces will get
% snagged on things like "@value{foo}".
\edef\temp{#1}%
\expandafter\skipspaces\temp|\relax
}
\ifnum\pdftexversion < 14
\let \startlink \pdfannotlink
\else
\let \startlink \pdfstartlink
\fi
% make a live url in pdf output.
\def\pdfurl#1{%
\begingroup
% it seems we really need yet another set of dummies; have not
% tried to figure out what each command should do in the context
% of @url. for now, just make @/ a no-op, that's the only one
% people have actually reported a problem with.
%
\normalturnoffactive
\def\@{@}%
\let\/=\empty
\makevalueexpandable
% do we want to go so far as to use \indexnofonts instead of just
% special-casing \var here?
\def\var##1{##1}%
%
\leavevmode\setcolor{\urlcolor}%
\startlink attr{/Border [0 0 0]}%
user{/Subtype /Link /A << /S /URI /URI (#1) >>}%
\endgroup}
\def\pdfgettoks#1.{\setbox\boxA=\hbox{\toksA={#1.}\toksB={}\maketoks}}
\def\addtokens#1#2{\edef\addtoks{\noexpand#1={\the#1#2}}\addtoks}
\def\adn#1{\addtokens{\toksC}{#1}\global\countA=1\let\next=\maketoks}
\def\poptoks#1#2|ENDTOKS|{\let\first=#1\toksD={#1}\toksA={#2}}
\def\maketoks{%
\expandafter\poptoks\the\toksA|ENDTOKS|\relax
\ifx\first0\adn0
\else\ifx\first1\adn1 \else\ifx\first2\adn2 \else\ifx\first3\adn3
\else\ifx\first4\adn4 \else\ifx\first5\adn5 \else\ifx\first6\adn6
\else\ifx\first7\adn7 \else\ifx\first8\adn8 \else\ifx\first9\adn9
\else
\ifnum0=\countA\else\makelink\fi
\ifx\first.\let\next=\done\else
\let\next=\maketoks
\addtokens{\toksB}{\the\toksD}
\ifx\first,\addtokens{\toksB}{\space}\fi
\fi
\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi
\next}
\def\makelink{\addtokens{\toksB}%
{\noexpand\pdflink{\the\toksC}}\toksC={}\global\countA=0}
\def\pdflink#1{%
\startlink attr{/Border [0 0 0]} goto name{\pdfmkpgn{#1}}
\setcolor{\linkcolor}#1\endlink}
\def\done{\edef\st{\global\noexpand\toksA={\the\toksB}}\st}
\else
% non-pdf mode
\let\pdfmkdest = \gobble
\let\pdfurl = \gobble
\let\endlink = \relax
\let\setcolor = \gobble
\let\pdfsetcolor = \gobble
\let\pdfmakeoutlines = \relax
\fi % \ifx\pdfoutput
\message{fonts,}
% Change the current font style to #1, remembering it in \curfontstyle.
% For now, we do not accumulate font styles: @b{@i{foo}} prints foo in
% italics, not bold italics.
%
\def\setfontstyle#1{%
\def\curfontstyle{#1}% not as a control sequence, because we are \edef'd.
\csname ten#1\endcsname % change the current font
}
% Select #1 fonts with the current style.
%
\def\selectfonts#1{\csname #1fonts\endcsname \csname\curfontstyle\endcsname}
\def\rm{\fam=0 \setfontstyle{rm}}
\def\it{\fam=\itfam \setfontstyle{it}}
\def\sl{\fam=\slfam \setfontstyle{sl}}
\def\bf{\fam=\bffam \setfontstyle{bf}}\def\bfstylename{bf}
\def\tt{\fam=\ttfam \setfontstyle{tt}}
% Unfortunately, we have to override this for titles and the like, since
% in those cases "rm" is bold. Sigh.
\def\rmisbold{\rm\def\curfontstyle{bf}}
% Texinfo sort of supports the sans serif font style, which plain TeX does not.
% So we set up a \sf.
\newfam\sffam
\def\sf{\fam=\sffam \setfontstyle{sf}}
\let\li = \sf % Sometimes we call it \li, not \sf.
% We don't need math for this font style.
\def\ttsl{\setfontstyle{ttsl}}
% Set the baselineskip to #1, and the lineskip and strut size
% correspondingly. There is no deep meaning behind these magic numbers
% used as factors; they just match (closely enough) what Knuth defined.
%
\def\lineskipfactor{.08333}
\def\strutheightpercent{.70833}
\def\strutdepthpercent {.29167}
%
% can get a sort of poor man's double spacing by redefining this.
\def\baselinefactor{1}
%
\newdimen\textleading
\def\setleading#1{%
\dimen0 = #1\relax
\normalbaselineskip = \baselinefactor\dimen0
\normallineskip = \lineskipfactor\normalbaselineskip
\normalbaselines
\setbox\strutbox =\hbox{%
\vrule width0pt height\strutheightpercent\baselineskip
depth \strutdepthpercent \baselineskip
}%
}
% PDF CMaps. See also LaTeX's t1.cmap.
%
% do nothing with this by default.
\expandafter\let\csname cmapOT1\endcsname\gobble
\expandafter\let\csname cmapOT1IT\endcsname\gobble
\expandafter\let\csname cmapOT1TT\endcsname\gobble
% if we are producing pdf, and we have \pdffontattr, then define cmaps.
% (\pdffontattr was introduced many years ago, but people still run
% older pdftex's; it's easy to conditionalize, so we do.)
\ifpdf \ifx\pdffontattr\thisisundefined \else
\begingroup
\catcode`\^^M=\active \def^^M{^^J}% Output line endings as the ^^J char.
\catcode`\%=12 \immediate\pdfobj stream {%!PS-Adobe-3.0 Resource-CMap
%%DocumentNeededResources: ProcSet (CIDInit)
%%IncludeResource: ProcSet (CIDInit)
%%BeginResource: CMap (TeX-OT1-0)
%%Title: (TeX-OT1-0 TeX OT1 0)
%%Version: 1.000
%%EndComments
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
/CIDSystemInfo
<< /Registry (TeX)
/Ordering (OT1)
/Supplement 0
>> def
/CMapName /TeX-OT1-0 def
/CMapType 2 def
1 begincodespacerange
<00> <7F>
endcodespacerange
8 beginbfrange
<00> <01> <0393>
<09> <0A> <03A8>
<23> <26> <0023>
<28> <3B> <0028>
<3F> <5B> <003F>
<5D> <5E> <005D>
<61> <7A> <0061>
<7B> <7C> <2013>
endbfrange
40 beginbfchar
<02> <0398>
<03> <039B>
<04> <039E>
<05> <03A0>
<06> <03A3>
<07> <03D2>
<08> <03A6>
<0B> <00660066>
<0C> <00660069>
<0D> <0066006C>
<0E> <006600660069>
<0F> <00660066006C>
<10> <0131>
<11> <0237>
<12> <0060>
<13> <00B4>
<14> <02C7>
<15> <02D8>
<16> <00AF>
<17> <02DA>
<18> <00B8>
<19> <00DF>
<1A> <00E6>
<1B> <0153>
<1C> <00F8>
<1D> <00C6>
<1E> <0152>
<1F> <00D8>
<21> <0021>
<22> <201D>
<27> <2019>
<3C> <00A1>
<3D> <003D>
<3E> <00BF>
<5C> <201C>
<5F> <02D9>
<60> <2018>
<7D> <02DD>
<7E> <007E>
<7F> <00A8>
endbfchar
endcmap
CMapName currentdict /CMap defineresource pop
end
end
%%EndResource
%%EOF
}\endgroup
\expandafter\edef\csname cmapOT1\endcsname#1{%
\pdffontattr#1{/ToUnicode \the\pdflastobj\space 0 R}%
}%
%
% \cmapOT1IT
\begingroup
\catcode`\^^M=\active \def^^M{^^J}% Output line endings as the ^^J char.
\catcode`\%=12 \immediate\pdfobj stream {%!PS-Adobe-3.0 Resource-CMap
%%DocumentNeededResources: ProcSet (CIDInit)
%%IncludeResource: ProcSet (CIDInit)
%%BeginResource: CMap (TeX-OT1IT-0)
%%Title: (TeX-OT1IT-0 TeX OT1IT 0)
%%Version: 1.000
%%EndComments
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
/CIDSystemInfo
<< /Registry (TeX)
/Ordering (OT1IT)
/Supplement 0
>> def
/CMapName /TeX-OT1IT-0 def
/CMapType 2 def
1 begincodespacerange
<00> <7F>
endcodespacerange
8 beginbfrange
<00> <01> <0393>
<09> <0A> <03A8>
<25> <26> <0025>
<28> <3B> <0028>
<3F> <5B> <003F>
<5D> <5E> <005D>
<61> <7A> <0061>
<7B> <7C> <2013>
endbfrange
42 beginbfchar
<02> <0398>
<03> <039B>
<04> <039E>
<05> <03A0>
<06> <03A3>
<07> <03D2>
<08> <03A6>
<0B> <00660066>
<0C> <00660069>
<0D> <0066006C>
<0E> <006600660069>
<0F> <00660066006C>
<10> <0131>
<11> <0237>
<12> <0060>
<13> <00B4>
<14> <02C7>
<15> <02D8>
<16> <00AF>
<17> <02DA>
<18> <00B8>
<19> <00DF>
<1A> <00E6>
<1B> <0153>
<1C> <00F8>
<1D> <00C6>
<1E> <0152>
<1F> <00D8>
<21> <0021>
<22> <201D>
<23> <0023>
<24> <00A3>
<27> <2019>
<3C> <00A1>
<3D> <003D>
<3E> <00BF>
<5C> <201C>
<5F> <02D9>
<60> <2018>
<7D> <02DD>
<7E> <007E>
<7F> <00A8>
endbfchar
endcmap
CMapName currentdict /CMap defineresource pop
end
end
%%EndResource
%%EOF
}\endgroup
\expandafter\edef\csname cmapOT1IT\endcsname#1{%
\pdffontattr#1{/ToUnicode \the\pdflastobj\space 0 R}%
}%
%
% \cmapOT1TT
\begingroup
\catcode`\^^M=\active \def^^M{^^J}% Output line endings as the ^^J char.
\catcode`\%=12 \immediate\pdfobj stream {%!PS-Adobe-3.0 Resource-CMap
%%DocumentNeededResources: ProcSet (CIDInit)
%%IncludeResource: ProcSet (CIDInit)
%%BeginResource: CMap (TeX-OT1TT-0)
%%Title: (TeX-OT1TT-0 TeX OT1TT 0)
%%Version: 1.000
%%EndComments
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
/CIDSystemInfo
<< /Registry (TeX)
/Ordering (OT1TT)
/Supplement 0
>> def
/CMapName /TeX-OT1TT-0 def
/CMapType 2 def
1 begincodespacerange
<00> <7F>
endcodespacerange
5 beginbfrange
<00> <01> <0393>
<09> <0A> <03A8>
<21> <26> <0021>
<28> <5F> <0028>
<61> <7E> <0061>
endbfrange
32 beginbfchar
<02> <0398>
<03> <039B>
<04> <039E>
<05> <03A0>
<06> <03A3>
<07> <03D2>
<08> <03A6>
<0B> <2191>
<0C> <2193>
<0D> <0027>
<0E> <00A1>
<0F> <00BF>
<10> <0131>
<11> <0237>
<12> <0060>
<13> <00B4>
<14> <02C7>
<15> <02D8>
<16> <00AF>
<17> <02DA>
<18> <00B8>
<19> <00DF>
<1A> <00E6>
<1B> <0153>
<1C> <00F8>
<1D> <00C6>
<1E> <0152>
<1F> <00D8>
<20> <2423>
<27> <2019>
<60> <2018>
<7F> <00A8>
endbfchar
endcmap
CMapName currentdict /CMap defineresource pop
end
end
%%EndResource
%%EOF
}\endgroup
\expandafter\edef\csname cmapOT1TT\endcsname#1{%
\pdffontattr#1{/ToUnicode \the\pdflastobj\space 0 R}%
}%
\fi\fi
% Set the font macro #1 to the font named \fontprefix#2.
% #3 is the font's design size, #4 is a scale factor, #5 is the CMap
% encoding (only OT1, OT1IT and OT1TT are allowed, or empty to omit).
% Example:
% #1 = \textrm
% #2 = \rmshape
% #3 = 10
% #4 = \mainmagstep
% #5 = OT1
%
\def\setfont#1#2#3#4#5{%
\font#1=\fontprefix#2#3 scaled #4
\csname cmap#5\endcsname#1%
}
% This is what gets called when #5 of \setfont is empty.
\let\cmap\gobble
%
% (end of cmaps)
% Use cm as the default font prefix.
% To specify the font prefix, you must define \fontprefix
% before you read in texinfo.tex.
\ifx\fontprefix\thisisundefined
\def\fontprefix{cm}
\fi
% Support font families that don't use the same naming scheme as CM.
\def\rmshape{r}
\def\rmbshape{bx} % where the normal face is bold
\def\bfshape{b}
\def\bxshape{bx}
\def\ttshape{tt}
\def\ttbshape{tt}
\def\ttslshape{sltt}
\def\itshape{ti}
\def\itbshape{bxti}
\def\slshape{sl}
\def\slbshape{bxsl}
\def\sfshape{ss}
\def\sfbshape{ss}
\def\scshape{csc}
\def\scbshape{csc}
% Definitions for a main text size of 11pt. (The default in Texinfo.)
%
\def\definetextfontsizexi{%
% Text fonts (11.2pt, magstep1).
\def\textnominalsize{11pt}
\edef\mainmagstep{\magstephalf}
\setfont\textrm\rmshape{10}{\mainmagstep}{OT1}
\setfont\texttt\ttshape{10}{\mainmagstep}{OT1TT}
\setfont\textbf\bfshape{10}{\mainmagstep}{OT1}
\setfont\textit\itshape{10}{\mainmagstep}{OT1IT}
\setfont\textsl\slshape{10}{\mainmagstep}{OT1}
\setfont\textsf\sfshape{10}{\mainmagstep}{OT1}
\setfont\textsc\scshape{10}{\mainmagstep}{OT1}
\setfont\textttsl\ttslshape{10}{\mainmagstep}{OT1TT}
\font\texti=cmmi10 scaled \mainmagstep
\font\textsy=cmsy10 scaled \mainmagstep
\def\textecsize{1095}
% A few fonts for @defun names and args.
\setfont\defbf\bfshape{10}{\magstep1}{OT1}
\setfont\deftt\ttshape{10}{\magstep1}{OT1TT}
\setfont\defttsl\ttslshape{10}{\magstep1}{OT1TT}
\def\df{\let\tentt=\deftt \let\tenbf = \defbf \let\tenttsl=\defttsl \bf}
% Fonts for indices, footnotes, small examples (9pt).
\def\smallnominalsize{9pt}
\setfont\smallrm\rmshape{9}{1000}{OT1}
\setfont\smalltt\ttshape{9}{1000}{OT1TT}
\setfont\smallbf\bfshape{10}{900}{OT1}
\setfont\smallit\itshape{9}{1000}{OT1IT}
\setfont\smallsl\slshape{9}{1000}{OT1}
\setfont\smallsf\sfshape{9}{1000}{OT1}
\setfont\smallsc\scshape{10}{900}{OT1}
\setfont\smallttsl\ttslshape{10}{900}{OT1TT}
\font\smalli=cmmi9
\font\smallsy=cmsy9
\def\smallecsize{0900}
% Fonts for small examples (8pt).
\def\smallernominalsize{8pt}
\setfont\smallerrm\rmshape{8}{1000}{OT1}
\setfont\smallertt\ttshape{8}{1000}{OT1TT}
\setfont\smallerbf\bfshape{10}{800}{OT1}
\setfont\smallerit\itshape{8}{1000}{OT1IT}
\setfont\smallersl\slshape{8}{1000}{OT1}
\setfont\smallersf\sfshape{8}{1000}{OT1}
\setfont\smallersc\scshape{10}{800}{OT1}
\setfont\smallerttsl\ttslshape{10}{800}{OT1TT}
\font\smalleri=cmmi8
\font\smallersy=cmsy8
\def\smallerecsize{0800}
% Fonts for title page (20.4pt):
\def\titlenominalsize{20pt}
\setfont\titlerm\rmbshape{12}{\magstep3}{OT1}
\setfont\titleit\itbshape{10}{\magstep4}{OT1IT}
\setfont\titlesl\slbshape{10}{\magstep4}{OT1}
\setfont\titlett\ttbshape{12}{\magstep3}{OT1TT}
\setfont\titlettsl\ttslshape{10}{\magstep4}{OT1TT}
\setfont\titlesf\sfbshape{17}{\magstep1}{OT1}
\let\titlebf=\titlerm
\setfont\titlesc\scbshape{10}{\magstep4}{OT1}
\font\titlei=cmmi12 scaled \magstep3
\font\titlesy=cmsy10 scaled \magstep4
\def\titleecsize{2074}
% Chapter (and unnumbered) fonts (17.28pt).
\def\chapnominalsize{17pt}
\setfont\chaprm\rmbshape{12}{\magstep2}{OT1}
\setfont\chapit\itbshape{10}{\magstep3}{OT1IT}
\setfont\chapsl\slbshape{10}{\magstep3}{OT1}
\setfont\chaptt\ttbshape{12}{\magstep2}{OT1TT}
\setfont\chapttsl\ttslshape{10}{\magstep3}{OT1TT}
\setfont\chapsf\sfbshape{17}{1000}{OT1}
\let\chapbf=\chaprm
\setfont\chapsc\scbshape{10}{\magstep3}{OT1}
\font\chapi=cmmi12 scaled \magstep2
\font\chapsy=cmsy10 scaled \magstep3
\def\chapecsize{1728}
% Section fonts (14.4pt).
\def\secnominalsize{14pt}
\setfont\secrm\rmbshape{12}{\magstep1}{OT1}
\setfont\secit\itbshape{10}{\magstep2}{OT1IT}
\setfont\secsl\slbshape{10}{\magstep2}{OT1}
\setfont\sectt\ttbshape{12}{\magstep1}{OT1TT}
\setfont\secttsl\ttslshape{10}{\magstep2}{OT1TT}
\setfont\secsf\sfbshape{12}{\magstep1}{OT1}
\let\secbf\secrm
\setfont\secsc\scbshape{10}{\magstep2}{OT1}
\font\seci=cmmi12 scaled \magstep1
\font\secsy=cmsy10 scaled \magstep2
\def\sececsize{1440}
% Subsection fonts (13.15pt).
\def\ssecnominalsize{13pt}
\setfont\ssecrm\rmbshape{12}{\magstephalf}{OT1}
\setfont\ssecit\itbshape{10}{1315}{OT1IT}
\setfont\ssecsl\slbshape{10}{1315}{OT1}
\setfont\ssectt\ttbshape{12}{\magstephalf}{OT1TT}
\setfont\ssecttsl\ttslshape{10}{1315}{OT1TT}
\setfont\ssecsf\sfbshape{12}{\magstephalf}{OT1}
\let\ssecbf\ssecrm
\setfont\ssecsc\scbshape{10}{1315}{OT1}
\font\sseci=cmmi12 scaled \magstephalf
\font\ssecsy=cmsy10 scaled 1315
\def\ssececsize{1200}
% Reduced fonts for @acro in text (10pt).
\def\reducednominalsize{10pt}
\setfont\reducedrm\rmshape{10}{1000}{OT1}
\setfont\reducedtt\ttshape{10}{1000}{OT1TT}
\setfont\reducedbf\bfshape{10}{1000}{OT1}
\setfont\reducedit\itshape{10}{1000}{OT1IT}
\setfont\reducedsl\slshape{10}{1000}{OT1}
\setfont\reducedsf\sfshape{10}{1000}{OT1}
\setfont\reducedsc\scshape{10}{1000}{OT1}
\setfont\reducedttsl\ttslshape{10}{1000}{OT1TT}
\font\reducedi=cmmi10
\font\reducedsy=cmsy10
\def\reducedecsize{1000}
\textleading = 13.2pt % line spacing for 11pt CM
\textfonts % reset the current fonts
\rm
} % end of 11pt text font size definitions, \definetextfontsizexi
% Definitions to make the main text be 10pt Computer Modern, with
% section, chapter, etc., sizes following suit. This is for the GNU
% Press printing of the Emacs 22 manual. Maybe other manuals in the
% future. Used with @smallbook, which sets the leading to 12pt.
%
\def\definetextfontsizex{%
% Text fonts (10pt).
\def\textnominalsize{10pt}
\edef\mainmagstep{1000}
\setfont\textrm\rmshape{10}{\mainmagstep}{OT1}
\setfont\texttt\ttshape{10}{\mainmagstep}{OT1TT}
\setfont\textbf\bfshape{10}{\mainmagstep}{OT1}
\setfont\textit\itshape{10}{\mainmagstep}{OT1IT}
\setfont\textsl\slshape{10}{\mainmagstep}{OT1}
\setfont\textsf\sfshape{10}{\mainmagstep}{OT1}
\setfont\textsc\scshape{10}{\mainmagstep}{OT1}
\setfont\textttsl\ttslshape{10}{\mainmagstep}{OT1TT}
\font\texti=cmmi10 scaled \mainmagstep
\font\textsy=cmsy10 scaled \mainmagstep
\def\textecsize{1000}
% A few fonts for @defun names and args.
\setfont\defbf\bfshape{10}{\magstephalf}{OT1}
\setfont\deftt\ttshape{10}{\magstephalf}{OT1TT}
\setfont\defttsl\ttslshape{10}{\magstephalf}{OT1TT}
\def\df{\let\tentt=\deftt \let\tenbf = \defbf \let\tenttsl=\defttsl \bf}
% Fonts for indices, footnotes, small examples (9pt).
\def\smallnominalsize{9pt}
\setfont\smallrm\rmshape{9}{1000}{OT1}
\setfont\smalltt\ttshape{9}{1000}{OT1TT}
\setfont\smallbf\bfshape{10}{900}{OT1}
\setfont\smallit\itshape{9}{1000}{OT1IT}
\setfont\smallsl\slshape{9}{1000}{OT1}
\setfont\smallsf\sfshape{9}{1000}{OT1}
\setfont\smallsc\scshape{10}{900}{OT1}
\setfont\smallttsl\ttslshape{10}{900}{OT1TT}
\font\smalli=cmmi9
\font\smallsy=cmsy9
\def\smallecsize{0900}
% Fonts for small examples (8pt).
\def\smallernominalsize{8pt}
\setfont\smallerrm\rmshape{8}{1000}{OT1}
\setfont\smallertt\ttshape{8}{1000}{OT1TT}
\setfont\smallerbf\bfshape{10}{800}{OT1}
\setfont\smallerit\itshape{8}{1000}{OT1IT}
\setfont\smallersl\slshape{8}{1000}{OT1}
\setfont\smallersf\sfshape{8}{1000}{OT1}
\setfont\smallersc\scshape{10}{800}{OT1}
\setfont\smallerttsl\ttslshape{10}{800}{OT1TT}
\font\smalleri=cmmi8
\font\smallersy=cmsy8
\def\smallerecsize{0800}
% Fonts for title page (20.4pt):
\def\titlenominalsize{20pt}
\setfont\titlerm\rmbshape{12}{\magstep3}{OT1}
\setfont\titleit\itbshape{10}{\magstep4}{OT1IT}
\setfont\titlesl\slbshape{10}{\magstep4}{OT1}
\setfont\titlett\ttbshape{12}{\magstep3}{OT1TT}
\setfont\titlettsl\ttslshape{10}{\magstep4}{OT1TT}
\setfont\titlesf\sfbshape{17}{\magstep1}{OT1}
\let\titlebf=\titlerm
\setfont\titlesc\scbshape{10}{\magstep4}{OT1}
\font\titlei=cmmi12 scaled \magstep3
\font\titlesy=cmsy10 scaled \magstep4
\def\titleecsize{2074}
% Chapter fonts (14.4pt).
\def\chapnominalsize{14pt}
\setfont\chaprm\rmbshape{12}{\magstep1}{OT1}
\setfont\chapit\itbshape{10}{\magstep2}{OT1IT}
\setfont\chapsl\slbshape{10}{\magstep2}{OT1}
\setfont\chaptt\ttbshape{12}{\magstep1}{OT1TT}
\setfont\chapttsl\ttslshape{10}{\magstep2}{OT1TT}
\setfont\chapsf\sfbshape{12}{\magstep1}{OT1}
\let\chapbf\chaprm
\setfont\chapsc\scbshape{10}{\magstep2}{OT1}
\font\chapi=cmmi12 scaled \magstep1
\font\chapsy=cmsy10 scaled \magstep2
\def\chapecsize{1440}
% Section fonts (12pt).
\def\secnominalsize{12pt}
\setfont\secrm\rmbshape{12}{1000}{OT1}
\setfont\secit\itbshape{10}{\magstep1}{OT1IT}
\setfont\secsl\slbshape{10}{\magstep1}{OT1}
\setfont\sectt\ttbshape{12}{1000}{OT1TT}
\setfont\secttsl\ttslshape{10}{\magstep1}{OT1TT}
\setfont\secsf\sfbshape{12}{1000}{OT1}
\let\secbf\secrm
\setfont\secsc\scbshape{10}{\magstep1}{OT1}
\font\seci=cmmi12
\font\secsy=cmsy10 scaled \magstep1
\def\sececsize{1200}
% Subsection fonts (10pt).
\def\ssecnominalsize{10pt}
\setfont\ssecrm\rmbshape{10}{1000}{OT1}
\setfont\ssecit\itbshape{10}{1000}{OT1IT}
\setfont\ssecsl\slbshape{10}{1000}{OT1}
\setfont\ssectt\ttbshape{10}{1000}{OT1TT}
\setfont\ssecttsl\ttslshape{10}{1000}{OT1TT}
\setfont\ssecsf\sfbshape{10}{1000}{OT1}
\let\ssecbf\ssecrm
\setfont\ssecsc\scbshape{10}{1000}{OT1}
\font\sseci=cmmi10
\font\ssecsy=cmsy10
\def\ssececsize{1000}
% Reduced fonts for @acro in text (9pt).
\def\reducednominalsize{9pt}
\setfont\reducedrm\rmshape{9}{1000}{OT1}
\setfont\reducedtt\ttshape{9}{1000}{OT1TT}
\setfont\reducedbf\bfshape{10}{900}{OT1}
\setfont\reducedit\itshape{9}{1000}{OT1IT}
\setfont\reducedsl\slshape{9}{1000}{OT1}
\setfont\reducedsf\sfshape{9}{1000}{OT1}
\setfont\reducedsc\scshape{10}{900}{OT1}
\setfont\reducedttsl\ttslshape{10}{900}{OT1TT}
\font\reducedi=cmmi9
\font\reducedsy=cmsy9
\def\reducedecsize{0900}
\divide\parskip by 2 % reduce space between paragraphs
\textleading = 12pt % line spacing for 10pt CM
\textfonts % reset the current fonts
\rm
} % end of 10pt text font size definitions, \definetextfontsizex
% We provide the user-level command
% @fonttextsize 10
% (or 11) to redefine the text font size. pt is assumed.
%
\def\xiword{11}
\def\xword{10}
\def\xwordpt{10pt}
%
\parseargdef\fonttextsize{%
\def\textsizearg{#1}%
%\wlog{doing @fonttextsize \textsizearg}%
%
% Set \globaldefs so that documents can use this inside @tex, since
% makeinfo 4.8 does not support it, but we need it nonetheless.
%
\begingroup \globaldefs=1
\ifx\textsizearg\xword \definetextfontsizex
\else \ifx\textsizearg\xiword \definetextfontsizexi
\else
\errhelp=\EMsimple
\errmessage{@fonttextsize only supports `10' or `11', not `\textsizearg'}
\fi\fi
\endgroup
}
% In order for the font changes to affect most math symbols and letters,
% we have to define the \textfont of the standard families. Since
% texinfo doesn't allow for producing subscripts and superscripts except
% in the main text, we don't bother to reset \scriptfont and
% \scriptscriptfont (which would also require loading a lot more fonts).
%
\def\resetmathfonts{%
\textfont0=\tenrm \textfont1=\teni \textfont2=\tensy
\textfont\itfam=\tenit \textfont\slfam=\tensl \textfont\bffam=\tenbf
\textfont\ttfam=\tentt \textfont\sffam=\tensf
}
% The font-changing commands redefine the meanings of \tenSTYLE, instead
% of just \STYLE. We do this because \STYLE needs to also set the
% current \fam for math mode. Our \STYLE (e.g., \rm) commands hardwire
% \tenSTYLE to set the current font.
%
% Each font-changing command also sets the names \lsize (one size lower)
% and \lllsize (three sizes lower). These relative commands are used in
% the LaTeX logo and acronyms.
%
% This all needs generalizing, badly.
%
\def\textfonts{%
\let\tenrm=\textrm \let\tenit=\textit \let\tensl=\textsl
\let\tenbf=\textbf \let\tentt=\texttt \let\smallcaps=\textsc
\let\tensf=\textsf \let\teni=\texti \let\tensy=\textsy
\let\tenttsl=\textttsl
\def\curfontsize{text}%
\def\lsize{reduced}\def\lllsize{smaller}%
\resetmathfonts \setleading{\textleading}}
\def\titlefonts{%
\let\tenrm=\titlerm \let\tenit=\titleit \let\tensl=\titlesl
\let\tenbf=\titlebf \let\tentt=\titlett \let\smallcaps=\titlesc
\let\tensf=\titlesf \let\teni=\titlei \let\tensy=\titlesy
\let\tenttsl=\titlettsl
\def\curfontsize{title}%
\def\lsize{chap}\def\lllsize{subsec}%
\resetmathfonts \setleading{27pt}}
\def\titlefont#1{{\titlefonts\rmisbold #1}}
\def\chapfonts{%
\let\tenrm=\chaprm \let\tenit=\chapit \let\tensl=\chapsl
\let\tenbf=\chapbf \let\tentt=\chaptt \let\smallcaps=\chapsc
\let\tensf=\chapsf \let\teni=\chapi \let\tensy=\chapsy
\let\tenttsl=\chapttsl
\def\curfontsize{chap}%
\def\lsize{sec}\def\lllsize{text}%
\resetmathfonts \setleading{19pt}}
\def\secfonts{%
\let\tenrm=\secrm \let\tenit=\secit \let\tensl=\secsl
\let\tenbf=\secbf \let\tentt=\sectt \let\smallcaps=\secsc
\let\tensf=\secsf \let\teni=\seci \let\tensy=\secsy
\let\tenttsl=\secttsl
\def\curfontsize{sec}%
\def\lsize{subsec}\def\lllsize{reduced}%
\resetmathfonts \setleading{16pt}}
\def\subsecfonts{%
\let\tenrm=\ssecrm \let\tenit=\ssecit \let\tensl=\ssecsl
\let\tenbf=\ssecbf \let\tentt=\ssectt \let\smallcaps=\ssecsc
\let\tensf=\ssecsf \let\teni=\sseci \let\tensy=\ssecsy
\let\tenttsl=\ssecttsl
\def\curfontsize{ssec}%
\def\lsize{text}\def\lllsize{small}%
\resetmathfonts \setleading{15pt}}
\let\subsubsecfonts = \subsecfonts
\def\reducedfonts{%
\let\tenrm=\reducedrm \let\tenit=\reducedit \let\tensl=\reducedsl
\let\tenbf=\reducedbf \let\tentt=\reducedtt \let\reducedcaps=\reducedsc
\let\tensf=\reducedsf \let\teni=\reducedi \let\tensy=\reducedsy
\let\tenttsl=\reducedttsl
\def\curfontsize{reduced}%
\def\lsize{small}\def\lllsize{smaller}%
\resetmathfonts \setleading{10.5pt}}
\def\smallfonts{%
\let\tenrm=\smallrm \let\tenit=\smallit \let\tensl=\smallsl
\let\tenbf=\smallbf \let\tentt=\smalltt \let\smallcaps=\smallsc
\let\tensf=\smallsf \let\teni=\smalli \let\tensy=\smallsy
\let\tenttsl=\smallttsl
\def\curfontsize{small}%
\def\lsize{smaller}\def\lllsize{smaller}%
\resetmathfonts \setleading{10.5pt}}
\def\smallerfonts{%
\let\tenrm=\smallerrm \let\tenit=\smallerit \let\tensl=\smallersl
\let\tenbf=\smallerbf \let\tentt=\smallertt \let\smallcaps=\smallersc
\let\tensf=\smallersf \let\teni=\smalleri \let\tensy=\smallersy
\let\tenttsl=\smallerttsl
\def\curfontsize{smaller}%
\def\lsize{smaller}\def\lllsize{smaller}%
\resetmathfonts \setleading{9.5pt}}
% Fonts for short table of contents.
\setfont\shortcontrm\rmshape{12}{1000}{OT1}
\setfont\shortcontbf\bfshape{10}{\magstep1}{OT1} % no cmb12
\setfont\shortcontsl\slshape{12}{1000}{OT1}
\setfont\shortconttt\ttshape{12}{1000}{OT1TT}
% Define these just so they can be easily changed for other fonts.
\def\angleleft{$\langle$}
\def\angleright{$\rangle$}
% Set the fonts to use with the @small... environments.
\let\smallexamplefonts = \smallfonts
% About \smallexamplefonts. If we use \smallfonts (9pt), @smallexample
% can fit this many characters:
% 8.5x11=86 smallbook=72 a4=90 a5=69
% If we use \scriptfonts (8pt), then we can fit this many characters:
% 8.5x11=90+ smallbook=80 a4=90+ a5=77
% For me, subjectively, the few extra characters that fit aren't worth
% the additional smallness of 8pt. So I'm making the default 9pt.
%
% By the way, for comparison, here's what fits with @example (10pt):
% 8.5x11=71 smallbook=60 a4=75 a5=58
% --karl, 24jan03.
% Set up the default fonts, so we can use them for creating boxes.
%
\definetextfontsizexi
\message{markup,}
% Check if we are currently using a typewriter font. Since all the
% Computer Modern typewriter fonts have zero interword stretch (and
% shrink), and it is reasonable to expect all typewriter fonts to have
% this property, we can check that font parameter.
%
\def\ifmonospace{\ifdim\fontdimen3\font=0pt }
% Markup style infrastructure. \defmarkupstylesetup\INITMACRO will
% define and register \INITMACRO to be called on markup style changes.
% \INITMACRO can check \currentmarkupstyle for the innermost
% style and the set of \ifmarkupSTYLE switches for all styles
% currently in effect.
\newif\ifmarkupvar
\newif\ifmarkupsamp
\newif\ifmarkupkey
%\newif\ifmarkupfile % @file == @samp.
%\newif\ifmarkupoption % @option == @samp.
\newif\ifmarkupcode
\newif\ifmarkupkbd
%\newif\ifmarkupenv % @env == @code.
%\newif\ifmarkupcommand % @command == @code.
\newif\ifmarkuptex % @tex (and part of @math, for now).
\newif\ifmarkupexample
\newif\ifmarkupverb
\newif\ifmarkupverbatim
\let\currentmarkupstyle\empty
\def\setupmarkupstyle#1{%
\csname markup#1true\endcsname
\def\currentmarkupstyle{#1}%
\markupstylesetup
}
\let\markupstylesetup\empty
\def\defmarkupstylesetup#1{%
\expandafter\def\expandafter\markupstylesetup
\expandafter{\markupstylesetup #1}%
\def#1%
}
% Markup style setup for left and right quotes.
\defmarkupstylesetup\markupsetuplq{%
\expandafter\let\expandafter \temp
\csname markupsetuplq\currentmarkupstyle\endcsname
\ifx\temp\relax \markupsetuplqdefault \else \temp \fi
}
\defmarkupstylesetup\markupsetuprq{%
\expandafter\let\expandafter \temp
\csname markupsetuprq\currentmarkupstyle\endcsname
\ifx\temp\relax \markupsetuprqdefault \else \temp \fi
}
{
\catcode`\'=\active
\catcode`\`=\active
\gdef\markupsetuplqdefault{\let`\lq}
\gdef\markupsetuprqdefault{\let'\rq}
\gdef\markupsetcodequoteleft{\let`\codequoteleft}
\gdef\markupsetcodequoteright{\let'\codequoteright}
}
\let\markupsetuplqcode \markupsetcodequoteleft
\let\markupsetuprqcode \markupsetcodequoteright
%
\let\markupsetuplqexample \markupsetcodequoteleft
\let\markupsetuprqexample \markupsetcodequoteright
%
\let\markupsetuplqkbd \markupsetcodequoteleft
\let\markupsetuprqkbd \markupsetcodequoteright
%
\let\markupsetuplqsamp \markupsetcodequoteleft
\let\markupsetuprqsamp \markupsetcodequoteright
%
\let\markupsetuplqverb \markupsetcodequoteleft
\let\markupsetuprqverb \markupsetcodequoteright
%
\let\markupsetuplqverbatim \markupsetcodequoteleft
\let\markupsetuprqverbatim \markupsetcodequoteright
% Allow an option to not use regular directed right quote/apostrophe
% (char 0x27), but instead the undirected quote from cmtt (char 0x0d).
% The undirected quote is ugly, so don't make it the default, but it
% works for pasting with more pdf viewers (at least evince), the
% lilypond developers report. xpdf does work with the regular 0x27.
%
\def\codequoteright{%
\expandafter\ifx\csname SETtxicodequoteundirected\endcsname\relax
\expandafter\ifx\csname SETcodequoteundirected\endcsname\relax
'%
\else \char'15 \fi
\else \char'15 \fi
}
%
% and a similar option for the left quote char vs. a grave accent.
% Modern fonts display ASCII 0x60 as a grave accent, so some people like
% the code environments to do likewise.
%
\def\codequoteleft{%
\expandafter\ifx\csname SETtxicodequotebacktick\endcsname\relax
\expandafter\ifx\csname SETcodequotebacktick\endcsname\relax
% [Knuth] pp. 380,381,391
% \relax disables Spanish ligatures ?` and !` of \tt font.
\relax`%
\else \char'22 \fi
\else \char'22 \fi
}
% Commands to set the quote options.
%
\parseargdef\codequoteundirected{%
\def\temp{#1}%
\ifx\temp\onword
\expandafter\let\csname SETtxicodequoteundirected\endcsname
= t%
\else\ifx\temp\offword
\expandafter\let\csname SETtxicodequoteundirected\endcsname
= \relax
\else
\errhelp = \EMsimple
\errmessage{Unknown @codequoteundirected value `\temp', must be on|off}%
\fi\fi
}
%
\parseargdef\codequotebacktick{%
\def\temp{#1}%
\ifx\temp\onword
\expandafter\let\csname SETtxicodequotebacktick\endcsname
= t%
\else\ifx\temp\offword
\expandafter\let\csname SETtxicodequotebacktick\endcsname
= \relax
\else
\errhelp = \EMsimple
\errmessage{Unknown @codequotebacktick value `\temp', must be on|off}%
\fi\fi
}
% [Knuth] pp. 380,381,391, disable Spanish ligatures ?` and !` of \tt font.
\def\noligaturesquoteleft{\relax\lq}
% Count depth in font-changes, for error checks
\newcount\fontdepth \fontdepth=0
% Font commands.
% #1 is the font command (\sl or \it), #2 is the text to slant.
% If we are in a monospaced environment, however, 1) always use \ttsl,
% and 2) do not add an italic correction.
\def\dosmartslant#1#2{%
\ifusingtt
{{\ttsl #2}\let\next=\relax}%
{\def\next{{#1#2}\futurelet\next\smartitaliccorrection}}%
\next
}
\def\smartslanted{\dosmartslant\sl}
\def\smartitalic{\dosmartslant\it}
% Output an italic correction unless \next (presumed to be the following
% character) is such as not to need one.
\def\smartitaliccorrection{%
\ifx\next,%
\else\ifx\next-%
\else\ifx\next.%
\else\ifx\next\.%
\else\ifx\next\comma%
\else\ptexslash
\fi\fi\fi\fi\fi
\aftersmartic
}
% Unconditional use \ttsl, and no ic. @var is set to this for defuns.
\def\ttslanted#1{{\ttsl #1}}
% @cite is like \smartslanted except unconditionally use \sl. We never want
% ttsl for book titles, do we?
\def\cite#1{{\sl #1}\futurelet\next\smartitaliccorrection}
\def\aftersmartic{}
\def\var#1{%
\let\saveaftersmartic = \aftersmartic
\def\aftersmartic{\null\let\aftersmartic=\saveaftersmartic}%
\smartslanted{#1}%
}
\let\i=\smartitalic
\let\slanted=\smartslanted
\let\dfn=\smartslanted
\let\emph=\smartitalic
% Explicit font changes: @r, @sc, undocumented @ii.
\def\r#1{{\rm #1}} % roman font
\def\sc#1{{\smallcaps#1}} % smallcaps font
\def\ii#1{{\it #1}} % italic font
% @b, explicit bold. Also @strong.
\def\b#1{{\bf #1}}
\let\strong=\b
% @sansserif, explicit sans.
\def\sansserif#1{{\sf #1}}
% We can't just use \exhyphenpenalty, because that only has effect at
% the end of a paragraph. Restore normal hyphenation at the end of the
% group within which \nohyphenation is presumably called.
%
\def\nohyphenation{\hyphenchar\font = -1 \aftergroup\restorehyphenation}
\def\restorehyphenation{\hyphenchar\font = `- }
% Set sfcode to normal for the chars that usually have another value.
% Can't use plain's \frenchspacing because it uses the `\x notation, and
% sometimes \x has an active definition that messes things up.
%
\catcode`@=11
\def\plainfrenchspacing{%
\sfcode\dotChar =\@m \sfcode\questChar=\@m \sfcode\exclamChar=\@m
\sfcode\colonChar=\@m \sfcode\semiChar =\@m \sfcode\commaChar =\@m
\def\endofsentencespacefactor{1000}% for @. and friends
}
\def\plainnonfrenchspacing{%
\sfcode`\.3000\sfcode`\?3000\sfcode`\!3000
\sfcode`\:2000\sfcode`\;1500\sfcode`\,1250
\def\endofsentencespacefactor{3000}% for @. and friends
}
\catcode`@=\other
\def\endofsentencespacefactor{3000}% default
% @t, explicit typewriter.
\def\t#1{%
{\tt \rawbackslash \plainfrenchspacing #1}%
\null
}
% @samp.
\def\samp#1{{\setupmarkupstyle{samp}\lq\tclose{#1}\rq\null}}
% @indicateurl is \samp, that is, with quotes.
\let\indicateurl=\samp
% @code (and similar) prints in typewriter, but with spaces the same
% size as normal in the surrounding text, without hyphenation, etc.
% This is a subroutine for that.
\def\tclose#1{%
{%
% Change normal interword space to be same as for the current font.
\spaceskip = \fontdimen2\font
%
% Switch to typewriter.
\tt
%
% But `\ ' produces the large typewriter interword space.
\def\ {{\spaceskip = 0pt{} }}%
%
% Turn off hyphenation.
\nohyphenation
%
\rawbackslash
\plainfrenchspacing
#1%
}%
\null % reset spacefactor to 1000
}
% We *must* turn on hyphenation at `-' and `_' in @code.
% (But see \codedashfinish below.)
% Otherwise, it is too hard to avoid overfull hboxes
% in the Emacs manual, the Library manual, etc.
%
% Unfortunately, TeX uses one parameter (\hyphenchar) to control
% both hyphenation at - and hyphenation within words.
% We must therefore turn them both off (\tclose does that)
% and arrange explicitly to hyphenate at a dash. -- rms.
{
\catcode`\-=\active \catcode`\_=\active
\catcode`\'=\active \catcode`\`=\active
\global\let'=\rq \global\let`=\lq % default definitions
%
\global\def\code{\begingroup
\setupmarkupstyle{code}%
% The following should really be moved into \setupmarkupstyle handlers.
\catcode\dashChar=\active \catcode\underChar=\active
\ifallowcodebreaks
\let-\codedash
\let_\codeunder
\else
\let-\normaldash
\let_\realunder
\fi
% Given -foo (with a single dash), we do not want to allow a break
% after the hyphen.
\global\let\codedashprev=\codedash
%
\codex
}
%
\gdef\codedash{\futurelet\next\codedashfinish}
\gdef\codedashfinish{%
\normaldash % always output the dash character itself.
%
% Now, output a discretionary to allow a line break, unless
% (a) the next character is a -, or
% (b) the preceding character is a -.
% E.g., given --posix, we do not want to allow a break after either -.
% Given --foo-bar, we do want to allow a break between the - and the b.
\ifx\next\codedash \else
\ifx\codedashprev\codedash
\else \discretionary{}{}{}\fi
\fi
% we need the space after the = for the case when \next itself is a
% space token; it would get swallowed otherwise. As in @code{- a}.
\global\let\codedashprev= \next
}
}
\def\normaldash{-}
%
\def\codex #1{\tclose{#1}\endgroup}
\def\codeunder{%
% this is all so @math{@code{var_name}+1} can work. In math mode, _
% is "active" (mathcode"8000) and \normalunderscore (or \char95, etc.)
% will therefore expand the active definition of _, which is us
% (inside @code that is), therefore an endless loop.
\ifusingtt{\ifmmode
\mathchar"075F % class 0=ordinary, family 7=ttfam, pos 0x5F=_.
\else\normalunderscore \fi
\discretionary{}{}{}}%
{\_}%
}
% An additional complication: the above will allow breaks after, e.g.,
% each of the four underscores in __typeof__. This is bad.
% @allowcodebreaks provides a document-level way to turn breaking at -
% and _ on and off.
%
\newif\ifallowcodebreaks \allowcodebreakstrue
\def\keywordtrue{true}
\def\keywordfalse{false}
\parseargdef\allowcodebreaks{%
\def\txiarg{#1}%
\ifx\txiarg\keywordtrue
\allowcodebreakstrue
\else\ifx\txiarg\keywordfalse
\allowcodebreaksfalse
\else
\errhelp = \EMsimple
\errmessage{Unknown @allowcodebreaks option `\txiarg', must be true|false}%
\fi\fi
}
% For @command, @env, @file, @option quotes seem unnecessary,
% so use \code rather than \samp.
\let\command=\code
\let\env=\code
\let\file=\code
\let\option=\code
% @uref (abbreviation for `urlref') takes an optional (comma-separated)
% second argument specifying the text to display and an optional third
% arg as text to display instead of (rather than in addition to) the url
% itself. First (mandatory) arg is the url.
% secret option to allow changing PDF output to show only the second
% arg (if given), and not the url (which is then just the link target).
\newif\ifurefurlonlylink
% The main macro is \urefbreak, which allows breaking at expected
% places within the url. (There used to be another version, which
% didn't support automatic breaking.)
\def\urefbreak{\begingroup \urefcatcodes \dourefbreak}
\let\uref=\urefbreak
%
\def\dourefbreak#1{\urefbreakfinish #1,,,\finish}
\def\urefbreakfinish#1,#2,#3,#4\finish{% doesn't work in @example
\unsepspaces
\pdfurl{#1}%
\setbox0 = \hbox{\ignorespaces #3}%
\ifdim\wd0 > 0pt
\unhbox0 % third arg given, show only that
\else
\setbox0 = \hbox{\ignorespaces #2}% look for second arg
\ifdim\wd0 > 0pt
\ifpdf
\ifurefurlonlylink
% PDF plus option to not display url, show just arg
\unhbox0
\else
% PDF, normally display both arg and url for consistency,
% visibility, if the pdf is eventually used to print, etc.
\unhbox0\ (\urefcode{#1})%
\fi
\else
\unhbox0\ (\urefcode{#1})% DVI, always show arg and url
\fi
\else
\urefcode{#1}% only url given, so show it
\fi
\fi
\endlink
\endgroup}
% Allow line breaks around only a few characters (only).
\def\urefcatcodes{%
\catcode\ampChar=\active \catcode\dotChar=\active
\catcode\hashChar=\active \catcode\questChar=\active
\catcode\slashChar=\active
}
{
\urefcatcodes
%
\global\def\urefcode{\begingroup
\setupmarkupstyle{code}%
\urefcatcodes
\let&\urefcodeamp
\let.\urefcodedot
\let#\urefcodehash
\let?\urefcodequest
\let/\urefcodeslash
\codex
}
%
% By default, they are just regular characters.
\global\def&{\normalamp}
\global\def.{\normaldot}
\global\def#{\normalhash}
\global\def?{\normalquest}
\global\def/{\normalslash}
}
% we put a little stretch before and after the breakable chars, to help
% line breaking of long url's. The unequal skips make look better in
% cmtt at least, especially for dots.
\def\urefprestretch{\urefprebreak \hskip0pt plus.13em }
\def\urefpoststretch{\urefpostbreak \hskip0pt plus.1em }
%
\def\urefcodeamp{\urefprestretch \&\urefpoststretch}
\def\urefcodedot{\urefprestretch .\urefpoststretch}
\def\urefcodehash{\urefprestretch \#\urefpoststretch}
\def\urefcodequest{\urefprestretch ?\urefpoststretch}
\def\urefcodeslash{\futurelet\next\urefcodeslashfinish}
{
\catcode`\/=\active
\global\def\urefcodeslashfinish{%
\urefprestretch \slashChar
% Allow line break only after the final / in a sequence of
% slashes, to avoid line break between the slashes in http://.
\ifx\next/\else \urefpoststretch \fi
}
}
% One more complication: by default we'll break after the special
% characters, but some people like to break before the special chars, so
% allow that. Also allow no breaking at all, for manual control.
%
\parseargdef\urefbreakstyle{%
\def\txiarg{#1}%
\ifx\txiarg\wordnone
\def\urefprebreak{\nobreak}\def\urefpostbreak{\nobreak}
\else\ifx\txiarg\wordbefore
\def\urefprebreak{\allowbreak}\def\urefpostbreak{\nobreak}
\else\ifx\txiarg\wordafter
\def\urefprebreak{\nobreak}\def\urefpostbreak{\allowbreak}
\else
\errhelp = \EMsimple
\errmessage{Unknown @urefbreakstyle setting `\txiarg'}%
\fi\fi\fi
}
\def\wordafter{after}
\def\wordbefore{before}
\def\wordnone{none}
\urefbreakstyle after
% @url synonym for @uref, since that's how everyone uses it.
%
\let\url=\uref
% rms does not like angle brackets --karl, 17may97.
% So now @email is just like @uref, unless we are pdf.
%
%\def\email#1{\angleleft{\tt #1}\angleright}
\ifpdf
\def\email#1{\doemail#1,,\finish}
\def\doemail#1,#2,#3\finish{\begingroup
\unsepspaces
\pdfurl{mailto:#1}%
\setbox0 = \hbox{\ignorespaces #2}%
\ifdim\wd0>0pt\unhbox0\else\code{#1}\fi
\endlink
\endgroup}
\else
\let\email=\uref
\fi
% @kbdinputstyle -- arg is `distinct' (@kbd uses slanted tty font always),
% `example' (@kbd uses ttsl only inside of @example and friends),
% or `code' (@kbd uses normal tty font always).
\parseargdef\kbdinputstyle{%
\def\txiarg{#1}%
\ifx\txiarg\worddistinct
\gdef\kbdexamplefont{\ttsl}\gdef\kbdfont{\ttsl}%
\else\ifx\txiarg\wordexample
\gdef\kbdexamplefont{\ttsl}\gdef\kbdfont{\tt}%
\else\ifx\txiarg\wordcode
\gdef\kbdexamplefont{\tt}\gdef\kbdfont{\tt}%
\else
\errhelp = \EMsimple
\errmessage{Unknown @kbdinputstyle setting `\txiarg'}%
\fi\fi\fi
}
\def\worddistinct{distinct}
\def\wordexample{example}
\def\wordcode{code}
% Default is `distinct'.
\kbdinputstyle distinct
% @kbd is like @code, except that if the argument is just one @key command,
% then @kbd has no effect.
\def\kbd#1{{\def\look{#1}\expandafter\kbdsub\look??\par}}
\def\xkey{\key}
\def\kbdsub#1#2#3\par{%
\def\one{#1}\def\three{#3}\def\threex{??}%
\ifx\one\xkey\ifx\threex\three \key{#2}%
\else{\tclose{\kbdfont\setupmarkupstyle{kbd}\look}}\fi
\else{\tclose{\kbdfont\setupmarkupstyle{kbd}\look}}\fi
}
% definition of @key that produces a lozenge. Doesn't adjust to text size.
%\setfont\keyrm\rmshape{8}{1000}{OT1}
%\font\keysy=cmsy9
%\def\key#1{{\keyrm\textfont2=\keysy \leavevmode\hbox{%
% \raise0.4pt\hbox{\angleleft}\kern-.08em\vtop{%
% \vbox{\hrule\kern-0.4pt
% \hbox{\raise0.4pt\hbox{\vphantom{\angleleft}}#1}}%
% \kern-0.4pt\hrule}%
% \kern-.06em\raise0.4pt\hbox{\angleright}}}}
% definition of @key with no lozenge. If the current font is already
% monospace, don't change it; that way, we respect @kbdinputstyle. But
% if it isn't monospace, then use \tt.
%
\def\key#1{{\setupmarkupstyle{key}%
\nohyphenation
\ifmonospace\else\tt\fi
#1}\null}
% @clicksequence{File @click{} Open ...}
\def\clicksequence#1{\begingroup #1\endgroup}
% @clickstyle @arrow (by default)
\parseargdef\clickstyle{\def\click{#1}}
\def\click{\arrow}
% Typeset a dimension, e.g., `in' or `pt'. The only reason for the
% argument is to make the input look right: @dmn{pt} instead of @dmn{}pt.
%
\def\dmn#1{\thinspace #1}
% @l was never documented to mean ``switch to the Lisp font'',
% and it is not used as such in any manual I can find. We need it for
% Polish suppressed-l. --karl, 22sep96.
%\def\l#1{{\li #1}\null}
% @acronym for "FBI", "NATO", and the like.
% We print this one point size smaller, since it's intended for
% all-uppercase.
%
\def\acronym#1{\doacronym #1,,\finish}
\def\doacronym#1,#2,#3\finish{%
{\selectfonts\lsize #1}%
\def\temp{#2}%
\ifx\temp\empty \else
\space ({\unsepspaces \ignorespaces \temp \unskip})%
\fi
\null % reset \spacefactor=1000
}
% @abbr for "Comput. J." and the like.
% No font change, but don't do end-of-sentence spacing.
%
\def\abbr#1{\doabbr #1,,\finish}
\def\doabbr#1,#2,#3\finish{%
{\plainfrenchspacing #1}%
\def\temp{#2}%
\ifx\temp\empty \else
\space ({\unsepspaces \ignorespaces \temp \unskip})%
\fi
\null % reset \spacefactor=1000
}
% @asis just yields its argument. Used with @table, for example.
%
\def\asis#1{#1}
% @math outputs its argument in math mode.
%
% One complication: _ usually means subscripts, but it could also mean
% an actual _ character, as in @math{@var{some_variable} + 1}. So make
% _ active, and distinguish by seeing if the current family is \slfam,
% which is what @var uses.
{
\catcode`\_ = \active
\gdef\mathunderscore{%
\catcode`\_=\active
\def_{\ifnum\fam=\slfam \_\else\sb\fi}%
}
}
% Another complication: we want \\ (and @\) to output a math (or tt) \.
% FYI, plain.tex uses \\ as a temporary control sequence (for no
% particular reason), but this is not advertised and we don't care.
%
% The \mathchar is class=0=ordinary, family=7=ttfam, position=5C=\.
\def\mathbackslash{\ifnum\fam=\ttfam \mathchar"075C \else\backslash \fi}
%
\def\math{%
\tex
\mathunderscore
\let\\ = \mathbackslash
\mathactive
% make the texinfo accent commands work in math mode
\let\"=\ddot
\let\'=\acute
\let\==\bar
\let\^=\hat
\let\`=\grave
\let\u=\breve
\let\v=\check
\let\~=\tilde
\let\dotaccent=\dot
$\finishmath
}
\def\finishmath#1{#1$\endgroup} % Close the group opened by \tex.
% Some active characters (such as <) are spaced differently in math.
% We have to reset their definitions in case the @math was an argument
% to a command which sets the catcodes (such as @item or @section).
%
{
\catcode`^ = \active
\catcode`< = \active
\catcode`> = \active
\catcode`+ = \active
\catcode`' = \active
\gdef\mathactive{%
\let^ = \ptexhat
\let< = \ptexless
\let> = \ptexgtr
\let+ = \ptexplus
\let' = \ptexquoteright
}
}
% ctrl is no longer a Texinfo command, but leave this definition for fun.
\def\ctrl #1{{\tt \rawbackslash \hat}#1}
% @inlinefmt{FMTNAME,PROCESSED-TEXT} and @inlineraw{FMTNAME,RAW-TEXT}.
% Ignore unless FMTNAME == tex; then it is like @iftex and @tex,
% except specified as a normal braced arg, so no newlines to worry about.
%
\def\outfmtnametex{tex}
%
\long\def\inlinefmt#1{\doinlinefmt #1,\finish}
\long\def\doinlinefmt#1,#2,\finish{%
\def\inlinefmtname{#1}%
\ifx\inlinefmtname\outfmtnametex \ignorespaces #2\fi
}
%
% @inlinefmtifelse{FMTNAME,THEN-TEXT,ELSE-TEXT} expands THEN-TEXT if
% FMTNAME is tex, else ELSE-TEXT.
\long\def\inlinefmtifelse#1{\doinlinefmtifelse #1,,,\finish}
\long\def\doinlinefmtifelse#1,#2,#3,#4,\finish{%
\def\inlinefmtname{#1}%
\ifx\inlinefmtname\outfmtnametex \ignorespaces #2\else \ignorespaces #3\fi
}
%
% For raw, must switch into @tex before parsing the argument, to avoid
% setting catcodes prematurely. Doing it this way means that, for
% example, @inlineraw{html, foo{bar} gets a parse error instead of being
% ignored. But this isn't important because if people want a literal
% *right* brace they would have to use a command anyway, so they may as
% well use a command to get a left brace too. We could re-use the
% delimiter character idea from \verb, but it seems like overkill.
%
\long\def\inlineraw{\tex \doinlineraw}
\long\def\doinlineraw#1{\doinlinerawtwo #1,\finish}
\def\doinlinerawtwo#1,#2,\finish{%
\def\inlinerawname{#1}%
\ifx\inlinerawname\outfmtnametex \ignorespaces #2\fi
\endgroup % close group opened by \tex.
}
% @inlineifset{VAR, TEXT} expands TEXT if VAR is @set.
%
\long\def\inlineifset#1{\doinlineifset #1,\finish}
\long\def\doinlineifset#1,#2,\finish{%
\def\inlinevarname{#1}%
\expandafter\ifx\csname SET\inlinevarname\endcsname\relax
\else\ignorespaces#2\fi
}
% @inlineifclear{VAR, TEXT} expands TEXT if VAR is not @set.
%
\long\def\inlineifclear#1{\doinlineifclear #1,\finish}
\long\def\doinlineifclear#1,#2,\finish{%
\def\inlinevarname{#1}%
\expandafter\ifx\csname SET\inlinevarname\endcsname\relax \ignorespaces#2\fi
}
\message{glyphs,}
% and logos.
% @@ prints an @, as does @atchar{}.
\def\@{\char64 }
\let\atchar=\@
% @{ @} @lbracechar{} @rbracechar{} all generate brace characters.
% Unless we're in typewriter, use \ecfont because the CM text fonts do
% not have braces, and we don't want to switch into math.
\def\mylbrace{{\ifmonospace\else\ecfont\fi \char123}}
\def\myrbrace{{\ifmonospace\else\ecfont\fi \char125}}
\let\{=\mylbrace \let\lbracechar=\{
\let\}=\myrbrace \let\rbracechar=\}
\begingroup
% Definitions to produce \{ and \} commands for indices,
% and @{ and @} for the aux/toc files.
\catcode`\{ = \other \catcode`\} = \other
\catcode`\[ = 1 \catcode`\] = 2
\catcode`\! = 0 \catcode`\\ = \other
!gdef!lbracecmd[\{]%
!gdef!rbracecmd[\}]%
!gdef!lbraceatcmd[@{]%
!gdef!rbraceatcmd[@}]%
!endgroup
% @comma{} to avoid , parsing problems.
\let\comma = ,
% Accents: @, @dotaccent @ringaccent @ubaraccent @udotaccent
% Others are defined by plain TeX: @` @' @" @^ @~ @= @u @v @H.
\let\, = \ptexc
\let\dotaccent = \ptexdot
\def\ringaccent#1{{\accent23 #1}}
\let\tieaccent = \ptext
\let\ubaraccent = \ptexb
\let\udotaccent = \d
% Other special characters: @questiondown @exclamdown @ordf @ordm
% Plain TeX defines: @AA @AE @O @OE @L (plus lowercase versions) @ss.
\def\questiondown{?`}
\def\exclamdown{!`}
\def\ordf{\leavevmode\raise1ex\hbox{\selectfonts\lllsize \underbar{a}}}
\def\ordm{\leavevmode\raise1ex\hbox{\selectfonts\lllsize \underbar{o}}}
% Dotless i and dotless j, used for accents.
\def\imacro{i}
\def\jmacro{j}
\def\dotless#1{%
\def\temp{#1}%
\ifx\temp\imacro \ifmmode\imath \else\ptexi \fi
\else\ifx\temp\jmacro \ifmmode\jmath \else\j \fi
\else \errmessage{@dotless can be used only with i or j}%
\fi\fi
}
% The \TeX{} logo, as in plain, but resetting the spacing so that a
% period following counts as ending a sentence. (Idea found in latex.)
%
\edef\TeX{\TeX \spacefactor=1000 }
% @LaTeX{} logo. Not quite the same results as the definition in
% latex.ltx, since we use a different font for the raised A; it's most
% convenient for us to use an explicitly smaller font, rather than using
% the \scriptstyle font (since we don't reset \scriptstyle and
% \scriptscriptstyle).
%
\def\LaTeX{%
L\kern-.36em
{\setbox0=\hbox{T}%
\vbox to \ht0{\hbox{%
\ifx\textnominalsize\xwordpt
% for 10pt running text, \lllsize (8pt) is too small for the A in LaTeX.
% Revert to plain's \scriptsize, which is 7pt.
\count255=\the\fam $\fam\count255 \scriptstyle A$%
\else
% For 11pt, we can use our lllsize.
\selectfonts\lllsize A%
\fi
}%
\vss
}}%
\kern-.15em
\TeX
}
% Some math mode symbols.
\def\bullet{$\ptexbullet$}
\def\geq{\ifmmode \ge\else $\ge$\fi}
\def\leq{\ifmmode \le\else $\le$\fi}
\def\minus{\ifmmode -\else $-$\fi}
% @dots{} outputs an ellipsis using the current font.
% We do .5em per period so that it has the same spacing in the cm
% typewriter fonts as three actual period characters; on the other hand,
% in other typewriter fonts three periods are wider than 1.5em. So do
% whichever is larger.
%
\def\dots{%
\leavevmode
\setbox0=\hbox{...}% get width of three periods
\ifdim\wd0 > 1.5em
\dimen0 = \wd0
\else
\dimen0 = 1.5em
\fi
\hbox to \dimen0{%
\hskip 0pt plus.25fil
.\hskip 0pt plus1fil
.\hskip 0pt plus1fil
.\hskip 0pt plus.5fil
}%
}
% @enddots{} is an end-of-sentence ellipsis.
%
\def\enddots{%
\dots
\spacefactor=\endofsentencespacefactor
}
% @point{}, @result{}, @expansion{}, @print{}, @equiv{}.
%
% Since these characters are used in examples, they should be an even number of
% \tt widths. Each \tt character is 1en, so two makes it 1em.
%
\def\point{$\star$}
\def\arrow{\leavevmode\raise.05ex\hbox to 1em{\hfil$\rightarrow$\hfil}}
\def\result{\leavevmode\raise.05ex\hbox to 1em{\hfil$\Rightarrow$\hfil}}
\def\expansion{\leavevmode\hbox to 1em{\hfil$\mapsto$\hfil}}
\def\print{\leavevmode\lower.1ex\hbox to 1em{\hfil$\dashv$\hfil}}
\def\equiv{\leavevmode\hbox to 1em{\hfil$\ptexequiv$\hfil}}
% The @error{} command.
% Adapted from the TeXbook's \boxit.
%
\newbox\errorbox
%
{\tentt \global\dimen0 = 3em}% Width of the box.
\dimen2 = .55pt % Thickness of rules
% The text. (`r' is open on the right, `e' somewhat less so on the left.)
\setbox0 = \hbox{\kern-.75pt \reducedsf \putworderror\kern-1.5pt}
%
\setbox\errorbox=\hbox to \dimen0{\hfil
\hsize = \dimen0 \advance\hsize by -5.8pt % Space to left+right.
\advance\hsize by -2\dimen2 % Rules.
\vbox{%
\hrule height\dimen2
\hbox{\vrule width\dimen2 \kern3pt % Space to left of text.
\vtop{\kern2.4pt \box0 \kern2.4pt}% Space above/below.
\kern3pt\vrule width\dimen2}% Space to right.
\hrule height\dimen2}
\hfil}
%
\def\error{\leavevmode\lower.7ex\copy\errorbox}
% @pounds{} is a sterling sign, which Knuth put in the CM italic font.
%
\def\pounds{{\it\$}}
% @euro{} comes from a separate font, depending on the current style.
% We use the free feym* fonts from the eurosym package by Henrik
% Theiling, which support regular, slanted, bold and bold slanted (and
% "outlined" (blackboard board, sort of) versions, which we don't need).
% It is available from http://www.ctan.org/tex-archive/fonts/eurosym.
%
% Although only regular is the truly official Euro symbol, we ignore
% that. The Euro is designed to be slightly taller than the regular
% font height.
%
% feymr - regular
% feymo - slanted
% feybr - bold
% feybo - bold slanted
%
% There is no good (free) typewriter version, to my knowledge.
% A feymr10 euro is ~7.3pt wide, while a normal cmtt10 char is ~5.25pt wide.
% Hmm.
%
% Also doesn't work in math. Do we need to do math with euro symbols?
% Hope not.
%
%
\def\euro{{\eurofont e}}
\def\eurofont{%
% We set the font at each command, rather than predefining it in
% \textfonts and the other font-switching commands, so that
% installations which never need the symbol don't have to have the
% font installed.
%
% There is only one designed size (nominal 10pt), so we always scale
% that to the current nominal size.
%
% By the way, simply using "at 1em" works for cmr10 and the like, but
% does not work for cmbx10 and other extended/shrunken fonts.
%
\def\eurosize{\csname\curfontsize nominalsize\endcsname}%
%
\ifx\curfontstyle\bfstylename
% bold:
\font\thiseurofont = \ifusingit{feybo10}{feybr10} at \eurosize
\else
% regular:
\font\thiseurofont = \ifusingit{feymo10}{feymr10} at \eurosize
\fi
\thiseurofont
}
% Glyphs from the EC fonts. We don't use \let for the aliases, because
% sometimes we redefine the original macro, and the alias should reflect
% the redefinition.
%
% Use LaTeX names for the Icelandic letters.
\def\DH{{\ecfont \char"D0}} % Eth
\def\dh{{\ecfont \char"F0}} % eth
\def\TH{{\ecfont \char"DE}} % Thorn
\def\th{{\ecfont \char"FE}} % thorn
%
\def\guillemetleft{{\ecfont \char"13}}
\def\guillemotleft{\guillemetleft}
\def\guillemetright{{\ecfont \char"14}}
\def\guillemotright{\guillemetright}
\def\guilsinglleft{{\ecfont \char"0E}}
\def\guilsinglright{{\ecfont \char"0F}}
\def\quotedblbase{{\ecfont \char"12}}
\def\quotesinglbase{{\ecfont \char"0D}}
%
% This positioning is not perfect (see the ogonek LaTeX package), but
% we have the precomposed glyphs for the most common cases. We put the
% tests to use those glyphs in the single \ogonek macro so we have fewer
% dummy definitions to worry about for index entries, etc.
%
% ogonek is also used with other letters in Lithuanian (IOU), but using
% the precomposed glyphs for those is not so easy since they aren't in
% the same EC font.
\def\ogonek#1{{%
\def\temp{#1}%
\ifx\temp\macrocharA\Aogonek
\else\ifx\temp\macrochara\aogonek
\else\ifx\temp\macrocharE\Eogonek
\else\ifx\temp\macrochare\eogonek
\else
\ecfont \setbox0=\hbox{#1}%
\ifdim\ht0=1ex\accent"0C #1%
\else\ooalign{\unhbox0\crcr\hidewidth\char"0C \hidewidth}%
\fi
\fi\fi\fi\fi
}%
}
\def\Aogonek{{\ecfont \char"81}}\def\macrocharA{A}
\def\aogonek{{\ecfont \char"A1}}\def\macrochara{a}
\def\Eogonek{{\ecfont \char"86}}\def\macrocharE{E}
\def\eogonek{{\ecfont \char"A6}}\def\macrochare{e}
%
% Use the ec* fonts (cm-super in outline format) for non-CM glyphs.
\def\ecfont{%
% We can't distinguish serif/sans and italic/slanted, but this
% is used for crude hacks anyway (like adding French and German
% quotes to documents typeset with CM, where we lose kerning), so
% hopefully nobody will notice/care.
\edef\ecsize{\csname\curfontsize ecsize\endcsname}%
\edef\nominalsize{\csname\curfontsize nominalsize\endcsname}%
\ifmonospace
% typewriter:
\font\thisecfont = ectt\ecsize \space at \nominalsize
\else
\ifx\curfontstyle\bfstylename
% bold:
\font\thisecfont = ecb\ifusingit{i}{x}\ecsize \space at \nominalsize
\else
% regular:
\font\thisecfont = ec\ifusingit{ti}{rm}\ecsize \space at \nominalsize
\fi
\fi
\thisecfont
}
% @registeredsymbol - R in a circle. The font for the R should really
% be smaller yet, but lllsize is the best we can do for now.
% Adapted from the plain.tex definition of \copyright.
%
\def\registeredsymbol{%
$^{{\ooalign{\hfil\raise.07ex\hbox{\selectfonts\lllsize R}%
\hfil\crcr\Orb}}%
}$%
}
% @textdegree - the normal degrees sign.
%
\def\textdegree{$^\circ$}
% Laurent Siebenmann reports \Orb undefined with:
% Textures 1.7.7 (preloaded format=plain 93.10.14) (68K) 16 APR 2004 02:38
% so we'll define it if necessary.
%
\ifx\Orb\thisisundefined
\def\Orb{\mathhexbox20D}
\fi
% Quotes.
\chardef\quotedblleft="5C
\chardef\quotedblright=`\"
\chardef\quoteleft=`\`
\chardef\quoteright=`\'
\message{page headings,}
\newskip\titlepagetopglue \titlepagetopglue = 1.5in
\newskip\titlepagebottomglue \titlepagebottomglue = 2pc
% First the title page. Must do @settitle before @titlepage.
\newif\ifseenauthor
\newif\iffinishedtitlepage
% Do an implicit @contents or @shortcontents after @end titlepage if the
% user says @setcontentsaftertitlepage or @setshortcontentsaftertitlepage.
%
\newif\ifsetcontentsaftertitlepage
\let\setcontentsaftertitlepage = \setcontentsaftertitlepagetrue
\newif\ifsetshortcontentsaftertitlepage
\let\setshortcontentsaftertitlepage = \setshortcontentsaftertitlepagetrue
\parseargdef\shorttitlepage{%
\begingroup \hbox{}\vskip 1.5in \chaprm \centerline{#1}%
\endgroup\page\hbox{}\page}
\envdef\titlepage{%
% Open one extra group, as we want to close it in the middle of \Etitlepage.
\begingroup
\parindent=0pt \textfonts
% Leave some space at the very top of the page.
\vglue\titlepagetopglue
% No rule at page bottom unless we print one at the top with @title.
\finishedtitlepagetrue
%
% Most title ``pages'' are actually two pages long, with space
% at the top of the second. We don't want the ragged left on the second.
\let\oldpage = \page
\def\page{%
\iffinishedtitlepage\else
\finishtitlepage
\fi
\let\page = \oldpage
\page
\null
}%
}
\def\Etitlepage{%
\iffinishedtitlepage\else
\finishtitlepage
\fi
% It is important to do the page break before ending the group,
% because the headline and footline are only empty inside the group.
% If we use the new definition of \page, we always get a blank page
% after the title page, which we certainly don't want.
\oldpage
\endgroup
%
% Need this before the \...aftertitlepage checks so that if they are
% in effect the toc pages will come out with page numbers.
\HEADINGSon
%
% If they want short, they certainly want long too.
\ifsetshortcontentsaftertitlepage
\shortcontents
\contents
\global\let\shortcontents = \relax
\global\let\contents = \relax
\fi
%
\ifsetcontentsaftertitlepage
\contents
\global\let\contents = \relax
\global\let\shortcontents = \relax
\fi
}
\def\finishtitlepage{%
\vskip4pt \hrule height 2pt width \hsize
\vskip\titlepagebottomglue
\finishedtitlepagetrue
}
% Settings used for typesetting titles: no hyphenation, no indentation,
% don't worry much about spacing, ragged right. This should be used
% inside a \vbox, and fonts need to be set appropriately first. Because
% it is always used for titles, nothing else, we call \rmisbold. \par
% should be specified before the end of the \vbox, since a vbox is a group.
%
\def\raggedtitlesettings{%
\rmisbold
\hyphenpenalty=10000
\parindent=0pt
\tolerance=5000
\ptexraggedright
}
% Macros to be used within @titlepage:
\let\subtitlerm=\tenrm
\def\subtitlefont{\subtitlerm \normalbaselineskip = 13pt \normalbaselines}
\parseargdef\title{%
\checkenv\titlepage
\vbox{\titlefonts \raggedtitlesettings #1\par}%
% print a rule at the page bottom also.
\finishedtitlepagefalse
\vskip4pt \hrule height 4pt width \hsize \vskip4pt
}
\parseargdef\subtitle{%
\checkenv\titlepage
{\subtitlefont \rightline{#1}}%
}
% @author should come last, but may come many times.
% It can also be used inside @quotation.
%
\parseargdef\author{%
\def\temp{\quotation}%
\ifx\thisenv\temp
\def\quotationauthor{#1}% printed in \Equotation.
\else
\checkenv\titlepage
\ifseenauthor\else \vskip 0pt plus 1filll \seenauthortrue \fi
{\secfonts\rmisbold \leftline{#1}}%
\fi
}
% Set up page headings and footings.
\let\thispage=\folio
\newtoks\evenheadline % headline on even pages
\newtoks\oddheadline % headline on odd pages
\newtoks\evenfootline % footline on even pages
\newtoks\oddfootline % footline on odd pages
% Now make TeX use those variables
\headline={{\textfonts\rm \ifodd\pageno \the\oddheadline
\else \the\evenheadline \fi}}
\footline={{\textfonts\rm \ifodd\pageno \the\oddfootline
\else \the\evenfootline \fi}\HEADINGShook}
\let\HEADINGShook=\relax
% Commands to set those variables.
% For example, this is what @headings on does
% @evenheading @thistitle|@thispage|@thischapter
% @oddheading @thischapter|@thispage|@thistitle
% @evenfooting @thisfile||
% @oddfooting ||@thisfile
\def\evenheading{\parsearg\evenheadingxxx}
\def\evenheadingxxx #1{\evenheadingyyy #1\|\|\|\|\finish}
\def\evenheadingyyy #1\|#2\|#3\|#4\finish{%
\global\evenheadline={\rlap{\centerline{#2}}\line{#1\hfil#3}}}
\def\oddheading{\parsearg\oddheadingxxx}
\def\oddheadingxxx #1{\oddheadingyyy #1\|\|\|\|\finish}
\def\oddheadingyyy #1\|#2\|#3\|#4\finish{%
\global\oddheadline={\rlap{\centerline{#2}}\line{#1\hfil#3}}}
\parseargdef\everyheading{\oddheadingxxx{#1}\evenheadingxxx{#1}}%
\def\evenfooting{\parsearg\evenfootingxxx}
\def\evenfootingxxx #1{\evenfootingyyy #1\|\|\|\|\finish}
\def\evenfootingyyy #1\|#2\|#3\|#4\finish{%
\global\evenfootline={\rlap{\centerline{#2}}\line{#1\hfil#3}}}
\def\oddfooting{\parsearg\oddfootingxxx}
\def\oddfootingxxx #1{\oddfootingyyy #1\|\|\|\|\finish}
\def\oddfootingyyy #1\|#2\|#3\|#4\finish{%
\global\oddfootline = {\rlap{\centerline{#2}}\line{#1\hfil#3}}%
%
% Leave some space for the footline. Hopefully ok to assume
% @evenfooting will not be used by itself.
\global\advance\pageheight by -12pt
\global\advance\vsize by -12pt
}
\parseargdef\everyfooting{\oddfootingxxx{#1}\evenfootingxxx{#1}}
% @evenheadingmarks top \thischapter <- chapter at the top of a page
% @evenheadingmarks bottom \thischapter <- chapter at the bottom of a page
%
% The same set of arguments for:
%
% @oddheadingmarks
% @evenfootingmarks
% @oddfootingmarks
% @everyheadingmarks
% @everyfootingmarks
\def\evenheadingmarks{\headingmarks{even}{heading}}
\def\oddheadingmarks{\headingmarks{odd}{heading}}
\def\evenfootingmarks{\headingmarks{even}{footing}}
\def\oddfootingmarks{\headingmarks{odd}{footing}}
\def\everyheadingmarks#1 {\headingmarks{even}{heading}{#1}
\headingmarks{odd}{heading}{#1} }
\def\everyfootingmarks#1 {\headingmarks{even}{footing}{#1}
\headingmarks{odd}{footing}{#1} }
% #1 = even/odd, #2 = heading/footing, #3 = top/bottom.
\def\headingmarks#1#2#3 {%
\expandafter\let\expandafter\temp \csname get#3headingmarks\endcsname
\global\expandafter\let\csname get#1#2marks\endcsname \temp
}
\everyheadingmarks bottom
\everyfootingmarks bottom
% @headings double turns headings on for double-sided printing.
% @headings single turns headings on for single-sided printing.
% @headings off turns them off.
% @headings on same as @headings double, retained for compatibility.
% @headings after turns on double-sided headings after this page.
% @headings doubleafter turns on double-sided headings after this page.
% @headings singleafter turns on single-sided headings after this page.
% By default, they are off at the start of a document,
% and turned `on' after @end titlepage.
\def\headings #1 {\csname HEADINGS#1\endcsname}
\def\headingsoff{% non-global headings elimination
\evenheadline={\hfil}\evenfootline={\hfil}%
\oddheadline={\hfil}\oddfootline={\hfil}%
}
\def\HEADINGSoff{{\globaldefs=1 \headingsoff}} % global setting
\HEADINGSoff % it's the default
% When we turn headings on, set the page number to 1.
% For double-sided printing, put current file name in lower left corner,
% chapter name on inside top of right hand pages, document
% title on inside top of left hand pages, and page numbers on outside top
% edge of all pages.
\def\HEADINGSdouble{%
\global\pageno=1
\global\evenfootline={\hfil}
\global\oddfootline={\hfil}
\global\evenheadline={\line{\folio\hfil\thistitle}}
\global\oddheadline={\line{\thischapter\hfil\folio}}
\global\let\contentsalignmacro = \chapoddpage
}
\let\contentsalignmacro = \chappager
% For single-sided printing, chapter title goes across top left of page,
% page number on top right.
\def\HEADINGSsingle{%
\global\pageno=1
\global\evenfootline={\hfil}
\global\oddfootline={\hfil}
\global\evenheadline={\line{\thischapter\hfil\folio}}
\global\oddheadline={\line{\thischapter\hfil\folio}}
\global\let\contentsalignmacro = \chappager
}
\def\HEADINGSon{\HEADINGSdouble}
\def\HEADINGSafter{\let\HEADINGShook=\HEADINGSdoublex}
\let\HEADINGSdoubleafter=\HEADINGSafter
\def\HEADINGSdoublex{%
\global\evenfootline={\hfil}
\global\oddfootline={\hfil}
\global\evenheadline={\line{\folio\hfil\thistitle}}
\global\oddheadline={\line{\thischapter\hfil\folio}}
\global\let\contentsalignmacro = \chapoddpage
}
\def\HEADINGSsingleafter{\let\HEADINGShook=\HEADINGSsinglex}
\def\HEADINGSsinglex{%
\global\evenfootline={\hfil}
\global\oddfootline={\hfil}
\global\evenheadline={\line{\thischapter\hfil\folio}}
\global\oddheadline={\line{\thischapter\hfil\folio}}
\global\let\contentsalignmacro = \chappager
}
% Subroutines used in generating headings
% This produces Day Month Year style of output.
% Only define if not already defined, in case a txi-??.tex file has set
% up a different format (e.g., txi-cs.tex does this).
\ifx\today\thisisundefined
\def\today{%
\number\day\space
\ifcase\month
\or\putwordMJan\or\putwordMFeb\or\putwordMMar\or\putwordMApr
\or\putwordMMay\or\putwordMJun\or\putwordMJul\or\putwordMAug
\or\putwordMSep\or\putwordMOct\or\putwordMNov\or\putwordMDec
\fi
\space\number\year}
\fi
% @settitle line... specifies the title of the document, for headings.
% It generates no output of its own.
\def\thistitle{\putwordNoTitle}
\def\settitle{\parsearg{\gdef\thistitle}}
\message{tables,}
% Tables -- @table, @ftable, @vtable, @item(x).
% default indentation of table text
\newdimen\tableindent \tableindent=.8in
% default indentation of @itemize and @enumerate text
\newdimen\itemindent \itemindent=.3in
% margin between end of table item and start of table text.
\newdimen\itemmargin \itemmargin=.1in
% used internally for \itemindent minus \itemmargin
\newdimen\itemmax
% Note @table, @ftable, and @vtable define @item, @itemx, etc., with
% these defs.
% They also define \itemindex
% to index the item name in whatever manner is desired (perhaps none).
\newif\ifitemxneedsnegativevskip
\def\itemxpar{\par\ifitemxneedsnegativevskip\nobreak\vskip-\parskip\nobreak\fi}
\def\internalBitem{\smallbreak \parsearg\itemzzz}
\def\internalBitemx{\itemxpar \parsearg\itemzzz}
\def\itemzzz #1{\begingroup %
\advance\hsize by -\rightskip
\advance\hsize by -\tableindent
\setbox0=\hbox{\itemindicate{#1}}%
\itemindex{#1}%
\nobreak % This prevents a break before @itemx.
%
% If the item text does not fit in the space we have, put it on a line
% by itself, and do not allow a page break either before or after that
% line. We do not start a paragraph here because then if the next
% command is, e.g., @kindex, the whatsit would get put into the
% horizontal list on a line by itself, resulting in extra blank space.
\ifdim \wd0>\itemmax
%
% Make this a paragraph so we get the \parskip glue and wrapping,
% but leave it ragged-right.
\begingroup
\advance\leftskip by-\tableindent
\advance\hsize by\tableindent
\advance\rightskip by0pt plus1fil\relax
\leavevmode\unhbox0\par
\endgroup
%
% We're going to be starting a paragraph, but we don't want the
% \parskip glue -- logically it's part of the @item we just started.
\nobreak \vskip-\parskip
%
% Stop a page break at the \parskip glue coming up. However, if
% what follows is an environment such as @example, there will be no
% \parskip glue; then the negative vskip we just inserted would
% cause the example and the item to crash together. So we use this
% bizarre value of 10001 as a signal to \aboveenvbreak to insert
% \parskip glue after all. Section titles are handled this way also.
%
\penalty 10001
\endgroup
\itemxneedsnegativevskipfalse
\else
% The item text fits into the space. Start a paragraph, so that the
% following text (if any) will end up on the same line.
\noindent
% Do this with kerns and \unhbox so that if there is a footnote in
% the item text, it can migrate to the main vertical list and
% eventually be printed.
\nobreak\kern-\tableindent
\dimen0 = \itemmax \advance\dimen0 by \itemmargin \advance\dimen0 by -\wd0
\unhbox0
\nobreak\kern\dimen0
\endgroup
\itemxneedsnegativevskiptrue
\fi
}
\def\item{\errmessage{@item while not in a list environment}}
\def\itemx{\errmessage{@itemx while not in a list environment}}
% @table, @ftable, @vtable.
\envdef\table{%
\let\itemindex\gobble
\tablecheck{table}%
}
\envdef\ftable{%
\def\itemindex ##1{\doind {fn}{\code{##1}}}%
\tablecheck{ftable}%
}
\envdef\vtable{%
\def\itemindex ##1{\doind {vr}{\code{##1}}}%
\tablecheck{vtable}%
}
\def\tablecheck#1{%
\ifnum \the\catcode`\^^M=\active
\endgroup
\errmessage{This command won't work in this context; perhaps the problem is
that we are \inenvironment\thisenv}%
\def\next{\doignore{#1}}%
\else
\let\next\tablex
\fi
\next
}
\def\tablex#1{%
\def\itemindicate{#1}%
\parsearg\tabley
}
\def\tabley#1{%
{%
\makevalueexpandable
\edef\temp{\noexpand\tablez #1\space\space\space}%
\expandafter
}\temp \endtablez
}
\def\tablez #1 #2 #3 #4\endtablez{%
\aboveenvbreak
\ifnum 0#1>0 \advance \leftskip by #1\mil \fi
\ifnum 0#2>0 \tableindent=#2\mil \fi
\ifnum 0#3>0 \advance \rightskip by #3\mil \fi
\itemmax=\tableindent
\advance \itemmax by -\itemmargin
\advance \leftskip by \tableindent
\exdentamount=\tableindent
\parindent = 0pt
\parskip = \smallskipamount
\ifdim \parskip=0pt \parskip=2pt \fi
\let\item = \internalBitem
\let\itemx = \internalBitemx
}
\def\Etable{\endgraf\afterenvbreak}
\let\Eftable\Etable
\let\Evtable\Etable
\let\Eitemize\Etable
\let\Eenumerate\Etable
% This is the counter used by @enumerate, which is really @itemize
\newcount \itemno
\envdef\itemize{\parsearg\doitemize}
\def\doitemize#1{%
\aboveenvbreak
\itemmax=\itemindent
\advance\itemmax by -\itemmargin
\advance\leftskip by \itemindent
\exdentamount=\itemindent
\parindent=0pt
\parskip=\smallskipamount
\ifdim\parskip=0pt \parskip=2pt \fi
%
% Try typesetting the item mark so that if the document erroneously says
% something like @itemize @samp (intending @table), there's an error
% right away at the @itemize. It's not the best error message in the
% world, but it's better than leaving it to the @item. This means if
% the user wants an empty mark, they have to say @w{} not just @w.
\def\itemcontents{#1}%
\setbox0 = \hbox{\itemcontents}%
%
% @itemize with no arg is equivalent to @itemize @bullet.
\ifx\itemcontents\empty\def\itemcontents{\bullet}\fi
%
\let\item=\itemizeitem
}
% Definition of @item while inside @itemize and @enumerate.
%
\def\itemizeitem{%
\advance\itemno by 1 % for enumerations
{\let\par=\endgraf \smallbreak}% reasonable place to break
{%
% If the document has an @itemize directly after a section title, a
% \nobreak will be last on the list, and \sectionheading will have
% done a \vskip-\parskip. In that case, we don't want to zero
% parskip, or the item text will crash with the heading. On the
% other hand, when there is normal text preceding the item (as there
% usually is), we do want to zero parskip, or there would be too much
% space. In that case, we won't have a \nobreak before. At least
% that's the theory.
\ifnum\lastpenalty<10000 \parskip=0in \fi
\noindent
\hbox to 0pt{\hss \itemcontents \kern\itemmargin}%
%
\vadjust{\penalty 1200}}% not good to break after first line of item.
\flushcr
}
% \splitoff TOKENS\endmark defines \first to be the first token in
% TOKENS, and \rest to be the remainder.
%
\def\splitoff#1#2\endmark{\def\first{#1}\def\rest{#2}}%
% Allow an optional argument of an uppercase letter, lowercase letter,
% or number, to specify the first label in the enumerated list. No
% argument is the same as `1'.
%
\envparseargdef\enumerate{\enumeratey #1 \endenumeratey}
\def\enumeratey #1 #2\endenumeratey{%
% If we were given no argument, pretend we were given `1'.
\def\thearg{#1}%
\ifx\thearg\empty \def\thearg{1}\fi
%
% Detect if the argument is a single token. If so, it might be a
% letter. Otherwise, the only valid thing it can be is a number.
% (We will always have one token, because of the test we just made.
% This is a good thing, since \splitoff doesn't work given nothing at
% all -- the first parameter is undelimited.)
\expandafter\splitoff\thearg\endmark
\ifx\rest\empty
% Only one token in the argument. It could still be anything.
% A ``lowercase letter'' is one whose \lccode is nonzero.
% An ``uppercase letter'' is one whose \lccode is both nonzero, and
% not equal to itself.
% Otherwise, we assume it's a number.
%
% We need the \relax at the end of the \ifnum lines to stop TeX from
% continuing to look for a .
%
\ifnum\lccode\expandafter`\thearg=0\relax
\numericenumerate % a number (we hope)
\else
% It's a letter.
\ifnum\lccode\expandafter`\thearg=\expandafter`\thearg\relax
\lowercaseenumerate % lowercase letter
\else
\uppercaseenumerate % uppercase letter
\fi
\fi
\else
% Multiple tokens in the argument. We hope it's a number.
\numericenumerate
\fi
}
% An @enumerate whose labels are integers. The starting integer is
% given in \thearg.
%
\def\numericenumerate{%
\itemno = \thearg
\startenumeration{\the\itemno}%
}
% The starting (lowercase) letter is in \thearg.
\def\lowercaseenumerate{%
\itemno = \expandafter`\thearg
\startenumeration{%
% Be sure we're not beyond the end of the alphabet.
\ifnum\itemno=0
\errmessage{No more lowercase letters in @enumerate; get a bigger
alphabet}%
\fi
\char\lccode\itemno
}%
}
% The starting (uppercase) letter is in \thearg.
\def\uppercaseenumerate{%
\itemno = \expandafter`\thearg
\startenumeration{%
% Be sure we're not beyond the end of the alphabet.
\ifnum\itemno=0
\errmessage{No more uppercase letters in @enumerate; get a bigger
alphabet}
\fi
\char\uccode\itemno
}%
}
% Call \doitemize, adding a period to the first argument and supplying the
% common last two arguments. Also subtract one from the initial value in
% \itemno, since @item increments \itemno.
%
\def\startenumeration#1{%
\advance\itemno by -1
\doitemize{#1.}\flushcr
}
% @alphaenumerate and @capsenumerate are abbreviations for giving an arg
% to @enumerate.
%
\def\alphaenumerate{\enumerate{a}}
\def\capsenumerate{\enumerate{A}}
\def\Ealphaenumerate{\Eenumerate}
\def\Ecapsenumerate{\Eenumerate}
% @multitable macros
% Amy Hendrickson, 8/18/94, 3/6/96
%
% @multitable ... @end multitable will make as many columns as desired.
% Contents of each column will wrap at width given in preamble. Width
% can be specified either with sample text given in a template line,
% or in percent of \hsize, the current width of text on page.
% Table can continue over pages but will only break between lines.
% To make preamble:
%
% Either define widths of columns in terms of percent of \hsize:
% @multitable @columnfractions .25 .3 .45
% @item ...
%
% Numbers following @columnfractions are the percent of the total
% current hsize to be used for each column. You may use as many
% columns as desired.
% Or use a template:
% @multitable {Column 1 template} {Column 2 template} {Column 3 template}
% @item ...
% using the widest term desired in each column.
% Each new table line starts with @item, each subsequent new column
% starts with @tab. Empty columns may be produced by supplying @tab's
% with nothing between them for as many times as empty columns are needed,
% ie, @tab@tab@tab will produce two empty columns.
% @item, @tab do not need to be on their own lines, but it will not hurt
% if they are.
% Sample multitable:
% @multitable {Column 1 template} {Column 2 template} {Column 3 template}
% @item first col stuff @tab second col stuff @tab third col
% @item
% first col stuff
% @tab
% second col stuff
% @tab
% third col
% @item first col stuff @tab second col stuff
% @tab Many paragraphs of text may be used in any column.
%
% They will wrap at the width determined by the template.
% @item@tab@tab This will be in third column.
% @end multitable
% Default dimensions may be reset by user.
% @multitableparskip is vertical space between paragraphs in table.
% @multitableparindent is paragraph indent in table.
% @multitablecolmargin is horizontal space to be left between columns.
% @multitablelinespace is space to leave between table items, baseline
% to baseline.
% 0pt means it depends on current normal line spacing.
%
\newskip\multitableparskip
\newskip\multitableparindent
\newdimen\multitablecolspace
\newskip\multitablelinespace
\multitableparskip=0pt
\multitableparindent=6pt
\multitablecolspace=12pt
\multitablelinespace=0pt
% Macros used to set up halign preamble:
%
\let\endsetuptable\relax
\def\xendsetuptable{\endsetuptable}
\let\columnfractions\relax
\def\xcolumnfractions{\columnfractions}
\newif\ifsetpercent
% #1 is the @columnfraction, usually a decimal number like .5, but might
% be just 1. We just use it, whatever it is.
%
\def\pickupwholefraction#1 {%
\global\advance\colcount by 1
\expandafter\xdef\csname col\the\colcount\endcsname{#1\hsize}%
\setuptable
}
\newcount\colcount
\def\setuptable#1{%
\def\firstarg{#1}%
\ifx\firstarg\xendsetuptable
\let\go = \relax
\else
\ifx\firstarg\xcolumnfractions
\global\setpercenttrue
\else
\ifsetpercent
\let\go\pickupwholefraction
\else
\global\advance\colcount by 1
\setbox0=\hbox{#1\unskip\space}% Add a normal word space as a
% separator; typically that is always in the input, anyway.
\expandafter\xdef\csname col\the\colcount\endcsname{\the\wd0}%
\fi
\fi
\ifx\go\pickupwholefraction
% Put the argument back for the \pickupwholefraction call, so
% we'll always have a period there to be parsed.
\def\go{\pickupwholefraction#1}%
\else
\let\go = \setuptable
\fi%
\fi
\go
}
% multitable-only commands.
%
% @headitem starts a heading row, which we typeset in bold.
% Assignments have to be global since we are inside the implicit group
% of an alignment entry. \everycr resets \everytab so we don't have to
% undo it ourselves.
\def\headitemfont{\b}% for people to use in the template row; not changeable
\def\headitem{%
\checkenv\multitable
\crcr
\global\everytab={\bf}% can't use \headitemfont since the parsing differs
\the\everytab % for the first item
}%
%
% A \tab used to include \hskip1sp. But then the space in a template
% line is not enough. That is bad. So let's go back to just `&' until
% we again encounter the problem the 1sp was intended to solve.
% --karl, nathan@acm.org, 20apr99.
\def\tab{\checkenv\multitable &\the\everytab}%
% @multitable ... @end multitable definitions:
%
\newtoks\everytab % insert after every tab.
%
\envdef\multitable{%
\vskip\parskip
\startsavinginserts
%
% @item within a multitable starts a normal row.
% We use \def instead of \let so that if one of the multitable entries
% contains an @itemize, we don't choke on the \item (seen as \crcr aka
% \endtemplate) expanding \doitemize.
\def\item{\crcr}%
%
\tolerance=9500
\hbadness=9500
\setmultitablespacing
\parskip=\multitableparskip
\parindent=\multitableparindent
\overfullrule=0pt
\global\colcount=0
%
\everycr = {%
\noalign{%
\global\everytab={}%
\global\colcount=0 % Reset the column counter.
% Check for saved footnotes, etc.
\checkinserts
% Keeps underfull box messages off when table breaks over pages.
%\filbreak
% Maybe so, but it also creates really weird page breaks when the
% table breaks over pages. Wouldn't \vfil be better? Wait until the
% problem manifests itself, so it can be fixed for real --karl.
}%
}%
%
\parsearg\domultitable
}
\def\domultitable#1{%
% To parse everything between @multitable and @item:
\setuptable#1 \endsetuptable
%
% This preamble sets up a generic column definition, which will
% be used as many times as user calls for columns.
% \vtop will set a single line and will also let text wrap and
% continue for many paragraphs if desired.
\halign\bgroup &%
\global\advance\colcount by 1
\multistrut
\vtop{%
% Use the current \colcount to find the correct column width:
\hsize=\expandafter\csname col\the\colcount\endcsname
%
% In order to keep entries from bumping into each other
% we will add a \leftskip of \multitablecolspace to all columns after
% the first one.
%
% If a template has been used, we will add \multitablecolspace
% to the width of each template entry.
%
% If the user has set preamble in terms of percent of \hsize we will
% use that dimension as the width of the column, and the \leftskip
% will keep entries from bumping into each other. Table will start at
% left margin and final column will justify at right margin.
%
% Make sure we don't inherit \rightskip from the outer environment.
\rightskip=0pt
\ifnum\colcount=1
% The first column will be indented with the surrounding text.
\advance\hsize by\leftskip
\else
\ifsetpercent \else
% If user has not set preamble in terms of percent of \hsize
% we will advance \hsize by \multitablecolspace.
\advance\hsize by \multitablecolspace
\fi
% In either case we will make \leftskip=\multitablecolspace:
\leftskip=\multitablecolspace
\fi
% Ignoring space at the beginning and end avoids an occasional spurious
% blank line, when TeX decides to break the line at the space before the
% box from the multistrut, so the strut ends up on a line by itself.
% For example:
% @multitable @columnfractions .11 .89
% @item @code{#}
% @tab Legal holiday which is valid in major parts of the whole country.
% Is automatically provided with highlighting sequences respectively
% marking characters.
\noindent\ignorespaces##\unskip\multistrut
}\cr
}
\def\Emultitable{%
\crcr
\egroup % end the \halign
\global\setpercentfalse
}
\def\setmultitablespacing{%
\def\multistrut{\strut}% just use the standard line spacing
%
% Compute \multitablelinespace (if not defined by user) for use in
% \multitableparskip calculation. We used define \multistrut based on
% this, but (ironically) that caused the spacing to be off.
% See bug-texinfo report from Werner Lemberg, 31 Oct 2004 12:52:20 +0100.
\ifdim\multitablelinespace=0pt
\setbox0=\vbox{X}\global\multitablelinespace=\the\baselineskip
\global\advance\multitablelinespace by-\ht0
\fi
% Test to see if parskip is larger than space between lines of
% table. If not, do nothing.
% If so, set to same dimension as multitablelinespace.
\ifdim\multitableparskip>\multitablelinespace
\global\multitableparskip=\multitablelinespace
\global\advance\multitableparskip-7pt % to keep parskip somewhat smaller
% than skip between lines in the table.
\fi%
\ifdim\multitableparskip=0pt
\global\multitableparskip=\multitablelinespace
\global\advance\multitableparskip-7pt % to keep parskip somewhat smaller
% than skip between lines in the table.
\fi}
\message{conditionals,}
% @iftex, @ifnotdocbook, @ifnothtml, @ifnotinfo, @ifnotplaintext,
% @ifnotxml always succeed. They currently do nothing; we don't
% attempt to check whether the conditionals are properly nested. But we
% have to remember that they are conditionals, so that @end doesn't
% attempt to close an environment group.
%
\def\makecond#1{%
\expandafter\let\csname #1\endcsname = \relax
\expandafter\let\csname iscond.#1\endcsname = 1
}
\makecond{iftex}
\makecond{ifnotdocbook}
\makecond{ifnothtml}
\makecond{ifnotinfo}
\makecond{ifnotplaintext}
\makecond{ifnotxml}
% Ignore @ignore, @ifhtml, @ifinfo, and the like.
%
\def\direntry{\doignore{direntry}}
\def\documentdescription{\doignore{documentdescription}}
\def\docbook{\doignore{docbook}}
\def\html{\doignore{html}}
\def\ifdocbook{\doignore{ifdocbook}}
\def\ifhtml{\doignore{ifhtml}}
\def\ifinfo{\doignore{ifinfo}}
\def\ifnottex{\doignore{ifnottex}}
\def\ifplaintext{\doignore{ifplaintext}}
\def\ifxml{\doignore{ifxml}}
\def\ignore{\doignore{ignore}}
\def\menu{\doignore{menu}}
\def\xml{\doignore{xml}}
% Ignore text until a line `@end #1', keeping track of nested conditionals.
%
% A count to remember the depth of nesting.
\newcount\doignorecount
\def\doignore#1{\begingroup
% Scan in ``verbatim'' mode:
\obeylines
\catcode`\@ = \other
\catcode`\{ = \other
\catcode`\} = \other
%
% Make sure that spaces turn into tokens that match what \doignoretext wants.
\spaceisspace
%
% Count number of #1's that we've seen.
\doignorecount = 0
%
% Swallow text until we reach the matching `@end #1'.
\dodoignore{#1}%
}
{ \catcode`_=11 % We want to use \_STOP_ which cannot appear in texinfo source.
\obeylines %
%
\gdef\dodoignore#1{%
% #1 contains the command name as a string, e.g., `ifinfo'.
%
% Define a command to find the next `@end #1'.
\long\def\doignoretext##1^^M@end #1{%
\doignoretextyyy##1^^M@#1\_STOP_}%
%
% And this command to find another #1 command, at the beginning of a
% line. (Otherwise, we would consider a line `@c @ifset', for
% example, to count as an @ifset for nesting.)
\long\def\doignoretextyyy##1^^M@#1##2\_STOP_{\doignoreyyy{##2}\_STOP_}%
%
% And now expand that command.
\doignoretext ^^M%
}%
}
\def\doignoreyyy#1{%
\def\temp{#1}%
\ifx\temp\empty % Nothing found.
\let\next\doignoretextzzz
\else % Found a nested condition, ...
\advance\doignorecount by 1
\let\next\doignoretextyyy % ..., look for another.
% If we're here, #1 ends with ^^M\ifinfo (for example).
\fi
\next #1% the token \_STOP_ is present just after this macro.
}
% We have to swallow the remaining "\_STOP_".
%
\def\doignoretextzzz#1{%
\ifnum\doignorecount = 0 % We have just found the outermost @end.
\let\next\enddoignore
\else % Still inside a nested condition.
\advance\doignorecount by -1
\let\next\doignoretext % Look for the next @end.
\fi
\next
}
% Finish off ignored text.
{ \obeylines%
% Ignore anything after the last `@end #1'; this matters in verbatim
% environments, where otherwise the newline after an ignored conditional
% would result in a blank line in the output.
\gdef\enddoignore#1^^M{\endgroup\ignorespaces}%
}
% @set VAR sets the variable VAR to an empty value.
% @set VAR REST-OF-LINE sets VAR to the value REST-OF-LINE.
%
% Since we want to separate VAR from REST-OF-LINE (which might be
% empty), we can't just use \parsearg; we have to insert a space of our
% own to delimit the rest of the line, and then take it out again if we
% didn't need it.
% We rely on the fact that \parsearg sets \catcode`\ =10.
%
\parseargdef\set{\setyyy#1 \endsetyyy}
\def\setyyy#1 #2\endsetyyy{%
{%
\makevalueexpandable
\def\temp{#2}%
\edef\next{\gdef\makecsname{SET#1}}%
\ifx\temp\empty
\next{}%
\else
\setzzz#2\endsetzzz
\fi
}%
}
% Remove the trailing space \setxxx inserted.
\def\setzzz#1 \endsetzzz{\next{#1}}
% @clear VAR clears (i.e., unsets) the variable VAR.
%
\parseargdef\clear{%
{%
\makevalueexpandable
\global\expandafter\let\csname SET#1\endcsname=\relax
}%
}
% @value{foo} gets the text saved in variable foo.
\def\value{\begingroup\makevalueexpandable\valuexxx}
\def\valuexxx#1{\expandablevalue{#1}\endgroup}
{
\catcode`\-=\active \catcode`\_=\active
%
\gdef\makevalueexpandable{%
\let\value = \expandablevalue
% We don't want these characters active, ...
\catcode`\-=\other \catcode`\_=\other
% ..., but we might end up with active ones in the argument if
% we're called from @code, as @code{@value{foo-bar_}}, though.
% So \let them to their normal equivalents.
\let-\normaldash \let_\normalunderscore
}
}
% We have this subroutine so that we can handle at least some @value's
% properly in indexes (we call \makevalueexpandable in \indexdummies).
% The command has to be fully expandable (if the variable is set), since
% the result winds up in the index file. This means that if the
% variable's value contains other Texinfo commands, it's almost certain
% it will fail (although perhaps we could fix that with sufficient work
% to do a one-level expansion on the result, instead of complete).
%
% Unfortunately, this has the consequence that when _ is in the *value*
% of an @set, it does not print properly in the roman fonts (get the cmr
% dot accent at position 126 instead). No fix comes to mind, and it's
% been this way since 2003 or earlier, so just ignore it.
%
\def\expandablevalue#1{%
\expandafter\ifx\csname SET#1\endcsname\relax
{[No value for ``#1'']}%
\message{Variable `#1', used in @value, is not set.}%
\else
\csname SET#1\endcsname
\fi
}
% @ifset VAR ... @end ifset reads the `...' iff VAR has been defined
% with @set.
%
% To get the special treatment we need for `@end ifset,' we call
% \makecond and then redefine.
%
\makecond{ifset}
\def\ifset{\parsearg{\doifset{\let\next=\ifsetfail}}}
\def\doifset#1#2{%
{%
\makevalueexpandable
\let\next=\empty
\expandafter\ifx\csname SET#2\endcsname\relax
#1% If not set, redefine \next.
\fi
\expandafter
}\next
}
\def\ifsetfail{\doignore{ifset}}
% @ifclear VAR ... @end executes the `...' iff VAR has never been
% defined with @set, or has been undefined with @clear.
%
% The `\else' inside the `\doifset' parameter is a trick to reuse the
% above code: if the variable is not set, do nothing, if it is set,
% then redefine \next to \ifclearfail.
%
\makecond{ifclear}
\def\ifclear{\parsearg{\doifset{\else \let\next=\ifclearfail}}}
\def\ifclearfail{\doignore{ifclear}}
% @ifcommandisdefined CMD ... @end executes the `...' if CMD (written
% without the @) is in fact defined. We can only feasibly check at the
% TeX level, so something like `mathcode' is going to considered
% defined even though it is not a Texinfo command.
%
\makecond{ifcommanddefined}
\def\ifcommanddefined{\parsearg{\doifcmddefined{\let\next=\ifcmddefinedfail}}}
%
\def\doifcmddefined#1#2{{%
\makevalueexpandable
\let\next=\empty
\expandafter\ifx\csname #2\endcsname\relax
#1% If not defined, \let\next as above.
\fi
\expandafter
}\next
}
\def\ifcmddefinedfail{\doignore{ifcommanddefined}}
% @ifcommandnotdefined CMD ... handled similar to @ifclear above.
\makecond{ifcommandnotdefined}
\def\ifcommandnotdefined{%
\parsearg{\doifcmddefined{\else \let\next=\ifcmdnotdefinedfail}}}
\def\ifcmdnotdefinedfail{\doignore{ifcommandnotdefined}}
% Set the `txicommandconditionals' variable, so documents have a way to
% test if the @ifcommand...defined conditionals are available.
\set txicommandconditionals
% @dircategory CATEGORY -- specify a category of the dir file
% which this file should belong to. Ignore this in TeX.
\let\dircategory=\comment
% @defininfoenclose.
\let\definfoenclose=\comment
\message{indexing,}
% Index generation facilities
% Define \newwrite to be identical to plain tex's \newwrite
% except not \outer, so it can be used within macros and \if's.
\edef\newwrite{\makecsname{ptexnewwrite}}
% \newindex {foo} defines an index named foo.
% It automatically defines \fooindex such that
% \fooindex ...rest of line... puts an entry in the index foo.
% It also defines \fooindfile to be the number of the output channel for
% the file that accumulates this index. The file's extension is foo.
% The name of an index should be no more than 2 characters long
% for the sake of vms.
%
\def\newindex#1{%
\iflinks
\expandafter\newwrite \csname#1indfile\endcsname
\openout \csname#1indfile\endcsname \jobname.#1 % Open the file
\fi
\expandafter\xdef\csname#1index\endcsname{% % Define @#1index
\noexpand\doindex{#1}}
}
% @defindex foo == \newindex{foo}
%
\def\defindex{\parsearg\newindex}
% Define @defcodeindex, like @defindex except put all entries in @code.
%
\def\defcodeindex{\parsearg\newcodeindex}
%
\def\newcodeindex#1{%
\iflinks
\expandafter\newwrite \csname#1indfile\endcsname
\openout \csname#1indfile\endcsname \jobname.#1
\fi
\expandafter\xdef\csname#1index\endcsname{%
\noexpand\docodeindex{#1}}%
}
% @synindex foo bar makes index foo feed into index bar.
% Do this instead of @defindex foo if you don't want it as a separate index.
%
% @syncodeindex foo bar similar, but put all entries made for index foo
% inside @code.
%
\def\synindex#1 #2 {\dosynindex\doindex{#1}{#2}}
\def\syncodeindex#1 #2 {\dosynindex\docodeindex{#1}{#2}}
% #1 is \doindex or \docodeindex, #2 the index getting redefined (foo),
% #3 the target index (bar).
\def\dosynindex#1#2#3{%
% Only do \closeout if we haven't already done it, else we'll end up
% closing the target index.
\expandafter \ifx\csname donesynindex#2\endcsname \relax
% The \closeout helps reduce unnecessary open files; the limit on the
% Acorn RISC OS is a mere 16 files.
\expandafter\closeout\csname#2indfile\endcsname
\expandafter\let\csname donesynindex#2\endcsname = 1
\fi
% redefine \fooindfile:
\expandafter\let\expandafter\temp\expandafter=\csname#3indfile\endcsname
\expandafter\let\csname#2indfile\endcsname=\temp
% redefine \fooindex:
\expandafter\xdef\csname#2index\endcsname{\noexpand#1{#3}}%
}
% Define \doindex, the driver for all \fooindex macros.
% Argument #1 is generated by the calling \fooindex macro,
% and it is "foo", the name of the index.
% \doindex just uses \parsearg; it calls \doind for the actual work.
% This is because \doind is more useful to call from other macros.
% There is also \dosubind {index}{topic}{subtopic}
% which makes an entry in a two-level index such as the operation index.
\def\doindex#1{\edef\indexname{#1}\parsearg\singleindexer}
\def\singleindexer #1{\doind{\indexname}{#1}}
% like the previous two, but they put @code around the argument.
\def\docodeindex#1{\edef\indexname{#1}\parsearg\singlecodeindexer}
\def\singlecodeindexer #1{\doind{\indexname}{\code{#1}}}
% Take care of Texinfo commands that can appear in an index entry.
% Since there are some commands we want to expand, and others we don't,
% we have to laboriously prevent expansion for those that we don't.
%
\def\indexdummies{%
\escapechar = `\\ % use backslash in output files.
\def\@{@}% change to @@ when we switch to @ as escape char in index files.
\def\ {\realbackslash\space }%
%
% Need these unexpandable (because we define \tt as a dummy)
% definitions when @{ or @} appear in index entry text. Also, more
% complicated, when \tex is in effect and \{ is a \delimiter again.
% We can't use \lbracecmd and \rbracecmd because texindex assumes
% braces and backslashes are used only as delimiters. Perhaps we
% should define @lbrace and @rbrace commands a la @comma.
\def\{{{\tt\char123}}%
\def\}{{\tt\char125}}%
%
% I don't entirely understand this, but when an index entry is
% generated from a macro call, the \endinput which \scanmacro inserts
% causes processing to be prematurely terminated. This is,
% apparently, because \indexsorttmp is fully expanded, and \endinput
% is an expandable command. The redefinition below makes \endinput
% disappear altogether for that purpose -- although logging shows that
% processing continues to some further point. On the other hand, it
% seems \endinput does not hurt in the printed index arg, since that
% is still getting written without apparent harm.
%
% Sample source (mac-idx3.tex, reported by Graham Percival to
% help-texinfo, 22may06):
% @macro funindex {WORD}
% @findex xyz
% @end macro
% ...
% @funindex commtest
%
% The above is not enough to reproduce the bug, but it gives the flavor.
%
% Sample whatsit resulting:
% .@write3{\entry{xyz}{@folio }{@code {xyz@endinput }}}
%
% So:
\let\endinput = \empty
%
% Do the redefinitions.
\commondummies
}
% For the aux and toc files, @ is the escape character. So we want to
% redefine everything using @ as the escape character (instead of
% \realbackslash, still used for index files). When everything uses @,
% this will be simpler.
%
\def\atdummies{%
\def\@{@@}%
\def\ {@ }%
\let\{ = \lbraceatcmd
\let\} = \rbraceatcmd
%
% Do the redefinitions.
\commondummies
\otherbackslash
}
% Called from \indexdummies and \atdummies.
%
\def\commondummies{%
%
% \definedummyword defines \#1 as \string\#1\space, thus effectively
% preventing its expansion. This is used only for control words,
% not control letters, because the \space would be incorrect for
% control characters, but is needed to separate the control word
% from whatever follows.
%
% For control letters, we have \definedummyletter, which omits the
% space.
%
% These can be used both for control words that take an argument and
% those that do not. If it is followed by {arg} in the input, then
% that will dutifully get written to the index (or wherever).
%
\def\definedummyword ##1{\def##1{\string##1\space}}%
\def\definedummyletter##1{\def##1{\string##1}}%
\let\definedummyaccent\definedummyletter
%
\commondummiesnofonts
%
\definedummyletter\_%
\definedummyletter\-%
%
% Non-English letters.
\definedummyword\AA
\definedummyword\AE
\definedummyword\DH
\definedummyword\L
\definedummyword\O
\definedummyword\OE
\definedummyword\TH
\definedummyword\aa
\definedummyword\ae
\definedummyword\dh
\definedummyword\exclamdown
\definedummyword\l
\definedummyword\o
\definedummyword\oe
\definedummyword\ordf
\definedummyword\ordm
\definedummyword\questiondown
\definedummyword\ss
\definedummyword\th
%
% Although these internal commands shouldn't show up, sometimes they do.
\definedummyword\bf
\definedummyword\gtr
\definedummyword\hat
\definedummyword\less
\definedummyword\sf
\definedummyword\sl
\definedummyword\tclose
\definedummyword\tt
%
\definedummyword\LaTeX
\definedummyword\TeX
%
% Assorted special characters.
\definedummyword\arrow
\definedummyword\bullet
\definedummyword\comma
\definedummyword\copyright
\definedummyword\registeredsymbol
\definedummyword\dots
\definedummyword\enddots
\definedummyword\entrybreak
\definedummyword\equiv
\definedummyword\error
\definedummyword\euro
\definedummyword\expansion
\definedummyword\geq
\definedummyword\guillemetleft
\definedummyword\guillemetright
\definedummyword\guilsinglleft
\definedummyword\guilsinglright
\definedummyword\lbracechar
\definedummyword\leq
\definedummyword\minus
\definedummyword\ogonek
\definedummyword\pounds
\definedummyword\point
\definedummyword\print
\definedummyword\quotedblbase
\definedummyword\quotedblleft
\definedummyword\quotedblright
\definedummyword\quoteleft
\definedummyword\quoteright
\definedummyword\quotesinglbase
\definedummyword\rbracechar
\definedummyword\result
\definedummyword\textdegree
%
% We want to disable all macros so that they are not expanded by \write.
\macrolist
%
\normalturnoffactive
%
% Handle some cases of @value -- where it does not contain any
% (non-fully-expandable) commands.
\makevalueexpandable
}
% \commondummiesnofonts: common to \commondummies and \indexnofonts.
%
\def\commondummiesnofonts{%
% Control letters and accents.
\definedummyletter\!%
\definedummyaccent\"%
\definedummyaccent\'%
\definedummyletter\*%
\definedummyaccent\,%
\definedummyletter\.%
\definedummyletter\/%
\definedummyletter\:%
\definedummyaccent\=%
\definedummyletter\?%
\definedummyaccent\^%
\definedummyaccent\`%
\definedummyaccent\~%
\definedummyword\u
\definedummyword\v
\definedummyword\H
\definedummyword\dotaccent
\definedummyword\ogonek
\definedummyword\ringaccent
\definedummyword\tieaccent
\definedummyword\ubaraccent
\definedummyword\udotaccent
\definedummyword\dotless
%
% Texinfo font commands.
\definedummyword\b
\definedummyword\i
\definedummyword\r
\definedummyword\sansserif
\definedummyword\sc
\definedummyword\slanted
\definedummyword\t
%
% Commands that take arguments.
\definedummyword\abbr
\definedummyword\acronym
\definedummyword\anchor
\definedummyword\cite
\definedummyword\code
\definedummyword\command
\definedummyword\dfn
\definedummyword\dmn
\definedummyword\email
\definedummyword\emph
\definedummyword\env
\definedummyword\file
\definedummyword\image
\definedummyword\indicateurl
\definedummyword\inforef
\definedummyword\kbd
\definedummyword\key
\definedummyword\math
\definedummyword\option
\definedummyword\pxref
\definedummyword\ref
\definedummyword\samp
\definedummyword\strong
\definedummyword\tie
\definedummyword\uref
\definedummyword\url
\definedummyword\var
\definedummyword\verb
\definedummyword\w
\definedummyword\xref
}
% \indexnofonts is used when outputting the strings to sort the index
% by, and when constructing control sequence names. It eliminates all
% control sequences and just writes whatever the best ASCII sort string
% would be for a given command (usually its argument).
%
\def\indexnofonts{%
% Accent commands should become @asis.
\def\definedummyaccent##1{\let##1\asis}%
% We can just ignore other control letters.
\def\definedummyletter##1{\let##1\empty}%
% All control words become @asis by default; overrides below.
\let\definedummyword\definedummyaccent
%
\commondummiesnofonts
%
% Don't no-op \tt, since it isn't a user-level command
% and is used in the definitions of the active chars like <, >, |, etc.
% Likewise with the other plain tex font commands.
%\let\tt=\asis
%
\def\ { }%
\def\@{@}%
\def\_{\normalunderscore}%
\def\-{}% @- shouldn't affect sorting
%
% Unfortunately, texindex is not prepared to handle braces in the
% content at all. So for index sorting, we map @{ and @} to strings
% starting with |, since that ASCII character is between ASCII { and }.
\def\{{|a}%
\def\lbracechar{|a}%
%
\def\}{|b}%
\def\rbracechar{|b}%
%
% Non-English letters.
\def\AA{AA}%
\def\AE{AE}%
\def\DH{DZZ}%
\def\L{L}%
\def\OE{OE}%
\def\O{O}%
\def\TH{ZZZ}%
\def\aa{aa}%
\def\ae{ae}%
\def\dh{dzz}%
\def\exclamdown{!}%
\def\l{l}%
\def\oe{oe}%
\def\ordf{a}%
\def\ordm{o}%
\def\o{o}%
\def\questiondown{?}%
\def\ss{ss}%
\def\th{zzz}%
%
\def\LaTeX{LaTeX}%
\def\TeX{TeX}%
%
% Assorted special characters.
% (The following {} will end up in the sort string, but that's ok.)
\def\arrow{->}%
\def\bullet{bullet}%
\def\comma{,}%
\def\copyright{copyright}%
\def\dots{...}%
\def\enddots{...}%
\def\equiv{==}%
\def\error{error}%
\def\euro{euro}%
\def\expansion{==>}%
\def\geq{>=}%
\def\guillemetleft{<<}%
\def\guillemetright{>>}%
\def\guilsinglleft{<}%
\def\guilsinglright{>}%
\def\leq{<=}%
\def\minus{-}%
\def\point{.}%
\def\pounds{pounds}%
\def\print{-|}%
\def\quotedblbase{"}%
\def\quotedblleft{"}%
\def\quotedblright{"}%
\def\quoteleft{`}%
\def\quoteright{'}%
\def\quotesinglbase{,}%
\def\registeredsymbol{R}%
\def\result{=>}%
\def\textdegree{o}%
%
\expandafter\ifx\csname SETtxiindexlquoteignore\endcsname\relax
\else \indexlquoteignore \fi
%
% We need to get rid of all macros, leaving only the arguments (if present).
% Of course this is not nearly correct, but it is the best we can do for now.
% makeinfo does not expand macros in the argument to @deffn, which ends up
% writing an index entry, and texindex isn't prepared for an index sort entry
% that starts with \.
%
% Since macro invocations are followed by braces, we can just redefine them
% to take a single TeX argument. The case of a macro invocation that
% goes to end-of-line is not handled.
%
\macrolist
}
% Undocumented (for FSFS 2nd ed.): @set txiindexlquoteignore makes us
% ignore left quotes in the sort term.
{\catcode`\`=\active
\gdef\indexlquoteignore{\let`=\empty}}
\let\indexbackslash=0 %overridden during \printindex.
\let\SETmarginindex=\relax % put index entries in margin (undocumented)?
% Most index entries go through here, but \dosubind is the general case.
% #1 is the index name, #2 is the entry text.
\def\doind#1#2{\dosubind{#1}{#2}{}}
% Workhorse for all \fooindexes.
% #1 is name of index, #2 is stuff to put there, #3 is subentry --
% empty if called from \doind, as we usually are (the main exception
% is with most defuns, which call us directly).
%
\def\dosubind#1#2#3{%
\iflinks
{%
% Store the main index entry text (including the third arg).
\toks0 = {#2}%
% If third arg is present, precede it with a space.
\def\thirdarg{#3}%
\ifx\thirdarg\empty \else
\toks0 = \expandafter{\the\toks0 \space #3}%
\fi
%
\edef\writeto{\csname#1indfile\endcsname}%
%
\safewhatsit\dosubindwrite
}%
\fi
}
% Write the entry in \toks0 to the index file:
%
\def\dosubindwrite{%
% Put the index entry in the margin if desired.
\ifx\SETmarginindex\relax\else
\insert\margin{\hbox{\vrule height8pt depth3pt width0pt \the\toks0}}%
\fi
%
% Remember, we are within a group.
\indexdummies % Must do this here, since \bf, etc expand at this stage
\def\backslashcurfont{\indexbackslash}% \indexbackslash isn't defined now
% so it will be output as is; and it will print as backslash.
%
% Process the index entry with all font commands turned off, to
% get the string to sort by.
{\indexnofonts
\edef\temp{\the\toks0}% need full expansion
\xdef\indexsorttmp{\temp}%
}%
%
% Set up the complete index entry, with both the sort key and
% the original text, including any font commands. We write
% three arguments to \entry to the .?? file (four in the
% subentry case), texindex reduces to two when writing the .??s
% sorted result.
\edef\temp{%
\write\writeto{%
\string\entry{\indexsorttmp}{\noexpand\folio}{\the\toks0}}%
}%
\temp
}
% Take care of unwanted page breaks/skips around a whatsit:
%
% If a skip is the last thing on the list now, preserve it
% by backing up by \lastskip, doing the \write, then inserting
% the skip again. Otherwise, the whatsit generated by the
% \write or \pdfdest will make \lastskip zero. The result is that
% sequences like this:
% @end defun
% @tindex whatever
% @defun ...
% will have extra space inserted, because the \medbreak in the
% start of the @defun won't see the skip inserted by the @end of
% the previous defun.
%
% But don't do any of this if we're not in vertical mode. We
% don't want to do a \vskip and prematurely end a paragraph.
%
% Avoid page breaks due to these extra skips, too.
%
% But wait, there is a catch there:
% We'll have to check whether \lastskip is zero skip. \ifdim is not
% sufficient for this purpose, as it ignores stretch and shrink parts
% of the skip. The only way seems to be to check the textual
% representation of the skip.
%
% The following is almost like \def\zeroskipmacro{0.0pt} except that
% the ``p'' and ``t'' characters have catcode \other, not 11 (letter).
%
\edef\zeroskipmacro{\expandafter\the\csname z@skip\endcsname}
%
\newskip\whatsitskip
\newcount\whatsitpenalty
%
% ..., ready, GO:
%
\def\safewhatsit#1{\ifhmode
#1%
\else
% \lastskip and \lastpenalty cannot both be nonzero simultaneously.
\whatsitskip = \lastskip
\edef\lastskipmacro{\the\lastskip}%
\whatsitpenalty = \lastpenalty
%
% If \lastskip is nonzero, that means the last item was a
% skip. And since a skip is discardable, that means this
% -\whatsitskip glue we're inserting is preceded by a
% non-discardable item, therefore it is not a potential
% breakpoint, therefore no \nobreak needed.
\ifx\lastskipmacro\zeroskipmacro
\else
\vskip-\whatsitskip
\fi
%
#1%
%
\ifx\lastskipmacro\zeroskipmacro
% If \lastskip was zero, perhaps the last item was a penalty, and
% perhaps it was >=10000, e.g., a \nobreak. In that case, we want
% to re-insert the same penalty (values >10000 are used for various
% signals); since we just inserted a non-discardable item, any
% following glue (such as a \parskip) would be a breakpoint. For example:
% @deffn deffn-whatever
% @vindex index-whatever
% Description.
% would allow a break between the index-whatever whatsit
% and the "Description." paragraph.
\ifnum\whatsitpenalty>9999 \penalty\whatsitpenalty \fi
\else
% On the other hand, if we had a nonzero \lastskip,
% this make-up glue would be preceded by a non-discardable item
% (the whatsit from the \write), so we must insert a \nobreak.
\nobreak\vskip\whatsitskip
\fi
\fi}
% The index entry written in the file actually looks like
% \entry {sortstring}{page}{topic}
% or
% \entry {sortstring}{page}{topic}{subtopic}
% The texindex program reads in these files and writes files
% containing these kinds of lines:
% \initial {c}
% before the first topic whose initial is c
% \entry {topic}{pagelist}
% for a topic that is used without subtopics
% \primary {topic}
% for the beginning of a topic that is used with subtopics
% \secondary {subtopic}{pagelist}
% for each subtopic.
% Define the user-accessible indexing commands
% @findex, @vindex, @kindex, @cindex.
\def\findex {\fnindex}
\def\kindex {\kyindex}
\def\cindex {\cpindex}
\def\vindex {\vrindex}
\def\tindex {\tpindex}
\def\pindex {\pgindex}
\def\cindexsub {\begingroup\obeylines\cindexsub}
{\obeylines %
\gdef\cindexsub "#1" #2^^M{\endgroup %
\dosubind{cp}{#2}{#1}}}
% Define the macros used in formatting output of the sorted index material.
% @printindex causes a particular index (the ??s file) to get printed.
% It does not print any chapter heading (usually an @unnumbered).
%
\parseargdef\printindex{\begingroup
\dobreak \chapheadingskip{10000}%
%
\smallfonts \rm
\tolerance = 9500
\plainfrenchspacing
\everypar = {}% don't want the \kern\-parindent from indentation suppression.
%
% See if the index file exists and is nonempty.
% Change catcode of @ here so that if the index file contains
% \initial {@}
% as its first line, TeX doesn't complain about mismatched braces
% (because it thinks @} is a control sequence).
\catcode`\@ = 11
\openin 1 \jobname.#1s
\ifeof 1
% \enddoublecolumns gets confused if there is no text in the index,
% and it loses the chapter title and the aux file entries for the
% index. The easiest way to prevent this problem is to make sure
% there is some text.
\putwordIndexNonexistent
\else
%
% If the index file exists but is empty, then \openin leaves \ifeof
% false. We have to make TeX try to read something from the file, so
% it can discover if there is anything in it.
\read 1 to \temp
\ifeof 1
\putwordIndexIsEmpty
\else
% Index files are almost Texinfo source, but we use \ as the escape
% character. It would be better to use @, but that's too big a change
% to make right now.
\def\indexbackslash{\backslashcurfont}%
\catcode`\\ = 0
\escapechar = `\\
\begindoublecolumns
\input \jobname.#1s
\enddoublecolumns
\fi
\fi
\closein 1
\endgroup}
% These macros are used by the sorted index file itself.
% Change them to control the appearance of the index.
\def\initial#1{{%
% Some minor font changes for the special characters.
\let\tentt=\sectt \let\tt=\sectt \let\sf=\sectt
%
% Remove any glue we may have, we'll be inserting our own.
\removelastskip
%
% We like breaks before the index initials, so insert a bonus.
\nobreak
\vskip 0pt plus 3\baselineskip
\penalty 0
\vskip 0pt plus -3\baselineskip
%
% Typeset the initial. Making this add up to a whole number of
% baselineskips increases the chance of the dots lining up from column
% to column. It still won't often be perfect, because of the stretch
% we need before each entry, but it's better.
%
% No shrink because it confuses \balancecolumns.
\vskip 1.67\baselineskip plus .5\baselineskip
\leftline{\secbf #1}%
% Do our best not to break after the initial.
\nobreak
\vskip .33\baselineskip plus .1\baselineskip
}}
% \entry typesets a paragraph consisting of the text (#1), dot leaders, and
% then page number (#2) flushed to the right margin. It is used for index
% and table of contents entries. The paragraph is indented by \leftskip.
%
% A straightforward implementation would start like this:
% \def\entry#1#2{...
% But this freezes the catcodes in the argument, and can cause problems to
% @code, which sets - active. This problem was fixed by a kludge---
% ``-'' was active throughout whole index, but this isn't really right.
% The right solution is to prevent \entry from swallowing the whole text.
% --kasal, 21nov03
\def\entry{%
\begingroup
%
% Start a new paragraph if necessary, so our assignments below can't
% affect previous text.
\par
%
% Do not fill out the last line with white space.
\parfillskip = 0in
%
% No extra space above this paragraph.
\parskip = 0in
%
% Do not prefer a separate line ending with a hyphen to fewer lines.
\finalhyphendemerits = 0
%
% \hangindent is only relevant when the entry text and page number
% don't both fit on one line. In that case, bob suggests starting the
% dots pretty far over on the line. Unfortunately, a large
% indentation looks wrong when the entry text itself is broken across
% lines. So we use a small indentation and put up with long leaders.
%
% \hangafter is reset to 1 (which is the value we want) at the start
% of each paragraph, so we need not do anything with that.
\hangindent = 2em
%
% When the entry text needs to be broken, just fill out the first line
% with blank space.
\rightskip = 0pt plus1fil
%
% A bit of stretch before each entry for the benefit of balancing
% columns.
\vskip 0pt plus1pt
%
% When reading the text of entry, convert explicit line breaks
% from @* into spaces. The user might give these in long section
% titles, for instance.
\def\*{\unskip\space\ignorespaces}%
\def\entrybreak{\hfil\break}%
%
% Swallow the left brace of the text (first parameter):
\afterassignment\doentry
\let\temp =
}
\def\entrybreak{\unskip\space\ignorespaces}%
\def\doentry{%
\bgroup % Instead of the swallowed brace.
\noindent
\aftergroup\finishentry
% And now comes the text of the entry.
}
\def\finishentry#1{%
% #1 is the page number.
%
% The following is kludged to not output a line of dots in the index if
% there are no page numbers. The next person who breaks this will be
% cursed by a Unix daemon.
\setbox\boxA = \hbox{#1}%
\ifdim\wd\boxA = 0pt
\ %
\else
%
% If we must, put the page number on a line of its own, and fill out
% this line with blank space. (The \hfil is overwhelmed with the
% fill leaders glue in \indexdotfill if the page number does fit.)
\hfil\penalty50
\null\nobreak\indexdotfill % Have leaders before the page number.
%
% The `\ ' here is removed by the implicit \unskip that TeX does as
% part of (the primitive) \par. Without it, a spurious underfull
% \hbox ensues.
\ifpdf
\pdfgettoks#1.%
\ \the\toksA
\else
\ #1%
\fi
\fi
\par
\endgroup
}
% Like plain.tex's \dotfill, except uses up at least 1 em.
\def\indexdotfill{\cleaders
\hbox{$\mathsurround=0pt \mkern1.5mu.\mkern1.5mu$}\hskip 1em plus 1fill}
\def\primary #1{\line{#1\hfil}}
\newskip\secondaryindent \secondaryindent=0.5cm
\def\secondary#1#2{{%
\parfillskip=0in
\parskip=0in
\hangindent=1in
\hangafter=1
\noindent\hskip\secondaryindent\hbox{#1}\indexdotfill
\ifpdf
\pdfgettoks#2.\ \the\toksA % The page number ends the paragraph.
\else
#2
\fi
\par
}}
% Define two-column mode, which we use to typeset indexes.
% Adapted from the TeXbook, page 416, which is to say,
% the manmac.tex format used to print the TeXbook itself.
\catcode`\@=11
\newbox\partialpage
\newdimen\doublecolumnhsize
\def\begindoublecolumns{\begingroup % ended by \enddoublecolumns
% Grab any single-column material above us.
\output = {%
%
% Here is a possibility not foreseen in manmac: if we accumulate a
% whole lot of material, we might end up calling this \output
% routine twice in a row (see the doublecol-lose test, which is
% essentially a couple of indexes with @setchapternewpage off). In
% that case we just ship out what is in \partialpage with the normal
% output routine. Generally, \partialpage will be empty when this
% runs and this will be a no-op. See the indexspread.tex test case.
\ifvoid\partialpage \else
\onepageout{\pagecontents\partialpage}%
\fi
%
\global\setbox\partialpage = \vbox{%
% Unvbox the main output page.
\unvbox\PAGE
\kern-\topskip \kern\baselineskip
}%
}%
\eject % run that output routine to set \partialpage
%
% Use the double-column output routine for subsequent pages.
\output = {\doublecolumnout}%
%
% Change the page size parameters. We could do this once outside this
% routine, in each of @smallbook, @afourpaper, and the default 8.5x11
% format, but then we repeat the same computation. Repeating a couple
% of assignments once per index is clearly meaningless for the
% execution time, so we may as well do it in one place.
%
% First we halve the line length, less a little for the gutter between
% the columns. We compute the gutter based on the line length, so it
% changes automatically with the paper format. The magic constant
% below is chosen so that the gutter has the same value (well, +-<1pt)
% as it did when we hard-coded it.
%
% We put the result in a separate register, \doublecolumhsize, so we
% can restore it in \pagesofar, after \hsize itself has (potentially)
% been clobbered.
%
\doublecolumnhsize = \hsize
\advance\doublecolumnhsize by -.04154\hsize
\divide\doublecolumnhsize by 2
\hsize = \doublecolumnhsize
%
% Double the \vsize as well. (We don't need a separate register here,
% since nobody clobbers \vsize.)
\vsize = 2\vsize
}
% The double-column output routine for all double-column pages except
% the last.
%
\def\doublecolumnout{%
\splittopskip=\topskip \splitmaxdepth=\maxdepth
% Get the available space for the double columns -- the normal
% (undoubled) page height minus any material left over from the
% previous page.
\dimen@ = \vsize
\divide\dimen@ by 2
\advance\dimen@ by -\ht\partialpage
%
% box0 will be the left-hand column, box2 the right.
\setbox0=\vsplit255 to\dimen@ \setbox2=\vsplit255 to\dimen@
\onepageout\pagesofar
\unvbox255
\penalty\outputpenalty
}
%
% Re-output the contents of the output page -- any previous material,
% followed by the two boxes we just split, in box0 and box2.
\def\pagesofar{%
\unvbox\partialpage
%
\hsize = \doublecolumnhsize
\wd0=\hsize \wd2=\hsize
\hbox to\pagewidth{\box0\hfil\box2}%
}
%
% All done with double columns.
\def\enddoublecolumns{%
% The following penalty ensures that the page builder is exercised
% _before_ we change the output routine. This is necessary in the
% following situation:
%
% The last section of the index consists only of a single entry.
% Before this section, \pagetotal is less than \pagegoal, so no
% break occurs before the last section starts. However, the last
% section, consisting of \initial and the single \entry, does not
% fit on the page and has to be broken off. Without the following
% penalty the page builder will not be exercised until \eject
% below, and by that time we'll already have changed the output
% routine to the \balancecolumns version, so the next-to-last
% double-column page will be processed with \balancecolumns, which
% is wrong: The two columns will go to the main vertical list, with
% the broken-off section in the recent contributions. As soon as
% the output routine finishes, TeX starts reconsidering the page
% break. The two columns and the broken-off section both fit on the
% page, because the two columns now take up only half of the page
% goal. When TeX sees \eject from below which follows the final
% section, it invokes the new output routine that we've set after
% \balancecolumns below; \onepageout will try to fit the two columns
% and the final section into the vbox of \pageheight (see
% \pagebody), causing an overfull box.
%
% Note that glue won't work here, because glue does not exercise the
% page builder, unlike penalties (see The TeXbook, pp. 280-281).
\penalty0
%
\output = {%
% Split the last of the double-column material. Leave it on the
% current page, no automatic page break.
\balancecolumns
%
% If we end up splitting too much material for the current page,
% though, there will be another page break right after this \output
% invocation ends. Having called \balancecolumns once, we do not
% want to call it again. Therefore, reset \output to its normal
% definition right away. (We hope \balancecolumns will never be
% called on to balance too much material, but if it is, this makes
% the output somewhat more palatable.)
\global\output = {\onepageout{\pagecontents\PAGE}}%
}%
\eject
\endgroup % started in \begindoublecolumns
%
% \pagegoal was set to the doubled \vsize above, since we restarted
% the current page. We're now back to normal single-column
% typesetting, so reset \pagegoal to the normal \vsize (after the
% \endgroup where \vsize got restored).
\pagegoal = \vsize
}
%
% Called at the end of the double column material.
\def\balancecolumns{%
\setbox0 = \vbox{\unvbox255}% like \box255 but more efficient, see p.120.
\dimen@ = \ht0
\advance\dimen@ by \topskip
\advance\dimen@ by-\baselineskip
\divide\dimen@ by 2 % target to split to
%debug\message{final 2-column material height=\the\ht0, target=\the\dimen@.}%
\splittopskip = \topskip
% Loop until we get a decent breakpoint.
{%
\vbadness = 10000
\loop
\global\setbox3 = \copy0
\global\setbox1 = \vsplit3 to \dimen@
\ifdim\ht3>\dimen@
\global\advance\dimen@ by 1pt
\repeat
}%
%debug\message{split to \the\dimen@, column heights: \the\ht1, \the\ht3.}%
\setbox0=\vbox to\dimen@{\unvbox1}%
\setbox2=\vbox to\dimen@{\unvbox3}%
%
\pagesofar
}
\catcode`\@ = \other
\message{sectioning,}
% Chapters, sections, etc.
% Let's start with @part.
\outer\parseargdef\part{\partzzz{#1}}
\def\partzzz#1{%
\chapoddpage
\null
\vskip.3\vsize % move it down on the page a bit
\begingroup
\noindent \titlefonts\rmisbold #1\par % the text
\let\lastnode=\empty % no node to associate with
\writetocentry{part}{#1}{}% but put it in the toc
\headingsoff % no headline or footline on the part page
\chapoddpage
\endgroup
}
% \unnumberedno is an oxymoron. But we count the unnumbered
% sections so that we can refer to them unambiguously in the pdf
% outlines by their "section number". We avoid collisions with chapter
% numbers by starting them at 10000. (If a document ever has 10000
% chapters, we're in trouble anyway, I'm sure.)
\newcount\unnumberedno \unnumberedno = 10000
\newcount\chapno
\newcount\secno \secno=0
\newcount\subsecno \subsecno=0
\newcount\subsubsecno \subsubsecno=0
% This counter is funny since it counts through charcodes of letters A, B, ...
\newcount\appendixno \appendixno = `\@
%
% \def\appendixletter{\char\the\appendixno}
% We do the following ugly conditional instead of the above simple
% construct for the sake of pdftex, which needs the actual
% letter in the expansion, not just typeset.
%
\def\appendixletter{%
\ifnum\appendixno=`A A%
\else\ifnum\appendixno=`B B%
\else\ifnum\appendixno=`C C%
\else\ifnum\appendixno=`D D%
\else\ifnum\appendixno=`E E%
\else\ifnum\appendixno=`F F%
\else\ifnum\appendixno=`G G%
\else\ifnum\appendixno=`H H%
\else\ifnum\appendixno=`I I%
\else\ifnum\appendixno=`J J%
\else\ifnum\appendixno=`K K%
\else\ifnum\appendixno=`L L%
\else\ifnum\appendixno=`M M%
\else\ifnum\appendixno=`N N%
\else\ifnum\appendixno=`O O%
\else\ifnum\appendixno=`P P%
\else\ifnum\appendixno=`Q Q%
\else\ifnum\appendixno=`R R%
\else\ifnum\appendixno=`S S%
\else\ifnum\appendixno=`T T%
\else\ifnum\appendixno=`U U%
\else\ifnum\appendixno=`V V%
\else\ifnum\appendixno=`W W%
\else\ifnum\appendixno=`X X%
\else\ifnum\appendixno=`Y Y%
\else\ifnum\appendixno=`Z Z%
% The \the is necessary, despite appearances, because \appendixletter is
% expanded while writing the .toc file. \char\appendixno is not
% expandable, thus it is written literally, thus all appendixes come out
% with the same letter (or @) in the toc without it.
\else\char\the\appendixno
\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi
\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi}
% Each @chapter defines these (using marks) as the number+name, number
% and name of the chapter. Page headings and footings can use
% these. @section does likewise.
\def\thischapter{}
\def\thischapternum{}
\def\thischaptername{}
\def\thissection{}
\def\thissectionnum{}
\def\thissectionname{}
\newcount\absseclevel % used to calculate proper heading level
\newcount\secbase\secbase=0 % @raisesections/@lowersections modify this count
% @raisesections: treat @section as chapter, @subsection as section, etc.
\def\raisesections{\global\advance\secbase by -1}
\let\up=\raisesections % original BFox name
% @lowersections: treat @chapter as section, @section as subsection, etc.
\def\lowersections{\global\advance\secbase by 1}
\let\down=\lowersections % original BFox name
% we only have subsub.
\chardef\maxseclevel = 3
%
% A numbered section within an unnumbered changes to unnumbered too.
% To achieve this, remember the "biggest" unnum. sec. we are currently in:
\chardef\unnlevel = \maxseclevel
%
% Trace whether the current chapter is an appendix or not:
% \chapheadtype is "N" or "A", unnumbered chapters are ignored.
\def\chapheadtype{N}
% Choose a heading macro
% #1 is heading type
% #2 is heading level
% #3 is text for heading
\def\genhead#1#2#3{%
% Compute the abs. sec. level:
\absseclevel=#2
\advance\absseclevel by \secbase
% Make sure \absseclevel doesn't fall outside the range:
\ifnum \absseclevel < 0
\absseclevel = 0
\else
\ifnum \absseclevel > 3
\absseclevel = 3
\fi
\fi
% The heading type:
\def\headtype{#1}%
\if \headtype U%
\ifnum \absseclevel < \unnlevel
\chardef\unnlevel = \absseclevel
\fi
\else
% Check for appendix sections:
\ifnum \absseclevel = 0
\edef\chapheadtype{\headtype}%
\else
\if \headtype A\if \chapheadtype N%
\errmessage{@appendix... within a non-appendix chapter}%
\fi\fi
\fi
% Check for numbered within unnumbered:
\ifnum \absseclevel > \unnlevel
\def\headtype{U}%
\else
\chardef\unnlevel = 3
\fi
\fi
% Now print the heading:
\if \headtype U%
\ifcase\absseclevel
\unnumberedzzz{#3}%
\or \unnumberedseczzz{#3}%
\or \unnumberedsubseczzz{#3}%
\or \unnumberedsubsubseczzz{#3}%
\fi
\else
\if \headtype A%
\ifcase\absseclevel
\appendixzzz{#3}%
\or \appendixsectionzzz{#3}%
\or \appendixsubseczzz{#3}%
\or \appendixsubsubseczzz{#3}%
\fi
\else
\ifcase\absseclevel
\chapterzzz{#3}%
\or \seczzz{#3}%
\or \numberedsubseczzz{#3}%
\or \numberedsubsubseczzz{#3}%
\fi
\fi
\fi
\suppressfirstparagraphindent
}
% an interface:
\def\numhead{\genhead N}
\def\apphead{\genhead A}
\def\unnmhead{\genhead U}
% @chapter, @appendix, @unnumbered. Increment top-level counter, reset
% all lower-level sectioning counters to zero.
%
% Also set \chaplevelprefix, which we prepend to @float sequence numbers
% (e.g., figures), q.v. By default (before any chapter), that is empty.
\let\chaplevelprefix = \empty
%
\outer\parseargdef\chapter{\numhead0{#1}} % normally numhead0 calls chapterzzz
\def\chapterzzz#1{%
% section resetting is \global in case the chapter is in a group, such
% as an @include file.
\global\secno=0 \global\subsecno=0 \global\subsubsecno=0
\global\advance\chapno by 1
%
% Used for \float.
\gdef\chaplevelprefix{\the\chapno.}%
\resetallfloatnos
%
% \putwordChapter can contain complex things in translations.
\toks0=\expandafter{\putwordChapter}%
\message{\the\toks0 \space \the\chapno}%
%
% Write the actual heading.
\chapmacro{#1}{Ynumbered}{\the\chapno}%
%
% So @section and the like are numbered underneath this chapter.
\global\let\section = \numberedsec
\global\let\subsection = \numberedsubsec
\global\let\subsubsection = \numberedsubsubsec
}
\outer\parseargdef\appendix{\apphead0{#1}} % normally calls appendixzzz
%
\def\appendixzzz#1{%
\global\secno=0 \global\subsecno=0 \global\subsubsecno=0
\global\advance\appendixno by 1
\gdef\chaplevelprefix{\appendixletter.}%
\resetallfloatnos
%
% \putwordAppendix can contain complex things in translations.
\toks0=\expandafter{\putwordAppendix}%
\message{\the\toks0 \space \appendixletter}%
%
\chapmacro{#1}{Yappendix}{\appendixletter}%
%
\global\let\section = \appendixsec
\global\let\subsection = \appendixsubsec
\global\let\subsubsection = \appendixsubsubsec
}
% normally unnmhead0 calls unnumberedzzz:
\outer\parseargdef\unnumbered{\unnmhead0{#1}}
\def\unnumberedzzz#1{%
\global\secno=0 \global\subsecno=0 \global\subsubsecno=0
\global\advance\unnumberedno by 1
%
% Since an unnumbered has no number, no prefix for figures.
\global\let\chaplevelprefix = \empty
\resetallfloatnos
%
% This used to be simply \message{#1}, but TeX fully expands the
% argument to \message. Therefore, if #1 contained @-commands, TeX
% expanded them. For example, in `@unnumbered The @cite{Book}', TeX
% expanded @cite (which turns out to cause errors because \cite is meant
% to be executed, not expanded).
%
% Anyway, we don't want the fully-expanded definition of @cite to appear
% as a result of the \message, we just want `@cite' itself. We use
% \the to achieve this: TeX expands \the only once,
% simply yielding the contents of . (We also do this for
% the toc entries.)
\toks0 = {#1}%
\message{(\the\toks0)}%
%
\chapmacro{#1}{Ynothing}{\the\unnumberedno}%
%
\global\let\section = \unnumberedsec
\global\let\subsection = \unnumberedsubsec
\global\let\subsubsection = \unnumberedsubsubsec
}
% @centerchap is like @unnumbered, but the heading is centered.
\outer\parseargdef\centerchap{%
% Well, we could do the following in a group, but that would break
% an assumption that \chapmacro is called at the outermost level.
% Thus we are safer this way: --kasal, 24feb04
\let\centerparametersmaybe = \centerparameters
\unnmhead0{#1}%
\let\centerparametersmaybe = \relax
}
% @top is like @unnumbered.
\let\top\unnumbered
% Sections.
%
\outer\parseargdef\numberedsec{\numhead1{#1}} % normally calls seczzz
\def\seczzz#1{%
\global\subsecno=0 \global\subsubsecno=0 \global\advance\secno by 1
\sectionheading{#1}{sec}{Ynumbered}{\the\chapno.\the\secno}%
}
% normally calls appendixsectionzzz:
\outer\parseargdef\appendixsection{\apphead1{#1}}
\def\appendixsectionzzz#1{%
\global\subsecno=0 \global\subsubsecno=0 \global\advance\secno by 1
\sectionheading{#1}{sec}{Yappendix}{\appendixletter.\the\secno}%
}
\let\appendixsec\appendixsection
% normally calls unnumberedseczzz:
\outer\parseargdef\unnumberedsec{\unnmhead1{#1}}
\def\unnumberedseczzz#1{%
\global\subsecno=0 \global\subsubsecno=0 \global\advance\secno by 1
\sectionheading{#1}{sec}{Ynothing}{\the\unnumberedno.\the\secno}%
}
% Subsections.
%
% normally calls numberedsubseczzz:
\outer\parseargdef\numberedsubsec{\numhead2{#1}}
\def\numberedsubseczzz#1{%
\global\subsubsecno=0 \global\advance\subsecno by 1
\sectionheading{#1}{subsec}{Ynumbered}{\the\chapno.\the\secno.\the\subsecno}%
}
% normally calls appendixsubseczzz:
\outer\parseargdef\appendixsubsec{\apphead2{#1}}
\def\appendixsubseczzz#1{%
\global\subsubsecno=0 \global\advance\subsecno by 1
\sectionheading{#1}{subsec}{Yappendix}%
{\appendixletter.\the\secno.\the\subsecno}%
}
% normally calls unnumberedsubseczzz:
\outer\parseargdef\unnumberedsubsec{\unnmhead2{#1}}
\def\unnumberedsubseczzz#1{%
\global\subsubsecno=0 \global\advance\subsecno by 1
\sectionheading{#1}{subsec}{Ynothing}%
{\the\unnumberedno.\the\secno.\the\subsecno}%
}
% Subsubsections.
%
% normally numberedsubsubseczzz:
\outer\parseargdef\numberedsubsubsec{\numhead3{#1}}
\def\numberedsubsubseczzz#1{%
\global\advance\subsubsecno by 1
\sectionheading{#1}{subsubsec}{Ynumbered}%
{\the\chapno.\the\secno.\the\subsecno.\the\subsubsecno}%
}
% normally appendixsubsubseczzz:
\outer\parseargdef\appendixsubsubsec{\apphead3{#1}}
\def\appendixsubsubseczzz#1{%
\global\advance\subsubsecno by 1
\sectionheading{#1}{subsubsec}{Yappendix}%
{\appendixletter.\the\secno.\the\subsecno.\the\subsubsecno}%
}
% normally unnumberedsubsubseczzz:
\outer\parseargdef\unnumberedsubsubsec{\unnmhead3{#1}}
\def\unnumberedsubsubseczzz#1{%
\global\advance\subsubsecno by 1
\sectionheading{#1}{subsubsec}{Ynothing}%
{\the\unnumberedno.\the\secno.\the\subsecno.\the\subsubsecno}%
}
% These macros control what the section commands do, according
% to what kind of chapter we are in (ordinary, appendix, or unnumbered).
% Define them by default for a numbered chapter.
\let\section = \numberedsec
\let\subsection = \numberedsubsec
\let\subsubsection = \numberedsubsubsec
% Define @majorheading, @heading and @subheading
\def\majorheading{%
{\advance\chapheadingskip by 10pt \chapbreak }%
\parsearg\chapheadingzzz
}
\def\chapheading{\chapbreak \parsearg\chapheadingzzz}
\def\chapheadingzzz#1{%
\vbox{\chapfonts \raggedtitlesettings #1\par}%
\nobreak\bigskip \nobreak
\suppressfirstparagraphindent
}
% @heading, @subheading, @subsubheading.
\parseargdef\heading{\sectionheading{#1}{sec}{Yomitfromtoc}{}
\suppressfirstparagraphindent}
\parseargdef\subheading{\sectionheading{#1}{subsec}{Yomitfromtoc}{}
\suppressfirstparagraphindent}
\parseargdef\subsubheading{\sectionheading{#1}{subsubsec}{Yomitfromtoc}{}
\suppressfirstparagraphindent}
% These macros generate a chapter, section, etc. heading only
% (including whitespace, linebreaking, etc. around it),
% given all the information in convenient, parsed form.
% Args are the skip and penalty (usually negative)
\def\dobreak#1#2{\par\ifdim\lastskip<#1\removelastskip\penalty#2\vskip#1\fi}
% Parameter controlling skip before chapter headings (if needed)
\newskip\chapheadingskip
% Define plain chapter starts, and page on/off switching for it.
\def\chapbreak{\dobreak \chapheadingskip {-4000}}
\def\chappager{\par\vfill\supereject}
% Because \domark is called before \chapoddpage, the filler page will
% get the headings for the next chapter, which is wrong. But we don't
% care -- we just disable all headings on the filler page.
\def\chapoddpage{%
\chappager
\ifodd\pageno \else
\begingroup
\headingsoff
\null
\chappager
\endgroup
\fi
}
\def\setchapternewpage #1 {\csname CHAPPAG#1\endcsname}
\def\CHAPPAGoff{%
\global\let\contentsalignmacro = \chappager
\global\let\pchapsepmacro=\chapbreak
\global\let\pagealignmacro=\chappager}
\def\CHAPPAGon{%
\global\let\contentsalignmacro = \chappager
\global\let\pchapsepmacro=\chappager
\global\let\pagealignmacro=\chappager
\global\def\HEADINGSon{\HEADINGSsingle}}
\def\CHAPPAGodd{%
\global\let\contentsalignmacro = \chapoddpage
\global\let\pchapsepmacro=\chapoddpage
\global\let\pagealignmacro=\chapoddpage
\global\def\HEADINGSon{\HEADINGSdouble}}
\CHAPPAGon
% Chapter opening.
%
% #1 is the text, #2 is the section type (Ynumbered, Ynothing,
% Yappendix, Yomitfromtoc), #3 the chapter number.
%
% To test against our argument.
\def\Ynothingkeyword{Ynothing}
\def\Yomitfromtockeyword{Yomitfromtoc}
\def\Yappendixkeyword{Yappendix}
%
\def\chapmacro#1#2#3{%
% Insert the first mark before the heading break (see notes for \domark).
\let\prevchapterdefs=\lastchapterdefs
\let\prevsectiondefs=\lastsectiondefs
\gdef\lastsectiondefs{\gdef\thissectionname{}\gdef\thissectionnum{}%
\gdef\thissection{}}%
%
\def\temptype{#2}%
\ifx\temptype\Ynothingkeyword
\gdef\lastchapterdefs{\gdef\thischaptername{#1}\gdef\thischapternum{}%
\gdef\thischapter{\thischaptername}}%
\else\ifx\temptype\Yomitfromtockeyword
\gdef\lastchapterdefs{\gdef\thischaptername{#1}\gdef\thischapternum{}%
\gdef\thischapter{}}%
\else\ifx\temptype\Yappendixkeyword
\toks0={#1}%
\xdef\lastchapterdefs{%
\gdef\noexpand\thischaptername{\the\toks0}%
\gdef\noexpand\thischapternum{\appendixletter}%
% \noexpand\putwordAppendix avoids expanding indigestible
% commands in some of the translations.
\gdef\noexpand\thischapter{\noexpand\putwordAppendix{}
\noexpand\thischapternum:
\noexpand\thischaptername}%
}%
\else
\toks0={#1}%
\xdef\lastchapterdefs{%
\gdef\noexpand\thischaptername{\the\toks0}%
\gdef\noexpand\thischapternum{\the\chapno}%
% \noexpand\putwordChapter avoids expanding indigestible
% commands in some of the translations.
\gdef\noexpand\thischapter{\noexpand\putwordChapter{}
\noexpand\thischapternum:
\noexpand\thischaptername}%
}%
\fi\fi\fi
%
% Output the mark. Pass it through \safewhatsit, to take care of
% the preceding space.
\safewhatsit\domark
%
% Insert the chapter heading break.
\pchapsepmacro
%
% Now the second mark, after the heading break. No break points
% between here and the heading.
\let\prevchapterdefs=\lastchapterdefs
\let\prevsectiondefs=\lastsectiondefs
\domark
%
{%
\chapfonts \rmisbold
%
% Have to define \lastsection before calling \donoderef, because the
% xref code eventually uses it. On the other hand, it has to be called
% after \pchapsepmacro, or the headline will change too soon.
\gdef\lastsection{#1}%
%
% Only insert the separating space if we have a chapter/appendix
% number, and don't print the unnumbered ``number''.
\ifx\temptype\Ynothingkeyword
\setbox0 = \hbox{}%
\def\toctype{unnchap}%
\else\ifx\temptype\Yomitfromtockeyword
\setbox0 = \hbox{}% contents like unnumbered, but no toc entry
\def\toctype{omit}%
\else\ifx\temptype\Yappendixkeyword
\setbox0 = \hbox{\putwordAppendix{} #3\enspace}%
\def\toctype{app}%
\else
\setbox0 = \hbox{#3\enspace}%
\def\toctype{numchap}%
\fi\fi\fi
%
% Write the toc entry for this chapter. Must come before the
% \donoderef, because we include the current node name in the toc
% entry, and \donoderef resets it to empty.
\writetocentry{\toctype}{#1}{#3}%
%
% For pdftex, we have to write out the node definition (aka, make
% the pdfdest) after any page break, but before the actual text has
% been typeset. If the destination for the pdf outline is after the
% text, then jumping from the outline may wind up with the text not
% being visible, for instance under high magnification.
\donoderef{#2}%
%
% Typeset the actual heading.
\nobreak % Avoid page breaks at the interline glue.
\vbox{\raggedtitlesettings \hangindent=\wd0 \centerparametersmaybe
\unhbox0 #1\par}%
}%
\nobreak\bigskip % no page break after a chapter title
\nobreak
}
% @centerchap -- centered and unnumbered.
\let\centerparametersmaybe = \relax
\def\centerparameters{%
\advance\rightskip by 3\rightskip
\leftskip = \rightskip
\parfillskip = 0pt
}
% I don't think this chapter style is supported any more, so I'm not
% updating it with the new noderef stuff. We'll see. --karl, 11aug03.
%
\def\setchapterstyle #1 {\csname CHAPF#1\endcsname}
%
\def\unnchfopen #1{%
\chapoddpage
\vbox{\chapfonts \raggedtitlesettings #1\par}%
\nobreak\bigskip\nobreak
}
\def\chfopen #1#2{\chapoddpage {\chapfonts
\vbox to 3in{\vfil \hbox to\hsize{\hfil #2} \hbox to\hsize{\hfil #1} \vfil}}%
\par\penalty 5000 %
}
\def\centerchfopen #1{%
\chapoddpage
\vbox{\chapfonts \raggedtitlesettings \hfill #1\hfill}%
\nobreak\bigskip \nobreak
}
\def\CHAPFopen{%
\global\let\chapmacro=\chfopen
\global\let\centerchapmacro=\centerchfopen}
% Section titles. These macros combine the section number parts and
% call the generic \sectionheading to do the printing.
%
\newskip\secheadingskip
\def\secheadingbreak{\dobreak \secheadingskip{-1000}}
% Subsection titles.
\newskip\subsecheadingskip
\def\subsecheadingbreak{\dobreak \subsecheadingskip{-500}}
% Subsubsection titles.
\def\subsubsecheadingskip{\subsecheadingskip}
\def\subsubsecheadingbreak{\subsecheadingbreak}
% Print any size, any type, section title.
%
% #1 is the text, #2 is the section level (sec/subsec/subsubsec), #3 is
% the section type for xrefs (Ynumbered, Ynothing, Yappendix), #4 is the
% section number.
%
\def\seckeyword{sec}
%
\def\sectionheading#1#2#3#4{%
{%
\checkenv{}% should not be in an environment.
%
% Switch to the right set of fonts.
\csname #2fonts\endcsname \rmisbold
%
\def\sectionlevel{#2}%
\def\temptype{#3}%
%
% Insert first mark before the heading break (see notes for \domark).
\let\prevsectiondefs=\lastsectiondefs
\ifx\temptype\Ynothingkeyword
\ifx\sectionlevel\seckeyword
\gdef\lastsectiondefs{\gdef\thissectionname{#1}\gdef\thissectionnum{}%
\gdef\thissection{\thissectionname}}%
\fi
\else\ifx\temptype\Yomitfromtockeyword
% Don't redefine \thissection.
\else\ifx\temptype\Yappendixkeyword
\ifx\sectionlevel\seckeyword
\toks0={#1}%
\xdef\lastsectiondefs{%
\gdef\noexpand\thissectionname{\the\toks0}%
\gdef\noexpand\thissectionnum{#4}%
% \noexpand\putwordSection avoids expanding indigestible
% commands in some of the translations.
\gdef\noexpand\thissection{\noexpand\putwordSection{}
\noexpand\thissectionnum:
\noexpand\thissectionname}%
}%
\fi
\else
\ifx\sectionlevel\seckeyword
\toks0={#1}%
\xdef\lastsectiondefs{%
\gdef\noexpand\thissectionname{\the\toks0}%
\gdef\noexpand\thissectionnum{#4}%
% \noexpand\putwordSection avoids expanding indigestible
% commands in some of the translations.
\gdef\noexpand\thissection{\noexpand\putwordSection{}
\noexpand\thissectionnum:
\noexpand\thissectionname}%
}%
\fi
\fi\fi\fi
%
% Go into vertical mode. Usually we'll already be there, but we
% don't want the following whatsit to end up in a preceding paragraph
% if the document didn't happen to have a blank line.
\par
%
% Output the mark. Pass it through \safewhatsit, to take care of
% the preceding space.
\safewhatsit\domark
%
% Insert space above the heading.
\csname #2headingbreak\endcsname
%
% Now the second mark, after the heading break. No break points
% between here and the heading.
\global\let\prevsectiondefs=\lastsectiondefs
\domark
%
% Only insert the space after the number if we have a section number.
\ifx\temptype\Ynothingkeyword
\setbox0 = \hbox{}%
\def\toctype{unn}%
\gdef\lastsection{#1}%
\else\ifx\temptype\Yomitfromtockeyword
% for @headings -- no section number, don't include in toc,
% and don't redefine \lastsection.
\setbox0 = \hbox{}%
\def\toctype{omit}%
\let\sectionlevel=\empty
\else\ifx\temptype\Yappendixkeyword
\setbox0 = \hbox{#4\enspace}%
\def\toctype{app}%
\gdef\lastsection{#1}%
\else
\setbox0 = \hbox{#4\enspace}%
\def\toctype{num}%
\gdef\lastsection{#1}%
\fi\fi\fi
%
% Write the toc entry (before \donoderef). See comments in \chapmacro.
\writetocentry{\toctype\sectionlevel}{#1}{#4}%
%
% Write the node reference (= pdf destination for pdftex).
% Again, see comments in \chapmacro.
\donoderef{#3}%
%
% Interline glue will be inserted when the vbox is completed.
% That glue will be a valid breakpoint for the page, since it'll be
% preceded by a whatsit (usually from the \donoderef, or from the
% \writetocentry if there was no node). We don't want to allow that
% break, since then the whatsits could end up on page n while the
% section is on page n+1, thus toc/etc. are wrong. Debian bug 276000.
\nobreak
%
% Output the actual section heading.
\vbox{\hyphenpenalty=10000 \tolerance=5000 \parindent=0pt \ptexraggedright
\hangindent=\wd0 % zero if no section number
\unhbox0 #1}%
}%
% Add extra space after the heading -- half of whatever came above it.
% Don't allow stretch, though.
\kern .5 \csname #2headingskip\endcsname
%
% Do not let the kern be a potential breakpoint, as it would be if it
% was followed by glue.
\nobreak
%
% We'll almost certainly start a paragraph next, so don't let that
% glue accumulate. (Not a breakpoint because it's preceded by a
% discardable item.) However, when a paragraph is not started next
% (\startdefun, \cartouche, \center, etc.), this needs to be wiped out
% or the negative glue will cause weirdly wrong output, typically
% obscuring the section heading with something else.
\vskip-\parskip
%
% This is so the last item on the main vertical list is a known
% \penalty > 10000, so \startdefun, etc., can recognize the situation
% and do the needful.
\penalty 10001
}
\message{toc,}
% Table of contents.
\newwrite\tocfile
% Write an entry to the toc file, opening it if necessary.
% Called from @chapter, etc.
%
% Example usage: \writetocentry{sec}{Section Name}{\the\chapno.\the\secno}
% We append the current node name (if any) and page number as additional
% arguments for the \{chap,sec,...}entry macros which will eventually
% read this. The node name is used in the pdf outlines as the
% destination to jump to.
%
% We open the .toc file for writing here instead of at @setfilename (or
% any other fixed time) so that @contents can be anywhere in the document.
% But if #1 is `omit', then we don't do anything. This is used for the
% table of contents chapter openings themselves.
%
\newif\iftocfileopened
\def\omitkeyword{omit}%
%
\def\writetocentry#1#2#3{%
\edef\writetoctype{#1}%
\ifx\writetoctype\omitkeyword \else
\iftocfileopened\else
\immediate\openout\tocfile = \jobname.toc
\global\tocfileopenedtrue
\fi
%
\iflinks
{\atdummies
\edef\temp{%
\write\tocfile{@#1entry{#2}{#3}{\lastnode}{\noexpand\folio}}}%
\temp
}%
\fi
\fi
%
% Tell \shipout to create a pdf destination on each page, if we're
% writing pdf. These are used in the table of contents. We can't
% just write one on every page because the title pages are numbered
% 1 and 2 (the page numbers aren't printed), and so are the first
% two pages of the document. Thus, we'd have two destinations named
% `1', and two named `2'.
\ifpdf \global\pdfmakepagedesttrue \fi
}
% These characters do not print properly in the Computer Modern roman
% fonts, so we must take special care. This is more or less redundant
% with the Texinfo input format setup at the end of this file.
%
\def\activecatcodes{%
\catcode`\"=\active
\catcode`\$=\active
\catcode`\<=\active
\catcode`\>=\active
\catcode`\\=\active
\catcode`\^=\active
\catcode`\_=\active
\catcode`\|=\active
\catcode`\~=\active
}
% Read the toc file, which is essentially Texinfo input.
\def\readtocfile{%
\setupdatafile
\activecatcodes
\input \tocreadfilename
}
\newskip\contentsrightmargin \contentsrightmargin=1in
\newcount\savepageno
\newcount\lastnegativepageno \lastnegativepageno = -1
% Prepare to read what we've written to \tocfile.
%
\def\startcontents#1{%
% If @setchapternewpage on, and @headings double, the contents should
% start on an odd page, unlike chapters. Thus, we maintain
% \contentsalignmacro in parallel with \pagealignmacro.
% From: Torbjorn Granlund
\contentsalignmacro
\immediate\closeout\tocfile
%
% Don't need to put `Contents' or `Short Contents' in the headline.
% It is abundantly clear what they are.
\chapmacro{#1}{Yomitfromtoc}{}%
%
\savepageno = \pageno
\begingroup % Set up to handle contents files properly.
\raggedbottom % Worry more about breakpoints than the bottom.
\advance\hsize by -\contentsrightmargin % Don't use the full line length.
%
% Roman numerals for page numbers.
\ifnum \pageno>0 \global\pageno = \lastnegativepageno \fi
}
% redefined for the two-volume lispref. We always output on
% \jobname.toc even if this is redefined.
%
\def\tocreadfilename{\jobname.toc}
% Normal (long) toc.
%
\def\contents{%
\startcontents{\putwordTOC}%
\openin 1 \tocreadfilename\space
\ifeof 1 \else
\readtocfile
\fi
\vfill \eject
\contentsalignmacro % in case @setchapternewpage odd is in effect
\ifeof 1 \else
\pdfmakeoutlines
\fi
\closein 1
\endgroup
\lastnegativepageno = \pageno
\global\pageno = \savepageno
}
% And just the chapters.
\def\summarycontents{%
\startcontents{\putwordShortTOC}%
%
\let\partentry = \shortpartentry
\let\numchapentry = \shortchapentry
\let\appentry = \shortchapentry
\let\unnchapentry = \shortunnchapentry
% We want a true roman here for the page numbers.
\secfonts
\let\rm=\shortcontrm \let\bf=\shortcontbf
\let\sl=\shortcontsl \let\tt=\shortconttt
\rm
\hyphenpenalty = 10000
\advance\baselineskip by 1pt % Open it up a little.
\def\numsecentry##1##2##3##4{}
\let\appsecentry = \numsecentry
\let\unnsecentry = \numsecentry
\let\numsubsecentry = \numsecentry
\let\appsubsecentry = \numsecentry
\let\unnsubsecentry = \numsecentry
\let\numsubsubsecentry = \numsecentry
\let\appsubsubsecentry = \numsecentry
\let\unnsubsubsecentry = \numsecentry
\openin 1 \tocreadfilename\space
\ifeof 1 \else
\readtocfile
\fi
\closein 1
\vfill \eject
\contentsalignmacro % in case @setchapternewpage odd is in effect
\endgroup
\lastnegativepageno = \pageno
\global\pageno = \savepageno
}
\let\shortcontents = \summarycontents
% Typeset the label for a chapter or appendix for the short contents.
% The arg is, e.g., `A' for an appendix, or `3' for a chapter.
%
\def\shortchaplabel#1{%
% This space should be enough, since a single number is .5em, and the
% widest letter (M) is 1em, at least in the Computer Modern fonts.
% But use \hss just in case.
% (This space doesn't include the extra space that gets added after
% the label; that gets put in by \shortchapentry above.)
%
% We'd like to right-justify chapter numbers, but that looks strange
% with appendix letters. And right-justifying numbers and
% left-justifying letters looks strange when there is less than 10
% chapters. Have to read the whole toc once to know how many chapters
% there are before deciding ...
\hbox to 1em{#1\hss}%
}
% These macros generate individual entries in the table of contents.
% The first argument is the chapter or section name.
% The last argument is the page number.
% The arguments in between are the chapter number, section number, ...
% Parts, in the main contents. Replace the part number, which doesn't
% exist, with an empty box. Let's hope all the numbers have the same width.
% Also ignore the page number, which is conventionally not printed.
\def\numeralbox{\setbox0=\hbox{8}\hbox to \wd0{\hfil}}
\def\partentry#1#2#3#4{\dochapentry{\numeralbox\labelspace#1}{}}
%
% Parts, in the short toc.
\def\shortpartentry#1#2#3#4{%
\penalty-300
\vskip.5\baselineskip plus.15\baselineskip minus.1\baselineskip
\shortchapentry{{\bf #1}}{\numeralbox}{}{}%
}
% Chapters, in the main contents.
\def\numchapentry#1#2#3#4{\dochapentry{#2\labelspace#1}{#4}}
%
% Chapters, in the short toc.
% See comments in \dochapentry re vbox and related settings.
\def\shortchapentry#1#2#3#4{%
\tocentry{\shortchaplabel{#2}\labelspace #1}{\doshortpageno\bgroup#4\egroup}%
}
% Appendices, in the main contents.
% Need the word Appendix, and a fixed-size box.
%
\def\appendixbox#1{%
% We use M since it's probably the widest letter.
\setbox0 = \hbox{\putwordAppendix{} M}%
\hbox to \wd0{\putwordAppendix{} #1\hss}}
%
\def\appentry#1#2#3#4{\dochapentry{\appendixbox{#2}\labelspace#1}{#4}}
% Unnumbered chapters.
\def\unnchapentry#1#2#3#4{\dochapentry{#1}{#4}}
\def\shortunnchapentry#1#2#3#4{\tocentry{#1}{\doshortpageno\bgroup#4\egroup}}
% Sections.
\def\numsecentry#1#2#3#4{\dosecentry{#2\labelspace#1}{#4}}
\let\appsecentry=\numsecentry
\def\unnsecentry#1#2#3#4{\dosecentry{#1}{#4}}
% Subsections.
\def\numsubsecentry#1#2#3#4{\dosubsecentry{#2\labelspace#1}{#4}}
\let\appsubsecentry=\numsubsecentry
\def\unnsubsecentry#1#2#3#4{\dosubsecentry{#1}{#4}}
% And subsubsections.
\def\numsubsubsecentry#1#2#3#4{\dosubsubsecentry{#2\labelspace#1}{#4}}
\let\appsubsubsecentry=\numsubsubsecentry
\def\unnsubsubsecentry#1#2#3#4{\dosubsubsecentry{#1}{#4}}
% This parameter controls the indentation of the various levels.
% Same as \defaultparindent.
\newdimen\tocindent \tocindent = 15pt
% Now for the actual typesetting. In all these, #1 is the text and #2 is the
% page number.
%
% If the toc has to be broken over pages, we want it to be at chapters
% if at all possible; hence the \penalty.
\def\dochapentry#1#2{%
\penalty-300 \vskip1\baselineskip plus.33\baselineskip minus.25\baselineskip
\begingroup
\chapentryfonts
\tocentry{#1}{\dopageno\bgroup#2\egroup}%
\endgroup
\nobreak\vskip .25\baselineskip plus.1\baselineskip
}
\def\dosecentry#1#2{\begingroup
\secentryfonts \leftskip=\tocindent
\tocentry{#1}{\dopageno\bgroup#2\egroup}%
\endgroup}
\def\dosubsecentry#1#2{\begingroup
\subsecentryfonts \leftskip=2\tocindent
\tocentry{#1}{\dopageno\bgroup#2\egroup}%
\endgroup}
\def\dosubsubsecentry#1#2{\begingroup
\subsubsecentryfonts \leftskip=3\tocindent
\tocentry{#1}{\dopageno\bgroup#2\egroup}%
\endgroup}
% We use the same \entry macro as for the index entries.
\let\tocentry = \entry
% Space between chapter (or whatever) number and the title.
\def\labelspace{\hskip1em \relax}
\def\dopageno#1{{\rm #1}}
\def\doshortpageno#1{{\rm #1}}
\def\chapentryfonts{\secfonts \rm}
\def\secentryfonts{\textfonts}
\def\subsecentryfonts{\textfonts}
\def\subsubsecentryfonts{\textfonts}
\message{environments,}
% @foo ... @end foo.
% @tex ... @end tex escapes into raw TeX temporarily.
% One exception: @ is still an escape character, so that @end tex works.
% But \@ or @@ will get a plain @ character.
\envdef\tex{%
\setupmarkupstyle{tex}%
\catcode `\\=0 \catcode `\{=1 \catcode `\}=2
\catcode `\$=3 \catcode `\&=4 \catcode `\#=6
\catcode `\^=7 \catcode `\_=8 \catcode `\~=\active \let~=\tie
\catcode `\%=14
\catcode `\+=\other
\catcode `\"=\other
\catcode `\|=\other
\catcode `\<=\other
\catcode `\>=\other
\catcode `\`=\other
\catcode `\'=\other
\escapechar=`\\
%
% ' is active in math mode (mathcode"8000). So reset it, and all our
% other math active characters (just in case), to plain's definitions.
\mathactive
%
\let\b=\ptexb
\let\bullet=\ptexbullet
\let\c=\ptexc
\let\,=\ptexcomma
\let\.=\ptexdot
\let\dots=\ptexdots
\let\equiv=\ptexequiv
\let\!=\ptexexclam
\let\i=\ptexi
\let\indent=\ptexindent
\let\noindent=\ptexnoindent
\let\{=\ptexlbrace
\let\+=\tabalign
\let\}=\ptexrbrace
\let\/=\ptexslash
\let\*=\ptexstar
\let\t=\ptext
\expandafter \let\csname top\endcsname=\ptextop % we've made it outer
\let\frenchspacing=\plainfrenchspacing
%
\def\endldots{\mathinner{\ldots\ldots\ldots\ldots}}%
\def\enddots{\relax\ifmmode\endldots\else$\mathsurround=0pt \endldots\,$\fi}%
\def\@{@}%
}
% There is no need to define \Etex.
% Define @lisp ... @end lisp.
% @lisp environment forms a group so it can rebind things,
% including the definition of @end lisp (which normally is erroneous).
% Amount to narrow the margins by for @lisp.
\newskip\lispnarrowing \lispnarrowing=0.4in
% This is the definition that ^^M gets inside @lisp, @example, and other
% such environments. \null is better than a space, since it doesn't
% have any width.
\def\lisppar{\null\endgraf}
% This space is always present above and below environments.
\newskip\envskipamount \envskipamount = 0pt
% Make spacing and below environment symmetrical. We use \parskip here
% to help in doing that, since in @example-like environments \parskip
% is reset to zero; thus the \afterenvbreak inserts no space -- but the
% start of the next paragraph will insert \parskip.
%
\def\aboveenvbreak{{%
% =10000 instead of <10000 because of a special case in \itemzzz and
% \sectionheading, q.v.
\ifnum \lastpenalty=10000 \else
\advance\envskipamount by \parskip
\endgraf
\ifdim\lastskip<\envskipamount
\removelastskip
% it's not a good place to break if the last penalty was \nobreak
% or better ...
\ifnum\lastpenalty<10000 \penalty-50 \fi
\vskip\envskipamount
\fi
\fi
}}
\let\afterenvbreak = \aboveenvbreak
% \nonarrowing is a flag. If "set", @lisp etc don't narrow margins; it will
% also clear it, so that its embedded environments do the narrowing again.
\let\nonarrowing=\relax
% @cartouche ... @end cartouche: draw rectangle w/rounded corners around
% environment contents.
\font\circle=lcircle10
\newdimen\circthick
\newdimen\cartouter\newdimen\cartinner
\newskip\normbskip\newskip\normpskip\newskip\normlskip
\circthick=\fontdimen8\circle
%
\def\ctl{{\circle\char'013\hskip -6pt}}% 6pt from pl file: 1/2charwidth
\def\ctr{{\hskip 6pt\circle\char'010}}
\def\cbl{{\circle\char'012\hskip -6pt}}
\def\cbr{{\hskip 6pt\circle\char'011}}
\def\carttop{\hbox to \cartouter{\hskip\lskip
\ctl\leaders\hrule height\circthick\hfil\ctr
\hskip\rskip}}
\def\cartbot{\hbox to \cartouter{\hskip\lskip
\cbl\leaders\hrule height\circthick\hfil\cbr
\hskip\rskip}}
%
\newskip\lskip\newskip\rskip
\envdef\cartouche{%
\ifhmode\par\fi % can't be in the midst of a paragraph.
\startsavinginserts
\lskip=\leftskip \rskip=\rightskip
\leftskip=0pt\rightskip=0pt % we want these *outside*.
\cartinner=\hsize \advance\cartinner by-\lskip
\advance\cartinner by-\rskip
\cartouter=\hsize
\advance\cartouter by 18.4pt % allow for 3pt kerns on either
% side, and for 6pt waste from
% each corner char, and rule thickness
\normbskip=\baselineskip \normpskip=\parskip \normlskip=\lineskip
% Flag to tell @lisp, etc., not to narrow margin.
\let\nonarrowing = t%
%
% If this cartouche directly follows a sectioning command, we need the
% \parskip glue (backspaced over by default) or the cartouche can
% collide with the section heading.
\ifnum\lastpenalty>10000 \vskip\parskip \penalty\lastpenalty \fi
%
\vbox\bgroup
\baselineskip=0pt\parskip=0pt\lineskip=0pt
\carttop
\hbox\bgroup
\hskip\lskip
\vrule\kern3pt
\vbox\bgroup
\kern3pt
\hsize=\cartinner
\baselineskip=\normbskip
\lineskip=\normlskip
\parskip=\normpskip
\vskip -\parskip
\comment % For explanation, see the end of def\group.
}
\def\Ecartouche{%
\ifhmode\par\fi
\kern3pt
\egroup
\kern3pt\vrule
\hskip\rskip
\egroup
\cartbot
\egroup
\checkinserts
}
% This macro is called at the beginning of all the @example variants,
% inside a group.
\newdimen\nonfillparindent
\def\nonfillstart{%
\aboveenvbreak
\ifdim\hfuzz < 12pt \hfuzz = 12pt \fi % Don't be fussy
\sepspaces % Make spaces be word-separators rather than space tokens.
\let\par = \lisppar % don't ignore blank lines
\obeylines % each line of input is a line of output
\parskip = 0pt
% Turn off paragraph indentation but redefine \indent to emulate
% the normal \indent.
\nonfillparindent=\parindent
\parindent = 0pt
\let\indent\nonfillindent
%
\emergencystretch = 0pt % don't try to avoid overfull boxes
\ifx\nonarrowing\relax
\advance \leftskip by \lispnarrowing
\exdentamount=\lispnarrowing
\else
\let\nonarrowing = \relax
\fi
\let\exdent=\nofillexdent
}
\begingroup
\obeyspaces
% We want to swallow spaces (but not other tokens) after the fake
% @indent in our nonfill-environments, where spaces are normally
% active and set to @tie, resulting in them not being ignored after
% @indent.
\gdef\nonfillindent{\futurelet\temp\nonfillindentcheck}%
\gdef\nonfillindentcheck{%
\ifx\temp %
\expandafter\nonfillindentgobble%
\else%
\leavevmode\nonfillindentbox%
\fi%
}%
\endgroup
\def\nonfillindentgobble#1{\nonfillindent}
\def\nonfillindentbox{\hbox to \nonfillparindent{\hss}}
% If you want all examples etc. small: @set dispenvsize small.
% If you want even small examples the full size: @set dispenvsize nosmall.
% This affects the following displayed environments:
% @example, @display, @format, @lisp
%
\def\smallword{small}
\def\nosmallword{nosmall}
\let\SETdispenvsize\relax
\def\setnormaldispenv{%
\ifx\SETdispenvsize\smallword
% end paragraph for sake of leading, in case document has no blank
% line. This is redundant with what happens in \aboveenvbreak, but
% we need to do it before changing the fonts, and it's inconvenient
% to change the fonts afterward.
\ifnum \lastpenalty=10000 \else \endgraf \fi
\smallexamplefonts \rm
\fi
}
\def\setsmalldispenv{%
\ifx\SETdispenvsize\nosmallword
\else
\ifnum \lastpenalty=10000 \else \endgraf \fi
\smallexamplefonts \rm
\fi
}
% We often define two environments, @foo and @smallfoo.
% Let's do it in one command. #1 is the env name, #2 the definition.
\def\makedispenvdef#1#2{%
\expandafter\envdef\csname#1\endcsname {\setnormaldispenv #2}%
\expandafter\envdef\csname small#1\endcsname {\setsmalldispenv #2}%
\expandafter\let\csname E#1\endcsname \afterenvbreak
\expandafter\let\csname Esmall#1\endcsname \afterenvbreak
}
% Define two environment synonyms (#1 and #2) for an environment.
\def\maketwodispenvdef#1#2#3{%
\makedispenvdef{#1}{#3}%
\makedispenvdef{#2}{#3}%
}
%
% @lisp: indented, narrowed, typewriter font;
% @example: same as @lisp.
%
% @smallexample and @smalllisp: use smaller fonts.
% Originally contributed by Pavel@xerox.
%
\maketwodispenvdef{lisp}{example}{%
\nonfillstart
\tt\setupmarkupstyle{example}%
\let\kbdfont = \kbdexamplefont % Allow @kbd to do something special.
\gobble % eat return
}
% @display/@smalldisplay: same as @lisp except keep current font.
%
\makedispenvdef{display}{%
\nonfillstart
\gobble
}
% @format/@smallformat: same as @display except don't narrow margins.
%
\makedispenvdef{format}{%
\let\nonarrowing = t%
\nonfillstart
\gobble
}
% @flushleft: same as @format, but doesn't obey \SETdispenvsize.
\envdef\flushleft{%
\let\nonarrowing = t%
\nonfillstart
\gobble
}
\let\Eflushleft = \afterenvbreak
% @flushright.
%
\envdef\flushright{%
\let\nonarrowing = t%
\nonfillstart
\advance\leftskip by 0pt plus 1fill\relax
\gobble
}
\let\Eflushright = \afterenvbreak
% @raggedright does more-or-less normal line breaking but no right
% justification. From plain.tex.
\envdef\raggedright{%
\rightskip0pt plus2em \spaceskip.3333em \xspaceskip.5em\relax
}
\let\Eraggedright\par
\envdef\raggedleft{%
\parindent=0pt \leftskip0pt plus2em
\spaceskip.3333em \xspaceskip.5em \parfillskip=0pt
\hbadness=10000 % Last line will usually be underfull, so turn off
% badness reporting.
}
\let\Eraggedleft\par
\envdef\raggedcenter{%
\parindent=0pt \rightskip0pt plus1em \leftskip0pt plus1em
\spaceskip.3333em \xspaceskip.5em \parfillskip=0pt
\hbadness=10000 % Last line will usually be underfull, so turn off
% badness reporting.
}
\let\Eraggedcenter\par
% @quotation does normal linebreaking (hence we can't use \nonfillstart)
% and narrows the margins. We keep \parskip nonzero in general, since
% we're doing normal filling. So, when using \aboveenvbreak and
% \afterenvbreak, temporarily make \parskip 0.
%
\makedispenvdef{quotation}{\quotationstart}
%
\def\quotationstart{%
\indentedblockstart % same as \indentedblock, but increase right margin too.
\ifx\nonarrowing\relax
\advance\rightskip by \lispnarrowing
\fi
\parsearg\quotationlabel
}
% We have retained a nonzero parskip for the environment, since we're
% doing normal filling.
%
\def\Equotation{%
\par
\ifx\quotationauthor\thisisundefined\else
% indent a bit.
\leftline{\kern 2\leftskip \sl ---\quotationauthor}%
\fi
{\parskip=0pt \afterenvbreak}%
}
\def\Esmallquotation{\Equotation}
% If we're given an argument, typeset it in bold with a colon after.
\def\quotationlabel#1{%
\def\temp{#1}%
\ifx\temp\empty \else
{\bf #1: }%
\fi
}
% @indentedblock is like @quotation, but indents only on the left and
% has no optional argument.
%
\makedispenvdef{indentedblock}{\indentedblockstart}
%
\def\indentedblockstart{%
{\parskip=0pt \aboveenvbreak}% because \aboveenvbreak inserts \parskip
\parindent=0pt
%
% @cartouche defines \nonarrowing to inhibit narrowing at next level down.
\ifx\nonarrowing\relax
\advance\leftskip by \lispnarrowing
\exdentamount = \lispnarrowing
\else
\let\nonarrowing = \relax
\fi
}
% Keep a nonzero parskip for the environment, since we're doing normal filling.
%
\def\Eindentedblock{%
\par
{\parskip=0pt \afterenvbreak}%
}
\def\Esmallindentedblock{\Eindentedblock}
% LaTeX-like @verbatim...@end verbatim and @verb{...}
% If we want to allow any as delimiter,
% we need the curly braces so that makeinfo sees the @verb command, eg:
% `@verbx...x' would look like the '@verbx' command. --janneke@gnu.org
%
% [Knuth]: Donald Ervin Knuth, 1996. The TeXbook.
%
% [Knuth] p.344; only we need to do the other characters Texinfo sets
% active too. Otherwise, they get lost as the first character on a
% verbatim line.
\def\dospecials{%
\do\ \do\\\do\{\do\}\do\$\do\&%
\do\#\do\^\do\^^K\do\_\do\^^A\do\%\do\~%
\do\<\do\>\do\|\do\@\do+\do\"%
% Don't do the quotes -- if we do, @set txicodequoteundirected and
% @set txicodequotebacktick will not have effect on @verb and
% @verbatim, and ?` and !` ligatures won't get disabled.
%\do\`\do\'%
}
%
% [Knuth] p. 380
\def\uncatcodespecials{%
\def\do##1{\catcode`##1=\other}\dospecials}
%
% Setup for the @verb command.
%
% Eight spaces for a tab
\begingroup
\catcode`\^^I=\active
\gdef\tabeightspaces{\catcode`\^^I=\active\def^^I{\ \ \ \ \ \ \ \ }}
\endgroup
%
\def\setupverb{%
\tt % easiest (and conventionally used) font for verbatim
\def\par{\leavevmode\endgraf}%
\setupmarkupstyle{verb}%
\tabeightspaces
% Respect line breaks,
% print special symbols as themselves, and
% make each space count
% must do in this order:
\obeylines \uncatcodespecials \sepspaces
}
% Setup for the @verbatim environment
%
% Real tab expansion.
\newdimen\tabw \setbox0=\hbox{\tt\space} \tabw=8\wd0 % tab amount
%
% We typeset each line of the verbatim in an \hbox, so we can handle
% tabs. The \global is in case the verbatim line starts with an accent,
% or some other command that starts with a begin-group. Otherwise, the
% entire \verbbox would disappear at the corresponding end-group, before
% it is typeset. Meanwhile, we can't have nested verbatim commands
% (can we?), so the \global won't be overwriting itself.
\newbox\verbbox
\def\starttabbox{\global\setbox\verbbox=\hbox\bgroup}
%
\begingroup
\catcode`\^^I=\active
\gdef\tabexpand{%
\catcode`\^^I=\active
\def^^I{\leavevmode\egroup
\dimen\verbbox=\wd\verbbox % the width so far, or since the previous tab
\divide\dimen\verbbox by\tabw
\multiply\dimen\verbbox by\tabw % compute previous multiple of \tabw
\advance\dimen\verbbox by\tabw % advance to next multiple of \tabw
\wd\verbbox=\dimen\verbbox \box\verbbox \starttabbox
}%
}
\endgroup
% start the verbatim environment.
\def\setupverbatim{%
\let\nonarrowing = t%
\nonfillstart
\tt % easiest (and conventionally used) font for verbatim
% The \leavevmode here is for blank lines. Otherwise, we would
% never \starttabox and the \egroup would end verbatim mode.
\def\par{\leavevmode\egroup\box\verbbox\endgraf}%
\tabexpand
\setupmarkupstyle{verbatim}%
% Respect line breaks,
% print special symbols as themselves, and
% make each space count.
% Must do in this order:
\obeylines \uncatcodespecials \sepspaces
\everypar{\starttabbox}%
}
% Do the @verb magic: verbatim text is quoted by unique
% delimiter characters. Before first delimiter expect a
% right brace, after last delimiter expect closing brace:
%
% \def\doverb'{'#1'}'{#1}
%
% [Knuth] p. 382; only eat outer {}
\begingroup
\catcode`[=1\catcode`]=2\catcode`\{=\other\catcode`\}=\other
\gdef\doverb{#1[\def\next##1#1}[##1\endgroup]\next]
\endgroup
%
\def\verb{\begingroup\setupverb\doverb}
%
%
% Do the @verbatim magic: define the macro \doverbatim so that
% the (first) argument ends when '@end verbatim' is reached, ie:
%
% \def\doverbatim#1@end verbatim{#1}
%
% For Texinfo it's a lot easier than for LaTeX,
% because texinfo's \verbatim doesn't stop at '\end{verbatim}':
% we need not redefine '\', '{' and '}'.
%
% Inspired by LaTeX's verbatim command set [latex.ltx]
%
\begingroup
\catcode`\ =\active
\obeylines %
% ignore everything up to the first ^^M, that's the newline at the end
% of the @verbatim input line itself. Otherwise we get an extra blank
% line in the output.
\xdef\doverbatim#1^^M#2@end verbatim{#2\noexpand\end\gobble verbatim}%
% We really want {...\end verbatim} in the body of the macro, but
% without the active space; thus we have to use \xdef and \gobble.
\endgroup
%
\envdef\verbatim{%
\setupverbatim\doverbatim
}
\let\Everbatim = \afterenvbreak
% @verbatiminclude FILE - insert text of file in verbatim environment.
%
\def\verbatiminclude{\parseargusing\filenamecatcodes\doverbatiminclude}
%
\def\doverbatiminclude#1{%
{%
\makevalueexpandable
\setupverbatim
\indexnofonts % Allow `@@' and other weird things in file names.
\wlog{texinfo.tex: doing @verbatiminclude of #1^^J}%
\input #1
\afterenvbreak
}%
}
% @copying ... @end copying.
% Save the text away for @insertcopying later.
%
% We save the uninterpreted tokens, rather than creating a box.
% Saving the text in a box would be much easier, but then all the
% typesetting commands (@smallbook, font changes, etc.) have to be done
% beforehand -- and a) we want @copying to be done first in the source
% file; b) letting users define the frontmatter in as flexible order as
% possible is very desirable.
%
\def\copying{\checkenv{}\begingroup\scanargctxt\docopying}
\def\docopying#1@end copying{\endgroup\def\copyingtext{#1}}
%
\def\insertcopying{%
\begingroup
\parindent = 0pt % paragraph indentation looks wrong on title page
\scanexp\copyingtext
\endgroup
}
\message{defuns,}
% @defun etc.
\newskip\defbodyindent \defbodyindent=.4in
\newskip\defargsindent \defargsindent=50pt
\newskip\deflastargmargin \deflastargmargin=18pt
\newcount\defunpenalty
% Start the processing of @deffn:
\def\startdefun{%
\ifnum\lastpenalty<10000
\medbreak
\defunpenalty=10003 % Will keep this @deffn together with the
% following @def command, see below.
\else
% If there are two @def commands in a row, we'll have a \nobreak,
% which is there to keep the function description together with its
% header. But if there's nothing but headers, we need to allow a
% break somewhere. Check specifically for penalty 10002, inserted
% by \printdefunline, instead of 10000, since the sectioning
% commands also insert a nobreak penalty, and we don't want to allow
% a break between a section heading and a defun.
%
% As a further refinement, we avoid "club" headers by signalling
% with penalty of 10003 after the very first @deffn in the
% sequence (see above), and penalty of 10002 after any following
% @def command.
\ifnum\lastpenalty=10002 \penalty2000 \else \defunpenalty=10002 \fi
%
% Similarly, after a section heading, do not allow a break.
% But do insert the glue.
\medskip % preceded by discardable penalty, so not a breakpoint
\fi
%
\parindent=0in
\advance\leftskip by \defbodyindent
\exdentamount=\defbodyindent
}
\def\dodefunx#1{%
% First, check whether we are in the right environment:
\checkenv#1%
%
% As above, allow line break if we have multiple x headers in a row.
% It's not a great place, though.
\ifnum\lastpenalty=10002 \penalty3000 \else \defunpenalty=10002 \fi
%
% And now, it's time to reuse the body of the original defun:
\expandafter\gobbledefun#1%
}
\def\gobbledefun#1\startdefun{}
% \printdefunline \deffnheader{text}
%
\def\printdefunline#1#2{%
\begingroup
% call \deffnheader:
#1#2 \endheader
% common ending:
\interlinepenalty = 10000
\advance\rightskip by 0pt plus 1fil\relax
\endgraf
\nobreak\vskip -\parskip
\penalty\defunpenalty % signal to \startdefun and \dodefunx
% Some of the @defun-type tags do not enable magic parentheses,
% rendering the following check redundant. But we don't optimize.
\checkparencounts
\endgroup
}
\def\Edefun{\endgraf\medbreak}
% \makedefun{deffn} creates \deffn, \deffnx and \Edeffn;
% the only thing remaining is to define \deffnheader.
%
\def\makedefun#1{%
\expandafter\let\csname E#1\endcsname = \Edefun
\edef\temp{\noexpand\domakedefun
\makecsname{#1}\makecsname{#1x}\makecsname{#1header}}%
\temp
}
% \domakedefun \deffn \deffnx \deffnheader
%
% Define \deffn and \deffnx, without parameters.
% \deffnheader has to be defined explicitly.
%
\def\domakedefun#1#2#3{%
\envdef#1{%
\startdefun
\doingtypefnfalse % distinguish typed functions from all else
\parseargusing\activeparens{\printdefunline#3}%
}%
\def#2{\dodefunx#1}%
\def#3%
}
\newif\ifdoingtypefn % doing typed function?
\newif\ifrettypeownline % typeset return type on its own line?
% @deftypefnnewline on|off says whether the return type of typed functions
% are printed on their own line. This affects @deftypefn, @deftypefun,
% @deftypeop, and @deftypemethod.
%
\parseargdef\deftypefnnewline{%
\def\temp{#1}%
\ifx\temp\onword
\expandafter\let\csname SETtxideftypefnnl\endcsname
= \empty
\else\ifx\temp\offword
\expandafter\let\csname SETtxideftypefnnl\endcsname
= \relax
\else
\errhelp = \EMsimple
\errmessage{Unknown @txideftypefnnl value `\temp',
must be on|off}%
\fi\fi
}
% Untyped functions:
% @deffn category name args
\makedefun{deffn}{\deffngeneral{}}
% @deffn category class name args
\makedefun{defop}#1 {\defopon{#1\ \putwordon}}
% \defopon {category on}class name args
\def\defopon#1#2 {\deffngeneral{\putwordon\ \code{#2}}{#1\ \code{#2}} }
% \deffngeneral {subind}category name args
%
\def\deffngeneral#1#2 #3 #4\endheader{%
% Remember that \dosubind{fn}{foo}{} is equivalent to \doind{fn}{foo}.
\dosubind{fn}{\code{#3}}{#1}%
\defname{#2}{}{#3}\magicamp\defunargs{#4\unskip}%
}
% Typed functions:
% @deftypefn category type name args
\makedefun{deftypefn}{\deftypefngeneral{}}
% @deftypeop category class type name args
\makedefun{deftypeop}#1 {\deftypeopon{#1\ \putwordon}}
% \deftypeopon {category on}class type name args
\def\deftypeopon#1#2 {\deftypefngeneral{\putwordon\ \code{#2}}{#1\ \code{#2}} }
% \deftypefngeneral {subind}category type name args
%
\def\deftypefngeneral#1#2 #3 #4 #5\endheader{%
\dosubind{fn}{\code{#4}}{#1}%
\doingtypefntrue
\defname{#2}{#3}{#4}\defunargs{#5\unskip}%
}
% Typed variables:
% @deftypevr category type var args
\makedefun{deftypevr}{\deftypecvgeneral{}}
% @deftypecv category class type var args
\makedefun{deftypecv}#1 {\deftypecvof{#1\ \putwordof}}
% \deftypecvof {category of}class type var args
\def\deftypecvof#1#2 {\deftypecvgeneral{\putwordof\ \code{#2}}{#1\ \code{#2}} }
% \deftypecvgeneral {subind}category type var args
%
\def\deftypecvgeneral#1#2 #3 #4 #5\endheader{%
\dosubind{vr}{\code{#4}}{#1}%
\defname{#2}{#3}{#4}\defunargs{#5\unskip}%
}
% Untyped variables:
% @defvr category var args
\makedefun{defvr}#1 {\deftypevrheader{#1} {} }
% @defcv category class var args
\makedefun{defcv}#1 {\defcvof{#1\ \putwordof}}
% \defcvof {category of}class var args
\def\defcvof#1#2 {\deftypecvof{#1}#2 {} }
% Types:
% @deftp category name args
\makedefun{deftp}#1 #2 #3\endheader{%
\doind{tp}{\code{#2}}%
\defname{#1}{}{#2}\defunargs{#3\unskip}%
}
% Remaining @defun-like shortcuts:
\makedefun{defun}{\deffnheader{\putwordDeffunc} }
\makedefun{defmac}{\deffnheader{\putwordDefmac} }
\makedefun{defspec}{\deffnheader{\putwordDefspec} }
\makedefun{deftypefun}{\deftypefnheader{\putwordDeffunc} }
\makedefun{defvar}{\defvrheader{\putwordDefvar} }
\makedefun{defopt}{\defvrheader{\putwordDefopt} }
\makedefun{deftypevar}{\deftypevrheader{\putwordDefvar} }
\makedefun{defmethod}{\defopon\putwordMethodon}
\makedefun{deftypemethod}{\deftypeopon\putwordMethodon}
\makedefun{defivar}{\defcvof\putwordInstanceVariableof}
\makedefun{deftypeivar}{\deftypecvof\putwordInstanceVariableof}
% \defname, which formats the name of the @def (not the args).
% #1 is the category, such as "Function".
% #2 is the return type, if any.
% #3 is the function name.
%
% We are followed by (but not passed) the arguments, if any.
%
\def\defname#1#2#3{%
\par
% Get the values of \leftskip and \rightskip as they were outside the @def...
\advance\leftskip by -\defbodyindent
%
% Determine if we are typesetting the return type of a typed function
% on a line by itself.
\rettypeownlinefalse
\ifdoingtypefn % doing a typed function specifically?
% then check user option for putting return type on its own line:
\expandafter\ifx\csname SETtxideftypefnnl\endcsname\relax \else
\rettypeownlinetrue
\fi
\fi
%
% How we'll format the category name. Putting it in brackets helps
% distinguish it from the body text that may end up on the next line
% just below it.
\def\temp{#1}%
\setbox0=\hbox{\kern\deflastargmargin \ifx\temp\empty\else [\rm\temp]\fi}
%
% Figure out line sizes for the paragraph shape. We'll always have at
% least two.
\tempnum = 2
%
% The first line needs space for \box0; but if \rightskip is nonzero,
% we need only space for the part of \box0 which exceeds it:
\dimen0=\hsize \advance\dimen0 by -\wd0 \advance\dimen0 by \rightskip
%
% If doing a return type on its own line, we'll have another line.
\ifrettypeownline
\advance\tempnum by 1
\def\maybeshapeline{0in \hsize}%
\else
\def\maybeshapeline{}%
\fi
%
% The continuations:
\dimen2=\hsize \advance\dimen2 by -\defargsindent
%
% The final paragraph shape:
\parshape \tempnum 0in \dimen0 \maybeshapeline \defargsindent \dimen2
%
% Put the category name at the right margin.
\noindent
\hbox to 0pt{%
\hfil\box0 \kern-\hsize
% \hsize has to be shortened this way:
\kern\leftskip
% Intentionally do not respect \rightskip, since we need the space.
}%
%
% Allow all lines to be underfull without complaint:
\tolerance=10000 \hbadness=10000
\exdentamount=\defbodyindent
{%
% defun fonts. We use typewriter by default (used to be bold) because:
% . we're printing identifiers, they should be in tt in principle.
% . in languages with many accents, such as Czech or French, it's
% common to leave accents off identifiers. The result looks ok in
% tt, but exceedingly strange in rm.
% . we don't want -- and --- to be treated as ligatures.
% . this still does not fix the ?` and !` ligatures, but so far no
% one has made identifiers using them :).
\df \tt
\def\temp{#2}% text of the return type
\ifx\temp\empty\else
\tclose{\temp}% typeset the return type
\ifrettypeownline
% put return type on its own line; prohibit line break following:
\hfil\vadjust{\nobreak}\break
\else
\space % type on same line, so just followed by a space
\fi
\fi % no return type
#3% output function name
}%
{\rm\enskip}% hskip 0.5 em of \tenrm
%
\boldbrax
% arguments will be output next, if any.
}
% Print arguments in slanted roman (not ttsl), inconsistently with using
% tt for the name. This is because literal text is sometimes needed in
% the argument list (groff manual), and ttsl and tt are not very
% distinguishable. Prevent hyphenation at `-' chars.
%
\def\defunargs#1{%
% use sl by default (not ttsl),
% tt for the names.
\df \sl \hyphenchar\font=0
%
% On the other hand, if an argument has two dashes (for instance), we
% want a way to get ttsl. We used to recommend @var for that, so
% leave the code in, but it's strange for @var to lead to typewriter.
% Nowadays we recommend @code, since the difference between a ttsl hyphen
% and a tt hyphen is pretty tiny. @code also disables ?` !`.
\def\var##1{{\setupmarkupstyle{var}\ttslanted{##1}}}%
#1%
\sl\hyphenchar\font=45
}
% We want ()&[] to print specially on the defun line.
%
\def\activeparens{%
\catcode`\(=\active \catcode`\)=\active
\catcode`\[=\active \catcode`\]=\active
\catcode`\&=\active
}
% Make control sequences which act like normal parenthesis chars.
\let\lparen = ( \let\rparen = )
% Be sure that we always have a definition for `(', etc. For example,
% if the fn name has parens in it, \boldbrax will not be in effect yet,
% so TeX would otherwise complain about undefined control sequence.
{
\activeparens
\global\let(=\lparen \global\let)=\rparen
\global\let[=\lbrack \global\let]=\rbrack
\global\let& = \&
\gdef\boldbrax{\let(=\opnr\let)=\clnr\let[=\lbrb\let]=\rbrb}
\gdef\magicamp{\let&=\amprm}
}
\newcount\parencount
% If we encounter &foo, then turn on ()-hacking afterwards
\newif\ifampseen
\def\amprm#1 {\ampseentrue{\bf\ }}
\def\parenfont{%
\ifampseen
% At the first level, print parens in roman,
% otherwise use the default font.
\ifnum \parencount=1 \rm \fi
\else
% The \sf parens (in \boldbrax) actually are a little bolder than
% the contained text. This is especially needed for [ and ] .
\sf
\fi
}
\def\infirstlevel#1{%
\ifampseen
\ifnum\parencount=1
#1%
\fi
\fi
}
\def\bfafterword#1 {#1 \bf}
\def\opnr{%
\global\advance\parencount by 1
{\parenfont(}%
\infirstlevel \bfafterword
}
\def\clnr{%
{\parenfont)}%
\infirstlevel \sl
\global\advance\parencount by -1
}
\newcount\brackcount
\def\lbrb{%
\global\advance\brackcount by 1
{\bf[}%
}
\def\rbrb{%
{\bf]}%
\global\advance\brackcount by -1
}
\def\checkparencounts{%
\ifnum\parencount=0 \else \badparencount \fi
\ifnum\brackcount=0 \else \badbrackcount \fi
}
% these should not use \errmessage; the glibc manual, at least, actually
% has such constructs (when documenting function pointers).
\def\badparencount{%
\message{Warning: unbalanced parentheses in @def...}%
\global\parencount=0
}
\def\badbrackcount{%
\message{Warning: unbalanced square brackets in @def...}%
\global\brackcount=0
}
\message{macros,}
% @macro.
% To do this right we need a feature of e-TeX, \scantokens,
% which we arrange to emulate with a temporary file in ordinary TeX.
\ifx\eTeXversion\thisisundefined
\newwrite\macscribble
\def\scantokens#1{%
\toks0={#1}%
\immediate\openout\macscribble=\jobname.tmp
\immediate\write\macscribble{\the\toks0}%
\immediate\closeout\macscribble
\input \jobname.tmp
}
\fi
\def\scanmacro#1{\begingroup
\newlinechar`\^^M
\let\xeatspaces\eatspaces
%
% Undo catcode changes of \startcontents and \doprintindex
% When called from @insertcopying or (short)caption, we need active
% backslash to get it printed correctly. Previously, we had
% \catcode`\\=\other instead. We'll see whether a problem appears
% with macro expansion. --kasal, 19aug04
\catcode`\@=0 \catcode`\\=\active \escapechar=`\@
%
% ... and for \example:
\spaceisspace
%
% The \empty here causes a following catcode 5 newline to be eaten as
% part of reading whitespace after a control sequence. It does not
% eat a catcode 13 newline. There's no good way to handle the two
% cases (untried: maybe e-TeX's \everyeof could help, though plain TeX
% would then have different behavior). See the Macro Details node in
% the manual for the workaround we recommend for macros and
% line-oriented commands.
%
\scantokens{#1\empty}%
\endgroup}
\def\scanexp#1{%
\edef\temp{\noexpand\scanmacro{#1}}%
\temp
}
\newcount\paramno % Count of parameters
\newtoks\macname % Macro name
\newif\ifrecursive % Is it recursive?
% List of all defined macros in the form
% \definedummyword\macro1\definedummyword\macro2...
% Currently is also contains all @aliases; the list can be split
% if there is a need.
\def\macrolist{}
% Add the macro to \macrolist
\def\addtomacrolist#1{\expandafter \addtomacrolistxxx \csname#1\endcsname}
\def\addtomacrolistxxx#1{%
\toks0 = \expandafter{\macrolist\definedummyword#1}%
\xdef\macrolist{\the\toks0}%
}
% Utility routines.
% This does \let #1 = #2, with \csnames; that is,
% \let \csname#1\endcsname = \csname#2\endcsname
% (except of course we have to play expansion games).
%
\def\cslet#1#2{%
\expandafter\let
\csname#1\expandafter\endcsname
\csname#2\endcsname
}
% Trim leading and trailing spaces off a string.
% Concepts from aro-bend problem 15 (see CTAN).
{\catcode`\@=11
\gdef\eatspaces #1{\expandafter\trim@\expandafter{#1 }}
\gdef\trim@ #1{\trim@@ @#1 @ #1 @ @@}
\gdef\trim@@ #1@ #2@ #3@@{\trim@@@\empty #2 @}
\def\unbrace#1{#1}
\unbrace{\gdef\trim@@@ #1 } #2@{#1}
}
% Trim a single trailing ^^M off a string.
{\catcode`\^^M=\other \catcode`\Q=3%
\gdef\eatcr #1{\eatcra #1Q^^MQ}%
\gdef\eatcra#1^^MQ{\eatcrb#1Q}%
\gdef\eatcrb#1Q#2Q{#1}%
}
% Macro bodies are absorbed as an argument in a context where
% all characters are catcode 10, 11 or 12, except \ which is active
% (as in normal texinfo). It is necessary to change the definition of \
% to recognize macro arguments; this is the job of \mbodybackslash.
%
% Non-ASCII encodings make 8-bit characters active, so un-activate
% them to avoid their expansion. Must do this non-globally, to
% confine the change to the current group.
%
% It's necessary to have hard CRs when the macro is executed. This is
% done by making ^^M (\endlinechar) catcode 12 when reading the macro
% body, and then making it the \newlinechar in \scanmacro.
%
\def\scanctxt{% used as subroutine
\catcode`\"=\other
\catcode`\+=\other
\catcode`\<=\other
\catcode`\>=\other
\catcode`\@=\other
\catcode`\^=\other
\catcode`\_=\other
\catcode`\|=\other
\catcode`\~=\other
\ifx\declaredencoding\ascii \else \setnonasciicharscatcodenonglobal\other \fi
}
\def\scanargctxt{% used for copying and captions, not macros.
\scanctxt
\catcode`\\=\other
\catcode`\^^M=\other
}
\def\macrobodyctxt{% used for @macro definitions
\scanctxt
\catcode`\{=\other
\catcode`\}=\other
\catcode`\^^M=\other
\usembodybackslash
}
\def\macroargctxt{% used when scanning invocations
\scanctxt
\catcode`\\=0
}
% why catcode 0 for \ in the above? To recognize \\ \{ \} as "escapes"
% for the single characters \ { }. Thus, we end up with the "commands"
% that would be written @\ @{ @} in a Texinfo document.
%
% We already have @{ and @}. For @\, we define it here, and only for
% this purpose, to produce a typewriter backslash (so, the @\ that we
% define for @math can't be used with @macro calls):
%
\def\\{\normalbackslash}%
%
% We would like to do this for \, too, since that is what makeinfo does.
% But it is not possible, because Texinfo already has a command @, for a
% cedilla accent. Documents must use @comma{} instead.
%
% \anythingelse will almost certainly be an error of some kind.
% \mbodybackslash is the definition of \ in @macro bodies.
% It maps \foo\ => \csname macarg.foo\endcsname => #N
% where N is the macro parameter number.
% We define \csname macarg.\endcsname to be \realbackslash, so
% \\ in macro replacement text gets you a backslash.
%
{\catcode`@=0 @catcode`@\=@active
@gdef@usembodybackslash{@let\=@mbodybackslash}
@gdef@mbodybackslash#1\{@csname macarg.#1@endcsname}
}
\expandafter\def\csname macarg.\endcsname{\realbackslash}
\def\margbackslash#1{\char`\#1 }
\def\macro{\recursivefalse\parsearg\macroxxx}
\def\rmacro{\recursivetrue\parsearg\macroxxx}
\def\macroxxx#1{%
\getargs{#1}% now \macname is the macname and \argl the arglist
\ifx\argl\empty % no arguments
\paramno=0\relax
\else
\expandafter\parsemargdef \argl;%
\if\paramno>256\relax
\ifx\eTeXversion\thisisundefined
\errhelp = \EMsimple
\errmessage{You need eTeX to compile a file with macros with more than 256 arguments}
\fi
\fi
\fi
\if1\csname ismacro.\the\macname\endcsname
\message{Warning: redefining \the\macname}%
\else
\expandafter\ifx\csname \the\macname\endcsname \relax
\else \errmessage{Macro name \the\macname\space already defined}\fi
\global\cslet{macsave.\the\macname}{\the\macname}%
\global\expandafter\let\csname ismacro.\the\macname\endcsname=1%
\addtomacrolist{\the\macname}%
\fi
\begingroup \macrobodyctxt
\ifrecursive \expandafter\parsermacbody
\else \expandafter\parsemacbody
\fi}
\parseargdef\unmacro{%
\if1\csname ismacro.#1\endcsname
\global\cslet{#1}{macsave.#1}%
\global\expandafter\let \csname ismacro.#1\endcsname=0%
% Remove the macro name from \macrolist:
\begingroup
\expandafter\let\csname#1\endcsname \relax
\let\definedummyword\unmacrodo
\xdef\macrolist{\macrolist}%
\endgroup
\else
\errmessage{Macro #1 not defined}%
\fi
}
% Called by \do from \dounmacro on each macro. The idea is to omit any
% macro definitions that have been changed to \relax.
%
\def\unmacrodo#1{%
\ifx #1\relax
% remove this
\else
\noexpand\definedummyword \noexpand#1%
\fi
}
% This makes use of the obscure feature that if the last token of a
% is #, then the preceding argument is delimited by
% an opening brace, and that opening brace is not consumed.
\def\getargs#1{\getargsxxx#1{}}
\def\getargsxxx#1#{\getmacname #1 \relax\getmacargs}
\def\getmacname#1 #2\relax{\macname={#1}}
\def\getmacargs#1{\def\argl{#1}}
% For macro processing make @ a letter so that we can make Texinfo private macro names.
\edef\texiatcatcode{\the\catcode`\@}
\catcode `@=11\relax
% Parse the optional {params} list. Set up \paramno and \paramlist
% so \defmacro knows what to do. Define \macarg.BLAH for each BLAH
% in the params list to some hook where the argument si to be expanded. If
% there are less than 10 arguments that hook is to be replaced by ##N where N
% is the position in that list, that is to say the macro arguments are to be
% defined `a la TeX in the macro body.
%
% That gets used by \mbodybackslash (above).
%
% We need to get `macro parameter char #' into several definitions.
% The technique used is stolen from LaTeX: let \hash be something
% unexpandable, insert that wherever you need a #, and then redefine
% it to # just before using the token list produced.
%
% The same technique is used to protect \eatspaces till just before
% the macro is used.
%
% If there are 10 or more arguments, a different technique is used, where the
% hook remains in the body, and when macro is to be expanded the body is
% processed again to replace the arguments.
%
% In that case, the hook is \the\toks N-1, and we simply set \toks N-1 to the
% argument N value and then \edef the body (nothing else will expand because of
% the catcode regime underwhich the body was input).
%
% If you compile with TeX (not eTeX), and you have macros with 10 or more
% arguments, you need that no macro has more than 256 arguments, otherwise an
% error is produced.
\def\parsemargdef#1;{%
\paramno=0\def\paramlist{}%
\let\hash\relax
\let\xeatspaces\relax
\parsemargdefxxx#1,;,%
% In case that there are 10 or more arguments we parse again the arguments
% list to set new definitions for the \macarg.BLAH macros corresponding to
% each BLAH argument. It was anyhow needed to parse already once this list
% in order to count the arguments, and as macros with at most 9 arguments
% are by far more frequent than macro with 10 or more arguments, defining
% twice the \macarg.BLAH macros does not cost too much processing power.
\ifnum\paramno<10\relax\else
\paramno0\relax
\parsemmanyargdef@@#1,;,% 10 or more arguments
\fi
}
\def\parsemargdefxxx#1,{%
\if#1;\let\next=\relax
\else \let\next=\parsemargdefxxx
\advance\paramno by 1
\expandafter\edef\csname macarg.\eatspaces{#1}\endcsname
{\xeatspaces{\hash\the\paramno}}%
\edef\paramlist{\paramlist\hash\the\paramno,}%
\fi\next}
\def\parsemmanyargdef@@#1,{%
\if#1;\let\next=\relax
\else
\let\next=\parsemmanyargdef@@
\edef\tempb{\eatspaces{#1}}%
\expandafter\def\expandafter\tempa
\expandafter{\csname macarg.\tempb\endcsname}%
% Note that we need some extra \noexpand\noexpand, this is because we
% don't want \the to be expanded in the \parsermacbody as it uses an
% \xdef .
\expandafter\edef\tempa
{\noexpand\noexpand\noexpand\the\toks\the\paramno}%
\advance\paramno by 1\relax
\fi\next}
% These two commands read recursive and nonrecursive macro bodies.
% (They're different since rec and nonrec macros end differently.)
%
\catcode `\@\texiatcatcode
\long\def\parsemacbody#1@end macro%
{\xdef\temp{\eatcr{#1}}\endgroup\defmacro}%
\long\def\parsermacbody#1@end rmacro%
{\xdef\temp{\eatcr{#1}}\endgroup\defmacro}%
\catcode `\@=11\relax
\let\endargs@\relax
\let\nil@\relax
\def\nilm@{\nil@}%
\long\def\nillm@{\nil@}%
% This macro is expanded during the Texinfo macro expansion, not during its
% definition. It gets all the arguments values and assigns them to macros
% macarg.ARGNAME
%
% #1 is the macro name
% #2 is the list of argument names
% #3 is the list of argument values
\def\getargvals@#1#2#3{%
\def\macargdeflist@{}%
\def\saveparamlist@{#2}% Need to keep a copy for parameter expansion.
\def\paramlist{#2,\nil@}%
\def\macroname{#1}%
\begingroup
\macroargctxt
\def\argvaluelist{#3,\nil@}%
\def\@tempa{#3}%
\ifx\@tempa\empty
\setemptyargvalues@
\else
\getargvals@@
\fi
}
%
\def\getargvals@@{%
\ifx\paramlist\nilm@
% Some sanity check needed here that \argvaluelist is also empty.
\ifx\argvaluelist\nillm@
\else
\errhelp = \EMsimple
\errmessage{Too many arguments in macro `\macroname'!}%
\fi
\let\next\macargexpandinbody@
\else
\ifx\argvaluelist\nillm@
% No more arguments values passed to macro. Set remaining named-arg
% macros to empty.
\let\next\setemptyargvalues@
\else
% pop current arg name into \@tempb
\def\@tempa##1{\pop@{\@tempb}{\paramlist}##1\endargs@}%
\expandafter\@tempa\expandafter{\paramlist}%
% pop current argument value into \@tempc
\def\@tempa##1{\longpop@{\@tempc}{\argvaluelist}##1\endargs@}%
\expandafter\@tempa\expandafter{\argvaluelist}%
% Here \@tempb is the current arg name and \@tempc is the current arg value.
% First place the new argument macro definition into \@tempd
\expandafter\macname\expandafter{\@tempc}%
\expandafter\let\csname macarg.\@tempb\endcsname\relax
\expandafter\def\expandafter\@tempe\expandafter{%
\csname macarg.\@tempb\endcsname}%
\edef\@tempd{\long\def\@tempe{\the\macname}}%
\push@\@tempd\macargdeflist@
\let\next\getargvals@@
\fi
\fi
\next
}
\def\push@#1#2{%
\expandafter\expandafter\expandafter\def
\expandafter\expandafter\expandafter#2%
\expandafter\expandafter\expandafter{%
\expandafter#1#2}%
}
% Replace arguments by their values in the macro body, and place the result
% in macro \@tempa
\def\macvalstoargs@{%
% To do this we use the property that token registers that are \the'ed
% within an \edef expand only once. So we are going to place all argument
% values into respective token registers.
%
% First we save the token context, and initialize argument numbering.
\begingroup
\paramno0\relax
% Then, for each argument number #N, we place the corresponding argument
% value into a new token list register \toks#N
\expandafter\putargsintokens@\saveparamlist@,;,%
% Then, we expand the body so that argument are replaced by their
% values. The trick for values not to be expanded themselves is that they
% are within tokens and that tokens expand only once in an \edef .
\edef\@tempc{\csname mac.\macroname .body\endcsname}%
% Now we restore the token stack pointer to free the token list registers
% which we have used, but we make sure that expanded body is saved after
% group.
\expandafter
\endgroup
\expandafter\def\expandafter\@tempa\expandafter{\@tempc}%
}
\def\macargexpandinbody@{%
%% Define the named-macro outside of this group and then close this group.
\expandafter
\endgroup
\macargdeflist@
% First the replace in body the macro arguments by their values, the result
% is in \@tempa .
\macvalstoargs@
% Then we point at the \norecurse or \gobble (for recursive) macro value
% with \@tempb .
\expandafter\let\expandafter\@tempb\csname mac.\macroname .recurse\endcsname
% Depending on whether it is recursive or not, we need some tailing
% \egroup .
\ifx\@tempb\gobble
\let\@tempc\relax
\else
\let\@tempc\egroup
\fi
% And now we do the real job:
\edef\@tempd{\noexpand\@tempb{\macroname}\noexpand\scanmacro{\@tempa}\@tempc}%
\@tempd
}
\def\putargsintokens@#1,{%
\if#1;\let\next\relax
\else
\let\next\putargsintokens@
% First we allocate the new token list register, and give it a temporary
% alias \@tempb .
\toksdef\@tempb\the\paramno
% Then we place the argument value into that token list register.
\expandafter\let\expandafter\@tempa\csname macarg.#1\endcsname
\expandafter\@tempb\expandafter{\@tempa}%
\advance\paramno by 1\relax
\fi
\next
}
% Save the token stack pointer into macro #1
\def\texisavetoksstackpoint#1{\edef#1{\the\@cclvi}}
% Restore the token stack pointer from number in macro #1
\def\texirestoretoksstackpoint#1{\expandafter\mathchardef\expandafter\@cclvi#1\relax}
% newtoks that can be used non \outer .
\def\texinonouternewtoks{\alloc@ 5\toks \toksdef \@cclvi}
% Tailing missing arguments are set to empty
\def\setemptyargvalues@{%
\ifx\paramlist\nilm@
\let\next\macargexpandinbody@
\else
\expandafter\setemptyargvaluesparser@\paramlist\endargs@
\let\next\setemptyargvalues@
\fi
\next
}
\def\setemptyargvaluesparser@#1,#2\endargs@{%
\expandafter\def\expandafter\@tempa\expandafter{%
\expandafter\def\csname macarg.#1\endcsname{}}%
\push@\@tempa\macargdeflist@
\def\paramlist{#2}%
}
% #1 is the element target macro
% #2 is the list macro
% #3,#4\endargs@ is the list value
\def\pop@#1#2#3,#4\endargs@{%
\def#1{#3}%
\def#2{#4}%
}
\long\def\longpop@#1#2#3,#4\endargs@{%
\long\def#1{#3}%
\long\def#2{#4}%
}
% This defines a Texinfo @macro. There are eight cases: recursive and
% nonrecursive macros of zero, one, up to nine, and many arguments.
% Much magic with \expandafter here.
% \xdef is used so that macro definitions will survive the file
% they're defined in; @include reads the file inside a group.
%
\def\defmacro{%
\let\hash=##% convert placeholders to macro parameter chars
\ifrecursive
\ifcase\paramno
% 0
\expandafter\xdef\csname\the\macname\endcsname{%
\noexpand\scanmacro{\temp}}%
\or % 1
\expandafter\xdef\csname\the\macname\endcsname{%
\bgroup\noexpand\macroargctxt
\noexpand\braceorline
\expandafter\noexpand\csname\the\macname xxx\endcsname}%
\expandafter\xdef\csname\the\macname xxx\endcsname##1{%
\egroup\noexpand\scanmacro{\temp}}%
\else
\ifnum\paramno<10\relax % at most 9
\expandafter\xdef\csname\the\macname\endcsname{%
\bgroup\noexpand\macroargctxt
\noexpand\csname\the\macname xx\endcsname}%
\expandafter\xdef\csname\the\macname xx\endcsname##1{%
\expandafter\noexpand\csname\the\macname xxx\endcsname ##1,}%
\expandafter\expandafter
\expandafter\xdef
\expandafter\expandafter
\csname\the\macname xxx\endcsname
\paramlist{\egroup\noexpand\scanmacro{\temp}}%
\else % 10 or more
\expandafter\xdef\csname\the\macname\endcsname{%
\noexpand\getargvals@{\the\macname}{\argl}%
}%
\global\expandafter\let\csname mac.\the\macname .body\endcsname\temp
\global\expandafter\let\csname mac.\the\macname .recurse\endcsname\gobble
\fi
\fi
\else
\ifcase\paramno
% 0
\expandafter\xdef\csname\the\macname\endcsname{%
\noexpand\norecurse{\the\macname}%
\noexpand\scanmacro{\temp}\egroup}%
\or % 1
\expandafter\xdef\csname\the\macname\endcsname{%
\bgroup\noexpand\macroargctxt
\noexpand\braceorline
\expandafter\noexpand\csname\the\macname xxx\endcsname}%
\expandafter\xdef\csname\the\macname xxx\endcsname##1{%
\egroup
\noexpand\norecurse{\the\macname}%
\noexpand\scanmacro{\temp}\egroup}%
\else % at most 9
\ifnum\paramno<10\relax
\expandafter\xdef\csname\the\macname\endcsname{%
\bgroup\noexpand\macroargctxt
\expandafter\noexpand\csname\the\macname xx\endcsname}%
\expandafter\xdef\csname\the\macname xx\endcsname##1{%
\expandafter\noexpand\csname\the\macname xxx\endcsname ##1,}%
\expandafter\expandafter
\expandafter\xdef
\expandafter\expandafter
\csname\the\macname xxx\endcsname
\paramlist{%
\egroup
\noexpand\norecurse{\the\macname}%
\noexpand\scanmacro{\temp}\egroup}%
\else % 10 or more:
\expandafter\xdef\csname\the\macname\endcsname{%
\noexpand\getargvals@{\the\macname}{\argl}%
}%
\global\expandafter\let\csname mac.\the\macname .body\endcsname\temp
\global\expandafter\let\csname mac.\the\macname .recurse\endcsname\norecurse
\fi
\fi
\fi}
\catcode `\@\texiatcatcode\relax
\def\norecurse#1{\bgroup\cslet{#1}{macsave.#1}}
% \braceorline decides whether the next nonwhitespace character is a
% {. If so it reads up to the closing }, if not, it reads the whole
% line. Whatever was read is then fed to the next control sequence
% as an argument (by \parsebrace or \parsearg).
%
\def\braceorline#1{\let\macnamexxx=#1\futurelet\nchar\braceorlinexxx}
\def\braceorlinexxx{%
\ifx\nchar\bgroup\else
\expandafter\parsearg
\fi \macnamexxx}
% @alias.
% We need some trickery to remove the optional spaces around the equal
% sign. Make them active and then expand them all to nothing.
%
\def\alias{\parseargusing\obeyspaces\aliasxxx}
\def\aliasxxx #1{\aliasyyy#1\relax}
\def\aliasyyy #1=#2\relax{%
{%
\expandafter\let\obeyedspace=\empty
\addtomacrolist{#1}%
\xdef\next{\global\let\makecsname{#1}=\makecsname{#2}}%
}%
\next
}
\message{cross references,}
\newwrite\auxfile
\newif\ifhavexrefs % True if xref values are known.
\newif\ifwarnedxrefs % True if we warned once that they aren't known.
% @inforef is relatively simple.
\def\inforef #1{\inforefzzz #1,,,,**}
\def\inforefzzz #1,#2,#3,#4**{%
\putwordSee{} \putwordInfo{} \putwordfile{} \file{\ignorespaces #3{}},
node \samp{\ignorespaces#1{}}}
% @node's only job in TeX is to define \lastnode, which is used in
% cross-references. The @node line might or might not have commas, and
% might or might not have spaces before the first comma, like:
% @node foo , bar , ...
% We don't want such trailing spaces in the node name.
%
\parseargdef\node{\checkenv{}\donode #1 ,\finishnodeparse}
%
% also remove a trailing comma, in case of something like this:
% @node Help-Cross, , , Cross-refs
\def\donode#1 ,#2\finishnodeparse{\dodonode #1,\finishnodeparse}
\def\dodonode#1,#2\finishnodeparse{\gdef\lastnode{#1}}
\let\nwnode=\node
\let\lastnode=\empty
% Write a cross-reference definition for the current node. #1 is the
% type (Ynumbered, Yappendix, Ynothing).
%
\def\donoderef#1{%
\ifx\lastnode\empty\else
\setref{\lastnode}{#1}%
\global\let\lastnode=\empty
\fi
}
% @anchor{NAME} -- define xref target at arbitrary point.
%
\newcount\savesfregister
%
\def\savesf{\relax \ifhmode \savesfregister=\spacefactor \fi}
\def\restoresf{\relax \ifhmode \spacefactor=\savesfregister \fi}
\def\anchor#1{\savesf \setref{#1}{Ynothing}\restoresf \ignorespaces}
% \setref{NAME}{SNT} defines a cross-reference point NAME (a node or an
% anchor), which consists of three parts:
% 1) NAME-title - the current sectioning name taken from \lastsection,
% or the anchor name.
% 2) NAME-snt - section number and type, passed as the SNT arg, or
% empty for anchors.
% 3) NAME-pg - the page number.
%
% This is called from \donoderef, \anchor, and \dofloat. In the case of
% floats, there is an additional part, which is not written here:
% 4) NAME-lof - the text as it should appear in a @listoffloats.
%
\def\setref#1#2{%
\pdfmkdest{#1}%
\iflinks
{%
\atdummies % preserve commands, but don't expand them
\edef\writexrdef##1##2{%
\write\auxfile{@xrdef{#1-% #1 of \setref, expanded by the \edef
##1}{##2}}% these are parameters of \writexrdef
}%
\toks0 = \expandafter{\lastsection}%
\immediate \writexrdef{title}{\the\toks0 }%
\immediate \writexrdef{snt}{\csname #2\endcsname}% \Ynumbered etc.
\safewhatsit{\writexrdef{pg}{\folio}}% will be written later, at \shipout
}%
\fi
}
% @xrefautosectiontitle on|off says whether @section(ing) names are used
% automatically in xrefs, if the third arg is not explicitly specified.
% This was provided as a "secret" @set xref-automatic-section-title
% variable, now it's official.
%
\parseargdef\xrefautomaticsectiontitle{%
\def\temp{#1}%
\ifx\temp\onword
\expandafter\let\csname SETxref-automatic-section-title\endcsname
= \empty
\else\ifx\temp\offword
\expandafter\let\csname SETxref-automatic-section-title\endcsname
= \relax
\else
\errhelp = \EMsimple
\errmessage{Unknown @xrefautomaticsectiontitle value `\temp',
must be on|off}%
\fi\fi
}
%
% @xref, @pxref, and @ref generate cross-references. For \xrefX, #1 is
% the node name, #2 the name of the Info cross-reference, #3 the printed
% node name, #4 the name of the Info file, #5 the name of the printed
% manual. All but the node name can be omitted.
%
\def\pxref#1{\putwordsee{} \xrefX[#1,,,,,,,]}
\def\xref#1{\putwordSee{} \xrefX[#1,,,,,,,]}
\def\ref#1{\xrefX[#1,,,,,,,]}
%
\newbox\toprefbox
\newbox\printedrefnamebox
\newbox\infofilenamebox
\newbox\printedmanualbox
%
\def\xrefX[#1,#2,#3,#4,#5,#6]{\begingroup
\unsepspaces
%
% Get args without leading/trailing spaces.
\def\printedrefname{\ignorespaces #3}%
\setbox\printedrefnamebox = \hbox{\printedrefname\unskip}%
%
\def\infofilename{\ignorespaces #4}%
\setbox\infofilenamebox = \hbox{\infofilename\unskip}%
%
\def\printedmanual{\ignorespaces #5}%
\setbox\printedmanualbox = \hbox{\printedmanual\unskip}%
%
% If the printed reference name (arg #3) was not explicitly given in
% the @xref, figure out what we want to use.
\ifdim \wd\printedrefnamebox = 0pt
% No printed node name was explicitly given.
\expandafter\ifx\csname SETxref-automatic-section-title\endcsname \relax
% Not auto section-title: use node name inside the square brackets.
\def\printedrefname{\ignorespaces #1}%
\else
% Auto section-title: use chapter/section title inside
% the square brackets if we have it.
\ifdim \wd\printedmanualbox > 0pt
% It is in another manual, so we don't have it; use node name.
\def\printedrefname{\ignorespaces #1}%
\else
\ifhavexrefs
% We (should) know the real title if we have the xref values.
\def\printedrefname{\refx{#1-title}{}}%
\else
% Otherwise just copy the Info node name.
\def\printedrefname{\ignorespaces #1}%
\fi%
\fi
\fi
\fi
%
% Make link in pdf output.
\ifpdf
{\indexnofonts
\turnoffactive
\makevalueexpandable
% This expands tokens, so do it after making catcode changes, so _
% etc. don't get their TeX definitions. This ignores all spaces in
% #4, including (wrongly) those in the middle of the filename.
\getfilename{#4}%
%
% This (wrongly) does not take account of leading or trailing
% spaces in #1, which should be ignored.
\edef\pdfxrefdest{#1}%
\ifx\pdfxrefdest\empty
\def\pdfxrefdest{Top}% no empty targets
\else
\txiescapepdf\pdfxrefdest % escape PDF special chars
\fi
%
\leavevmode
\startlink attr{/Border [0 0 0]}%
\ifnum\filenamelength>0
goto file{\the\filename.pdf} name{\pdfxrefdest}%
\else
goto name{\pdfmkpgn{\pdfxrefdest}}%
\fi
}%
\setcolor{\linkcolor}%
\fi
%
% Float references are printed completely differently: "Figure 1.2"
% instead of "[somenode], p.3". We distinguish them by the
% LABEL-title being set to a magic string.
{%
% Have to otherify everything special to allow the \csname to
% include an _ in the xref name, etc.
\indexnofonts
\turnoffactive
\expandafter\global\expandafter\let\expandafter\Xthisreftitle
\csname XR#1-title\endcsname
}%
\iffloat\Xthisreftitle
% If the user specified the print name (third arg) to the ref,
% print it instead of our usual "Figure 1.2".
\ifdim\wd\printedrefnamebox = 0pt
\refx{#1-snt}{}%
\else
\printedrefname
\fi
%
% If the user also gave the printed manual name (fifth arg), append
% "in MANUALNAME".
\ifdim \wd\printedmanualbox > 0pt
\space \putwordin{} \cite{\printedmanual}%
\fi
\else
% node/anchor (non-float) references.
%
% If we use \unhbox to print the node names, TeX does not insert
% empty discretionaries after hyphens, which means that it will not
% find a line break at a hyphen in a node names. Since some manuals
% are best written with fairly long node names, containing hyphens,
% this is a loss. Therefore, we give the text of the node name
% again, so it is as if TeX is seeing it for the first time.
%
\ifdim \wd\printedmanualbox > 0pt
% Cross-manual reference with a printed manual name.
%
\crossmanualxref{\cite{\printedmanual\unskip}}%
%
\else\ifdim \wd\infofilenamebox > 0pt
% Cross-manual reference with only an info filename (arg 4), no
% printed manual name (arg 5). This is essentially the same as
% the case above; we output the filename, since we have nothing else.
%
\crossmanualxref{\code{\infofilename\unskip}}%
%
\else
% Reference within this manual.
%
% _ (for example) has to be the character _ for the purposes of the
% control sequence corresponding to the node, but it has to expand
% into the usual \leavevmode...\vrule stuff for purposes of
% printing. So we \turnoffactive for the \refx-snt, back on for the
% printing, back off for the \refx-pg.
{\turnoffactive
% Only output a following space if the -snt ref is nonempty; for
% @unnumbered and @anchor, it won't be.
\setbox2 = \hbox{\ignorespaces \refx{#1-snt}{}}%
\ifdim \wd2 > 0pt \refx{#1-snt}\space\fi
}%
% output the `[mynode]' via the macro below so it can be overridden.
\xrefprintnodename\printedrefname
%
% But we always want a comma and a space:
,\space
%
% output the `page 3'.
\turnoffactive \putwordpage\tie\refx{#1-pg}{}%
\fi\fi
\fi
\endlink
\endgroup}
% Output a cross-manual xref to #1. Used just above (twice).
%
% Only include the text "Section ``foo'' in" if the foo is neither
% missing or Top. Thus, @xref{,,,foo,The Foo Manual} outputs simply
% "see The Foo Manual", the idea being to refer to the whole manual.
%
% But, this being TeX, we can't easily compare our node name against the
% string "Top" while ignoring the possible spaces before and after in
% the input. By adding the arbitrary 7sp below, we make it much less
% likely that a real node name would have the same width as "Top" (e.g.,
% in a monospaced font). Hopefully it will never happen in practice.
%
% For the same basic reason, we retypeset the "Top" at every
% reference, since the current font is indeterminate.
%
\def\crossmanualxref#1{%
\setbox\toprefbox = \hbox{Top\kern7sp}%
\setbox2 = \hbox{\ignorespaces \printedrefname \unskip \kern7sp}%
\ifdim \wd2 > 7sp % nonempty?
\ifdim \wd2 = \wd\toprefbox \else % same as Top?
\putwordSection{} ``\printedrefname'' \putwordin{}\space
\fi
\fi
#1%
}
% This macro is called from \xrefX for the `[nodename]' part of xref
% output. It's a separate macro only so it can be changed more easily,
% since square brackets don't work well in some documents. Particularly
% one that Bob is working on :).
%
\def\xrefprintnodename#1{[#1]}
% Things referred to by \setref.
%
\def\Ynothing{}
\def\Yomitfromtoc{}
\def\Ynumbered{%
\ifnum\secno=0
\putwordChapter@tie \the\chapno
\else \ifnum\subsecno=0
\putwordSection@tie \the\chapno.\the\secno
\else \ifnum\subsubsecno=0
\putwordSection@tie \the\chapno.\the\secno.\the\subsecno
\else
\putwordSection@tie \the\chapno.\the\secno.\the\subsecno.\the\subsubsecno
\fi\fi\fi
}
\def\Yappendix{%
\ifnum\secno=0
\putwordAppendix@tie @char\the\appendixno{}%
\else \ifnum\subsecno=0
\putwordSection@tie @char\the\appendixno.\the\secno
\else \ifnum\subsubsecno=0
\putwordSection@tie @char\the\appendixno.\the\secno.\the\subsecno
\else
\putwordSection@tie
@char\the\appendixno.\the\secno.\the\subsecno.\the\subsubsecno
\fi\fi\fi
}
% Define \refx{NAME}{SUFFIX} to reference a cross-reference string named NAME.
% If its value is nonempty, SUFFIX is output afterward.
%
\def\refx#1#2{%
{%
\indexnofonts
\otherbackslash
\expandafter\global\expandafter\let\expandafter\thisrefX
\csname XR#1\endcsname
}%
\ifx\thisrefX\relax
% If not defined, say something at least.
\angleleft un\-de\-fined\angleright
\iflinks
\ifhavexrefs
{\toks0 = {#1}% avoid expansion of possibly-complex value
\message{\linenumber Undefined cross reference `\the\toks0'.}}%
\else
\ifwarnedxrefs\else
\global\warnedxrefstrue
\message{Cross reference values unknown; you must run TeX again.}%
\fi
\fi
\fi
\else
% It's defined, so just use it.
\thisrefX
\fi
#2% Output the suffix in any case.
}
% This is the macro invoked by entries in the aux file. Usually it's
% just a \def (we prepend XR to the control sequence name to avoid
% collisions). But if this is a float type, we have more work to do.
%
\def\xrdef#1#2{%
{% The node name might contain 8-bit characters, which in our current
% implementation are changed to commands like @'e. Don't let these
% mess up the control sequence name.
\indexnofonts
\turnoffactive
\xdef\safexrefname{#1}%
}%
%
\expandafter\gdef\csname XR\safexrefname\endcsname{#2}% remember this xref
%
% Was that xref control sequence that we just defined for a float?
\expandafter\iffloat\csname XR\safexrefname\endcsname
% it was a float, and we have the (safe) float type in \iffloattype.
\expandafter\let\expandafter\floatlist
\csname floatlist\iffloattype\endcsname
%
% Is this the first time we've seen this float type?
\expandafter\ifx\floatlist\relax
\toks0 = {\do}% yes, so just \do
\else
% had it before, so preserve previous elements in list.
\toks0 = \expandafter{\floatlist\do}%
\fi
%
% Remember this xref in the control sequence \floatlistFLOATTYPE,
% for later use in \listoffloats.
\expandafter\xdef\csname floatlist\iffloattype\endcsname{\the\toks0
{\safexrefname}}%
\fi
}
% Read the last existing aux file, if any. No error if none exists.
%
\def\tryauxfile{%
\openin 1 \jobname.aux
\ifeof 1 \else
\readdatafile{aux}%
\global\havexrefstrue
\fi
\closein 1
}
\def\setupdatafile{%
\catcode`\^^@=\other
\catcode`\^^A=\other
\catcode`\^^B=\other
\catcode`\^^C=\other
\catcode`\^^D=\other
\catcode`\^^E=\other
\catcode`\^^F=\other
\catcode`\^^G=\other
\catcode`\^^H=\other
\catcode`\^^K=\other
\catcode`\^^L=\other
\catcode`\^^N=\other
\catcode`\^^P=\other
\catcode`\^^Q=\other
\catcode`\^^R=\other
\catcode`\^^S=\other
\catcode`\^^T=\other
\catcode`\^^U=\other
\catcode`\^^V=\other
\catcode`\^^W=\other
\catcode`\^^X=\other
\catcode`\^^Z=\other
\catcode`\^^[=\other
\catcode`\^^\=\other
\catcode`\^^]=\other
\catcode`\^^^=\other
\catcode`\^^_=\other
% It was suggested to set the catcode of ^ to 7, which would allow ^^e4 etc.
% in xref tags, i.e., node names. But since ^^e4 notation isn't
% supported in the main text, it doesn't seem desirable. Furthermore,
% that is not enough: for node names that actually contain a ^
% character, we would end up writing a line like this: 'xrdef {'hat
% b-title}{'hat b} and \xrdef does a \csname...\endcsname on the first
% argument, and \hat is not an expandable control sequence. It could
% all be worked out, but why? Either we support ^^ or we don't.
%
% The other change necessary for this was to define \auxhat:
% \def\auxhat{\def^{'hat }}% extra space so ok if followed by letter
% and then to call \auxhat in \setq.
%
\catcode`\^=\other
%
% Special characters. Should be turned off anyway, but...
\catcode`\~=\other
\catcode`\[=\other
\catcode`\]=\other
\catcode`\"=\other
\catcode`\_=\other
\catcode`\|=\other
\catcode`\<=\other
\catcode`\>=\other
\catcode`\$=\other
\catcode`\#=\other
\catcode`\&=\other
\catcode`\%=\other
\catcode`+=\other % avoid \+ for paranoia even though we've turned it off
%
% This is to support \ in node names and titles, since the \
% characters end up in a \csname. It's easier than
% leaving it active and making its active definition an actual \
% character. What I don't understand is why it works in the *value*
% of the xrdef. Seems like it should be a catcode12 \, and that
% should not typeset properly. But it works, so I'm moving on for
% now. --karl, 15jan04.
\catcode`\\=\other
%
% Make the characters 128-255 be printing characters.
{%
\count1=128
\def\loop{%
\catcode\count1=\other
\advance\count1 by 1
\ifnum \count1<256 \loop \fi
}%
}%
%
% @ is our escape character in .aux files, and we need braces.
\catcode`\{=1
\catcode`\}=2
\catcode`\@=0
}
\def\readdatafile#1{%
\begingroup
\setupdatafile
\input\jobname.#1
\endgroup}
\message{insertions,}
% including footnotes.
\newcount \footnoteno
% The trailing space in the following definition for supereject is
% vital for proper filling; pages come out unaligned when you do a
% pagealignmacro call if that space before the closing brace is
% removed. (Generally, numeric constants should always be followed by a
% space to prevent strange expansion errors.)
\def\supereject{\par\penalty -20000\footnoteno =0 }
% @footnotestyle is meaningful for Info output only.
\let\footnotestyle=\comment
{\catcode `\@=11
%
% Auto-number footnotes. Otherwise like plain.
\gdef\footnote{%
\let\indent=\ptexindent
\let\noindent=\ptexnoindent
\global\advance\footnoteno by \@ne
\edef\thisfootno{$^{\the\footnoteno}$}%
%
% In case the footnote comes at the end of a sentence, preserve the
% extra spacing after we do the footnote number.
\let\@sf\empty
\ifhmode\edef\@sf{\spacefactor\the\spacefactor}\ptexslash\fi
%
% Remove inadvertent blank space before typesetting the footnote number.
\unskip
\thisfootno\@sf
\dofootnote
}%
% Don't bother with the trickery in plain.tex to not require the
% footnote text as a parameter. Our footnotes don't need to be so general.
%
% Oh yes, they do; otherwise, @ifset (and anything else that uses
% \parseargline) fails inside footnotes because the tokens are fixed when
% the footnote is read. --karl, 16nov96.
%
\gdef\dofootnote{%
\insert\footins\bgroup
% We want to typeset this text as a normal paragraph, even if the
% footnote reference occurs in (for example) a display environment.
% So reset some parameters.
\hsize=\pagewidth
\interlinepenalty\interfootnotelinepenalty
\splittopskip\ht\strutbox % top baseline for broken footnotes
\splitmaxdepth\dp\strutbox
\floatingpenalty\@MM
\leftskip\z@skip
\rightskip\z@skip
\spaceskip\z@skip
\xspaceskip\z@skip
\parindent\defaultparindent
%
\smallfonts \rm
%
% Because we use hanging indentation in footnotes, a @noindent appears
% to exdent this text, so make it be a no-op. makeinfo does not use
% hanging indentation so @noindent can still be needed within footnote
% text after an @example or the like (not that this is good style).
\let\noindent = \relax
%
% Hang the footnote text off the number. Use \everypar in case the
% footnote extends for more than one paragraph.
\everypar = {\hang}%
\textindent{\thisfootno}%
%
% Don't crash into the line above the footnote text. Since this
% expands into a box, it must come within the paragraph, lest it
% provide a place where TeX can split the footnote.
\footstrut
%
% Invoke rest of plain TeX footnote routine.
\futurelet\next\fo@t
}
}%end \catcode `\@=11
% In case a @footnote appears in a vbox, save the footnote text and create
% the real \insert just after the vbox finished. Otherwise, the insertion
% would be lost.
% Similarly, if a @footnote appears inside an alignment, save the footnote
% text to a box and make the \insert when a row of the table is finished.
% And the same can be done for other insert classes. --kasal, 16nov03.
% Replace the \insert primitive by a cheating macro.
% Deeper inside, just make sure that the saved insertions are not spilled
% out prematurely.
%
\def\startsavinginserts{%
\ifx \insert\ptexinsert
\let\insert\saveinsert
\else
\let\checkinserts\relax
\fi
}
% This \insert replacement works for both \insert\footins{foo} and
% \insert\footins\bgroup foo\egroup, but it doesn't work for \insert27{foo}.
%
\def\saveinsert#1{%
\edef\next{\noexpand\savetobox \makeSAVEname#1}%
\afterassignment\next
% swallow the left brace
\let\temp =
}
\def\makeSAVEname#1{\makecsname{SAVE\expandafter\gobble\string#1}}
\def\savetobox#1{\global\setbox#1 = \vbox\bgroup \unvbox#1}
\def\checksaveins#1{\ifvoid#1\else \placesaveins#1\fi}
\def\placesaveins#1{%
\ptexinsert \csname\expandafter\gobblesave\string#1\endcsname
{\box#1}%
}
% eat @SAVE -- beware, all of them have catcode \other:
{
\def\dospecials{\do S\do A\do V\do E} \uncatcodespecials % ;-)
\gdef\gobblesave @SAVE{}
}
% initialization:
\def\newsaveins #1{%
\edef\next{\noexpand\newsaveinsX \makeSAVEname#1}%
\next
}
\def\newsaveinsX #1{%
\csname newbox\endcsname #1%
\expandafter\def\expandafter\checkinserts\expandafter{\checkinserts
\checksaveins #1}%
}
% initialize:
\let\checkinserts\empty
\newsaveins\footins
\newsaveins\margin
% @image. We use the macros from epsf.tex to support this.
% If epsf.tex is not installed and @image is used, we complain.
%
% Check for and read epsf.tex up front. If we read it only at @image
% time, we might be inside a group, and then its definitions would get
% undone and the next image would fail.
\openin 1 = epsf.tex
\ifeof 1 \else
% Do not bother showing banner with epsf.tex v2.7k (available in
% doc/epsf.tex and on ctan).
\def\epsfannounce{\toks0 = }%
\input epsf.tex
\fi
\closein 1
%
% We will only complain once about lack of epsf.tex.
\newif\ifwarnednoepsf
\newhelp\noepsfhelp{epsf.tex must be installed for images to
work. It is also included in the Texinfo distribution, or you can get
it from ftp://tug.org/tex/epsf.tex.}
%
\def\image#1{%
\ifx\epsfbox\thisisundefined
\ifwarnednoepsf \else
\errhelp = \noepsfhelp
\errmessage{epsf.tex not found, images will be ignored}%
\global\warnednoepsftrue
\fi
\else
\imagexxx #1,,,,,\finish
\fi
}
%
% Arguments to @image:
% #1 is (mandatory) image filename; we tack on .eps extension.
% #2 is (optional) width, #3 is (optional) height.
% #4 is (ignored optional) html alt text.
% #5 is (ignored optional) extension.
% #6 is just the usual extra ignored arg for parsing stuff.
\newif\ifimagevmode
\def\imagexxx#1,#2,#3,#4,#5,#6\finish{\begingroup
\catcode`\^^M = 5 % in case we're inside an example
\normalturnoffactive % allow _ et al. in names
% If the image is by itself, center it.
\ifvmode
\imagevmodetrue
\else \ifx\centersub\centerV
% for @center @image, we need a vbox so we can have our vertical space
\imagevmodetrue
\vbox\bgroup % vbox has better behavior than vtop herev
\fi\fi
%
\ifimagevmode
\nobreak\medskip
% Usually we'll have text after the image which will insert
% \parskip glue, so insert it here too to equalize the space
% above and below.
\nobreak\vskip\parskip
\nobreak
\fi
%
% Leave vertical mode so that indentation from an enclosing
% environment such as @quotation is respected.
% However, if we're at the top level, we don't want the
% normal paragraph indentation.
% On the other hand, if we are in the case of @center @image, we don't
% want to start a paragraph, which will create a hsize-width box and
% eradicate the centering.
\ifx\centersub\centerV\else \noindent \fi
%
% Output the image.
\ifpdf
\dopdfimage{#1}{#2}{#3}%
\else
% \epsfbox itself resets \epsf?size at each figure.
\setbox0 = \hbox{\ignorespaces #2}\ifdim\wd0 > 0pt \epsfxsize=#2\relax \fi
\setbox0 = \hbox{\ignorespaces #3}\ifdim\wd0 > 0pt \epsfysize=#3\relax \fi
\epsfbox{#1.eps}%
\fi
%
\ifimagevmode
\medskip % space after a standalone image
\fi
\ifx\centersub\centerV \egroup \fi
\endgroup}
% @float FLOATTYPE,LABEL,LOC ... @end float for displayed figures, tables,
% etc. We don't actually implement floating yet, we always include the
% float "here". But it seemed the best name for the future.
%
\envparseargdef\float{\eatcommaspace\eatcommaspace\dofloat#1, , ,\finish}
% There may be a space before second and/or third parameter; delete it.
\def\eatcommaspace#1, {#1,}
% #1 is the optional FLOATTYPE, the text label for this float, typically
% "Figure", "Table", "Example", etc. Can't contain commas. If omitted,
% this float will not be numbered and cannot be referred to.
%
% #2 is the optional xref label. Also must be present for the float to
% be referable.
%
% #3 is the optional positioning argument; for now, it is ignored. It
% will somehow specify the positions allowed to float to (here, top, bottom).
%
% We keep a separate counter for each FLOATTYPE, which we reset at each
% chapter-level command.
\let\resetallfloatnos=\empty
%
\def\dofloat#1,#2,#3,#4\finish{%
\let\thiscaption=\empty
\let\thisshortcaption=\empty
%
% don't lose footnotes inside @float.
%
% BEWARE: when the floats start float, we have to issue warning whenever an
% insert appears inside a float which could possibly float. --kasal, 26may04
%
\startsavinginserts
%
% We can't be used inside a paragraph.
\par
%
\vtop\bgroup
\def\floattype{#1}%
\def\floatlabel{#2}%
\def\floatloc{#3}% we do nothing with this yet.
%
\ifx\floattype\empty
\let\safefloattype=\empty
\else
{%
% the floattype might have accents or other special characters,
% but we need to use it in a control sequence name.
\indexnofonts
\turnoffactive
\xdef\safefloattype{\floattype}%
}%
\fi
%
% If label is given but no type, we handle that as the empty type.
\ifx\floatlabel\empty \else
% We want each FLOATTYPE to be numbered separately (Figure 1,
% Table 1, Figure 2, ...). (And if no label, no number.)
%
\expandafter\getfloatno\csname\safefloattype floatno\endcsname
\global\advance\floatno by 1
%
{%
% This magic value for \lastsection is output by \setref as the
% XREFLABEL-title value. \xrefX uses it to distinguish float
% labels (which have a completely different output format) from
% node and anchor labels. And \xrdef uses it to construct the
% lists of floats.
%
\edef\lastsection{\floatmagic=\safefloattype}%
\setref{\floatlabel}{Yfloat}%
}%
\fi
%
% start with \parskip glue, I guess.
\vskip\parskip
%
% Don't suppress indentation if a float happens to start a section.
\restorefirstparagraphindent
}
% we have these possibilities:
% @float Foo,lbl & @caption{Cap}: Foo 1.1: Cap
% @float Foo,lbl & no caption: Foo 1.1
% @float Foo & @caption{Cap}: Foo: Cap
% @float Foo & no caption: Foo
% @float ,lbl & Caption{Cap}: 1.1: Cap
% @float ,lbl & no caption: 1.1
% @float & @caption{Cap}: Cap
% @float & no caption:
%
\def\Efloat{%
\let\floatident = \empty
%
% In all cases, if we have a float type, it comes first.
\ifx\floattype\empty \else \def\floatident{\floattype}\fi
%
% If we have an xref label, the number comes next.
\ifx\floatlabel\empty \else
\ifx\floattype\empty \else % if also had float type, need tie first.
\appendtomacro\floatident{\tie}%
\fi
% the number.
\appendtomacro\floatident{\chaplevelprefix\the\floatno}%
\fi
%
% Start the printed caption with what we've constructed in
% \floatident, but keep it separate; we need \floatident again.
\let\captionline = \floatident
%
\ifx\thiscaption\empty \else
\ifx\floatident\empty \else
\appendtomacro\captionline{: }% had ident, so need a colon between
\fi
%
% caption text.
\appendtomacro\captionline{\scanexp\thiscaption}%
\fi
%
% If we have anything to print, print it, with space before.
% Eventually this needs to become an \insert.
\ifx\captionline\empty \else
\vskip.5\parskip
\captionline
%
% Space below caption.
\vskip\parskip
\fi
%
% If have an xref label, write the list of floats info. Do this
% after the caption, to avoid chance of it being a breakpoint.
\ifx\floatlabel\empty \else
% Write the text that goes in the lof to the aux file as
% \floatlabel-lof. Besides \floatident, we include the short
% caption if specified, else the full caption if specified, else nothing.
{%
\atdummies
%
% since we read the caption text in the macro world, where ^^M
% is turned into a normal character, we have to scan it back, so
% we don't write the literal three characters "^^M" into the aux file.
\scanexp{%
\xdef\noexpand\gtemp{%
\ifx\thisshortcaption\empty
\thiscaption
\else
\thisshortcaption
\fi
}%
}%
\immediate\write\auxfile{@xrdef{\floatlabel-lof}{\floatident
\ifx\gtemp\empty \else : \gtemp \fi}}%
}%
\fi
\egroup % end of \vtop
%
% place the captured inserts
%
% BEWARE: when the floats start floating, we have to issue warning
% whenever an insert appears inside a float which could possibly
% float. --kasal, 26may04
%
\checkinserts
}
% Append the tokens #2 to the definition of macro #1, not expanding either.
%
\def\appendtomacro#1#2{%
\expandafter\def\expandafter#1\expandafter{#1#2}%
}
% @caption, @shortcaption
%
\def\caption{\docaption\thiscaption}
\def\shortcaption{\docaption\thisshortcaption}
\def\docaption{\checkenv\float \bgroup\scanargctxt\defcaption}
\def\defcaption#1#2{\egroup \def#1{#2}}
% The parameter is the control sequence identifying the counter we are
% going to use. Create it if it doesn't exist and assign it to \floatno.
\def\getfloatno#1{%
\ifx#1\relax
% Haven't seen this figure type before.
\csname newcount\endcsname #1%
%
% Remember to reset this floatno at the next chap.
\expandafter\gdef\expandafter\resetallfloatnos
\expandafter{\resetallfloatnos #1=0 }%
\fi
\let\floatno#1%
}
% \setref calls this to get the XREFLABEL-snt value. We want an @xref
% to the FLOATLABEL to expand to "Figure 3.1". We call \setref when we
% first read the @float command.
%
\def\Yfloat{\floattype@tie \chaplevelprefix\the\floatno}%
% Magic string used for the XREFLABEL-title value, so \xrefX can
% distinguish floats from other xref types.
\def\floatmagic{!!float!!}
% #1 is the control sequence we are passed; we expand into a conditional
% which is true if #1 represents a float ref. That is, the magic
% \lastsection value which we \setref above.
%
\def\iffloat#1{\expandafter\doiffloat#1==\finish}
%
% #1 is (maybe) the \floatmagic string. If so, #2 will be the
% (safe) float type for this float. We set \iffloattype to #2.
%
\def\doiffloat#1=#2=#3\finish{%
\def\temp{#1}%
\def\iffloattype{#2}%
\ifx\temp\floatmagic
}
% @listoffloats FLOATTYPE - print a list of floats like a table of contents.
%
\parseargdef\listoffloats{%
\def\floattype{#1}% floattype
{%
% the floattype might have accents or other special characters,
% but we need to use it in a control sequence name.
\indexnofonts
\turnoffactive
\xdef\safefloattype{\floattype}%
}%
%
% \xrdef saves the floats as a \do-list in \floatlistSAFEFLOATTYPE.
\expandafter\ifx\csname floatlist\safefloattype\endcsname \relax
\ifhavexrefs
% if the user said @listoffloats foo but never @float foo.
\message{\linenumber No `\safefloattype' floats to list.}%
\fi
\else
\begingroup
\leftskip=\tocindent % indent these entries like a toc
\let\do=\listoffloatsdo
\csname floatlist\safefloattype\endcsname
\endgroup
\fi
}
% This is called on each entry in a list of floats. We're passed the
% xref label, in the form LABEL-title, which is how we save it in the
% aux file. We strip off the -title and look up \XRLABEL-lof, which
% has the text we're supposed to typeset here.
%
% Figures without xref labels will not be included in the list (since
% they won't appear in the aux file).
%
\def\listoffloatsdo#1{\listoffloatsdoentry#1\finish}
\def\listoffloatsdoentry#1-title\finish{{%
% Can't fully expand XR#1-lof because it can contain anything. Just
% pass the control sequence. On the other hand, XR#1-pg is just the
% page number, and we want to fully expand that so we can get a link
% in pdf output.
\toksA = \expandafter{\csname XR#1-lof\endcsname}%
%
% use the same \entry macro we use to generate the TOC and index.
\edef\writeentry{\noexpand\entry{\the\toksA}{\csname XR#1-pg\endcsname}}%
\writeentry
}}
\message{localization,}
% For single-language documents, @documentlanguage is usually given very
% early, just after @documentencoding. Single argument is the language
% (de) or locale (de_DE) abbreviation.
%
{
\catcode`\_ = \active
\globaldefs=1
\parseargdef\documentlanguage{\begingroup
\let_=\normalunderscore % normal _ character for filenames
\tex % read txi-??.tex file in plain TeX.
% Read the file by the name they passed if it exists.
\openin 1 txi-#1.tex
\ifeof 1
\documentlanguagetrywithoutunderscore{#1_\finish}%
\else
\globaldefs = 1 % everything in the txi-LL files needs to persist
\input txi-#1.tex
\fi
\closein 1
\endgroup % end raw TeX
\endgroup}
%
% If they passed de_DE, and txi-de_DE.tex doesn't exist,
% try txi-de.tex.
%
\gdef\documentlanguagetrywithoutunderscore#1_#2\finish{%
\openin 1 txi-#1.tex
\ifeof 1
\errhelp = \nolanghelp
\errmessage{Cannot read language file txi-#1.tex}%
\else
\globaldefs = 1 % everything in the txi-LL files needs to persist
\input txi-#1.tex
\fi
\closein 1
}
}% end of special _ catcode
%
\newhelp\nolanghelp{The given language definition file cannot be found or
is empty. Maybe you need to install it? Putting it in the current
directory should work if nowhere else does.}
% This macro is called from txi-??.tex files; the first argument is the
% \language name to set (without the "\lang@" prefix), the second and
% third args are \{left,right}hyphenmin.
%
% The language names to pass are determined when the format is built.
% See the etex.log file created at that time, e.g.,
% /usr/local/texlive/2008/texmf-var/web2c/pdftex/etex.log.
%
% With TeX Live 2008, etex now includes hyphenation patterns for all
% available languages. This means we can support hyphenation in
% Texinfo, at least to some extent. (This still doesn't solve the
% accented characters problem.)
%
\catcode`@=11
\def\txisetlanguage#1#2#3{%
% do not set the language if the name is undefined in the current TeX.
\expandafter\ifx\csname lang@#1\endcsname \relax
\message{no patterns for #1}%
\else
\global\language = \csname lang@#1\endcsname
\fi
% but there is no harm in adjusting the hyphenmin values regardless.
\global\lefthyphenmin = #2\relax
\global\righthyphenmin = #3\relax
}
% Helpers for encodings.
% Set the catcode of characters 128 through 255 to the specified number.
%
\def\setnonasciicharscatcode#1{%
\count255=128
\loop\ifnum\count255<256
\global\catcode\count255=#1\relax
\advance\count255 by 1
\repeat
}
\def\setnonasciicharscatcodenonglobal#1{%
\count255=128
\loop\ifnum\count255<256
\catcode\count255=#1\relax
\advance\count255 by 1
\repeat
}
% @documentencoding sets the definition of non-ASCII characters
% according to the specified encoding.
%
\parseargdef\documentencoding{%
% Encoding being declared for the document.
\def\declaredencoding{\csname #1.enc\endcsname}%
%
% Supported encodings: names converted to tokens in order to be able
% to compare them with \ifx.
\def\ascii{\csname US-ASCII.enc\endcsname}%
\def\latnine{\csname ISO-8859-15.enc\endcsname}%
\def\latone{\csname ISO-8859-1.enc\endcsname}%
\def\lattwo{\csname ISO-8859-2.enc\endcsname}%
\def\utfeight{\csname UTF-8.enc\endcsname}%
%
\ifx \declaredencoding \ascii
\asciichardefs
%
\else \ifx \declaredencoding \lattwo
\setnonasciicharscatcode\active
\lattwochardefs
%
\else \ifx \declaredencoding \latone
\setnonasciicharscatcode\active
\latonechardefs
%
\else \ifx \declaredencoding \latnine
\setnonasciicharscatcode\active
\latninechardefs
%
\else \ifx \declaredencoding \utfeight
\setnonasciicharscatcode\active
\utfeightchardefs
%
\else
\message{Unknown document encoding #1, ignoring.}%
%
\fi % utfeight
\fi % latnine
\fi % latone
\fi % lattwo
\fi % ascii
}
% A message to be logged when using a character that isn't available
% the default font encoding (OT1).
%
\def\missingcharmsg#1{\message{Character missing in OT1 encoding: #1.}}
% Take account of \c (plain) vs. \, (Texinfo) difference.
\def\cedilla#1{\ifx\c\ptexc\c{#1}\else\,{#1}\fi}
% First, make active non-ASCII characters in order for them to be
% correctly categorized when TeX reads the replacement text of
% macros containing the character definitions.
\setnonasciicharscatcode\active
%
% Latin1 (ISO-8859-1) character definitions.
\def\latonechardefs{%
\gdef^^a0{\tie}
\gdef^^a1{\exclamdown}
\gdef^^a2{\missingcharmsg{CENT SIGN}}
\gdef^^a3{{\pounds}}
\gdef^^a4{\missingcharmsg{CURRENCY SIGN}}
\gdef^^a5{\missingcharmsg{YEN SIGN}}
\gdef^^a6{\missingcharmsg{BROKEN BAR}}
\gdef^^a7{\S}
\gdef^^a8{\"{}}
\gdef^^a9{\copyright}
\gdef^^aa{\ordf}
\gdef^^ab{\guillemetleft}
\gdef^^ac{$\lnot$}
\gdef^^ad{\-}
\gdef^^ae{\registeredsymbol}
\gdef^^af{\={}}
%
\gdef^^b0{\textdegree}
\gdef^^b1{$\pm$}
\gdef^^b2{$^2$}
\gdef^^b3{$^3$}
\gdef^^b4{\'{}}
\gdef^^b5{$\mu$}
\gdef^^b6{\P}
%
\gdef^^b7{$^.$}
\gdef^^b8{\cedilla\ }
\gdef^^b9{$^1$}
\gdef^^ba{\ordm}
%
\gdef^^bb{\guillemetright}
\gdef^^bc{$1\over4$}
\gdef^^bd{$1\over2$}
\gdef^^be{$3\over4$}
\gdef^^bf{\questiondown}
%
\gdef^^c0{\`A}
\gdef^^c1{\'A}
\gdef^^c2{\^A}
\gdef^^c3{\~A}
\gdef^^c4{\"A}
\gdef^^c5{\ringaccent A}
\gdef^^c6{\AE}
\gdef^^c7{\cedilla C}
\gdef^^c8{\`E}
\gdef^^c9{\'E}
\gdef^^ca{\^E}
\gdef^^cb{\"E}
\gdef^^cc{\`I}
\gdef^^cd{\'I}
\gdef^^ce{\^I}
\gdef^^cf{\"I}
%
\gdef^^d0{\DH}
\gdef^^d1{\~N}
\gdef^^d2{\`O}
\gdef^^d3{\'O}
\gdef^^d4{\^O}
\gdef^^d5{\~O}
\gdef^^d6{\"O}
\gdef^^d7{$\times$}
\gdef^^d8{\O}
\gdef^^d9{\`U}
\gdef^^da{\'U}
\gdef^^db{\^U}
\gdef^^dc{\"U}
\gdef^^dd{\'Y}
\gdef^^de{\TH}
\gdef^^df{\ss}
%
\gdef^^e0{\`a}
\gdef^^e1{\'a}
\gdef^^e2{\^a}
\gdef^^e3{\~a}
\gdef^^e4{\"a}
\gdef^^e5{\ringaccent a}
\gdef^^e6{\ae}
\gdef^^e7{\cedilla c}
\gdef^^e8{\`e}
\gdef^^e9{\'e}
\gdef^^ea{\^e}
\gdef^^eb{\"e}
\gdef^^ec{\`{\dotless i}}
\gdef^^ed{\'{\dotless i}}
\gdef^^ee{\^{\dotless i}}
\gdef^^ef{\"{\dotless i}}
%
\gdef^^f0{\dh}
\gdef^^f1{\~n}
\gdef^^f2{\`o}
\gdef^^f3{\'o}
\gdef^^f4{\^o}
\gdef^^f5{\~o}
\gdef^^f6{\"o}
\gdef^^f7{$\div$}
\gdef^^f8{\o}
\gdef^^f9{\`u}
\gdef^^fa{\'u}
\gdef^^fb{\^u}
\gdef^^fc{\"u}
\gdef^^fd{\'y}
\gdef^^fe{\th}
\gdef^^ff{\"y}
}
% Latin9 (ISO-8859-15) encoding character definitions.
\def\latninechardefs{%
% Encoding is almost identical to Latin1.
\latonechardefs
%
\gdef^^a4{\euro}
\gdef^^a6{\v S}
\gdef^^a8{\v s}
\gdef^^b4{\v Z}
\gdef^^b8{\v z}
\gdef^^bc{\OE}
\gdef^^bd{\oe}
\gdef^^be{\"Y}
}
% Latin2 (ISO-8859-2) character definitions.
\def\lattwochardefs{%
\gdef^^a0{\tie}
\gdef^^a1{\ogonek{A}}
\gdef^^a2{\u{}}
\gdef^^a3{\L}
\gdef^^a4{\missingcharmsg{CURRENCY SIGN}}
\gdef^^a5{\v L}
\gdef^^a6{\'S}
\gdef^^a7{\S}
\gdef^^a8{\"{}}
\gdef^^a9{\v S}
\gdef^^aa{\cedilla S}
\gdef^^ab{\v T}
\gdef^^ac{\'Z}
\gdef^^ad{\-}
\gdef^^ae{\v Z}
\gdef^^af{\dotaccent Z}
%
\gdef^^b0{\textdegree}
\gdef^^b1{\ogonek{a}}
\gdef^^b2{\ogonek{ }}
\gdef^^b3{\l}
\gdef^^b4{\'{}}
\gdef^^b5{\v l}
\gdef^^b6{\'s}
\gdef^^b7{\v{}}
\gdef^^b8{\cedilla\ }
\gdef^^b9{\v s}
\gdef^^ba{\cedilla s}
\gdef^^bb{\v t}
\gdef^^bc{\'z}
\gdef^^bd{\H{}}
\gdef^^be{\v z}
\gdef^^bf{\dotaccent z}
%
\gdef^^c0{\'R}
\gdef^^c1{\'A}
\gdef^^c2{\^A}
\gdef^^c3{\u A}
\gdef^^c4{\"A}
\gdef^^c5{\'L}
\gdef^^c6{\'C}
\gdef^^c7{\cedilla C}
\gdef^^c8{\v C}
\gdef^^c9{\'E}
\gdef^^ca{\ogonek{E}}
\gdef^^cb{\"E}
\gdef^^cc{\v E}
\gdef^^cd{\'I}
\gdef^^ce{\^I}
\gdef^^cf{\v D}
%
\gdef^^d0{\DH}
\gdef^^d1{\'N}
\gdef^^d2{\v N}
\gdef^^d3{\'O}
\gdef^^d4{\^O}
\gdef^^d5{\H O}
\gdef^^d6{\"O}
\gdef^^d7{$\times$}
\gdef^^d8{\v R}
\gdef^^d9{\ringaccent U}
\gdef^^da{\'U}
\gdef^^db{\H U}
\gdef^^dc{\"U}
\gdef^^dd{\'Y}
\gdef^^de{\cedilla T}
\gdef^^df{\ss}
%
\gdef^^e0{\'r}
\gdef^^e1{\'a}
\gdef^^e2{\^a}
\gdef^^e3{\u a}
\gdef^^e4{\"a}
\gdef^^e5{\'l}
\gdef^^e6{\'c}
\gdef^^e7{\cedilla c}
\gdef^^e8{\v c}
\gdef^^e9{\'e}
\gdef^^ea{\ogonek{e}}
\gdef^^eb{\"e}
\gdef^^ec{\v e}
\gdef^^ed{\'{\dotless{i}}}
\gdef^^ee{\^{\dotless{i}}}
\gdef^^ef{\v d}
%
\gdef^^f0{\dh}
\gdef^^f1{\'n}
\gdef^^f2{\v n}
\gdef^^f3{\'o}
\gdef^^f4{\^o}
\gdef^^f5{\H o}
\gdef^^f6{\"o}
\gdef^^f7{$\div$}
\gdef^^f8{\v r}
\gdef^^f9{\ringaccent u}
\gdef^^fa{\'u}
\gdef^^fb{\H u}
\gdef^^fc{\"u}
\gdef^^fd{\'y}
\gdef^^fe{\cedilla t}
\gdef^^ff{\dotaccent{}}
}
% UTF-8 character definitions.
%
% This code to support UTF-8 is based on LaTeX's utf8.def, with some
% changes for Texinfo conventions. It is included here under the GPL by
% permission from Frank Mittelbach and the LaTeX team.
%
\newcount\countUTFx
\newcount\countUTFy
\newcount\countUTFz
\gdef\UTFviiiTwoOctets#1#2{\expandafter
\UTFviiiDefined\csname u8:#1\string #2\endcsname}
%
\gdef\UTFviiiThreeOctets#1#2#3{\expandafter
\UTFviiiDefined\csname u8:#1\string #2\string #3\endcsname}
%
\gdef\UTFviiiFourOctets#1#2#3#4{\expandafter
\UTFviiiDefined\csname u8:#1\string #2\string #3\string #4\endcsname}
\gdef\UTFviiiDefined#1{%
\ifx #1\relax
\message{\linenumber Unicode char \string #1 not defined for Texinfo}%
\else
\expandafter #1%
\fi
}
\begingroup
\catcode`\~13
\catcode`\"12
\def\UTFviiiLoop{%
\global\catcode\countUTFx\active
\uccode`\~\countUTFx
\uppercase\expandafter{\UTFviiiTmp}%
\advance\countUTFx by 1
\ifnum\countUTFx < \countUTFy
\expandafter\UTFviiiLoop
\fi}
\countUTFx = "C2
\countUTFy = "E0
\def\UTFviiiTmp{%
\xdef~{\noexpand\UTFviiiTwoOctets\string~}}
\UTFviiiLoop
\countUTFx = "E0
\countUTFy = "F0
\def\UTFviiiTmp{%
\xdef~{\noexpand\UTFviiiThreeOctets\string~}}
\UTFviiiLoop
\countUTFx = "F0
\countUTFy = "F4
\def\UTFviiiTmp{%
\xdef~{\noexpand\UTFviiiFourOctets\string~}}
\UTFviiiLoop
\endgroup
\begingroup
\catcode`\"=12
\catcode`\<=12
\catcode`\.=12
\catcode`\,=12
\catcode`\;=12
\catcode`\!=12
\catcode`\~=13
\gdef\DeclareUnicodeCharacter#1#2{%
\countUTFz = "#1\relax
%\wlog{\space\space defining Unicode char U+#1 (decimal \the\countUTFz)}%
\begingroup
\parseXMLCharref
\def\UTFviiiTwoOctets##1##2{%
\csname u8:##1\string ##2\endcsname}%
\def\UTFviiiThreeOctets##1##2##3{%
\csname u8:##1\string ##2\string ##3\endcsname}%
\def\UTFviiiFourOctets##1##2##3##4{%
\csname u8:##1\string ##2\string ##3\string ##4\endcsname}%
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter
\gdef\UTFviiiTmp{#2}%
\endgroup}
\gdef\parseXMLCharref{%
\ifnum\countUTFz < "A0\relax
\errhelp = \EMsimple
\errmessage{Cannot define Unicode char value < 00A0}%
\else\ifnum\countUTFz < "800\relax
\parseUTFviiiA,%
\parseUTFviiiB C\UTFviiiTwoOctets.,%
\else\ifnum\countUTFz < "10000\relax
\parseUTFviiiA;%
\parseUTFviiiA,%
\parseUTFviiiB E\UTFviiiThreeOctets.{,;}%
\else
\parseUTFviiiA;%
\parseUTFviiiA,%
\parseUTFviiiA!%
\parseUTFviiiB F\UTFviiiFourOctets.{!,;}%
\fi\fi\fi
}
\gdef\parseUTFviiiA#1{%
\countUTFx = \countUTFz
\divide\countUTFz by 64
\countUTFy = \countUTFz
\multiply\countUTFz by 64
\advance\countUTFx by -\countUTFz
\advance\countUTFx by 128
\uccode `#1\countUTFx
\countUTFz = \countUTFy}
\gdef\parseUTFviiiB#1#2#3#4{%
\advance\countUTFz by "#10\relax
\uccode `#3\countUTFz
\uppercase{\gdef\UTFviiiTmp{#2#3#4}}}
\endgroup
\def\utfeightchardefs{%
\DeclareUnicodeCharacter{00A0}{\tie}
\DeclareUnicodeCharacter{00A1}{\exclamdown}
\DeclareUnicodeCharacter{00A3}{\pounds}
\DeclareUnicodeCharacter{00A8}{\"{ }}
\DeclareUnicodeCharacter{00A9}{\copyright}
\DeclareUnicodeCharacter{00AA}{\ordf}
\DeclareUnicodeCharacter{00AB}{\guillemetleft}
\DeclareUnicodeCharacter{00AD}{\-}
\DeclareUnicodeCharacter{00AE}{\registeredsymbol}
\DeclareUnicodeCharacter{00AF}{\={ }}
\DeclareUnicodeCharacter{00B0}{\ringaccent{ }}
\DeclareUnicodeCharacter{00B4}{\'{ }}
\DeclareUnicodeCharacter{00B8}{\cedilla{ }}
\DeclareUnicodeCharacter{00BA}{\ordm}
\DeclareUnicodeCharacter{00BB}{\guillemetright}
\DeclareUnicodeCharacter{00BF}{\questiondown}
\DeclareUnicodeCharacter{00C0}{\`A}
\DeclareUnicodeCharacter{00C1}{\'A}
\DeclareUnicodeCharacter{00C2}{\^A}
\DeclareUnicodeCharacter{00C3}{\~A}
\DeclareUnicodeCharacter{00C4}{\"A}
\DeclareUnicodeCharacter{00C5}{\AA}
\DeclareUnicodeCharacter{00C6}{\AE}
\DeclareUnicodeCharacter{00C7}{\cedilla{C}}
\DeclareUnicodeCharacter{00C8}{\`E}
\DeclareUnicodeCharacter{00C9}{\'E}
\DeclareUnicodeCharacter{00CA}{\^E}
\DeclareUnicodeCharacter{00CB}{\"E}
\DeclareUnicodeCharacter{00CC}{\`I}
\DeclareUnicodeCharacter{00CD}{\'I}
\DeclareUnicodeCharacter{00CE}{\^I}
\DeclareUnicodeCharacter{00CF}{\"I}
\DeclareUnicodeCharacter{00D0}{\DH}
\DeclareUnicodeCharacter{00D1}{\~N}
\DeclareUnicodeCharacter{00D2}{\`O}
\DeclareUnicodeCharacter{00D3}{\'O}
\DeclareUnicodeCharacter{00D4}{\^O}
\DeclareUnicodeCharacter{00D5}{\~O}
\DeclareUnicodeCharacter{00D6}{\"O}
\DeclareUnicodeCharacter{00D8}{\O}
\DeclareUnicodeCharacter{00D9}{\`U}
\DeclareUnicodeCharacter{00DA}{\'U}
\DeclareUnicodeCharacter{00DB}{\^U}
\DeclareUnicodeCharacter{00DC}{\"U}
\DeclareUnicodeCharacter{00DD}{\'Y}
\DeclareUnicodeCharacter{00DE}{\TH}
\DeclareUnicodeCharacter{00DF}{\ss}
\DeclareUnicodeCharacter{00E0}{\`a}
\DeclareUnicodeCharacter{00E1}{\'a}
\DeclareUnicodeCharacter{00E2}{\^a}
\DeclareUnicodeCharacter{00E3}{\~a}
\DeclareUnicodeCharacter{00E4}{\"a}
\DeclareUnicodeCharacter{00E5}{\aa}
\DeclareUnicodeCharacter{00E6}{\ae}
\DeclareUnicodeCharacter{00E7}{\cedilla{c}}
\DeclareUnicodeCharacter{00E8}{\`e}
\DeclareUnicodeCharacter{00E9}{\'e}
\DeclareUnicodeCharacter{00EA}{\^e}
\DeclareUnicodeCharacter{00EB}{\"e}
\DeclareUnicodeCharacter{00EC}{\`{\dotless{i}}}
\DeclareUnicodeCharacter{00ED}{\'{\dotless{i}}}
\DeclareUnicodeCharacter{00EE}{\^{\dotless{i}}}
\DeclareUnicodeCharacter{00EF}{\"{\dotless{i}}}
\DeclareUnicodeCharacter{00F0}{\dh}
\DeclareUnicodeCharacter{00F1}{\~n}
\DeclareUnicodeCharacter{00F2}{\`o}
\DeclareUnicodeCharacter{00F3}{\'o}
\DeclareUnicodeCharacter{00F4}{\^o}
\DeclareUnicodeCharacter{00F5}{\~o}
\DeclareUnicodeCharacter{00F6}{\"o}
\DeclareUnicodeCharacter{00F8}{\o}
\DeclareUnicodeCharacter{00F9}{\`u}
\DeclareUnicodeCharacter{00FA}{\'u}
\DeclareUnicodeCharacter{00FB}{\^u}
\DeclareUnicodeCharacter{00FC}{\"u}
\DeclareUnicodeCharacter{00FD}{\'y}
\DeclareUnicodeCharacter{00FE}{\th}
\DeclareUnicodeCharacter{00FF}{\"y}
\DeclareUnicodeCharacter{0100}{\=A}
\DeclareUnicodeCharacter{0101}{\=a}
\DeclareUnicodeCharacter{0102}{\u{A}}
\DeclareUnicodeCharacter{0103}{\u{a}}
\DeclareUnicodeCharacter{0104}{\ogonek{A}}
\DeclareUnicodeCharacter{0105}{\ogonek{a}}
\DeclareUnicodeCharacter{0106}{\'C}
\DeclareUnicodeCharacter{0107}{\'c}
\DeclareUnicodeCharacter{0108}{\^C}
\DeclareUnicodeCharacter{0109}{\^c}
\DeclareUnicodeCharacter{0118}{\ogonek{E}}
\DeclareUnicodeCharacter{0119}{\ogonek{e}}
\DeclareUnicodeCharacter{010A}{\dotaccent{C}}
\DeclareUnicodeCharacter{010B}{\dotaccent{c}}
\DeclareUnicodeCharacter{010C}{\v{C}}
\DeclareUnicodeCharacter{010D}{\v{c}}
\DeclareUnicodeCharacter{010E}{\v{D}}
\DeclareUnicodeCharacter{0112}{\=E}
\DeclareUnicodeCharacter{0113}{\=e}
\DeclareUnicodeCharacter{0114}{\u{E}}
\DeclareUnicodeCharacter{0115}{\u{e}}
\DeclareUnicodeCharacter{0116}{\dotaccent{E}}
\DeclareUnicodeCharacter{0117}{\dotaccent{e}}
\DeclareUnicodeCharacter{011A}{\v{E}}
\DeclareUnicodeCharacter{011B}{\v{e}}
\DeclareUnicodeCharacter{011C}{\^G}
\DeclareUnicodeCharacter{011D}{\^g}
\DeclareUnicodeCharacter{011E}{\u{G}}
\DeclareUnicodeCharacter{011F}{\u{g}}
\DeclareUnicodeCharacter{0120}{\dotaccent{G}}
\DeclareUnicodeCharacter{0121}{\dotaccent{g}}
\DeclareUnicodeCharacter{0124}{\^H}
\DeclareUnicodeCharacter{0125}{\^h}
\DeclareUnicodeCharacter{0128}{\~I}
\DeclareUnicodeCharacter{0129}{\~{\dotless{i}}}
\DeclareUnicodeCharacter{012A}{\=I}
\DeclareUnicodeCharacter{012B}{\={\dotless{i}}}
\DeclareUnicodeCharacter{012C}{\u{I}}
\DeclareUnicodeCharacter{012D}{\u{\dotless{i}}}
\DeclareUnicodeCharacter{0130}{\dotaccent{I}}
\DeclareUnicodeCharacter{0131}{\dotless{i}}
\DeclareUnicodeCharacter{0132}{IJ}
\DeclareUnicodeCharacter{0133}{ij}
\DeclareUnicodeCharacter{0134}{\^J}
\DeclareUnicodeCharacter{0135}{\^{\dotless{j}}}
\DeclareUnicodeCharacter{0139}{\'L}
\DeclareUnicodeCharacter{013A}{\'l}
\DeclareUnicodeCharacter{0141}{\L}
\DeclareUnicodeCharacter{0142}{\l}
\DeclareUnicodeCharacter{0143}{\'N}
\DeclareUnicodeCharacter{0144}{\'n}
\DeclareUnicodeCharacter{0147}{\v{N}}
\DeclareUnicodeCharacter{0148}{\v{n}}
\DeclareUnicodeCharacter{014C}{\=O}
\DeclareUnicodeCharacter{014D}{\=o}
\DeclareUnicodeCharacter{014E}{\u{O}}
\DeclareUnicodeCharacter{014F}{\u{o}}
\DeclareUnicodeCharacter{0150}{\H{O}}
\DeclareUnicodeCharacter{0151}{\H{o}}
\DeclareUnicodeCharacter{0152}{\OE}
\DeclareUnicodeCharacter{0153}{\oe}
\DeclareUnicodeCharacter{0154}{\'R}
\DeclareUnicodeCharacter{0155}{\'r}
\DeclareUnicodeCharacter{0158}{\v{R}}
\DeclareUnicodeCharacter{0159}{\v{r}}
\DeclareUnicodeCharacter{015A}{\'S}
\DeclareUnicodeCharacter{015B}{\'s}
\DeclareUnicodeCharacter{015C}{\^S}
\DeclareUnicodeCharacter{015D}{\^s}
\DeclareUnicodeCharacter{015E}{\cedilla{S}}
\DeclareUnicodeCharacter{015F}{\cedilla{s}}
\DeclareUnicodeCharacter{0160}{\v{S}}
\DeclareUnicodeCharacter{0161}{\v{s}}
\DeclareUnicodeCharacter{0162}{\cedilla{t}}
\DeclareUnicodeCharacter{0163}{\cedilla{T}}
\DeclareUnicodeCharacter{0164}{\v{T}}
\DeclareUnicodeCharacter{0168}{\~U}
\DeclareUnicodeCharacter{0169}{\~u}
\DeclareUnicodeCharacter{016A}{\=U}
\DeclareUnicodeCharacter{016B}{\=u}
\DeclareUnicodeCharacter{016C}{\u{U}}
\DeclareUnicodeCharacter{016D}{\u{u}}
\DeclareUnicodeCharacter{016E}{\ringaccent{U}}
\DeclareUnicodeCharacter{016F}{\ringaccent{u}}
\DeclareUnicodeCharacter{0170}{\H{U}}
\DeclareUnicodeCharacter{0171}{\H{u}}
\DeclareUnicodeCharacter{0174}{\^W}
\DeclareUnicodeCharacter{0175}{\^w}
\DeclareUnicodeCharacter{0176}{\^Y}
\DeclareUnicodeCharacter{0177}{\^y}
\DeclareUnicodeCharacter{0178}{\"Y}
\DeclareUnicodeCharacter{0179}{\'Z}
\DeclareUnicodeCharacter{017A}{\'z}
\DeclareUnicodeCharacter{017B}{\dotaccent{Z}}
\DeclareUnicodeCharacter{017C}{\dotaccent{z}}
\DeclareUnicodeCharacter{017D}{\v{Z}}
\DeclareUnicodeCharacter{017E}{\v{z}}
\DeclareUnicodeCharacter{01C4}{D\v{Z}}
\DeclareUnicodeCharacter{01C5}{D\v{z}}
\DeclareUnicodeCharacter{01C6}{d\v{z}}
\DeclareUnicodeCharacter{01C7}{LJ}
\DeclareUnicodeCharacter{01C8}{Lj}
\DeclareUnicodeCharacter{01C9}{lj}
\DeclareUnicodeCharacter{01CA}{NJ}
\DeclareUnicodeCharacter{01CB}{Nj}
\DeclareUnicodeCharacter{01CC}{nj}
\DeclareUnicodeCharacter{01CD}{\v{A}}
\DeclareUnicodeCharacter{01CE}{\v{a}}
\DeclareUnicodeCharacter{01CF}{\v{I}}
\DeclareUnicodeCharacter{01D0}{\v{\dotless{i}}}
\DeclareUnicodeCharacter{01D1}{\v{O}}
\DeclareUnicodeCharacter{01D2}{\v{o}}
\DeclareUnicodeCharacter{01D3}{\v{U}}
\DeclareUnicodeCharacter{01D4}{\v{u}}
\DeclareUnicodeCharacter{01E2}{\={\AE}}
\DeclareUnicodeCharacter{01E3}{\={\ae}}
\DeclareUnicodeCharacter{01E6}{\v{G}}
\DeclareUnicodeCharacter{01E7}{\v{g}}
\DeclareUnicodeCharacter{01E8}{\v{K}}
\DeclareUnicodeCharacter{01E9}{\v{k}}
\DeclareUnicodeCharacter{01F0}{\v{\dotless{j}}}
\DeclareUnicodeCharacter{01F1}{DZ}
\DeclareUnicodeCharacter{01F2}{Dz}
\DeclareUnicodeCharacter{01F3}{dz}
\DeclareUnicodeCharacter{01F4}{\'G}
\DeclareUnicodeCharacter{01F5}{\'g}
\DeclareUnicodeCharacter{01F8}{\`N}
\DeclareUnicodeCharacter{01F9}{\`n}
\DeclareUnicodeCharacter{01FC}{\'{\AE}}
\DeclareUnicodeCharacter{01FD}{\'{\ae}}
\DeclareUnicodeCharacter{01FE}{\'{\O}}
\DeclareUnicodeCharacter{01FF}{\'{\o}}
\DeclareUnicodeCharacter{021E}{\v{H}}
\DeclareUnicodeCharacter{021F}{\v{h}}
\DeclareUnicodeCharacter{0226}{\dotaccent{A}}
\DeclareUnicodeCharacter{0227}{\dotaccent{a}}
\DeclareUnicodeCharacter{0228}{\cedilla{E}}
\DeclareUnicodeCharacter{0229}{\cedilla{e}}
\DeclareUnicodeCharacter{022E}{\dotaccent{O}}
\DeclareUnicodeCharacter{022F}{\dotaccent{o}}
\DeclareUnicodeCharacter{0232}{\=Y}
\DeclareUnicodeCharacter{0233}{\=y}
\DeclareUnicodeCharacter{0237}{\dotless{j}}
\DeclareUnicodeCharacter{02DB}{\ogonek{ }}
\DeclareUnicodeCharacter{1E02}{\dotaccent{B}}
\DeclareUnicodeCharacter{1E03}{\dotaccent{b}}
\DeclareUnicodeCharacter{1E04}{\udotaccent{B}}
\DeclareUnicodeCharacter{1E05}{\udotaccent{b}}
\DeclareUnicodeCharacter{1E06}{\ubaraccent{B}}
\DeclareUnicodeCharacter{1E07}{\ubaraccent{b}}
\DeclareUnicodeCharacter{1E0A}{\dotaccent{D}}
\DeclareUnicodeCharacter{1E0B}{\dotaccent{d}}
\DeclareUnicodeCharacter{1E0C}{\udotaccent{D}}
\DeclareUnicodeCharacter{1E0D}{\udotaccent{d}}
\DeclareUnicodeCharacter{1E0E}{\ubaraccent{D}}
\DeclareUnicodeCharacter{1E0F}{\ubaraccent{d}}
\DeclareUnicodeCharacter{1E1E}{\dotaccent{F}}
\DeclareUnicodeCharacter{1E1F}{\dotaccent{f}}
\DeclareUnicodeCharacter{1E20}{\=G}
\DeclareUnicodeCharacter{1E21}{\=g}
\DeclareUnicodeCharacter{1E22}{\dotaccent{H}}
\DeclareUnicodeCharacter{1E23}{\dotaccent{h}}
\DeclareUnicodeCharacter{1E24}{\udotaccent{H}}
\DeclareUnicodeCharacter{1E25}{\udotaccent{h}}
\DeclareUnicodeCharacter{1E26}{\"H}
\DeclareUnicodeCharacter{1E27}{\"h}
\DeclareUnicodeCharacter{1E30}{\'K}
\DeclareUnicodeCharacter{1E31}{\'k}
\DeclareUnicodeCharacter{1E32}{\udotaccent{K}}
\DeclareUnicodeCharacter{1E33}{\udotaccent{k}}
\DeclareUnicodeCharacter{1E34}{\ubaraccent{K}}
\DeclareUnicodeCharacter{1E35}{\ubaraccent{k}}
\DeclareUnicodeCharacter{1E36}{\udotaccent{L}}
\DeclareUnicodeCharacter{1E37}{\udotaccent{l}}
\DeclareUnicodeCharacter{1E3A}{\ubaraccent{L}}
\DeclareUnicodeCharacter{1E3B}{\ubaraccent{l}}
\DeclareUnicodeCharacter{1E3E}{\'M}
\DeclareUnicodeCharacter{1E3F}{\'m}
\DeclareUnicodeCharacter{1E40}{\dotaccent{M}}
\DeclareUnicodeCharacter{1E41}{\dotaccent{m}}
\DeclareUnicodeCharacter{1E42}{\udotaccent{M}}
\DeclareUnicodeCharacter{1E43}{\udotaccent{m}}
\DeclareUnicodeCharacter{1E44}{\dotaccent{N}}
\DeclareUnicodeCharacter{1E45}{\dotaccent{n}}
\DeclareUnicodeCharacter{1E46}{\udotaccent{N}}
\DeclareUnicodeCharacter{1E47}{\udotaccent{n}}
\DeclareUnicodeCharacter{1E48}{\ubaraccent{N}}
\DeclareUnicodeCharacter{1E49}{\ubaraccent{n}}
\DeclareUnicodeCharacter{1E54}{\'P}
\DeclareUnicodeCharacter{1E55}{\'p}
\DeclareUnicodeCharacter{1E56}{\dotaccent{P}}
\DeclareUnicodeCharacter{1E57}{\dotaccent{p}}
\DeclareUnicodeCharacter{1E58}{\dotaccent{R}}
\DeclareUnicodeCharacter{1E59}{\dotaccent{r}}
\DeclareUnicodeCharacter{1E5A}{\udotaccent{R}}
\DeclareUnicodeCharacter{1E5B}{\udotaccent{r}}
\DeclareUnicodeCharacter{1E5E}{\ubaraccent{R}}
\DeclareUnicodeCharacter{1E5F}{\ubaraccent{r}}
\DeclareUnicodeCharacter{1E60}{\dotaccent{S}}
\DeclareUnicodeCharacter{1E61}{\dotaccent{s}}
\DeclareUnicodeCharacter{1E62}{\udotaccent{S}}
\DeclareUnicodeCharacter{1E63}{\udotaccent{s}}
\DeclareUnicodeCharacter{1E6A}{\dotaccent{T}}
\DeclareUnicodeCharacter{1E6B}{\dotaccent{t}}
\DeclareUnicodeCharacter{1E6C}{\udotaccent{T}}
\DeclareUnicodeCharacter{1E6D}{\udotaccent{t}}
\DeclareUnicodeCharacter{1E6E}{\ubaraccent{T}}
\DeclareUnicodeCharacter{1E6F}{\ubaraccent{t}}
\DeclareUnicodeCharacter{1E7C}{\~V}
\DeclareUnicodeCharacter{1E7D}{\~v}
\DeclareUnicodeCharacter{1E7E}{\udotaccent{V}}
\DeclareUnicodeCharacter{1E7F}{\udotaccent{v}}
\DeclareUnicodeCharacter{1E80}{\`W}
\DeclareUnicodeCharacter{1E81}{\`w}
\DeclareUnicodeCharacter{1E82}{\'W}
\DeclareUnicodeCharacter{1E83}{\'w}
\DeclareUnicodeCharacter{1E84}{\"W}
\DeclareUnicodeCharacter{1E85}{\"w}
\DeclareUnicodeCharacter{1E86}{\dotaccent{W}}
\DeclareUnicodeCharacter{1E87}{\dotaccent{w}}
\DeclareUnicodeCharacter{1E88}{\udotaccent{W}}
\DeclareUnicodeCharacter{1E89}{\udotaccent{w}}
\DeclareUnicodeCharacter{1E8A}{\dotaccent{X}}
\DeclareUnicodeCharacter{1E8B}{\dotaccent{x}}
\DeclareUnicodeCharacter{1E8C}{\"X}
\DeclareUnicodeCharacter{1E8D}{\"x}
\DeclareUnicodeCharacter{1E8E}{\dotaccent{Y}}
\DeclareUnicodeCharacter{1E8F}{\dotaccent{y}}
\DeclareUnicodeCharacter{1E90}{\^Z}
\DeclareUnicodeCharacter{1E91}{\^z}
\DeclareUnicodeCharacter{1E92}{\udotaccent{Z}}
\DeclareUnicodeCharacter{1E93}{\udotaccent{z}}
\DeclareUnicodeCharacter{1E94}{\ubaraccent{Z}}
\DeclareUnicodeCharacter{1E95}{\ubaraccent{z}}
\DeclareUnicodeCharacter{1E96}{\ubaraccent{h}}
\DeclareUnicodeCharacter{1E97}{\"t}
\DeclareUnicodeCharacter{1E98}{\ringaccent{w}}
\DeclareUnicodeCharacter{1E99}{\ringaccent{y}}
\DeclareUnicodeCharacter{1EA0}{\udotaccent{A}}
\DeclareUnicodeCharacter{1EA1}{\udotaccent{a}}
\DeclareUnicodeCharacter{1EB8}{\udotaccent{E}}
\DeclareUnicodeCharacter{1EB9}{\udotaccent{e}}
\DeclareUnicodeCharacter{1EBC}{\~E}
\DeclareUnicodeCharacter{1EBD}{\~e}
\DeclareUnicodeCharacter{1ECA}{\udotaccent{I}}
\DeclareUnicodeCharacter{1ECB}{\udotaccent{i}}
\DeclareUnicodeCharacter{1ECC}{\udotaccent{O}}
\DeclareUnicodeCharacter{1ECD}{\udotaccent{o}}
\DeclareUnicodeCharacter{1EE4}{\udotaccent{U}}
\DeclareUnicodeCharacter{1EE5}{\udotaccent{u}}
\DeclareUnicodeCharacter{1EF2}{\`Y}
\DeclareUnicodeCharacter{1EF3}{\`y}
\DeclareUnicodeCharacter{1EF4}{\udotaccent{Y}}
\DeclareUnicodeCharacter{1EF8}{\~Y}
\DeclareUnicodeCharacter{1EF9}{\~y}
\DeclareUnicodeCharacter{2013}{--}
\DeclareUnicodeCharacter{2014}{---}
\DeclareUnicodeCharacter{2018}{\quoteleft}
\DeclareUnicodeCharacter{2019}{\quoteright}
\DeclareUnicodeCharacter{201A}{\quotesinglbase}
\DeclareUnicodeCharacter{201C}{\quotedblleft}
\DeclareUnicodeCharacter{201D}{\quotedblright}
\DeclareUnicodeCharacter{201E}{\quotedblbase}
\DeclareUnicodeCharacter{2022}{\bullet}
\DeclareUnicodeCharacter{2026}{\dots}
\DeclareUnicodeCharacter{2039}{\guilsinglleft}
\DeclareUnicodeCharacter{203A}{\guilsinglright}
\DeclareUnicodeCharacter{20AC}{\euro}
\DeclareUnicodeCharacter{2192}{\expansion}
\DeclareUnicodeCharacter{21D2}{\result}
\DeclareUnicodeCharacter{2212}{\minus}
\DeclareUnicodeCharacter{2217}{\point}
\DeclareUnicodeCharacter{2261}{\equiv}
}% end of \utfeightchardefs
% US-ASCII character definitions.
\def\asciichardefs{% nothing need be done
\relax
}
% Make non-ASCII characters printable again for compatibility with
% existing Texinfo documents that may use them, even without declaring a
% document encoding.
%
\setnonasciicharscatcode \other
\message{formatting,}
\newdimen\defaultparindent \defaultparindent = 15pt
\chapheadingskip = 15pt plus 4pt minus 2pt
\secheadingskip = 12pt plus 3pt minus 2pt
\subsecheadingskip = 9pt plus 2pt minus 2pt
% Prevent underfull vbox error messages.
\vbadness = 10000
% Don't be very finicky about underfull hboxes, either.
\hbadness = 6666
% Following George Bush, get rid of widows and orphans.
\widowpenalty=10000
\clubpenalty=10000
% Use TeX 3.0's \emergencystretch to help line breaking, but if we're
% using an old version of TeX, don't do anything. We want the amount of
% stretch added to depend on the line length, hence the dependence on
% \hsize. We call this whenever the paper size is set.
%
\def\setemergencystretch{%
\ifx\emergencystretch\thisisundefined
% Allow us to assign to \emergencystretch anyway.
\def\emergencystretch{\dimen0}%
\else
\emergencystretch = .15\hsize
\fi
}
% Parameters in order: 1) textheight; 2) textwidth;
% 3) voffset; 4) hoffset; 5) binding offset; 6) topskip;
% 7) physical page height; 8) physical page width.
%
% We also call \setleading{\textleading}, so the caller should define
% \textleading. The caller should also set \parskip.
%
\def\internalpagesizes#1#2#3#4#5#6#7#8{%
\voffset = #3\relax
\topskip = #6\relax
\splittopskip = \topskip
%
\vsize = #1\relax
\advance\vsize by \topskip
\outervsize = \vsize
\advance\outervsize by 2\topandbottommargin
\pageheight = \vsize
%
\hsize = #2\relax
\outerhsize = \hsize
\advance\outerhsize by 0.5in
\pagewidth = \hsize
%
\normaloffset = #4\relax
\bindingoffset = #5\relax
%
\ifpdf
\pdfpageheight #7\relax
\pdfpagewidth #8\relax
% if we don't reset these, they will remain at "1 true in" of
% whatever layout pdftex was dumped with.
\pdfhorigin = 1 true in
\pdfvorigin = 1 true in
\fi
%
\setleading{\textleading}
%
\parindent = \defaultparindent
\setemergencystretch
}
% @letterpaper (the default).
\def\letterpaper{{\globaldefs = 1
\parskip = 3pt plus 2pt minus 1pt
\textleading = 13.2pt
%
% If page is nothing but text, make it come out even.
\internalpagesizes{607.2pt}{6in}% that's 46 lines
{\voffset}{.25in}%
{\bindingoffset}{36pt}%
{11in}{8.5in}%
}}
% Use @smallbook to reset parameters for 7x9.25 trim size.
\def\smallbook{{\globaldefs = 1
\parskip = 2pt plus 1pt
\textleading = 12pt
%
\internalpagesizes{7.5in}{5in}%
{-.2in}{0in}%
{\bindingoffset}{16pt}%
{9.25in}{7in}%
%
\lispnarrowing = 0.3in
\tolerance = 700
\hfuzz = 1pt
\contentsrightmargin = 0pt
\defbodyindent = .5cm
}}
% Use @smallerbook to reset parameters for 6x9 trim size.
% (Just testing, parameters still in flux.)
\def\smallerbook{{\globaldefs = 1
\parskip = 1.5pt plus 1pt
\textleading = 12pt
%
\internalpagesizes{7.4in}{4.8in}%
{-.2in}{-.4in}%
{0pt}{14pt}%
{9in}{6in}%
%
\lispnarrowing = 0.25in
\tolerance = 700
\hfuzz = 1pt
\contentsrightmargin = 0pt
\defbodyindent = .4cm
}}
% Use @afourpaper to print on European A4 paper.
\def\afourpaper{{\globaldefs = 1
\parskip = 3pt plus 2pt minus 1pt
\textleading = 13.2pt
%
% Double-side printing via postscript on Laserjet 4050
% prints double-sided nicely when \bindingoffset=10mm and \hoffset=-6mm.
% To change the settings for a different printer or situation, adjust
% \normaloffset until the front-side and back-side texts align. Then
% do the same for \bindingoffset. You can set these for testing in
% your texinfo source file like this:
% @tex
% \global\normaloffset = -6mm
% \global\bindingoffset = 10mm
% @end tex
\internalpagesizes{673.2pt}{160mm}% that's 51 lines
{\voffset}{\hoffset}%
{\bindingoffset}{44pt}%
{297mm}{210mm}%
%
\tolerance = 700
\hfuzz = 1pt
\contentsrightmargin = 0pt
\defbodyindent = 5mm
}}
% Use @afivepaper to print on European A5 paper.
% From romildo@urano.iceb.ufop.br, 2 July 2000.
% He also recommends making @example and @lisp be small.
\def\afivepaper{{\globaldefs = 1
\parskip = 2pt plus 1pt minus 0.1pt
\textleading = 12.5pt
%
\internalpagesizes{160mm}{120mm}%
{\voffset}{\hoffset}%
{\bindingoffset}{8pt}%
{210mm}{148mm}%
%
\lispnarrowing = 0.2in
\tolerance = 800
\hfuzz = 1.2pt
\contentsrightmargin = 0pt
\defbodyindent = 2mm
\tableindent = 12mm
}}
% A specific text layout, 24x15cm overall, intended for A4 paper.
\def\afourlatex{{\globaldefs = 1
\afourpaper
\internalpagesizes{237mm}{150mm}%
{\voffset}{4.6mm}%
{\bindingoffset}{7mm}%
{297mm}{210mm}%
%
% Must explicitly reset to 0 because we call \afourpaper.
\globaldefs = 0
}}
% Use @afourwide to print on A4 paper in landscape format.
\def\afourwide{{\globaldefs = 1
\afourpaper
\internalpagesizes{241mm}{165mm}%
{\voffset}{-2.95mm}%
{\bindingoffset}{7mm}%
{297mm}{210mm}%
\globaldefs = 0
}}
% @pagesizes TEXTHEIGHT[,TEXTWIDTH]
% Perhaps we should allow setting the margins, \topskip, \parskip,
% and/or leading, also. Or perhaps we should compute them somehow.
%
\parseargdef\pagesizes{\pagesizesyyy #1,,\finish}
\def\pagesizesyyy#1,#2,#3\finish{{%
\setbox0 = \hbox{\ignorespaces #2}\ifdim\wd0 > 0pt \hsize=#2\relax \fi
\globaldefs = 1
%
\parskip = 3pt plus 2pt minus 1pt
\setleading{\textleading}%
%
\dimen0 = #1\relax
\advance\dimen0 by \voffset
%
\dimen2 = \hsize
\advance\dimen2 by \normaloffset
%
\internalpagesizes{#1}{\hsize}%
{\voffset}{\normaloffset}%
{\bindingoffset}{44pt}%
{\dimen0}{\dimen2}%
}}
% Set default to letter.
%
\letterpaper
\message{and turning on texinfo input format.}
\def^^L{\par} % remove \outer, so ^L can appear in an @comment
% DEL is a comment character, in case @c does not suffice.
\catcode`\^^? = 14
% Define macros to output various characters with catcode for normal text.
\catcode`\"=\other \def\normaldoublequote{"}
\catcode`\$=\other \def\normaldollar{$}%$ font-lock fix
\catcode`\+=\other \def\normalplus{+}
\catcode`\<=\other \def\normalless{<}
\catcode`\>=\other \def\normalgreater{>}
\catcode`\^=\other \def\normalcaret{^}
\catcode`\_=\other \def\normalunderscore{_}
\catcode`\|=\other \def\normalverticalbar{|}
\catcode`\~=\other \def\normaltilde{~}
% This macro is used to make a character print one way in \tt
% (where it can probably be output as-is), and another way in other fonts,
% where something hairier probably needs to be done.
%
% #1 is what to print if we are indeed using \tt; #2 is what to print
% otherwise. Since all the Computer Modern typewriter fonts have zero
% interword stretch (and shrink), and it is reasonable to expect all
% typewriter fonts to have this, we can check that font parameter.
%
\def\ifusingtt#1#2{\ifdim \fontdimen3\font=0pt #1\else #2\fi}
% Same as above, but check for italic font. Actually this also catches
% non-italic slanted fonts since it is impossible to distinguish them from
% italic fonts. But since this is only used by $ and it uses \sl anyway
% this is not a problem.
\def\ifusingit#1#2{\ifdim \fontdimen1\font>0pt #1\else #2\fi}
% Turn off all special characters except @
% (and those which the user can use as if they were ordinary).
% Most of these we simply print from the \tt font, but for some, we can
% use math or other variants that look better in normal text.
\catcode`\"=\active
\def\activedoublequote{{\tt\char34}}
\let"=\activedoublequote
\catcode`\~=\active \def\activetilde{{\tt\char126}} \let~ = \activetilde
\chardef\hat=`\^
\catcode`\^=\active \def\activehat{{\tt \hat}} \let^ = \activehat
\catcode`\_=\active
\def_{\ifusingtt\normalunderscore\_}
\let\realunder=_
% Subroutine for the previous macro.
\def\_{\leavevmode \kern.07em \vbox{\hrule width.3em height.1ex}\kern .07em }
\catcode`\|=\active
\def|{{\tt\char124}}
\chardef \less=`\<
\catcode`\<=\active \def\activeless{{\tt \less}}\let< = \activeless
\chardef \gtr=`\>
\catcode`\>=\active \def\activegtr{{\tt \gtr}}\let> = \activegtr
\catcode`\+=\active \def+{{\tt \char 43}}
\catcode`\$=\active \def${\ifusingit{{\sl\$}}\normaldollar}%$ font-lock fix
% used for headline/footline in the output routine, in case the page
% breaks in the middle of an @tex block.
\def\texinfochars{%
\let< = \activeless
\let> = \activegtr
\let~ = \activetilde
\let^ = \activehat
\markupsetuplqdefault \markupsetuprqdefault
\let\b = \strong
\let\i = \smartitalic
% in principle, all other definitions in \tex have to be undone too.
}
% If a .fmt file is being used, characters that might appear in a file
% name cannot be active until we have parsed the command line.
% So turn them off again, and have \everyjob (or @setfilename) turn them on.
% \otherifyactive is called near the end of this file.
\def\otherifyactive{\catcode`+=\other \catcode`\_=\other}
% Used sometimes to turn off (effectively) the active characters even after
% parsing them.
\def\turnoffactive{%
\normalturnoffactive
\otherbackslash
}
\catcode`\@=0
% \backslashcurfont outputs one backslash character in current font,
% as in \char`\\.
\global\chardef\backslashcurfont=`\\
\global\let\rawbackslashxx=\backslashcurfont % let existing .??s files work
% \realbackslash is an actual character `\' with catcode other, and
% \doublebackslash is two of them (for the pdf outlines).
{\catcode`\\=\other @gdef@realbackslash{\} @gdef@doublebackslash{\\}}
% In texinfo, backslash is an active character; it prints the backslash
% in fixed width font.
\catcode`\\=\active % @ for escape char from now on.
% The story here is that in math mode, the \char of \backslashcurfont
% ends up printing the roman \ from the math symbol font (because \char
% in math mode uses the \mathcode, and plain.tex sets
% \mathcode`\\="026E). It seems better for @backslashchar{} to always
% print a typewriter backslash, hence we use an explicit \mathchar,
% which is the decimal equivalent of "715c (class 7, e.g., use \fam;
% ignored family value; char position "5C). We can't use " for the
% usual hex value because it has already been made active.
@def@normalbackslash{{@tt @ifmmode @mathchar29020 @else @backslashcurfont @fi}}
@let@backslashchar = @normalbackslash % @backslashchar{} is for user documents.
% On startup, @fixbackslash assigns:
% @let \ = @normalbackslash
% \rawbackslash defines an active \ to do \backslashcurfont.
% \otherbackslash defines an active \ to be a literal `\' character with
% catcode other. We switch back and forth between these.
@gdef@rawbackslash{@let\=@backslashcurfont}
@gdef@otherbackslash{@let\=@realbackslash}
% Same as @turnoffactive except outputs \ as {\tt\char`\\} instead of
% the literal character `\'. Also revert - to its normal character, in
% case the active - from code has slipped in.
%
{@catcode`- = @active
@gdef@normalturnoffactive{%
@let-=@normaldash
@let"=@normaldoublequote
@let$=@normaldollar %$ font-lock fix
@let+=@normalplus
@let<=@normalless
@let>=@normalgreater
@let\=@normalbackslash
@let^=@normalcaret
@let_=@normalunderscore
@let|=@normalverticalbar
@let~=@normaltilde
@markupsetuplqdefault
@markupsetuprqdefault
@unsepspaces
}
}
% Make _ and + \other characters, temporarily.
% This is canceled by @fixbackslash.
@otherifyactive
% If a .fmt file is being used, we don't want the `\input texinfo' to show up.
% That is what \eatinput is for; after that, the `\' should revert to printing
% a backslash.
%
@gdef@eatinput input texinfo{@fixbackslash}
@global@let\ = @eatinput
% On the other hand, perhaps the file did not have a `\input texinfo'. Then
% the first `\' in the file would cause an error. This macro tries to fix
% that, assuming it is called before the first `\' could plausibly occur.
% Also turn back on active characters that might appear in the input
% file name, in case not using a pre-dumped format.
%
@gdef@fixbackslash{%
@ifx\@eatinput @let\ = @normalbackslash @fi
@catcode`+=@active
@catcode`@_=@active
}
% Say @foo, not \foo, in error messages.
@escapechar = `@@
% These (along with & and #) are made active for url-breaking, so need
% active definitions as the normal characters.
@def@normaldot{.}
@def@normalquest{?}
@def@normalslash{/}
% These look ok in all fonts, so just make them not special.
% @hashchar{} gets its own user-level command, because of #line.
@catcode`@& = @other @def@normalamp{&}
@catcode`@# = @other @def@normalhash{#}
@catcode`@% = @other @def@normalpercent{%}
@let @hashchar = @normalhash
@c Finally, make ` and ' active, so that txicodequoteundirected and
@c txicodequotebacktick work right in, e.g., @w{@code{`foo'}}. If we
@c don't make ` and ' active, @code will not get them as active chars.
@c Do this last of all since we use ` in the previous @catcode assignments.
@catcode`@'=@active
@catcode`@`=@active
@markupsetuplqdefault
@markupsetuprqdefault
@c Local variables:
@c eval: (add-hook 'write-file-hooks 'time-stamp)
@c page-delimiter: "^\\\\message"
@c time-stamp-start: "def\\\\texinfoversion{"
@c time-stamp-format: "%:y-%02m-%02d.%02H"
@c time-stamp-end: "}"
@c End:
@c vim:sw=2:
@ignore
arch-tag: e1b36e32-c96e-4135-a41a-0b2efa2ea115
@end ignore
glibc-doc-reference-2.19.orig/manual/ctype.texi 0000664 0001750 0001750 00000066126 12275120646 021611 0 ustar adconrad adconrad @node Character Handling, String and Array Utilities, Memory, Top
@c %MENU% Character testing and conversion functions
@chapter Character Handling
Programs that work with characters and strings often need to classify a
character---is it alphabetic, is it a digit, is it whitespace, and so
on---and perform case conversion operations on characters. The
functions in the header file @file{ctype.h} are provided for this
purpose.
@pindex ctype.h
Since the choice of locale and character set can alter the
classifications of particular character codes, all of these functions
are affected by the current locale. (More precisely, they are affected
by the locale currently selected for character classification---the
@code{LC_CTYPE} category; see @ref{Locale Categories}.)
The @w{ISO C} standard specifies two different sets of functions. The
one set works on @code{char} type characters, the other one on
@code{wchar_t} wide characters (@pxref{Extended Char Intro}).
@menu
* Classification of Characters:: Testing whether characters are
letters, digits, punctuation, etc.
* Case Conversion:: Case mapping, and the like.
* Classification of Wide Characters:: Character class determination for
wide characters.
* Using Wide Char Classes:: Notes on using the wide character
classes.
* Wide Character Case Conversion:: Mapping of wide characters.
@end menu
@node Classification of Characters, Case Conversion, , Character Handling
@section Classification of Characters
@cindex character testing
@cindex classification of characters
@cindex predicates on characters
@cindex character predicates
This section explains the library functions for classifying characters.
For example, @code{isalpha} is the function to test for an alphabetic
character. It takes one argument, the character to test, and returns a
nonzero integer if the character is alphabetic, and zero otherwise. You
would use it like this:
@smallexample
if (isalpha (c))
printf ("The character `%c' is alphabetic.\n", c);
@end smallexample
Each of the functions in this section tests for membership in a
particular class of characters; each has a name starting with @samp{is}.
Each of them takes one argument, which is a character to test, and
returns an @code{int} which is treated as a boolean value. The
character argument is passed as an @code{int}, and it may be the
constant value @code{EOF} instead of a real character.
The attributes of any given character can vary between locales.
@xref{Locales}, for more information on locales.@refill
These functions are declared in the header file @file{ctype.h}.
@pindex ctype.h
@cindex lower-case character
@comment ctype.h
@comment ISO
@deftypefun int islower (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c The is* macros call __ctype_b_loc to get the ctype array from the
@c current locale, and then index it by c. __ctype_b_loc reads from
@c thread-local memory the (indirect) pointer to the ctype array, which
@c may involve one word access to the global locale object, if that's
@c the active locale for the thread, and the array, being part of the
@c locale data, is undeletable, so there's no thread-safety issue. We
@c might want to mark these with @mtslocale to flag to callers that
@c changing locales might affect them, even if not these simpler
@c functions.
Returns true if @var{c} is a lower-case letter. The letter need not be
from the Latin alphabet, any alphabet representable is valid.
@end deftypefun
@cindex upper-case character
@comment ctype.h
@comment ISO
@deftypefun int isupper (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is an upper-case letter. The letter need not be
from the Latin alphabet, any alphabet representable is valid.
@end deftypefun
@cindex alphabetic character
@comment ctype.h
@comment ISO
@deftypefun int isalpha (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is an alphabetic character (a letter). If
@code{islower} or @code{isupper} is true of a character, then
@code{isalpha} is also true.
In some locales, there may be additional characters for which
@code{isalpha} is true---letters which are neither upper case nor lower
case. But in the standard @code{"C"} locale, there are no such
additional characters.
@end deftypefun
@cindex digit character
@cindex decimal digit character
@comment ctype.h
@comment ISO
@deftypefun int isdigit (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a decimal digit (@samp{0} through @samp{9}).
@end deftypefun
@cindex alphanumeric character
@comment ctype.h
@comment ISO
@deftypefun int isalnum (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is an alphanumeric character (a letter or
number); in other words, if either @code{isalpha} or @code{isdigit} is
true of a character, then @code{isalnum} is also true.
@end deftypefun
@cindex hexadecimal digit character
@comment ctype.h
@comment ISO
@deftypefun int isxdigit (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a hexadecimal digit.
Hexadecimal digits include the normal decimal digits @samp{0} through
@samp{9} and the letters @samp{A} through @samp{F} and
@samp{a} through @samp{f}.
@end deftypefun
@cindex punctuation character
@comment ctype.h
@comment ISO
@deftypefun int ispunct (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a punctuation character.
This means any printing character that is not alphanumeric or a space
character.
@end deftypefun
@cindex whitespace character
@comment ctype.h
@comment ISO
@deftypefun int isspace (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a @dfn{whitespace} character. In the standard
@code{"C"} locale, @code{isspace} returns true for only the standard
whitespace characters:
@table @code
@item ' '
space
@item '\f'
formfeed
@item '\n'
newline
@item '\r'
carriage return
@item '\t'
horizontal tab
@item '\v'
vertical tab
@end table
@end deftypefun
@cindex blank character
@comment ctype.h
@comment ISO
@deftypefun int isblank (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a blank character; that is, a space or a tab.
This function was originally a GNU extension, but was added in @w{ISO C99}.
@end deftypefun
@cindex graphic character
@comment ctype.h
@comment ISO
@deftypefun int isgraph (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a graphic character; that is, a character
that has a glyph associated with it. The whitespace characters are not
considered graphic.
@end deftypefun
@cindex printing character
@comment ctype.h
@comment ISO
@deftypefun int isprint (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a printing character. Printing characters
include all the graphic characters, plus the space (@samp{ }) character.
@end deftypefun
@cindex control character
@comment ctype.h
@comment ISO
@deftypefun int iscntrl (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a control character (that is, a character that
is not a printing character).
@end deftypefun
@cindex ASCII character
@comment ctype.h
@comment SVID, BSD
@deftypefun int isascii (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Returns true if @var{c} is a 7-bit @code{unsigned char} value that fits
into the US/UK ASCII character set. This function is a BSD extension
and is also an SVID extension.
@end deftypefun
@node Case Conversion, Classification of Wide Characters, Classification of Characters, Character Handling
@section Case Conversion
@cindex character case conversion
@cindex case conversion of characters
@cindex converting case of characters
This section explains the library functions for performing conversions
such as case mappings on characters. For example, @code{toupper}
converts any character to upper case if possible. If the character
can't be converted, @code{toupper} returns it unchanged.
These functions take one argument of type @code{int}, which is the
character to convert, and return the converted character as an
@code{int}. If the conversion is not applicable to the argument given,
the argument is returned unchanged.
@strong{Compatibility Note:} In pre-@w{ISO C} dialects, instead of
returning the argument unchanged, these functions may fail when the
argument is not suitable for the conversion. Thus for portability, you
may need to write @code{islower(c) ? toupper(c) : c} rather than just
@code{toupper(c)}.
These functions are declared in the header file @file{ctype.h}.
@pindex ctype.h
@comment ctype.h
@comment ISO
@deftypefun int tolower (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c The to* macros/functions call different functions that use different
@c arrays than those of__ctype_b_loc, but the access patterns and
@c thus safety guarantees are the same.
If @var{c} is an upper-case letter, @code{tolower} returns the corresponding
lower-case letter. If @var{c} is not an upper-case letter,
@var{c} is returned unchanged.
@end deftypefun
@comment ctype.h
@comment ISO
@deftypefun int toupper (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @var{c} is a lower-case letter, @code{toupper} returns the corresponding
upper-case letter. Otherwise @var{c} is returned unchanged.
@end deftypefun
@comment ctype.h
@comment SVID, BSD
@deftypefun int toascii (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function converts @var{c} to a 7-bit @code{unsigned char} value
that fits into the US/UK ASCII character set, by clearing the high-order
bits. This function is a BSD extension and is also an SVID extension.
@end deftypefun
@comment ctype.h
@comment SVID
@deftypefun int _tolower (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is identical to @code{tolower}, and is provided for compatibility
with the SVID. @xref{SVID}.@refill
@end deftypefun
@comment ctype.h
@comment SVID
@deftypefun int _toupper (int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is identical to @code{toupper}, and is provided for compatibility
with the SVID.
@end deftypefun
@node Classification of Wide Characters, Using Wide Char Classes, Case Conversion, Character Handling
@section Character class determination for wide characters
@w{Amendment 1} to @w{ISO C90} defines functions to classify wide
characters. Although the original @w{ISO C90} standard already defined
the type @code{wchar_t}, no functions operating on them were defined.
The general design of the classification functions for wide characters
is more general. It allows extensions to the set of available
classifications, beyond those which are always available. The POSIX
standard specifies how extensions can be made, and this is already
implemented in the @glibcadj{} implementation of the @code{localedef}
program.
The character class functions are normally implemented with bitsets,
with a bitset per character. For a given character, the appropriate
bitset is read from a table and a test is performed as to whether a
certain bit is set. Which bit is tested for is determined by the
class.
For the wide character classification functions this is made visible.
There is a type classification type defined, a function to retrieve this
value for a given class, and a function to test whether a given
character is in this class, using the classification value. On top of
this the normal character classification functions as used for
@code{char} objects can be defined.
@comment wctype.h
@comment ISO
@deftp {Data type} wctype_t
The @code{wctype_t} can hold a value which represents a character class.
The only defined way to generate such a value is by using the
@code{wctype} function.
@pindex wctype.h
This type is defined in @file{wctype.h}.
@end deftp
@comment wctype.h
@comment ISO
@deftypefun wctype_t wctype (const char *@var{property})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Although the source code of wctype contains multiple references to
@c the locale, that could each reference different locale_data objects
@c should the global locale object change while active, the compiler can
@c and does combine them all into a single dereference that resolves
@c once to the LCTYPE locale object used throughout the function, so it
@c is safe in (optimized) practice, if not in theory, even when the
@c locale changes. Ideally we'd explicitly save the resolved
@c locale_data object to make it visibly safe instead of safe only under
@c compiler optimizations, but given the decision that setlocale is
@c MT-Unsafe, all this would afford us would be the ability to not mark
@c this function with @mtslocale.
The @code{wctype} returns a value representing a class of wide
characters which is identified by the string @var{property}. Beside
some standard properties each locale can define its own ones. In case
no property with the given name is known for the current locale
selected for the @code{LC_CTYPE} category, the function returns zero.
@noindent
The properties known in every locale are:
@multitable @columnfractions .25 .25 .25 .25
@item
@code{"alnum"} @tab @code{"alpha"} @tab @code{"cntrl"} @tab @code{"digit"}
@item
@code{"graph"} @tab @code{"lower"} @tab @code{"print"} @tab @code{"punct"}
@item
@code{"space"} @tab @code{"upper"} @tab @code{"xdigit"}
@end multitable
@pindex wctype.h
This function is declared in @file{wctype.h}.
@end deftypefun
To test the membership of a character to one of the non-standard classes
the @w{ISO C} standard defines a completely new function.
@comment wctype.h
@comment ISO
@deftypefun int iswctype (wint_t @var{wc}, wctype_t @var{desc})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c The compressed lookup table returned by wctype is read-only.
This function returns a nonzero value if @var{wc} is in the character
class specified by @var{desc}. @var{desc} must previously be returned
by a successful call to @code{wctype}.
@pindex wctype.h
This function is declared in @file{wctype.h}.
@end deftypefun
To make it easier to use the commonly-used classification functions,
they are defined in the C library. There is no need to use
@code{wctype} if the property string is one of the known character
classes. In some situations it is desirable to construct the property
strings, and then it is important that @code{wctype} can also handle the
standard classes.
@cindex alphanumeric character
@comment wctype.h
@comment ISO
@deftypefun int iswalnum (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c The implicit wctype call in the isw* functions is actually an
@c optimized version because the category has a known offset, but the
@c wctype is equally safe when optimized, unsafe with changing locales
@c if not optimized (thus @mtslocale). Since it's not a macro, we
@c always optimize, and the locale can't change in any MT-Safe way, it's
@c fine. The test whether wc is ASCII to use the non-wide is*
@c macro/function doesn't bring any other safety issues: the test does
@c not depend on the locale, and each path after the decision resolves
@c the locale object only once.
This function returns a nonzero value if @var{wc} is an alphanumeric
character (a letter or number); in other words, if either @code{iswalpha}
or @code{iswdigit} is true of a character, then @code{iswalnum} is also
true.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("alnum"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex alphabetic character
@comment wctype.h
@comment ISO
@deftypefun int iswalpha (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is an alphabetic character (a letter). If
@code{iswlower} or @code{iswupper} is true of a character, then
@code{iswalpha} is also true.
In some locales, there may be additional characters for which
@code{iswalpha} is true---letters which are neither upper case nor lower
case. But in the standard @code{"C"} locale, there are no such
additional characters.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("alpha"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex control character
@comment wctype.h
@comment ISO
@deftypefun int iswcntrl (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a control character (that is, a character that
is not a printing character).
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("cntrl"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex digit character
@comment wctype.h
@comment ISO
@deftypefun int iswdigit (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a digit (e.g., @samp{0} through @samp{9}).
Please note that this function does not only return a nonzero value for
@emph{decimal} digits, but for all kinds of digits. A consequence is
that code like the following will @strong{not} work unconditionally for
wide characters:
@smallexample
n = 0;
while (iswdigit (*wc))
@{
n *= 10;
n += *wc++ - L'0';
@}
@end smallexample
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("digit"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex graphic character
@comment wctype.h
@comment ISO
@deftypefun int iswgraph (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a graphic character; that is, a character
that has a glyph associated with it. The whitespace characters are not
considered graphic.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("graph"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex lower-case character
@comment ctype.h
@comment ISO
@deftypefun int iswlower (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a lower-case letter. The letter need not be
from the Latin alphabet, any alphabet representable is valid.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("lower"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex printing character
@comment wctype.h
@comment ISO
@deftypefun int iswprint (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a printing character. Printing characters
include all the graphic characters, plus the space (@samp{ }) character.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("print"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex punctuation character
@comment wctype.h
@comment ISO
@deftypefun int iswpunct (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a punctuation character.
This means any printing character that is not alphanumeric or a space
character.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("punct"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex whitespace character
@comment wctype.h
@comment ISO
@deftypefun int iswspace (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a @dfn{whitespace} character. In the standard
@code{"C"} locale, @code{iswspace} returns true for only the standard
whitespace characters:
@table @code
@item L' '
space
@item L'\f'
formfeed
@item L'\n'
newline
@item L'\r'
carriage return
@item L'\t'
horizontal tab
@item L'\v'
vertical tab
@end table
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("space"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex upper-case character
@comment wctype.h
@comment ISO
@deftypefun int iswupper (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is an upper-case letter. The letter need not be
from the Latin alphabet, any alphabet representable is valid.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("upper"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@cindex hexadecimal digit character
@comment wctype.h
@comment ISO
@deftypefun int iswxdigit (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a hexadecimal digit.
Hexadecimal digits include the normal decimal digits @samp{0} through
@samp{9} and the letters @samp{A} through @samp{F} and
@samp{a} through @samp{f}.
@noindent
This function can be implemented using
@smallexample
iswctype (wc, wctype ("xdigit"))
@end smallexample
@pindex wctype.h
It is declared in @file{wctype.h}.
@end deftypefun
@Theglibc{} also provides a function which is not defined in the
@w{ISO C} standard but which is available as a version for single byte
characters as well.
@cindex blank character
@comment wctype.h
@comment ISO
@deftypefun int iswblank (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
Returns true if @var{wc} is a blank character; that is, a space or a tab.
This function was originally a GNU extension, but was added in @w{ISO C99}.
It is declared in @file{wchar.h}.
@end deftypefun
@node Using Wide Char Classes, Wide Character Case Conversion, Classification of Wide Characters, Character Handling
@section Notes on using the wide character classes
The first note is probably not astonishing but still occasionally a
cause of problems. The @code{isw@var{XXX}} functions can be implemented
using macros and in fact, @theglibc{} does this. They are still
available as real functions but when the @file{wctype.h} header is
included the macros will be used. This is the same as the
@code{char} type versions of these functions.
The second note covers something new. It can be best illustrated by a
(real-world) example. The first piece of code is an excerpt from the
original code. It is truncated a bit but the intention should be clear.
@smallexample
int
is_in_class (int c, const char *class)
@{
if (strcmp (class, "alnum") == 0)
return isalnum (c);
if (strcmp (class, "alpha") == 0)
return isalpha (c);
if (strcmp (class, "cntrl") == 0)
return iscntrl (c);
@dots{}
return 0;
@}
@end smallexample
Now, with the @code{wctype} and @code{iswctype} you can avoid the
@code{if} cascades, but rewriting the code as follows is wrong:
@smallexample
int
is_in_class (int c, const char *class)
@{
wctype_t desc = wctype (class);
return desc ? iswctype ((wint_t) c, desc) : 0;
@}
@end smallexample
The problem is that it is not guaranteed that the wide character
representation of a single-byte character can be found using casting.
In fact, usually this fails miserably. The correct solution to this
problem is to write the code as follows:
@smallexample
int
is_in_class (int c, const char *class)
@{
wctype_t desc = wctype (class);
return desc ? iswctype (btowc (c), desc) : 0;
@}
@end smallexample
@xref{Converting a Character}, for more information on @code{btowc}.
Note that this change probably does not improve the performance
of the program a lot since the @code{wctype} function still has to make
the string comparisons. It gets really interesting if the
@code{is_in_class} function is called more than once for the
same class name. In this case the variable @var{desc} could be computed
once and reused for all the calls. Therefore the above form of the
function is probably not the final one.
@node Wide Character Case Conversion, , Using Wide Char Classes, Character Handling
@section Mapping of wide characters.
The classification functions are also generalized by the @w{ISO C}
standard. Instead of just allowing the two standard mappings, a
locale can contain others. Again, the @code{localedef} program
already supports generating such locale data files.
@comment wctype.h
@comment ISO
@deftp {Data Type} wctrans_t
This data type is defined as a scalar type which can hold a value
representing the locale-dependent character mapping. There is no way to
construct such a value apart from using the return value of the
@code{wctrans} function.
@pindex wctype.h
@noindent
This type is defined in @file{wctype.h}.
@end deftp
@comment wctype.h
@comment ISO
@deftypefun wctrans_t wctrans (const char *@var{property})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Similar implementation, same caveats as wctype.
The @code{wctrans} function has to be used to find out whether a named
mapping is defined in the current locale selected for the
@code{LC_CTYPE} category. If the returned value is non-zero, you can use
it afterwards in calls to @code{towctrans}. If the return value is
zero no such mapping is known in the current locale.
Beside locale-specific mappings there are two mappings which are
guaranteed to be available in every locale:
@multitable @columnfractions .5 .5
@item
@code{"tolower"} @tab @code{"toupper"}
@end multitable
@pindex wctype.h
@noindent
These functions are declared in @file{wctype.h}.
@end deftypefun
@comment wctype.h
@comment ISO
@deftypefun wint_t towctrans (wint_t @var{wc}, wctrans_t @var{desc})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Same caveats as iswctype.
@code{towctrans} maps the input character @var{wc}
according to the rules of the mapping for which @var{desc} is a
descriptor, and returns the value it finds. @var{desc} must be
obtained by a successful call to @code{wctrans}.
@pindex wctype.h
@noindent
This function is declared in @file{wctype.h}.
@end deftypefun
For the generally available mappings, the @w{ISO C} standard defines
convenient shortcuts so that it is not necessary to call @code{wctrans}
for them.
@comment wctype.h
@comment ISO
@deftypefun wint_t towlower (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c Same caveats as iswalnum, just using a wctrans rather than a wctype
@c table.
If @var{wc} is an upper-case letter, @code{towlower} returns the corresponding
lower-case letter. If @var{wc} is not an upper-case letter,
@var{wc} is returned unchanged.
@noindent
@code{towlower} can be implemented using
@smallexample
towctrans (wc, wctrans ("tolower"))
@end smallexample
@pindex wctype.h
@noindent
This function is declared in @file{wctype.h}.
@end deftypefun
@comment wctype.h
@comment ISO
@deftypefun wint_t towupper (wint_t @var{wc})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
If @var{wc} is a lower-case letter, @code{towupper} returns the corresponding
upper-case letter. Otherwise @var{wc} is returned unchanged.
@noindent
@code{towupper} can be implemented using
@smallexample
towctrans (wc, wctrans ("toupper"))
@end smallexample
@pindex wctype.h
@noindent
This function is declared in @file{wctype.h}.
@end deftypefun
The same warnings given in the last section for the use of the wide
character classification functions apply here. It is not possible to
simply cast a @code{char} type value to a @code{wint_t} and use it as an
argument to @code{towctrans} calls.
glibc-doc-reference-2.19.orig/manual/lgpl-2.1.texi 0000664 0001750 0001750 00000063677 12275120646 021731 0 ustar adconrad adconrad @c The GNU Lesser General Public License.
@center Version 2.1, February 1999
@c This file is intended to be included within another document,
@c hence no sectioning command or @node.
@display
Copyright @copyright{} 1991, 1999 Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
[This is the first released version of the Lesser GPL. It also counts
as the successor of the GNU Library Public License, version 2, hence the
version number 2.1.]
@end display
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@subheading TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
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@subheading END OF TERMS AND CONDITIONS
@page
@subheading How to Apply These Terms to Your New Libraries
If you develop a new library, and you want it to be of the greatest
possible use to the public, we recommend making it free software that
everyone can redistribute and change. You can do so by permitting
redistribution under these terms (or, alternatively, under the terms of the
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safest to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least the
``copyright'' line and a pointer to where the full notice is found.
@smallexample
@var{one line to give the library's name and an idea of what it does.}
Copyright (C) @var{year} @var{name of author}
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at
your option) any later version.
This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
USA.
@end smallexample
Also add information on how to contact you by electronic and paper mail.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the library, if
necessary. Here is a sample; alter the names:
@smallexample
Yoyodyne, Inc., hereby disclaims all copyright interest in the library
`Frob' (a library for tweaking knobs) written by James Random Hacker.
@var{signature of Ty Coon}, 1 April 1990
Ty Coon, President of Vice
@end smallexample
That's all there is to it!
glibc-doc-reference-2.19.orig/manual/libm-err-tab.pl 0000775 0001750 0001750 00000015452 12275120646 022403 0 ustar adconrad adconrad #!/usr/bin/perl -w
# Copyright (C) 1999-2014 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
# Contributed by Andreas Jaeger , 1999.
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# .
# Information about tests are stored in: %results
# $results{$test}{"type"} is the result type, e.g. normal or complex.
# In the following description $platform, $type and $float are:
# - $platform is the used platform
# - $type is either "normal", "real" (for the real part of a complex number)
# or "imag" (for the imaginary part # of a complex number).
# - $float is either of float, ifloat, double, idouble, ldouble, ildouble;
# It represents the underlying floating point type (float, double or long
# double) and if inline functions (the leading i stands for inline)
# are used.
# $results{$test}{$platform}{$type}{$float} is defined and has a delta
# or 'fail' as value.
use File::Find;
use strict;
use vars qw ($sources @platforms %pplatforms);
use vars qw (%results @all_floats %suffices @all_functions);
# all_floats is in output order and contains all recognised float types that
# we're going to output
@all_floats = ('float', 'double', 'ldouble');
%suffices =
( 'float' => 'f',
'double' => '',
'ldouble' => 'l'
);
# Pretty description of platform
%pplatforms =
( "i386/fpu" => "ix86",
"generic" => "Generic",
"alpha/fpu" => "Alpha",
"ia64/fpu" => "IA64",
"m68k/fpu" => "M68k",
"mips/fpu" => "MIPS",
"powerpc/fpu" => "PowerPC",
"sparc/sparc32/fpu" => "Sparc 32-bit",
"sparc/sparc64/fpu" => "Sparc 64-bit",
"sh/sh4/fpu" => "SH4",
"s390/fpu" => "S/390",
"arm" => "ARM"
);
@all_functions =
( "acos", "acosh", "asin", "asinh", "atan", "atanh",
"atan2", "cabs", "cacos", "cacosh", "carg", "casin", "casinh",
"catan", "catanh", "cbrt", "ccos", "ccosh", "ceil", "cexp", "cimag",
"clog", "clog10", "conj", "copysign", "cos", "cosh", "cpow", "cproj",
"creal", "csin", "csinh", "csqrt", "ctan", "ctanh", "erf", "erfc",
"exp", "exp10", "exp2", "expm1", "fabs", "fdim", "floor", "fma",
"fmax", "fmin", "fmod", "frexp", "gamma", "hypot",
"ilogb", "j0", "j1", "jn", "lgamma", "lrint",
"llrint", "log", "log10", "log1p", "log2", "logb", "lround",
"llround", "modf", "nearbyint", "nextafter", "nexttoward", "pow",
"remainder", "remquo", "rint", "round", "scalb", "scalbn", "scalbln",
"sin", "sincos", "sinh", "sqrt", "tan", "tanh", "tgamma",
"trunc", "y0", "y1", "yn" );
# fpclassify, isnormal, isfinite, isinf, isnan, issignaling, signbit,
# isgreater, isgreaterequal, isless, islessequal, islessgreater, isunordered
# are not tabulated.
if ($#ARGV == 0) {
$sources = $ARGV[0];
} else {
$sources = '/usr/src/cvs/libc';
}
find (\&find_files, $sources);
@platforms = sort by_platforms @platforms;
&print_all;
sub find_files {
if ($_ eq 'libm-test-ulps') {
# print "Parsing $File::Find::name\n";
push @platforms, $File::Find::dir;
&parse_ulps ($File::Find::name, $File::Find::dir);
}
}
# Parse ulps file
sub parse_ulps {
my ($file, $platform) = @_;
my ($test, $type, $float, $eps, $kind);
# $type has the following values:
# "normal": No complex variable
# "real": Real part of complex result
# "imag": Imaginary part of complex result
open ULP, $file or die ("Can't open $file: $!");
while () {
chop;
# ignore comments and empty lines
next if /^#/;
next if /^\s*$/;
if (/^Test/) {
$kind = 'test';
next;
}
if (/^Function: /) {
if (/Real part of/) {
s/Real part of //;
$type = 'real';
} elsif (/Imaginary part of/) {
s/Imaginary part of //;
$type = 'imag';
} else {
$type = 'normal';
}
($test) = ($_ =~ /^Function:\s*\"([a-zA-Z0-9_]+)\"/);
$kind = 'fct';
next;
}
# Only handle maximal errors of functions
next if ($kind eq 'test');
if (/^i?(float|double|ldouble):/) {
($float, $eps) = split /\s*:\s*/,$_,2;
if ($eps eq 'fail') {
$results{$test}{$platform}{$type}{$float} = 'fail';
} elsif ($eps eq "0") {
# ignore
next;
} elsif (!exists $results{$test}{$platform}{$type}{$float}
|| $results{$test}{$platform}{$type}{$float} ne 'fail') {
$results{$test}{$platform}{$type}{$float} = $eps;
}
if ($type =~ /^real|imag$/) {
$results{$test}{'type'} = 'complex';
} elsif ($type eq 'normal') {
$results{$test}{'type'} = 'normal';
}
next;
}
print "Skipping unknown entry: `$_'\n";
}
close ULP;
}
sub get_value {
my ($fct, $platform, $type, $float) = @_;
return (exists $results{$fct}{$platform}{$type}{$float}
? $results{$fct}{$platform}{$type}{$float} : "0");
}
sub canonicalize_platform {
my ($platform) = @_;
$platform =~ s|^(.*/sysdeps/)||;
return exists $pplatforms{$platform} ? $pplatforms{$platform} : $platform;
}
sub print_platforms {
my (@p) = @_;
my ($fct, $platform, $float, $first, $i, $platform_no, $platform_total);
print '@multitable {nexttowardf} ';
foreach (@p) {
print ' {1000 + i 1000}';
}
print "\n";
print '@item Function ';
foreach (@p) {
print ' @tab ';
print &canonicalize_platform ($_);
}
print "\n";
foreach $fct (@all_functions) {
foreach $float (@all_floats) {
print "\@item $fct$suffices{$float} ";
foreach $platform (@p) {
print ' @tab ';
if (exists $results{$fct}{$platform}{'normal'}{$float}
|| exists $results{$fct}{$platform}{'real'}{$float}
|| exists $results{$fct}{$platform}{'imag'}{$float}) {
if ($results{$fct}{'type'} eq 'complex') {
print &get_value ($fct, $platform, 'real', $float),
' + i ', &get_value ($fct, $platform, 'imag', $float);
} else {
print $results{$fct}{$platform}{'normal'}{$float};
}
} else {
print '-';
}
}
print "\n";
}
}
print "\@end multitable\n";
}
sub print_all {
my ($i, $max);
my ($columns) = 5;
# Print only 5 platforms at a time.
for ($i=0; $i < $#platforms; $i+=$columns) {
$max = $i+$columns-1 > $#platforms ? $#platforms : $i+$columns-1;
print_platforms (@platforms[$i .. $max]);
}
}
sub by_platforms {
my ($pa, $pb);
$pa = $pplatforms{$a} ? $pplatforms{$a} : $a;
$pb = $pplatforms{$b} ? $pplatforms{$b} : $b;
return $pa cmp $pb;
}
glibc-doc-reference-2.19.orig/manual/header.texi 0000664 0001750 0001750 00000001364 12275120646 021706 0 ustar adconrad adconrad @node Library Summary, Installation, Language Features, Top
@c %MENU% A summary showing the syntax, header file, and derivation of each library feature
@appendix Summary of Library Facilities
This appendix is a complete list of the facilities declared within the
header files supplied with @theglibc{}. Each entry also lists the
standard or other source from which each facility is derived, and tells
you where in the manual you can find more information about how to use
it.
@c This table runs wide. Shrink fonts.
@iftex
@smallfonts @rm
@end iftex
@table @code
@comment summary.texi is generated from the other Texinfo files.
@comment See the Makefile and summary.awk for the details.
@include summary.texi
@end table
@iftex
@textfonts @rm
@end iftex
glibc-doc-reference-2.19.orig/manual/users.texi 0000664 0001750 0001750 00000351363 12275120646 021626 0 ustar adconrad adconrad @node Users and Groups, System Management, Name Service Switch, Top
@c %MENU% How users are identified and classified
@chapter Users and Groups
Every user who can log in on the system is identified by a unique number
called the @dfn{user ID}. Each process has an effective user ID which
says which user's access permissions it has.
Users are classified into @dfn{groups} for access control purposes. Each
process has one or more @dfn{group ID values} which say which groups the
process can use for access to files.
The effective user and group IDs of a process collectively form its
@dfn{persona}. This determines which files the process can access.
Normally, a process inherits its persona from the parent process, but
under special circumstances a process can change its persona and thus
change its access permissions.
Each file in the system also has a user ID and a group ID. Access
control works by comparing the user and group IDs of the file with those
of the running process.
The system keeps a database of all the registered users, and another
database of all the defined groups. There are library functions you
can use to examine these databases.
@menu
* User and Group IDs:: Each user has a unique numeric ID;
likewise for groups.
* Process Persona:: The user IDs and group IDs of a process.
* Why Change Persona:: Why a program might need to change
its user and/or group IDs.
* How Change Persona:: Changing the user and group IDs.
* Reading Persona:: How to examine the user and group IDs.
* Setting User ID:: Functions for setting the user ID.
* Setting Groups:: Functions for setting the group IDs.
* Enable/Disable Setuid:: Turning setuid access on and off.
* Setuid Program Example:: The pertinent parts of one sample program.
* Tips for Setuid:: How to avoid granting unlimited access.
* Who Logged In:: Getting the name of the user who logged in,
or of the real user ID of the current process.
* User Accounting Database:: Keeping information about users and various
actions in databases.
* User Database:: Functions and data structures for
accessing the user database.
* Group Database:: Functions and data structures for
accessing the group database.
* Database Example:: Example program showing the use of database
inquiry functions.
* Netgroup Database:: Functions for accessing the netgroup database.
@end menu
@node User and Group IDs
@section User and Group IDs
@cindex login name
@cindex user name
@cindex user ID
Each user account on a computer system is identified by a @dfn{user
name} (or @dfn{login name}) and @dfn{user ID}. Normally, each user name
has a unique user ID, but it is possible for several login names to have
the same user ID. The user names and corresponding user IDs are stored
in a data base which you can access as described in @ref{User Database}.
@cindex group name
@cindex group ID
Users are classified in @dfn{groups}. Each user name belongs to one
@dfn{default group} and may also belong to any number of
@dfn{supplementary groups}. Users who are members of the same group can
share resources (such as files) that are not accessible to users who are
not a member of that group. Each group has a @dfn{group name} and
@dfn{group ID}. @xref{Group Database}, for how to find information
about a group ID or group name.
@node Process Persona
@section The Persona of a Process
@cindex persona
@cindex effective user ID
@cindex effective group ID
@cindex supplementary group IDs
@c When Hurd is more widely used, explain multiple effective user IDs
@c here. -zw
At any time, each process has an @dfn{effective user ID}, a @dfn{effective
group ID}, and a set of @dfn{supplementary group IDs}. These IDs
determine the privileges of the process. They are collectively
called the @dfn{persona} of the process, because they determine ``who it
is'' for purposes of access control.
Your login shell starts out with a persona which consists of your user
ID, your default group ID, and your supplementary group IDs (if you are
in more than one group). In normal circumstances, all your other processes
inherit these values.
@cindex real user ID
@cindex real group ID
A process also has a @dfn{real user ID} which identifies the user who
created the process, and a @dfn{real group ID} which identifies that
user's default group. These values do not play a role in access
control, so we do not consider them part of the persona. But they are
also important.
Both the real and effective user ID can be changed during the lifetime
of a process. @xref{Why Change Persona}.
For details on how a process's effective user ID and group IDs affect
its permission to access files, see @ref{Access Permission}.
The effective user ID of a process also controls permissions for sending
signals using the @code{kill} function. @xref{Signaling Another
Process}.
Finally, there are many operations which can only be performed by a
process whose effective user ID is zero. A process with this user ID is
a @dfn{privileged process}. Commonly the user name @code{root} is
associated with user ID 0, but there may be other user names with this
ID.
@c !!! should mention POSIX capabilities here.
@node Why Change Persona
@section Why Change the Persona of a Process?
The most obvious situation where it is necessary for a process to change
its user and/or group IDs is the @code{login} program. When
@code{login} starts running, its user ID is @code{root}. Its job is to
start a shell whose user and group IDs are those of the user who is
logging in. (To accomplish this fully, @code{login} must set the real
user and group IDs as well as its persona. But this is a special case.)
The more common case of changing persona is when an ordinary user
program needs access to a resource that wouldn't ordinarily be
accessible to the user actually running it.
For example, you may have a file that is controlled by your program but
that shouldn't be read or modified directly by other users, either
because it implements some kind of locking protocol, or because you want
to preserve the integrity or privacy of the information it contains.
This kind of restricted access can be implemented by having the program
change its effective user or group ID to match that of the resource.
Thus, imagine a game program that saves scores in a file. The game
program itself needs to be able to update this file no matter who is
running it, but if users can write the file without going through the
game, they can give themselves any scores they like. Some people
consider this undesirable, or even reprehensible. It can be prevented
by creating a new user ID and login name (say, @code{games}) to own the
scores file, and make the file writable only by this user. Then, when
the game program wants to update this file, it can change its effective
user ID to be that for @code{games}. In effect, the program must
adopt the persona of @code{games} so it can write the scores file.
@node How Change Persona
@section How an Application Can Change Persona
@cindex @code{setuid} programs
@cindex saved set-user-ID
@cindex saved set-group-ID
@cindex @code{_POSIX_SAVED_IDS}
The ability to change the persona of a process can be a source of
unintentional privacy violations, or even intentional abuse. Because of
the potential for problems, changing persona is restricted to special
circumstances.
You can't arbitrarily set your user ID or group ID to anything you want;
only privileged processes can do that. Instead, the normal way for a
program to change its persona is that it has been set up in advance to
change to a particular user or group. This is the function of the setuid
and setgid bits of a file's access mode. @xref{Permission Bits}.
When the setuid bit of an executable file is on, executing that file
gives the process a third user ID: the @dfn{file user ID}. This ID is
set to the owner ID of the file. The system then changes the effective
user ID to the file user ID. The real user ID remains as it was.
Likewise, if the setgid bit is on, the process is given a @dfn{file
group ID} equal to the group ID of the file, and its effective group ID
is changed to the file group ID.
If a process has a file ID (user or group), then it can at any time
change its effective ID to its real ID and back to its file ID.
Programs use this feature to relinquish their special privileges except
when they actually need them. This makes it less likely that they can
be tricked into doing something inappropriate with their privileges.
@strong{Portability Note:} Older systems do not have file IDs.
To determine if a system has this feature, you can test the compiler
define @code{_POSIX_SAVED_IDS}. (In the POSIX standard, file IDs are
known as saved IDs.)
@xref{File Attributes}, for a more general discussion of file modes and
accessibility.
@node Reading Persona
@section Reading the Persona of a Process
Here are detailed descriptions of the functions for reading the user and
group IDs of a process, both real and effective. To use these
facilities, you must include the header files @file{sys/types.h} and
@file{unistd.h}.
@pindex unistd.h
@pindex sys/types.h
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} uid_t
This is an integer data type used to represent user IDs. In
@theglibc{}, this is an alias for @code{unsigned int}.
@end deftp
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} gid_t
This is an integer data type used to represent group IDs. In
@theglibc{}, this is an alias for @code{unsigned int}.
@end deftp
@comment unistd.h
@comment POSIX.1
@deftypefun uid_t getuid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Atomic syscall, except on hurd, where it takes a lock within a hurd
@c critical section.
The @code{getuid} function returns the real user ID of the process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun gid_t getgid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getgid} function returns the real group ID of the process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun uid_t geteuid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{geteuid} function returns the effective user ID of the process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun gid_t getegid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getegid} function returns the effective group ID of the process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int getgroups (int @var{count}, gid_t *@var{groups})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getgroups} function is used to inquire about the supplementary
group IDs of the process. Up to @var{count} of these group IDs are
stored in the array @var{groups}; the return value from the function is
the number of group IDs actually stored. If @var{count} is smaller than
the total number of supplementary group IDs, then @code{getgroups}
returns a value of @code{-1} and @code{errno} is set to @code{EINVAL}.
If @var{count} is zero, then @code{getgroups} just returns the total
number of supplementary group IDs. On systems that do not support
supplementary groups, this will always be zero.
Here's how to use @code{getgroups} to read all the supplementary group
IDs:
@smallexample
@group
gid_t *
read_all_groups (void)
@{
int ngroups = getgroups (0, NULL);
gid_t *groups
= (gid_t *) xmalloc (ngroups * sizeof (gid_t));
int val = getgroups (ngroups, groups);
if (val < 0)
@{
free (groups);
return NULL;
@}
return groups;
@}
@end group
@end smallexample
@end deftypefun
@node Setting User ID
@section Setting the User ID
This section describes the functions for altering the user ID (real
and/or effective) of a process. To use these facilities, you must
include the header files @file{sys/types.h} and @file{unistd.h}.
@pindex unistd.h
@pindex sys/types.h
@comment unistd.h
@comment POSIX.1
@deftypefun int seteuid (uid_t @var{neweuid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c seteuid @asulock @aculock
@c INLINE_SETXID_SYSCALL @asulock @aculock
@c This may be just a unix syscall, or the ugliness below used by
@c nptl to propagate the syscall to all cloned processes used to
@c implement threads.
@c nptl_setxid @asulock @aculock
@c while holding the stack_alloc_lock, mark with SETXID_BITMASK all
@c threads that are not exiting, signal them until no thread remains
@c marked, clear the marks and run the syscall, then release the lock.
@c lll_lock @asulock @aculock
@c list_for_each ok
@c list_entry ok
@c setxid_mark_thread ok
@c if a thread is initializing, wait for it to be cloned.
@c mark it with SETXID_BITMASK if it's not exiting
@c setxid_signal_thread ok
@c if a thread is marked with SETXID_BITMASK,
@c send it the SIGSETXID signal
@c setxid_unmark_thread ok
@c clear SETXID_BITMASK and release the futex if SETXID_BITMASK is
@c set.
@c ok
@c lll_unlock @aculock
@c
@c sighandler_setxid ok
@c issue the syscall, clear SETXID_BITMASK, release the futex, and
@c wake up the signaller loop if the counter reached zero.
This function sets the effective user ID of a process to @var{neweuid},
provided that the process is allowed to change its effective user ID. A
privileged process (effective user ID zero) can change its effective
user ID to any legal value. An unprivileged process with a file user ID
can change its effective user ID to its real user ID or to its file user
ID. Otherwise, a process may not change its effective user ID at all.
The @code{seteuid} function returns a value of @code{0} to indicate
successful completion, and a value of @code{-1} to indicate an error.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EINVAL
The value of the @var{neweuid} argument is invalid.
@item EPERM
The process may not change to the specified ID.
@end table
Older systems (those without the @code{_POSIX_SAVED_IDS} feature) do not
have this function.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int setuid (uid_t @var{newuid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setuid @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
If the calling process is privileged, this function sets both the real
and effective user ID of the process to @var{newuid}. It also deletes
the file user ID of the process, if any. @var{newuid} may be any
legal value. (Once this has been done, there is no way to recover the
old effective user ID.)
If the process is not privileged, and the system supports the
@code{_POSIX_SAVED_IDS} feature, then this function behaves like
@code{seteuid}.
The return values and error conditions are the same as for @code{seteuid}.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int setreuid (uid_t @var{ruid}, uid_t @var{euid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setreuid @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
This function sets the real user ID of the process to @var{ruid} and the
effective user ID to @var{euid}. If @var{ruid} is @code{-1}, it means
not to change the real user ID; likewise if @var{euid} is @code{-1}, it
means not to change the effective user ID.
The @code{setreuid} function exists for compatibility with 4.3 BSD Unix,
which does not support file IDs. You can use this function to swap the
effective and real user IDs of the process. (Privileged processes are
not limited to this particular usage.) If file IDs are supported, you
should use that feature instead of this function. @xref{Enable/Disable
Setuid}.
The return value is @code{0} on success and @code{-1} on failure.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EPERM
The process does not have the appropriate privileges; you do not
have permission to change to the specified ID.
@end table
@end deftypefun
@node Setting Groups
@section Setting the Group IDs
This section describes the functions for altering the group IDs (real
and effective) of a process. To use these facilities, you must include
the header files @file{sys/types.h} and @file{unistd.h}.
@pindex unistd.h
@pindex sys/types.h
@comment unistd.h
@comment POSIX.1
@deftypefun int setegid (gid_t @var{newgid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setegid @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
This function sets the effective group ID of the process to
@var{newgid}, provided that the process is allowed to change its group
ID. Just as with @code{seteuid}, if the process is privileged it may
change its effective group ID to any value; if it isn't, but it has a
file group ID, then it may change to its real group ID or file group ID;
otherwise it may not change its effective group ID.
Note that a process is only privileged if its effective @emph{user} ID
is zero. The effective group ID only affects access permissions.
The return values and error conditions for @code{setegid} are the same
as those for @code{seteuid}.
This function is only present if @code{_POSIX_SAVED_IDS} is defined.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int setgid (gid_t @var{newgid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setgid @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
This function sets both the real and effective group ID of the process
to @var{newgid}, provided that the process is privileged. It also
deletes the file group ID, if any.
If the process is not privileged, then @code{setgid} behaves like
@code{setegid}.
The return values and error conditions for @code{setgid} are the same
as those for @code{seteuid}.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int setregid (gid_t @var{rgid}, gid_t @var{egid})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setregid @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
This function sets the real group ID of the process to @var{rgid} and
the effective group ID to @var{egid}. If @var{rgid} is @code{-1}, it
means not to change the real group ID; likewise if @var{egid} is
@code{-1}, it means not to change the effective group ID.
The @code{setregid} function is provided for compatibility with 4.3 BSD
Unix, which does not support file IDs. You can use this function to
swap the effective and real group IDs of the process. (Privileged
processes are not limited to this usage.) If file IDs are supported,
you should use that feature instead of using this function.
@xref{Enable/Disable Setuid}.
The return values and error conditions for @code{setregid} are the same
as those for @code{setreuid}.
@end deftypefun
@code{setuid} and @code{setgid} behave differently depending on whether
the effective user ID at the time is zero. If it is not zero, they
behave like @code{seteuid} and @code{setegid}. If it is, they change
both effective and real IDs and delete the file ID. To avoid confusion,
we recommend you always use @code{seteuid} and @code{setegid} except
when you know the effective user ID is zero and your intent is to change
the persona permanently. This case is rare---most of the programs that
need it, such as @code{login} and @code{su}, have already been written.
Note that if your program is setuid to some user other than @code{root},
there is no way to drop privileges permanently.
The system also lets privileged processes change their supplementary
group IDs. To use @code{setgroups} or @code{initgroups}, your programs
should include the header file @file{grp.h}.
@pindex grp.h
@comment grp.h
@comment BSD
@deftypefun int setgroups (size_t @var{count}, const gid_t *@var{groups})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c setgroups @asulock @aculock
@c INLINE_SETXID_SYSCALL dup @asulock @aculock
This function sets the process's supplementary group IDs. It can only
be called from privileged processes. The @var{count} argument specifies
the number of group IDs in the array @var{groups}.
This function returns @code{0} if successful and @code{-1} on error.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EPERM
The calling process is not privileged.
@end table
@end deftypefun
@comment grp.h
@comment BSD
@deftypefun int initgroups (const char *@var{user}, gid_t @var{group})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @acsmem{} @acsfd{} @aculock{}}}
@c initgroups @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c sysconf(_SC_NGROUPS_MAX) dup @acsfd
@c MIN dup ok
@c malloc @ascuheap @acsmem
@c internal_getgrouplist @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getgrouplist @ascuheap @acsfd @acsmem
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c nscd_cache_search dup ok
@c nscd_open_socket dup @acsfd
@c realloc dup @ascuheap @acsmem
@c readall dup ok
@c memcpy dup ok
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c nss_database_lookup dup @mtslocale @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c compat_call @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c sysconf(_SC_GETGR_R_SIZE_MAX) ok
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *getgrent_fct @ascuplugin
@c *setgrent_fct @ascuplugin
@c *endgrent_fct @ascuplugin
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c *initgroups_dyn_fct @ascuplugin
@c nss_next_action dup ok
@c setgroups dup @asulock @aculock
@c free dup @ascuheap @acsmem
The @code{initgroups} function sets the process's supplementary group
IDs to be the normal default for the user name @var{user}. The group
@var{group} is automatically included.
This function works by scanning the group database for all the groups
@var{user} belongs to. It then calls @code{setgroups} with the list it
has constructed.
The return values and error conditions are the same as for
@code{setgroups}.
@end deftypefun
If you are interested in the groups a particular user belongs to, but do
not want to change the process's supplementary group IDs, you can use
@code{getgrouplist}. To use @code{getgrouplist}, your programs should
include the header file @file{grp.h}.
@pindex grp.h
@comment grp.h
@comment BSD
@deftypefun int getgrouplist (const char *@var{user}, gid_t @var{group}, gid_t *@var{groups}, int *@var{ngroups})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @acsmem{} @acsfd{} @aculock{}}}
@c getgrouplist @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c MAX dup ok
@c malloc dup @ascuheap @acsmem
@c internal_getgrouplist dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c memcpy dup ok
@c free dup @ascuheap @acsmem
The @code{getgrouplist} function scans the group database for all the
groups @var{user} belongs to. Up to *@var{ngroups} group IDs
corresponding to these groups are stored in the array @var{groups}; the
return value from the function is the number of group IDs actually
stored. If *@var{ngroups} is smaller than the total number of groups
found, then @code{getgrouplist} returns a value of @code{-1} and stores
the actual number of groups in *@var{ngroups}. The group @var{group} is
automatically included in the list of groups returned by
@code{getgrouplist}.
Here's how to use @code{getgrouplist} to read all supplementary groups
for @var{user}:
@smallexample
@group
gid_t *
supplementary_groups (char *user)
@{
int ngroups = 16;
gid_t *groups
= (gid_t *) xmalloc (ngroups * sizeof (gid_t));
struct passwd *pw = getpwnam (user);
if (pw == NULL)
return NULL;
if (getgrouplist (pw->pw_name, pw->pw_gid, groups, &ngroups) < 0)
@{
groups = xrealloc (ngroups * sizeof (gid_t));
getgrouplist (pw->pw_name, pw->pw_gid, groups, &ngroups);
@}
return groups;
@}
@end group
@end smallexample
@end deftypefun
@node Enable/Disable Setuid
@section Enabling and Disabling Setuid Access
A typical setuid program does not need its special access all of the
time. It's a good idea to turn off this access when it isn't needed,
so it can't possibly give unintended access.
If the system supports the @code{_POSIX_SAVED_IDS} feature, you can
accomplish this with @code{seteuid}. When the game program starts, its
real user ID is @code{jdoe}, its effective user ID is @code{games}, and
its saved user ID is also @code{games}. The program should record both
user ID values once at the beginning, like this:
@smallexample
user_user_id = getuid ();
game_user_id = geteuid ();
@end smallexample
Then it can turn off game file access with
@smallexample
seteuid (user_user_id);
@end smallexample
@noindent
and turn it on with
@smallexample
seteuid (game_user_id);
@end smallexample
@noindent
Throughout this process, the real user ID remains @code{jdoe} and the
file user ID remains @code{games}, so the program can always set its
effective user ID to either one.
On other systems that don't support file user IDs, you can
turn setuid access on and off by using @code{setreuid} to swap the real
and effective user IDs of the process, as follows:
@smallexample
setreuid (geteuid (), getuid ());
@end smallexample
@noindent
This special case is always allowed---it cannot fail.
Why does this have the effect of toggling the setuid access? Suppose a
game program has just started, and its real user ID is @code{jdoe} while
its effective user ID is @code{games}. In this state, the game can
write the scores file. If it swaps the two uids, the real becomes
@code{games} and the effective becomes @code{jdoe}; now the program has
only @code{jdoe} access. Another swap brings @code{games} back to
the effective user ID and restores access to the scores file.
In order to handle both kinds of systems, test for the saved user ID
feature with a preprocessor conditional, like this:
@smallexample
#ifdef _POSIX_SAVED_IDS
seteuid (user_user_id);
#else
setreuid (geteuid (), getuid ());
#endif
@end smallexample
@node Setuid Program Example
@section Setuid Program Example
Here's an example showing how to set up a program that changes its
effective user ID.
This is part of a game program called @code{caber-toss} that manipulates
a file @file{scores} that should be writable only by the game program
itself. The program assumes that its executable file will be installed
with the setuid bit set and owned by the same user as the @file{scores}
file. Typically, a system administrator will set up an account like
@code{games} for this purpose.
The executable file is given mode @code{4755}, so that doing an
@samp{ls -l} on it produces output like:
@smallexample
-rwsr-xr-x 1 games 184422 Jul 30 15:17 caber-toss
@end smallexample
@noindent
The setuid bit shows up in the file modes as the @samp{s}.
The scores file is given mode @code{644}, and doing an @samp{ls -l} on
it shows:
@smallexample
-rw-r--r-- 1 games 0 Jul 31 15:33 scores
@end smallexample
Here are the parts of the program that show how to set up the changed
user ID. This program is conditionalized so that it makes use of the
file IDs feature if it is supported, and otherwise uses @code{setreuid}
to swap the effective and real user IDs.
@smallexample
#include
#include
#include
#include
/* @r{Remember the effective and real UIDs.} */
static uid_t euid, ruid;
/* @r{Restore the effective UID to its original value.} */
void
do_setuid (void)
@{
int status;
#ifdef _POSIX_SAVED_IDS
status = seteuid (euid);
#else
status = setreuid (ruid, euid);
#endif
if (status < 0) @{
fprintf (stderr, "Couldn't set uid.\n");
exit (status);
@}
@}
@group
/* @r{Set the effective UID to the real UID.} */
void
undo_setuid (void)
@{
int status;
#ifdef _POSIX_SAVED_IDS
status = seteuid (ruid);
#else
status = setreuid (euid, ruid);
#endif
if (status < 0) @{
fprintf (stderr, "Couldn't set uid.\n");
exit (status);
@}
@}
@end group
/* @r{Main program.} */
int
main (void)
@{
/* @r{Remember the real and effective user IDs.} */
ruid = getuid ();
euid = geteuid ();
undo_setuid ();
/* @r{Do the game and record the score.} */
@dots{}
@}
@end smallexample
Notice how the first thing the @code{main} function does is to set the
effective user ID back to the real user ID. This is so that any other
file accesses that are performed while the user is playing the game use
the real user ID for determining permissions. Only when the program
needs to open the scores file does it switch back to the file user ID,
like this:
@smallexample
/* @r{Record the score.} */
int
record_score (int score)
@{
FILE *stream;
char *myname;
/* @r{Open the scores file.} */
do_setuid ();
stream = fopen (SCORES_FILE, "a");
undo_setuid ();
@group
/* @r{Write the score to the file.} */
if (stream)
@{
myname = cuserid (NULL);
if (score < 0)
fprintf (stream, "%10s: Couldn't lift the caber.\n", myname);
else
fprintf (stream, "%10s: %d feet.\n", myname, score);
fclose (stream);
return 0;
@}
else
return -1;
@}
@end group
@end smallexample
@node Tips for Setuid
@section Tips for Writing Setuid Programs
It is easy for setuid programs to give the user access that isn't
intended---in fact, if you want to avoid this, you need to be careful.
Here are some guidelines for preventing unintended access and
minimizing its consequences when it does occur:
@itemize @bullet
@item
Don't have @code{setuid} programs with privileged user IDs such as
@code{root} unless it is absolutely necessary. If the resource is
specific to your particular program, it's better to define a new,
nonprivileged user ID or group ID just to manage that resource.
It's better if you can write your program to use a special group than a
special user.
@item
Be cautious about using the @code{exec} functions in combination with
changing the effective user ID. Don't let users of your program execute
arbitrary programs under a changed user ID. Executing a shell is
especially bad news. Less obviously, the @code{execlp} and @code{execvp}
functions are a potential risk (since the program they execute depends
on the user's @code{PATH} environment variable).
If you must @code{exec} another program under a changed ID, specify an
absolute file name (@pxref{File Name Resolution}) for the executable,
and make sure that the protections on that executable and @emph{all}
containing directories are such that ordinary users cannot replace it
with some other program.
You should also check the arguments passed to the program to make sure
they do not have unexpected effects. Likewise, you should examine the
environment variables. Decide which arguments and variables are safe,
and reject all others.
You should never use @code{system} in a privileged program, because it
invokes a shell.
@item
Only use the user ID controlling the resource in the part of the program
that actually uses that resource. When you're finished with it, restore
the effective user ID back to the actual user's user ID.
@xref{Enable/Disable Setuid}.
@item
If the @code{setuid} part of your program needs to access other files
besides the controlled resource, it should verify that the real user
would ordinarily have permission to access those files. You can use the
@code{access} function (@pxref{Access Permission}) to check this; it
uses the real user and group IDs, rather than the effective IDs.
@end itemize
@node Who Logged In
@section Identifying Who Logged In
@cindex login name, determining
@cindex user ID, determining
You can use the functions listed in this section to determine the login
name of the user who is running a process, and the name of the user who
logged in the current session. See also the function @code{getuid} and
friends (@pxref{Reading Persona}). How this information is collected by
the system and how to control/add/remove information from the background
storage is described in @ref{User Accounting Database}.
The @code{getlogin} function is declared in @file{unistd.h}, while
@code{cuserid} and @code{L_cuserid} are declared in @file{stdio.h}.
@pindex stdio.h
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun {char *} getlogin (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:getlogin} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getlogin (linux) @mtasurace:getlogin @mtasurace:utent @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getlogin_r_loginuid dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getlogin_fd0 (unix) @mtasurace:getlogin @mtasurace:utent @mtascusig:ALRM @mtascutimer @ascuheap @asulock @aculock @acsfd @acsmem
@c uses static buffer name => @mtasurace:getlogin
@c ttyname_r dup @ascuheap @acsmem @acsfd
@c strncpy dup ok
@c setutent dup @mtasurace:utent @asulock @aculock @acsfd
@c getutline_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c endutent dup @mtasurace:utent @asulock @aculock
@c libc_lock_unlock dup ok
@c strlen dup ok
@c memcpy dup ok
@c
@c getlogin_r (linux) @mtasurace:utent @mtascusig:ALRM @mtascutimer @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getlogin_r_loginuid @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c open_not_cancel_2 dup @acsfd
@c read_not_cancel dup ok
@c close_not_cancel_no_status dup @acsfd
@c strtoul @mtslocale
@c getpwuid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @asulock @aculock @acsfd @acsmem
@c strlen dup ok
@c memcpy dup ok
@c free dup @asulock @aculock @acsfd @acsmem
@c getlogin_r_fd0 (unix) @mtasurace:utent @mtascusig:ALRM @mtascutimer @ascuheap @asulock @aculock @acsmem @acsfd
@c ttyname_r dup @ascuheap @acsmem @acsfd
@c strncpy dup ok
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->setutent dup @mtasurace:utent @acsfd
@c *libc_utmp_jump_table->getutline_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer
@c *libc_utmp_jump_table->endutent dup @mtasurace:utent @asulock @aculock
@c libc_lock_unlock dup ok
@c strlen dup ok
@c memcpy dup ok
The @code{getlogin} function returns a pointer to a string containing the
name of the user logged in on the controlling terminal of the process,
or a null pointer if this information cannot be determined. The string
is statically allocated and might be overwritten on subsequent calls to
this function or to @code{cuserid}.
@end deftypefun
@comment stdio.h
@comment POSIX.1
@deftypefun {char *} cuserid (char *@var{string})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c cuserid @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c geteuid dup ok
@c getpwuid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c strncpy dup ok
The @code{cuserid} function returns a pointer to a string containing a
user name associated with the effective ID of the process. If
@var{string} is not a null pointer, it should be an array that can hold
at least @code{L_cuserid} characters; the string is returned in this
array. Otherwise, a pointer to a string in a static area is returned.
This string is statically allocated and might be overwritten on
subsequent calls to this function or to @code{getlogin}.
The use of this function is deprecated since it is marked to be
withdrawn in XPG4.2 and has already been removed from newer revisions of
POSIX.1.
@end deftypefun
@comment stdio.h
@comment POSIX.1
@deftypevr Macro int L_cuserid
An integer constant that indicates how long an array you might need to
store a user name.
@end deftypevr
These functions let your program identify positively the user who is
running or the user who logged in this session. (These can differ when
setuid programs are involved; see @ref{Process Persona}.) The user cannot
do anything to fool these functions.
For most purposes, it is more useful to use the environment variable
@code{LOGNAME} to find out who the user is. This is more flexible
precisely because the user can set @code{LOGNAME} arbitrarily.
@xref{Standard Environment}.
@node User Accounting Database
@section The User Accounting Database
@cindex user accounting database
Most Unix-like operating systems keep track of logged in users by
maintaining a user accounting database. This user accounting database
stores for each terminal, who has logged on, at what time, the process
ID of the user's login shell, etc., etc., but also stores information
about the run level of the system, the time of the last system reboot,
and possibly more.
The user accounting database typically lives in @file{/etc/utmp},
@file{/var/adm/utmp} or @file{/var/run/utmp}. However, these files
should @strong{never} be accessed directly. For reading information
from and writing information to the user accounting database, the
functions described in this section should be used.
@menu
* Manipulating the Database:: Scanning and modifying the user
accounting database.
* XPG Functions:: A standardized way for doing the same thing.
* Logging In and Out:: Functions from BSD that modify the user
accounting database.
@end menu
@node Manipulating the Database
@subsection Manipulating the User Accounting Database
These functions and the corresponding data structures are declared in
the header file @file{utmp.h}.
@pindex utmp.h
@comment utmp.h
@comment SVID
@deftp {Data Type} {struct exit_status}
The @code{exit_status} data structure is used to hold information about
the exit status of processes marked as @code{DEAD_PROCESS} in the user
accounting database.
@table @code
@item short int e_termination
The exit status of the process.
@item short int e_exit
The exit status of the process.
@end table
@end deftp
@deftp {Data Type} {struct utmp}
The @code{utmp} data structure is used to hold information about entries
in the user accounting database. On @gnusystems{} it has the following
members:
@table @code
@item short int ut_type
Specifies the type of login; one of @code{EMPTY}, @code{RUN_LVL},
@code{BOOT_TIME}, @code{OLD_TIME}, @code{NEW_TIME}, @code{INIT_PROCESS},
@code{LOGIN_PROCESS}, @code{USER_PROCESS}, @code{DEAD_PROCESS} or
@code{ACCOUNTING}.
@item pid_t ut_pid
The process ID number of the login process.
@item char ut_line[]
The device name of the tty (without @file{/dev/}).
@item char ut_id[]
The inittab ID of the process.
@item char ut_user[]
The user's login name.
@item char ut_host[]
The name of the host from which the user logged in.
@item struct exit_status ut_exit
The exit status of a process marked as @code{DEAD_PROCESS}.
@item long ut_session
The Session ID, used for windowing.
@item struct timeval ut_tv
Time the entry was made. For entries of type @code{OLD_TIME} this is
the time when the system clock changed, and for entries of type
@code{NEW_TIME} this is the time the system clock was set to.
@item int32_t ut_addr_v6[4]
The Internet address of a remote host.
@end table
@end deftp
The @code{ut_type}, @code{ut_pid}, @code{ut_id}, @code{ut_tv}, and
@code{ut_host} fields are not available on all systems. Portable
applications therefore should be prepared for these situations. To help
doing this the @file{utmp.h} header provides macros
@code{_HAVE_UT_TYPE}, @code{_HAVE_UT_PID}, @code{_HAVE_UT_ID},
@code{_HAVE_UT_TV}, and @code{_HAVE_UT_HOST} if the respective field is
available. The programmer can handle the situations by using
@code{#ifdef} in the program code.
The following macros are defined for use as values for the
@code{ut_type} member of the @code{utmp} structure. The values are
integer constants.
@table @code
@comment utmp.h
@comment SVID
@vindex EMPTY
@item EMPTY
This macro is used to indicate that the entry contains no valid user
accounting information.
@comment utmp.h
@comment SVID
@vindex RUN_LVL
@item RUN_LVL
This macro is used to identify the systems runlevel.
@comment utmp.h
@comment SVID
@vindex BOOT_TIME
@item BOOT_TIME
This macro is used to identify the time of system boot.
@comment utmp.h
@comment SVID
@vindex OLD_TIME
@item OLD_TIME
This macro is used to identify the time when the system clock changed.
@comment utmp.h
@comment SVID
@vindex NEW_TIME
@item NEW_TIME
This macro is used to identify the time after the system changed.
@comment utmp.h
@comment SVID
@vindex INIT_PROCESS
@item INIT_PROCESS
This macro is used to identify a process spawned by the init process.
@comment utmp.h
@comment SVID
@vindex LOGIN_PROCESS
@item LOGIN_PROCESS
This macro is used to identify the session leader of a logged in user.
@comment utmp.h
@comment SVID
@vindex USER_PROCESS
@item USER_PROCESS
This macro is used to identify a user process.
@comment utmp.h
@comment SVID
@vindex DEAD_PROCESS
@item DEAD_PROCESS
This macro is used to identify a terminated process.
@comment utmp.h
@comment SVID
@vindex ACCOUNTING
@item ACCOUNTING
???
@end table
The size of the @code{ut_line}, @code{ut_id}, @code{ut_user} and
@code{ut_host} arrays can be found using the @code{sizeof} operator.
Many older systems have, instead of an @code{ut_tv} member, an
@code{ut_time} member, usually of type @code{time_t}, for representing
the time associated with the entry. Therefore, for backwards
compatibility only, @file{utmp.h} defines @code{ut_time} as an alias for
@code{ut_tv.tv_sec}.
@comment utmp.h
@comment SVID
@deftypefun void setutent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c Besides the static variables in utmp_file.c, there's the jump_table.
@c They're both modified while holding a lock, but other threads may
@c cause the variables to be modified between calling this function and
@c others that rely on the internal state it sets up.
@c setutent @mtasurace:utent @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->setutent @mtasurace:utent @acsfd
@c setutent_unknown @mtasurace:utent @acsfd
@c *libc_utmp_file_functions.setutent = setutent_file @mtasurace:utent @acsfd
@c open_not_cancel_2 dup @acsfd
@c fcntl_not_cancel dup ok
@c close_not_cancel_no_status dup @acsfd
@c lseek64 dup ok
@c libc_lock_unlock dup ok
This function opens the user accounting database to begin scanning it.
You can then call @code{getutent}, @code{getutid} or @code{getutline} to
read entries and @code{pututline} to write entries.
If the database is already open, it resets the input to the beginning of
the database.
@end deftypefun
@comment utmp.h
@comment SVID
@deftypefun {struct utmp *} getutent (void)
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtasurace{:utentbuf} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c The static buffer that holds results is allocated with malloc at
@c the first call; the test is not thread-safe, so multiple concurrent
@c calls could malloc multiple buffers.
@c getutent @mtuinit @mtasurace:utent @mtasurace:utentbuf @mtascusig:ALRM @mtascutimer @ascuheap @asulock @aculock @acsfd @acsmem
@c malloc @asulock @aculock @acsfd @acsmem
@c getutent_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
The @code{getutent} function reads the next entry from the user
accounting database. It returns a pointer to the entry, which is
statically allocated and may be overwritten by subsequent calls to
@code{getutent}. You must copy the contents of the structure if you
wish to save the information or you can use the @code{getutent_r}
function which stores the data in a user-provided buffer.
A null pointer is returned in case no further entry is available.
@end deftypefun
@comment utmp.h
@comment SVID
@deftypefun void endutent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c endutent @mtasurace:utent @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->endutent @mtasurace:utent @acsfd
@c endutent_unknown ok
@c endutent_file @mtasurace:utent @acsfd
@c close_not_cancel_no_status dup @acsfd
@c libc_lock_unlock dup ok
This function closes the user accounting database.
@end deftypefun
@comment utmp.h
@comment SVID
@deftypefun {struct utmp *} getutid (const struct utmp *@var{id})
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
@c Same caveats as getutline.
@c
@c getutid @mtuinit @mtasurace:utent @mtascusig:ALRM @mtascutimer @ascuheap @asulock @aculock @acsmem @acsfd
@c uses a static buffer malloced on the first call
@c malloc dup @ascuheap @acsmem
@c getutid_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
This function searches forward from the current point in the database
for an entry that matches @var{id}. If the @code{ut_type} member of the
@var{id} structure is one of @code{RUN_LVL}, @code{BOOT_TIME},
@code{OLD_TIME} or @code{NEW_TIME} the entries match if the
@code{ut_type} members are identical. If the @code{ut_type} member of
the @var{id} structure is @code{INIT_PROCESS}, @code{LOGIN_PROCESS},
@code{USER_PROCESS} or @code{DEAD_PROCESS}, the entries match if the
@code{ut_type} member of the entry read from the database is one of
these four, and the @code{ut_id} members match. However if the
@code{ut_id} member of either the @var{id} structure or the entry read
from the database is empty it checks if the @code{ut_line} members match
instead. If a matching entry is found, @code{getutid} returns a pointer
to the entry, which is statically allocated, and may be overwritten by a
subsequent call to @code{getutent}, @code{getutid} or @code{getutline}.
You must copy the contents of the structure if you wish to save the
information.
A null pointer is returned in case the end of the database is reached
without a match.
The @code{getutid} function may cache the last read entry. Therefore,
if you are using @code{getutid} to search for multiple occurrences, it
is necessary to zero out the static data after each call. Otherwise
@code{getutid} could just return a pointer to the same entry over and
over again.
@end deftypefun
@comment utmp.h
@comment SVID
@deftypefun {struct utmp *} getutline (const struct utmp *@var{line})
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c The static buffer that holds results is allocated with malloc at
@c the first call; the test is not thread-safe, so multiple concurrent
@c calls could malloc multiple buffers.
@c getutline @mtuinit @mtasurace:utent @mtascusig:ALRM @mtascutimer @ascuheap @asulock @aculock @acsfd @acsmem
@c malloc @asulock @aculock @acsfd @acsmem
@c getutline_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
This function searches forward from the current point in the database
until it finds an entry whose @code{ut_type} value is
@code{LOGIN_PROCESS} or @code{USER_PROCESS}, and whose @code{ut_line}
member matches the @code{ut_line} member of the @var{line} structure.
If it finds such an entry, it returns a pointer to the entry which is
statically allocated, and may be overwritten by a subsequent call to
@code{getutent}, @code{getutid} or @code{getutline}. You must copy the
contents of the structure if you wish to save the information.
A null pointer is returned in case the end of the database is reached
without a match.
The @code{getutline} function may cache the last read entry. Therefore
if you are using @code{getutline} to search for multiple occurrences, it
is necessary to zero out the static data after each call. Otherwise
@code{getutline} could just return a pointer to the same entry over and
over again.
@end deftypefun
@comment utmp.h
@comment SVID
@deftypefun {struct utmp *} pututline (const struct utmp *@var{utmp})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c pututline @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->pututline @mtasurace:utent @mtascusig:ALRM @mtascutimer @acsfd
@c pututline_unknown @mtasurace:utent @acsfd
@c setutent_unknown dup @mtasurace:utent @acsfd
@c pututline_file @mtascusig:ALRM @mtascutimer @acsfd
@c TRANSFORM_UTMP_FILE_NAME ok
@c strcmp dup ok
@c acesss dup ok
@c open_not_cancel_2 dup @acsfd
@c fcntl_not_cancel dup ok
@c close_not_cancel_no_status dup @acsfd
@c llseek dup ok
@c dup2 dup ok
@c utmp_equal dup ok
@c internal_getut_r dup @mtascusig:ALRM @mtascutimer
@c LOCK_FILE dup @mtascusig:ALRM @mtasctimer
@c LOCKING_FAILED dup ok
@c ftruncate64 dup ok
@c write_not_cancel dup ok
@c UNLOCK_FILE dup @mtasctimer
@c libc_lock_unlock dup @aculock
The @code{pututline} function inserts the entry @code{*@var{utmp}} at
the appropriate place in the user accounting database. If it finds that
it is not already at the correct place in the database, it uses
@code{getutid} to search for the position to insert the entry, however
this will not modify the static structure returned by @code{getutent},
@code{getutid} and @code{getutline}. If this search fails, the entry
is appended to the database.
The @code{pututline} function returns a pointer to a copy of the entry
inserted in the user accounting database, or a null pointer if the entry
could not be added. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EPERM
The process does not have the appropriate privileges; you cannot modify
the user accounting database.
@end table
@end deftypefun
All the @code{get*} functions mentioned before store the information
they return in a static buffer. This can be a problem in multi-threaded
programs since the data returned for the request is overwritten by the
return value data in another thread. Therefore @theglibc{}
provides as extensions three more functions which return the data in a
user-provided buffer.
@comment utmp.h
@comment GNU
@deftypefun int getutent_r (struct utmp *@var{buffer}, struct utmp **@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c getutent_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->getutent_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @acsfd
@c getutent_r_unknown @mtasurace:utent @acsfd
@c setutent_unknown dup @mtasurace:utent @acsfd
@c getutent_r_file @mtasurace:utent @mtascusig:ALRM @mtascutimer
@c LOCK_FILE @mtascusig:ALRM @mtascutimer
@c alarm dup @mtascutimer
@c sigemptyset dup ok
@c sigaction dup ok
@c memset dup ok
@c fcntl_not_cancel dup ok
@c LOCKING_FAILED ok
@c read_not_cancel dup ok
@c UNLOCK_FILE @mtascutimer
@c fcntl_not_cancel dup ok
@c alarm dup @mtascutimer
@c sigaction dup ok
@c memcpy dup ok
@c libc_lock_unlock dup ok
The @code{getutent_r} is equivalent to the @code{getutent} function. It
returns the next entry from the database. But instead of storing the
information in a static buffer it stores it in the buffer pointed to by
the parameter @var{buffer}.
If the call was successful, the function returns @code{0} and the
pointer variable pointed to by the parameter @var{result} contains a
pointer to the buffer which contains the result (this is most probably
the same value as @var{buffer}). If something went wrong during the
execution of @code{getutent_r} the function returns @code{-1}.
This function is a GNU extension.
@end deftypefun
@comment utmp.h
@comment GNU
@deftypefun int getutid_r (const struct utmp *@var{id}, struct utmp *@var{buffer}, struct utmp **@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c getutid_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->getutid_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @acsfd
@c getutid_r_unknown @mtasurace:utent @acsfd
@c setutent_unknown dup @mtasurace:utent @acsfd
@c getutid_r_file @mtascusig:ALRM @mtascutimer
@c internal_getut_r @mtascusig:ALRM @mtascutimer
@c LOCK_FILE dup @mtascusig:ALRM @mtascutimer
@c LOCKING_FAILED dup ok
@c read_not_cancel dup ok
@c utmp_equal ok
@c strncmp dup ok
@c UNLOCK_FILE dup @mtascutimer
@c memcpy dup ok
@c libc_lock_unlock dup @aculock
This function retrieves just like @code{getutid} the next entry matching
the information stored in @var{id}. But the result is stored in the
buffer pointed to by the parameter @var{buffer}.
If successful the function returns @code{0} and the pointer variable
pointed to by the parameter @var{result} contains a pointer to the
buffer with the result (probably the same as @var{result}. If not
successful the function return @code{-1}.
This function is a GNU extension.
@end deftypefun
@comment utmp.h
@comment GNU
@deftypefun int getutline_r (const struct utmp *@var{line}, struct utmp *@var{buffer}, struct utmp **@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c getutline_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->getutline_r @mtasurace:utent @mtascusig:ALRM @mtascutimer @acsfd
@c getutline_r_unknown @mtasurace:utent @acsfd
@c setutent_unknown dup @mtasurace:utent @acsfd
@c getutline_r_file @mtasurace:utent @mtascusig:ALRM @mtascutimer
@c LOCK_FILE @mtascusig:ALRM @mtascutimer
@c alarm dup @mtascutimer
@c sigemptyset dup ok
@c sigaction dup ok
@c memset dup ok
@c fcntl_not_cancel dup ok
@c LOCKING_FAILED ok
@c read_not_cancel dup ok
@c strncmp dup ok
@c UNLOCK_FILE @mtascutimer
@c fcntl_not_cancel dup ok
@c alarm dup @mtascutimer
@c sigaction dup ok
@c memcpy dup ok
@c libc_lock_unlock dup ok
This function retrieves just like @code{getutline} the next entry
matching the information stored in @var{line}. But the result is stored
in the buffer pointed to by the parameter @var{buffer}.
If successful the function returns @code{0} and the pointer variable
pointed to by the parameter @var{result} contains a pointer to the
buffer with the result (probably the same as @var{result}. If not
successful the function return @code{-1}.
This function is a GNU extension.
@end deftypefun
In addition to the user accounting database, most systems keep a number
of similar databases. For example most systems keep a log file with all
previous logins (usually in @file{/etc/wtmp} or @file{/var/log/wtmp}).
For specifying which database to examine, the following function should
be used.
@comment utmp.h
@comment SVID
@deftypefun int utmpname (const char *@var{file})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c utmpname @mtasurace:utent @asulock @ascuheap @aculock @acsmem
@c libc_lock_lock dup @asulock @aculock
@c *libc_utmp_jump_table->endutent dup @mtasurace:utent
@c strcmp dup ok
@c free dup @ascuheap @acsmem
@c strdup dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
The @code{utmpname} function changes the name of the database to be
examined to @var{file}, and closes any previously opened database. By
default @code{getutent}, @code{getutid}, @code{getutline} and
@code{pututline} read from and write to the user accounting database.
The following macros are defined for use as the @var{file} argument:
@deftypevr Macro {char *} _PATH_UTMP
This macro is used to specify the user accounting database.
@end deftypevr
@deftypevr Macro {char *} _PATH_WTMP
This macro is used to specify the user accounting log file.
@end deftypevr
The @code{utmpname} function returns a value of @code{0} if the new name
was successfully stored, and a value of @code{-1} to indicate an error.
Note that @code{utmpname} does not try to open the database, and that
therefore the return value does not say anything about whether the
database can be successfully opened.
@end deftypefun
Specially for maintaining log-like databases @theglibc{} provides
the following function:
@comment utmp.h
@comment SVID
@deftypefun void updwtmp (const char *@var{wtmp_file}, const struct utmp *@var{utmp})
@safety{@prelim{}@mtunsafe{@mtascusig{:ALRM} @mtascutimer{}}@asunsafe{}@acunsafe{@acsfd{}}}
@c updwtmp @mtascusig:ALRM @mtascutimer @acsfd
@c TRANSFORM_UTMP_FILE_NAME dup ok
@c *libc_utmp_file_functions->updwtmp = updwtmp_file @mtascusig:ALRM @mtascutimer @acsfd
@c open_not_cancel_2 dup @acsfd
@c LOCK_FILE dup @mtascusig:ALRM @mtascutimer
@c LOCKING_FAILED dup ok
@c lseek64 dup ok
@c ftruncate64 dup ok
@c write_not_cancel dup ok
@c UNLOCK_FILE dup @mtascutimer
@c close_not_cancel_no_status dup @acsfd
The @code{updwtmp} function appends the entry *@var{utmp} to the
database specified by @var{wtmp_file}. For possible values for the
@var{wtmp_file} argument see the @code{utmpname} function.
@end deftypefun
@strong{Portability Note:} Although many operating systems provide a
subset of these functions, they are not standardized. There are often
subtle differences in the return types, and there are considerable
differences between the various definitions of @code{struct utmp}. When
programming for @theglibc{}, it is probably best to stick
with the functions described in this section. If however, you want your
program to be portable, consider using the XPG functions described in
@ref{XPG Functions}, or take a look at the BSD compatible functions in
@ref{Logging In and Out}.
@node XPG Functions
@subsection XPG User Accounting Database Functions
These functions, described in the X/Open Portability Guide, are declared
in the header file @file{utmpx.h}.
@pindex utmpx.h
@deftp {Data Type} {struct utmpx}
The @code{utmpx} data structure contains at least the following members:
@table @code
@item short int ut_type
Specifies the type of login; one of @code{EMPTY}, @code{RUN_LVL},
@code{BOOT_TIME}, @code{OLD_TIME}, @code{NEW_TIME}, @code{INIT_PROCESS},
@code{LOGIN_PROCESS}, @code{USER_PROCESS} or @code{DEAD_PROCESS}.
@item pid_t ut_pid
The process ID number of the login process.
@item char ut_line[]
The device name of the tty (without @file{/dev/}).
@item char ut_id[]
The inittab ID of the process.
@item char ut_user[]
The user's login name.
@item struct timeval ut_tv
Time the entry was made. For entries of type @code{OLD_TIME} this is
the time when the system clock changed, and for entries of type
@code{NEW_TIME} this is the time the system clock was set to.
@end table
In @theglibc{}, @code{struct utmpx} is identical to @code{struct
utmp} except for the fact that including @file{utmpx.h} does not make
visible the declaration of @code{struct exit_status}.
@end deftp
The following macros are defined for use as values for the
@code{ut_type} member of the @code{utmpx} structure. The values are
integer constants and are, in @theglibc{}, identical to the
definitions in @file{utmp.h}.
@table @code
@comment utmpx.h
@comment XPG4.2
@vindex EMPTY
@item EMPTY
This macro is used to indicate that the entry contains no valid user
accounting information.
@comment utmpx.h
@comment XPG4.2
@vindex RUN_LVL
@item RUN_LVL
This macro is used to identify the systems runlevel.
@comment utmpx.h
@comment XPG4.2
@vindex BOOT_TIME
@item BOOT_TIME
This macro is used to identify the time of system boot.
@comment utmpx.h
@comment XPG4.2
@vindex OLD_TIME
@item OLD_TIME
This macro is used to identify the time when the system clock changed.
@comment utmpx.h
@comment XPG4.2
@vindex NEW_TIME
@item NEW_TIME
This macro is used to identify the time after the system changed.
@comment utmpx.h
@comment XPG4.2
@vindex INIT_PROCESS
@item INIT_PROCESS
This macro is used to identify a process spawned by the init process.
@comment utmpx.h
@comment XPG4.2
@vindex LOGIN_PROCESS
@item LOGIN_PROCESS
This macro is used to identify the session leader of a logged in user.
@comment utmpx.h
@comment XPG4.2
@vindex USER_PROCESS
@item USER_PROCESS
This macro is used to identify a user process.
@comment utmpx.h
@comment XPG4.2
@vindex DEAD_PROCESS
@item DEAD_PROCESS
This macro is used to identify a terminated process.
@end table
The size of the @code{ut_line}, @code{ut_id} and @code{ut_user} arrays
can be found using the @code{sizeof} operator.
@comment utmpx.h
@comment XPG4.2
@deftypefun void setutxent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
This function is similar to @code{setutent}. In @theglibc{} it is
simply an alias for @code{setutent}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun {struct utmpx *} getutxent (void)
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
The @code{getutxent} function is similar to @code{getutent}, but returns
a pointer to a @code{struct utmpx} instead of @code{struct utmp}. In
@theglibc{} it simply is an alias for @code{getutent}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun void endutxent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
This function is similar to @code{endutent}. In @theglibc{} it is
simply an alias for @code{endutent}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun {struct utmpx *} getutxid (const struct utmpx *@var{id})
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
This function is similar to @code{getutid}, but uses @code{struct utmpx}
instead of @code{struct utmp}. In @theglibc{} it is simply an alias
for @code{getutid}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun {struct utmpx *} getutxline (const struct utmpx *@var{line})
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
This function is similar to @code{getutid}, but uses @code{struct utmpx}
instead of @code{struct utmp}. In @theglibc{} it is simply an alias
for @code{getutline}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun {struct utmpx *} pututxline (const struct utmpx *@var{utmp})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
The @code{pututxline} function is functionally identical to
@code{pututline}, but uses @code{struct utmpx} instead of @code{struct
utmp}. In @theglibc{}, @code{pututxline} is simply an alias for
@code{pututline}.
@end deftypefun
@comment utmpx.h
@comment XPG4.2
@deftypefun int utmpxname (const char *@var{file})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
The @code{utmpxname} function is functionally identical to
@code{utmpname}. In @theglibc{}, @code{utmpxname} is simply an
alias for @code{utmpname}.
@end deftypefun
You can translate between a traditional @code{struct utmp} and an XPG
@code{struct utmpx} with the following functions. In @theglibc{},
these functions are merely copies, since the two structures are
identical.
@comment utmpx.h
@comment utmp.h
@comment GNU
@deftypefun int getutmp (const struct utmpx *@var{utmpx}, struct utmp *@var{utmp})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{getutmp} copies the information, insofar as the structures are
compatible, from @var{utmpx} to @var{utmp}.
@end deftypefun
@comment utmpx.h
@comment utmp.h
@comment GNU
@deftypefun int getutmpx (const struct utmp *@var{utmp}, struct utmpx *@var{utmpx})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{getutmpx} copies the information, insofar as the structures are
compatible, from @var{utmp} to @var{utmpx}.
@end deftypefun
@node Logging In and Out
@subsection Logging In and Out
These functions, derived from BSD, are available in the separate
@file{libutil} library, and declared in @file{utmp.h}.
@pindex utmp.h
Note that the @code{ut_user} member of @code{struct utmp} is called
@code{ut_name} in BSD. Therefore, @code{ut_name} is defined as an alias
for @code{ut_user} in @file{utmp.h}.
@comment utmp.h
@comment BSD
@deftypefun int login_tty (int @var{filedes})
@safety{@prelim{}@mtunsafe{@mtasurace{:ttyname}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c If this function is canceled, it may have succeeded in redirecting
@c only some of the standard streams to the newly opened terminal.
@c Should there be a safety annotation for this?
@c login_tty @mtasurace:ttyname @ascuheap @asulock @aculock @acsmem @acsfd
@c setsid dup ok
@c ioctl dup ok
@c ttyname dup @mtasurace:ttyname @ascuheap @asulock @aculock @acsmem @acsfd
@c close dup @acsfd
@c open dup @acsfd
@c dup2 dup ok
This function makes @var{filedes} the controlling terminal of the
current process, redirects standard input, standard output and
standard error output to this terminal, and closes @var{filedes}.
This function returns @code{0} on successful completion, and @code{-1}
on error.
@end deftypefun
@comment utmp.h
@comment BSD
@deftypefun void login (const struct utmp *@var{entry})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acucorrupt{} @acsfd{} @acsmem{}}}
@c login @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @ascuheap @aculock @acucorrupt @acsfd @acsmem
@c getpid dup ok
@c tty_name @ascuheap @acucorrupt @acsmem @acsfd
@c ttyname_r dup @ascuheap @acsmem @acsfd
@c memchr dup ok
@c realloc dup @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c strncmp dup ok
@c basename dup ok
@c strncpy dup ok
@c utmpname dup @mtasurace:utent @asulock @ascuheap @aculock @acsmem
@c setutent dup @mtasurace:utent @asulock @aculock @acsfd
@c pututline dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c endutent dup @mtasurace:utent @asulock @aculock
@c free dup @ascuheap @acsmem
@c updwtmp dup @mtascusig:ALRM @mtascutimer @acsfd
The @code{login} functions inserts an entry into the user accounting
database. The @code{ut_line} member is set to the name of the terminal
on standard input. If standard input is not a terminal @code{login}
uses standard output or standard error output to determine the name of
the terminal. If @code{struct utmp} has a @code{ut_type} member,
@code{login} sets it to @code{USER_PROCESS}, and if there is an
@code{ut_pid} member, it will be set to the process ID of the current
process. The remaining entries are copied from @var{entry}.
A copy of the entry is written to the user accounting log file.
@end deftypefun
@comment utmp.h
@comment BSD
@deftypefun int logout (const char *@var{ut_line})
@safety{@prelim{}@mtunsafe{@mtasurace{:utent} @mtascusig{:ALRM} @mtascutimer{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c logout @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @ascuheap @aculock @acsfd @acsmem
@c utmpname dup @mtasurace:utent @asulock @ascuheap @aculock @acsmem
@c setutent dup @mtasurace:utent @asulock @aculock @acsfd
@c strncpy dup ok
@c getutline_r dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c bzero dup ok
@c gettimeofday dup ok
@c time dup ok
@c pututline dup @mtasurace:utent @mtascusig:ALRM @mtascutimer @asulock @aculock @acsfd
@c endutent dup @mtasurace:utent @asulock @aculock
This function modifies the user accounting database to indicate that the
user on @var{ut_line} has logged out.
The @code{logout} function returns @code{1} if the entry was successfully
written to the database, or @code{0} on error.
@end deftypefun
@comment utmp.h
@comment BSD
@deftypefun void logwtmp (const char *@var{ut_line}, const char *@var{ut_name}, const char *@var{ut_host})
@safety{@prelim{}@mtunsafe{@mtascusig{:ALRM} @mtascutimer{}}@asunsafe{}@acunsafe{@acsfd{}}}
@c logwtmp @mtascusig:ALRM @mtascutimer @acsfd
@c memset dup ok
@c getpid dup ok
@c strncpy dup ok
@c gettimeofday dup ok
@c time dup ok
@c updwtmp dup @mtascusig:ALRM @mtascutimer @acsfd
The @code{logwtmp} function appends an entry to the user accounting log
file, for the current time and the information provided in the
@var{ut_line}, @var{ut_name} and @var{ut_host} arguments.
@end deftypefun
@strong{Portability Note:} The BSD @code{struct utmp} only has the
@code{ut_line}, @code{ut_name}, @code{ut_host} and @code{ut_time}
members. Older systems do not even have the @code{ut_host} member.
@node User Database
@section User Database
@cindex user database
@cindex password database
@pindex /etc/passwd
This section describes how to search and scan the database of registered
users. The database itself is kept in the file @file{/etc/passwd} on
most systems, but on some systems a special network server gives access
to it.
@menu
* User Data Structure:: What each user record contains.
* Lookup User:: How to look for a particular user.
* Scanning All Users:: Scanning the list of all users, one by one.
* Writing a User Entry:: How a program can rewrite a user's record.
@end menu
@node User Data Structure
@subsection The Data Structure that Describes a User
The functions and data structures for accessing the system user database
are declared in the header file @file{pwd.h}.
@pindex pwd.h
@comment pwd.h
@comment POSIX.1
@deftp {Data Type} {struct passwd}
The @code{passwd} data structure is used to hold information about
entries in the system user data base. It has at least the following members:
@table @code
@item char *pw_name
The user's login name.
@item char *pw_passwd.
The encrypted password string.
@item uid_t pw_uid
The user ID number.
@item gid_t pw_gid
The user's default group ID number.
@item char *pw_gecos
A string typically containing the user's real name, and possibly other
information such as a phone number.
@item char *pw_dir
The user's home directory, or initial working directory. This might be
a null pointer, in which case the interpretation is system-dependent.
@item char *pw_shell
The user's default shell, or the initial program run when the user logs in.
This might be a null pointer, indicating that the system default should
be used.
@end table
@end deftp
@node Lookup User
@subsection Looking Up One User
@cindex converting user ID to user name
@cindex converting user name to user ID
You can search the system user database for information about a
specific user using @code{getpwuid} or @code{getpwnam}. These
functions are declared in @file{pwd.h}.
@comment pwd.h
@comment POSIX.1
@deftypefun {struct passwd *} getpwuid (uid_t @var{uid})
@safety{@prelim{}@mtunsafe{@mtasurace{:pwuid} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getpwuid @mtasurace:pwuid @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getpwuid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
This function returns a pointer to a statically-allocated structure
containing information about the user whose user ID is @var{uid}. This
structure may be overwritten on subsequent calls to @code{getpwuid}.
A null pointer value indicates there is no user in the data base with
user ID @var{uid}.
@end deftypefun
@comment pwd.h
@comment POSIX.1c
@deftypefun int getpwuid_r (uid_t @var{uid}, struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getpwuid_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getpwuid_r @ascuheap @acsfd @acsmem
@c itoa_word dup ok
@c nscd_getpw_r @ascuheap @acsfd @acsmem
@c nscd_get_map_ref @ascuheap @acsfd @acsmem
@c nscd_acquire_maplock ok
@c nscd_get_mapping @ascuheap @acsfd @acsmem
@c open_socket dup @acsfd
@c memset dup ok
@c wait_on_socket dup ok
@c recvmsg dup ok
@c strcmp dup ok
@c fstat64 dup ok
@c mmap dup @acsmem
@c munmap dup @acsmem
@c malloc dup @ascuheap @acsmem
@c close dup ok
@c nscd_unmap dup @ascuheap @acsmem
@c nscd_cache_search ok
@c nis_hash ok
@c memcmp dup ok
@c nscd_open_socket @acsfd
@c open_socket @acsfd
@c socket dup @acsfd
@c fcntl dup ok
@c strcpy dup ok
@c connect dup ok
@c send dup ok
@c gettimeofday dup ok
@c poll dup ok
@c close_not_cancel_no_status dup @acsfd
@c wait_on_socket dup ok
@c read dup ok
@c close_not_cancel_no_status dup @acsfd
@c readall ok
@c read dup ok
@c wait_on_socket ok
@c poll dup ok
@c gettimeofday dup ok
@c memcpy dup ok
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c nscd_unmap @ascuheap @acsmem
@c munmap dup ok
@c free dup @ascuheap @acsmem
@c nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_database_lookup @mtslocale @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c libc_lock_lock @asulock @aculock
@c libc_lock_unlock @aculock
@c nss_parse_file @mtslocale @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking dup ok [no concurrent uses]
@c malloc dup @asulock @aculock @acsfd @acsmem
@c fclose dup @ascuheap @asulock @acsmem @acsfd @aculock
@c getline dup @ascuheap @aculock @acucorrupt @acsmem
@c strchrnul dup ok
@c nss_getline @mtslocale @ascuheap @acsmem
@c isspace @mtslocale^^
@c strlen dup ok
@c malloc dup @asulock @aculock @acsfd @acsmem
@c memcpy dup ok
@c nss_parse_service_list dup @mtslocale^, @ascuheap @acsmem
@c feof_unlocked dup ok
@c free dup @asulock @aculock @acsfd @acsmem
@c strcmp dup ok
@c nss_parse_service_list @mtslocale^, @ascuheap @acsmem
@c isspace @mtslocale^^
@c malloc dup @asulock @aculock @acsfd @acsmem
@c mempcpy dup ok
@c strncasecmp dup ok
@c free dup @asulock @aculock @acsfd @acsmem
@c malloc dup @asulock @aculock @acsfd @acsmem
@c nss_lookup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup_function @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c tsearch @ascuheap @acucorrupt @acsmem [no @mtsrace or @asucorrupt due to locking]
@c known_compare ok
@c strcmp dup ok
@c malloc dup @ascuheap @acsmem
@c tdelete @ascuheap @acucorrupt @acsmem [no @mtsrace or @asucorrupt due to locking]
@c free dup @ascuheap @acsmem
@c nss_load_library @ascudlopen @ascuplugin @ascuheap @asulock @aculock @acsfd @acsmem
@c nss_new_service @ascuheap @acsmem
@c strcmp dup ok
@c malloc dup @ascuheap @acsmem
@c strlen dup ok
@c stpcpy dup ok
@c libc_dlopen @ascudlopen @ascuheap @asulock @aculock @acsfd @acsmem
@c libc_dlsym dup @asulock @aculock @acsfd @acsmem
@c *ifct(*nscd_init_cb) @ascuplugin
@c stpcpy dup ok
@c libc_dlsym dup @asulock @aculock @acsfd @acsmem
@c libc_lock_unlock dup ok
@c nss_next_action ok
@c *fct.l -> _nss_*_getpwuid_r @ascuplugin
@c nss_next2 @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_next_action dup ok
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c _nss_files_getpwuid_r @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c internal_setent @ascuheap @asulock @aculock @acsmem @acsfd
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fileno dup ok
@c fcntl dup ok
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c rewind dup @aculock [stream guarded by non-recursive pwent lock]
@c internal_getent @mtslocale^
@c fgets_unlocked dup ok [stream guarded by non-recursive pwent lock]
@c isspace dup @mtslocale^^
@c _nss_files_parse_pwent = parse_line ok
@c strpbrk dup ok
@c internal_endent @ascuheap @asulock @aculock @acsmem @acsfd
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_unlock dup @aculock
@c _nss_nis_getpwuid_r ... not fully reviewed (assumed) @asuinit @asulock @acucorrupt @aculock
@c yp_get_default_domain @asulock @aculock
@c libc_lock_lock dup @asulock @aculock
@c getdomainname dup ok
@c strcmp dup ok
@c libc_lock_unlock dup @aculock
@c snprintf dup @ascuheap @acsmem
@c yp_match
@c do_ypcall_tr(xdr_ypreq_key,xdr_ypresp_val)
@c do_ypcall(xdr_ypreq_key,xdr_ypresp_val)
@c libc_lock_lock @asulock @aculock
@c strcmp
@c yp_bind
@c ypclnt_call
@c clnt_call
@c clnt_perror
@c libc_lock_unlock @aculock
@c yp_unbind_locked
@c yp_unbind
@c strcmp dup ok
@c calloc dup @asulock @aculock @acsfd @acsmem
@c yp_bind_file
@c strlen dup ok
@c snprintf dup @ascuheap @acsmem
@c open dup @acsfd [cancelpt]
@c pread dup [cancelpt]
@c yp_bind_client_create
@c close dup @acsfd [cancelpt]
@c yp_bind_ypbindprog
@c clnttcp_create
@c clnt_destroy
@c clnt_call(xdr_domainname,xdr_ypbind_resp)
@c memset dup ok
@c yp_bind_client_create
@c free dup @asulock @aculock @acsfd @acsmem
@c calloc dup @asulock @aculock @acsfd @acsmem
@c free dup @asulock @aculock @acsfd @acsmem
@c ypprot_err
@c memcpy dup ok
@c xdr_free(xdr_ypresp_val)
@c xdr_ypresp_val
@c xdr_ypstat
@c xdr_enum
@c XDR_PUTLONG
@c *x_putlong
@c XDR_GETLONG
@c *x_getlong
@c xdr_long
@c XDR_PUTLONG dup
@c XDR_GETLONG dup
@c xdr_short
@c XDR_PUTLONG dup
@c XDR_GETLONG dup
@c xdr_valdat
@c xdr_bytes
@c xdr_u_int
@c XDR_PUTLONG dup
@c XDR_GETLONG dup
@c mem_alloc @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c xdr_opaque
@c XDR_GETBYTES
@c *x_getbytes
@c XDR_PUTBYTES
@c *x_putbytes
@c mem_free @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c yperr2nss ok
@c strchr dup ok
@c _nls_default_nss @asuinit @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c init @asuinit^, @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking ok [no concurrent uses]
@c feof_unlocked dup ok
@c getline dup @ascuheap @aculock @acucorrupt @acsmem
@c isspace dup @mtslocale^^
@c strncmp dup ok
@c free dup @asulock @acsmem @acsfd @aculock
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c free dup @asulock @acsmem @acsfd @aculock
@c mempcpy dup ok
@c strncpy dup ok
@c isspace dup @mtslocale^^
@c _nss_files_parse_pwent ok
This function is similar to @code{getpwuid} in that it returns
information about the user whose user ID is @var{uid}. However, it
fills the user supplied structure pointed to by @var{result_buf} with
the information instead of using a static buffer. The first
@var{buflen} bytes of the additional buffer pointed to by @var{buffer}
are used to contain additional information, normally strings which are
pointed to by the elements of the result structure.
If a user with ID @var{uid} is found, the pointer returned in
@var{result} points to the record which contains the wanted data (i.e.,
@var{result} contains the value @var{result_buf}). If no user is found
or if an error occurred, the pointer returned in @var{result} is a null
pointer. The function returns zero or an error code. If the buffer
@var{buffer} is too small to contain all the needed information, the
error code @code{ERANGE} is returned and @var{errno} is set to
@code{ERANGE}.
@end deftypefun
@comment pwd.h
@comment POSIX.1
@deftypefun {struct passwd *} getpwnam (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:pwnam} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getpwnam @mtasurace:pwnam @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getpwnam_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
This function returns a pointer to a statically-allocated structure
containing information about the user whose user name is @var{name}.
This structure may be overwritten on subsequent calls to
@code{getpwnam}.
A null pointer return indicates there is no user named @var{name}.
@end deftypefun
@comment pwd.h
@comment POSIX.1c
@deftypefun int getpwnam_r (const char *@var{name}, struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getpwnam_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getpwnam_r @ascuheap @asulock @aculock @acsfd @acsmem
@c strlen dup ok
@c nscd_getpw_r dup @ascuheap @asulock @aculock @acsfd @acsmem
@c nss_passwd_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c
@c _nss_files_getpwnam_r @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c internal_setent dup @ascuheap @asulock @aculock @acsmem @acsfd
@c internal_getent dup @mtslocale^
@c strcmp dup ok
@c internal_endent dup @ascuheap @asulock @aculock @acsmem @acsfd
@c libc_lock_unlock dup @aculock
@c
@c _nss_*_getpwnam_r (assumed) @asuinit @asulock @acucorrupt @aculock
This function is similar to @code{getpwnam} in that is returns
information about the user whose user name is @var{name}. However, like
@code{getpwuid_r}, it fills the user supplied buffers in
@var{result_buf} and @var{buffer} with the information instead of using
a static buffer.
The return values are the same as for @code{getpwuid_r}.
@end deftypefun
@node Scanning All Users
@subsection Scanning the List of All Users
@cindex scanning the user list
This section explains how a program can read the list of all users in
the system, one user at a time. The functions described here are
declared in @file{pwd.h}.
You can use the @code{fgetpwent} function to read user entries from a
particular file.
@comment pwd.h
@comment SVID
@deftypefun {struct passwd *} fgetpwent (FILE *@var{stream})
@safety{@prelim{}@mtunsafe{@mtasurace{:fpwent}}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c fgetpwent @mtasurace:fpwent @asucorrupt @asulock @acucorrupt @aculock
@c fgetpos dup @asucorrupt @aculock @acucorrupt
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c fgetpwent_r dup @asucorrupt @acucorrupt @aculock
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c fsetpos dup @asucorrupt @aculock @acucorrupt
@c libc_lock_unlock dup @aculock
This function reads the next user entry from @var{stream} and returns a
pointer to the entry. The structure is statically allocated and is
rewritten on subsequent calls to @code{fgetpwent}. You must copy the
contents of the structure if you wish to save the information.
The stream must correspond to a file in the same format as the standard
password database file.
@end deftypefun
@comment pwd.h
@comment GNU
@deftypefun int fgetpwent_r (FILE *@var{stream}, struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c fgetpwent_r @asucorrupt @acucorrupt @aculock
@c flockfile dup @aculock
@c fgets_unlocked @asucorrupt @acucorrupt [no @mtsrace due to explicit locking]
@c feof_unlocked dup ok
@c funlockfile dup @aculock
@c isspace dup @mtslocale^^
@c parse_line dup ok
This function is similar to @code{fgetpwent} in that it reads the next
user entry from @var{stream}. But the result is returned in the
structure pointed to by @var{result_buf}. The
first @var{buflen} bytes of the additional buffer pointed to by
@var{buffer} are used to contain additional information, normally
strings which are pointed to by the elements of the result structure.
The stream must correspond to a file in the same format as the standard
password database file.
If the function returns zero @var{result} points to the structure with
the wanted data (normally this is in @var{result_buf}). If errors
occurred the return value is nonzero and @var{result} contains a null
pointer.
@end deftypefun
The way to scan all the entries in the user database is with
@code{setpwent}, @code{getpwent}, and @code{endpwent}.
@comment pwd.h
@comment SVID, BSD
@deftypefun void setpwent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:pwent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setpwent @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_setent(nss_passwd_lookup2) @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c ** resolv's res_maybe_init not called here
@c setup(nss_passwd_lookup2) @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *lookup_fct = nss_passwd_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:pwent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function initializes a stream which @code{getpwent} and
@code{getpwent_r} use to read the user database.
@end deftypefun
@comment pwd.h
@comment POSIX.1
@deftypefun {struct passwd *} getpwent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:pwent} @mtasurace{:pwentbuf} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getpwent @mtasurace:pwent @mtasurace:pwentbuf @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent(getpwent_r) @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c *func = getpwent_r dup @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
The @code{getpwent} function reads the next entry from the stream
initialized by @code{setpwent}. It returns a pointer to the entry. The
structure is statically allocated and is rewritten on subsequent calls
to @code{getpwent}. You must copy the contents of the structure if you
wish to save the information.
A null pointer is returned when no more entries are available.
@end deftypefun
@comment pwd.h
@comment GNU
@deftypefun int getpwent_r (struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:pwent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c The static buffer here is not the result_buf, but rather the
@c variables that keep track of what nss backend we've last used, and
@c whatever internal state the nss backend uses to keep track of the
@c last read entry.
@c getpwent_r @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent_r(nss_passwd_lookup2) @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_passwd_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:pwent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *sfct.f @mtasurace:pwent @ascuplugin
@c libc_lock_unlock dup @aculock
This function is similar to @code{getpwent} in that it returns the next
entry from the stream initialized by @code{setpwent}. Like
@code{fgetpwent_r}, it uses the user-supplied buffers in
@var{result_buf} and @var{buffer} to return the information requested.
The return values are the same as for @code{fgetpwent_r}.
@end deftypefun
@comment pwd.h
@comment SVID, BSD
@deftypefun void endpwent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:pwent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endpwent @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_endent(nss_passwd_lookup2) @mtasurace:pwent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c ** resolv's res_maybe_init not called here
@c setup(nss_passwd_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:pwent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function closes the internal stream used by @code{getpwent} or
@code{getpwent_r}.
@end deftypefun
@node Writing a User Entry
@subsection Writing a User Entry
@comment pwd.h
@comment SVID
@deftypefun int putpwent (const struct passwd *@var{p}, FILE *@var{stream})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
@c putpwent @mtslocale @asucorrupt @aculock @acucorrupt
@c fprintf dup @mtslocale @asucorrupt @aculock @acucorrupt [no @ascuheap @acsmem]
This function writes the user entry @code{*@var{p}} to the stream
@var{stream}, in the format used for the standard user database
file. The return value is zero on success and nonzero on failure.
This function exists for compatibility with SVID. We recommend that you
avoid using it, because it makes sense only on the assumption that the
@code{struct passwd} structure has no members except the standard ones;
on a system which merges the traditional Unix data base with other
extended information about users, adding an entry using this function
would inevitably leave out much of the important information.
@c Then how are programmers to modify the password file? -zw
The group and user ID fields are left empty if the group or user name
starts with a - or +.
The function @code{putpwent} is declared in @file{pwd.h}.
@end deftypefun
@node Group Database
@section Group Database
@cindex group database
@pindex /etc/group
This section describes how to search and scan the database of
registered groups. The database itself is kept in the file
@file{/etc/group} on most systems, but on some systems a special network
service provides access to it.
@menu
* Group Data Structure:: What each group record contains.
* Lookup Group:: How to look for a particular group.
* Scanning All Groups:: Scanning the list of all groups.
@end menu
@node Group Data Structure
@subsection The Data Structure for a Group
The functions and data structures for accessing the system group
database are declared in the header file @file{grp.h}.
@pindex grp.h
@comment grp.h
@comment POSIX.1
@deftp {Data Type} {struct group}
The @code{group} structure is used to hold information about an entry in
the system group database. It has at least the following members:
@table @code
@item char *gr_name
The name of the group.
@item gid_t gr_gid
The group ID of the group.
@item char **gr_mem
A vector of pointers to the names of users in the group. Each user name
is a null-terminated string, and the vector itself is terminated by a
null pointer.
@end table
@end deftp
@node Lookup Group
@subsection Looking Up One Group
@cindex converting group name to group ID
@cindex converting group ID to group name
You can search the group database for information about a specific
group using @code{getgrgid} or @code{getgrnam}. These functions are
declared in @file{grp.h}.
@comment grp.h
@comment POSIX.1
@deftypefun {struct group *} getgrgid (gid_t @var{gid})
@safety{@prelim{}@mtunsafe{@mtasurace{:grgid} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrgid =~ getpwuid dup @mtasurace:grgid @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getgrgid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function returns a pointer to a statically-allocated structure
containing information about the group whose group ID is @var{gid}.
This structure may be overwritten by subsequent calls to
@code{getgrgid}.
A null pointer indicates there is no group with ID @var{gid}.
@end deftypefun
@comment grp.h
@comment POSIX.1c
@deftypefun int getgrgid_r (gid_t @var{gid}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrgid_r =~ getpwuid_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getgrgid_r @ascuheap @acsfd @acsmem
@c itoa_word dup ok
@c nscd_getgr_r @ascuheap @acsfd @acsmem
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c nscd_cache_search dup ok
@c nscd_open_socket dup @acsfd
@c readvall ok
@c readv dup ok
@c memcpy dup ok
@c wait_on_socket dup ok
@c memcpy dup ok
@c readall dup ok
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c nss_group_lookup2 =~ nss_passwd_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getgrgid_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function is similar to @code{getgrgid} in that it returns
information about the group whose group ID is @var{gid}. However, it
fills the user supplied structure pointed to by @var{result_buf} with
the information instead of using a static buffer. The first
@var{buflen} bytes of the additional buffer pointed to by @var{buffer}
are used to contain additional information, normally strings which are
pointed to by the elements of the result structure.
If a group with ID @var{gid} is found, the pointer returned in
@var{result} points to the record which contains the wanted data (i.e.,
@var{result} contains the value @var{result_buf}). If no group is found
or if an error occurred, the pointer returned in @var{result} is a null
pointer. The function returns zero or an error code. If the buffer
@var{buffer} is too small to contain all the needed information, the
error code @code{ERANGE} is returned and @var{errno} is set to
@code{ERANGE}.
@end deftypefun
@comment grp.h
@comment SVID, BSD
@deftypefun {struct group *} getgrnam (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:grnam} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrnam =~ getpwnam dup @mtasurace:grnam @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getgrnam_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function returns a pointer to a statically-allocated structure
containing information about the group whose group name is @var{name}.
This structure may be overwritten by subsequent calls to
@code{getgrnam}.
A null pointer indicates there is no group named @var{name}.
@end deftypefun
@comment grp.h
@comment POSIX.1c
@deftypefun int getgrnam_r (const char *@var{name}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrnam_r =~ getpwnam_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getgrnam_r @ascuheap @asulock @aculock @acsfd @acsmem
@c strlen dup ok
@c nscd_getgr_r dup @ascuheap @asulock @aculock @acsfd @acsmem
@c nss_group_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function is similar to @code{getgrnam} in that is returns
information about the group whose group name is @var{name}. Like
@code{getgrgid_r}, it uses the user supplied buffers in
@var{result_buf} and @var{buffer}, not a static buffer.
The return values are the same as for @code{getgrgid_r}
@code{ERANGE}.
@end deftypefun
@node Scanning All Groups
@subsection Scanning the List of All Groups
@cindex scanning the group list
This section explains how a program can read the list of all groups in
the system, one group at a time. The functions described here are
declared in @file{grp.h}.
You can use the @code{fgetgrent} function to read group entries from a
particular file.
@comment grp.h
@comment SVID
@deftypefun {struct group *} fgetgrent (FILE *@var{stream})
@safety{@prelim{}@mtunsafe{@mtasurace{:fgrent}}@asunsafe{@asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c fgetgrent @mtasurace:fgrent @asucorrupt @asulock @acucorrupt @aculock
@c fgetpos dup @asucorrupt @aculock @acucorrupt
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c fgetgrent_r dup @asucorrupt @acucorrupt @aculock
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c fsetpos dup @asucorrupt @aculock @acucorrupt
@c libc_lock_unlock dup @aculock
The @code{fgetgrent} function reads the next entry from @var{stream}.
It returns a pointer to the entry. The structure is statically
allocated and is overwritten on subsequent calls to @code{fgetgrent}. You
must copy the contents of the structure if you wish to save the
information.
The stream must correspond to a file in the same format as the standard
group database file.
@end deftypefun
@comment grp.h
@comment GNU
@deftypefun int fgetgrent_r (FILE *@var{stream}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c fgetgrent_r @asucorrupt @acucorrupt @aculock
@c flockfile dup @aculock
@c fgets_unlocked @asucorrupt @acucorrupt [no @mtsrace due to explicit locking]
@c feof_unlocked dup ok
@c funlockfile dup @aculock
@c isspace dup @mtslocale^^
@c parse_line dup ok
This function is similar to @code{fgetgrent} in that it reads the next
user entry from @var{stream}. But the result is returned in the
structure pointed to by @var{result_buf}. The first @var{buflen} bytes
of the additional buffer pointed to by @var{buffer} are used to contain
additional information, normally strings which are pointed to by the
elements of the result structure.
This stream must correspond to a file in the same format as the standard
group database file.
If the function returns zero @var{result} points to the structure with
the wanted data (normally this is in @var{result_buf}). If errors
occurred the return value is non-zero and @var{result} contains a null
pointer.
@end deftypefun
The way to scan all the entries in the group database is with
@code{setgrent}, @code{getgrent}, and @code{endgrent}.
@comment grp.h
@comment SVID, BSD
@deftypefun void setgrent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:grent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setgrent =~ setpwent dup @mtasurace:grent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c ...*lookup_fct = nss_group_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function initializes a stream for reading from the group data base.
You use this stream by calling @code{getgrent} or @code{getgrent_r}.
@end deftypefun
@comment grp.h
@comment SVID, BSD
@deftypefun {struct group *} getgrent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:grent} @mtasurace{:grentbuf} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrent =~ getpwent dup @mtasurace:grent @mtasurace:grentbuf @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *func = getgrent_r dup @mtasurace:grent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getgrent} function reads the next entry from the stream
initialized by @code{setgrent}. It returns a pointer to the entry. The
structure is statically allocated and is overwritten on subsequent calls
to @code{getgrent}. You must copy the contents of the structure if you
wish to save the information.
@end deftypefun
@comment grp.h
@comment GNU
@deftypefun int getgrent_r (struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
@safety{@prelim{}@mtunsafe{@mtasurace{:grent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getgrent_r =~ getpwent_r dup @mtasurace:grent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function is similar to @code{getgrent} in that it returns the next
entry from the stream initialized by @code{setgrent}. Like
@code{fgetgrent_r}, it places the result in user-supplied buffers
pointed to @var{result_buf} and @var{buffer}.
If the function returns zero @var{result} contains a pointer to the data
(normally equal to @var{result_buf}). If errors occurred the return
value is non-zero and @var{result} contains a null pointer.
@end deftypefun
@comment grp.h
@comment SVID, BSD
@deftypefun void endgrent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:grent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endgrent =~ endpwent dup @mtasurace:grent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function closes the internal stream used by @code{getgrent} or
@code{getgrent_r}.
@end deftypefun
@node Database Example
@section User and Group Database Example
Here is an example program showing the use of the system database inquiry
functions. The program prints some information about the user running
the program.
@smallexample
@include db.c.texi
@end smallexample
Here is some output from this program:
@smallexample
I am Throckmorton Snurd.
My login name is snurd.
My uid is 31093.
My home directory is /home/fsg/snurd.
My default shell is /bin/sh.
My default group is guest (12).
The members of this group are:
friedman
tami
@end smallexample
@node Netgroup Database
@section Netgroup Database
@menu
* Netgroup Data:: Data in the Netgroup database and where
it comes from.
* Lookup Netgroup:: How to look for a particular netgroup.
* Netgroup Membership:: How to test for netgroup membership.
@end menu
@node Netgroup Data
@subsection Netgroup Data
@cindex Netgroup
Sometimes it is useful to group users according to other criteria
(@pxref{Group Database}). E.g., it is useful to associate a certain
group of users with a certain machine. On the other hand grouping of
host names is not supported so far.
In Sun Microsystems SunOS appeared a new kind of database, the netgroup
database. It allows grouping hosts, users, and domains freely, giving
them individual names. To be more concrete, a netgroup is a list of triples
consisting of a host name, a user name, and a domain name where any of
the entries can be a wildcard entry matching all inputs. A last
possibility is that names of other netgroups can also be given in the
list specifying a netgroup. So one can construct arbitrary hierarchies
without loops.
Sun's implementation allows netgroups only for the @code{nis} or
@code{nisplus} service, @pxref{Services in the NSS configuration}. The
implementation in @theglibc{} has no such restriction. An entry
in either of the input services must have the following form:
@smallexample
@var{groupname} ( @var{groupname} | @code{(}@var{hostname}@code{,}@var{username}@code{,}@code{domainname}@code{)} )+
@end smallexample
Any of the fields in the triple can be empty which means anything
matches. While describing the functions we will see that the opposite
case is useful as well. I.e., there may be entries which will not
match any input. For entries like this, a name consisting of the single
character @code{-} shall be used.
@node Lookup Netgroup
@subsection Looking up one Netgroup
The lookup functions for netgroups are a bit different to all other
system database handling functions. Since a single netgroup can contain
many entries a two-step process is needed. First a single netgroup is
selected and then one can iterate over all entries in this netgroup.
These functions are declared in @file{netdb.h}.
@comment netdb.h
@comment BSD
@deftypefun int setnetgrent (const char *@var{netgroup})
@safety{@prelim{}@mtunsafe{@mtasurace{:netgrent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setnetgrent @mtasurace:netgrent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nscd_setnetgrent @ascuheap @acsfd @acsmem
@c __nscd_setnetgrent @ascuheap @acsfd @acsmem
@c strlen dup ok
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c nscd_cache_search dup ok
@c nscd_open_socket dup @acsfd
@c malloc dup @ascuheap @acsmem
@c readall dup ok
@c free dup @ascuheap @acsmem
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c internal_setnetgrent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c free_memory dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c internal_setnetgrent_reuse @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c endnetgrent_hook dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *endfct @ascuplugin
@c (netgroup::)setup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_netgroup_lookup dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_netgroup_lookup2 =~ nss_passwd_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *endfct @ascuplugin
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c memcpy dup ok
@c libc_lock_unlock dup @aculock
A call to this function initializes the internal state of the library to
allow following calls of the @code{getnetgrent} to iterate over all entries
in the netgroup with name @var{netgroup}.
When the call is successful (i.e., when a netgroup with this name exists)
the return value is @code{1}. When the return value is @code{0} no
netgroup of this name is known or some other error occurred.
@end deftypefun
It is important to remember that there is only one single state for
iterating the netgroups. Even if the programmer uses the
@code{getnetgrent_r} function the result is not really reentrant since
always only one single netgroup at a time can be processed. If the
program needs to process more than one netgroup simultaneously she
must protect this by using external locking. This problem was
introduced in the original netgroups implementation in SunOS and since
we must stay compatible it is not possible to change this.
Some other functions also use the netgroups state. Currently these are
the @code{innetgr} function and parts of the implementation of the
@code{compat} service part of the NSS implementation.
@comment netdb.h
@comment BSD
@deftypefun int getnetgrent (char **@var{hostp}, char **@var{userp}, char **@var{domainp})
@safety{@prelim{}@mtunsafe{@mtasurace{:netgrent} @mtasurace{:netgrentbuf} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getnetgrent @mtasurace:netgrent @mtasurace:netgrentbuf @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c uses unsafely a static buffer allocated within a libc_once call
@c allocate (libc_once) @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c getnetgrent_r dup @mtasurace:netgrent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
This function returns the next unprocessed entry of the currently
selected netgroup. The string pointers, in which addresses are passed in
the arguments @var{hostp}, @var{userp}, and @var{domainp}, will contain
after a successful call pointers to appropriate strings. If the string
in the next entry is empty the pointer has the value @code{NULL}.
The returned string pointers are only valid if none of the netgroup
related functions are called.
The return value is @code{1} if the next entry was successfully read. A
value of @code{0} means no further entries exist or internal errors occurred.
@end deftypefun
@comment netdb.h
@comment GNU
@deftypefun int getnetgrent_r (char **@var{hostp}, char **@var{userp}, char **@var{domainp}, char *@var{buffer}, size_t @var{buflen})
@safety{@prelim{}@mtunsafe{@mtasurace{:netgrent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getnetgrent_r @mtasurace:netgrent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c internal_getnetgrent_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct @ascuplugin
@c nscd_getnetgrent ok
@c rawmemchr dup ok
@c internal_setnetgrent_reuse dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c strcmp dup ok
@c malloc dup @ascuheap @acsmem
@c memcpy dup ok
@c libc_lock_unlock dup @aculock
This function is similar to @code{getnetgrent} with only one exception:
the strings the three string pointers @var{hostp}, @var{userp}, and
@var{domainp} point to, are placed in the buffer of @var{buflen} bytes
starting at @var{buffer}. This means the returned values are valid
even after other netgroup related functions are called.
The return value is @code{1} if the next entry was successfully read and
the buffer contains enough room to place the strings in it. @code{0} is
returned in case no more entries are found, the buffer is too small, or
internal errors occurred.
This function is a GNU extension. The original implementation in the
SunOS libc does not provide this function.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun void endnetgrent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:netgrent}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endnetgrent @mtasurace:netgrent @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c internal_endnetgrent @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c endnetgrent_hook dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c free_memory dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
This function frees all buffers which were allocated to process the last
selected netgroup. As a result all string pointers returned by calls
to @code{getnetgrent} are invalid afterwards.
@end deftypefun
@node Netgroup Membership
@subsection Testing for Netgroup Membership
It is often not necessary to scan the whole netgroup since often the
only interesting question is whether a given entry is part of the
selected netgroup.
@comment netdb.h
@comment BSD
@deftypefun int innetgr (const char *@var{netgroup}, const char *@var{host}, const char *@var{user}, const char *@var{domain})
@safety{@prelim{}@mtunsafe{@mtasurace{:netgrent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c This function does not use the static data structure that the
@c *netgrent* ones do, but since each nss must maintains internal state
@c to support iteration and concurrent iteration will interfere
@c destructively, we regard this internal state as a static buffer.
@c getnetgrent_r iteration in each nss backend.
@c innetgr @mtasurace:netgrent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_innetgr @ascuheap @acsfd @acsmem
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c stpcpy dup ok
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c nscd_cache_search dup ok
@c nscd_open_socket dup @acsfd
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c memset dup ok
@c (netgroup::)setup dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *setfct.f @ascuplugin
@c nss_lookup_function dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *getfct @ascuplugin
@c strcmp dup ok
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c memcpy dup ok
@c strcasecmp dup
@c *endfct @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c free_memory dup @ascuheap @acsmem
This function tests whether the triple specified by the parameters
@var{hostp}, @var{userp}, and @var{domainp} is part of the netgroup
@var{netgroup}. Using this function has the advantage that
@enumerate
@item
no other netgroup function can use the global netgroup state since
internal locking is used and
@item
the function is implemented more efficiently than successive calls
to the other @code{set}/@code{get}/@code{endnetgrent} functions.
@end enumerate
Any of the pointers @var{hostp}, @var{userp}, and @var{domainp} can be
@code{NULL} which means any value is accepted in this position. This is
also true for the name @code{-} which should not match any other string
otherwise.
The return value is @code{1} if an entry matching the given triple is
found in the netgroup. The return value is @code{0} if the netgroup
itself is not found, the netgroup does not contain the triple or
internal errors occurred.
@end deftypefun
@c FIXME these are undocumented:
@c setresgid
@c setresuid
glibc-doc-reference-2.19.orig/manual/pipe.texi 0000664 0001750 0001750 00000032465 12275120646 021421 0 ustar adconrad adconrad @node Pipes and FIFOs, Sockets, File System Interface, Top
@c %MENU% A simple interprocess communication mechanism
@chapter Pipes and FIFOs
@cindex pipe
A @dfn{pipe} is a mechanism for interprocess communication; data written
to the pipe by one process can be read by another process. The data is
handled in a first-in, first-out (FIFO) order. The pipe has no name; it
is created for one use and both ends must be inherited from the single
process which created the pipe.
@cindex FIFO special file
A @dfn{FIFO special file} is similar to a pipe, but instead of being an
anonymous, temporary connection, a FIFO has a name or names like any
other file. Processes open the FIFO by name in order to communicate
through it.
A pipe or FIFO has to be open at both ends simultaneously. If you read
from a pipe or FIFO file that doesn't have any processes writing to it
(perhaps because they have all closed the file, or exited), the read
returns end-of-file. Writing to a pipe or FIFO that doesn't have a
reading process is treated as an error condition; it generates a
@code{SIGPIPE} signal, and fails with error code @code{EPIPE} if the
signal is handled or blocked.
Neither pipes nor FIFO special files allow file positioning. Both
reading and writing operations happen sequentially; reading from the
beginning of the file and writing at the end.
@menu
* Creating a Pipe:: Making a pipe with the @code{pipe} function.
* Pipe to a Subprocess:: Using a pipe to communicate with a
child process.
* FIFO Special Files:: Making a FIFO special file.
* Pipe Atomicity:: When pipe (or FIFO) I/O is atomic.
@end menu
@node Creating a Pipe
@section Creating a Pipe
@cindex creating a pipe
@cindex opening a pipe
@cindex interprocess communication, with pipes
The primitive for creating a pipe is the @code{pipe} function. This
creates both the reading and writing ends of the pipe. It is not very
useful for a single process to use a pipe to talk to itself. In typical
use, a process creates a pipe just before it forks one or more child
processes (@pxref{Creating a Process}). The pipe is then used for
communication either between the parent or child processes, or between
two sibling processes.
The @code{pipe} function is declared in the header file
@file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun int pipe (int @var{filedes}@t{[2]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
@c On Linux, syscall pipe2. On HURD, call socketpair.
The @code{pipe} function creates a pipe and puts the file descriptors
for the reading and writing ends of the pipe (respectively) into
@code{@var{filedes}[0]} and @code{@var{filedes}[1]}.
An easy way to remember that the input end comes first is that file
descriptor @code{0} is standard input, and file descriptor @code{1} is
standard output.
If successful, @code{pipe} returns a value of @code{0}. On failure,
@code{-1} is returned. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EMFILE
The process has too many files open.
@item ENFILE
There are too many open files in the entire system. @xref{Error Codes},
for more information about @code{ENFILE}. This error never occurs on
@gnuhurdsystems{}.
@end table
@end deftypefun
Here is an example of a simple program that creates a pipe. This program
uses the @code{fork} function (@pxref{Creating a Process}) to create
a child process. The parent process writes data to the pipe, which is
read by the child process.
@smallexample
@include pipe.c.texi
@end smallexample
@node Pipe to a Subprocess
@section Pipe to a Subprocess
@cindex creating a pipe to a subprocess
@cindex pipe to a subprocess
@cindex filtering i/o through subprocess
A common use of pipes is to send data to or receive data from a program
being run as a subprocess. One way of doing this is by using a combination of
@code{pipe} (to create the pipe), @code{fork} (to create the subprocess),
@code{dup2} (to force the subprocess to use the pipe as its standard input
or output channel), and @code{exec} (to execute the new program). Or,
you can use @code{popen} and @code{pclose}.
The advantage of using @code{popen} and @code{pclose} is that the
interface is much simpler and easier to use. But it doesn't offer as
much flexibility as using the low-level functions directly.
@comment stdio.h
@comment POSIX.2, SVID, BSD
@deftypefun {FILE *} popen (const char *@var{command}, const char *@var{mode})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c popen @ascuheap @asucorrupt @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c _IO_init ok
@c _IO_no_init ok
@c _IO_old_init ok
@c _IO_lock_init ok
@c _IO_new_file_init @asucorrupt @acucorrupt @aculock @acsfd
@c _IO_link_in @asucorrupt @acucorrupt @aculock @acsfd
@c the linked list is guarded by a recursive lock;
@c it may get corrupted with async signals and cancellation
@c _IO_lock_lock dup @aculock
@c _IO_flockfile dup @aculock
@c _IO_funlockfile dup @aculock
@c _IO_lock_unlock dup @aculock
@c _IO_new_proc_open @asucorrupt @acucorrupt @aculock @acsfd
@c the linked list is guarded by a recursive lock;
@c it may get corrupted with async signals and cancellation
@c _IO_file_is_open ok
@c pipe2 dup @acsfd
@c pipe dup @acsfd
@c _IO_fork=fork @aculock
@c _IO_close=close_not_cancel dup @acsfd
@c fcntl dup ok
@c _IO_lock_lock @aculock
@c _IO_lock_unlock @aculock
@c _IO_mask_flags ok [no @mtasurace:stream, nearly but sufficiently exclusive access]
@c _IO_un_link @asucorrupt @acucorrupt @aculock @acsfd
@c the linked list is guarded by a recursive lock;
@c it may get corrupted with async signals and cancellation
@c _IO_lock_lock dup @aculock
@c _IO_flockfile dup @aculock
@c _IO_funlockfile dup @aculock
@c _IO_lock_unlock dup @aculock
@c free dup @ascuheap @acsmem
The @code{popen} function is closely related to the @code{system}
function; see @ref{Running a Command}. It executes the shell command
@var{command} as a subprocess. However, instead of waiting for the
command to complete, it creates a pipe to the subprocess and returns a
stream that corresponds to that pipe.
If you specify a @var{mode} argument of @code{"r"}, you can read from the
stream to retrieve data from the standard output channel of the subprocess.
The subprocess inherits its standard input channel from the parent process.
Similarly, if you specify a @var{mode} argument of @code{"w"}, you can
write to the stream to send data to the standard input channel of the
subprocess. The subprocess inherits its standard output channel from
the parent process.
In the event of an error @code{popen} returns a null pointer. This
might happen if the pipe or stream cannot be created, if the subprocess
cannot be forked, or if the program cannot be executed.
@end deftypefun
@comment stdio.h
@comment POSIX.2, SVID, BSD
@deftypefun int pclose (FILE *@var{stream})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @ascuplugin{} @asucorrupt{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Although the stream cannot be used after the call, even in case of
@c async cancellation, because the stream must not be used after pclose
@c is called, other stdio linked lists and their locks may be left in
@c corrupt states; that's where the corrupt and lock annotations come
@c from.
@c
@c pclose @ascuheap @ascuplugin @asucorrupt @asulock @acucorrupt @aculock @acsfd @acsmem
@c _IO_new_fclose @ascuheap @ascuplugin @asucorrupt @asulock @acucorrupt @aculock @acsfd @acsmem
@c _IO_un_link dup @asucorrupt @acucorrupt @aculock @acsfd
@c _IO_acquire_lock dup @aculock
@c _IO_flockfile dup @aculock
@c _IO_file_close_it @ascuheap @ascuplugin @asucorrupt @aculock @acucorrupt @acsfd @acsmem
@c _IO_file_is_open dup ok
@c _IO_do_flush @asucorrupt @ascuplugin @acucorrupt
@c _IO_do_write @asucorrupt @acucorrupt
@c new_do_write @asucorrupt @acucorrupt
@c _IO_SYSSEEK ok
@c lseek64 dup ok
@c _IO_SYSWRITE ok
@c write_not_cancel dup ok
@c write dup ok
@c _IO_adjust_column ok
@c _IO_setg dup @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_wdo_write @asucorrupt @ascuplugin @acucorrupt
@c _IO_new_do_write=_IO_do_write dup @asucorrupt @acucorrupt
@c *cc->__codecvt_do_out @ascuplugin
@c _IO_wsetg dup @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_unsave_markers @ascuheap @asucorrupt @acucorrupt @acsmem
@c _IO_have_backup dup ok
@c _IO_free_backup_area dup @ascuheap @asucorrupt @acucorrupt @acsmem
@c _IO_SYSCLOSE @aculock @acucorrupt @acsfd
@c _IO_lock_lock dup @aculock
@c _IO_close=close_not_cancel dup @acsfd
@c _IO_lock_unlock dup @aculock
@c _IO_waitpid=waitpid_not_cancel dup ok
@c _IO_have_wbackup ok
@c _IO_free_wbackup_area @ascuheap @asucorrupt @acucorrupt @acsmem
@c _IO_in_backup dup ok
@c _IO_switch_to_main_wget_area @asucorrupt @acucorrupt
@c free dup @ascuheap @acsmem
@c _IO_wsetb @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_wsetg @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_wsetp @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_setb @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_setg @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_setp @asucorrupt @acucorrupt [no @mtasurace:stream, locked]
@c _IO_un_link dup @asucorrupt @acucorrupt @aculock @acsfd
@c _IO_release_lock dup @aculock
@c _IO_funlockfile dup @aculock
@c _IO_FINISH @ascuheap @ascuplugin @asucorrupt @acucorrupt @aculock @acsfd @acsmem
@c _IO_new_file_finish @ascuheap @ascuplugin @asucorrupt @acucorrupt @aculock @acsfd @acsmem
@c _IO_file_is_open dup ok
@c _IO_do_flush dup @ascuplugin @asucorrupt @acucorrupt
@c _IO_SYSCLOSE dup @aculock @acucorrupt @acsfd
@c _IO_default_finish @ascuheap @asucorrupt @acucorrupt @aculock @acsfd @acsmem
@c FREE_BUF @acsmem
@c munmap dup @acsmem
@c free dup @ascuheap @acsmem
@c _IO_un_link dup @asucorrupt @acucorrupt @aculock @acsfd
@c _IO_lock_fini ok
@c libc_lock_fini_recursive ok
@c libc_lock_lock dup @asulock @aculock
@c gconv_release_step ok
@c libc_lock_unlock dup @asulock @aculock
@c _IO_have_backup ok
@c _IO_free_backup_area @ascuheap @asucorrupt @acucorrupt @acsmem
@c _IO_in_backup ok
@c _IO_switch_to_main_get_area @asucorrupt @acucorrupt
@c free dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
The @code{pclose} function is used to close a stream created by @code{popen}.
It waits for the child process to terminate and returns its status value,
as for the @code{system} function.
@end deftypefun
Here is an example showing how to use @code{popen} and @code{pclose} to
filter output through another program, in this case the paging program
@code{more}.
@smallexample
@include popen.c.texi
@end smallexample
@node FIFO Special Files
@section FIFO Special Files
@cindex creating a FIFO special file
@cindex interprocess communication, with FIFO
A FIFO special file is similar to a pipe, except that it is created in a
different way. Instead of being an anonymous communications channel, a
FIFO special file is entered into the file system by calling
@code{mkfifo}.
Once you have created a FIFO special file in this way, any process can
open it for reading or writing, in the same way as an ordinary file.
However, it has to be open at both ends simultaneously before you can
proceed to do any input or output operations on it. Opening a FIFO for
reading normally blocks until some other process opens the same FIFO for
writing, and vice versa.
The @code{mkfifo} function is declared in the header file
@file{sys/stat.h}.
@pindex sys/stat.h
@comment sys/stat.h
@comment POSIX.1
@deftypefun int mkfifo (const char *@var{filename}, mode_t @var{mode})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c On generic Posix, calls xmknod.
The @code{mkfifo} function makes a FIFO special file with name
@var{filename}. The @var{mode} argument is used to set the file's
permissions; see @ref{Setting Permissions}.
The normal, successful return value from @code{mkfifo} is @code{0}. In
the case of an error, @code{-1} is returned. In addition to the usual
file name errors (@pxref{File Name Errors}), the following
@code{errno} error conditions are defined for this function:
@table @code
@item EEXIST
The named file already exists.
@item ENOSPC
The directory or file system cannot be extended.
@item EROFS
The directory that would contain the file resides on a read-only file
system.
@end table
@end deftypefun
@node Pipe Atomicity
@section Atomicity of Pipe I/O
Reading or writing pipe data is @dfn{atomic} if the size of data written
is not greater than @code{PIPE_BUF}. This means that the data transfer
seems to be an instantaneous unit, in that nothing else in the system
can observe a state in which it is partially complete. Atomic I/O may
not begin right away (it may need to wait for buffer space or for data),
but once it does begin it finishes immediately.
Reading or writing a larger amount of data may not be atomic; for
example, output data from other processes sharing the descriptor may be
interspersed. Also, once @code{PIPE_BUF} characters have been written,
further writes will block until some characters are read.
@xref{Limits for Files}, for information about the @code{PIPE_BUF}
parameter.
glibc-doc-reference-2.19.orig/manual/io.texi 0000664 0001750 0001750 00000041762 12275120646 021073 0 ustar adconrad adconrad @node I/O Overview, I/O on Streams, Pattern Matching, Top
@c %MENU% Introduction to the I/O facilities
@chapter Input/Output Overview
Most programs need to do either input (reading data) or output (writing
data), or most frequently both, in order to do anything useful. @Theglibc{}
provides such a large selection of input and output functions
that the hardest part is often deciding which function is most
appropriate!
This chapter introduces concepts and terminology relating to input
and output. Other chapters relating to the GNU I/O facilities are:
@itemize @bullet
@item
@ref{I/O on Streams}, which covers the high-level functions
that operate on streams, including formatted input and output.
@item
@ref{Low-Level I/O}, which covers the basic I/O and control
functions on file descriptors.
@item
@ref{File System Interface}, which covers functions for operating on
directories and for manipulating file attributes such as access modes
and ownership.
@item
@ref{Pipes and FIFOs}, which includes information on the basic interprocess
communication facilities.
@item
@ref{Sockets}, which covers a more complicated interprocess communication
facility with support for networking.
@item
@ref{Low-Level Terminal Interface}, which covers functions for changing
how input and output to terminals or other serial devices are processed.
@end itemize
@menu
* I/O Concepts:: Some basic information and terminology.
* File Names:: How to refer to a file.
@end menu
@node I/O Concepts, File Names, , I/O Overview
@section Input/Output Concepts
Before you can read or write the contents of a file, you must establish
a connection or communications channel to the file. This process is
called @dfn{opening} the file. You can open a file for reading, writing,
or both.
@cindex opening a file
The connection to an open file is represented either as a stream or as a
file descriptor. You pass this as an argument to the functions that do
the actual read or write operations, to tell them which file to operate
on. Certain functions expect streams, and others are designed to
operate on file descriptors.
When you have finished reading to or writing from the file, you can
terminate the connection by @dfn{closing} the file. Once you have
closed a stream or file descriptor, you cannot do any more input or
output operations on it.
@menu
* Streams and File Descriptors:: The GNU C Library provides two ways
to access the contents of files.
* File Position:: The number of bytes from the
beginning of the file.
@end menu
@node Streams and File Descriptors, File Position, , I/O Concepts
@subsection Streams and File Descriptors
When you want to do input or output to a file, you have a choice of two
basic mechanisms for representing the connection between your program
and the file: file descriptors and streams. File descriptors are
represented as objects of type @code{int}, while streams are represented
as @code{FILE *} objects.
File descriptors provide a primitive, low-level interface to input and
output operations. Both file descriptors and streams can represent a
connection to a device (such as a terminal), or a pipe or socket for
communicating with another process, as well as a normal file. But, if
you want to do control operations that are specific to a particular kind
of device, you must use a file descriptor; there are no facilities to
use streams in this way. You must also use file descriptors if your
program needs to do input or output in special modes, such as
nonblocking (or polled) input (@pxref{File Status Flags}).
Streams provide a higher-level interface, layered on top of the
primitive file descriptor facilities. The stream interface treats all
kinds of files pretty much alike---the sole exception being the three
styles of buffering that you can choose (@pxref{Stream Buffering}).
The main advantage of using the stream interface is that the set of
functions for performing actual input and output operations (as opposed
to control operations) on streams is much richer and more powerful than
the corresponding facilities for file descriptors. The file descriptor
interface provides only simple functions for transferring blocks of
characters, but the stream interface also provides powerful formatted
input and output functions (@code{printf} and @code{scanf}) as well as
functions for character- and line-oriented input and output.
@c !!! glibc has dprintf, which lets you do printf on an fd.
Since streams are implemented in terms of file descriptors, you can
extract the file descriptor from a stream and perform low-level
operations directly on the file descriptor. You can also initially open
a connection as a file descriptor and then make a stream associated with
that file descriptor.
In general, you should stick with using streams rather than file
descriptors, unless there is some specific operation you want to do that
can only be done on a file descriptor. If you are a beginning
programmer and aren't sure what functions to use, we suggest that you
concentrate on the formatted input functions (@pxref{Formatted Input})
and formatted output functions (@pxref{Formatted Output}).
If you are concerned about portability of your programs to systems other
than GNU, you should also be aware that file descriptors are not as
portable as streams. You can expect any system running @w{ISO C} to
support streams, but @nongnusystems{} may not support file descriptors at
all, or may only implement a subset of the GNU functions that operate on
file descriptors. Most of the file descriptor functions in @theglibc{}
are included in the POSIX.1 standard, however.
@node File Position, , Streams and File Descriptors, I/O Concepts
@subsection File Position
One of the attributes of an open file is its @dfn{file position} that
keeps track of where in the file the next character is to be read or
written. On @gnusystems{}, and all POSIX.1 systems, the file position
is simply an integer representing the number of bytes from the beginning
of the file.
The file position is normally set to the beginning of the file when it
is opened, and each time a character is read or written, the file
position is incremented. In other words, access to the file is normally
@dfn{sequential}.
@cindex file position
@cindex sequential-access files
Ordinary files permit read or write operations at any position within
the file. Some other kinds of files may also permit this. Files which
do permit this are sometimes referred to as @dfn{random-access} files.
You can change the file position using the @code{fseek} function on a
stream (@pxref{File Positioning}) or the @code{lseek} function on a file
descriptor (@pxref{I/O Primitives}). If you try to change the file
position on a file that doesn't support random access, you get the
@code{ESPIPE} error.
@cindex random-access files
Streams and descriptors that are opened for @dfn{append access} are
treated specially for output: output to such files is @emph{always}
appended sequentially to the @emph{end} of the file, regardless of the
file position. However, the file position is still used to control where in
the file reading is done.
@cindex append-access files
If you think about it, you'll realize that several programs can read a
given file at the same time. In order for each program to be able to
read the file at its own pace, each program must have its own file
pointer, which is not affected by anything the other programs do.
In fact, each opening of a file creates a separate file position.
Thus, if you open a file twice even in the same program, you get two
streams or descriptors with independent file positions.
By contrast, if you open a descriptor and then duplicate it to get
another descriptor, these two descriptors share the same file position:
changing the file position of one descriptor will affect the other.
@node File Names, , I/O Concepts, I/O Overview
@section File Names
In order to open a connection to a file, or to perform other operations
such as deleting a file, you need some way to refer to the file. Nearly
all files have names that are strings---even files which are actually
devices such as tape drives or terminals. These strings are called
@dfn{file names}. You specify the file name to say which file you want
to open or operate on.
This section describes the conventions for file names and how the
operating system works with them.
@cindex file name
@menu
* Directories:: Directories contain entries for files.
* File Name Resolution:: A file name specifies how to look up a file.
* File Name Errors:: Error conditions relating to file names.
* File Name Portability:: File name portability and syntax issues.
@end menu
@node Directories, File Name Resolution, , File Names
@subsection Directories
In order to understand the syntax of file names, you need to understand
how the file system is organized into a hierarchy of directories.
@cindex directory
@cindex link
@cindex directory entry
A @dfn{directory} is a file that contains information to associate other
files with names; these associations are called @dfn{links} or
@dfn{directory entries}. Sometimes, people speak of ``files in a
directory'', but in reality, a directory only contains pointers to
files, not the files themselves.
@cindex file name component
The name of a file contained in a directory entry is called a @dfn{file
name component}. In general, a file name consists of a sequence of one
or more such components, separated by the slash character (@samp{/}). A
file name which is just one component names a file with respect to its
directory. A file name with multiple components names a directory, and
then a file in that directory, and so on.
Some other documents, such as the POSIX standard, use the term
@dfn{pathname} for what we call a file name, and either @dfn{filename}
or @dfn{pathname component} for what this manual calls a file name
component. We don't use this terminology because a ``path'' is
something completely different (a list of directories to search), and we
think that ``pathname'' used for something else will confuse users. We
always use ``file name'' and ``file name component'' (or sometimes just
``component'', where the context is obvious) in GNU documentation. Some
macros use the POSIX terminology in their names, such as
@code{PATH_MAX}. These macros are defined by the POSIX standard, so we
cannot change their names.
You can find more detailed information about operations on directories
in @ref{File System Interface}.
@node File Name Resolution, File Name Errors, Directories, File Names
@subsection File Name Resolution
A file name consists of file name components separated by slash
(@samp{/}) characters. On the systems that @theglibc{} supports,
multiple successive @samp{/} characters are equivalent to a single
@samp{/} character.
@cindex file name resolution
The process of determining what file a file name refers to is called
@dfn{file name resolution}. This is performed by examining the
components that make up a file name in left-to-right order, and locating
each successive component in the directory named by the previous
component. Of course, each of the files that are referenced as
directories must actually exist, be directories instead of regular
files, and have the appropriate permissions to be accessible by the
process; otherwise the file name resolution fails.
@cindex root directory
@cindex absolute file name
If a file name begins with a @samp{/}, the first component in the file
name is located in the @dfn{root directory} of the process (usually all
processes on the system have the same root directory). Such a file name
is called an @dfn{absolute file name}.
@c !!! xref here to chroot, if we ever document chroot. -rm
@cindex relative file name
Otherwise, the first component in the file name is located in the
current working directory (@pxref{Working Directory}). This kind of
file name is called a @dfn{relative file name}.
@cindex parent directory
The file name components @file{.} (``dot'') and @file{..} (``dot-dot'')
have special meanings. Every directory has entries for these file name
components. The file name component @file{.} refers to the directory
itself, while the file name component @file{..} refers to its
@dfn{parent directory} (the directory that contains the link for the
directory in question). As a special case, @file{..} in the root
directory refers to the root directory itself, since it has no parent;
thus @file{/..} is the same as @file{/}.
Here are some examples of file names:
@table @file
@item /a
The file named @file{a}, in the root directory.
@item /a/b
The file named @file{b}, in the directory named @file{a} in the root directory.
@item a
The file named @file{a}, in the current working directory.
@item /a/./b
This is the same as @file{/a/b}.
@item ./a
The file named @file{a}, in the current working directory.
@item ../a
The file named @file{a}, in the parent directory of the current working
directory.
@end table
@c An empty string may ``work'', but I think it's confusing to
@c try to describe it. It's not a useful thing for users to use--rms.
A file name that names a directory may optionally end in a @samp{/}.
You can specify a file name of @file{/} to refer to the root directory,
but the empty string is not a meaningful file name. If you want to
refer to the current working directory, use a file name of @file{.} or
@file{./}.
Unlike some other operating systems, @gnusystems{} don't have any
built-in support for file types (or extensions) or file versions as part
of its file name syntax. Many programs and utilities use conventions
for file names---for example, files containing C source code usually
have names suffixed with @samp{.c}---but there is nothing in the file
system itself that enforces this kind of convention.
@node File Name Errors, File Name Portability, File Name Resolution, File Names
@subsection File Name Errors
@cindex file name errors
@cindex usual file name errors
Functions that accept file name arguments usually detect these
@code{errno} error conditions relating to the file name syntax or
trouble finding the named file. These errors are referred to throughout
this manual as the @dfn{usual file name errors}.
@table @code
@item EACCES
The process does not have search permission for a directory component
of the file name.
@item ENAMETOOLONG
This error is used when either the total length of a file name is
greater than @code{PATH_MAX}, or when an individual file name component
has a length greater than @code{NAME_MAX}. @xref{Limits for Files}.
On @gnuhurdsystems{}, there is no imposed limit on overall file name
length, but some file systems may place limits on the length of a
component.
@item ENOENT
This error is reported when a file referenced as a directory component
in the file name doesn't exist, or when a component is a symbolic link
whose target file does not exist. @xref{Symbolic Links}.
@item ENOTDIR
A file that is referenced as a directory component in the file name
exists, but it isn't a directory.
@item ELOOP
Too many symbolic links were resolved while trying to look up the file
name. The system has an arbitrary limit on the number of symbolic links
that may be resolved in looking up a single file name, as a primitive
way to detect loops. @xref{Symbolic Links}.
@end table
@node File Name Portability, , File Name Errors, File Names
@subsection Portability of File Names
The rules for the syntax of file names discussed in @ref{File Names},
are the rules normally used by @gnusystems{} and by other POSIX
systems. However, other operating systems may use other conventions.
There are two reasons why it can be important for you to be aware of
file name portability issues:
@itemize @bullet
@item
If your program makes assumptions about file name syntax, or contains
embedded literal file name strings, it is more difficult to get it to
run under other operating systems that use different syntax conventions.
@item
Even if you are not concerned about running your program on machines
that run other operating systems, it may still be possible to access
files that use different naming conventions. For example, you may be
able to access file systems on another computer running a different
operating system over a network, or read and write disks in formats used
by other operating systems.
@end itemize
The @w{ISO C} standard says very little about file name syntax, only that
file names are strings. In addition to varying restrictions on the
length of file names and what characters can validly appear in a file
name, different operating systems use different conventions and syntax
for concepts such as structured directories and file types or
extensions. Some concepts such as file versions might be supported in
some operating systems and not by others.
The POSIX.1 standard allows implementations to put additional
restrictions on file name syntax, concerning what characters are
permitted in file names and on the length of file name and file name
component strings. However, on @gnusystems{}, any character except
the null character is permitted in a file name string, and
on @gnuhurdsystems{} there are no limits on the length of file name
strings.
glibc-doc-reference-2.19.orig/manual/message.texi 0000664 0001750 0001750 00000235056 12275120646 022111 0 ustar adconrad adconrad @node Message Translation, Searching and Sorting, Locales, Top
@c %MENU% How to make the program speak the user's language
@chapter Message Translation
The program's interface with the user should be designed to ease the user's
task. One way to ease the user's task is to use messages in whatever
language the user prefers.
Printing messages in different languages can be implemented in different
ways. One could add all the different languages in the source code and
choose among the variants every time a message has to be printed. This is
certainly not a good solution since extending the set of languages is
cumbersome (the code must be changed) and the code itself can become
really big with dozens of message sets.
A better solution is to keep the message sets for each language
in separate files which are loaded at runtime depending on the language
selection of the user.
@Theglibc{} provides two different sets of functions to support
message translation. The problem is that neither of the interfaces is
officially defined by the POSIX standard. The @code{catgets} family of
functions is defined in the X/Open standard but this is derived from
industry decisions and therefore not necessarily based on reasonable
decisions.
As mentioned above the message catalog handling provides easy
extendibility by using external data files which contain the message
translations. I.e., these files contain for each of the messages used
in the program a translation for the appropriate language. So the tasks
of the message handling functions are
@itemize @bullet
@item
locate the external data file with the appropriate translations
@item
load the data and make it possible to address the messages
@item
map a given key to the translated message
@end itemize
The two approaches mainly differ in the implementation of this last
step. Decisions made in the last step influence the rest of the design.
@menu
* Message catalogs a la X/Open:: The @code{catgets} family of functions.
* The Uniforum approach:: The @code{gettext} family of functions.
@end menu
@node Message catalogs a la X/Open
@section X/Open Message Catalog Handling
The @code{catgets} functions are based on the simple scheme:
@quotation
Associate every message to translate in the source code with a unique
identifier. To retrieve a message from a catalog file solely the
identifier is used.
@end quotation
This means for the author of the program that s/he will have to make
sure the meaning of the identifier in the program code and in the
message catalogs are always the same.
Before a message can be translated the catalog file must be located.
The user of the program must be able to guide the responsible function
to find whatever catalog the user wants. This is separated from what
the programmer had in mind.
All the types, constants and functions for the @code{catgets} functions
are defined/declared in the @file{nl_types.h} header file.
@menu
* The catgets Functions:: The @code{catgets} function family.
* The message catalog files:: Format of the message catalog files.
* The gencat program:: How to generate message catalogs files which
can be used by the functions.
* Common Usage:: How to use the @code{catgets} interface.
@end menu
@node The catgets Functions
@subsection The @code{catgets} function family
@comment nl_types.h
@comment X/Open
@deftypefun nl_catd catopen (const char *@var{cat_name}, int @var{flag})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c catopen @mtsenv @ascuheap @acsmem
@c strchr ok
@c setlocale(,NULL) ok
@c getenv @mtsenv
@c strlen ok
@c alloca ok
@c stpcpy ok
@c malloc @ascuheap @acsmem
@c __open_catalog @ascuheap @acsmem
@c strchr ok
@c open_not_cancel_2 @acsfd
@c strlen ok
@c ENOUGH ok
@c alloca ok
@c memcpy ok
@c fxstat64 ok
@c __set_errno ok
@c mmap @acsmem
@c malloc dup @ascuheap @acsmem
@c read_not_cancel ok
@c free dup @ascuheap @acsmem
@c munmap ok
@c close_not_cancel_no_status ok
@c free @ascuheap @acsmem
The @code{catopen} function tries to locate the message data file names
@var{cat_name} and loads it when found. The return value is of an
opaque type and can be used in calls to the other functions to refer to
this loaded catalog.
The return value is @code{(nl_catd) -1} in case the function failed and
no catalog was loaded. The global variable @var{errno} contains a code
for the error causing the failure. But even if the function call
succeeded this does not mean that all messages can be translated.
Locating the catalog file must happen in a way which lets the user of
the program influence the decision. It is up to the user to decide
about the language to use and sometimes it is useful to use alternate
catalog files. All this can be specified by the user by setting some
environment variables.
The first problem is to find out where all the message catalogs are
stored. Every program could have its own place to keep all the
different files but usually the catalog files are grouped by languages
and the catalogs for all programs are kept in the same place.
@cindex NLSPATH environment variable
To tell the @code{catopen} function where the catalog for the program
can be found the user can set the environment variable @code{NLSPATH} to
a value which describes her/his choice. Since this value must be usable
for different languages and locales it cannot be a simple string.
Instead it is a format string (similar to @code{printf}'s). An example
is
@smallexample
/usr/share/locale/%L/%N:/usr/share/locale/%L/LC_MESSAGES/%N
@end smallexample
First one can see that more than one directory can be specified (with
the usual syntax of separating them by colons). The next things to
observe are the format string, @code{%L} and @code{%N} in this case.
The @code{catopen} function knows about several of them and the
replacement for all of them is of course different.
@table @code
@item %N
This format element is substituted with the name of the catalog file.
This is the value of the @var{cat_name} argument given to
@code{catgets}.
@item %L
This format element is substituted with the name of the currently
selected locale for translating messages. How this is determined is
explained below.
@item %l
(This is the lowercase ell.) This format element is substituted with the
language element of the locale name. The string describing the selected
locale is expected to have the form
@code{@var{lang}[_@var{terr}[.@var{codeset}]]} and this format uses the
first part @var{lang}.
@item %t
This format element is substituted by the territory part @var{terr} of
the name of the currently selected locale. See the explanation of the
format above.
@item %c
This format element is substituted by the codeset part @var{codeset} of
the name of the currently selected locale. See the explanation of the
format above.
@item %%
Since @code{%} is used in a meta character there must be a way to
express the @code{%} character in the result itself. Using @code{%%}
does this just like it works for @code{printf}.
@end table
Using @code{NLSPATH} allows arbitrary directories to be searched for
message catalogs while still allowing different languages to be used.
If the @code{NLSPATH} environment variable is not set, the default value
is
@smallexample
@var{prefix}/share/locale/%L/%N:@var{prefix}/share/locale/%L/LC_MESSAGES/%N
@end smallexample
@noindent
where @var{prefix} is given to @code{configure} while installing @theglibc{}
(this value is in many cases @code{/usr} or the empty string).
The remaining problem is to decide which must be used. The value
decides about the substitution of the format elements mentioned above.
First of all the user can specify a path in the message catalog name
(i.e., the name contains a slash character). In this situation the
@code{NLSPATH} environment variable is not used. The catalog must exist
as specified in the program, perhaps relative to the current working
directory. This situation in not desirable and catalogs names never
should be written this way. Beside this, this behavior is not portable
to all other platforms providing the @code{catgets} interface.
@cindex LC_ALL environment variable
@cindex LC_MESSAGES environment variable
@cindex LANG environment variable
Otherwise the values of environment variables from the standard
environment are examined (@pxref{Standard Environment}). Which
variables are examined is decided by the @var{flag} parameter of
@code{catopen}. If the value is @code{NL_CAT_LOCALE} (which is defined
in @file{nl_types.h}) then the @code{catopen} function use the name of
the locale currently selected for the @code{LC_MESSAGES} category.
If @var{flag} is zero the @code{LANG} environment variable is examined.
This is a left-over from the early days where the concept of the locales
had not even reached the level of POSIX locales.
The environment variable and the locale name should have a value of the
form @code{@var{lang}[_@var{terr}[.@var{codeset}]]} as explained above.
If no environment variable is set the @code{"C"} locale is used which
prevents any translation.
The return value of the function is in any case a valid string. Either
it is a translation from a message catalog or it is the same as the
@var{string} parameter. So a piece of code to decide whether a
translation actually happened must look like this:
@smallexample
@{
char *trans = catgets (desc, set, msg, input_string);
if (trans == input_string)
@{
/* Something went wrong. */
@}
@}
@end smallexample
@noindent
When an error occurred the global variable @var{errno} is set to
@table @var
@item EBADF
The catalog does not exist.
@item ENOMSG
The set/message tuple does not name an existing element in the
message catalog.
@end table
While it sometimes can be useful to test for errors programs normally
will avoid any test. If the translation is not available it is no big
problem if the original, untranslated message is printed. Either the
user understands this as well or s/he will look for the reason why the
messages are not translated.
@end deftypefun
Please note that the currently selected locale does not depend on a call
to the @code{setlocale} function. It is not necessary that the locale
data files for this locale exist and calling @code{setlocale} succeeds.
The @code{catopen} function directly reads the values of the environment
variables.
@deftypefun {char *} catgets (nl_catd @var{catalog_desc}, int @var{set}, int @var{message}, const char *@var{string})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The function @code{catgets} has to be used to access the massage catalog
previously opened using the @code{catopen} function. The
@var{catalog_desc} parameter must be a value previously returned by
@code{catopen}.
The next two parameters, @var{set} and @var{message}, reflect the
internal organization of the message catalog files. This will be
explained in detail below. For now it is interesting to know that a
catalog can consists of several set and the messages in each thread are
individually numbered using numbers. Neither the set number nor the
message number must be consecutive. They can be arbitrarily chosen.
But each message (unless equal to another one) must have its own unique
pair of set and message number.
Since it is not guaranteed that the message catalog for the language
selected by the user exists the last parameter @var{string} helps to
handle this case gracefully. If no matching string can be found
@var{string} is returned. This means for the programmer that
@itemize @bullet
@item
the @var{string} parameters should contain reasonable text (this also
helps to understand the program seems otherwise there would be no hint
on the string which is expected to be returned.
@item
all @var{string} arguments should be written in the same language.
@end itemize
@end deftypefun
It is somewhat uncomfortable to write a program using the @code{catgets}
functions if no supporting functionality is available. Since each
set/message number tuple must be unique the programmer must keep lists
of the messages at the same time the code is written. And the work
between several people working on the same project must be coordinated.
We will see some how these problems can be relaxed a bit (@pxref{Common
Usage}).
@deftypefun int catclose (nl_catd @var{catalog_desc})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}}
@c catclose @ascuheap @acucorrupt @acsmem
@c __set_errno ok
@c munmap ok
@c free @ascuheap @acsmem
The @code{catclose} function can be used to free the resources
associated with a message catalog which previously was opened by a call
to @code{catopen}. If the resources can be successfully freed the
function returns @code{0}. Otherwise it return @code{@minus{}1} and the
global variable @var{errno} is set. Errors can occur if the catalog
descriptor @var{catalog_desc} is not valid in which case @var{errno} is
set to @code{EBADF}.
@end deftypefun
@node The message catalog files
@subsection Format of the message catalog files
The only reasonable way the translate all the messages of a function and
store the result in a message catalog file which can be read by the
@code{catopen} function is to write all the message text to the
translator and let her/him translate them all. I.e., we must have a
file with entries which associate the set/message tuple with a specific
translation. This file format is specified in the X/Open standard and
is as follows:
@itemize @bullet
@item
Lines containing only whitespace characters or empty lines are ignored.
@item
Lines which contain as the first non-whitespace character a @code{$}
followed by a whitespace character are comment and are also ignored.
@item
If a line contains as the first non-whitespace characters the sequence
@code{$set} followed by a whitespace character an additional argument
is required to follow. This argument can either be:
@itemize @minus
@item
a number. In this case the value of this number determines the set
to which the following messages are added.
@item
an identifier consisting of alphanumeric characters plus the underscore
character. In this case the set get automatically a number assigned.
This value is one added to the largest set number which so far appeared.
How to use the symbolic names is explained in section @ref{Common Usage}.
It is an error if a symbol name appears more than once. All following
messages are placed in a set with this number.
@end itemize
@item
If a line contains as the first non-whitespace characters the sequence
@code{$delset} followed by a whitespace character an additional argument
is required to follow. This argument can either be:
@itemize @minus
@item
a number. In this case the value of this number determines the set
which will be deleted.
@item
an identifier consisting of alphanumeric characters plus the underscore
character. This symbolic identifier must match a name for a set which
previously was defined. It is an error if the name is unknown.
@end itemize
In both cases all messages in the specified set will be removed. They
will not appear in the output. But if this set is later again selected
with a @code{$set} command again messages could be added and these
messages will appear in the output.
@item
If a line contains after leading whitespaces the sequence
@code{$quote}, the quoting character used for this input file is
changed to the first non-whitespace character following the
@code{$quote}. If no non-whitespace character is present before the
line ends quoting is disable.
By default no quoting character is used. In this mode strings are
terminated with the first unescaped line break. If there is a
@code{$quote} sequence present newline need not be escaped. Instead a
string is terminated with the first unescaped appearance of the quote
character.
A common usage of this feature would be to set the quote character to
@code{"}. Then any appearance of the @code{"} in the strings must
be escaped using the backslash (i.e., @code{\"} must be written).
@item
Any other line must start with a number or an alphanumeric identifier
(with the underscore character included). The following characters
(starting after the first whitespace character) will form the string
which gets associated with the currently selected set and the message
number represented by the number and identifier respectively.
If the start of the line is a number the message number is obvious. It
is an error if the same message number already appeared for this set.
If the leading token was an identifier the message number gets
automatically assigned. The value is the current maximum messages
number for this set plus one. It is an error if the identifier was
already used for a message in this set. It is OK to reuse the
identifier for a message in another thread. How to use the symbolic
identifiers will be explained below (@pxref{Common Usage}). There is
one limitation with the identifier: it must not be @code{Set}. The
reason will be explained below.
The text of the messages can contain escape characters. The usual bunch
of characters known from the @w{ISO C} language are recognized
(@code{\n}, @code{\t}, @code{\v}, @code{\b}, @code{\r}, @code{\f},
@code{\\}, and @code{\@var{nnn}}, where @var{nnn} is the octal coding of
a character code).
@end itemize
@strong{Important:} The handling of identifiers instead of numbers for
the set and messages is a GNU extension. Systems strictly following the
X/Open specification do not have this feature. An example for a message
catalog file is this:
@smallexample
$ This is a leading comment.
$quote "
$set SetOne
1 Message with ID 1.
two " Message with ID \"two\", which gets the value 2 assigned"
$set SetTwo
$ Since the last set got the number 1 assigned this set has number 2.
4000 "The numbers can be arbitrary, they need not start at one."
@end smallexample
This small example shows various aspects:
@itemize @bullet
@item
Lines 1 and 9 are comments since they start with @code{$} followed by
a whitespace.
@item
The quoting character is set to @code{"}. Otherwise the quotes in the
message definition would have to be left away and in this case the
message with the identifier @code{two} would loose its leading whitespace.
@item
Mixing numbered messages with message having symbolic names is no
problem and the numbering happens automatically.
@end itemize
While this file format is pretty easy it is not the best possible for
use in a running program. The @code{catopen} function would have to
parser the file and handle syntactic errors gracefully. This is not so
easy and the whole process is pretty slow. Therefore the @code{catgets}
functions expect the data in another more compact and ready-to-use file
format. There is a special program @code{gencat} which is explained in
detail in the next section.
Files in this other format are not human readable. To be easy to use by
programs it is a binary file. But the format is byte order independent
so translation files can be shared by systems of arbitrary architecture
(as long as they use @theglibc{}).
Details about the binary file format are not important to know since
these files are always created by the @code{gencat} program. The
sources of @theglibc{} also provide the sources for the
@code{gencat} program and so the interested reader can look through
these source files to learn about the file format.
@node The gencat program
@subsection Generate Message Catalogs files
@cindex gencat
The @code{gencat} program is specified in the X/Open standard and the
GNU implementation follows this specification and so processes
all correctly formed input files. Additionally some extension are
implemented which help to work in a more reasonable way with the
@code{catgets} functions.
The @code{gencat} program can be invoked in two ways:
@example
`gencat [@var{Option}]@dots{} [@var{Output-File} [@var{Input-File}]@dots{}]`
@end example
This is the interface defined in the X/Open standard. If no
@var{Input-File} parameter is given input will be read from standard
input. Multiple input files will be read as if they are concatenated.
If @var{Output-File} is also missing, the output will be written to
standard output. To provide the interface one is used to from other
programs a second interface is provided.
@smallexample
`gencat [@var{Option}]@dots{} -o @var{Output-File} [@var{Input-File}]@dots{}`
@end smallexample
The option @samp{-o} is used to specify the output file and all file
arguments are used as input files.
Beside this one can use @file{-} or @file{/dev/stdin} for
@var{Input-File} to denote the standard input. Corresponding one can
use @file{-} and @file{/dev/stdout} for @var{Output-File} to denote
standard output. Using @file{-} as a file name is allowed in X/Open
while using the device names is a GNU extension.
The @code{gencat} program works by concatenating all input files and
then @strong{merge} the resulting collection of message sets with a
possibly existing output file. This is done by removing all messages
with set/message number tuples matching any of the generated messages
from the output file and then adding all the new messages. To
regenerate a catalog file while ignoring the old contents therefore
requires to remove the output file if it exists. If the output is
written to standard output no merging takes place.
@noindent
The following table shows the options understood by the @code{gencat}
program. The X/Open standard does not specify any option for the
program so all of these are GNU extensions.
@table @samp
@item -V
@itemx --version
Print the version information and exit.
@item -h
@itemx --help
Print a usage message listing all available options, then exit successfully.
@item --new
Do never merge the new messages from the input files with the old content
of the output files. The old content of the output file is discarded.
@item -H
@itemx --header=name
This option is used to emit the symbolic names given to sets and
messages in the input files for use in the program. Details about how
to use this are given in the next section. The @var{name} parameter to
this option specifies the name of the output file. It will contain a
number of C preprocessor @code{#define}s to associate a name with a
number.
Please note that the generated file only contains the symbols from the
input files. If the output is merged with the previous content of the
output file the possibly existing symbols from the file(s) which
generated the old output files are not in the generated header file.
@end table
@node Common Usage
@subsection How to use the @code{catgets} interface
The @code{catgets} functions can be used in two different ways. By
following slavishly the X/Open specs and not relying on the extension
and by using the GNU extensions. We will take a look at the former
method first to understand the benefits of extensions.
@subsubsection Not using symbolic names
Since the X/Open format of the message catalog files does not allow
symbol names we have to work with numbers all the time. When we start
writing a program we have to replace all appearances of translatable
strings with something like
@smallexample
catgets (catdesc, set, msg, "string")
@end smallexample
@noindent
@var{catgets} is retrieved from a call to @code{catopen} which is
normally done once at the program start. The @code{"string"} is the
string we want to translate. The problems start with the set and
message numbers.
In a bigger program several programmers usually work at the same time on
the program and so coordinating the number allocation is crucial.
Though no two different strings must be indexed by the same tuple of
numbers it is highly desirable to reuse the numbers for equal strings
with equal translations (please note that there might be strings which
are equal in one language but have different translations due to
difference contexts).
The allocation process can be relaxed a bit by different set numbers for
different parts of the program. So the number of developers who have to
coordinate the allocation can be reduced. But still lists must be keep
track of the allocation and errors can easily happen. These errors
cannot be discovered by the compiler or the @code{catgets} functions.
Only the user of the program might see wrong messages printed. In the
worst cases the messages are so irritating that they cannot be
recognized as wrong. Think about the translations for @code{"true"} and
@code{"false"} being exchanged. This could result in a disaster.
@subsubsection Using symbolic names
The problems mentioned in the last section derive from the fact that:
@enumerate
@item
the numbers are allocated once and due to the possibly frequent use of
them it is difficult to change a number later.
@item
the numbers do not allow to guess anything about the string and
therefore collisions can easily happen.
@end enumerate
By constantly using symbolic names and by providing a method which maps
the string content to a symbolic name (however this will happen) one can
prevent both problems above. The cost of this is that the programmer
has to write a complete message catalog file while s/he is writing the
program itself.
This is necessary since the symbolic names must be mapped to numbers
before the program sources can be compiled. In the last section it was
described how to generate a header containing the mapping of the names.
E.g., for the example message file given in the last section we could
call the @code{gencat} program as follow (assume @file{ex.msg} contains
the sources).
@smallexample
gencat -H ex.h -o ex.cat ex.msg
@end smallexample
@noindent
This generates a header file with the following content:
@smallexample
#define SetTwoSet 0x2 /* ex.msg:8 */
#define SetOneSet 0x1 /* ex.msg:4 */
#define SetOnetwo 0x2 /* ex.msg:6 */
@end smallexample
As can be seen the various symbols given in the source file are mangled
to generate unique identifiers and these identifiers get numbers
assigned. Reading the source file and knowing about the rules will
allow to predict the content of the header file (it is deterministic)
but this is not necessary. The @code{gencat} program can take care for
everything. All the programmer has to do is to put the generated header
file in the dependency list of the source files of her/his project and
to add a rules to regenerate the header of any of the input files
change.
One word about the symbol mangling. Every symbol consists of two parts:
the name of the message set plus the name of the message or the special
string @code{Set}. So @code{SetOnetwo} means this macro can be used to
access the translation with identifier @code{two} in the message set
@code{SetOne}.
The other names denote the names of the message sets. The special
string @code{Set} is used in the place of the message identifier.
If in the code the second string of the set @code{SetOne} is used the C
code should look like this:
@smallexample
catgets (catdesc, SetOneSet, SetOnetwo,
" Message with ID \"two\", which gets the value 2 assigned")
@end smallexample
Writing the function this way will allow to change the message number
and even the set number without requiring any change in the C source
code. (The text of the string is normally not the same; this is only
for this example.)
@subsubsection How does to this allow to develop
To illustrate the usual way to work with the symbolic version numbers
here is a little example. Assume we want to write the very complex and
famous greeting program. We start by writing the code as usual:
@smallexample
#include
int
main (void)
@{
printf ("Hello, world!\n");
return 0;
@}
@end smallexample
Now we want to internationalize the message and therefore replace the
message with whatever the user wants.
@smallexample
#include
#include
#include "msgnrs.h"
int
main (void)
@{
nl_catd catdesc = catopen ("hello.cat", NL_CAT_LOCALE);
printf (catgets (catdesc, SetMainSet, SetMainHello,
"Hello, world!\n"));
catclose (catdesc);
return 0;
@}
@end smallexample
We see how the catalog object is opened and the returned descriptor used
in the other function calls. It is not really necessary to check for
failure of any of the functions since even in these situations the
functions will behave reasonable. They simply will be return a
translation.
What remains unspecified here are the constants @code{SetMainSet} and
@code{SetMainHello}. These are the symbolic names describing the
message. To get the actual definitions which match the information in
the catalog file we have to create the message catalog source file and
process it using the @code{gencat} program.
@smallexample
$ Messages for the famous greeting program.
$quote "
$set Main
Hello "Hallo, Welt!\n"
@end smallexample
Now we can start building the program (assume the message catalog source
file is named @file{hello.msg} and the program source file @file{hello.c}):
@smallexample
% gencat -H msgnrs.h -o hello.cat hello.msg
% cat msgnrs.h
#define MainSet 0x1 /* hello.msg:4 */
#define MainHello 0x1 /* hello.msg:5 */
% gcc -o hello hello.c -I.
% cp hello.cat /usr/share/locale/de/LC_MESSAGES
% echo $LC_ALL
de
% ./hello
Hallo, Welt!
%
@end smallexample
The call of the @code{gencat} program creates the missing header file
@file{msgnrs.h} as well as the message catalog binary. The former is
used in the compilation of @file{hello.c} while the later is placed in a
directory in which the @code{catopen} function will try to locate it.
Please check the @code{LC_ALL} environment variable and the default path
for @code{catopen} presented in the description above.
@node The Uniforum approach
@section The Uniforum approach to Message Translation
Sun Microsystems tried to standardize a different approach to message
translation in the Uniforum group. There never was a real standard
defined but still the interface was used in Sun's operating systems.
Since this approach fits better in the development process of free
software it is also used throughout the GNU project and the GNU
@file{gettext} package provides support for this outside @theglibc{}.
The code of the @file{libintl} from GNU @file{gettext} is the same as
the code in @theglibc{}. So the documentation in the GNU
@file{gettext} manual is also valid for the functionality here. The
following text will describe the library functions in detail. But the
numerous helper programs are not described in this manual. Instead
people should read the GNU @file{gettext} manual
(@pxref{Top,,GNU gettext utilities,gettext,Native Language Support Library and Tools}).
We will only give a short overview.
Though the @code{catgets} functions are available by default on more
systems the @code{gettext} interface is at least as portable as the
former. The GNU @file{gettext} package can be used wherever the
functions are not available.
@menu
* Message catalogs with gettext:: The @code{gettext} family of functions.
* Helper programs for gettext:: Programs to handle message catalogs
for @code{gettext}.
@end menu
@node Message catalogs with gettext
@subsection The @code{gettext} family of functions
The paradigms underlying the @code{gettext} approach to message
translations is different from that of the @code{catgets} functions the
basic functionally is equivalent. There are functions of the following
categories:
@menu
* Translation with gettext:: What has to be done to translate a message.
* Locating gettext catalog:: How to determine which catalog to be used.
* Advanced gettext functions:: Additional functions for more complicated
situations.
* Charset conversion in gettext:: How to specify the output character set
@code{gettext} uses.
* GUI program problems:: How to use @code{gettext} in GUI programs.
* Using gettextized software:: The possibilities of the user to influence
the way @code{gettext} works.
@end menu
@node Translation with gettext
@subsubsection What has to be done to translate a message?
The @code{gettext} functions have a very simple interface. The most
basic function just takes the string which shall be translated as the
argument and it returns the translation. This is fundamentally
different from the @code{catgets} approach where an extra key is
necessary and the original string is only used for the error case.
If the string which has to be translated is the only argument this of
course means the string itself is the key. I.e., the translation will
be selected based on the original string. The message catalogs must
therefore contain the original strings plus one translation for any such
string. The task of the @code{gettext} function is it to compare the
argument string with the available strings in the catalog and return the
appropriate translation. Of course this process is optimized so that
this process is not more expensive than an access using an atomic key
like in @code{catgets}.
The @code{gettext} approach has some advantages but also some
disadvantages. Please see the GNU @file{gettext} manual for a detailed
discussion of the pros and cons.
All the definitions and declarations for @code{gettext} can be found in
the @file{libintl.h} header file. On systems where these functions are
not part of the C library they can be found in a separate library named
@file{libintl.a} (or accordingly different for shared libraries).
@comment libintl.h
@comment GNU
@deftypefun {char *} gettext (const char *@var{msgid})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Wrapper for dcgettext.
The @code{gettext} function searches the currently selected message
catalogs for a string which is equal to @var{msgid}. If there is such a
string available it is returned. Otherwise the argument string
@var{msgid} is returned.
Please note that although the return value is @code{char *} the
returned string must not be changed. This broken type results from the
history of the function and does not reflect the way the function should
be used.
Please note that above we wrote ``message catalogs'' (plural). This is
a specialty of the GNU implementation of these functions and we will
say more about this when we talk about the ways message catalogs are
selected (@pxref{Locating gettext catalog}).
The @code{gettext} function does not modify the value of the global
@var{errno} variable. This is necessary to make it possible to write
something like
@smallexample
printf (gettext ("Operation failed: %m\n"));
@end smallexample
Here the @var{errno} value is used in the @code{printf} function while
processing the @code{%m} format element and if the @code{gettext}
function would change this value (it is called before @code{printf} is
called) we would get a wrong message.
So there is no easy way to detect a missing message catalog beside
comparing the argument string with the result. But it is normally the
task of the user to react on missing catalogs. The program cannot guess
when a message catalog is really necessary since for a user who speaks
the language the program was developed in does not need any translation.
@end deftypefun
The remaining two functions to access the message catalog add some
functionality to select a message catalog which is not the default one.
This is important if parts of the program are developed independently.
Every part can have its own message catalog and all of them can be used
at the same time. The C library itself is an example: internally it
uses the @code{gettext} functions but since it must not depend on a
currently selected default message catalog it must specify all ambiguous
information.
@comment libintl.h
@comment GNU
@deftypefun {char *} dgettext (const char *@var{domainname}, const char *@var{msgid})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Wrapper for dcgettext.
The @code{dgettext} functions acts just like the @code{gettext}
function. It only takes an additional first argument @var{domainname}
which guides the selection of the message catalogs which are searched
for the translation. If the @var{domainname} parameter is the null
pointer the @code{dgettext} function is exactly equivalent to
@code{gettext} since the default value for the domain name is used.
As for @code{gettext} the return value type is @code{char *} which is an
anachronism. The returned string must never be modified.
@end deftypefun
@comment libintl.h
@comment GNU
@deftypefun {char *} dcgettext (const char *@var{domainname}, const char *@var{msgid}, int @var{category})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c dcgettext @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c dcigettext @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c libc_rwlock_rdlock @asulock @aculock
@c current_locale_name ok [protected from @mtslocale]
@c tfind ok
@c libc_rwlock_unlock ok
@c plural_lookup ok
@c plural_eval ok
@c rawmemchr ok
@c DETERMINE_SECURE ok, nothing
@c strcmp ok
@c strlen ok
@c getcwd @ascuheap @acsmem @acsfd
@c strchr ok
@c stpcpy ok
@c category_to_name ok
@c guess_category_value @mtsenv
@c getenv @mtsenv
@c current_locale_name dup ok [protected from @mtslocale by dcigettext]
@c strcmp ok
@c ENABLE_SECURE ok
@c _nl_find_domain @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c libc_rwlock_rdlock dup @asulock @aculock
@c _nl_make_l10nflist dup @ascuheap @acsmem
@c libc_rwlock_unlock dup ok
@c _nl_load_domain @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock_recursive @aculock
@c libc_lock_unlock_recursive @aculock
@c open->open_not_cancel_2 @acsfd
@c fstat ok
@c mmap dup @acsmem
@c close->close_not_cancel_no_status @acsfd
@c malloc dup @ascuheap @acsmem
@c read->read_not_cancel ok
@c munmap dup @acsmem
@c W dup ok
@c strlen dup ok
@c get_sysdep_segment_value ok
@c memcpy dup ok
@c hash_string dup ok
@c free dup @ascuheap @acsmem
@c libc_rwlock_init ok
@c _nl_find_msg dup @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c libc_rwlock_fini ok
@c EXTRACT_PLURAL_EXPRESSION @ascuheap @acsmem
@c strstr dup ok
@c isspace ok
@c strtoul ok
@c PLURAL_PARSE @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c INIT_GERMANIC_PLURAL ok, nothing
@c the pre-C99 variant is @acucorrupt [protected from @mtuinit by dcigettext]
@c _nl_expand_alias dup @ascuheap @asulock @acsmem @acsfd @aculock
@c _nl_explode_name dup @ascuheap @acsmem
@c libc_rwlock_wrlock dup @asulock @aculock
@c free dup @asulock @aculock @acsfd @acsmem
@c _nl_find_msg @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c _nl_load_domain dup @mtsenv @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsfd @acsmem
@c strlen ok
@c hash_string ok
@c W ok
@c SWAP ok
@c bswap_32 ok
@c strcmp ok
@c get_output_charset @mtsenv @ascuheap @acsmem
@c getenv dup @mtsenv
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c memcpy dup ok
@c libc_rwlock_rdlock dup @asulock @aculock
@c libc_rwlock_unlock dup ok
@c libc_rwlock_wrlock dup @asulock @aculock
@c realloc @ascuheap @acsmem
@c strdup @ascuheap @acsmem
@c strstr ok
@c strcspn ok
@c mempcpy dup ok
@c norm_add_slashes dup ok
@c gconv_open @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
@c [protected from @mtslocale by dcigettext locale lock]
@c free dup @ascuheap @acsmem
@c libc_lock_lock @asulock @aculock
@c calloc @ascuheap @acsmem
@c gconv dup @acucorrupt [protected from @mtsrace and @asucorrupt by lock]
@c libc_lock_unlock ok
@c malloc @ascuheap @acsmem
@c mempcpy ok
@c memcpy ok
@c strcpy ok
@c libc_rwlock_wrlock @asulock @aculock
@c tsearch @ascuheap @acucorrupt @acsmem [protected from @mtsrace and @asucorrupt]
@c transcmp ok
@c strmp dup ok
@c free @ascuheap @acsmem
The @code{dcgettext} adds another argument to those which
@code{dgettext} takes. This argument @var{category} specifies the last
piece of information needed to localize the message catalog. I.e., the
domain name and the locale category exactly specify which message
catalog has to be used (relative to a given directory, see below).
The @code{dgettext} function can be expressed in terms of
@code{dcgettext} by using
@smallexample
dcgettext (domain, string, LC_MESSAGES)
@end smallexample
@noindent
instead of
@smallexample
dgettext (domain, string)
@end smallexample
This also shows which values are expected for the third parameter. One
has to use the available selectors for the categories available in
@file{locale.h}. Normally the available values are @code{LC_CTYPE},
@code{LC_COLLATE}, @code{LC_MESSAGES}, @code{LC_MONETARY},
@code{LC_NUMERIC}, and @code{LC_TIME}. Please note that @code{LC_ALL}
must not be used and even though the names might suggest this, there is
no relation to the environments variables of this name.
The @code{dcgettext} function is only implemented for compatibility with
other systems which have @code{gettext} functions. There is not really
any situation where it is necessary (or useful) to use a different value
but @code{LC_MESSAGES} in for the @var{category} parameter. We are
dealing with messages here and any other choice can only be irritating.
As for @code{gettext} the return value type is @code{char *} which is an
anachronism. The returned string must never be modified.
@end deftypefun
When using the three functions above in a program it is a frequent case
that the @var{msgid} argument is a constant string. So it is worth to
optimize this case. Thinking shortly about this one will realize that
as long as no new message catalog is loaded the translation of a message
will not change. This optimization is actually implemented by the
@code{gettext}, @code{dgettext} and @code{dcgettext} functions.
@node Locating gettext catalog
@subsubsection How to determine which catalog to be used
The functions to retrieve the translations for a given message have a
remarkable simple interface. But to provide the user of the program
still the opportunity to select exactly the translation s/he wants and
also to provide the programmer the possibility to influence the way to
locate the search for catalogs files there is a quite complicated
underlying mechanism which controls all this. The code is complicated
the use is easy.
Basically we have two different tasks to perform which can also be
performed by the @code{catgets} functions:
@enumerate
@item
Locate the set of message catalogs. There are a number of files for
different languages and which all belong to the package. Usually they
are all stored in the filesystem below a certain directory.
There can be arbitrary many packages installed and they can follow
different guidelines for the placement of their files.
@item
Relative to the location specified by the package the actual translation
files must be searched, based on the wishes of the user. I.e., for each
language the user selects the program should be able to locate the
appropriate file.
@end enumerate
This is the functionality required by the specifications for
@code{gettext} and this is also what the @code{catgets} functions are
able to do. But there are some problems unresolved:
@itemize @bullet
@item
The language to be used can be specified in several different ways.
There is no generally accepted standard for this and the user always
expects the program understand what s/he means. E.g., to select the
German translation one could write @code{de}, @code{german}, or
@code{deutsch} and the program should always react the same.
@item
Sometimes the specification of the user is too detailed. If s/he, e.g.,
specifies @code{de_DE.ISO-8859-1} which means German, spoken in Germany,
coded using the @w{ISO 8859-1} character set there is the possibility
that a message catalog matching this exactly is not available. But
there could be a catalog matching @code{de} and if the character set
used on the machine is always @w{ISO 8859-1} there is no reason why this
later message catalog should not be used. (We call this @dfn{message
inheritance}.)
@item
If a catalog for a wanted language is not available it is not always the
second best choice to fall back on the language of the developer and
simply not translate any message. Instead a user might be better able
to read the messages in another language and so the user of the program
should be able to define a precedence order of languages.
@end itemize
We can divide the configuration actions in two parts: the one is
performed by the programmer, the other by the user. We will start with
the functions the programmer can use since the user configuration will
be based on this.
As the functions described in the last sections already mention separate
sets of messages can be selected by a @dfn{domain name}. This is a
simple string which should be unique for each program part with uses a
separate domain. It is possible to use in one program arbitrary many
domains at the same time. E.g., @theglibc{} itself uses a domain
named @code{libc} while the program using the C Library could use a
domain named @code{foo}. The important point is that at any time
exactly one domain is active. This is controlled with the following
function.
@comment libintl.h
@comment GNU
@deftypefun {char *} textdomain (const char *@var{domainname})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{}}}
@c textdomain @asulock @ascuheap @aculock @acsmem
@c libc_rwlock_wrlock @asulock @aculock
@c strcmp ok
@c strdup @ascuheap @acsmem
@c free @ascuheap @acsmem
@c libc_rwlock_unlock ok
The @code{textdomain} function sets the default domain, which is used in
all future @code{gettext} calls, to @var{domainname}. Please note that
@code{dgettext} and @code{dcgettext} calls are not influenced if the
@var{domainname} parameter of these functions is not the null pointer.
Before the first call to @code{textdomain} the default domain is
@code{messages}. This is the name specified in the specification of
the @code{gettext} API. This name is as good as any other name. No
program should ever really use a domain with this name since this can
only lead to problems.
The function returns the value which is from now on taken as the default
domain. If the system went out of memory the returned value is
@code{NULL} and the global variable @var{errno} is set to @code{ENOMEM}.
Despite the return value type being @code{char *} the return string must
not be changed. It is allocated internally by the @code{textdomain}
function.
If the @var{domainname} parameter is the null pointer no new default
domain is set. Instead the currently selected default domain is
returned.
If the @var{domainname} parameter is the empty string the default domain
is reset to its initial value, the domain with the name @code{messages}.
This possibility is questionable to use since the domain @code{messages}
really never should be used.
@end deftypefun
@comment libintl.h
@comment GNU
@deftypefun {char *} bindtextdomain (const char *@var{domainname}, const char *@var{dirname})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c bindtextdomain @ascuheap @acsmem
@c set_binding_values @ascuheap @acsmem
@c libc_rwlock_wrlock dup @asulock @aculock
@c strcmp dup ok
@c strdup dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
The @code{bindtextdomain} function can be used to specify the directory
which contains the message catalogs for domain @var{domainname} for the
different languages. To be correct, this is the directory where the
hierarchy of directories is expected. Details are explained below.
For the programmer it is important to note that the translations which
come with the program have be placed in a directory hierarchy starting
at, say, @file{/foo/bar}. Then the program should make a
@code{bindtextdomain} call to bind the domain for the current program to
this directory. So it is made sure the catalogs are found. A correctly
running program does not depend on the user setting an environment
variable.
The @code{bindtextdomain} function can be used several times and if the
@var{domainname} argument is different the previously bound domains
will not be overwritten.
If the program which wish to use @code{bindtextdomain} at some point of
time use the @code{chdir} function to change the current working
directory it is important that the @var{dirname} strings ought to be an
absolute pathname. Otherwise the addressed directory might vary with
the time.
If the @var{dirname} parameter is the null pointer @code{bindtextdomain}
returns the currently selected directory for the domain with the name
@var{domainname}.
The @code{bindtextdomain} function returns a pointer to a string
containing the name of the selected directory name. The string is
allocated internally in the function and must not be changed by the
user. If the system went out of core during the execution of
@code{bindtextdomain} the return value is @code{NULL} and the global
variable @var{errno} is set accordingly.
@end deftypefun
@node Advanced gettext functions
@subsubsection Additional functions for more complicated situations
The functions of the @code{gettext} family described so far (and all the
@code{catgets} functions as well) have one problem in the real world
which have been neglected completely in all existing approaches. What
is meant here is the handling of plural forms.
Looking through Unix source code before the time anybody thought about
internationalization (and, sadly, even afterwards) one can often find
code similar to the following:
@smallexample
printf ("%d file%s deleted", n, n == 1 ? "" : "s");
@end smallexample
@noindent
After the first complaints from people internationalizing the code people
either completely avoided formulations like this or used strings like
@code{"file(s)"}. Both look unnatural and should be avoided. First
tries to solve the problem correctly looked like this:
@smallexample
if (n == 1)
printf ("%d file deleted", n);
else
printf ("%d files deleted", n);
@end smallexample
But this does not solve the problem. It helps languages where the
plural form of a noun is not simply constructed by adding an `s' but
that is all. Once again people fell into the trap of believing the
rules their language is using are universal. But the handling of plural
forms differs widely between the language families. There are two
things we can differ between (and even inside language families);
@itemize @bullet
@item
The form how plural forms are build differs. This is a problem with
language which have many irregularities. German, for instance, is a
drastic case. Though English and German are part of the same language
family (Germanic), the almost regular forming of plural noun forms
(appending an `s') is hardly found in German.
@item
The number of plural forms differ. This is somewhat surprising for
those who only have experiences with Romanic and Germanic languages
since here the number is the same (there are two).
But other language families have only one form or many forms. More
information on this in an extra section.
@end itemize
The consequence of this is that application writers should not try to
solve the problem in their code. This would be localization since it is
only usable for certain, hardcoded language environments. Instead the
extended @code{gettext} interface should be used.
These extra functions are taking instead of the one key string two
strings and a numerical argument. The idea behind this is that using
the numerical argument and the first string as a key, the implementation
can select using rules specified by the translator the right plural
form. The two string arguments then will be used to provide a return
value in case no message catalog is found (similar to the normal
@code{gettext} behavior). In this case the rules for Germanic language
is used and it is assumed that the first string argument is the singular
form, the second the plural form.
This has the consequence that programs without language catalogs can
display the correct strings only if the program itself is written using
a Germanic language. This is a limitation but since @theglibc{}
(as well as the GNU @code{gettext} package) are written as part of the
GNU package and the coding standards for the GNU project require program
being written in English, this solution nevertheless fulfills its
purpose.
@comment libintl.h
@comment GNU
@deftypefun {char *} ngettext (const char *@var{msgid1}, const char *@var{msgid2}, unsigned long int @var{n})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Wrapper for dcngettext.
The @code{ngettext} function is similar to the @code{gettext} function
as it finds the message catalogs in the same way. But it takes two
extra arguments. The @var{msgid1} parameter must contain the singular
form of the string to be converted. It is also used as the key for the
search in the catalog. The @var{msgid2} parameter is the plural form.
The parameter @var{n} is used to determine the plural form. If no
message catalog is found @var{msgid1} is returned if @code{n == 1},
otherwise @code{msgid2}.
An example for the us of this function is:
@smallexample
printf (ngettext ("%d file removed", "%d files removed", n), n);
@end smallexample
Please note that the numeric value @var{n} has to be passed to the
@code{printf} function as well. It is not sufficient to pass it only to
@code{ngettext}.
@end deftypefun
@comment libintl.h
@comment GNU
@deftypefun {char *} dngettext (const char *@var{domain}, const char *@var{msgid1}, const char *@var{msgid2}, unsigned long int @var{n})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Wrapper for dcngettext.
The @code{dngettext} is similar to the @code{dgettext} function in the
way the message catalog is selected. The difference is that it takes
two extra parameter to provide the correct plural form. These two
parameters are handled in the same way @code{ngettext} handles them.
@end deftypefun
@comment libintl.h
@comment GNU
@deftypefun {char *} dcngettext (const char *@var{domain}, const char *@var{msgid1}, const char *@var{msgid2}, unsigned long int @var{n}, int @var{category})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Wrapper for dcigettext.
The @code{dcngettext} is similar to the @code{dcgettext} function in the
way the message catalog is selected. The difference is that it takes
two extra parameter to provide the correct plural form. These two
parameters are handled in the same way @code{ngettext} handles them.
@end deftypefun
@subsubheading The problem of plural forms
A description of the problem can be found at the beginning of the last
section. Now there is the question how to solve it. Without the input
of linguists (which was not available) it was not possible to determine
whether there are only a few different forms in which plural forms are
formed or whether the number can increase with every new supported
language.
Therefore the solution implemented is to allow the translator to specify
the rules of how to select the plural form. Since the formula varies
with every language this is the only viable solution except for
hardcoding the information in the code (which still would require the
possibility of extensions to not prevent the use of new languages). The
details are explained in the GNU @code{gettext} manual. Here only a
bit of information is provided.
The information about the plural form selection has to be stored in the
header entry (the one with the empty (@code{msgid} string). It looks
like this:
@smallexample
Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;
@end smallexample
The @code{nplurals} value must be a decimal number which specifies how
many different plural forms exist for this language. The string
following @code{plural} is an expression which is using the C language
syntax. Exceptions are that no negative number are allowed, numbers
must be decimal, and the only variable allowed is @code{n}. This
expression will be evaluated whenever one of the functions
@code{ngettext}, @code{dngettext}, or @code{dcngettext} is called. The
numeric value passed to these functions is then substituted for all uses
of the variable @code{n} in the expression. The resulting value then
must be greater or equal to zero and smaller than the value given as the
value of @code{nplurals}.
@noindent
The following rules are known at this point. The language with families
are listed. But this does not necessarily mean the information can be
generalized for the whole family (as can be easily seen in the table
below).@footnote{Additions are welcome. Send appropriate information to
@email{bug-glibc-manual@@gnu.org}.}
@table @asis
@item Only one form:
Some languages only require one single form. There is no distinction
between the singular and plural form. An appropriate header entry
would look like this:
@smallexample
Plural-Forms: nplurals=1; plural=0;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Finno-Ugric family
Hungarian
@item Asian family
Japanese, Korean
@item Turkic/Altaic family
Turkish
@end table
@item Two forms, singular used for one only
This is the form used in most existing programs since it is what English
is using. A header entry would look like this:
@smallexample
Plural-Forms: nplurals=2; plural=n != 1;
@end smallexample
(Note: this uses the feature of C expressions that boolean expressions
have to value zero or one.)
@noindent
Languages with this property include:
@table @asis
@item Germanic family
Danish, Dutch, English, German, Norwegian, Swedish
@item Finno-Ugric family
Estonian, Finnish
@item Latin/Greek family
Greek
@item Semitic family
Hebrew
@item Romance family
Italian, Portuguese, Spanish
@item Artificial
Esperanto
@end table
@item Two forms, singular used for zero and one
Exceptional case in the language family. The header entry would be:
@smallexample
Plural-Forms: nplurals=2; plural=n>1;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Romanic family
French, Brazilian Portuguese
@end table
@item Three forms, special case for zero
The header entry would be:
@smallexample
Plural-Forms: nplurals=3; plural=n%10==1 && n%100!=11 ? 0 : n != 0 ? 1 : 2;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Baltic family
Latvian
@end table
@item Three forms, special cases for one and two
The header entry would be:
@smallexample
Plural-Forms: nplurals=3; plural=n==1 ? 0 : n==2 ? 1 : 2;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Celtic
Gaeilge (Irish)
@end table
@item Three forms, special case for numbers ending in 1[2-9]
The header entry would look like this:
@smallexample
Plural-Forms: nplurals=3; \
plural=n%10==1 && n%100!=11 ? 0 : \
n%10>=2 && (n%100<10 || n%100>=20) ? 1 : 2;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Baltic family
Lithuanian
@end table
@item Three forms, special cases for numbers ending in 1 and 2, 3, 4, except those ending in 1[1-4]
The header entry would look like this:
@smallexample
Plural-Forms: nplurals=3; \
plural=n%100/10==1 ? 2 : n%10==1 ? 0 : (n+9)%10>3 ? 2 : 1;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Slavic family
Croatian, Czech, Russian, Ukrainian
@end table
@item Three forms, special cases for 1 and 2, 3, 4
The header entry would look like this:
@smallexample
Plural-Forms: nplurals=3; \
plural=(n==1) ? 1 : (n>=2 && n<=4) ? 2 : 0;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Slavic family
Slovak
@end table
@item Three forms, special case for one and some numbers ending in 2, 3, or 4
The header entry would look like this:
@smallexample
Plural-Forms: nplurals=3; \
plural=n==1 ? 0 : \
n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Slavic family
Polish
@end table
@item Four forms, special case for one and all numbers ending in 02, 03, or 04
The header entry would look like this:
@smallexample
Plural-Forms: nplurals=4; \
plural=n%100==1 ? 0 : n%100==2 ? 1 : n%100==3 || n%100==4 ? 2 : 3;
@end smallexample
@noindent
Languages with this property include:
@table @asis
@item Slavic family
Slovenian
@end table
@end table
@node Charset conversion in gettext
@subsubsection How to specify the output character set @code{gettext} uses
@code{gettext} not only looks up a translation in a message catalog. It
also converts the translation on the fly to the desired output character
set. This is useful if the user is working in a different character set
than the translator who created the message catalog, because it avoids
distributing variants of message catalogs which differ only in the
character set.
The output character set is, by default, the value of @code{nl_langinfo
(CODESET)}, which depends on the @code{LC_CTYPE} part of the current
locale. But programs which store strings in a locale independent way
(e.g. UTF-8) can request that @code{gettext} and related functions
return the translations in that encoding, by use of the
@code{bind_textdomain_codeset} function.
Note that the @var{msgid} argument to @code{gettext} is not subject to
character set conversion. Also, when @code{gettext} does not find a
translation for @var{msgid}, it returns @var{msgid} unchanged --
independently of the current output character set. It is therefore
recommended that all @var{msgid}s be US-ASCII strings.
@comment libintl.h
@comment GNU
@deftypefun {char *} bind_textdomain_codeset (const char *@var{domainname}, const char *@var{codeset})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c bind_textdomain_codeset @ascuheap @acsmem
@c set_binding_values dup @ascuheap @acsmem
The @code{bind_textdomain_codeset} function can be used to specify the
output character set for message catalogs for domain @var{domainname}.
The @var{codeset} argument must be a valid codeset name which can be used
for the @code{iconv_open} function, or a null pointer.
If the @var{codeset} parameter is the null pointer,
@code{bind_textdomain_codeset} returns the currently selected codeset
for the domain with the name @var{domainname}. It returns @code{NULL} if
no codeset has yet been selected.
The @code{bind_textdomain_codeset} function can be used several times.
If used multiple times with the same @var{domainname} argument, the
later call overrides the settings made by the earlier one.
The @code{bind_textdomain_codeset} function returns a pointer to a
string containing the name of the selected codeset. The string is
allocated internally in the function and must not be changed by the
user. If the system went out of core during the execution of
@code{bind_textdomain_codeset}, the return value is @code{NULL} and the
global variable @var{errno} is set accordingly.
@end deftypefun
@node GUI program problems
@subsubsection How to use @code{gettext} in GUI programs
One place where the @code{gettext} functions, if used normally, have big
problems is within programs with graphical user interfaces (GUIs). The
problem is that many of the strings which have to be translated are very
short. They have to appear in pull-down menus which restricts the
length. But strings which are not containing entire sentences or at
least large fragments of a sentence may appear in more than one
situation in the program but might have different translations. This is
especially true for the one-word strings which are frequently used in
GUI programs.
As a consequence many people say that the @code{gettext} approach is
wrong and instead @code{catgets} should be used which indeed does not
have this problem. But there is a very simple and powerful method to
handle these kind of problems with the @code{gettext} functions.
@noindent
As an example consider the following fictional situation. A GUI program
has a menu bar with the following entries:
@smallexample
+------------+------------+--------------------------------------+
| File | Printer | |
+------------+------------+--------------------------------------+
| Open | | Select |
| New | | Open |
+----------+ | Connect |
+----------+
@end smallexample
To have the strings @code{File}, @code{Printer}, @code{Open},
@code{New}, @code{Select}, and @code{Connect} translated there has to be
at some point in the code a call to a function of the @code{gettext}
family. But in two places the string passed into the function would be
@code{Open}. The translations might not be the same and therefore we
are in the dilemma described above.
One solution to this problem is to artificially enlengthen the strings
to make them unambiguous. But what would the program do if no
translation is available? The enlengthened string is not what should be
printed. So we should use a little bit modified version of the functions.
To enlengthen the strings a uniform method should be used. E.g., in the
example above the strings could be chosen as
@smallexample
Menu|File
Menu|Printer
Menu|File|Open
Menu|File|New
Menu|Printer|Select
Menu|Printer|Open
Menu|Printer|Connect
@end smallexample
Now all the strings are different and if now instead of @code{gettext}
the following little wrapper function is used, everything works just
fine:
@cindex sgettext
@smallexample
char *
sgettext (const char *msgid)
@{
char *msgval = gettext (msgid);
if (msgval == msgid)
msgval = strrchr (msgid, '|') + 1;
return msgval;
@}
@end smallexample
What this little function does is to recognize the case when no
translation is available. This can be done very efficiently by a
pointer comparison since the return value is the input value. If there
is no translation we know that the input string is in the format we used
for the Menu entries and therefore contains a @code{|} character. We
simply search for the last occurrence of this character and return a
pointer to the character following it. That's it!
If one now consistently uses the enlengthened string form and replaces
the @code{gettext} calls with calls to @code{sgettext} (this is normally
limited to very few places in the GUI implementation) then it is
possible to produce a program which can be internationalized.
With advanced compilers (such as GNU C) one can write the
@code{sgettext} functions as an inline function or as a macro like this:
@cindex sgettext
@smallexample
#define sgettext(msgid) \
(@{ const char *__msgid = (msgid); \
char *__msgstr = gettext (__msgid); \
if (__msgval == __msgid) \
__msgval = strrchr (__msgid, '|') + 1; \
__msgval; @})
@end smallexample
The other @code{gettext} functions (@code{dgettext}, @code{dcgettext}
and the @code{ngettext} equivalents) can and should have corresponding
functions as well which look almost identical, except for the parameters
and the call to the underlying function.
Now there is of course the question why such functions do not exist in
@theglibc{}? There are two parts of the answer to this question.
@itemize @bullet
@item
They are easy to write and therefore can be provided by the project they
are used in. This is not an answer by itself and must be seen together
with the second part which is:
@item
There is no way the C library can contain a version which can work
everywhere. The problem is the selection of the character to separate
the prefix from the actual string in the enlenghtened string. The
examples above used @code{|} which is a quite good choice because it
resembles a notation frequently used in this context and it also is a
character not often used in message strings.
But what if the character is used in message strings. Or if the chose
character is not available in the character set on the machine one
compiles (e.g., @code{|} is not required to exist for @w{ISO C}; this is
why the @file{iso646.h} file exists in @w{ISO C} programming environments).
@end itemize
There is only one more comment to make left. The wrapper function above
require that the translations strings are not enlengthened themselves.
This is only logical. There is no need to disambiguate the strings
(since they are never used as keys for a search) and one also saves
quite some memory and disk space by doing this.
@node Using gettextized software
@subsubsection User influence on @code{gettext}
The last sections described what the programmer can do to
internationalize the messages of the program. But it is finally up to
the user to select the message s/he wants to see. S/He must understand
them.
The POSIX locale model uses the environment variables @code{LC_COLLATE},
@code{LC_CTYPE}, @code{LC_MESSAGES}, @code{LC_MONETARY}, @code{LC_NUMERIC},
and @code{LC_TIME} to select the locale which is to be used. This way
the user can influence lots of functions. As we mentioned above the
@code{gettext} functions also take advantage of this.
To understand how this happens it is necessary to take a look at the
various components of the filename which gets computed to locate a
message catalog. It is composed as follows:
@smallexample
@var{dir_name}/@var{locale}/LC_@var{category}/@var{domain_name}.mo
@end smallexample
The default value for @var{dir_name} is system specific. It is computed
from the value given as the prefix while configuring the C library.
This value normally is @file{/usr} or @file{/}. For the former the
complete @var{dir_name} is:
@smallexample
/usr/share/locale
@end smallexample
We can use @file{/usr/share} since the @file{.mo} files containing the
message catalogs are system independent, so all systems can use the same
files. If the program executed the @code{bindtextdomain} function for
the message domain that is currently handled, the @code{dir_name}
component is exactly the value which was given to the function as
the second parameter. I.e., @code{bindtextdomain} allows overwriting
the only system dependent and fixed value to make it possible to
address files anywhere in the filesystem.
The @var{category} is the name of the locale category which was selected
in the program code. For @code{gettext} and @code{dgettext} this is
always @code{LC_MESSAGES}, for @code{dcgettext} this is selected by the
value of the third parameter. As said above it should be avoided to
ever use a category other than @code{LC_MESSAGES}.
The @var{locale} component is computed based on the category used. Just
like for the @code{setlocale} function here comes the user selection
into the play. Some environment variables are examined in a fixed order
and the first environment variable set determines the return value of
the lookup process. In detail, for the category @code{LC_xxx} the
following variables in this order are examined:
@table @code
@item LANGUAGE
@item LC_ALL
@item LC_xxx
@item LANG
@end table
This looks very familiar. With the exception of the @code{LANGUAGE}
environment variable this is exactly the lookup order the
@code{setlocale} function uses. But why introducing the @code{LANGUAGE}
variable?
The reason is that the syntax of the values these variables can have is
different to what is expected by the @code{setlocale} function. If we
would set @code{LC_ALL} to a value following the extended syntax that
would mean the @code{setlocale} function will never be able to use the
value of this variable as well. An additional variable removes this
problem plus we can select the language independently of the locale
setting which sometimes is useful.
While for the @code{LC_xxx} variables the value should consist of
exactly one specification of a locale the @code{LANGUAGE} variable's
value can consist of a colon separated list of locale names. The
attentive reader will realize that this is the way we manage to
implement one of our additional demands above: we want to be able to
specify an ordered list of language.
Back to the constructed filename we have only one component missing.
The @var{domain_name} part is the name which was either registered using
the @code{textdomain} function or which was given to @code{dgettext} or
@code{dcgettext} as the first parameter. Now it becomes obvious that a
good choice for the domain name in the program code is a string which is
closely related to the program/package name. E.g., for @theglibc{}
the domain name is @code{libc}.
@noindent
A limit piece of example code should show how the programmer is supposed
to work:
@smallexample
@{
setlocale (LC_ALL, "");
textdomain ("test-package");
bindtextdomain ("test-package", "/usr/local/share/locale");
puts (gettext ("Hello, world!"));
@}
@end smallexample
At the program start the default domain is @code{messages}, and the
default locale is "C". The @code{setlocale} call sets the locale
according to the user's environment variables; remember that correct
functioning of @code{gettext} relies on the correct setting of the
@code{LC_MESSAGES} locale (for looking up the message catalog) and
of the @code{LC_CTYPE} locale (for the character set conversion).
The @code{textdomain} call changes the default domain to
@code{test-package}. The @code{bindtextdomain} call specifies that
the message catalogs for the domain @code{test-package} can be found
below the directory @file{/usr/local/share/locale}.
If now the user set in her/his environment the variable @code{LANGUAGE}
to @code{de} the @code{gettext} function will try to use the
translations from the file
@smallexample
/usr/local/share/locale/de/LC_MESSAGES/test-package.mo
@end smallexample
From the above descriptions it should be clear which component of this
filename is determined by which source.
In the above example we assumed that the @code{LANGUAGE} environment
variable to @code{de}. This might be an appropriate selection but what
happens if the user wants to use @code{LC_ALL} because of the wider
usability and here the required value is @code{de_DE.ISO-8859-1}? We
already mentioned above that a situation like this is not infrequent.
E.g., a person might prefer reading a dialect and if this is not
available fall back on the standard language.
The @code{gettext} functions know about situations like this and can
handle them gracefully. The functions recognize the format of the value
of the environment variable. It can split the value is different pieces
and by leaving out the only or the other part it can construct new
values. This happens of course in a predictable way. To understand
this one must know the format of the environment variable value. There
is one more or less standardized form, originally from the X/Open
specification:
@code{language[_territory[.codeset]][@@modifier]}
Less specific locale names will be stripped of in the order of the
following list:
@enumerate
@item
@code{codeset}
@item
@code{normalized codeset}
@item
@code{territory}
@item
@code{modifier}
@end enumerate
The @code{language} field will never be dropped for obvious reasons.
The only new thing is the @code{normalized codeset} entry. This is
another goodie which is introduced to help reducing the chaos which
derives from the inability of the people to standardize the names of
character sets. Instead of @w{ISO-8859-1} one can often see @w{8859-1},
@w{88591}, @w{iso8859-1}, or @w{iso_8859-1}. The @code{normalized
codeset} value is generated from the user-provided character set name by
applying the following rules:
@enumerate
@item
Remove all characters beside numbers and letters.
@item
Fold letters to lowercase.
@item
If the same only contains digits prepend the string @code{"iso"}.
@end enumerate
@noindent
So all of the above name will be normalized to @code{iso88591}. This
allows the program user much more freely choosing the locale name.
Even this extended functionality still does not help to solve the
problem that completely different names can be used to denote the same
locale (e.g., @code{de} and @code{german}). To be of help in this
situation the locale implementation and also the @code{gettext}
functions know about aliases.
The file @file{/usr/share/locale/locale.alias} (replace @file{/usr} with
whatever prefix you used for configuring the C library) contains a
mapping of alternative names to more regular names. The system manager
is free to add new entries to fill her/his own needs. The selected
locale from the environment is compared with the entries in the first
column of this file ignoring the case. If they match the value of the
second column is used instead for the further handling.
In the description of the format of the environment variables we already
mentioned the character set as a factor in the selection of the message
catalog. In fact, only catalogs which contain text written using the
character set of the system/program can be used (directly; there will
come a solution for this some day). This means for the user that s/he
will always have to take care for this. If in the collection of the
message catalogs there are files for the same language but coded using
different character sets the user has to be careful.
@node Helper programs for gettext
@subsection Programs to handle message catalogs for @code{gettext}
@Theglibc{} does not contain the source code for the programs to
handle message catalogs for the @code{gettext} functions. As part of
the GNU project the GNU gettext package contains everything the
developer needs. The functionality provided by the tools in this
package by far exceeds the abilities of the @code{gencat} program
described above for the @code{catgets} functions.
There is a program @code{msgfmt} which is the equivalent program to the
@code{gencat} program. It generates from the human-readable and
-editable form of the message catalog a binary file which can be used by
the @code{gettext} functions. But there are several more programs
available.
The @code{xgettext} program can be used to automatically extract the
translatable messages from a source file. I.e., the programmer need not
take care of the translations and the list of messages which have to be
translated. S/He will simply wrap the translatable string in calls to
@code{gettext} et.al and the rest will be done by @code{xgettext}. This
program has a lot of options which help to customize the output or
help to understand the input better.
Other programs help to manage the development cycle when new messages appear
in the source files or when a new translation of the messages appears.
Here it should only be noted that using all the tools in GNU gettext it
is possible to @emph{completely} automate the handling of message
catalogs. Beside marking the translatable strings in the source code and
generating the translations the developers do not have anything to do
themselves.
glibc-doc-reference-2.19.orig/manual/debug.texi 0000664 0001750 0001750 00000015031 12275120646 021540 0 ustar adconrad adconrad @node Debugging Support
@c @node Debugging Support, POSIX Threads, Cryptographic Functions, Top
@c %MENU% Functions to help debugging applications
@chapter Debugging support
Applications are usually debugged using dedicated debugger programs.
But sometimes this is not possible and, in any case, it is useful to
provide the developer with as much information as possible at the time
the problems are experienced. For this reason a few functions are
provided which a program can use to help the developer more easily
locate the problem.
@menu
* Backtraces:: Obtaining and printing a back trace of the
current stack.
@end menu
@node Backtraces, , , Debugging Support
@section Backtraces
@cindex backtrace
@cindex backtrace_symbols
@cindex backtrace_fd
A @dfn{backtrace} is a list of the function calls that are currently
active in a thread. The usual way to inspect a backtrace of a program
is to use an external debugger such as gdb. However, sometimes it is
useful to obtain a backtrace programmatically from within a program,
e.g., for the purposes of logging or diagnostics.
The header file @file{execinfo.h} declares three functions that obtain
and manipulate backtraces of the current thread.
@pindex execinfo.h
@comment execinfo.h
@comment GNU
@deftypefun int backtrace (void **@var{buffer}, int @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asuinit{} @ascuheap{} @ascudlopen{} @ascuplugin{} @asulock{}}@acunsafe{@acuinit{} @acsmem{} @aculock{} @acsfd{}}}
@c The generic implementation just does pointer chasing within the local
@c stack, without any guarantees that this will handle signal frames
@c correctly, so it's AS-Unsafe to begin with. However, most (all?)
@c arches defer to libgcc_s's _Unwind_* implementation, dlopening
@c libgcc_s.so to that end except in a static version of libc.
@c libgcc_s's implementation may in turn defer to libunwind. We can't
@c assume those implementations are AS- or AC-safe, but even if we
@c could, our own initialization path isn't, and libgcc's implementation
@c calls malloc and performs internal locking, so...
The @code{backtrace} function obtains a backtrace for the current
thread, as a list of pointers, and places the information into
@var{buffer}. The argument @var{size} should be the number of
@w{@code{void *}} elements that will fit into @var{buffer}. The return
value is the actual number of entries of @var{buffer} that are obtained,
and is at most @var{size}.
The pointers placed in @var{buffer} are actually return addresses
obtained by inspecting the stack, one return address per stack frame.
Note that certain compiler optimizations may interfere with obtaining a
valid backtrace. Function inlining causes the inlined function to not
have a stack frame; tail call optimization replaces one stack frame with
another; frame pointer elimination will stop @code{backtrace} from
interpreting the stack contents correctly.
@end deftypefun
@comment execinfo.h
@comment GNU
@deftypefun {char **} backtrace_symbols (void *const *@var{buffer}, int @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @aculock{}}}
@c Collects info returned by _dl_addr in an auto array, allocates memory
@c for the whole return buffer with malloc then sprintfs into it storing
@c pointers to the strings into the array entries in the buffer.
@c _dl_addr takes the recursive dl_load_lock then calls
@c _dl_find_dso_for_object and determine_info.
@c _dl_find_dso_for_object calls _dl-addr_inside_object.
@c All of them are safe as long as the lock is held.
@c @asucorrupt? It doesn't look like the dynamic loader's data
@c structures could be in an inconsistent state that would cause
@c malfunction here.
The @code{backtrace_symbols} function translates the information
obtained from the @code{backtrace} function into an array of strings.
The argument @var{buffer} should be a pointer to an array of addresses
obtained via the @code{backtrace} function, and @var{size} is the number
of entries in that array (the return value of @code{backtrace}).
The return value is a pointer to an array of strings, which has
@var{size} entries just like the array @var{buffer}. Each string
contains a printable representation of the corresponding element of
@var{buffer}. It includes the function name (if this can be
determined), an offset into the function, and the actual return address
(in hexadecimal).
Currently, the function name and offset only be obtained on systems that
use the ELF binary format for programs and libraries. On other systems,
only the hexadecimal return address will be present. Also, you may need
to pass additional flags to the linker to make the function names
available to the program. (For example, on systems using GNU ld, you
must pass (@code{-rdynamic}.)
The return value of @code{backtrace_symbols} is a pointer obtained via
the @code{malloc} function, and it is the responsibility of the caller
to @code{free} that pointer. Note that only the return value need be
freed, not the individual strings.
The return value is @code{NULL} if sufficient memory for the strings
cannot be obtained.
@end deftypefun
@comment execinfo.h
@comment GNU
@deftypefun void backtrace_symbols_fd (void *const *@var{buffer}, int @var{size}, int @var{fd})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@aculock{}}}
@c Single loop of _dl_addr over addresses, collecting info into an iovec
@c written out with a writev call per iteration. Addresses and offsets
@c are converted to hex in auto buffers, so the only potential issue
@c here is leaking the dl lock in case of cancellation.
The @code{backtrace_symbols_fd} function performs the same translation
as the function @code{backtrace_symbols} function. Instead of returning
the strings to the caller, it writes the strings to the file descriptor
@var{fd}, one per line. It does not use the @code{malloc} function, and
can therefore be used in situations where that function might fail.
@end deftypefun
The following program illustrates the use of these functions. Note that
the array to contain the return addresses returned by @code{backtrace}
is allocated on the stack. Therefore code like this can be used in
situations where the memory handling via @code{malloc} does not work
anymore (in which case the @code{backtrace_symbols} has to be replaced
by a @code{backtrace_symbols_fd} call as well). The number of return
addresses is normally not very large. Even complicated programs rather
seldom have a nesting level of more than, say, 50 and with 200 possible
entries probably all programs should be covered.
@smallexample
@include execinfo.c.texi
@end smallexample
glibc-doc-reference-2.19.orig/manual/libc-texinfo.sh 0000664 0001750 0001750 00000005170 12275120646 022501 0 ustar adconrad adconrad #! /bin/sh
OUTDIR=$1
shift
# Create libc.texinfo from the chapter files.
trap "rm -f ${OUTDIR}*.$$; exit 1" 1 2 15
exec 3>${OUTDIR}incl.$$ 4>${OUTDIR}smenu.$$ 5>${OUTDIR}lmenu.$$
build_menu () {
while IFS=: read file node; do
echo "@include $file" >&3
echo "* $node:: `sed -n 's/^@c %MENU% //p' $file`" >&4
$AWK 'BEGIN { do_menu = 0 }
/^@node / { sub(/^@node /, ""); sub(/,.*$/, ""); node = $0 }
/^@menu/ { printf "\n%s\n\n", node; do_menu = 1; next }
/^@end menu/ { do_menu = 0 }
do_menu { print }' $file >&5
done
}
collect_nodes () {
egrep '^(@c )?@node.*Top' "$@" /dev/null | cut -d, -f-2 |
sed 's/@c //; s/, /:/; s/:@node /:/; s/ /_/g; s/:/ /g' |
$AWK '{ file[$2] = $1; nnode[$2] = $3 }
END { for (x in file)
if (file[x] != "")
print file[x] ":" x, file[nnode[x]] ":" nnode[x] }' |
$AWK -f tsort.awk | sed 's/_/ /g'
}
# Emit "@set ADD-ON" for each add-on contributing a manual chapter.
for addon in $2; do
addon=`basename $addon .texi`
echo >&3 "@set $addon"
done
collect_nodes $1 | build_menu
if [ -n "$2" ]; then
{ echo; echo 'Add-ons'; echo; } >&4
egrep '^(@c )?@node.*Top' `echo $2 /dev/null | tr ' ' '\n' | sort` |
cut -d, -f1 | sed 's/@c //;s/@node //' | build_menu
fi
{ echo; echo 'Appendices'; echo; } >&4
collect_nodes $3 | build_menu
exec 3>&- 4>&- 5>&-
mv -f ${OUTDIR}incl.$$ ${OUTDIR}chapters.texi
{
echo '@menu'
$AWK -F: '
/^\*/ {
printf("%-32s", $1 "::");
x = split($3, word, " ");
hpos = 34;
for (i = 1; i <= x; i++) {
hpos += length(word[i]) + 1;
if (hpos > 78) {
printf("\n%34s", "");
hpos = 35 + length(word[i]);
}
printf(" %s", word[i]);
}
print ".";
}
!/^\*/ { print; }
' ${OUTDIR}smenu.$$
cat <${OUTDIR}top-menu.texi.$$
mv -f ${OUTDIR}top-menu.texi.$$ ${OUTDIR}top-menu.texi
rm -f ${OUTDIR}*.$$
glibc-doc-reference-2.19.orig/manual/intro.texi 0000664 0001750 0001750 00000173461 12275120646 021621 0 ustar adconrad adconrad @node Introduction, Error Reporting, Top, Top
@chapter Introduction
@c %MENU% Purpose of the GNU C Library
The C language provides no built-in facilities for performing such
common operations as input/output, memory management, string
manipulation, and the like. Instead, these facilities are defined
in a standard @dfn{library}, which you compile and link with your
programs.
@cindex library
@Theglibc{}, described in this document, defines all of the
library functions that are specified by the @w{ISO C} standard, as well as
additional features specific to POSIX and other derivatives of the Unix
operating system, and extensions specific to @gnusystems{}.
The purpose of this manual is to tell you how to use the facilities
of @theglibc{}. We have mentioned which features belong to which
standards to help you identify things that are potentially non-portable
to other systems. But the emphasis in this manual is not on strict
portability.
@menu
* Getting Started:: What this manual is for and how to use it.
* Standards and Portability:: Standards and sources upon which the GNU
C library is based.
* Using the Library:: Some practical uses for the library.
* Roadmap to the Manual:: Overview of the remaining chapters in
this manual.
@end menu
@node Getting Started, Standards and Portability, , Introduction
@section Getting Started
This manual is written with the assumption that you are at least
somewhat familiar with the C programming language and basic programming
concepts. Specifically, familiarity with ISO standard C
(@pxref{ISO C}), rather than ``traditional'' pre-ISO C dialects, is
assumed.
@Theglibc{} includes several @dfn{header files}, each of which
provides definitions and declarations for a group of related facilities;
this information is used by the C compiler when processing your program.
For example, the header file @file{stdio.h} declares facilities for
performing input and output, and the header file @file{string.h}
declares string processing utilities. The organization of this manual
generally follows the same division as the header files.
If you are reading this manual for the first time, you should read all
of the introductory material and skim the remaining chapters. There are
a @emph{lot} of functions in @theglibc{} and it's not realistic to
expect that you will be able to remember exactly @emph{how} to use each
and every one of them. It's more important to become generally familiar
with the kinds of facilities that the library provides, so that when you
are writing your programs you can recognize @emph{when} to make use of
library functions, and @emph{where} in this manual you can find more
specific information about them.
@node Standards and Portability, Using the Library, Getting Started, Introduction
@section Standards and Portability
@cindex standards
This section discusses the various standards and other sources that @theglibc{}
is based upon. These sources include the @w{ISO C} and
POSIX standards, and the System V and Berkeley Unix implementations.
The primary focus of this manual is to tell you how to make effective
use of the @glibcadj{} facilities. But if you are concerned about
making your programs compatible with these standards, or portable to
operating systems other than GNU, this can affect how you use the
library. This section gives you an overview of these standards, so that
you will know what they are when they are mentioned in other parts of
the manual.
@xref{Library Summary}, for an alphabetical list of the functions and
other symbols provided by the library. This list also states which
standards each function or symbol comes from.
@menu
* ISO C:: The international standard for the C
programming language.
* POSIX:: The ISO/IEC 9945 (aka IEEE 1003) standards
for operating systems.
* Berkeley Unix:: BSD and SunOS.
* SVID:: The System V Interface Description.
* XPG:: The X/Open Portability Guide.
@end menu
@node ISO C, POSIX, , Standards and Portability
@subsection ISO C
@cindex ISO C
@Theglibc{} is compatible with the C standard adopted by the
American National Standards Institute (ANSI):
@cite{American National Standard X3.159-1989---``ANSI C''} and later
by the International Standardization Organization (ISO):
@cite{ISO/IEC 9899:1990, ``Programming languages---C''}.
We here refer to the standard as @w{ISO C} since this is the more
general standard in respect of ratification.
The header files and library facilities that make up @theglibc{} are
a superset of those specified by the @w{ISO C} standard.@refill
@pindex gcc
If you are concerned about strict adherence to the @w{ISO C} standard, you
should use the @samp{-ansi} option when you compile your programs with
the GNU C compiler. This tells the compiler to define @emph{only} ISO
standard features from the library header files, unless you explicitly
ask for additional features. @xref{Feature Test Macros}, for
information on how to do this.
Being able to restrict the library to include only @w{ISO C} features is
important because @w{ISO C} puts limitations on what names can be defined
by the library implementation, and the GNU extensions don't fit these
limitations. @xref{Reserved Names}, for more information about these
restrictions.
This manual does not attempt to give you complete details on the
differences between @w{ISO C} and older dialects. It gives advice on how
to write programs to work portably under multiple C dialects, but does
not aim for completeness.
@node POSIX, Berkeley Unix, ISO C, Standards and Portability
@subsection POSIX (The Portable Operating System Interface)
@cindex POSIX
@cindex POSIX.1
@cindex IEEE Std 1003.1
@cindex ISO/IEC 9945-1
@cindex POSIX.2
@cindex IEEE Std 1003.2
@cindex ISO/IEC 9945-2
@Theglibc{} is also compatible with the ISO @dfn{POSIX} family of
standards, known more formally as the @dfn{Portable Operating System
Interface for Computer Environments} (ISO/IEC 9945). They were also
published as ANSI/IEEE Std 1003. POSIX is derived mostly from various
versions of the Unix operating system.
The library facilities specified by the POSIX standards are a superset
of those required by @w{ISO C}; POSIX specifies additional features for
@w{ISO C} functions, as well as specifying new additional functions. In
general, the additional requirements and functionality defined by the
POSIX standards are aimed at providing lower-level support for a
particular kind of operating system environment, rather than general
programming language support which can run in many diverse operating
system environments.@refill
@Theglibc{} implements all of the functions specified in
@cite{ISO/IEC 9945-1:1996, the POSIX System Application Program
Interface}, commonly referred to as POSIX.1. The primary extensions to
the @w{ISO C} facilities specified by this standard include file system
interface primitives (@pxref{File System Interface}), device-specific
terminal control functions (@pxref{Low-Level Terminal Interface}), and
process control functions (@pxref{Processes}).
Some facilities from @cite{ISO/IEC 9945-2:1993, the POSIX Shell and
Utilities standard} (POSIX.2) are also implemented in @theglibc{}.
These include utilities for dealing with regular expressions and other
pattern matching facilities (@pxref{Pattern Matching}).
@menu
* POSIX Safety Concepts:: Safety concepts from POSIX.
* Unsafe Features:: Features that make functions unsafe.
* Conditionally Safe Features:: Features that make functions unsafe
in the absence of workarounds.
* Other Safety Remarks:: Additional safety features and remarks.
@end menu
@comment Roland sez:
@comment The GNU C library as it stands conforms to 1003.2 draft 11, which
@comment specifies:
@comment
@comment Several new macros in .
@comment popen, pclose
@comment (which is not yet fully implemented--wait on this)
@comment fnmatch
@comment getopt
@comment
@comment (not yet implemented)
@comment confstr
@node POSIX Safety Concepts, Unsafe Features, , POSIX
@subsubsection POSIX Safety Concepts
@cindex POSIX Safety Concepts
This manual documents various safety properties of @glibcadj{}
functions, in lines that follow their prototypes and look like:
@sampsafety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The properties are assessed according to the criteria set forth in the
POSIX standard for such safety contexts as Thread-, Async-Signal- and
Async-Cancel- -Safety. Intuitive definitions of these properties,
attempting to capture the meaning of the standard definitions, follow.
@itemize @bullet
@item
@cindex MT-Safe
@cindex Thread-Safe
@code{MT-Safe} or Thread-Safe functions are safe to call in the presence
of other threads. MT, in MT-Safe, stands for Multi Thread.
Being MT-Safe does not imply a function is atomic, nor that it uses any
of the memory synchronization mechanisms POSIX exposes to users. It is
even possible that calling MT-Safe functions in sequence does not yield
an MT-Safe combination. For example, having a thread call two MT-Safe
functions one right after the other does not guarantee behavior
equivalent to atomic execution of a combination of both functions, since
concurrent calls in other threads may interfere in a destructive way.
Whole-program optimizations that could inline functions across library
interfaces may expose unsafe reordering, and so performing inlining
across the @glibcadj{} interface is not recommended. The documented
MT-Safety status is not guaranteed under whole-program optimization.
However, functions defined in user-visible headers are designed to be
safe for inlining.
@item
@cindex AS-Safe
@cindex Async-Signal-Safe
@code{AS-Safe} or Async-Signal-Safe functions are safe to call from
asynchronous signal handlers. AS, in AS-Safe, stands for Asynchronous
Signal.
Many functions that are AS-Safe may set @code{errno}, or modify the
floating-point environment, because their doing so does not make them
unsuitable for use in signal handlers. However, programs could
misbehave should asynchronous signal handlers modify this thread-local
state, and the signal handling machinery cannot be counted on to
preserve it. Therefore, signal handlers that call functions that may
set @code{errno} or modify the floating-point environment @emph{must}
save their original values, and restore them before returning.
@item
@cindex AC-Safe
@cindex Async-Cancel-Safe
@code{AC-Safe} or Async-Cancel-Safe functions are safe to call when
asynchronous cancellation is enabled. AC in AC-Safe stands for
Asynchronous Cancellation.
The POSIX standard defines only three functions to be AC-Safe, namely
@code{pthread_cancel}, @code{pthread_setcancelstate}, and
@code{pthread_setcanceltype}. At present @theglibc{} provides no
guarantees beyond these three functions, but does document which
functions are presently AC-Safe. This documentation is provided for use
by @theglibc{} developers.
Just like signal handlers, cancellation cleanup routines must configure
the floating point environment they require. The routines cannot assume
a floating point environment, particularly when asynchronous
cancellation is enabled. If the configuration of the floating point
environment cannot be performed atomically then it is also possible that
the environment encountered is internally inconsistent.
@item
@cindex MT-Unsafe
@cindex Thread-Unsafe
@cindex AS-Unsafe
@cindex Async-Signal-Unsafe
@cindex AC-Unsafe
@cindex Async-Cancel-Unsafe
@code{MT-Unsafe}, @code{AS-Unsafe}, @code{AC-Unsafe} functions are not
safe to call within the safety contexts described above. Calling them
within such contexts invokes undefined behavior.
Functions not explicitly documented as safe in a safety context should
be regarded as Unsafe.
@item
@cindex Preliminary
@code{Preliminary} safety properties are documented, indicating these
properties may @emph{not} be counted on in future releases of
@theglibc{}.
Such preliminary properties are the result of an assessment of the
properties of our current implementation, rather than of what is
mandated and permitted by current and future standards.
Although we strive to abide by the standards, in some cases our
implementation is safe even when the standard does not demand safety,
and in other cases our implementation does not meet the standard safety
requirements. The latter are most likely bugs; the former, when marked
as @code{Preliminary}, should not be counted on: future standards may
require changes that are not compatible with the additional safety
properties afforded by the current implementation.
Furthermore, the POSIX standard does not offer a detailed definition of
safety. We assume that, by ``safe to call'', POSIX means that, as long
as the program does not invoke undefined behavior, the ``safe to call''
function behaves as specified, and does not cause other functions to
deviate from their specified behavior. We have chosen to use its loose
definitions of safety, not because they are the best definitions to use,
but because choosing them harmonizes this manual with POSIX.
Please keep in mind that these are preliminary definitions and
annotations, and certain aspects of the definitions are still under
discussion and might be subject to clarification or change.
Over time, we envision evolving the preliminary safety notes into stable
commitments, as stable as those of our interfaces. As we do, we will
remove the @code{Preliminary} keyword from safety notes. As long as the
keyword remains, however, they are not to be regarded as a promise of
future behavior.
@end itemize
Other keywords that appear in safety notes are defined in subsequent
sections.
@node Unsafe Features, Conditionally Safe Features, POSIX Safety Concepts, POSIX
@subsubsection Unsafe Features
@cindex Unsafe Features
Functions that are unsafe to call in certain contexts are annotated with
keywords that document their features that make them unsafe to call.
AS-Unsafe features in this section indicate the functions are never safe
to call when asynchronous signals are enabled. AC-Unsafe features
indicate they are never safe to call when asynchronous cancellation is
enabled. There are no MT-Unsafe marks in this section.
@itemize @bullet
@item @code{lock}
@cindex lock
Functions marked with @code{lock} as an AS-Unsafe feature may be
interrupted by a signal while holding a non-recursive lock. If the
signal handler calls another such function that takes the same lock, the
result is a deadlock.
Functions annotated with @code{lock} as an AC-Unsafe feature may, if
cancelled asynchronously, fail to release a lock that would have been
released if their execution had not been interrupted by asynchronous
thread cancellation. Once a lock is left taken, attempts to take that
lock will block indefinitely.
@item @code{corrupt}
@cindex corrupt
Functions marked with @code{corrupt} as an AS-Unsafe feature may corrupt
data structures and misbehave when they interrupt, or are interrupted
by, another such function. Unlike functions marked with @code{lock},
these take recursive locks to avoid MT-Safety problems, but this is not
enough to stop a signal handler from observing a partially-updated data
structure. Further corruption may arise from the interrupted function's
failure to notice updates made by signal handlers.
Functions marked with @code{corrupt} as an AC-Unsafe feature may leave
data structures in a corrupt, partially updated state. Subsequent uses
of the data structure may misbehave.
@c A special case, probably not worth documenting separately, involves
@c reallocing, or even freeing pointers. Any case involving free could
@c be easily turned into an ac-safe leak by resetting the pointer before
@c releasing it; I don't think we have any case that calls for this sort
@c of fixing. Fixing the realloc cases would require a new interface:
@c instead of @code{ptr=realloc(ptr,size)} we'd have to introduce
@c @code{acsafe_realloc(&ptr,size)} that would modify ptr before
@c releasing the old memory. The ac-unsafe realloc could be implemented
@c in terms of an internal interface with this semantics (say
@c __acsafe_realloc), but since realloc can be overridden, the function
@c we call to implement realloc should not be this internal interface,
@c but another internal interface that calls __acsafe_realloc if realloc
@c was not overridden, and calls the overridden realloc with async
@c cancel disabled. --lxoliva
@item @code{heap}
@cindex heap
Functions marked with @code{heap} may call heap memory management
functions from the @code{malloc}/@code{free} family of functions and are
only as safe as those functions. This note is thus equivalent to:
@sampsafety{@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Check for cases that should have used plugin instead of or in
@c addition to this. Then, after rechecking gettext, adjust i18n if
@c needed.
@item @code{dlopen}
@cindex dlopen
Functions marked with @code{dlopen} use the dynamic loader to load
shared libraries into the current execution image. This involves
opening files, mapping them into memory, allocating additional memory,
resolving symbols, applying relocations and more, all of this while
holding internal dynamic loader locks.
The locks are enough for these functions to be AS- and AC-Unsafe, but
other issues may arise. At present this is a placeholder for all
potential safety issues raised by @code{dlopen}.
@c dlopen runs init and fini sections of the module; does this mean
@c dlopen always implies plugin?
@item @code{plugin}
@cindex plugin
Functions annotated with @code{plugin} may run code from plugins that
may be external to @theglibc{}. Such plugin functions are assumed to be
MT-Safe, AS-Unsafe and AC-Unsafe. Examples of such plugins are stack
@cindex NSS
unwinding libraries, name service switch (NSS) and character set
@cindex iconv
conversion (iconv) back-ends.
Although the plugins mentioned as examples are all brought in by means
of dlopen, the @code{plugin} keyword does not imply any direct
involvement of the dynamic loader or the @code{libdl} interfaces, those
are covered by @code{dlopen}. For example, if one function loads a
module and finds the addresses of some of its functions, while another
just calls those already-resolved functions, the former will be marked
with @code{dlopen}, whereas the latter will get the @code{plugin}. When
a single function takes all of these actions, then it gets both marks.
@item @code{i18n}
@cindex i18n
Functions marked with @code{i18n} may call internationalization
functions of the @code{gettext} family and will be only as safe as those
functions. This note is thus equivalent to:
@sampsafety{@mtsafe{@mtsenv{}}@asunsafe{@asucorrupt{} @ascuheap{} @ascudlopen{}}@acunsafe{@acucorrupt{}}}
@item @code{timer}
@cindex timer
Functions marked with @code{timer} use the @code{alarm} function or
similar to set a time-out for a system call or a long-running operation.
In a multi-threaded program, there is a risk that the time-out signal
will be delivered to a different thread, thus failing to interrupt the
intended thread. Besides being MT-Unsafe, such functions are always
AS-Unsafe, because calling them in signal handlers may interfere with
timers set in the interrupted code, and AC-Unsafe, because there is no
safe way to guarantee an earlier timer will be reset in case of
asynchronous cancellation.
@end itemize
@node Conditionally Safe Features, Other Safety Remarks, Unsafe Features, POSIX
@subsubsection Conditionally Safe Features
@cindex Conditionally Safe Features
For some features that make functions unsafe to call in certain
contexts, there are known ways to avoid the safety problem other than
refraining from calling the function altogether. The keywords that
follow refer to such features, and each of their definitions indicate
how the whole program needs to be constrained in order to remove the
safety problem indicated by the keyword. Only when all the reasons that
make a function unsafe are observed and addressed, by applying the
documented constraints, does the function become safe to call in a
context.
@itemize @bullet
@item @code{init}
@cindex init
Functions marked with @code{init} as an MT-Unsafe feature perform
MT-Unsafe initialization when they are first called.
Calling such a function at least once in single-threaded mode removes
this specific cause for the function to be regarded as MT-Unsafe. If no
other cause for that remains, the function can then be safely called
after other threads are started.
Functions marked with @code{init} as an AS- or AC-Unsafe feature use the
internal @code{libc_once} machinery or similar to initialize internal
data structures.
If a signal handler interrupts such an initializer, and calls any
function that also performs @code{libc_once} initialization, it will
deadlock if the thread library has been loaded.
Furthermore, if an initializer is partially complete before it is
canceled or interrupted by a signal whose handler requires the same
initialization, some or all of the initialization may be performed more
than once, leaking resources or even resulting in corrupt internal data.
Applications that need to call functions marked with @code{init} as an
AS- or AC-Unsafe feature should ensure the initialization is performed
before configuring signal handlers or enabling cancellation, so that the
AS- and AC-Safety issues related with @code{libc_once} do not arise.
@c We may have to extend the annotations to cover conditions in which
@c initialization may or may not occur, since an initial call in a safe
@c context is no use if the initialization doesn't take place at that
@c time: it doesn't remove the risk for later calls.
@item @code{race}
@cindex race
Functions annotated with @code{race} as an MT-Safety issue operate on
objects in ways that may cause data races or similar forms of
destructive interference out of concurrent execution. In some cases,
the objects are passed to the functions by users; in others, they are
used by the functions to return values to users; in others, they are not
even exposed to users.
We consider access to objects passed as (indirect) arguments to
functions to be data race free. The assurance of data race free objects
is the caller's responsibility. We will not mark a function as
MT-Unsafe or AS-Unsafe if it misbehaves when users fail to take the
measures required by POSIX to avoid data races when dealing with such
objects. As a general rule, if a function is documented as reading from
an object passed (by reference) to it, or modifying it, users ought to
use memory synchronization primitives to avoid data races just as they
would should they perform the accesses themselves rather than by calling
the library function. @code{FILE} streams are the exception to the
general rule, in that POSIX mandates the library to guard against data
races in many functions that manipulate objects of this specific opaque
type. We regard this as a convenience provided to users, rather than as
a general requirement whose expectations should extend to other types.
In order to remind users that guarding certain arguments is their
responsibility, we will annotate functions that take objects of certain
types as arguments. We draw the line for objects passed by users as
follows: objects whose types are exposed to users, and that users are
expected to access directly, such as memory buffers, strings, and
various user-visible @code{struct} types, do @emph{not} give reason for
functions to be annotated with @code{race}. It would be noisy and
redundant with the general requirement, and not many would be surprised
by the library's lack of internal guards when accessing objects that can
be accessed directly by users.
As for objects that are opaque or opaque-like, in that they are to be
manipulated only by passing them to library functions (e.g.,
@code{FILE}, @code{DIR}, @code{obstack}, @code{iconv_t}), there might be
additional expectations as to internal coordination of access by the
library. We will annotate, with @code{race} followed by a colon and the
argument name, functions that take such objects but that do not take
care of synchronizing access to them by default. For example,
@code{FILE} stream @code{unlocked} functions will be annotated, but
those that perform implicit locking on @code{FILE} streams by default
will not, even though the implicit locking may be disabled on a
per-stream basis.
In either case, we will not regard as MT-Unsafe functions that may
access user-supplied objects in unsafe ways should users fail to ensure
the accesses are well defined. The notion prevails that users are
expected to safeguard against data races any user-supplied objects that
the library accesses on their behalf.
@c The above describes @mtsrace; @mtasurace is described below.
This user responsibility does not apply, however, to objects controlled
by the library itself, such as internal objects and static buffers used
to return values from certain calls. When the library doesn't guard
them against concurrent uses, these cases are regarded as MT-Unsafe and
AS-Unsafe (although the @code{race} mark under AS-Unsafe will be omitted
as redundant with the one under MT-Unsafe). As in the case of
user-exposed objects, the mark may be followed by a colon and an
identifier. The identifier groups all functions that operate on a
certain unguarded object; users may avoid the MT-Safety issues related
with unguarded concurrent access to such internal objects by creating a
non-recursive mutex related with the identifier, and always holding the
mutex when calling any function marked as racy on that identifier, as
they would have to should the identifier be an object under user
control. The non-recursive mutex avoids the MT-Safety issue, but it
trades one AS-Safety issue for another, so use in asynchronous signals
remains undefined.
When the identifier relates to a static buffer used to hold return
values, the mutex must be held for as long as the buffer remains in use
by the caller. Many functions that return pointers to static buffers
offer reentrant variants that store return values in caller-supplied
buffers instead. In some cases, such as @code{tmpname}, the variant is
chosen not by calling an alternate entry point, but by passing a
non-@code{NULL} pointer to the buffer in which the returned values are
to be stored. These variants are generally preferable in multi-threaded
programs, although some of them are not MT-Safe because of other
internal buffers, also documented with @code{race} notes.
@item @code{const}
@cindex const
Functions marked with @code{const} as an MT-Safety issue non-atomically
modify internal objects that are better regarded as constant, because a
substantial portion of @theglibc{} accesses them without
synchronization. Unlike @code{race}, that causes both readers and
writers of internal objects to be regarded as MT-Unsafe and AS-Unsafe,
this mark is applied to writers only. Writers remain equally MT- and
AS-Unsafe to call, but the then-mandatory constness of objects they
modify enables readers to be regarded as MT-Safe and AS-Safe (as long as
no other reasons for them to be unsafe remain), since the lack of
synchronization is not a problem when the objects are effectively
constant.
The identifier that follows the @code{const} mark will appear by itself
as a safety note in readers. Programs that wish to work around this
safety issue, so as to call writers, may use a non-recursve
@code{rwlock} associated with the identifier, and guard @emph{all} calls
to functions marked with @code{const} followed by the identifier with a
write lock, and @emph{all} calls to functions marked with the identifier
by itself with a read lock. The non-recursive locking removes the
MT-Safety problem, but it trades one AS-Safety problem for another, so
use in asynchronous signals remains undefined.
@c But what if, instead of marking modifiers with const:id and readers
@c with just id, we marked writers with race:id and readers with ro:id?
@c Instead of having to define each instance of “id”, we'd have a
@c general pattern governing all such “id”s, wherein race:id would
@c suggest the need for an exclusive/write lock to make the function
@c safe, whereas ro:id would indicate “id” is expected to be read-only,
@c but if any modifiers are called (while holding an exclusive lock),
@c then ro:id-marked functions ought to be guarded with a read lock for
@c safe operation. ro:env or ro:locale, for example, seems to convey
@c more clearly the expectations and the meaning, than just env or
@c locale.
@item @code{sig}
@cindex sig
Functions marked with @code{sig} as a MT-Safety issue (that implies an
identical AS-Safety issue, omitted for brevity) may temporarily install
a signal handler for internal purposes, which may interfere with other
uses of the signal, identified after a colon.
This safety problem can be worked around by ensuring that no other uses
of the signal will take place for the duration of the call. Holding a
non-recursive mutex while calling all functions that use the same
temporary signal; blocking that signal before the call and resetting its
handler afterwards is recommended.
There is no safe way to guarantee the original signal handler is
restored in case of asynchronous cancellation, therefore so-marked
functions are also AC-Unsafe.
@c fixme: at least deferred cancellation should get it right, and would
@c obviate the restoring bit below, and the qualifier above.
Besides the measures recommended to work around the MT- and AS-Safety
problem, in order to avert the cancellation problem, disabling
asynchronous cancellation @emph{and} installing a cleanup handler to
restore the signal to the desired state and to release the mutex are
recommended.
@item @code{term}
@cindex term
Functions marked with @code{term} as an MT-Safety issue may change the
terminal settings in the recommended way, namely: call @code{tcgetattr},
modify some flags, and then call @code{tcsetattr}; this creates a window
in which changes made by other threads are lost. Thus, functions marked
with @code{term} are MT-Unsafe. The same window enables changes made by
asynchronous signals to be lost. These functions are also AS-Unsafe,
but the corresponding mark is omitted as redundant.
It is thus advisable for applications using the terminal to avoid
concurrent and reentrant interactions with it, by not using it in signal
handlers or blocking signals that might use it, and holding a lock while
calling these functions and interacting with the terminal. This lock
should also be used for mutual exclusion with functions marked with
@code{@mtasurace{:tcattr(fd)}}, where @var{fd} is a file descriptor for
the controlling terminal. The caller may use a single mutex for
simplicity, or use one mutex per terminal, even if referenced by
different file descriptors.
Functions marked with @code{term} as an AC-Safety issue are supposed to
restore terminal settings to their original state, after temporarily
changing them, but they may fail to do so if cancelled.
@c fixme: at least deferred cancellation should get it right, and would
@c obviate the restoring bit below, and the qualifier above.
Besides the measures recommended to work around the MT- and AS-Safety
problem, in order to avert the cancellation problem, disabling
asynchronous cancellation @emph{and} installing a cleanup handler to
restore the terminal settings to the original state and to release the
mutex are recommended.
@end itemize
@node Other Safety Remarks, , Conditionally Safe Features, POSIX
@subsubsection Other Safety Remarks
@cindex Other Safety Remarks
Additional keywords may be attached to functions, indicating features
that do not make a function unsafe to call, but that may need to be
taken into account in certain classes of programs:
@itemize @bullet
@item @code{locale}
@cindex locale
Functions annotated with @code{locale} as an MT-Safety issue read from
the locale object without any form of synchronization. Functions
annotated with @code{locale} called concurrently with locale changes may
behave in ways that do not correspond to any of the locales active
during their execution, but an unpredictable mix thereof.
We do not mark these functions as MT- or AS-Unsafe, however, because
functions that modify the locale object are marked with
@code{const:locale} and regarded as unsafe. Being unsafe, the latter
are not to be called when multiple threads are running or asynchronous
signals are enabled, and so the locale can be considered effectively
constant in these contexts, which makes the former safe.
@c Should the locking strategy suggested under @code{const} be used,
@c failure to guard locale uses is not as fatal as data races in
@c general: unguarded uses will @emph{not} follow dangling pointers or
@c access uninitialized, unmapped or recycled memory. Each access will
@c read from a consistent locale object that is or was active at some
@c point during its execution. Without synchronization, however, it
@c cannot even be assumed that, after a change in locale, earlier
@c locales will no longer be used, even after the newly-chosen one is
@c used in the thread. Nevertheless, even though unguarded reads from
@c the locale will not violate type safety, functions that access the
@c locale multiple times may invoke all sorts of undefined behavior
@c because of the unexpected locale changes.
@item @code{env}
@cindex env
Functions marked with @code{env} as an MT-Safety issue access the
environment with @code{getenv} or similar, without any guards to ensure
safety in the presence of concurrent modifications.
We do not mark these functions as MT- or AS-Unsafe, however, because
functions that modify the environment are all marked with
@code{const:env} and regarded as unsafe. Being unsafe, the latter are
not to be called when multiple threads are running or asynchronous
signals are enabled, and so the environment can be considered
effectively constant in these contexts, which makes the former safe.
@item @code{hostid}
@cindex hostid
The function marked with @code{hostid} as an MT-Safety issue reads from
the system-wide data structures that hold the ``host ID'' of the
machine. These data structures cannot generally be modified atomically.
Since it is expected that the ``host ID'' will not normally change, the
function that reads from it (@code{gethostid}) is regarded as safe,
whereas the function that modifies it (@code{sethostid}) is marked with
@code{@mtasuconst{:@mtshostid{}}}, indicating it may require special
care if it is to be called. In this specific case, the special care
amounts to system-wide (not merely intra-process) coordination.
@item @code{sigintr}
@cindex sigintr
Functions marked with @code{sigintr} as an MT-Safety issue access the
@code{_sigintr} internal data structure without any guards to ensure
safety in the presence of concurrent modifications.
We do not mark these functions as MT- or AS-Unsafe, however, because
functions that modify the this data structure are all marked with
@code{const:sigintr} and regarded as unsafe. Being unsafe, the latter
are not to be called when multiple threads are running or asynchronous
signals are enabled, and so the data structure can be considered
effectively constant in these contexts, which makes the former safe.
@item @code{fd}
@cindex fd
Functions annotated with @code{fd} as an AC-Safety issue may leak file
descriptors if asynchronous thread cancellation interrupts their
execution.
Functions that allocate or deallocate file descriptors will generally be
marked as such. Even if they attempted to protect the file descriptor
allocation and deallocation with cleanup regions, allocating a new
descriptor and storing its number where the cleanup region could release
it cannot be performed as a single atomic operation. Similarly,
releasing the descriptor and taking it out of the data structure
normally responsible for releasing it cannot be performed atomically.
There will always be a window in which the descriptor cannot be released
because it was not stored in the cleanup handler argument yet, or it was
already taken out before releasing it. It cannot be taken out after
release: an open descriptor could mean either that the descriptor still
has to be closed, or that it already did so but the descriptor was
reallocated by another thread or signal handler.
Such leaks could be internally avoided, with some performance penalty,
by temporarily disabling asynchronous thread cancellation. However,
since callers of allocation or deallocation functions would have to do
this themselves, to avoid the same sort of leak in their own layer, it
makes more sense for the library to assume they are taking care of it
than to impose a performance penalty that is redundant when the problem
is solved in upper layers, and insufficient when it is not.
This remark by itself does not cause a function to be regarded as
AC-Unsafe. However, cumulative effects of such leaks may pose a
problem for some programs. If this is the case, suspending asynchronous
cancellation for the duration of calls to such functions is recommended.
@item @code{mem}
@cindex mem
Functions annotated with @code{mem} as an AC-Safety issue may leak
memory if asynchronous thread cancellation interrupts their execution.
The problem is similar to that of file descriptors: there is no atomic
interface to allocate memory and store its address in the argument to a
cleanup handler, or to release it and remove its address from that
argument, without at least temporarily disabling asynchronous
cancellation, which these functions do not do.
This remark does not by itself cause a function to be regarded as
generally AC-Unsafe. However, cumulative effects of such leaks may be
severe enough for some programs that disabling asynchronous cancellation
for the duration of calls to such functions may be required.
@item @code{cwd}
@cindex cwd
Functions marked with @code{cwd} as an MT-Safety issue may temporarily
change the current working directory during their execution, which may
cause relative pathnames to be resolved in unexpected ways in other
threads or within asynchronous signal or cancellation handlers.
This is not enough of a reason to mark so-marked functions as MT- or
AS-Unsafe, but when this behavior is optional (e.g., @code{nftw} with
@code{FTW_CHDIR}), avoiding the option may be a good alternative to
using full pathnames or file descriptor-relative (e.g. @code{openat})
system calls.
@item @code{!posix}
@cindex !posix
This remark, as an MT-, AS- or AC-Safety note to a function, indicates
the safety status of the function is known to differ from the specified
status in the POSIX standard. For example, POSIX does not require a
function to be Safe, but our implementation is, or vice-versa.
For the time being, the absence of this remark does not imply the safety
properties we documented are identical to those mandated by POSIX for
the corresponding functions.
@item @code{:identifier}
@cindex :identifier
Annotations may sometimes be followed by identifiers, intended to group
several functions that e.g. access the data structures in an unsafe way,
as in @code{race} and @code{const}, or to provide more specific
information, such as naming a signal in a function marked with
@code{sig}. It is envisioned that it may be applied to @code{lock} and
@code{corrupt} as well in the future.
In most cases, the identifier will name a set of functions, but it may
name global objects or function arguments, or identifiable properties or
logical components associated with them, with a notation such as
e.g. @code{:buf(arg)} to denote a buffer associated with the argument
@var{arg}, or @code{:tcattr(fd)} to denote the terminal attributes of a
file descriptor @var{fd}.
The most common use for identifiers is to provide logical groups of
functions and arguments that need to be protected by the same
synchronization primitive in order to ensure safe operation in a given
context.
@item @code{/condition}
@cindex /condition
Some safety annotations may be conditional, in that they only apply if a
boolean expression involving arguments, global variables or even the
underlying kernel evaluates evaluates to true. Such conditions as
@code{/hurd} or @code{/!linux!bsd} indicate the preceding marker only
applies when the underlying kernel is the HURD, or when it is neither
Linux nor a BSD kernel, respectively. @code{/!ps} and
@code{/one_per_line} indicate the preceding marker only applies when
argument @var{ps} is NULL, or global variable @var{one_per_line} is
nonzero.
When all marks that render a function unsafe are adorned with such
conditions, and none of the named conditions hold, then the function can
be regarded as safe.
@end itemize
@node Berkeley Unix, SVID, POSIX, Standards and Portability
@subsection Berkeley Unix
@cindex BSD Unix
@cindex 4.@var{n} BSD Unix
@cindex Berkeley Unix
@cindex SunOS
@cindex Unix, Berkeley
@Theglibc{} defines facilities from some versions of Unix which
are not formally standardized, specifically from the 4.2 BSD, 4.3 BSD,
and 4.4 BSD Unix systems (also known as @dfn{Berkeley Unix}) and from
@dfn{SunOS} (a popular 4.2 BSD derivative that includes some Unix System
V functionality). These systems support most of the @w{ISO C} and POSIX
facilities, and 4.4 BSD and newer releases of SunOS in fact support them all.
The BSD facilities include symbolic links (@pxref{Symbolic Links}), the
@code{select} function (@pxref{Waiting for I/O}), the BSD signal
functions (@pxref{BSD Signal Handling}), and sockets (@pxref{Sockets}).
@node SVID, XPG, Berkeley Unix, Standards and Portability
@subsection SVID (The System V Interface Description)
@cindex SVID
@cindex System V Unix
@cindex Unix, System V
The @dfn{System V Interface Description} (SVID) is a document describing
the AT&T Unix System V operating system. It is to some extent a
superset of the POSIX standard (@pxref{POSIX}).
@Theglibc{} defines most of the facilities required by the SVID
that are not also required by the @w{ISO C} or POSIX standards, for
compatibility with System V Unix and other Unix systems (such as
SunOS) which include these facilities. However, many of the more
obscure and less generally useful facilities required by the SVID are
not included. (In fact, Unix System V itself does not provide them all.)
The supported facilities from System V include the methods for
inter-process communication and shared memory, the @code{hsearch} and
@code{drand48} families of functions, @code{fmtmsg} and several of the
mathematical functions.
@node XPG, , SVID, Standards and Portability
@subsection XPG (The X/Open Portability Guide)
The X/Open Portability Guide, published by the X/Open Company, Ltd., is
a more general standard than POSIX. X/Open owns the Unix copyright and
the XPG specifies the requirements for systems which are intended to be
a Unix system.
@Theglibc{} complies to the X/Open Portability Guide, Issue 4.2,
with all extensions common to XSI (X/Open System Interface)
compliant systems and also all X/Open UNIX extensions.
The additions on top of POSIX are mainly derived from functionality
available in @w{System V} and BSD systems. Some of the really bad
mistakes in @w{System V} systems were corrected, though. Since
fulfilling the XPG standard with the Unix extensions is a
precondition for getting the Unix brand chances are good that the
functionality is available on commercial systems.
@node Using the Library, Roadmap to the Manual, Standards and Portability, Introduction
@section Using the Library
This section describes some of the practical issues involved in using
@theglibc{}.
@menu
* Header Files:: How to include the header files in your
programs.
* Macro Definitions:: Some functions in the library may really
be implemented as macros.
* Reserved Names:: The C standard reserves some names for
the library, and some for users.
* Feature Test Macros:: How to control what names are defined.
@end menu
@node Header Files, Macro Definitions, , Using the Library
@subsection Header Files
@cindex header files
Libraries for use by C programs really consist of two parts: @dfn{header
files} that define types and macros and declare variables and
functions; and the actual library or @dfn{archive} that contains the
definitions of the variables and functions.
(Recall that in C, a @dfn{declaration} merely provides information that
a function or variable exists and gives its type. For a function
declaration, information about the types of its arguments might be
provided as well. The purpose of declarations is to allow the compiler
to correctly process references to the declared variables and functions.
A @dfn{definition}, on the other hand, actually allocates storage for a
variable or says what a function does.)
@cindex definition (compared to declaration)
@cindex declaration (compared to definition)
In order to use the facilities in @theglibc{}, you should be sure
that your program source files include the appropriate header files.
This is so that the compiler has declarations of these facilities
available and can correctly process references to them. Once your
program has been compiled, the linker resolves these references to
the actual definitions provided in the archive file.
Header files are included into a program source file by the
@samp{#include} preprocessor directive. The C language supports two
forms of this directive; the first,
@smallexample
#include "@var{header}"
@end smallexample
@noindent
is typically used to include a header file @var{header} that you write
yourself; this would contain definitions and declarations describing the
interfaces between the different parts of your particular application.
By contrast,
@smallexample
#include
@end smallexample
@noindent
is typically used to include a header file @file{file.h} that contains
definitions and declarations for a standard library. This file would
normally be installed in a standard place by your system administrator.
You should use this second form for the C library header files.
Typically, @samp{#include} directives are placed at the top of the C
source file, before any other code. If you begin your source files with
some comments explaining what the code in the file does (a good idea),
put the @samp{#include} directives immediately afterwards, following the
feature test macro definition (@pxref{Feature Test Macros}).
For more information about the use of header files and @samp{#include}
directives, @pxref{Header Files,,, cpp.info, The GNU C Preprocessor
Manual}.@refill
@Theglibc{} provides several header files, each of which contains
the type and macro definitions and variable and function declarations
for a group of related facilities. This means that your programs may
need to include several header files, depending on exactly which
facilities you are using.
Some library header files include other library header files
automatically. However, as a matter of programming style, you should
not rely on this; it is better to explicitly include all the header
files required for the library facilities you are using. The @glibcadj{}
header files have been written in such a way that it doesn't
matter if a header file is accidentally included more than once;
including a header file a second time has no effect. Likewise, if your
program needs to include multiple header files, the order in which they
are included doesn't matter.
@strong{Compatibility Note:} Inclusion of standard header files in any
order and any number of times works in any @w{ISO C} implementation.
However, this has traditionally not been the case in many older C
implementations.
Strictly speaking, you don't @emph{have to} include a header file to use
a function it declares; you could declare the function explicitly
yourself, according to the specifications in this manual. But it is
usually better to include the header file because it may define types
and macros that are not otherwise available and because it may define
more efficient macro replacements for some functions. It is also a sure
way to have the correct declaration.
@node Macro Definitions, Reserved Names, Header Files, Using the Library
@subsection Macro Definitions of Functions
@cindex shadowing functions with macros
@cindex removing macros that shadow functions
@cindex undefining macros that shadow functions
If we describe something as a function in this manual, it may have a
macro definition as well. This normally has no effect on how your
program runs---the macro definition does the same thing as the function
would. In particular, macro equivalents for library functions evaluate
arguments exactly once, in the same way that a function call would. The
main reason for these macro definitions is that sometimes they can
produce an inline expansion that is considerably faster than an actual
function call.
Taking the address of a library function works even if it is also
defined as a macro. This is because, in this context, the name of the
function isn't followed by the left parenthesis that is syntactically
necessary to recognize a macro call.
You might occasionally want to avoid using the macro definition of a
function---perhaps to make your program easier to debug. There are
two ways you can do this:
@itemize @bullet
@item
You can avoid a macro definition in a specific use by enclosing the name
of the function in parentheses. This works because the name of the
function doesn't appear in a syntactic context where it is recognizable
as a macro call.
@item
You can suppress any macro definition for a whole source file by using
the @samp{#undef} preprocessor directive, unless otherwise stated
explicitly in the description of that facility.
@end itemize
For example, suppose the header file @file{stdlib.h} declares a function
named @code{abs} with
@smallexample
extern int abs (int);
@end smallexample
@noindent
and also provides a macro definition for @code{abs}. Then, in:
@smallexample
#include
int f (int *i) @{ return abs (++*i); @}
@end smallexample
@noindent
the reference to @code{abs} might refer to either a macro or a function.
On the other hand, in each of the following examples the reference is
to a function and not a macro.
@smallexample
#include
int g (int *i) @{ return (abs) (++*i); @}
#undef abs
int h (int *i) @{ return abs (++*i); @}
@end smallexample
Since macro definitions that double for a function behave in
exactly the same way as the actual function version, there is usually no
need for any of these methods. In fact, removing macro definitions usually
just makes your program slower.
@node Reserved Names, Feature Test Macros, Macro Definitions, Using the Library
@subsection Reserved Names
@cindex reserved names
@cindex name space
The names of all library types, macros, variables and functions that
come from the @w{ISO C} standard are reserved unconditionally; your program
@strong{may not} redefine these names. All other library names are
reserved if your program explicitly includes the header file that
defines or declares them. There are several reasons for these
restrictions:
@itemize @bullet
@item
Other people reading your code could get very confused if you were using
a function named @code{exit} to do something completely different from
what the standard @code{exit} function does, for example. Preventing
this situation helps to make your programs easier to understand and
contributes to modularity and maintainability.
@item
It avoids the possibility of a user accidentally redefining a library
function that is called by other library functions. If redefinition
were allowed, those other functions would not work properly.
@item
It allows the compiler to do whatever special optimizations it pleases
on calls to these functions, without the possibility that they may have
been redefined by the user. Some library facilities, such as those for
dealing with variadic arguments (@pxref{Variadic Functions})
and non-local exits (@pxref{Non-Local Exits}), actually require a
considerable amount of cooperation on the part of the C compiler, and
with respect to the implementation, it might be easier for the compiler
to treat these as built-in parts of the language.
@end itemize
In addition to the names documented in this manual, reserved names
include all external identifiers (global functions and variables) that
begin with an underscore (@samp{_}) and all identifiers regardless of
use that begin with either two underscores or an underscore followed by
a capital letter are reserved names. This is so that the library and
header files can define functions, variables, and macros for internal
purposes without risk of conflict with names in user programs.
Some additional classes of identifier names are reserved for future
extensions to the C language or the POSIX.1 environment. While using these
names for your own purposes right now might not cause a problem, they do
raise the possibility of conflict with future versions of the C
or POSIX standards, so you should avoid these names.
@itemize @bullet
@item
Names beginning with a capital @samp{E} followed a digit or uppercase
letter may be used for additional error code names. @xref{Error
Reporting}.
@item
Names that begin with either @samp{is} or @samp{to} followed by a
lowercase letter may be used for additional character testing and
conversion functions. @xref{Character Handling}.
@item
Names that begin with @samp{LC_} followed by an uppercase letter may be
used for additional macros specifying locale attributes.
@xref{Locales}.
@item
Names of all existing mathematics functions (@pxref{Mathematics})
suffixed with @samp{f} or @samp{l} are reserved for corresponding
functions that operate on @code{float} and @code{long double} arguments,
respectively.
@item
Names that begin with @samp{SIG} followed by an uppercase letter are
reserved for additional signal names. @xref{Standard Signals}.
@item
Names that begin with @samp{SIG_} followed by an uppercase letter are
reserved for additional signal actions. @xref{Basic Signal Handling}.
@item
Names beginning with @samp{str}, @samp{mem}, or @samp{wcs} followed by a
lowercase letter are reserved for additional string and array functions.
@xref{String and Array Utilities}.
@item
Names that end with @samp{_t} are reserved for additional type names.
@end itemize
In addition, some individual header files reserve names beyond
those that they actually define. You only need to worry about these
restrictions if your program includes that particular header file.
@itemize @bullet
@item
The header file @file{dirent.h} reserves names prefixed with
@samp{d_}.
@pindex dirent.h
@item
The header file @file{fcntl.h} reserves names prefixed with
@samp{l_}, @samp{F_}, @samp{O_}, and @samp{S_}.
@pindex fcntl.h
@item
The header file @file{grp.h} reserves names prefixed with @samp{gr_}.
@pindex grp.h
@item
The header file @file{limits.h} reserves names suffixed with @samp{_MAX}.
@pindex limits.h
@item
The header file @file{pwd.h} reserves names prefixed with @samp{pw_}.
@pindex pwd.h
@item
The header file @file{signal.h} reserves names prefixed with @samp{sa_}
and @samp{SA_}.
@pindex signal.h
@item
The header file @file{sys/stat.h} reserves names prefixed with @samp{st_}
and @samp{S_}.
@pindex sys/stat.h
@item
The header file @file{sys/times.h} reserves names prefixed with @samp{tms_}.
@pindex sys/times.h
@item
The header file @file{termios.h} reserves names prefixed with @samp{c_},
@samp{V}, @samp{I}, @samp{O}, and @samp{TC}; and names prefixed with
@samp{B} followed by a digit.
@pindex termios.h
@end itemize
@comment Include the section on Creature Nest Macros.
@include creature.texi
@node Roadmap to the Manual, , Using the Library, Introduction
@section Roadmap to the Manual
Here is an overview of the contents of the remaining chapters of
this manual.
@itemize @bullet
@item
@ref{Error Reporting}, describes how errors detected by the library
are reported.
@item
@ref{Language Features}, contains information about library support for
standard parts of the C language, including things like the @code{sizeof}
operator and the symbolic constant @code{NULL}, how to write functions
accepting variable numbers of arguments, and constants describing the
ranges and other properties of the numerical types. There is also a simple
debugging mechanism which allows you to put assertions in your code, and
have diagnostic messages printed if the tests fail.
@item
@ref{Memory}, describes @theglibc{}'s facilities for managing and
using virtual and real memory, including dynamic allocation of virtual
memory. If you do not know in advance how much memory your program
needs, you can allocate it dynamically instead, and manipulate it via
pointers.
@item
@ref{Character Handling}, contains information about character
classification functions (such as @code{isspace}) and functions for
performing case conversion.
@item
@ref{String and Array Utilities}, has descriptions of functions for
manipulating strings (null-terminated character arrays) and general
byte arrays, including operations such as copying and comparison.
@item
@ref{I/O Overview}, gives an overall look at the input and output
facilities in the library, and contains information about basic concepts
such as file names.
@item
@ref{I/O on Streams}, describes I/O operations involving streams (or
@w{@code{FILE *}} objects). These are the normal C library functions
from @file{stdio.h}.
@item
@ref{Low-Level I/O}, contains information about I/O operations
on file descriptors. File descriptors are a lower-level mechanism
specific to the Unix family of operating systems.
@item
@ref{File System Interface}, has descriptions of operations on entire
files, such as functions for deleting and renaming them and for creating
new directories. This chapter also contains information about how you
can access the attributes of a file, such as its owner and file protection
modes.
@item
@ref{Pipes and FIFOs}, contains information about simple interprocess
communication mechanisms. Pipes allow communication between two related
processes (such as between a parent and child), while FIFOs allow
communication between processes sharing a common file system on the same
machine.
@item
@ref{Sockets}, describes a more complicated interprocess communication
mechanism that allows processes running on different machines to
communicate over a network. This chapter also contains information about
Internet host addressing and how to use the system network databases.
@item
@ref{Low-Level Terminal Interface}, describes how you can change the
attributes of a terminal device. If you want to disable echo of
characters typed by the user, for example, read this chapter.
@item
@ref{Mathematics}, contains information about the math library
functions. These include things like random-number generators and
remainder functions on integers as well as the usual trigonometric and
exponential functions on floating-point numbers.
@item
@ref{Arithmetic,, Low-Level Arithmetic Functions}, describes functions
for simple arithmetic, analysis of floating-point values, and reading
numbers from strings.
@item
@ref{Searching and Sorting}, contains information about functions
for searching and sorting arrays. You can use these functions on any
kind of array by providing an appropriate comparison function.
@item
@ref{Pattern Matching}, presents functions for matching regular expressions
and shell file name patterns, and for expanding words as the shell does.
@item
@ref{Date and Time}, describes functions for measuring both calendar time
and CPU time, as well as functions for setting alarms and timers.
@item
@ref{Character Set Handling}, contains information about manipulating
characters and strings using character sets larger than will fit in
the usual @code{char} data type.
@item
@ref{Locales}, describes how selecting a particular country
or language affects the behavior of the library. For example, the locale
affects collation sequences for strings and how monetary values are
formatted.
@item
@ref{Non-Local Exits}, contains descriptions of the @code{setjmp} and
@code{longjmp} functions. These functions provide a facility for
@code{goto}-like jumps which can jump from one function to another.
@item
@ref{Signal Handling}, tells you all about signals---what they are,
how to establish a handler that is called when a particular kind of
signal is delivered, and how to prevent signals from arriving during
critical sections of your program.
@item
@ref{Program Basics}, tells how your programs can access their
command-line arguments and environment variables.
@item
@ref{Processes}, contains information about how to start new processes
and run programs.
@item
@ref{Job Control}, describes functions for manipulating process groups
and the controlling terminal. This material is probably only of
interest if you are writing a shell or other program which handles job
control specially.
@item
@ref{Name Service Switch}, describes the services which are available
for looking up names in the system databases, how to determine which
service is used for which database, and how these services are
implemented so that contributors can design their own services.
@item
@ref{User Database}, and @ref{Group Database}, tell you how to access
the system user and group databases.
@item
@ref{System Management}, describes functions for controlling and getting
information about the hardware and software configuration your program
is executing under.
@item
@ref{System Configuration}, tells you how you can get information about
various operating system limits. Most of these parameters are provided for
compatibility with POSIX.
@item
@ref{Library Summary}, gives a summary of all the functions, variables, and
macros in the library, with complete data types and function prototypes,
and says what standard or system each is derived from.
@item
@ref{Installation}, explains how to build and install @theglibc{} on
your system, and how to report any bugs you might find.
@item
@ref{Maintenance}, explains how to add new functions or port the
library to a new system.
@end itemize
If you already know the name of the facility you are interested in, you
can look it up in @ref{Library Summary}. This gives you a summary of
its syntax and a pointer to where you can find a more detailed
description. This appendix is particularly useful if you just want to
verify the order and type of arguments to a function, for example. It
also tells you what standard or system each function, variable, or macro
is derived from.
glibc-doc-reference-2.19.orig/manual/locale.texi 0000664 0001750 0001750 00000155515 12275120646 021725 0 ustar adconrad adconrad @node Locales, Message Translation, Character Set Handling, Top
@c %MENU% The country and language can affect the behavior of library functions
@chapter Locales and Internationalization
Different countries and cultures have varying conventions for how to
communicate. These conventions range from very simple ones, such as the
format for representing dates and times, to very complex ones, such as
the language spoken.
@cindex internationalization
@cindex locales
@dfn{Internationalization} of software means programming it to be able
to adapt to the user's favorite conventions. In @w{ISO C},
internationalization works by means of @dfn{locales}. Each locale
specifies a collection of conventions, one convention for each purpose.
The user chooses a set of conventions by specifying a locale (via
environment variables).
All programs inherit the chosen locale as part of their environment.
Provided the programs are written to obey the choice of locale, they
will follow the conventions preferred by the user.
@menu
* Effects of Locale:: Actions affected by the choice of
locale.
* Choosing Locale:: How the user specifies a locale.
* Locale Categories:: Different purposes for which you can
select a locale.
* Setting the Locale:: How a program specifies the locale
with library functions.
* Standard Locales:: Locale names available on all systems.
* Locale Information:: How to access the information for the locale.
* Formatting Numbers:: A dedicated function to format numbers.
* Yes-or-No Questions:: Check a Response against the locale.
@end menu
@node Effects of Locale, Choosing Locale, , Locales
@section What Effects a Locale Has
Each locale specifies conventions for several purposes, including the
following:
@itemize @bullet
@item
What multibyte character sequences are valid, and how they are
interpreted (@pxref{Character Set Handling}).
@item
Classification of which characters in the local character set are
considered alphabetic, and upper- and lower-case conversion conventions
(@pxref{Character Handling}).
@item
The collating sequence for the local language and character set
(@pxref{Collation Functions}).
@item
Formatting of numbers and currency amounts (@pxref{General Numeric}).
@item
Formatting of dates and times (@pxref{Formatting Calendar Time}).
@item
What language to use for output, including error messages
(@pxref{Message Translation}).
@item
What language to use for user answers to yes-or-no questions
(@pxref{Yes-or-No Questions}).
@item
What language to use for more complex user input.
(The C library doesn't yet help you implement this.)
@end itemize
Some aspects of adapting to the specified locale are handled
automatically by the library subroutines. For example, all your program
needs to do in order to use the collating sequence of the chosen locale
is to use @code{strcoll} or @code{strxfrm} to compare strings.
Other aspects of locales are beyond the comprehension of the library.
For example, the library can't automatically translate your program's
output messages into other languages. The only way you can support
output in the user's favorite language is to program this more or less
by hand. The C library provides functions to handle translations for
multiple languages easily.
This chapter discusses the mechanism by which you can modify the current
locale. The effects of the current locale on specific library functions
are discussed in more detail in the descriptions of those functions.
@node Choosing Locale, Locale Categories, Effects of Locale, Locales
@section Choosing a Locale
The simplest way for the user to choose a locale is to set the
environment variable @code{LANG}. This specifies a single locale to use
for all purposes. For example, a user could specify a hypothetical
locale named @samp{espana-castellano} to use the standard conventions of
most of Spain.
The set of locales supported depends on the operating system you are
using, and so do their names. We can't make any promises about what
locales will exist, except for one standard locale called @samp{C} or
@samp{POSIX}. Later we will describe how to construct locales.
@comment (@pxref{Building Locale Files}).
@cindex combining locales
A user also has the option of specifying different locales for different
purposes---in effect, choosing a mixture of multiple locales.
For example, the user might specify the locale @samp{espana-castellano}
for most purposes, but specify the locale @samp{usa-english} for
currency formatting. This might make sense if the user is a
Spanish-speaking American, working in Spanish, but representing monetary
amounts in US dollars.
Note that both locales @samp{espana-castellano} and @samp{usa-english},
like all locales, would include conventions for all of the purposes to
which locales apply. However, the user can choose to use each locale
for a particular subset of those purposes.
@node Locale Categories, Setting the Locale, Choosing Locale, Locales
@section Categories of Activities that Locales Affect
@cindex categories for locales
@cindex locale categories
The purposes that locales serve are grouped into @dfn{categories}, so
that a user or a program can choose the locale for each category
independently. Here is a table of categories; each name is both an
environment variable that a user can set, and a macro name that you can
use as an argument to @code{setlocale}.
@vtable @code
@comment locale.h
@comment ISO
@item LC_COLLATE
This category applies to collation of strings (functions @code{strcoll}
and @code{strxfrm}); see @ref{Collation Functions}.
@comment locale.h
@comment ISO
@item LC_CTYPE
This category applies to classification and conversion of characters,
and to multibyte and wide characters;
see @ref{Character Handling}, and @ref{Character Set Handling}.
@comment locale.h
@comment ISO
@item LC_MONETARY
This category applies to formatting monetary values; see @ref{General Numeric}.
@comment locale.h
@comment ISO
@item LC_NUMERIC
This category applies to formatting numeric values that are not
monetary; see @ref{General Numeric}.
@comment locale.h
@comment ISO
@item LC_TIME
This category applies to formatting date and time values; see
@ref{Formatting Calendar Time}.
@comment locale.h
@comment XOPEN
@item LC_MESSAGES
This category applies to selecting the language used in the user
interface for message translation (@pxref{The Uniforum approach};
@pxref{Message catalogs a la X/Open}) and contains regular expressions
for affirmative and negative responses.
@comment locale.h
@comment ISO
@item LC_ALL
This is not an environment variable; it is only a macro that you can use
with @code{setlocale} to set a single locale for all purposes. Setting
this environment variable overwrites all selections by the other
@code{LC_*} variables or @code{LANG}.
@comment locale.h
@comment ISO
@item LANG
If this environment variable is defined, its value specifies the locale
to use for all purposes except as overridden by the variables above.
@end vtable
@vindex LANGUAGE
When developing the message translation functions it was felt that the
functionality provided by the variables above is not sufficient. For
example, it should be possible to specify more than one locale name.
Take a Swedish user who better speaks German than English, and a program
whose messages are output in English by default. It should be possible
to specify that the first choice of language is Swedish, the second
German, and if this also fails to use English. This is
possible with the variable @code{LANGUAGE}. For further description of
this GNU extension see @ref{Using gettextized software}.
@node Setting the Locale, Standard Locales, Locale Categories, Locales
@section How Programs Set the Locale
A C program inherits its locale environment variables when it starts up.
This happens automatically. However, these variables do not
automatically control the locale used by the library functions, because
@w{ISO C} says that all programs start by default in the standard @samp{C}
locale. To use the locales specified by the environment, you must call
@code{setlocale}. Call it as follows:
@smallexample
setlocale (LC_ALL, "");
@end smallexample
@noindent
to select a locale based on the user choice of the appropriate
environment variables.
@cindex changing the locale
@cindex locale, changing
You can also use @code{setlocale} to specify a particular locale, for
general use or for a specific category.
@pindex locale.h
The symbols in this section are defined in the header file @file{locale.h}.
@comment locale.h
@comment ISO
@deftypefun {char *} setlocale (int @var{category}, const char *@var{locale})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtslocale{}} @mtsenv{}}@asunsafe{@asuinit{} @asulock{} @ascuheap{} @asucorrupt{}}@acunsafe{@acuinit{} @acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Uses of the global locale object are unguarded in functions that
@c ought to be MT-Safe, so we're ruling out the use of this function
@c once threads are started. It takes a write lock itself, but it may
@c return a pointer loaded from the global locale object after releasing
@c the lock, or before taking it.
@c setlocale @mtasuconst:@mtslocale @mtsenv @asuinit @ascuheap @asulock @asucorrupt @acucorrupt @acsmem @acsfd @aculock
@c libc_rwlock_wrlock @asulock @aculock
@c libc_rwlock_unlock @aculock
@c getenv LOCPATH @mtsenv
@c malloc @ascuheap @acsmem
@c free @ascuheap @acsmem
@c new_composite_name ok
@c setdata ok
@c setname ok
@c _nl_find_locale @mtsenv @asuinit @ascuheap @asulock @asucorrupt @acucorrupt @acsmem @acsfd @aculock
@c getenv LC_ALL and LANG @mtsenv
@c _nl_load_locale_from_archive @ascuheap @acucorrupt @acsmem @acsfd
@c sysconf _SC_PAGE_SIZE ok
@c _nl_normalize_codeset @ascuheap @acsmem
@c isalnum_l ok (C locale)
@c isdigit_l ok (C locale)
@c malloc @ascuheap @acsmem
@c tolower_l ok (C locale)
@c open_not_cancel_2 @acsfd
@c fxstat64 ok
@c close_not_cancel_no_status ok
@c __mmap64 @acsmem
@c calculate_head_size ok
@c __munmap ok
@c compute_hashval ok
@c qsort dup @acucorrupt
@c rangecmp ok
@c malloc @ascuheap @acsmem
@c strdup @ascuheap @acsmem
@c _nl_intern_locale_data @ascuheap @acsmem
@c malloc @ascuheap @acsmem
@c free @ascuheap @acsmem
@c _nl_expand_alias @ascuheap @asulock @acsmem @acsfd @aculock
@c libc_lock_lock @asulock @aculock
@c bsearch ok
@c alias_compare ok
@c strcasecmp ok
@c read_alias_file @ascuheap @asulock @acsmem @acsfd @aculock
@c fopen @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking ok
@c feof_unlocked ok
@c fgets_unlocked ok
@c isspace ok (locale mutex is locked)
@c extend_alias_table @ascuheap @acsmem
@c realloc @ascuheap @acsmem
@c realloc @ascuheap @acsmem
@c fclose @ascuheap @asulock @acsmem @acsfd @aculock
@c qsort @ascuheap @acsmem
@c alias_compare dup
@c libc_lock_unlock @aculock
@c _nl_explode_name @ascuheap @acsmem
@c _nl_find_language ok
@c _nl_normalize_codeset dup @ascuheap @acsmem
@c _nl_make_l10nflist @ascuheap @acsmem
@c malloc @ascuheap @acsmem
@c free @ascuheap @acsmem
@c __argz_stringify ok
@c __argz_count ok
@c __argz_next ok
@c _nl_load_locale @ascuheap @acsmem @acsfd
@c open_not_cancel_2 @acsfd
@c __fxstat64 ok
@c close_not_cancel_no_status ok
@c mmap @acsmem
@c malloc @ascuheap @acsmem
@c read_not_cancel ok
@c free @ascuheap @acsmem
@c _nl_intern_locale_data dup @ascuheap @acsmem
@c munmap ok
@c __gconv_compare_alias @asuinit @ascuheap @asucorrupt @asulock @acsmem@acucorrupt @acsfd @aculock
@c __gconv_read_conf @asuinit @ascuheap @asucorrupt @asulock @acsmem@acucorrupt @acsfd @aculock
@c (libc_once-initializes gconv_cache and gconv_path_envvar; they're
@c never modified afterwards)
@c __gconv_load_cache @ascuheap @acsmem @acsfd
@c getenv GCONV_PATH @mtsenv
@c open_not_cancel @acsfd
@c __fxstat64 ok
@c close_not_cancel_no_status ok
@c mmap @acsmem
@c malloc @ascuheap @acsmem
@c __read ok
@c free @ascuheap @acsmem
@c munmap ok
@c __gconv_get_path @asulock @ascuheap @aculock @acsmem @acsfd
@c getcwd @ascuheap @acsmem @acsfd
@c libc_lock_lock @asulock @aculock
@c malloc @ascuheap @acsmem
@c strtok_r ok
@c libc_lock_unlock @aculock
@c read_conf_file @ascuheap @asucorrupt @asulock @acsmem @acucorrupt @acsfd @aculock
@c fopen @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking ok
@c feof_unlocked ok
@c getdelim @ascuheap @asucorrupt @acsmem @acucorrupt
@c isspace_l ok (C locale)
@c add_alias
@c isspace_l ok (C locale)
@c toupper_l ok (C locale)
@c add_alias2 dup @ascuheap @acucorrupt @acsmem
@c add_module @ascuheap @acsmem
@c isspace_l ok (C locale)
@c toupper_l ok (C locale)
@c strtol ok (@mtslocale but we hold the locale lock)
@c tfind __gconv_alias_db ok
@c __gconv_alias_compare dup ok
@c calloc @ascuheap @acsmem
@c insert_module dup @ascuheap
@c __tfind ok (because the tree is read only by then)
@c __gconv_alias_compare dup ok
@c insert_module @ascuheap
@c free @ascuheap
@c add_alias2 @ascuheap @acucorrupt @acsmem
@c detect_conflict ok, reads __gconv_modules_db
@c malloc @ascuheap @acsmem
@c tsearch __gconv_alias_db @ascuheap @acucorrupt @acsmem [exclusive tree, no @mtsrace]
@c __gconv_alias_compare ok
@c free @ascuheap
@c __gconv_compare_alias_cache ok
@c find_module_idx ok
@c do_lookup_alias ok
@c __tfind ok (because the tree is read only by then)
@c __gconv_alias_compare ok
@c strndup @ascuheap @acsmem
@c strcasecmp_l ok (C locale)
The function @code{setlocale} sets the current locale for category
@var{category} to @var{locale}. A list of all the locales the system
provides can be created by running
@pindex locale
@smallexample
locale -a
@end smallexample
If @var{category} is @code{LC_ALL}, this specifies the locale for all
purposes. The other possible values of @var{category} specify an
single purpose (@pxref{Locale Categories}).
You can also use this function to find out the current locale by passing
a null pointer as the @var{locale} argument. In this case,
@code{setlocale} returns a string that is the name of the locale
currently selected for category @var{category}.
The string returned by @code{setlocale} can be overwritten by subsequent
calls, so you should make a copy of the string (@pxref{Copying and
Concatenation}) if you want to save it past any further calls to
@code{setlocale}. (The standard library is guaranteed never to call
@code{setlocale} itself.)
You should not modify the string returned by @code{setlocale}. It might
be the same string that was passed as an argument in a previous call to
@code{setlocale}. One requirement is that the @var{category} must be
the same in the call the string was returned and the one when the string
is passed in as @var{locale} parameter.
When you read the current locale for category @code{LC_ALL}, the value
encodes the entire combination of selected locales for all categories.
In this case, the value is not just a single locale name. In fact, we
don't make any promises about what it looks like. But if you specify
the same ``locale name'' with @code{LC_ALL} in a subsequent call to
@code{setlocale}, it restores the same combination of locale selections.
To be sure you can use the returned string encoding the currently selected
locale at a later time, you must make a copy of the string. It is not
guaranteed that the returned pointer remains valid over time.
When the @var{locale} argument is not a null pointer, the string returned
by @code{setlocale} reflects the newly-modified locale.
If you specify an empty string for @var{locale}, this means to read the
appropriate environment variable and use its value to select the locale
for @var{category}.
If a nonempty string is given for @var{locale}, then the locale of that
name is used if possible.
If you specify an invalid locale name, @code{setlocale} returns a null
pointer and leaves the current locale unchanged.
@end deftypefun
The path used for finding locale data can be set using the
@code{LOCPATH} environment variable. The default path for finding
locale data is system specific. It is computed from the value given
as the prefix while configuring the C library. This value normally is
@file{/usr} or @file{/}. For the former the complete path is:
@smallexample
/usr/lib/locale
@end smallexample
Here is an example showing how you might use @code{setlocale} to
temporarily switch to a new locale.
@smallexample
#include
#include
#include
#include
void
with_other_locale (char *new_locale,
void (*subroutine) (int),
int argument)
@{
char *old_locale, *saved_locale;
/* @r{Get the name of the current locale.} */
old_locale = setlocale (LC_ALL, NULL);
/* @r{Copy the name so it won't be clobbered by @code{setlocale}.} */
saved_locale = strdup (old_locale);
if (saved_locale == NULL)
fatal ("Out of memory");
/* @r{Now change the locale and do some stuff with it.} */
setlocale (LC_ALL, new_locale);
(*subroutine) (argument);
/* @r{Restore the original locale.} */
setlocale (LC_ALL, saved_locale);
free (saved_locale);
@}
@end smallexample
@strong{Portability Note:} Some @w{ISO C} systems may define additional
locale categories, and future versions of the library will do so. For
portability, assume that any symbol beginning with @samp{LC_} might be
defined in @file{locale.h}.
@node Standard Locales, Locale Information, Setting the Locale, Locales
@section Standard Locales
The only locale names you can count on finding on all operating systems
are these three standard ones:
@table @code
@item "C"
This is the standard C locale. The attributes and behavior it provides
are specified in the @w{ISO C} standard. When your program starts up, it
initially uses this locale by default.
@item "POSIX"
This is the standard POSIX locale. Currently, it is an alias for the
standard C locale.
@item ""
The empty name says to select a locale based on environment variables.
@xref{Locale Categories}.
@end table
Defining and installing named locales is normally a responsibility of
the system administrator at your site (or the person who installed
@theglibc{}). It is also possible for the user to create private
locales. All this will be discussed later when describing the tool to
do so.
@comment (@pxref{Building Locale Files}).
If your program needs to use something other than the @samp{C} locale,
it will be more portable if you use whatever locale the user specifies
with the environment, rather than trying to specify some non-standard
locale explicitly by name. Remember, different machines might have
different sets of locales installed.
@node Locale Information, Formatting Numbers, Standard Locales, Locales
@section Accessing Locale Information
There are several ways to access locale information. The simplest
way is to let the C library itself do the work. Several of the
functions in this library implicitly access the locale data, and use
what information is provided by the currently selected locale. This is
how the locale model is meant to work normally.
As an example take the @code{strftime} function, which is meant to nicely
format date and time information (@pxref{Formatting Calendar Time}).
Part of the standard information contained in the @code{LC_TIME}
category is the names of the months. Instead of requiring the
programmer to take care of providing the translations the
@code{strftime} function does this all by itself. @code{%A}
in the format string is replaced by the appropriate weekday
name of the locale currently selected by @code{LC_TIME}. This is an
easy example, and wherever possible functions do things automatically
in this way.
But there are quite often situations when there is simply no function
to perform the task, or it is simply not possible to do the work
automatically. For these cases it is necessary to access the
information in the locale directly. To do this the C library provides
two functions: @code{localeconv} and @code{nl_langinfo}. The former is
part of @w{ISO C} and therefore portable, but has a brain-damaged
interface. The second is part of the Unix interface and is portable in
as far as the system follows the Unix standards.
@menu
* The Lame Way to Locale Data:: ISO C's @code{localeconv}.
* The Elegant and Fast Way:: X/Open's @code{nl_langinfo}.
@end menu
@node The Lame Way to Locale Data, The Elegant and Fast Way, ,Locale Information
@subsection @code{localeconv}: It is portable but @dots{}
Together with the @code{setlocale} function the @w{ISO C} people
invented the @code{localeconv} function. It is a masterpiece of poor
design. It is expensive to use, not extendable, and not generally
usable as it provides access to only @code{LC_MONETARY} and
@code{LC_NUMERIC} related information. Nevertheless, if it is
applicable to a given situation it should be used since it is very
portable. The function @code{strfmon} formats monetary amounts
according to the selected locale using this information.
@pindex locale.h
@cindex monetary value formatting
@cindex numeric value formatting
@comment locale.h
@comment ISO
@deftypefun {struct lconv *} localeconv (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:localeconv} @mtslocale{}}@asunsafe{}@acsafe{}}
@c This function reads from multiple components of the locale object,
@c without synchronization, while writing to the static buffer it uses
@c as the return value.
The @code{localeconv} function returns a pointer to a structure whose
components contain information about how numeric and monetary values
should be formatted in the current locale.
You should not modify the structure or its contents. The structure might
be overwritten by subsequent calls to @code{localeconv}, or by calls to
@code{setlocale}, but no other function in the library overwrites this
value.
@end deftypefun
@comment locale.h
@comment ISO
@deftp {Data Type} {struct lconv}
@code{localeconv}'s return value is of this data type. Its elements are
described in the following subsections.
@end deftp
If a member of the structure @code{struct lconv} has type @code{char},
and the value is @code{CHAR_MAX}, it means that the current locale has
no value for that parameter.
@menu
* General Numeric:: Parameters for formatting numbers and
currency amounts.
* Currency Symbol:: How to print the symbol that identifies an
amount of money (e.g. @samp{$}).
* Sign of Money Amount:: How to print the (positive or negative) sign
for a monetary amount, if one exists.
@end menu
@node General Numeric, Currency Symbol, , The Lame Way to Locale Data
@subsubsection Generic Numeric Formatting Parameters
These are the standard members of @code{struct lconv}; there may be
others.
@table @code
@item char *decimal_point
@itemx char *mon_decimal_point
These are the decimal-point separators used in formatting non-monetary
and monetary quantities, respectively. In the @samp{C} locale, the
value of @code{decimal_point} is @code{"."}, and the value of
@code{mon_decimal_point} is @code{""}.
@cindex decimal-point separator
@item char *thousands_sep
@itemx char *mon_thousands_sep
These are the separators used to delimit groups of digits to the left of
the decimal point in formatting non-monetary and monetary quantities,
respectively. In the @samp{C} locale, both members have a value of
@code{""} (the empty string).
@item char *grouping
@itemx char *mon_grouping
These are strings that specify how to group the digits to the left of
the decimal point. @code{grouping} applies to non-monetary quantities
and @code{mon_grouping} applies to monetary quantities. Use either
@code{thousands_sep} or @code{mon_thousands_sep} to separate the digit
groups.
@cindex grouping of digits
Each member of these strings is to be interpreted as an integer value of
type @code{char}. Successive numbers (from left to right) give the
sizes of successive groups (from right to left, starting at the decimal
point.) The last member is either @code{0}, in which case the previous
member is used over and over again for all the remaining groups, or
@code{CHAR_MAX}, in which case there is no more grouping---or, put
another way, any remaining digits form one large group without
separators.
For example, if @code{grouping} is @code{"\04\03\02"}, the correct
grouping for the number @code{123456787654321} is @samp{12}, @samp{34},
@samp{56}, @samp{78}, @samp{765}, @samp{4321}. This uses a group of 4
digits at the end, preceded by a group of 3 digits, preceded by groups
of 2 digits (as many as needed). With a separator of @samp{,}, the
number would be printed as @samp{12,34,56,78,765,4321}.
A value of @code{"\03"} indicates repeated groups of three digits, as
normally used in the U.S.
In the standard @samp{C} locale, both @code{grouping} and
@code{mon_grouping} have a value of @code{""}. This value specifies no
grouping at all.
@item char int_frac_digits
@itemx char frac_digits
These are small integers indicating how many fractional digits (to the
right of the decimal point) should be displayed in a monetary value in
international and local formats, respectively. (Most often, both
members have the same value.)
In the standard @samp{C} locale, both of these members have the value
@code{CHAR_MAX}, meaning ``unspecified''. The ISO standard doesn't say
what to do when you find this value; we recommend printing no
fractional digits. (This locale also specifies the empty string for
@code{mon_decimal_point}, so printing any fractional digits would be
confusing!)
@end table
@node Currency Symbol, Sign of Money Amount, General Numeric, The Lame Way to Locale Data
@subsubsection Printing the Currency Symbol
@cindex currency symbols
These members of the @code{struct lconv} structure specify how to print
the symbol to identify a monetary value---the international analog of
@samp{$} for US dollars.
Each country has two standard currency symbols. The @dfn{local currency
symbol} is used commonly within the country, while the
@dfn{international currency symbol} is used internationally to refer to
that country's currency when it is necessary to indicate the country
unambiguously.
For example, many countries use the dollar as their monetary unit, and
when dealing with international currencies it's important to specify
that one is dealing with (say) Canadian dollars instead of U.S. dollars
or Australian dollars. But when the context is known to be Canada,
there is no need to make this explicit---dollar amounts are implicitly
assumed to be in Canadian dollars.
@table @code
@item char *currency_symbol
The local currency symbol for the selected locale.
In the standard @samp{C} locale, this member has a value of @code{""}
(the empty string), meaning ``unspecified''. The ISO standard doesn't
say what to do when you find this value; we recommend you simply print
the empty string as you would print any other string pointed to by this
variable.
@item char *int_curr_symbol
The international currency symbol for the selected locale.
The value of @code{int_curr_symbol} should normally consist of a
three-letter abbreviation determined by the international standard
@cite{ISO 4217 Codes for the Representation of Currency and Funds},
followed by a one-character separator (often a space).
In the standard @samp{C} locale, this member has a value of @code{""}
(the empty string), meaning ``unspecified''. We recommend you simply print
the empty string as you would print any other string pointed to by this
variable.
@item char p_cs_precedes
@itemx char n_cs_precedes
@itemx char int_p_cs_precedes
@itemx char int_n_cs_precedes
These members are @code{1} if the @code{currency_symbol} or
@code{int_curr_symbol} strings should precede the value of a monetary
amount, or @code{0} if the strings should follow the value. The
@code{p_cs_precedes} and @code{int_p_cs_precedes} members apply to
positive amounts (or zero), and the @code{n_cs_precedes} and
@code{int_n_cs_precedes} members apply to negative amounts.
In the standard @samp{C} locale, all of these members have a value of
@code{CHAR_MAX}, meaning ``unspecified''. The ISO standard doesn't say
what to do when you find this value. We recommend printing the
currency symbol before the amount, which is right for most countries.
In other words, treat all nonzero values alike in these members.
The members with the @code{int_} prefix apply to the
@code{int_curr_symbol} while the other two apply to
@code{currency_symbol}.
@item char p_sep_by_space
@itemx char n_sep_by_space
@itemx char int_p_sep_by_space
@itemx char int_n_sep_by_space
These members are @code{1} if a space should appear between the
@code{currency_symbol} or @code{int_curr_symbol} strings and the
amount, or @code{0} if no space should appear. The
@code{p_sep_by_space} and @code{int_p_sep_by_space} members apply to
positive amounts (or zero), and the @code{n_sep_by_space} and
@code{int_n_sep_by_space} members apply to negative amounts.
In the standard @samp{C} locale, all of these members have a value of
@code{CHAR_MAX}, meaning ``unspecified''. The ISO standard doesn't say
what you should do when you find this value; we suggest you treat it as
1 (print a space). In other words, treat all nonzero values alike in
these members.
The members with the @code{int_} prefix apply to the
@code{int_curr_symbol} while the other two apply to
@code{currency_symbol}. There is one specialty with the
@code{int_curr_symbol}, though. Since all legal values contain a space
at the end the string one either printf this space (if the currency
symbol must appear in front and must be separated) or one has to avoid
printing this character at all (especially when at the end of the
string).
@end table
@node Sign of Money Amount, , Currency Symbol, The Lame Way to Locale Data
@subsubsection Printing the Sign of a Monetary Amount
These members of the @code{struct lconv} structure specify how to print
the sign (if any) of a monetary value.
@table @code
@item char *positive_sign
@itemx char *negative_sign
These are strings used to indicate positive (or zero) and negative
monetary quantities, respectively.
In the standard @samp{C} locale, both of these members have a value of
@code{""} (the empty string), meaning ``unspecified''.
The ISO standard doesn't say what to do when you find this value; we
recommend printing @code{positive_sign} as you find it, even if it is
empty. For a negative value, print @code{negative_sign} as you find it
unless both it and @code{positive_sign} are empty, in which case print
@samp{-} instead. (Failing to indicate the sign at all seems rather
unreasonable.)
@item char p_sign_posn
@itemx char n_sign_posn
@itemx char int_p_sign_posn
@itemx char int_n_sign_posn
These members are small integers that indicate how to
position the sign for nonnegative and negative monetary quantities,
respectively. (The string used by the sign is what was specified with
@code{positive_sign} or @code{negative_sign}.) The possible values are
as follows:
@table @code
@item 0
The currency symbol and quantity should be surrounded by parentheses.
@item 1
Print the sign string before the quantity and currency symbol.
@item 2
Print the sign string after the quantity and currency symbol.
@item 3
Print the sign string right before the currency symbol.
@item 4
Print the sign string right after the currency symbol.
@item CHAR_MAX
``Unspecified''. Both members have this value in the standard
@samp{C} locale.
@end table
The ISO standard doesn't say what you should do when the value is
@code{CHAR_MAX}. We recommend you print the sign after the currency
symbol.
The members with the @code{int_} prefix apply to the
@code{int_curr_symbol} while the other two apply to
@code{currency_symbol}.
@end table
@node The Elegant and Fast Way, , The Lame Way to Locale Data, Locale Information
@subsection Pinpoint Access to Locale Data
When writing the X/Open Portability Guide the authors realized that the
@code{localeconv} function is not enough to provide reasonable access to
locale information. The information which was meant to be available
in the locale (as later specified in the POSIX.1 standard) requires more
ways to access it. Therefore the @code{nl_langinfo} function
was introduced.
@comment langinfo.h
@comment XOPEN
@deftypefun {char *} nl_langinfo (nl_item @var{item})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c It calls _nl_langinfo_l with the current locale, which returns a
@c pointer into constant strings defined in locale data structures.
The @code{nl_langinfo} function can be used to access individual
elements of the locale categories. Unlike the @code{localeconv}
function, which returns all the information, @code{nl_langinfo}
lets the caller select what information it requires. This is very
fast and it is not a problem to call this function multiple times.
A second advantage is that in addition to the numeric and monetary
formatting information, information from the
@code{LC_TIME} and @code{LC_MESSAGES} categories is available.
@pindex langinfo.h
The type @code{nl_type} is defined in @file{nl_types.h}. The argument
@var{item} is a numeric value defined in the header @file{langinfo.h}.
The X/Open standard defines the following values:
@vtable @code
@item CODESET
@code{nl_langinfo} returns a string with the name of the coded character
set used in the selected locale.
@item ABDAY_1
@itemx ABDAY_2
@itemx ABDAY_3
@itemx ABDAY_4
@itemx ABDAY_5
@itemx ABDAY_6
@itemx ABDAY_7
@code{nl_langinfo} returns the abbreviated weekday name. @code{ABDAY_1}
corresponds to Sunday.
@item DAY_1
@itemx DAY_2
@itemx DAY_3
@itemx DAY_4
@itemx DAY_5
@itemx DAY_6
@itemx DAY_7
Similar to @code{ABDAY_1} etc., but here the return value is the
unabbreviated weekday name.
@item ABMON_1
@itemx ABMON_2
@itemx ABMON_3
@itemx ABMON_4
@itemx ABMON_5
@itemx ABMON_6
@itemx ABMON_7
@itemx ABMON_8
@itemx ABMON_9
@itemx ABMON_10
@itemx ABMON_11
@itemx ABMON_12
The return value is abbreviated name of the month. @code{ABMON_1}
corresponds to January.
@item MON_1
@itemx MON_2
@itemx MON_3
@itemx MON_4
@itemx MON_5
@itemx MON_6
@itemx MON_7
@itemx MON_8
@itemx MON_9
@itemx MON_10
@itemx MON_11
@itemx MON_12
Similar to @code{ABMON_1} etc., but here the month names are not abbreviated.
Here the first value @code{MON_1} also corresponds to January.
@item AM_STR
@itemx PM_STR
The return values are strings which can be used in the representation of time
as an hour from 1 to 12 plus an am/pm specifier.
Note that in locales which do not use this time representation
these strings might be empty, in which case the am/pm format
cannot be used at all.
@item D_T_FMT
The return value can be used as a format string for @code{strftime} to
represent time and date in a locale-specific way.
@item D_FMT
The return value can be used as a format string for @code{strftime} to
represent a date in a locale-specific way.
@item T_FMT
The return value can be used as a format string for @code{strftime} to
represent time in a locale-specific way.
@item T_FMT_AMPM
The return value can be used as a format string for @code{strftime} to
represent time in the am/pm format.
Note that if the am/pm format does not make any sense for the
selected locale, the return value might be the same as the one for
@code{T_FMT}.
@item ERA
The return value represents the era used in the current locale.
Most locales do not define this value. An example of a locale which
does define this value is the Japanese one. In Japan, the traditional
representation of dates includes the name of the era corresponding to
the then-emperor's reign.
Normally it should not be necessary to use this value directly.
Specifying the @code{E} modifier in their format strings causes the
@code{strftime} functions to use this information. The format of the
returned string is not specified, and therefore you should not assume
knowledge of it on different systems.
@item ERA_YEAR
The return value gives the year in the relevant era of the locale.
As for @code{ERA} it should not be necessary to use this value directly.
@item ERA_D_T_FMT
This return value can be used as a format string for @code{strftime} to
represent dates and times in a locale-specific era-based way.
@item ERA_D_FMT
This return value can be used as a format string for @code{strftime} to
represent a date in a locale-specific era-based way.
@item ERA_T_FMT
This return value can be used as a format string for @code{strftime} to
represent time in a locale-specific era-based way.
@item ALT_DIGITS
The return value is a representation of up to @math{100} values used to
represent the values @math{0} to @math{99}. As for @code{ERA} this
value is not intended to be used directly, but instead indirectly
through the @code{strftime} function. When the modifier @code{O} is
used in a format which would otherwise use numerals to represent hours,
minutes, seconds, weekdays, months, or weeks, the appropriate value for
the locale is used instead.
@item INT_CURR_SYMBOL
The same as the value returned by @code{localeconv} in the
@code{int_curr_symbol} element of the @code{struct lconv}.
@item CURRENCY_SYMBOL
@itemx CRNCYSTR
The same as the value returned by @code{localeconv} in the
@code{currency_symbol} element of the @code{struct lconv}.
@code{CRNCYSTR} is a deprecated alias still required by Unix98.
@item MON_DECIMAL_POINT
The same as the value returned by @code{localeconv} in the
@code{mon_decimal_point} element of the @code{struct lconv}.
@item MON_THOUSANDS_SEP
The same as the value returned by @code{localeconv} in the
@code{mon_thousands_sep} element of the @code{struct lconv}.
@item MON_GROUPING
The same as the value returned by @code{localeconv} in the
@code{mon_grouping} element of the @code{struct lconv}.
@item POSITIVE_SIGN
The same as the value returned by @code{localeconv} in the
@code{positive_sign} element of the @code{struct lconv}.
@item NEGATIVE_SIGN
The same as the value returned by @code{localeconv} in the
@code{negative_sign} element of the @code{struct lconv}.
@item INT_FRAC_DIGITS
The same as the value returned by @code{localeconv} in the
@code{int_frac_digits} element of the @code{struct lconv}.
@item FRAC_DIGITS
The same as the value returned by @code{localeconv} in the
@code{frac_digits} element of the @code{struct lconv}.
@item P_CS_PRECEDES
The same as the value returned by @code{localeconv} in the
@code{p_cs_precedes} element of the @code{struct lconv}.
@item P_SEP_BY_SPACE
The same as the value returned by @code{localeconv} in the
@code{p_sep_by_space} element of the @code{struct lconv}.
@item N_CS_PRECEDES
The same as the value returned by @code{localeconv} in the
@code{n_cs_precedes} element of the @code{struct lconv}.
@item N_SEP_BY_SPACE
The same as the value returned by @code{localeconv} in the
@code{n_sep_by_space} element of the @code{struct lconv}.
@item P_SIGN_POSN
The same as the value returned by @code{localeconv} in the
@code{p_sign_posn} element of the @code{struct lconv}.
@item N_SIGN_POSN
The same as the value returned by @code{localeconv} in the
@code{n_sign_posn} element of the @code{struct lconv}.
@item INT_P_CS_PRECEDES
The same as the value returned by @code{localeconv} in the
@code{int_p_cs_precedes} element of the @code{struct lconv}.
@item INT_P_SEP_BY_SPACE
The same as the value returned by @code{localeconv} in the
@code{int_p_sep_by_space} element of the @code{struct lconv}.
@item INT_N_CS_PRECEDES
The same as the value returned by @code{localeconv} in the
@code{int_n_cs_precedes} element of the @code{struct lconv}.
@item INT_N_SEP_BY_SPACE
The same as the value returned by @code{localeconv} in the
@code{int_n_sep_by_space} element of the @code{struct lconv}.
@item INT_P_SIGN_POSN
The same as the value returned by @code{localeconv} in the
@code{int_p_sign_posn} element of the @code{struct lconv}.
@item INT_N_SIGN_POSN
The same as the value returned by @code{localeconv} in the
@code{int_n_sign_posn} element of the @code{struct lconv}.
@item DECIMAL_POINT
@itemx RADIXCHAR
The same as the value returned by @code{localeconv} in the
@code{decimal_point} element of the @code{struct lconv}.
The name @code{RADIXCHAR} is a deprecated alias still used in Unix98.
@item THOUSANDS_SEP
@itemx THOUSEP
The same as the value returned by @code{localeconv} in the
@code{thousands_sep} element of the @code{struct lconv}.
The name @code{THOUSEP} is a deprecated alias still used in Unix98.
@item GROUPING
The same as the value returned by @code{localeconv} in the
@code{grouping} element of the @code{struct lconv}.
@item YESEXPR
The return value is a regular expression which can be used with the
@code{regex} function to recognize a positive response to a yes/no
question. @Theglibc{} provides the @code{rpmatch} function for
easier handling in applications.
@item NOEXPR
The return value is a regular expression which can be used with the
@code{regex} function to recognize a negative response to a yes/no
question.
@item YESSTR
The return value is a locale-specific translation of the positive response
to a yes/no question.
Using this value is deprecated since it is a very special case of
message translation, and is better handled by the message
translation functions (@pxref{Message Translation}).
The use of this symbol is deprecated. Instead message translation
should be used.
@item NOSTR
The return value is a locale-specific translation of the negative response
to a yes/no question. What is said for @code{YESSTR} is also true here.
The use of this symbol is deprecated. Instead message translation
should be used.
@end vtable
The file @file{langinfo.h} defines a lot more symbols but none of them
is official. Using them is not portable, and the format of the
return values might change. Therefore we recommended you not use
them.
Note that the return value for any valid argument can be used for
in all situations (with the possible exception of the am/pm time formatting
codes). If the user has not selected any locale for the
appropriate category, @code{nl_langinfo} returns the information from the
@code{"C"} locale. It is therefore possible to use this function as
shown in the example below.
If the argument @var{item} is not valid, a pointer to an empty string is
returned.
@end deftypefun
An example of @code{nl_langinfo} usage is a function which has to
print a given date and time in a locale-specific way. At first one
might think that, since @code{strftime} internally uses the locale
information, writing something like the following is enough:
@smallexample
size_t
i18n_time_n_data (char *s, size_t len, const struct tm *tp)
@{
return strftime (s, len, "%X %D", tp);
@}
@end smallexample
The format contains no weekday or month names and therefore is
internationally usable. Wrong! The output produced is something like
@code{"hh:mm:ss MM/DD/YY"}. This format is only recognizable in the
USA. Other countries use different formats. Therefore the function
should be rewritten like this:
@smallexample
size_t
i18n_time_n_data (char *s, size_t len, const struct tm *tp)
@{
return strftime (s, len, nl_langinfo (D_T_FMT), tp);
@}
@end smallexample
Now it uses the date and time format of the locale
selected when the program runs. If the user selects the locale
correctly there should never be a misunderstanding over the time and
date format.
@node Formatting Numbers, Yes-or-No Questions, Locale Information, Locales
@section A dedicated function to format numbers
We have seen that the structure returned by @code{localeconv} as well as
the values given to @code{nl_langinfo} allow you to retrieve the various
pieces of locale-specific information to format numbers and monetary
amounts. We have also seen that the underlying rules are quite complex.
Therefore the X/Open standards introduce a function which uses such
locale information, making it easier for the user to format
numbers according to these rules.
@deftypefun ssize_t strfmon (char *@var{s}, size_t @var{maxsize}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c It (and strfmon_l) both call vstrfmon_l, which, besides accessing the
@c locale object passed to it, accesses the active locale through
@c isdigit (but to_digit assumes ASCII digits only). It may call
@c __printf_fp (@mtslocale @ascuheap @acsmem) and guess_grouping (safe).
The @code{strfmon} function is similar to the @code{strftime} function
in that it takes a buffer, its size, a format string,
and values to write into the buffer as text in a form specified
by the format string. Like @code{strftime}, the function
also returns the number of bytes written into the buffer.
There are two differences: @code{strfmon} can take more than one
argument, and, of course, the format specification is different. Like
@code{strftime}, the format string consists of normal text, which is
output as is, and format specifiers, which are indicated by a @samp{%}.
Immediately after the @samp{%}, you can optionally specify various flags
and formatting information before the main formatting character, in a
similar way to @code{printf}:
@itemize @bullet
@item
Immediately following the @samp{%} there can be one or more of the
following flags:
@table @asis
@item @samp{=@var{f}}
The single byte character @var{f} is used for this field as the numeric
fill character. By default this character is a space character.
Filling with this character is only performed if a left precision
is specified. It is not just to fill to the given field width.
@item @samp{^}
The number is printed without grouping the digits according to the rules
of the current locale. By default grouping is enabled.
@item @samp{+}, @samp{(}
At most one of these flags can be used. They select which format to
represent the sign of a currency amount. By default, and if
@samp{+} is given, the locale equivalent of @math{+}/@math{-} is used. If
@samp{(} is given, negative amounts are enclosed in parentheses. The
exact format is determined by the values of the @code{LC_MONETARY}
category of the locale selected at program runtime.
@item @samp{!}
The output will not contain the currency symbol.
@item @samp{-}
The output will be formatted left-justified instead of right-justified if
it does not fill the entire field width.
@end table
@end itemize
The next part of a specification is an optional field width. If no
width is specified @math{0} is taken. During output, the function first
determines how much space is required. If it requires at least as many
characters as given by the field width, it is output using as much space
as necessary. Otherwise, it is extended to use the full width by
filling with the space character. The presence or absence of the
@samp{-} flag determines the side at which such padding occurs. If
present, the spaces are added at the right making the output
left-justified, and vice versa.
So far the format looks familiar, being similar to the @code{printf} and
@code{strftime} formats. However, the next two optional fields
introduce something new. The first one is a @samp{#} character followed
by a decimal digit string. The value of the digit string specifies the
number of @emph{digit} positions to the left of the decimal point (or
equivalent). This does @emph{not} include the grouping character when
the @samp{^} flag is not given. If the space needed to print the number
does not fill the whole width, the field is padded at the left side with
the fill character, which can be selected using the @samp{=} flag and by
default is a space. For example, if the field width is selected as 6
and the number is @math{123}, the fill character is @samp{*} the result
will be @samp{***123}.
The second optional field starts with a @samp{.} (period) and consists
of another decimal digit string. Its value describes the number of
characters printed after the decimal point. The default is selected
from the current locale (@code{frac_digits}, @code{int_frac_digits}, see
@pxref{General Numeric}). If the exact representation needs more digits
than given by the field width, the displayed value is rounded. If the
number of fractional digits is selected to be zero, no decimal point is
printed.
As a GNU extension, the @code{strfmon} implementation in @theglibc{}
allows an optional @samp{L} next as a format modifier. If this modifier
is given, the argument is expected to be a @code{long double} instead of
a @code{double} value.
Finally, the last component is a format specifier. There are three
specifiers defined:
@table @asis
@item @samp{i}
Use the locale's rules for formatting an international currency value.
@item @samp{n}
Use the locale's rules for formatting a national currency value.
@item @samp{%}
Place a @samp{%} in the output. There must be no flag, width
specifier or modifier given, only @samp{%%} is allowed.
@end table
As for @code{printf}, the function reads the format string
from left to right and uses the values passed to the function following
the format string. The values are expected to be either of type
@code{double} or @code{long double}, depending on the presence of the
modifier @samp{L}. The result is stored in the buffer pointed to by
@var{s}. At most @var{maxsize} characters are stored.
The return value of the function is the number of characters stored in
@var{s}, including the terminating @code{NULL} byte. If the number of
characters stored would exceed @var{maxsize}, the function returns
@math{-1} and the content of the buffer @var{s} is unspecified. In this
case @code{errno} is set to @code{E2BIG}.
@end deftypefun
A few examples should make clear how the function works. It is
assumed that all the following pieces of code are executed in a program
which uses the USA locale (@code{en_US}). The simplest
form of the format is this:
@smallexample
strfmon (buf, 100, "@@%n@@%n@@%n@@", 123.45, -567.89, 12345.678);
@end smallexample
@noindent
The output produced is
@smallexample
"@@$123.45@@-$567.89@@$12,345.68@@"
@end smallexample
We can notice several things here. First, the widths of the output
numbers are different. We have not specified a width in the format
string, and so this is no wonder. Second, the third number is printed
using thousands separators. The thousands separator for the
@code{en_US} locale is a comma. The number is also rounded.
@math{.678} is rounded to @math{.68} since the format does not specify a
precision and the default value in the locale is @math{2}. Finally,
note that the national currency symbol is printed since @samp{%n} was
used, not @samp{i}. The next example shows how we can align the output.
@smallexample
strfmon (buf, 100, "@@%=*11n@@%=*11n@@%=*11n@@", 123.45, -567.89, 12345.678);
@end smallexample
@noindent
The output this time is:
@smallexample
"@@ $123.45@@ -$567.89@@ $12,345.68@@"
@end smallexample
Two things stand out. Firstly, all fields have the same width (eleven
characters) since this is the width given in the format and since no
number required more characters to be printed. The second important
point is that the fill character is not used. This is correct since the
white space was not used to achieve a precision given by a @samp{#}
modifier, but instead to fill to the given width. The difference
becomes obvious if we now add a width specification.
@smallexample
strfmon (buf, 100, "@@%=*11#5n@@%=*11#5n@@%=*11#5n@@",
123.45, -567.89, 12345.678);
@end smallexample
@noindent
The output is
@smallexample
"@@ $***123.45@@-$***567.89@@ $12,456.68@@"
@end smallexample
Here we can see that all the currency symbols are now aligned, and that
the space between the currency sign and the number is filled with the
selected fill character. Note that although the width is selected to be
@math{5} and @math{123.45} has three digits left of the decimal point,
the space is filled with three asterisks. This is correct since, as
explained above, the width does not include the positions used to store
thousands separators. One last example should explain the remaining
functionality.
@smallexample
strfmon (buf, 100, "@@%=0(16#5.3i@@%=0(16#5.3i@@%=0(16#5.3i@@",
123.45, -567.89, 12345.678);
@end smallexample
@noindent
This rather complex format string produces the following output:
@smallexample
"@@ USD 000123,450 @@(USD 000567.890)@@ USD 12,345.678 @@"
@end smallexample
The most noticeable change is the alternative way of representing
negative numbers. In financial circles this is often done using
parentheses, and this is what the @samp{(} flag selected. The fill
character is now @samp{0}. Note that this @samp{0} character is not
regarded as a numeric zero, and therefore the first and second numbers
are not printed using a thousands separator. Since we used the format
specifier @samp{i} instead of @samp{n}, the international form of the
currency symbol is used. This is a four letter string, in this case
@code{"USD "}. The last point is that since the precision right of the
decimal point is selected to be three, the first and second numbers are
printed with an extra zero at the end and the third number is printed
without rounding.
@node Yes-or-No Questions, , Formatting Numbers , Locales
@section Yes-or-No Questions
Some non GUI programs ask a yes-or-no question. If the messages
(especially the questions) are translated into foreign languages, be
sure that you localize the answers too. It would be very bad habit to
ask a question in one language and request the answer in another, often
English.
@Theglibc{} contains @code{rpmatch} to give applications easy
access to the corresponding locale definitions.
@comment GNU
@comment stdlib.h
@deftypefun int rpmatch (const char *@var{response})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Calls nl_langinfo with YESEXPR and NOEXPR, triggering @mtslocale but
@c it's regcomp and regexec that bring in all of the safety issues.
@c regfree is also called, but it doesn't introduce any further issues.
The function @code{rpmatch} checks the string in @var{response} whether
or not it is a correct yes-or-no answer and if yes, which one. The
check uses the @code{YESEXPR} and @code{NOEXPR} data in the
@code{LC_MESSAGES} category of the currently selected locale. The
return value is as follows:
@table @code
@item 1
The user entered an affirmative answer.
@item 0
The user entered a negative answer.
@item -1
The answer matched neither the @code{YESEXPR} nor the @code{NOEXPR}
regular expression.
@end table
This function is not standardized but available beside in @theglibc{} at
least also in the IBM AIX library.
@end deftypefun
@noindent
This function would normally be used like this:
@smallexample
@dots{}
/* @r{Use a safe default.} */
_Bool doit = false;
fputs (gettext ("Do you really want to do this? "), stdout);
fflush (stdout);
/* @r{Prepare the @code{getline} call.} */
line = NULL;
len = 0;
while (getline (&line, &len, stdin) >= 0)
@{
/* @r{Check the response.} */
int res = rpmatch (line);
if (res >= 0)
@{
/* @r{We got a definitive answer.} */
if (res > 0)
doit = true;
break;
@}
@}
/* @r{Free what @code{getline} allocated.} */
free (line);
@end smallexample
Note that the loop continues until a read error is detected or until a
definitive (positive or negative) answer is read.
glibc-doc-reference-2.19.orig/manual/getopt.texi 0000664 0001750 0001750 00000032130 12275120646 021753 0 ustar adconrad adconrad @node Getopt, Argp, , Parsing Program Arguments
@section Parsing program options using @code{getopt}
The @code{getopt} and @code{getopt_long} functions automate some of the
chore involved in parsing typical unix command line options.
@menu
* Using Getopt:: Using the @code{getopt} function.
* Example of Getopt:: An example of parsing options with @code{getopt}.
* Getopt Long Options:: GNU suggests utilities accept long-named
options; here is one way to do.
* Getopt Long Option Example:: An example of using @code{getopt_long}.
@end menu
@node Using Getopt, Example of Getopt, , Getopt
@subsection Using the @code{getopt} function
Here are the details about how to call the @code{getopt} function. To
use this facility, your program must include the header file
@file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.2
@deftypevar int opterr
If the value of this variable is nonzero, then @code{getopt} prints an
error message to the standard error stream if it encounters an unknown
option character or an option with a missing required argument. This is
the default behavior. If you set this variable to zero, @code{getopt}
does not print any messages, but it still returns the character @code{?}
to indicate an error.
@end deftypevar
@comment unistd.h
@comment POSIX.2
@deftypevar int optopt
When @code{getopt} encounters an unknown option character or an option
with a missing required argument, it stores that option character in
this variable. You can use this for providing your own diagnostic
messages.
@end deftypevar
@comment unistd.h
@comment POSIX.2
@deftypevar int optind
This variable is set by @code{getopt} to the index of the next element
of the @var{argv} array to be processed. Once @code{getopt} has found
all of the option arguments, you can use this variable to determine
where the remaining non-option arguments begin. The initial value of
this variable is @code{1}.
@end deftypevar
@comment unistd.h
@comment POSIX.2
@deftypevar {char *} optarg
This variable is set by @code{getopt} to point at the value of the
option argument, for those options that accept arguments.
@end deftypevar
@comment unistd.h
@comment POSIX.2
@deftypefun int getopt (int @var{argc}, char *const *@var{argv}, const char *@var{options})
@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c Swapping elements of passed-in argv may be partial in case of
@c cancellation. Gettext brings about a whole lot of AS and AC safety
@c issues. The getopt API involves returning values in the
@c non-thread-specific optarg variable, which adds another thread-safety
@c issue. Given print_errors, it may output errors to stderr, which may
@c self-deadlock, leak locks, or encounter (in a signal handler) or
@c leave (in case of cancellation) stderr in an inconsistent state.
@c Various implicit, indirect uses of malloc, in uses of memstream and
@c asprintf for error-printing, bring about the usual malloc issues.
@c (The explicit use of malloc in a conditional situation in
@c _getopt_initialize is never exercised in glibc.)
@c
@c _getopt_internal
@c _getopt_internal_r
@c gettext
@c _getopt_initialize
@c getenv
@c malloc if USE_NONOPTION_FLAGS, never defined in libc
@c open_memstream
@c lockfile, unlockfile, __fxprintf -> stderr
@c asprintf
The @code{getopt} function gets the next option argument from the
argument list specified by the @var{argv} and @var{argc} arguments.
Normally these values come directly from the arguments received by
@code{main}.
The @var{options} argument is a string that specifies the option
characters that are valid for this program. An option character in this
string can be followed by a colon (@samp{:}) to indicate that it takes a
required argument. If an option character is followed by two colons
(@samp{::}), its argument is optional; this is a GNU extension.
@code{getopt} has three ways to deal with options that follow
non-options @var{argv} elements. The special argument @samp{--} forces
in all cases the end of option scanning.
@itemize @bullet
@item
The default is to permute the contents of @var{argv} while scanning it
so that eventually all the non-options are at the end. This allows
options to be given in any order, even with programs that were not
written to expect this.
@item
If the @var{options} argument string begins with a hyphen (@samp{-}), this
is treated specially. It permits arguments that are not options to be
returned as if they were associated with option character @samp{\1}.
@item
POSIX demands the following behavior: The first non-option stops option
processing. This mode is selected by either setting the environment
variable @code{POSIXLY_CORRECT} or beginning the @var{options} argument
string with a plus sign (@samp{+}).
@end itemize
The @code{getopt} function returns the option character for the next
command line option. When no more option arguments are available, it
returns @code{-1}. There may still be more non-option arguments; you
must compare the external variable @code{optind} against the @var{argc}
parameter to check this.
If the option has an argument, @code{getopt} returns the argument by
storing it in the variable @var{optarg}. You don't ordinarily need to
copy the @code{optarg} string, since it is a pointer into the original
@var{argv} array, not into a static area that might be overwritten.
If @code{getopt} finds an option character in @var{argv} that was not
included in @var{options}, or a missing option argument, it returns
@samp{?} and sets the external variable @code{optopt} to the actual
option character. If the first character of @var{options} is a colon
(@samp{:}), then @code{getopt} returns @samp{:} instead of @samp{?} to
indicate a missing option argument. In addition, if the external
variable @code{opterr} is nonzero (which is the default), @code{getopt}
prints an error message.
@end deftypefun
@node Example of Getopt
@subsection Example of Parsing Arguments with @code{getopt}
Here is an example showing how @code{getopt} is typically used. The
key points to notice are:
@itemize @bullet
@item
Normally, @code{getopt} is called in a loop. When @code{getopt} returns
@code{-1}, indicating no more options are present, the loop terminates.
@item
A @code{switch} statement is used to dispatch on the return value from
@code{getopt}. In typical use, each case just sets a variable that
is used later in the program.
@item
A second loop is used to process the remaining non-option arguments.
@end itemize
@smallexample
@include testopt.c.texi
@end smallexample
Here are some examples showing what this program prints with different
combinations of arguments:
@smallexample
% testopt
aflag = 0, bflag = 0, cvalue = (null)
% testopt -a -b
aflag = 1, bflag = 1, cvalue = (null)
% testopt -ab
aflag = 1, bflag = 1, cvalue = (null)
% testopt -c foo
aflag = 0, bflag = 0, cvalue = foo
% testopt -cfoo
aflag = 0, bflag = 0, cvalue = foo
% testopt arg1
aflag = 0, bflag = 0, cvalue = (null)
Non-option argument arg1
% testopt -a arg1
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument arg1
% testopt -c foo arg1
aflag = 0, bflag = 0, cvalue = foo
Non-option argument arg1
% testopt -a -- -b
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument -b
% testopt -a -
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument -
@end smallexample
@node Getopt Long Options
@subsection Parsing Long Options with @code{getopt_long}
To accept GNU-style long options as well as single-character options,
use @code{getopt_long} instead of @code{getopt}. This function is
declared in @file{getopt.h}, not @file{unistd.h}. You should make every
program accept long options if it uses any options, for this takes
little extra work and helps beginners remember how to use the program.
@comment getopt.h
@comment GNU
@deftp {Data Type} {struct option}
This structure describes a single long option name for the sake of
@code{getopt_long}. The argument @var{longopts} must be an array of
these structures, one for each long option. Terminate the array with an
element containing all zeros.
The @code{struct option} structure has these fields:
@table @code
@item const char *name
This field is the name of the option. It is a string.
@item int has_arg
This field says whether the option takes an argument. It is an integer,
and there are three legitimate values: @w{@code{no_argument}},
@code{required_argument} and @code{optional_argument}.
@item int *flag
@itemx int val
These fields control how to report or act on the option when it occurs.
If @code{flag} is a null pointer, then the @code{val} is a value which
identifies this option. Often these values are chosen to uniquely
identify particular long options.
If @code{flag} is not a null pointer, it should be the address of an
@code{int} variable which is the flag for this option. The value in
@code{val} is the value to store in the flag to indicate that the option
was seen.
@end table
@end deftp
@comment getopt.h
@comment GNU
@deftypefun int getopt_long (int @var{argc}, char *const *@var{argv}, const char *@var{shortopts}, const struct option *@var{longopts}, int *@var{indexptr})
@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c Same issues as getopt.
Decode options from the vector @var{argv} (whose length is @var{argc}).
The argument @var{shortopts} describes the short options to accept, just as
it does in @code{getopt}. The argument @var{longopts} describes the long
options to accept (see above).
When @code{getopt_long} encounters a short option, it does the same
thing that @code{getopt} would do: it returns the character code for the
option, and stores the options argument (if it has one) in @code{optarg}.
When @code{getopt_long} encounters a long option, it takes actions based
on the @code{flag} and @code{val} fields of the definition of that
option.
If @code{flag} is a null pointer, then @code{getopt_long} returns the
contents of @code{val} to indicate which option it found. You should
arrange distinct values in the @code{val} field for options with
different meanings, so you can decode these values after
@code{getopt_long} returns. If the long option is equivalent to a short
option, you can use the short option's character code in @code{val}.
If @code{flag} is not a null pointer, that means this option should just
set a flag in the program. The flag is a variable of type @code{int}
that you define. Put the address of the flag in the @code{flag} field.
Put in the @code{val} field the value you would like this option to
store in the flag. In this case, @code{getopt_long} returns @code{0}.
For any long option, @code{getopt_long} tells you the index in the array
@var{longopts} of the options definition, by storing it into
@code{*@var{indexptr}}. You can get the name of the option with
@code{@var{longopts}[*@var{indexptr}].name}. So you can distinguish among
long options either by the values in their @code{val} fields or by their
indices. You can also distinguish in this way among long options that
set flags.
When a long option has an argument, @code{getopt_long} puts the argument
value in the variable @code{optarg} before returning. When the option
has no argument, the value in @code{optarg} is a null pointer. This is
how you can tell whether an optional argument was supplied.
When @code{getopt_long} has no more options to handle, it returns
@code{-1}, and leaves in the variable @code{optind} the index in
@var{argv} of the next remaining argument.
@end deftypefun
Since long option names were used before the @code{getopt_long}
options was invented there are program interfaces which require programs
to recognize options like @w{@samp{-option value}} instead of
@w{@samp{--option value}}. To enable these programs to use the GNU
getopt functionality there is one more function available.
@comment getopt.h
@comment GNU
@deftypefun int getopt_long_only (int @var{argc}, char *const *@var{argv}, const char *@var{shortopts}, const struct option *@var{longopts}, int *@var{indexptr})
@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c Same issues as getopt.
The @code{getopt_long_only} function is equivalent to the
@code{getopt_long} function but it allows to specify the user of the
application to pass long options with only @samp{-} instead of
@samp{--}. The @samp{--} prefix is still recognized but instead of
looking through the short options if a @samp{-} is seen it is first
tried whether this parameter names a long option. If not, it is parsed
as a short option.
Assuming @code{getopt_long_only} is used starting an application with
@smallexample
app -foo
@end smallexample
@noindent
the @code{getopt_long_only} will first look for a long option named
@samp{foo}. If this is not found, the short options @samp{f}, @samp{o},
and again @samp{o} are recognized.
@end deftypefun
@node Getopt Long Option Example
@subsection Example of Parsing Long Options with @code{getopt_long}
@smallexample
@include longopt.c.texi
@end smallexample
glibc-doc-reference-2.19.orig/manual/platform.texi 0000664 0001750 0001750 00000010133 12275120646 022274 0 ustar adconrad adconrad @node Platform, Contributors, Maintenance, Top
@c %MENU% Describe all platform-specific facilities provided
@appendix Platform-specific facilities
@Theglibc{} can provide machine-specific functionality.
@menu
* PowerPC:: Facilities Specific to the PowerPC Architecture
@end menu
@node PowerPC
@appendixsec PowerPC-specific Facilities
Facilities specific to PowerPC that are not specific to a particular
operating system are declared in @file{sys/platform/ppc.h}.
@deftypefun {uint64_t} __ppc_get_timebase (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Read the current value of the Time Base Register.
The @dfn{Time Base Register} is a 64-bit register that stores a monotonically
incremented value updated at a system-dependent frequency that may be
different from the processor frequency. More information is available in
@cite{Power ISA 2.06b - Book II - Section 5.2}.
@code{__ppc_get_timebase} uses the processor's time base facility directly
without requiring assistance from the operating system, so it is very
efficient.
@end deftypefun
@deftypefun {uint64_t} __ppc_get_timebase_freq (void)
@safety{@prelim{}@mtunsafe{@mtuinit{}}@asunsafe{@asucorrupt{:init}}@acunsafe{@acucorrupt{:init}}}
@c __ppc_get_timebase_freq=__get_timebase_freq @mtuinit @acsfd
@c __get_clockfreq @mtuinit @asucorrupt:init @acucorrupt:init @acsfd
@c the initialization of the static timebase_freq is not exactly
@c safe, because hp_timing_t cannot be atomically set up.
@c syscall:get_tbfreq ok
@c open dup @acsfd
@c read dup ok
@c memcpy dup ok
@c memmem dup ok
@c close dup @acsfd
Read the current frequency at which the Time Base Register is updated.
This frequency is not related to the processor clock or the bus clock.
It is also possible that this frequency is not constant. More information is
available in @cite{Power ISA 2.06b - Book II - Section 5.2}.
@end deftypefun
The following functions provide hints about the usage of resources that are
shared with other processors. They can be used, for example, if a program
waiting on a lock intends to divert the shared resources to be used by other
processors. More information is available in @cite{Power ISA 2.06b - Book II -
Section 3.2}.
@deftypefun {void} __ppc_yield (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released for use by other processors.
@end deftypefun
@deftypefun {void} __ppc_mdoio (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released until all outstanding storage
accesses to caching-inhibited storage have been completed.
@end deftypefun
@deftypefun {void} __ppc_mdoom (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released until all outstanding storage
accesses to cacheable storage for which the data is not in the cache have been
completed.
@end deftypefun
@deftypefun {void} __ppc_set_ppr_med (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Set the Program Priority Register to medium value (default).
The @dfn{Program Priority Register} (PPR) is a 64-bit register that controls
the program's priority. By adjusting the PPR value the programmer may
improve system throughput by causing the system resources to be used
more efficiently, especially in contention situations.
The three unprivileged states available are covered by the functions
@code{__ppc_set_ppr_med} (medium -- default), @code{__ppc_set_ppc_low} (low)
and @code{__ppc_set_ppc_med_low} (medium low). More information
available in @cite{Power ISA 2.06b - Book II - Section 3.1}.
@end deftypefun
@deftypefun {void} __ppc_set_ppr_low (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Set the Program Priority Register to low value.
@end deftypefun
@deftypefun {void} __ppc_set_ppr_med_low (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
Set the Program Priority Register to medium low value.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/libcbook.texi 0000664 0001750 0001750 00000000057 12275120646 022240 0 ustar adconrad adconrad \input texinfo
@finalout
@include libc.texinfo
glibc-doc-reference-2.19.orig/manual/nss.texi 0000664 0001750 0001750 00000064656 12275120646 021276 0 ustar adconrad adconrad @node Name Service Switch, Users and Groups, Job Control, Top
@chapter System Databases and Name Service Switch
@c %MENU% Accessing system databases
@cindex Name Service Switch
@cindex NSS
@cindex databases
Various functions in the C Library need to be configured to work
correctly in the local environment. Traditionally, this was done by
using files (e.g., @file{/etc/passwd}), but other nameservices (like the
Network Information Service (NIS) and the Domain Name Service (DNS))
became popular, and were hacked into the C library, usually with a fixed
search order.
@Theglibc{} contains a cleaner solution of this problem. It is
designed after a method used by Sun Microsystems in the C library of
@w{Solaris 2}. @Theglibc{} follows their name and calls this
scheme @dfn{Name Service Switch} (NSS).
Though the interface might be similar to Sun's version there is no
common code. We never saw any source code of Sun's implementation and
so the internal interface is incompatible. This also manifests in the
file names we use as we will see later.
@menu
* NSS Basics:: What is this NSS good for.
* NSS Configuration File:: Configuring NSS.
* NSS Module Internals:: How does it work internally.
* Extending NSS:: What to do to add services or databases.
@end menu
@node NSS Basics, NSS Configuration File, Name Service Switch, Name Service Switch
@section NSS Basics
The basic idea is to put the implementation of the different services
offered to access the databases in separate modules. This has some
advantages:
@enumerate
@item
Contributors can add new services without adding them to @theglibc{}.
@item
The modules can be updated separately.
@item
The C library image is smaller.
@end enumerate
To fulfill the first goal above the ABI of the modules will be described
below. For getting the implementation of a new service right it is
important to understand how the functions in the modules get called.
They are in no way designed to be used by the programmer directly.
Instead the programmer should only use the documented and standardized
functions to access the databases.
@noindent
The databases available in the NSS are
@cindex ethers
@cindex group
@cindex hosts
@cindex netgroup
@cindex networks
@cindex protocols
@cindex passwd
@cindex rpc
@cindex services
@cindex shadow
@vtable @code
@item aliases
Mail aliases
@comment @pxref{Mail Aliases}.
@item ethers
Ethernet numbers,
@comment @pxref{Ethernet Numbers}.
@item group
Groups of users, @pxref{Group Database}.
@item hosts
Host names and numbers, @pxref{Host Names}.
@item netgroup
Network wide list of host and users, @pxref{Netgroup Database}.
@item networks
Network names and numbers, @pxref{Networks Database}.
@item protocols
Network protocols, @pxref{Protocols Database}.
@item passwd
User passwords, @pxref{User Database}.
@item rpc
Remote procedure call names and numbers,
@comment @pxref{RPC Database}.
@item services
Network services, @pxref{Services Database}.
@item shadow
Shadow user passwords,
@comment @pxref{Shadow Password Database}.
@end vtable
@noindent
There will be some more added later (@code{automount}, @code{bootparams},
@code{netmasks}, and @code{publickey}).
@node NSS Configuration File, NSS Module Internals, NSS Basics, Name Service Switch
@section The NSS Configuration File
@cindex @file{/etc/nsswitch.conf}
@cindex @file{nsswitch.conf}
Somehow the NSS code must be told about the wishes of the user. For
this reason there is the file @file{/etc/nsswitch.conf}. For each
database this file contain a specification how the lookup process should
work. The file could look like this:
@example
@include nsswitch.texi
@end example
The first column is the database as you can guess from the table above.
The rest of the line specifies how the lookup process works. Please
note that you specify the way it works for each database individually.
This cannot be done with the old way of a monolithic implementation.
The configuration specification for each database can contain two
different items:
@itemize @bullet
@item
the service specification like @code{files}, @code{db}, or @code{nis}.
@item
the reaction on lookup result like @code{[NOTFOUND=return]}.
@end itemize
@menu
* Services in the NSS configuration:: Service names in the NSS configuration.
* Actions in the NSS configuration:: React appropriately to the lookup result.
* Notes on NSS Configuration File:: Things to take care about while
configuring NSS.
@end menu
@node Services in the NSS configuration, Actions in the NSS configuration, NSS Configuration File, NSS Configuration File
@subsection Services in the NSS configuration File
The above example file mentions five different services: @code{files},
@code{db}, @code{dns}, @code{nis}, and @code{nisplus}. This does not
mean these
services are available on all sites and it does also not mean these are
all the services which will ever be available.
In fact, these names are simply strings which the NSS code uses to find
the implicitly addressed functions. The internal interface will be
described later. Visible to the user are the modules which implement an
individual service.
Assume the service @var{name} shall be used for a lookup. The code for
this service is implemented in a module called @file{libnss_@var{name}}.
On a system supporting shared libraries this is in fact a shared library
with the name (for example) @file{libnss_@var{name}.so.2}. The number
at the end is the currently used version of the interface which will not
change frequently. Normally the user should not have to be cognizant of
these files since they should be placed in a directory where they are
found automatically. Only the names of all available services are
important.
@node Actions in the NSS configuration, Notes on NSS Configuration File, Services in the NSS configuration, NSS Configuration File
@subsection Actions in the NSS configuration
The second item in the specification gives the user much finer control
on the lookup process. Action items are placed between two service
names and are written within brackets. The general form is
@display
@code{[} ( @code{!}? @var{status} @code{=} @var{action} )+ @code{]}
@end display
@noindent
where
@smallexample
@var{status} @result{} success | notfound | unavail | tryagain
@var{action} @result{} return | continue
@end smallexample
The case of the keywords is insignificant. The @var{status}
values are the results of a call to a lookup function of a specific
service. They mean
@ftable @samp
@item success
No error occurred and the wanted entry is returned. The default action
for this is @code{return}.
@item notfound
The lookup process works ok but the needed value was not found. The
default action is @code{continue}.
@item unavail
@cindex DNS server unavailable
The service is permanently unavailable. This can either mean the needed
file is not available, or, for DNS, the server is not available or does
not allow queries. The default action is @code{continue}.
@item tryagain
The service is temporarily unavailable. This could mean a file is
locked or a server currently cannot accept more connections. The
default action is @code{continue}.
@end ftable
@noindent
If we have a line like
@smallexample
ethers: nisplus [NOTFOUND=return] db files
@end smallexample
@noindent
this is equivalent to
@smallexample
ethers: nisplus [SUCCESS=return NOTFOUND=return UNAVAIL=continue
TRYAGAIN=continue]
db [SUCCESS=return NOTFOUND=continue UNAVAIL=continue
TRYAGAIN=continue]
files
@end smallexample
@noindent
(except that it would have to be written on one line). The default
value for the actions are normally what you want, and only need to be
changed in exceptional cases.
If the optional @code{!} is placed before the @var{status} this means
the following action is used for all statuses but @var{status} itself.
I.e., @code{!} is negation as in the C language (and others).
Before we explain the exception which makes this action item necessary
one more remark: obviously it makes no sense to add another action
item after the @code{files} service. Since there is no other service
following the action @emph{always} is @code{return}.
@cindex nisplus, and completeness
Now, why is this @code{[NOTFOUND=return]} action useful? To understand
this we should know that the @code{nisplus} service is often
complete; i.e., if an entry is not available in the NIS+ tables it is
not available anywhere else. This is what is expressed by this action
item: it is useless to examine further services since they will not give
us a result.
@cindex nisplus, and booting
@cindex bootstrapping, and services
The situation would be different if the NIS+ service is not available
because the machine is booting. In this case the return value of the
lookup function is not @code{notfound} but instead @code{unavail}. And
as you can see in the complete form above: in this situation the
@code{db} and @code{files} services are used. Neat, isn't it? The
system administrator need not pay special care for the time the system
is not completely ready to work (while booting or shutdown or
network problems).
@node Notes on NSS Configuration File, , Actions in the NSS configuration, NSS Configuration File
@subsection Notes on the NSS Configuration File
Finally a few more hints. The NSS implementation is not completely
helpless if @file{/etc/nsswitch.conf} does not exist. For
all supported databases there is a default value so it should normally
be possible to get the system running even if the file is corrupted or
missing.
@cindex default value, and NSS
For the @code{hosts} and @code{networks} databases the default value is
@code{dns [!UNAVAIL=return] files}. I.e., the system is prepared for
the DNS service not to be available but if it is available the answer it
returns is definitive.
The @code{passwd}, @code{group}, and @code{shadow} databases are
traditionally handled in a special way. The appropriate files in the
@file{/etc} directory are read but if an entry with a name starting
with a @code{+} character is found NIS is used. This kind of lookup
remains possible by using the special lookup service @code{compat}
and the default value for the three databases above is
@code{compat [NOTFOUND=return] files}.
For all other databases the default value is
@code{nis [NOTFOUND=return] files}. This solution give the best
chance to be correct since NIS and file based lookup is used.
@cindex optimizing NSS
A second point is that the user should try to optimize the lookup
process. The different service have different response times.
A simple file look up on a local file could be fast, but if the file
is long and the needed entry is near the end of the file this may take
quite some time. In this case it might be better to use the @code{db}
service which allows fast local access to large data sets.
Often the situation is that some global information like NIS must be
used. So it is unavoidable to use service entries like @code{nis} etc.
But one should avoid slow services like this if possible.
@node NSS Module Internals, Extending NSS, NSS Configuration File, Name Service Switch
@section NSS Module Internals
Now it is time to describe what the modules look like. The functions
contained in a module are identified by their names. I.e., there is no
jump table or the like. How this is done is of no interest here; those
interested in this topic should read about Dynamic Linking.
@comment @ref{Dynamic Linking}.
@menu
* NSS Module Names:: Construction of the interface function of
the NSS modules.
* NSS Modules Interface:: Programming interface in the NSS module
functions.
@end menu
@node NSS Module Names, NSS Modules Interface, NSS Module Internals, NSS Module Internals
@subsection The Naming Scheme of the NSS Modules
@noindent
The name of each function consist of various parts:
@quotation
_nss_@var{service}_@var{function}
@end quotation
@var{service} of course corresponds to the name of the module this
function is found in.@footnote{Now you might ask why this information is
duplicated. The answer is that we want to make it possible to link
directly with these shared objects.} The @var{function} part is derived
from the interface function in the C library itself. If the user calls
the function @code{gethostbyname} and the service used is @code{files}
the function
@smallexample
_nss_files_gethostbyname_r
@end smallexample
@noindent
in the module
@smallexample
libnss_files.so.2
@end smallexample
@noindent
@cindex reentrant NSS functions
is used. You see, what is explained above in not the whole truth. In
fact the NSS modules only contain reentrant versions of the lookup
functions. I.e., if the user would call the @code{gethostbyname_r}
function this also would end in the above function. For all user
interface functions the C library maps this call to a call to the
reentrant function. For reentrant functions this is trivial since the
interface is (nearly) the same. For the non-reentrant version The
library keeps internal buffers which are used to replace the user
supplied buffer.
I.e., the reentrant functions @emph{can} have counterparts. No service
module is forced to have functions for all databases and all kinds to
access them. If a function is not available it is simply treated as if
the function would return @code{unavail}
(@pxref{Actions in the NSS configuration}).
The file name @file{libnss_files.so.2} would be on a @w{Solaris 2}
system @file{nss_files.so.2}. This is the difference mentioned above.
Sun's NSS modules are usable as modules which get indirectly loaded
only.
The NSS modules in @theglibc{} are prepared to be used as normal
libraries themselves. This is @emph{not} true at the moment, though.
However, the organization of the name space in the modules does not make it
impossible like it is for Solaris. Now you can see why the modules are
still libraries.@footnote{There is a second explanation: we were too
lazy to change the Makefiles to allow the generation of shared objects
not starting with @file{lib} but don't tell this to anybody.}
@node NSS Modules Interface, , NSS Module Names, NSS Module Internals
@subsection The Interface of the Function in NSS Modules
Now we know about the functions contained in the modules. It is now
time to describe the types. When we mentioned the reentrant versions of
the functions above, this means there are some additional arguments
(compared with the standard, non-reentrant version). The prototypes for
the non-reentrant and reentrant versions of our function above are:
@smallexample
struct hostent *gethostbyname (const char *name)
int gethostbyname_r (const char *name, struct hostent *result_buf,
char *buf, size_t buflen, struct hostent **result,
int *h_errnop)
@end smallexample
@noindent
The actual prototype of the function in the NSS modules in this case is
@smallexample
enum nss_status _nss_files_gethostbyname_r (const char *name,
struct hostent *result_buf,
char *buf, size_t buflen,
int *errnop, int *h_errnop)
@end smallexample
I.e., the interface function is in fact the reentrant function with the
change of the return value and the omission of the @var{result}
parameter. While the user-level function returns a pointer to the
result the reentrant function return an @code{enum nss_status} value:
@vtable @code
@item NSS_STATUS_TRYAGAIN
numeric value @code{-2}
@item NSS_STATUS_UNAVAIL
numeric value @code{-1}
@item NSS_STATUS_NOTFOUND
numeric value @code{0}
@item NSS_STATUS_SUCCESS
numeric value @code{1}
@end vtable
@noindent
Now you see where the action items of the @file{/etc/nsswitch.conf} file
are used.
If you study the source code you will find there is a fifth value:
@code{NSS_STATUS_RETURN}. This is an internal use only value, used by a
few functions in places where none of the above value can be used. If
necessary the source code should be examined to learn about the details.
In case the interface function has to return an error it is important
that the correct error code is stored in @code{*@var{errnop}}. Some
return status value have only one associated error code, others have
more.
@multitable @columnfractions .3 .2 .50
@item
@code{NSS_STATUS_TRYAGAIN} @tab
@code{EAGAIN} @tab One of the functions used ran temporarily out of
resources or a service is currently not available.
@item
@tab
@code{ERANGE} @tab The provided buffer is not large enough.
The function should be called again with a larger buffer.
@item
@code{NSS_STATUS_UNAVAIL} @tab
@code{ENOENT} @tab A necessary input file cannot be found.
@item
@code{NSS_STATUS_NOTFOUND} @tab
@code{ENOENT} @tab The requested entry is not available.
@end multitable
These are proposed values. There can be other error codes and the
described error codes can have different meaning. @strong{With one
exception:} when returning @code{NSS_STATUS_TRYAGAIN} the error code
@code{ERANGE} @emph{must} mean that the user provided buffer is too
small. Everything is non-critical.
The above function has something special which is missing for almost all
the other module functions. There is an argument @var{h_errnop}. This
points to a variable which will be filled with the error code in case
the execution of the function fails for some reason. The reentrant
function cannot use the global variable @var{h_errno};
@code{gethostbyname} calls @code{gethostbyname_r} with the last argument
set to @code{&h_errno}.
The @code{get@var{XXX}by@var{YYY}} functions are the most important
functions in the NSS modules. But there are others which implement
the other ways to access system databases (say for the
password database, there are @code{setpwent}, @code{getpwent}, and
@code{endpwent}). These will be described in more detail later.
Here we give a general way to determine the
signature of the module function:
@itemize @bullet
@item
the return value is @code{int};
@item
the name is as explained in @pxref{NSS Module Names};
@item
the first arguments are identical to the arguments of the non-reentrant
function;
@item
the next three arguments are:
@table @code
@item STRUCT_TYPE *result_buf
pointer to buffer where the result is stored. @code{STRUCT_TYPE} is
normally a struct which corresponds to the database.
@item char *buffer
pointer to a buffer where the function can store additional data for
the result etc.
@item size_t buflen
length of the buffer pointed to by @var{buffer}.
@end table
@item
possibly a last argument @var{h_errnop}, for the host name and network
name lookup functions.
@end itemize
@noindent
This table is correct for all functions but the @code{set@dots{}ent}
and @code{end@dots{}ent} functions.
@node Extending NSS, , NSS Module Internals, Name Service Switch
@section Extending NSS
One of the advantages of NSS mentioned above is that it can be extended
quite easily. There are two ways in which the extension can happen:
adding another database or adding another service. The former is
normally done only by the C library developers. It is
here only important to remember that adding another database is
independent from adding another service because a service need not
support all databases or lookup functions.
A designer/implementor of a new service is therefore free to choose the
databases s/he is interested in and leave the rest for later (or
completely aside).
@menu
* Adding another Service to NSS:: What is to do to add a new service.
* NSS Module Function Internals:: Guidelines for writing new NSS
service functions.
@end menu
@node Adding another Service to NSS, NSS Module Function Internals, Extending NSS, Extending NSS
@subsection Adding another Service to NSS
The sources for a new service need not (and should not) be part of @theglibc{}
itself. The developer retains complete control over the
sources and its development. The links between the C library and the
new service module consists solely of the interface functions.
Each module is designed following a specific interface specification.
For now the version is 2 (the interface in version 1 was not adequate)
and this manifests in the version number of the shared library object of
the NSS modules: they have the extension @code{.2}. If the interface
changes again in an incompatible way, this number will be increased.
Modules using the old interface will still be usable.
Developers of a new service will have to make sure that their module is
created using the correct interface number. This means the file itself
must have the correct name and on ELF systems the @dfn{soname} (Shared
Object Name) must also have this number. Building a module from a bunch
of object files on an ELF system using GNU CC could be done like this:
@smallexample
gcc -shared -o libnss_NAME.so.2 -Wl,-soname,libnss_NAME.so.2 OBJECTS
@end smallexample
@noindent
@ref{Link Options, Options for Linking, , gcc, GNU CC}, to learn
more about this command line.
To use the new module the library must be able to find it. This can be
achieved by using options for the dynamic linker so that it will search
the directory where the binary is placed. For an ELF system this could be
done by adding the wanted directory to the value of
@code{LD_LIBRARY_PATH}.
But this is not always possible since some programs (those which run
under IDs which do not belong to the user) ignore this variable.
Therefore the stable version of the module should be placed into a
directory which is searched by the dynamic linker. Normally this should
be the directory @file{$prefix/lib}, where @file{$prefix} corresponds to
the value given to configure using the @code{--prefix} option. But be
careful: this should only be done if it is clear the module does not
cause any harm. System administrators should be careful.
@node NSS Module Function Internals, , Adding another Service to NSS, Extending NSS
@subsection Internals of the NSS Module Functions
Until now we only provided the syntactic interface for the functions in
the NSS module. In fact there is not much more we can say since the
implementation obviously is different for each function. But a few
general rules must be followed by all functions.
In fact there are four kinds of different functions which may appear in
the interface. All derive from the traditional ones for system databases.
@var{db} in the following table is normally an abbreviation for the
database (e.g., it is @code{pw} for the password database).
@table @code
@item enum nss_status _nss_@var{database}_set@var{db}ent (void)
This function prepares the service for following operations. For a
simple file based lookup this means files could be opened, for other
services this function simply is a noop.
One special case for this function is that it takes an additional
argument for some @var{database}s (i.e., the interface is
@code{int set@var{db}ent (int)}). @ref{Host Names}, which describes the
@code{sethostent} function.
The return value should be @var{NSS_STATUS_SUCCESS} or according to the
table above in case of an error (@pxref{NSS Modules Interface}).
@item enum nss_status _nss_@var{database}_end@var{db}ent (void)
This function simply closes all files which are still open or removes
buffer caches. If there are no files or buffers to remove this is again
a simple noop.
There normally is no return value different to @var{NSS_STATUS_SUCCESS}.
@item enum nss_status _nss_@var{database}_get@var{db}ent_r (@var{STRUCTURE} *result, char *buffer, size_t buflen, int *errnop)
Since this function will be called several times in a row to retrieve
one entry after the other it must keep some kind of state. But this
also means the functions are not really reentrant. They are reentrant
only in that simultaneous calls to this function will not try to
write the retrieved data in the same place (as it would be the case for
the non-reentrant functions); instead, it writes to the structure
pointed to by the @var{result} parameter. But the calls share a common
state and in the case of a file access this means they return neighboring
entries in the file.
The buffer of length @var{buflen} pointed to by @var{buffer} can be used
for storing some additional data for the result. It is @emph{not}
guaranteed that the same buffer will be passed for the next call of this
function. Therefore one must not misuse this buffer to save some state
information from one call to another.
Before the function returns the implementation should store the value of
the local @var{errno} variable in the variable pointed to be
@var{errnop}. This is important to guarantee the module working in
statically linked programs.
As explained above this function could also have an additional last
argument. This depends on the database used; it happens only for
@code{host} and @code{networks}.
The function shall return @code{NSS_STATUS_SUCCESS} as long as there are
more entries. When the last entry was read it should return
@code{NSS_STATUS_NOTFOUND}. When the buffer given as an argument is too
small for the data to be returned @code{NSS_STATUS_TRYAGAIN} should be
returned. When the service was not formerly initialized by a call to
@code{_nss_@var{DATABASE}_set@var{db}ent} all return value allowed for
this function can also be returned here.
@item enum nss_status _nss_@var{DATABASE}_get@var{db}by@var{XX}_r (@var{PARAMS}, @var{STRUCTURE} *result, char *buffer, size_t buflen, int *errnop)
This function shall return the entry from the database which is
addressed by the @var{PARAMS}. The type and number of these arguments
vary. It must be individually determined by looking to the user-level
interface functions. All arguments given to the non-reentrant version
are here described by @var{PARAMS}.
The result must be stored in the structure pointed to by @var{result}.
If there is additional data to return (say strings, where the
@var{result} structure only contains pointers) the function must use the
@var{buffer} or length @var{buflen}. There must not be any references
to non-constant global data.
The implementation of this function should honor the @var{stayopen}
flag set by the @code{set@var{DB}ent} function whenever this makes sense.
Before the function returns the implementation should store the value of
the local @var{errno} variable in the variable pointed to be
@var{errnop}. This is important to guarantee the module working in
statically linked programs.
Again, this function takes an additional last argument for the
@code{host} and @code{networks} database.
The return value should as always follow the rules given above
(@pxref{NSS Modules Interface}).
@end table
glibc-doc-reference-2.19.orig/manual/creature.texi 0000664 0001750 0001750 00000023354 12275120646 022273 0 ustar adconrad adconrad @node Feature Test Macros
@subsection Feature Test Macros
@cindex feature test macros
The exact set of features available when you compile a source file
is controlled by which @dfn{feature test macros} you define.
If you compile your programs using @samp{gcc -ansi}, you get only the
@w{ISO C} library features, unless you explicitly request additional
features by defining one or more of the feature macros.
@xref{Invoking GCC,, GNU CC Command Options, gcc.info, The GNU CC Manual},
for more information about GCC options.@refill
You should define these macros by using @samp{#define} preprocessor
directives at the top of your source code files. These directives
@emph{must} come before any @code{#include} of a system header file. It
is best to make them the very first thing in the file, preceded only by
comments. You could also use the @samp{-D} option to GCC, but it's
better if you make the source files indicate their own meaning in a
self-contained way.
This system exists to allow the library to conform to multiple standards.
Although the different standards are often described as supersets of each
other, they are usually incompatible because larger standards require
functions with names that smaller ones reserve to the user program. This
is not mere pedantry --- it has been a problem in practice. For instance,
some non-GNU programs define functions named @code{getline} that have
nothing to do with this library's @code{getline}. They would not be
compilable if all features were enabled indiscriminately.
This should not be used to verify that a program conforms to a limited
standard. It is insufficient for this purpose, as it will not protect you
from including header files outside the standard, or relying on semantics
undefined within the standard.
@comment (none)
@comment POSIX.1
@defvr Macro _POSIX_SOURCE
If you define this macro, then the functionality from the POSIX.1
standard (IEEE Standard 1003.1) is available, as well as all of the
@w{ISO C} facilities.
The state of @code{_POSIX_SOURCE} is irrelevant if you define the
macro @code{_POSIX_C_SOURCE} to a positive integer.
@end defvr
@comment (none)
@comment POSIX.2
@defvr Macro _POSIX_C_SOURCE
Define this macro to a positive integer to control which POSIX
functionality is made available. The greater the value of this macro,
the more functionality is made available.
If you define this macro to a value greater than or equal to @code{1},
then the functionality from the 1990 edition of the POSIX.1 standard
(IEEE Standard 1003.1-1990) is made available.
If you define this macro to a value greater than or equal to @code{2},
then the functionality from the 1992 edition of the POSIX.2 standard
(IEEE Standard 1003.2-1992) is made available.
If you define this macro to a value greater than or equal to @code{199309L},
then the functionality from the 1993 edition of the POSIX.1b standard
(IEEE Standard 1003.1b-1993) is made available.
Greater values for @code{_POSIX_C_SOURCE} will enable future extensions.
The POSIX standards process will define these values as necessary, and
@theglibc{} should support them some time after they become standardized.
The 1996 edition of POSIX.1 (ISO/IEC 9945-1: 1996) states that
if you define @code{_POSIX_C_SOURCE} to a value greater than
or equal to @code{199506L}, then the functionality from the 1996
edition is made available.
@end defvr
@comment (none)
@comment GNU
@defvr Macro _BSD_SOURCE
If you define this macro, functionality derived from 4.3 BSD Unix is
included as well as the @w{ISO C}, POSIX.1, and POSIX.2 material.
@end defvr
@comment (none)
@comment GNU
@defvr Macro _SVID_SOURCE
If you define this macro, functionality derived from SVID is
included as well as the @w{ISO C}, POSIX.1, POSIX.2, and X/Open material.
@end defvr
@comment (none)
@comment X/Open
@defvr Macro _XOPEN_SOURCE
@comment (none)
@comment X/Open
@defvrx Macro _XOPEN_SOURCE_EXTENDED
If you define this macro, functionality described in the X/Open
Portability Guide is included. This is a superset of the POSIX.1 and
POSIX.2 functionality and in fact @code{_POSIX_SOURCE} and
@code{_POSIX_C_SOURCE} are automatically defined.
As the unification of all Unices, functionality only available in
BSD and SVID is also included.
If the macro @code{_XOPEN_SOURCE_EXTENDED} is also defined, even more
functionality is available. The extra functions will make all functions
available which are necessary for the X/Open Unix brand.
If the macro @code{_XOPEN_SOURCE} has the value @math{500} this includes
all functionality described so far plus some new definitions from the
Single Unix Specification, @w{version 2}.
@end defvr
@comment (NONE)
@comment X/Open
@defvr Macro _LARGEFILE_SOURCE
If this macro is defined some extra functions are available which
rectify a few shortcomings in all previous standards. Specifically,
the functions @code{fseeko} and @code{ftello} are available. Without
these functions the difference between the @w{ISO C} interface
(@code{fseek}, @code{ftell}) and the low-level POSIX interface
(@code{lseek}) would lead to problems.
This macro was introduced as part of the Large File Support extension (LFS).
@end defvr
@comment (NONE)
@comment X/Open
@defvr Macro _LARGEFILE64_SOURCE
If you define this macro an additional set of functions is made available
which enables @w{32 bit} systems to use files of sizes beyond
the usual limit of 2GB. This interface is not available if the system
does not support files that large. On systems where the natural file
size limit is greater than 2GB (i.e., on @w{64 bit} systems) the new
functions are identical to the replaced functions.
The new functionality is made available by a new set of types and
functions which replace the existing ones. The names of these new objects
contain @code{64} to indicate the intention, e.g., @code{off_t}
vs. @code{off64_t} and @code{fseeko} vs. @code{fseeko64}.
This macro was introduced as part of the Large File Support extension
(LFS). It is a transition interface for the period when @w{64 bit}
offsets are not generally used (see @code{_FILE_OFFSET_BITS}).
@end defvr
@comment (NONE)
@comment X/Open
@defvr Macro _FILE_OFFSET_BITS
This macro determines which file system interface shall be used, one
replacing the other. Whereas @code{_LARGEFILE64_SOURCE} makes the @w{64
bit} interface available as an additional interface,
@code{_FILE_OFFSET_BITS} allows the @w{64 bit} interface to
replace the old interface.
If @code{_FILE_OFFSET_BITS} is undefined, or if it is defined to the
value @code{32}, nothing changes. The @w{32 bit} interface is used and
types like @code{off_t} have a size of @w{32 bits} on @w{32 bit}
systems.
If the macro is defined to the value @code{64}, the large file interface
replaces the old interface. I.e., the functions are not made available
under different names (as they are with @code{_LARGEFILE64_SOURCE}).
Instead the old function names now reference the new functions, e.g., a
call to @code{fseeko} now indeed calls @code{fseeko64}.
This macro should only be selected if the system provides mechanisms for
handling large files. On @w{64 bit} systems this macro has no effect
since the @code{*64} functions are identical to the normal functions.
This macro was introduced as part of the Large File Support extension
(LFS).
@end defvr
@comment (none)
@comment GNU
@defvr Macro _ISOC99_SOURCE
Until the revised @w{ISO C} standard is widely adopted the new features
are not automatically enabled. @Theglibc{} nevertheless has a complete
implementation of the new standard and to enable the new features the
macro @code{_ISOC99_SOURCE} should be defined.
@end defvr
@comment (none)
@comment GNU
@defvr Macro _GNU_SOURCE
If you define this macro, everything is included: @w{ISO C89}, @w{ISO
C99}, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU extensions. In
the cases where POSIX.1 conflicts with BSD, the POSIX definitions take
precedence.
@end defvr
@comment (none)
@comment GNU
@defvr Macro _DEFAULT_SOURCE
If you define this macro, most features are included apart from
X/Open, LFS and GNU extensions; the effect is similar to defining
@code{_POSIX_C_SOURCE} to @code{200809L} and @code{_POSIX_SOURCE},
@code{_SVID_SOURCE}, and @code{_BSD_SOURCE} to 1. Defining this
macro, on its own and without using compiler options such as
@option{-ansi} or @option{-std=c99}, has the same effect as not
defining any feature test macros; defining it together with other
feature test macros, or when options such as @option{-ansi} are used,
enables those features even when the other options would otherwise
cause them to be disabled.
@end defvr
@comment (none)
@comment GNU
@defvr Macro _REENTRANT
@defvrx Macro _THREAD_SAFE
If you define one of these macros, reentrant versions of several functions get
declared. Some of the functions are specified in POSIX.1c but many others
are only available on a few other systems or are unique to @theglibc{}.
The problem is the delay in the standardization of the thread safe C library
interface.
Unlike on some other systems, no special version of the C library must be
used for linking. There is only one version but while compiling this
it must have been specified to compile as thread safe.
@end defvr
We recommend you use @code{_GNU_SOURCE} in new programs. If you don't
specify the @samp{-ansi} option to GCC, or other conformance options
such as @option{-std=c99}, and don't define any of these macros
explicitly, the effect is the same as defining @code{_DEFAULT_SOURCE}
to 1.
When you define a feature test macro to request a larger class of features,
it is harmless to define in addition a feature test macro for a subset of
those features. For example, if you define @code{_POSIX_C_SOURCE}, then
defining @code{_POSIX_SOURCE} as well has no effect. Likewise, if you
define @code{_GNU_SOURCE}, then defining either @code{_POSIX_SOURCE} or
@code{_POSIX_C_SOURCE} or @code{_SVID_SOURCE} as well has no effect.
glibc-doc-reference-2.19.orig/manual/stdio-fp.c 0000664 0001750 0001750 00000000610 12275120646 021445 0 ustar adconrad adconrad /* This program is to generate one of the examples in stdio.texi. */
#include
static void
print (double v)
{
printf ("|%13.4a|%13.4f|%13.4e|%13.4g|\n", v, v, v, v);
}
int
main (void)
{
print (0.0);
print (0.5);
print (1.0);
print (-1.0);
print (100.0);
print (1000.0);
print (10000.0);
print (12345.0);
print (100000.0);
print (123456.0);
return 0;
}
glibc-doc-reference-2.19.orig/manual/socket.texi 0000664 0001750 0001750 00000462534 12275120646 021760 0 ustar adconrad adconrad @node Sockets, Low-Level Terminal Interface, Pipes and FIFOs, Top
@c %MENU% A more complicated IPC mechanism, with networking support
@chapter Sockets
This chapter describes the GNU facilities for interprocess
communication using sockets.
@cindex socket
@cindex interprocess communication, with sockets
A @dfn{socket} is a generalized interprocess communication channel.
Like a pipe, a socket is represented as a file descriptor. Unlike pipes
sockets support communication between unrelated processes, and even
between processes running on different machines that communicate over a
network. Sockets are the primary means of communicating with other
machines; @code{telnet}, @code{rlogin}, @code{ftp}, @code{talk} and the
other familiar network programs use sockets.
Not all operating systems support sockets. In @theglibc{}, the
header file @file{sys/socket.h} exists regardless of the operating
system, and the socket functions always exist, but if the system does
not really support sockets these functions always fail.
@strong{Incomplete:} We do not currently document the facilities for
broadcast messages or for configuring Internet interfaces. The
reentrant functions and some newer functions that are related to IPv6
aren't documented either so far.
@menu
* Socket Concepts:: Basic concepts you need to know about.
* Communication Styles::Stream communication, datagrams and other styles.
* Socket Addresses:: How socket names (``addresses'') work.
* Interface Naming:: Identifying specific network interfaces.
* Local Namespace:: Details about the local namespace.
* Internet Namespace:: Details about the Internet namespace.
* Misc Namespaces:: Other namespaces not documented fully here.
* Open/Close Sockets:: Creating sockets and destroying them.
* Connections:: Operations on sockets with connection state.
* Datagrams:: Operations on datagram sockets.
* Inetd:: Inetd is a daemon that starts servers on request.
The most convenient way to write a server
is to make it work with Inetd.
* Socket Options:: Miscellaneous low-level socket options.
* Networks Database:: Accessing the database of network names.
@end menu
@node Socket Concepts
@section Socket Concepts
@cindex communication style (of a socket)
@cindex style of communication (of a socket)
When you create a socket, you must specify the style of communication
you want to use and the type of protocol that should implement it.
The @dfn{communication style} of a socket defines the user-level
semantics of sending and receiving data on the socket. Choosing a
communication style specifies the answers to questions such as these:
@itemize @bullet
@item
@cindex packet
@cindex byte stream
@cindex stream (sockets)
@strong{What are the units of data transmission?} Some communication
styles regard the data as a sequence of bytes with no larger
structure; others group the bytes into records (which are known in
this context as @dfn{packets}).
@item
@cindex loss of data on sockets
@cindex data loss on sockets
@strong{Can data be lost during normal operation?} Some communication
styles guarantee that all the data sent arrives in the order it was
sent (barring system or network crashes); other styles occasionally
lose data as a normal part of operation, and may sometimes deliver
packets more than once or in the wrong order.
Designing a program to use unreliable communication styles usually
involves taking precautions to detect lost or misordered packets and
to retransmit data as needed.
@item
@strong{Is communication entirely with one partner?} Some
communication styles are like a telephone call---you make a
@dfn{connection} with one remote socket and then exchange data
freely. Other styles are like mailing letters---you specify a
destination address for each message you send.
@end itemize
@cindex namespace (of socket)
@cindex domain (of socket)
@cindex socket namespace
@cindex socket domain
You must also choose a @dfn{namespace} for naming the socket. A socket
name (``address'') is meaningful only in the context of a particular
namespace. In fact, even the data type to use for a socket name may
depend on the namespace. Namespaces are also called ``domains'', but we
avoid that word as it can be confused with other usage of the same
term. Each namespace has a symbolic name that starts with @samp{PF_}.
A corresponding symbolic name starting with @samp{AF_} designates the
address format for that namespace.
@cindex network protocol
@cindex protocol (of socket)
@cindex socket protocol
@cindex protocol family
Finally you must choose the @dfn{protocol} to carry out the
communication. The protocol determines what low-level mechanism is used
to transmit and receive data. Each protocol is valid for a particular
namespace and communication style; a namespace is sometimes called a
@dfn{protocol family} because of this, which is why the namespace names
start with @samp{PF_}.
The rules of a protocol apply to the data passing between two programs,
perhaps on different computers; most of these rules are handled by the
operating system and you need not know about them. What you do need to
know about protocols is this:
@itemize @bullet
@item
In order to have communication between two sockets, they must specify
the @emph{same} protocol.
@item
Each protocol is meaningful with particular style/namespace
combinations and cannot be used with inappropriate combinations. For
example, the TCP protocol fits only the byte stream style of
communication and the Internet namespace.
@item
For each combination of style and namespace there is a @dfn{default
protocol}, which you can request by specifying 0 as the protocol
number. And that's what you should normally do---use the default.
@end itemize
Throughout the following description at various places
variables/parameters to denote sizes are required. And here the trouble
starts. In the first implementations the type of these variables was
simply @code{int}. On most machines at that time an @code{int} was 32
bits wide, which created a @emph{de facto} standard requiring 32-bit
variables. This is important since references to variables of this type
are passed to the kernel.
Then the POSIX people came and unified the interface with the words "all
size values are of type @code{size_t}". On 64-bit machines
@code{size_t} is 64 bits wide, so pointers to variables were no longer
possible.
The Unix98 specification provides a solution by introducing a type
@code{socklen_t}. This type is used in all of the cases that POSIX
changed to use @code{size_t}. The only requirement of this type is that
it be an unsigned type of at least 32 bits. Therefore, implementations
which require that references to 32-bit variables be passed can be as
happy as implementations which use 64-bit values.
@node Communication Styles
@section Communication Styles
@Theglibc{} includes support for several different kinds of sockets,
each with different characteristics. This section describes the
supported socket types. The symbolic constants listed here are
defined in @file{sys/socket.h}.
@pindex sys/socket.h
@comment sys/socket.h
@comment BSD
@deftypevr Macro int SOCK_STREAM
The @code{SOCK_STREAM} style is like a pipe (@pxref{Pipes and FIFOs}).
It operates over a connection with a particular remote socket and
transmits data reliably as a stream of bytes.
Use of this style is covered in detail in @ref{Connections}.
@end deftypevr
@comment sys/socket.h
@comment BSD
@deftypevr Macro int SOCK_DGRAM
The @code{SOCK_DGRAM} style is used for sending
individually-addressed packets unreliably.
It is the diametrical opposite of @code{SOCK_STREAM}.
Each time you write data to a socket of this kind, that data becomes
one packet. Since @code{SOCK_DGRAM} sockets do not have connections,
you must specify the recipient address with each packet.
The only guarantee that the system makes about your requests to
transmit data is that it will try its best to deliver each packet you
send. It may succeed with the sixth packet after failing with the
fourth and fifth packets; the seventh packet may arrive before the
sixth, and may arrive a second time after the sixth.
The typical use for @code{SOCK_DGRAM} is in situations where it is
acceptable to simply re-send a packet if no response is seen in a
reasonable amount of time.
@xref{Datagrams}, for detailed information about how to use datagram
sockets.
@end deftypevr
@ignore
@c This appears to be only for the NS domain, which we aren't
@c discussing and probably won't support either.
@comment sys/socket.h
@comment BSD
@deftypevr Macro int SOCK_SEQPACKET
This style is like @code{SOCK_STREAM} except that the data are
structured into packets.
A program that receives data over a @code{SOCK_SEQPACKET} socket
should be prepared to read the entire message packet in a single call
to @code{read}; if it only reads part of the message, the remainder of
the message is simply discarded instead of being available for
subsequent calls to @code{read}.
Many protocols do not support this communication style.
@end deftypevr
@end ignore
@ignore
@comment sys/socket.h
@comment BSD
@deftypevr Macro int SOCK_RDM
This style is a reliable version of @code{SOCK_DGRAM}: it sends
individually addressed packets, but guarantees that each packet sent
arrives exactly once.
@strong{Warning:} It is not clear this is actually supported
by any operating system.
@end deftypevr
@end ignore
@comment sys/socket.h
@comment BSD
@deftypevr Macro int SOCK_RAW
This style provides access to low-level network protocols and
interfaces. Ordinary user programs usually have no need to use this
style.
@end deftypevr
@node Socket Addresses
@section Socket Addresses
@cindex address of socket
@cindex name of socket
@cindex binding a socket address
@cindex socket address (name) binding
The name of a socket is normally called an @dfn{address}. The
functions and symbols for dealing with socket addresses were named
inconsistently, sometimes using the term ``name'' and sometimes using
``address''. You can regard these terms as synonymous where sockets
are concerned.
A socket newly created with the @code{socket} function has no
address. Other processes can find it for communication only if you
give it an address. We call this @dfn{binding} the address to the
socket, and the way to do it is with the @code{bind} function.
You need be concerned with the address of a socket if other processes
are to find it and start communicating with it. You can specify an
address for other sockets, but this is usually pointless; the first time
you send data from a socket, or use it to initiate a connection, the
system assigns an address automatically if you have not specified one.
Occasionally a client needs to specify an address because the server
discriminates based on address; for example, the rsh and rlogin
protocols look at the client's socket address and only bypass password
checking if it is less than @code{IPPORT_RESERVED} (@pxref{Ports}).
The details of socket addresses vary depending on what namespace you are
using. @xref{Local Namespace}, or @ref{Internet Namespace}, for specific
information.
Regardless of the namespace, you use the same functions @code{bind} and
@code{getsockname} to set and examine a socket's address. These
functions use a phony data type, @code{struct sockaddr *}, to accept the
address. In practice, the address lives in a structure of some other
data type appropriate to the address format you are using, but you cast
its address to @code{struct sockaddr *} when you pass it to
@code{bind}.
@menu
* Address Formats:: About @code{struct sockaddr}.
* Setting Address:: Binding an address to a socket.
* Reading Address:: Reading the address of a socket.
@end menu
@node Address Formats
@subsection Address Formats
The functions @code{bind} and @code{getsockname} use the generic data
type @code{struct sockaddr *} to represent a pointer to a socket
address. You can't use this data type effectively to interpret an
address or construct one; for that, you must use the proper data type
for the socket's namespace.
Thus, the usual practice is to construct an address of the proper
namespace-specific type, then cast a pointer to @code{struct sockaddr *}
when you call @code{bind} or @code{getsockname}.
The one piece of information that you can get from the @code{struct
sockaddr} data type is the @dfn{address format designator}. This tells
you which data type to use to understand the address fully.
@pindex sys/socket.h
The symbols in this section are defined in the header file
@file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftp {Data Type} {struct sockaddr}
The @code{struct sockaddr} type itself has the following members:
@table @code
@item short int sa_family
This is the code for the address format of this address. It
identifies the format of the data which follows.
@item char sa_data[14]
This is the actual socket address data, which is format-dependent. Its
length also depends on the format, and may well be more than 14. The
length 14 of @code{sa_data} is essentially arbitrary.
@end table
@end deftp
Each address format has a symbolic name which starts with @samp{AF_}.
Each of them corresponds to a @samp{PF_} symbol which designates the
corresponding namespace. Here is a list of address format names:
@table @code
@comment sys/socket.h
@comment POSIX
@item AF_LOCAL
@vindex AF_LOCAL
This designates the address format that goes with the local namespace.
(@code{PF_LOCAL} is the name of that namespace.) @xref{Local Namespace
Details}, for information about this address format.
@comment sys/socket.h
@comment BSD, Unix98
@item AF_UNIX
@vindex AF_UNIX
This is a synonym for @code{AF_LOCAL}. Although @code{AF_LOCAL} is
mandated by POSIX.1g, @code{AF_UNIX} is portable to more systems.
@code{AF_UNIX} was the traditional name stemming from BSD, so even most
POSIX systems support it. It is also the name of choice in the Unix98
specification. (The same is true for @code{PF_UNIX}
vs. @code{PF_LOCAL}).
@comment sys/socket.h
@comment GNU
@item AF_FILE
@vindex AF_FILE
This is another synonym for @code{AF_LOCAL}, for compatibility.
(@code{PF_FILE} is likewise a synonym for @code{PF_LOCAL}.)
@comment sys/socket.h
@comment BSD
@item AF_INET
@vindex AF_INET
This designates the address format that goes with the Internet
namespace. (@code{PF_INET} is the name of that namespace.)
@xref{Internet Address Formats}.
@comment sys/socket.h
@comment IPv6 Basic API
@item AF_INET6
This is similar to @code{AF_INET}, but refers to the IPv6 protocol.
(@code{PF_INET6} is the name of the corresponding namespace.)
@comment sys/socket.h
@comment BSD
@item AF_UNSPEC
@vindex AF_UNSPEC
This designates no particular address format. It is used only in rare
cases, such as to clear out the default destination address of a
``connected'' datagram socket. @xref{Sending Datagrams}.
The corresponding namespace designator symbol @code{PF_UNSPEC} exists
for completeness, but there is no reason to use it in a program.
@end table
@file{sys/socket.h} defines symbols starting with @samp{AF_} for many
different kinds of networks, most or all of which are not actually
implemented. We will document those that really work as we receive
information about how to use them.
@node Setting Address
@subsection Setting the Address of a Socket
@pindex sys/socket.h
Use the @code{bind} function to assign an address to a socket. The
prototype for @code{bind} is in the header file @file{sys/socket.h}.
For examples of use, see @ref{Local Socket Example}, or see @ref{Inet Example}.
@comment sys/socket.h
@comment BSD
@deftypefun int bind (int @var{socket}, struct sockaddr *@var{addr}, socklen_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall, except on Hurd.
The @code{bind} function assigns an address to the socket
@var{socket}. The @var{addr} and @var{length} arguments specify the
address; the detailed format of the address depends on the namespace.
The first part of the address is always the format designator, which
specifies a namespace, and says that the address is in the format of
that namespace.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item EADDRNOTAVAIL
The specified address is not available on this machine.
@item EADDRINUSE
Some other socket is already using the specified address.
@item EINVAL
The socket @var{socket} already has an address.
@item EACCES
You do not have permission to access the requested address. (In the
Internet domain, only the super-user is allowed to specify a port number
in the range 0 through @code{IPPORT_RESERVED} minus one; see
@ref{Ports}.)
@end table
Additional conditions may be possible depending on the particular namespace
of the socket.
@end deftypefun
@node Reading Address
@subsection Reading the Address of a Socket
@pindex sys/socket.h
Use the function @code{getsockname} to examine the address of an
Internet socket. The prototype for this function is in the header file
@file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypefun int getsockname (int @var{socket}, struct sockaddr *@var{addr}, socklen_t *@var{length-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsmem{/hurd}}}
@c Direct syscall, except on Hurd, where it seems like it might leak
@c VM if cancelled.
The @code{getsockname} function returns information about the
address of the socket @var{socket} in the locations specified by the
@var{addr} and @var{length-ptr} arguments. Note that the
@var{length-ptr} is a pointer; you should initialize it to be the
allocation size of @var{addr}, and on return it contains the actual
size of the address data.
The format of the address data depends on the socket namespace. The
length of the information is usually fixed for a given namespace, so
normally you can know exactly how much space is needed and can provide
that much. The usual practice is to allocate a place for the value
using the proper data type for the socket's namespace, then cast its
address to @code{struct sockaddr *} to pass it to @code{getsockname}.
The return value is @code{0} on success and @code{-1} on error. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item ENOBUFS
There are not enough internal buffers available for the operation.
@end table
@end deftypefun
You can't read the address of a socket in the file namespace. This is
consistent with the rest of the system; in general, there's no way to
find a file's name from a descriptor for that file.
@node Interface Naming
@section Interface Naming
Each network interface has a name. This usually consists of a few
letters that relate to the type of interface, which may be followed by a
number if there is more than one interface of that type. Examples
might be @code{lo} (the loopback interface) and @code{eth0} (the first
Ethernet interface).
Although such names are convenient for humans, it would be clumsy to
have to use them whenever a program needs to refer to an interface. In
such situations an interface is referred to by its @dfn{index}, which is
an arbitrarily-assigned small positive integer.
The following functions, constants and data types are declared in the
header file @file{net/if.h}.
@comment net/if.h
@deftypevr Constant size_t IFNAMSIZ
This constant defines the maximum buffer size needed to hold an
interface name, including its terminating zero byte.
@end deftypevr
@comment net/if.h
@comment IPv6 basic API
@deftypefun {unsigned int} if_nametoindex (const char *@var{ifname})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c It opens a socket to use ioctl on the fd to get the index.
@c opensock may call socket and access multiple times until it finds a
@c socket family that works. The Linux implementation has a potential
@c concurrency issue WRT last_type and last_family not being updated
@c atomically, but it is harmless; the generic implementation, OTOH,
@c takes a lock, which makes all callers AS- and AC-Unsafe.
@c opensock @asulock @aculock @acsfd
This function yields the interface index corresponding to a particular
name. If no interface exists with the name given, it returns 0.
@end deftypefun
@comment net/if.h
@comment IPv6 basic API
@deftypefun {char *} if_indextoname (unsigned int @var{ifindex}, char *@var{ifname})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{}}}
@c It opens a socket with opensock to use ioctl on the fd to get the
@c name from the index.
This function maps an interface index to its corresponding name. The
returned name is placed in the buffer pointed to by @code{ifname}, which
must be at least @code{IFNAMSIZ} bytes in length. If the index was
invalid, the function's return value is a null pointer, otherwise it is
@code{ifname}.
@end deftypefun
@comment net/if.h
@comment IPv6 basic API
@deftp {Data Type} {struct if_nameindex}
This data type is used to hold the information about a single
interface. It has the following members:
@table @code
@item unsigned int if_index;
This is the interface index.
@item char *if_name
This is the null-terminated index name.
@end table
@end deftp
@comment net/if.h
@comment IPv6 basic API
@deftypefun {struct if_nameindex *} if_nameindex (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{/hurd}}@acunsafe{@aculock{/hurd} @acsfd{} @acsmem{}}}
@c if_nameindex @ascuheap @asulock/hurd @aculock/hurd @acsfd @acsmem
@c [linux]
@c netlink_open @acsfd @acsmem/hurd
@c socket dup @acsfd
@c memset dup ok
@c bind dup ok
@c netlink_close dup @acsfd
@c getsockname dup @acsmem/hurd
@c netlink_request @ascuheap @acsmem
@c getpagesize dup ok
@c malloc dup @ascuheap @acsmem
@c netlink_sendreq ok
@c memset dup ok
@c sendto dup ok
@c recvmsg dup ok
@c memcpy dup ok
@c free dup @ascuheap @acsmem
@c netlink_free_handle @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c netlink_close @acsfd
@c close dup @acsfd
@c malloc dup @asuheap @acsmem
@c strndup @ascuheap @acsmem
@c if_freenameindex @ascuheap @acsmem
@c [hurd]
@c opensock dup @asulock @aculock @acsfd
@c hurd_socket_server ok
@c pfinet_siocgifconf ok
@c malloc @ascuheap @acsmem
@c strdup @ascuheap @acsmem
@c ioctl dup ok
@c free @ascuheap @acsmem
This function returns an array of @code{if_nameindex} structures, one
for every interface that is present. The end of the list is indicated
by a structure with an interface of 0 and a null name pointer. If an
error occurs, this function returns a null pointer.
The returned structure must be freed with @code{if_freenameindex} after
use.
@end deftypefun
@comment net/if.h
@comment IPv6 basic API
@deftypefun void if_freenameindex (struct if_nameindex *@var{ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@c if_freenameindex @ascuheap @acsmem
@c free dup @ascuheap @acsmem
This function frees the structure returned by an earlier call to
@code{if_nameindex}.
@end deftypefun
@node Local Namespace
@section The Local Namespace
@cindex local namespace, for sockets
This section describes the details of the local namespace, whose
symbolic name (required when you create a socket) is @code{PF_LOCAL}.
The local namespace is also known as ``Unix domain sockets''. Another
name is file namespace since socket addresses are normally implemented
as file names.
@menu
* Concepts: Local Namespace Concepts. What you need to understand.
* Details: Local Namespace Details. Address format, symbolic names, etc.
* Example: Local Socket Example. Example of creating a socket.
@end menu
@node Local Namespace Concepts
@subsection Local Namespace Concepts
In the local namespace socket addresses are file names. You can specify
any file name you want as the address of the socket, but you must have
write permission on the directory containing it.
@c XXX The following was said to be wrong.
@c In order to connect to a socket you must have read permission for it.
It's common to put these files in the @file{/tmp} directory.
One peculiarity of the local namespace is that the name is only used
when opening the connection; once open the address is not meaningful and
may not exist.
Another peculiarity is that you cannot connect to such a socket from
another machine--not even if the other machine shares the file system
which contains the name of the socket. You can see the socket in a
directory listing, but connecting to it never succeeds. Some programs
take advantage of this, such as by asking the client to send its own
process ID, and using the process IDs to distinguish between clients.
However, we recommend you not use this method in protocols you design,
as we might someday permit connections from other machines that mount
the same file systems. Instead, send each new client an identifying
number if you want it to have one.
After you close a socket in the local namespace, you should delete the
file name from the file system. Use @code{unlink} or @code{remove} to
do this; see @ref{Deleting Files}.
The local namespace supports just one protocol for any communication
style; it is protocol number @code{0}.
@node Local Namespace Details
@subsection Details of Local Namespace
@pindex sys/socket.h
To create a socket in the local namespace, use the constant
@code{PF_LOCAL} as the @var{namespace} argument to @code{socket} or
@code{socketpair}. This constant is defined in @file{sys/socket.h}.
@comment sys/socket.h
@comment POSIX
@deftypevr Macro int PF_LOCAL
This designates the local namespace, in which socket addresses are local
names, and its associated family of protocols. @code{PF_Local} is the
macro used by Posix.1g.
@end deftypevr
@comment sys/socket.h
@comment BSD
@deftypevr Macro int PF_UNIX
This is a synonym for @code{PF_LOCAL}, for compatibility's sake.
@end deftypevr
@comment sys/socket.h
@comment GNU
@deftypevr Macro int PF_FILE
This is a synonym for @code{PF_LOCAL}, for compatibility's sake.
@end deftypevr
The structure for specifying socket names in the local namespace is
defined in the header file @file{sys/un.h}:
@pindex sys/un.h
@comment sys/un.h
@comment BSD
@deftp {Data Type} {struct sockaddr_un}
This structure is used to specify local namespace socket addresses. It has
the following members:
@table @code
@item short int sun_family
This identifies the address family or format of the socket address.
You should store the value @code{AF_LOCAL} to designate the local
namespace. @xref{Socket Addresses}.
@item char sun_path[108]
This is the file name to use.
@strong{Incomplete:} Why is 108 a magic number? RMS suggests making
this a zero-length array and tweaking the following example to use
@code{alloca} to allocate an appropriate amount of storage based on
the length of the filename.
@end table
@end deftp
You should compute the @var{length} parameter for a socket address in
the local namespace as the sum of the size of the @code{sun_family}
component and the string length (@emph{not} the allocation size!) of
the file name string. This can be done using the macro @code{SUN_LEN}:
@comment sys/un.h
@comment BSD
@deftypefn {Macro} int SUN_LEN (@emph{struct sockaddr_un *} @var{ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The macro computes the length of socket address in the local namespace.
@end deftypefn
@node Local Socket Example
@subsection Example of Local-Namespace Sockets
Here is an example showing how to create and name a socket in the local
namespace.
@smallexample
@include mkfsock.c.texi
@end smallexample
@node Internet Namespace
@section The Internet Namespace
@cindex Internet namespace, for sockets
This section describes the details of the protocols and socket naming
conventions used in the Internet namespace.
Originally the Internet namespace used only IP version 4 (IPv4). With
the growing number of hosts on the Internet, a new protocol with a
larger address space was necessary: IP version 6 (IPv6). IPv6
introduces 128-bit addresses (IPv4 has 32-bit addresses) and other
features, and will eventually replace IPv4.
To create a socket in the IPv4 Internet namespace, use the symbolic name
@code{PF_INET} of this namespace as the @var{namespace} argument to
@code{socket} or @code{socketpair}. For IPv6 addresses you need the
macro @code{PF_INET6}. These macros are defined in @file{sys/socket.h}.
@pindex sys/socket.h
@comment sys/socket.h
@comment BSD
@deftypevr Macro int PF_INET
This designates the IPv4 Internet namespace and associated family of
protocols.
@end deftypevr
@comment sys/socket.h
@comment X/Open
@deftypevr Macro int PF_INET6
This designates the IPv6 Internet namespace and associated family of
protocols.
@end deftypevr
A socket address for the Internet namespace includes the following components:
@itemize @bullet
@item
The address of the machine you want to connect to. Internet addresses
can be specified in several ways; these are discussed in @ref{Internet
Address Formats}, @ref{Host Addresses} and @ref{Host Names}.
@item
A port number for that machine. @xref{Ports}.
@end itemize
You must ensure that the address and port number are represented in a
canonical format called @dfn{network byte order}. @xref{Byte Order},
for information about this.
@menu
* Internet Address Formats:: How socket addresses are specified in the
Internet namespace.
* Host Addresses:: All about host addresses of Internet host.
* Ports:: Internet port numbers.
* Services Database:: Ports may have symbolic names.
* Byte Order:: Different hosts may use different byte
ordering conventions; you need to
canonicalize host address and port number.
* Protocols Database:: Referring to protocols by name.
* Inet Example:: Putting it all together.
@end menu
@node Internet Address Formats
@subsection Internet Socket Address Formats
In the Internet namespace, for both IPv4 (@code{AF_INET}) and IPv6
(@code{AF_INET6}), a socket address consists of a host address
and a port on that host. In addition, the protocol you choose serves
effectively as a part of the address because local port numbers are
meaningful only within a particular protocol.
The data types for representing socket addresses in the Internet namespace
are defined in the header file @file{netinet/in.h}.
@pindex netinet/in.h
@comment netinet/in.h
@comment BSD
@deftp {Data Type} {struct sockaddr_in}
This is the data type used to represent socket addresses in the
Internet namespace. It has the following members:
@table @code
@item sa_family_t sin_family
This identifies the address family or format of the socket address.
You should store the value @code{AF_INET} in this member.
@xref{Socket Addresses}.
@item struct in_addr sin_addr
This is the Internet address of the host machine. @xref{Host
Addresses}, and @ref{Host Names}, for how to get a value to store
here.
@item unsigned short int sin_port
This is the port number. @xref{Ports}.
@end table
@end deftp
When you call @code{bind} or @code{getsockname}, you should specify
@code{sizeof (struct sockaddr_in)} as the @var{length} parameter if
you are using an IPv4 Internet namespace socket address.
@deftp {Data Type} {struct sockaddr_in6}
This is the data type used to represent socket addresses in the IPv6
namespace. It has the following members:
@table @code
@item sa_family_t sin6_family
This identifies the address family or format of the socket address.
You should store the value of @code{AF_INET6} in this member.
@xref{Socket Addresses}.
@item struct in6_addr sin6_addr
This is the IPv6 address of the host machine. @xref{Host
Addresses}, and @ref{Host Names}, for how to get a value to store
here.
@item uint32_t sin6_flowinfo
This is a currently unimplemented field.
@item uint16_t sin6_port
This is the port number. @xref{Ports}.
@end table
@end deftp
@node Host Addresses
@subsection Host Addresses
Each computer on the Internet has one or more @dfn{Internet addresses},
numbers which identify that computer among all those on the Internet.
Users typically write IPv4 numeric host addresses as sequences of four
numbers, separated by periods, as in @samp{128.52.46.32}, and IPv6
numeric host addresses as sequences of up to eight numbers separated by
colons, as in @samp{5f03:1200:836f:c100::1}.
Each computer also has one or more @dfn{host names}, which are strings
of words separated by periods, as in @samp{www.gnu.org}.
Programs that let the user specify a host typically accept both numeric
addresses and host names. To open a connection a program needs a
numeric address, and so must convert a host name to the numeric address
it stands for.
@menu
* Abstract Host Addresses:: What a host number consists of.
* Data type: Host Address Data Type. Data type for a host number.
* Functions: Host Address Functions. Functions to operate on them.
* Names: Host Names. Translating host names to host numbers.
@end menu
@node Abstract Host Addresses
@subsubsection Internet Host Addresses
@cindex host address, Internet
@cindex Internet host address
@ifinfo
Each computer on the Internet has one or more Internet addresses,
numbers which identify that computer among all those on the Internet.
@end ifinfo
@cindex network number
@cindex local network address number
An IPv4 Internet host address is a number containing four bytes of data.
Historically these are divided into two parts, a @dfn{network number} and a
@dfn{local network address number} within that network. In the
mid-1990s classless addresses were introduced which changed this
behavior. Since some functions implicitly expect the old definitions,
we first describe the class-based network and will then describe
classless addresses. IPv6 uses only classless addresses and therefore
the following paragraphs don't apply.
The class-based IPv4 network number consists of the first one, two or
three bytes; the rest of the bytes are the local address.
IPv4 network numbers are registered with the Network Information Center
(NIC), and are divided into three classes---A, B and C. The local
network address numbers of individual machines are registered with the
administrator of the particular network.
Class A networks have single-byte numbers in the range 0 to 127. There
are only a small number of Class A networks, but they can each support a
very large number of hosts. Medium-sized Class B networks have two-byte
network numbers, with the first byte in the range 128 to 191. Class C
networks are the smallest; they have three-byte network numbers, with
the first byte in the range 192-255. Thus, the first 1, 2, or 3 bytes
of an Internet address specify a network. The remaining bytes of the
Internet address specify the address within that network.
The Class A network 0 is reserved for broadcast to all networks. In
addition, the host number 0 within each network is reserved for broadcast
to all hosts in that network. These uses are obsolete now but for
compatibility reasons you shouldn't use network 0 and host number 0.
The Class A network 127 is reserved for loopback; you can always use
the Internet address @samp{127.0.0.1} to refer to the host machine.
Since a single machine can be a member of multiple networks, it can
have multiple Internet host addresses. However, there is never
supposed to be more than one machine with the same host address.
@c !!! this section could document the IN_CLASS* macros in .
@c No, it shouldn't since they're obsolete.
@cindex standard dot notation, for Internet addresses
@cindex dot notation, for Internet addresses
There are four forms of the @dfn{standard numbers-and-dots notation}
for Internet addresses:
@table @code
@item @var{a}.@var{b}.@var{c}.@var{d}
This specifies all four bytes of the address individually and is the
commonly used representation.
@item @var{a}.@var{b}.@var{c}
The last part of the address, @var{c}, is interpreted as a 2-byte quantity.
This is useful for specifying host addresses in a Class B network with
network address number @code{@var{a}.@var{b}}.
@item @var{a}.@var{b}
The last part of the address, @var{b}, is interpreted as a 3-byte quantity.
This is useful for specifying host addresses in a Class A network with
network address number @var{a}.
@item @var{a}
If only one part is given, this corresponds directly to the host address
number.
@end table
Within each part of the address, the usual C conventions for specifying
the radix apply. In other words, a leading @samp{0x} or @samp{0X} implies
hexadecimal radix; a leading @samp{0} implies octal; and otherwise decimal
radix is assumed.
@subsubheading Classless Addresses
IPv4 addresses (and IPv6 addresses also) are now considered classless;
the distinction between classes A, B and C can be ignored. Instead an
IPv4 host address consists of a 32-bit address and a 32-bit mask. The
mask contains set bits for the network part and cleared bits for the
host part. The network part is contiguous from the left, with the
remaining bits representing the host. As a consequence, the netmask can
simply be specified as the number of set bits. Classes A, B and C are
just special cases of this general rule. For example, class A addresses
have a netmask of @samp{255.0.0.0} or a prefix length of 8.
Classless IPv4 network addresses are written in numbers-and-dots
notation with the prefix length appended and a slash as separator. For
example the class A network 10 is written as @samp{10.0.0.0/8}.
@subsubheading IPv6 Addresses
IPv6 addresses contain 128 bits (IPv4 has 32 bits) of data. A host
address is usually written as eight 16-bit hexadecimal numbers that are
separated by colons. Two colons are used to abbreviate strings of
consecutive zeros. For example, the IPv6 loopback address
@samp{0:0:0:0:0:0:0:1} can just be written as @samp{::1}.
@node Host Address Data Type
@subsubsection Host Address Data Type
IPv4 Internet host addresses are represented in some contexts as integers
(type @code{uint32_t}). In other contexts, the integer is
packaged inside a structure of type @code{struct in_addr}. It would
be better if the usage were made consistent, but it is not hard to extract
the integer from the structure or put the integer into a structure.
You will find older code that uses @code{unsigned long int} for
IPv4 Internet host addresses instead of @code{uint32_t} or @code{struct
in_addr}. Historically @code{unsigned long int} was a 32-bit number but
with 64-bit machines this has changed. Using @code{unsigned long int}
might break the code if it is used on machines where this type doesn't
have 32 bits. @code{uint32_t} is specified by Unix98 and guaranteed to have
32 bits.
IPv6 Internet host addresses have 128 bits and are packaged inside a
structure of type @code{struct in6_addr}.
The following basic definitions for Internet addresses are declared in
the header file @file{netinet/in.h}:
@pindex netinet/in.h
@comment netinet/in.h
@comment BSD
@deftp {Data Type} {struct in_addr}
This data type is used in certain contexts to contain an IPv4 Internet
host address. It has just one field, named @code{s_addr}, which records
the host address number as an @code{uint32_t}.
@end deftp
@comment netinet/in.h
@comment BSD
@deftypevr Macro {uint32_t} INADDR_LOOPBACK
You can use this constant to stand for ``the address of this machine,''
instead of finding its actual address. It is the IPv4 Internet address
@samp{127.0.0.1}, which is usually called @samp{localhost}. This
special constant saves you the trouble of looking up the address of your
own machine. Also, the system usually implements @code{INADDR_LOOPBACK}
specially, avoiding any network traffic for the case of one machine
talking to itself.
@end deftypevr
@comment netinet/in.h
@comment BSD
@deftypevr Macro {uint32_t} INADDR_ANY
You can use this constant to stand for ``any incoming address'' when
binding to an address. @xref{Setting Address}. This is the usual
address to give in the @code{sin_addr} member of @w{@code{struct
sockaddr_in}} when you want to accept Internet connections.
@end deftypevr
@comment netinet/in.h
@comment BSD
@deftypevr Macro {uint32_t} INADDR_BROADCAST
This constant is the address you use to send a broadcast message.
@c !!! broadcast needs further documented
@end deftypevr
@comment netinet/in.h
@comment BSD
@deftypevr Macro {uint32_t} INADDR_NONE
This constant is returned by some functions to indicate an error.
@end deftypevr
@comment netinet/in.h
@comment IPv6 basic API
@deftp {Data Type} {struct in6_addr}
This data type is used to store an IPv6 address. It stores 128 bits of
data, which can be accessed (via a union) in a variety of ways.
@end deftp
@comment netinet/in.h
@comment IPv6 basic API
@deftypevr Constant {struct in6_addr} in6addr_loopback
This constant is the IPv6 address @samp{::1}, the loopback address. See
above for a description of what this means. The macro
@code{IN6ADDR_LOOPBACK_INIT} is provided to allow you to initialize your
own variables to this value.
@end deftypevr
@comment netinet/in.h
@comment IPv6 basic API
@deftypevr Constant {struct in6_addr} in6addr_any
This constant is the IPv6 address @samp{::}, the unspecified address. See
above for a description of what this means. The macro
@code{IN6ADDR_ANY_INIT} is provided to allow you to initialize your
own variables to this value.
@end deftypevr
@node Host Address Functions
@subsubsection Host Address Functions
@pindex arpa/inet.h
@noindent
These additional functions for manipulating Internet addresses are
declared in the header file @file{arpa/inet.h}. They represent Internet
addresses in network byte order, and network numbers and
local-address-within-network numbers in host byte order. @xref{Byte
Order}, for an explanation of network and host byte order.
@comment arpa/inet.h
@comment BSD
@deftypefun int inet_aton (const char *@var{name}, struct in_addr *@var{addr})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c inet_aton @mtslocale
@c isdigit dup @mtslocale
@c strtoul dup @mtslocale
@c isascii dup @mtslocale
@c isspace dup @mtslocale
@c htonl dup ok
This function converts the IPv4 Internet host address @var{name}
from the standard numbers-and-dots notation into binary data and stores
it in the @code{struct in_addr} that @var{addr} points to.
@code{inet_aton} returns nonzero if the address is valid, zero if not.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun {uint32_t} inet_addr (const char *@var{name})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c inet_addr @mtslocale
@c inet_aton dup @mtslocale
This function converts the IPv4 Internet host address @var{name} from the
standard numbers-and-dots notation into binary data. If the input is
not valid, @code{inet_addr} returns @code{INADDR_NONE}. This is an
obsolete interface to @code{inet_aton}, described immediately above. It
is obsolete because @code{INADDR_NONE} is a valid address
(255.255.255.255), and @code{inet_aton} provides a cleaner way to
indicate error return.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun {uint32_t} inet_network (const char *@var{name})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c inet_network @mtslocale
@c isdigit dup @mtslocale
@c isxdigit dup @mtslocale
@c tolower dup @mtslocale
@c isspace dup @mtslocale
This function extracts the network number from the address @var{name},
given in the standard numbers-and-dots notation. The returned address is
in host order. If the input is not valid, @code{inet_network} returns
@code{-1}.
The function works only with traditional IPv4 class A, B and C network
types. It doesn't work with classless addresses and shouldn't be used
anymore.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun {char *} inet_ntoa (struct in_addr @var{addr})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asurace{}}@acsafe{}}
@c inet_ntoa @mtslocale @asurace
@c writes to a thread-local static buffer
@c snprintf @mtslocale [no @ascuheap or @acsmem]
This function converts the IPv4 Internet host address @var{addr} to a
string in the standard numbers-and-dots notation. The return value is
a pointer into a statically-allocated buffer. Subsequent calls will
overwrite the same buffer, so you should copy the string if you need
to save it.
In multi-threaded programs each thread has an own statically-allocated
buffer. But still subsequent calls of @code{inet_ntoa} in the same
thread will overwrite the result of the last call.
Instead of @code{inet_ntoa} the newer function @code{inet_ntop} which is
described below should be used since it handles both IPv4 and IPv6
addresses.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun {struct in_addr} inet_makeaddr (uint32_t @var{net}, uint32_t @var{local})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c inet_makeaddr ok
@c htonl dup ok
This function makes an IPv4 Internet host address by combining the network
number @var{net} with the local-address-within-network number
@var{local}.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun uint32_t inet_lnaof (struct in_addr @var{addr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c inet_lnaof ok
@c ntohl dup ok
@c IN_CLASSA ok
@c IN_CLASSB ok
This function returns the local-address-within-network part of the
Internet host address @var{addr}.
The function works only with traditional IPv4 class A, B and C network
types. It doesn't work with classless addresses and shouldn't be used
anymore.
@end deftypefun
@comment arpa/inet.h
@comment BSD
@deftypefun uint32_t inet_netof (struct in_addr @var{addr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c inet_netof ok
@c ntohl dup ok
@c IN_CLASSA ok
@c IN_CLASSB ok
This function returns the network number part of the Internet host
address @var{addr}.
The function works only with traditional IPv4 class A, B and C network
types. It doesn't work with classless addresses and shouldn't be used
anymore.
@end deftypefun
@comment arpa/inet.h
@comment IPv6 basic API
@deftypefun int inet_pton (int @var{af}, const char *@var{cp}, void *@var{buf})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c inet_pton @mtslocale
@c inet_pton4 ok
@c memcpy dup ok
@c inet_pton6 @mtslocale
@c memset dup ok
@c tolower dup @mtslocale
@c strchr dup ok
@c inet_pton4 dup ok
@c memcpy dup ok
This function converts an Internet address (either IPv4 or IPv6) from
presentation (textual) to network (binary) format. @var{af} should be
either @code{AF_INET} or @code{AF_INET6}, as appropriate for the type of
address being converted. @var{cp} is a pointer to the input string, and
@var{buf} is a pointer to a buffer for the result. It is the caller's
responsibility to make sure the buffer is large enough.
@end deftypefun
@comment arpa/inet.h
@comment IPv6 basic API
@deftypefun {const char *} inet_ntop (int @var{af}, const void *@var{cp}, char *@var{buf}, socklen_t @var{len})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
@c inet_ntop @mtslocale
@c inet_ntop4 @mtslocale
@c sprintf dup @mtslocale [no @ascuheap or @acsmem]
@c strcpy dup ok
@c inet_ntop6 @mtslocale
@c memset dup ok
@c inet_ntop4 dup @mtslocale
@c sprintf dup @mtslocale [no @ascuheap or @acsmem]
@c strcpy dup ok
This function converts an Internet address (either IPv4 or IPv6) from
network (binary) to presentation (textual) form. @var{af} should be
either @code{AF_INET} or @code{AF_INET6}, as appropriate. @var{cp} is a
pointer to the address to be converted. @var{buf} should be a pointer
to a buffer to hold the result, and @var{len} is the length of this
buffer. The return value from the function will be this buffer address.
@end deftypefun
@node Host Names
@subsubsection Host Names
@cindex hosts database
@cindex converting host name to address
@cindex converting host address to name
Besides the standard numbers-and-dots notation for Internet addresses,
you can also refer to a host by a symbolic name. The advantage of a
symbolic name is that it is usually easier to remember. For example,
the machine with Internet address @samp{158.121.106.19} is also known as
@samp{alpha.gnu.org}; and other machines in the @samp{gnu.org}
domain can refer to it simply as @samp{alpha}.
@pindex /etc/hosts
@pindex netdb.h
Internally, the system uses a database to keep track of the mapping
between host names and host numbers. This database is usually either
the file @file{/etc/hosts} or an equivalent provided by a name server.
The functions and other symbols for accessing this database are declared
in @file{netdb.h}. They are BSD features, defined unconditionally if
you include @file{netdb.h}.
@comment netdb.h
@comment BSD
@deftp {Data Type} {struct hostent}
This data type is used to represent an entry in the hosts database. It
has the following members:
@table @code
@item char *h_name
This is the ``official'' name of the host.
@item char **h_aliases
These are alternative names for the host, represented as a null-terminated
vector of strings.
@item int h_addrtype
This is the host address type; in practice, its value is always either
@code{AF_INET} or @code{AF_INET6}, with the latter being used for IPv6
hosts. In principle other kinds of addresses could be represented in
the database as well as Internet addresses; if this were done, you
might find a value in this field other than @code{AF_INET} or
@code{AF_INET6}. @xref{Socket Addresses}.
@item int h_length
This is the length, in bytes, of each address.
@item char **h_addr_list
This is the vector of addresses for the host. (Recall that the host
might be connected to multiple networks and have different addresses on
each one.) The vector is terminated by a null pointer.
@item char *h_addr
This is a synonym for @code{h_addr_list[0]}; in other words, it is the
first host address.
@end table
@end deftp
As far as the host database is concerned, each address is just a block
of memory @code{h_length} bytes long. But in other contexts there is an
implicit assumption that you can convert IPv4 addresses to a
@code{struct in_addr} or an @code{uint32_t}. Host addresses in
a @code{struct hostent} structure are always given in network byte
order; see @ref{Byte Order}.
You can use @code{gethostbyname}, @code{gethostbyname2} or
@code{gethostbyaddr} to search the hosts database for information about
a particular host. The information is returned in a
statically-allocated structure; you must copy the information if you
need to save it across calls. You can also use @code{getaddrinfo} and
@code{getnameinfo} to obtain this information.
@comment netdb.h
@comment BSD
@deftypefun {struct hostent *} gethostbyname (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:hostbyname} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyname @mtasurace:hostbyname @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c nss_hostname_digits_dots @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_maybe_init(!preinit) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_iclose @acsuheap @acsmem @acsfd
@c close_not_cancel_no_status dup @acsfd
@c free dup @acsuheap @acsmem
@c res_vinit @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_randomid ok
@c getpid dup ok
@c getenv dup @mtsenv
@c strncpy dup ok
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking dup ok [no concurrent uses]
@c fgets_unlocked dup ok [no concurrent uses]
@c MATCH ok
@c strncmp dup ok
@c strpbrk dup ok
@c strchr dup ok
@c inet_aton dup @mtslocale
@c htons dup
@c inet_pton dup @mtslocale
@c malloc dup @ascuheap @acsmem
@c IN6_IS_ADDR_LINKLOCAL ok
@c htonl dup ok
@c IN6_IS_ADDR_MC_LINKLOCAL ok
@c if_nametoindex dup @asulock @aculock @acsfd
@c strtoul dup @mtslocale
@c ISSORTMASK ok
@c strchr dup ok
@c isascii dup @mtslocale
@c isspace dup @mtslocale
@c net_mask ok
@c ntohl dup ok
@c IN_CLASSA dup ok
@c htonl dup ok
@c IN_CLASSB dup ok
@c res_setoptions @mtslocale
@c strncmp dup ok
@c atoi dup @mtslocale
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
@c inet_makeaddr dup ok
@c gethostname dup ok
@c strcpy dup ok
@c rawmemchr dup ok
@c res_ninit @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_vinit dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c isdigit dup @mtslocale
@c isxdigit dup @mtslocale
@c strlen dup ok
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c memset dup ok
@c inet_aton dup @mtslocale
@c inet_pton dup @mtslocale
@c strcpy dup ok
@c memcpy dup ok
@c strchr dup ok
@c gethostbyname_r dup @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c set_h_errno ok
The @code{gethostbyname} function returns information about the host
named @var{name}. If the lookup fails, it returns a null pointer.
@end deftypefun
@comment netdb.h
@comment IPv6 Basic API
@deftypefun {struct hostent *} gethostbyname2 (const char *@var{name}, int @var{af})
@safety{@prelim{}@mtunsafe{@mtasurace{:hostbyname2} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyname2 @mtasurace:hostbyname2 @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c nss_hostname_digits_dots dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c gethostbyname2_r dup @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c set_h_errno dup ok
The @code{gethostbyname2} function is like @code{gethostbyname}, but
allows the caller to specify the desired address family (e.g.@:
@code{AF_INET} or @code{AF_INET6}) of the result.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct hostent *} gethostbyaddr (const void *@var{addr}, socklen_t @var{length}, int @var{format})
@safety{@prelim{}@mtunsafe{@mtasurace{:hostbyaddr} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyaddr @mtasurace:hostbyaddr @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c gethostbyaddr_r dup @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c set_h_errno dup ok
The @code{gethostbyaddr} function returns information about the host
with Internet address @var{addr}. The parameter @var{addr} is not
really a pointer to char - it can be a pointer to an IPv4 or an IPv6
address. The @var{length} argument is the size (in bytes) of the address
at @var{addr}. @var{format} specifies the address format; for an IPv4
Internet address, specify a value of @code{AF_INET}; for an IPv6
Internet address, use @code{AF_INET6}.
If the lookup fails, @code{gethostbyaddr} returns a null pointer.
@end deftypefun
@vindex h_errno
If the name lookup by @code{gethostbyname} or @code{gethostbyaddr}
fails, you can find out the reason by looking at the value of the
variable @code{h_errno}. (It would be cleaner design for these
functions to set @code{errno}, but use of @code{h_errno} is compatible
with other systems.)
Here are the error codes that you may find in @code{h_errno}:
@table @code
@comment netdb.h
@comment BSD
@item HOST_NOT_FOUND
@vindex HOST_NOT_FOUND
No such host is known in the database.
@comment netdb.h
@comment BSD
@item TRY_AGAIN
@vindex TRY_AGAIN
This condition happens when the name server could not be contacted. If
you try again later, you may succeed then.
@comment netdb.h
@comment BSD
@item NO_RECOVERY
@vindex NO_RECOVERY
A non-recoverable error occurred.
@comment netdb.h
@comment BSD
@item NO_ADDRESS
@vindex NO_ADDRESS
The host database contains an entry for the name, but it doesn't have an
associated Internet address.
@end table
The lookup functions above all have one in common: they are not
reentrant and therefore unusable in multi-threaded applications.
Therefore provides @theglibc{} a new set of functions which can be
used in this context.
@comment netdb.h
@comment GNU
@deftypefun int gethostbyname_r (const char *restrict @var{name}, struct hostent *restrict @var{result_buf}, char *restrict @var{buf}, size_t @var{buflen}, struct hostent **restrict @var{result}, int *restrict @var{h_errnop})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyname_r @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c nss_hostname_digits_dots dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c nscd_gethostbyname_r @mtsenv @ascuheap @acsfd @acsmem
@c nscd_gethst_r @mtsenv @ascuheap @acsfd @acsmem
@c getenv dup @mtsenv
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c nscd_cache_search dup ok
@c memcpy dup ok
@c nscd_open_socket dup @acsfd
@c readvall dup ok
@c readall dup ok
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_hconf_init @mtsenv @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem [no @asuinit:reshconf @acuinit:reshconf, conditionally called]
@c res_hconf.c:do_init @mtsenv @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c memset dup ok
@c getenv dup @mtsenv
@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
@c fsetlocking dup ok [no concurrent uses]
@c fgets_unlocked dup ok [no concurrent uses]
@c strchrnul dup ok
@c res_hconf.c:parse_line @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c skip_ws dup @mtslocale
@c skip_string dup @mtslocale
@c strncasecmp dup @mtslocale
@c strlen dup ok
@c asprintf dup @mtslocale @ascuheap @acsmem
@c fxprintf dup @asucorrupt @aculock @acucorrupt
@c free dup @ascuheap @acsmem
@c arg_trimdomain_list dup @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c arg_spoof dup @mtslocale
@c arg_bool dup @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c isspace dup @mtslocale
@c fclose dup @ascuheap @asulock @acsmem @acsfd @aculock
@c arg_spoof @mtslocale
@c skip_string @mtslocale
@c isspace dup @mtslocale
@c strncasecmp dup @mtslocale
@c arg_bool @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c strncasecmp dup @mtslocale
@c asprintf dup @mtslocale @ascuheap @acsmem
@c fxprintf dup @asucorrupt @aculock @acucorrupt
@c free dup @ascuheap @acsmem
@c arg_trimdomain_list @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem
@c skip_string dup @mtslocale
@c asprintf dup @mtslocale @ascuheap @acsmem
@c fxprintf dup @asucorrupt @aculock @acucorrupt
@c free dup @ascuheap @acsmem
@c strndup dup @ascuheap @acsmem
@c skip_ws @mtslocale
@c isspace dup @mtslocale
@c nss_hosts_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_database_lookup dup @mtslocale @ascuheap @asulock @acucorrupt @acsmem @acsfd @aculock
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_gethostbyname_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_hconf_reorder_addrs @asulock @ascuheap @aculock @acsmem @acsfd
@c socket dup @acsfd
@c libc_lock_lock dup @asulock @aculock
@c ifreq @ascuheap @acsmem
@c malloc dup @ascuheap @acsmem
@c if_nextreq dup ok
@c ioctl dup ok
@c realloc dup @ascuheap @acsmem
@c if_freereq dup @acsmem
@c libc_lock_unlock dup @aculock
@c close dup @acsfd
The @code{gethostbyname_r} function returns information about the host
named @var{name}. The caller must pass a pointer to an object of type
@code{struct hostent} in the @var{result_buf} parameter. In addition
the function may need extra buffer space and the caller must pass an
pointer and the size of the buffer in the @var{buf} and @var{buflen}
parameters.
A pointer to the buffer, in which the result is stored, is available in
@code{*@var{result}} after the function call successfully returned. The
buffer passed as the @var{buf} parameter can be freed only once the caller
has finished with the result hostent struct, or has copied it including all
the other memory that it points to. If an error occurs or if no entry is
found, the pointer @code{*@var{result}} is a null pointer. Success is
signalled by a zero return value. If the function failed the return value
is an error number. In addition to the errors defined for
@code{gethostbyname} it can also be @code{ERANGE}. In this case the call
should be repeated with a larger buffer. Additional error information is
not stored in the global variable @code{h_errno} but instead in the object
pointed to by @var{h_errnop}.
Here's a small example:
@smallexample
struct hostent *
gethostname (char *host)
@{
struct hostent *hostbuf, *hp;
size_t hstbuflen;
char *tmphstbuf;
int res;
int herr;
hostbuf = malloc (sizeof (struct hostent));
hstbuflen = 1024;
tmphstbuf = malloc (hstbuflen);
while ((res = gethostbyname_r (host, hostbuf, tmphstbuf, hstbuflen,
&hp, &herr)) == ERANGE)
@{
/* Enlarge the buffer. */
hstbuflen *= 2;
tmphstbuf = realloc (tmphstbuf, hstbuflen);
@}
free (tmphstbuf);
/* Check for errors. */
if (res || hp == NULL)
return NULL;
return hp;
@}
@end smallexample
@end deftypefun
@comment netdb.h
@comment GNU
@deftypefun int gethostbyname2_r (const char *@var{name}, int @var{af}, struct hostent *restrict @var{result_buf}, char *restrict @var{buf}, size_t @var{buflen}, struct hostent **restrict @var{result}, int *restrict @var{h_errnop})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyname2_r @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c nss_hostname_digits_dots dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c nscd_gethostbyname2_r @mtsenv @ascuheap @asulock @aculock @acsfd @acsmem
@c nscd_gethst_r dup @mtsenv @ascuheap @asulock @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_hconf_init dup @mtsenv @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem [no @asuinit:reshconf @acuinit:reshconf, conditionally called]
@c nss_hosts_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_gethostbyname2_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_hconf_reorder_addrs dup @asulock @ascuheap @aculock @acsmem @acsfd
The @code{gethostbyname2_r} function is like @code{gethostbyname_r}, but
allows the caller to specify the desired address family (e.g.@:
@code{AF_INET} or @code{AF_INET6}) for the result.
@end deftypefun
@comment netdb.h
@comment GNU
@deftypefun int gethostbyaddr_r (const void *@var{addr}, socklen_t @var{length}, int @var{format}, struct hostent *restrict @var{result_buf}, char *restrict @var{buf}, size_t @var{buflen}, struct hostent **restrict @var{result}, int *restrict @var{h_errnop})
@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @asucorrupt{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acucorrupt{} @acsmem{} @acsfd{}}}
@c gethostbyaddr_r @mtsenv @mtslocale @ascudlopen @ascuplugin @asucorrupt @ascuheap @asulock @aculock @acucorrupt @acsmem @acsfd
@c memcmp dup ok
@c nscd_gethostbyaddr_r @mtsenv @ascuheap @asulock @aculock @acsfd @acsmem
@c nscd_gethst_r dup @mtsenv @ascuheap @asulock @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c res_hconf_init dup @mtsenv @mtslocale @asucorrupt @ascuheap @aculock @acucorrupt @acsmem [no @asuinit:reshconf @acuinit:reshconf, conditionally called]
@c nss_hosts_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_gethostbyaddr_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_hconf_reorder_addrs dup @asulock @ascuheap @aculock @acsmem @acsfd
@c res_hconf_trim_domains @mtslocale
@c res_hconf_trim_domain @mtslocale
@c strlen dup ok
@c strcasecmp dup @mtslocale
The @code{gethostbyaddr_r} function returns information about the host
with Internet address @var{addr}. The parameter @var{addr} is not
really a pointer to char - it can be a pointer to an IPv4 or an IPv6
address. The @var{length} argument is the size (in bytes) of the address
at @var{addr}. @var{format} specifies the address format; for an IPv4
Internet address, specify a value of @code{AF_INET}; for an IPv6
Internet address, use @code{AF_INET6}.
Similar to the @code{gethostbyname_r} function, the caller must provide
buffers for the result and memory used internally. In case of success
the function returns zero. Otherwise the value is an error number where
@code{ERANGE} has the special meaning that the caller-provided buffer is
too small.
@end deftypefun
You can also scan the entire hosts database one entry at a time using
@code{sethostent}, @code{gethostent} and @code{endhostent}. Be careful
when using these functions because they are not reentrant.
@comment netdb.h
@comment BSD
@deftypefun void sethostent (int @var{stayopen})
@safety{@prelim{}@mtunsafe{@mtasurace{:hostent} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c sethostent @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_setent(nss_hosts_lookup2) @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c set_h_errno dup ok
@c setup(nss_hosts_lookup2) @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *lookup_fct = nss_hosts_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:hostent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock dup @aculock
This function opens the hosts database to begin scanning it. You can
then call @code{gethostent} to read the entries.
@c There was a rumor that this flag has different meaning if using the DNS,
@c but it appears this description is accurate in that case also.
If the @var{stayopen} argument is nonzero, this sets a flag so that
subsequent calls to @code{gethostbyname} or @code{gethostbyaddr} will
not close the database (as they usually would). This makes for more
efficiency if you call those functions several times, by avoiding
reopening the database for each call.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct hostent *} gethostent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:hostent} @mtasurace{:hostentbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c gethostent @mtasurace:hostent @mtasurace:hostentbuf @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent(gethostent_r) @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c *func = gethostent_r dup @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c gethostent_r @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent_r(nss_hosts_lookup2) @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c setup(nss_hosts_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:hostent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *sfct.f @mtasurace:hostent @ascuplugin
@c libc_lock_unlock dup @aculock
This function returns the next entry in the hosts database. It
returns a null pointer if there are no more entries.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun void endhostent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:hostent} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endhostent @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_endent(nss_hosts_lookup2) @mtasurace:hostent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c setup(nss_passwd_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:hostent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function closes the hosts database.
@end deftypefun
@node Ports
@subsection Internet Ports
@cindex port number
A socket address in the Internet namespace consists of a machine's
Internet address plus a @dfn{port number} which distinguishes the
sockets on a given machine (for a given protocol). Port numbers range
from 0 to 65,535.
Port numbers less than @code{IPPORT_RESERVED} are reserved for standard
servers, such as @code{finger} and @code{telnet}. There is a database
that keeps track of these, and you can use the @code{getservbyname}
function to map a service name onto a port number; see @ref{Services
Database}.
If you write a server that is not one of the standard ones defined in
the database, you must choose a port number for it. Use a number
greater than @code{IPPORT_USERRESERVED}; such numbers are reserved for
servers and won't ever be generated automatically by the system.
Avoiding conflicts with servers being run by other users is up to you.
When you use a socket without specifying its address, the system
generates a port number for it. This number is between
@code{IPPORT_RESERVED} and @code{IPPORT_USERRESERVED}.
On the Internet, it is actually legitimate to have two different
sockets with the same port number, as long as they never both try to
communicate with the same socket address (host address plus port
number). You shouldn't duplicate a port number except in special
circumstances where a higher-level protocol requires it. Normally,
the system won't let you do it; @code{bind} normally insists on
distinct port numbers. To reuse a port number, you must set the
socket option @code{SO_REUSEADDR}. @xref{Socket-Level Options}.
@pindex netinet/in.h
These macros are defined in the header file @file{netinet/in.h}.
@comment netinet/in.h
@comment BSD
@deftypevr Macro int IPPORT_RESERVED
Port numbers less than @code{IPPORT_RESERVED} are reserved for
superuser use.
@end deftypevr
@comment netinet/in.h
@comment BSD
@deftypevr Macro int IPPORT_USERRESERVED
Port numbers greater than or equal to @code{IPPORT_USERRESERVED} are
reserved for explicit use; they will never be allocated automatically.
@end deftypevr
@node Services Database
@subsection The Services Database
@cindex services database
@cindex converting service name to port number
@cindex converting port number to service name
@pindex /etc/services
The database that keeps track of ``well-known'' services is usually
either the file @file{/etc/services} or an equivalent from a name server.
You can use these utilities, declared in @file{netdb.h}, to access
the services database.
@pindex netdb.h
@comment netdb.h
@comment BSD
@deftp {Data Type} {struct servent}
This data type holds information about entries from the services database.
It has the following members:
@table @code
@item char *s_name
This is the ``official'' name of the service.
@item char **s_aliases
These are alternate names for the service, represented as an array of
strings. A null pointer terminates the array.
@item int s_port
This is the port number for the service. Port numbers are given in
network byte order; see @ref{Byte Order}.
@item char *s_proto
This is the name of the protocol to use with this service.
@xref{Protocols Database}.
@end table
@end deftp
To get information about a particular service, use the
@code{getservbyname} or @code{getservbyport} functions. The information
is returned in a statically-allocated structure; you must copy the
information if you need to save it across calls.
@comment netdb.h
@comment BSD
@deftypefun {struct servent *} getservbyname (const char *@var{name}, const char *@var{proto})
@safety{@prelim{}@mtunsafe{@mtasurace{:servbyname} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getservbyname =~ getpwuid @mtasurace:servbyname @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getservbyname_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getservbyname_r =~ getpwuid_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getservbyname_r @ascuheap @acsfd @acsmem
@c nscd_getserv_r @ascuheap @acsfd @acsmem
@c nscd_get_map_ref dup @ascuheap @acsfd @acsmem
@c strlen dup ok
@c malloc dup @ascuheap @acsmem
@c mempcpy dup ok
@c memcpy dup ok
@c nscd_cache_search dup ok
@c nscd_open_socket dup @acsfd
@c readvall dup ok
@c readall dup ok
@c close_not_cancel_no_status dup @acsfd
@c nscd_drop_map_ref dup @ascuheap @acsmem
@c nscd_unmap dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c nss_services_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getservbyname_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getservbyname} function returns information about the
service named @var{name} using protocol @var{proto}. If it can't find
such a service, it returns a null pointer.
This function is useful for servers as well as for clients; servers
use it to determine which port they should listen on (@pxref{Listening}).
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct servent *} getservbyport (int @var{port}, const char *@var{proto})
@safety{@prelim{}@mtunsafe{@mtasurace{:servbyport} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getservbyport =~ getservbyname @mtasurace:servbyport @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getservbyport_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getservbyport_r =~ getservbyname_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nscd_getservbyport_r @ascuheap @acsfd @acsmem
@c nscd_getserv_r dup @ascuheap @acsfd @acsmem
@c nss_services_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getservbyport_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getservbyport} function returns information about the
service at port @var{port} using protocol @var{proto}. If it can't
find such a service, it returns a null pointer.
@end deftypefun
@noindent
You can also scan the services database using @code{setservent},
@code{getservent} and @code{endservent}. Be careful when using these
functions because they are not reentrant.
@comment netdb.h
@comment BSD
@deftypefun void setservent (int @var{stayopen})
@safety{@prelim{}@mtunsafe{@mtasurace{:servent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setservent @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_setent(nss_services_lookup2) @mtasurace:servenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_services_lookup2) @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *lookup_fct = nss_services_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:servent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock dup @aculock
This function opens the services database to begin scanning it.
If the @var{stayopen} argument is nonzero, this sets a flag so that
subsequent calls to @code{getservbyname} or @code{getservbyport} will
not close the database (as they usually would). This makes for more
efficiency if you call those functions several times, by avoiding
reopening the database for each call.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct servent *} getservent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:servent} @mtasurace{:serventbuf} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getservent @mtasurace:servent @mtasurace:serventbuf @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent(getservent_r) @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c *func = getservent_r dup @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getservent_r @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent_r(nss_services_lookup2) @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_services_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:servent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *sfct.f @mtasurace:servent @ascuplugin
@c libc_lock_unlock dup @aculock
This function returns the next entry in the services database. If
there are no more entries, it returns a null pointer.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun void endservent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:servent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endservent @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_endent(nss_services_lookup2) @mtasurace:servent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_services_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:servent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function closes the services database.
@end deftypefun
@node Byte Order
@subsection Byte Order Conversion
@cindex byte order conversion, for socket
@cindex converting byte order
@cindex big-endian
@cindex little-endian
Different kinds of computers use different conventions for the
ordering of bytes within a word. Some computers put the most
significant byte within a word first (this is called ``big-endian''
order), and others put it last (``little-endian'' order).
@cindex network byte order
So that machines with different byte order conventions can
communicate, the Internet protocols specify a canonical byte order
convention for data transmitted over the network. This is known
as @dfn{network byte order}.
When establishing an Internet socket connection, you must make sure that
the data in the @code{sin_port} and @code{sin_addr} members of the
@code{sockaddr_in} structure are represented in network byte order.
If you are encoding integer data in the messages sent through the
socket, you should convert this to network byte order too. If you don't
do this, your program may fail when running on or talking to other kinds
of machines.
If you use @code{getservbyname} and @code{gethostbyname} or
@code{inet_addr} to get the port number and host address, the values are
already in network byte order, and you can copy them directly into
the @code{sockaddr_in} structure.
Otherwise, you have to convert the values explicitly. Use @code{htons}
and @code{ntohs} to convert values for the @code{sin_port} member. Use
@code{htonl} and @code{ntohl} to convert IPv4 addresses for the
@code{sin_addr} member. (Remember, @code{struct in_addr} is equivalent
to @code{uint32_t}.) These functions are declared in
@file{netinet/in.h}.
@pindex netinet/in.h
@comment netinet/in.h
@comment BSD
@deftypefun {uint16_t} htons (uint16_t @var{hostshort})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c htons ok
@c bswap_16 ok
@c bswap_constant_16 ok
This function converts the @code{uint16_t} integer @var{hostshort} from
host byte order to network byte order.
@end deftypefun
@comment netinet/in.h
@comment BSD
@deftypefun {uint16_t} ntohs (uint16_t @var{netshort})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Alias to htons.
This function converts the @code{uint16_t} integer @var{netshort} from
network byte order to host byte order.
@end deftypefun
@comment netinet/in.h
@comment BSD
@deftypefun {uint32_t} htonl (uint32_t @var{hostlong})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c htonl ok
@c bswap_32 dup ok
This function converts the @code{uint32_t} integer @var{hostlong} from
host byte order to network byte order.
This is used for IPv4 Internet addresses.
@end deftypefun
@comment netinet/in.h
@comment BSD
@deftypefun {uint32_t} ntohl (uint32_t @var{netlong})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Alias to htonl.
This function converts the @code{uint32_t} integer @var{netlong} from
network byte order to host byte order.
This is used for IPv4 Internet addresses.
@end deftypefun
@node Protocols Database
@subsection Protocols Database
@cindex protocols database
The communications protocol used with a socket controls low-level
details of how data are exchanged. For example, the protocol implements
things like checksums to detect errors in transmissions, and routing
instructions for messages. Normal user programs have little reason to
mess with these details directly.
@cindex TCP (Internet protocol)
The default communications protocol for the Internet namespace depends on
the communication style. For stream communication, the default is TCP
(``transmission control protocol''). For datagram communication, the
default is UDP (``user datagram protocol''). For reliable datagram
communication, the default is RDP (``reliable datagram protocol'').
You should nearly always use the default.
@pindex /etc/protocols
Internet protocols are generally specified by a name instead of a
number. The network protocols that a host knows about are stored in a
database. This is usually either derived from the file
@file{/etc/protocols}, or it may be an equivalent provided by a name
server. You look up the protocol number associated with a named
protocol in the database using the @code{getprotobyname} function.
Here are detailed descriptions of the utilities for accessing the
protocols database. These are declared in @file{netdb.h}.
@pindex netdb.h
@comment netdb.h
@comment BSD
@deftp {Data Type} {struct protoent}
This data type is used to represent entries in the network protocols
database. It has the following members:
@table @code
@item char *p_name
This is the official name of the protocol.
@item char **p_aliases
These are alternate names for the protocol, specified as an array of
strings. The last element of the array is a null pointer.
@item int p_proto
This is the protocol number (in host byte order); use this member as the
@var{protocol} argument to @code{socket}.
@end table
@end deftp
You can use @code{getprotobyname} and @code{getprotobynumber} to search
the protocols database for a specific protocol. The information is
returned in a statically-allocated structure; you must copy the
information if you need to save it across calls.
@comment netdb.h
@comment BSD
@deftypefun {struct protoent *} getprotobyname (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:protobyname} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getprotobyname =~ getpwuid @mtasurace:protobyname @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getprotobyname_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getprotobyname_r =~ getpwuid_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c no nscd support
@c nss_protocols_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getprotobyname_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getprotobyname} function returns information about the
network protocol named @var{name}. If there is no such protocol, it
returns a null pointer.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct protoent *} getprotobynumber (int @var{protocol})
@safety{@prelim{}@mtunsafe{@mtasurace{:protobynumber} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getprotobynumber =~ getpwuid @mtasurace:protobynumber @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getprotobynumber_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getprotobynumber_r =~ getpwuid_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c no nscd support
@c nss_protocols_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getprotobynumber_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getprotobynumber} function returns information about the
network protocol with number @var{protocol}. If there is no such
protocol, it returns a null pointer.
@end deftypefun
You can also scan the whole protocols database one protocol at a time by
using @code{setprotoent}, @code{getprotoent} and @code{endprotoent}.
Be careful when using these functions because they are not reentrant.
@comment netdb.h
@comment BSD
@deftypefun void setprotoent (int @var{stayopen})
@safety{@prelim{}@mtunsafe{@mtasurace{:protoent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setprotoent @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_setent(nss_protocols_lookup2) @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_protocols_lookup2) @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *lookup_fct = nss_protocols_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:protoent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock dup @aculock
This function opens the protocols database to begin scanning it.
If the @var{stayopen} argument is nonzero, this sets a flag so that
subsequent calls to @code{getprotobyname} or @code{getprotobynumber} will
not close the database (as they usually would). This makes for more
efficiency if you call those functions several times, by avoiding
reopening the database for each call.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct protoent *} getprotoent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:protoent} @mtasurace{:protoentbuf} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getprotoent @mtasurace:protoent @mtasurace:protoentbuf @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent(getprotoent_r) @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c *func = getprotoent_r dup @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getprotoent_r @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent_r(nss_protocols_lookup2) @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_protocols_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:servent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *sfct.f @mtasurace:protoent @ascuplugin
@c libc_lock_unlock dup @aculock
This function returns the next entry in the protocols database. It
returns a null pointer if there are no more entries.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun void endprotoent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:protoent} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endprotoent @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_endent(nss_protocols_lookup2) @mtasurace:protoent @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c setup(nss_protocols_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:protoent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function closes the protocols database.
@end deftypefun
@node Inet Example
@subsection Internet Socket Example
Here is an example showing how to create and name a socket in the
Internet namespace. The newly created socket exists on the machine that
the program is running on. Rather than finding and using the machine's
Internet address, this example specifies @code{INADDR_ANY} as the host
address; the system replaces that with the machine's actual address.
@smallexample
@include mkisock.c.texi
@end smallexample
Here is another example, showing how you can fill in a @code{sockaddr_in}
structure, given a host name string and a port number:
@smallexample
@include isockad.c.texi
@end smallexample
@node Misc Namespaces
@section Other Namespaces
@vindex PF_NS
@vindex PF_ISO
@vindex PF_CCITT
@vindex PF_IMPLINK
@vindex PF_ROUTE
Certain other namespaces and associated protocol families are supported
but not documented yet because they are not often used. @code{PF_NS}
refers to the Xerox Network Software protocols. @code{PF_ISO} stands
for Open Systems Interconnect. @code{PF_CCITT} refers to protocols from
CCITT. @file{socket.h} defines these symbols and others naming protocols
not actually implemented.
@code{PF_IMPLINK} is used for communicating between hosts and Internet
Message Processors. For information on this and @code{PF_ROUTE}, an
occasionally-used local area routing protocol, see the GNU Hurd Manual
(to appear in the future).
@node Open/Close Sockets
@section Opening and Closing Sockets
This section describes the actual library functions for opening and
closing sockets. The same functions work for all namespaces and
connection styles.
@menu
* Creating a Socket:: How to open a socket.
* Closing a Socket:: How to close a socket.
* Socket Pairs:: These are created like pipes.
@end menu
@node Creating a Socket
@subsection Creating a Socket
@cindex creating a socket
@cindex socket, creating
@cindex opening a socket
The primitive for creating a socket is the @code{socket} function,
declared in @file{sys/socket.h}.
@pindex sys/socket.h
@comment sys/socket.h
@comment BSD
@deftypefun int socket (int @var{namespace}, int @var{style}, int @var{protocol})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function creates a socket and specifies communication style
@var{style}, which should be one of the socket styles listed in
@ref{Communication Styles}. The @var{namespace} argument specifies
the namespace; it must be @code{PF_LOCAL} (@pxref{Local Namespace}) or
@code{PF_INET} (@pxref{Internet Namespace}). @var{protocol}
designates the specific protocol (@pxref{Socket Concepts}); zero is
usually right for @var{protocol}.
The return value from @code{socket} is the file descriptor for the new
socket, or @code{-1} in case of error. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EPROTONOSUPPORT
The @var{protocol} or @var{style} is not supported by the
@var{namespace} specified.
@item EMFILE
The process already has too many file descriptors open.
@item ENFILE
The system already has too many file descriptors open.
@item EACCES
The process does not have the privilege to create a socket of the specified
@var{style} or @var{protocol}.
@item ENOBUFS
The system ran out of internal buffer space.
@end table
The file descriptor returned by the @code{socket} function supports both
read and write operations. However, like pipes, sockets do not support file
positioning operations.
@end deftypefun
For examples of how to call the @code{socket} function,
see @ref{Local Socket Example}, or @ref{Inet Example}.
@node Closing a Socket
@subsection Closing a Socket
@cindex socket, closing
@cindex closing a socket
@cindex shutting down a socket
@cindex socket shutdown
When you have finished using a socket, you can simply close its
file descriptor with @code{close}; see @ref{Opening and Closing Files}.
If there is still data waiting to be transmitted over the connection,
normally @code{close} tries to complete this transmission. You
can control this behavior using the @code{SO_LINGER} socket option to
specify a timeout period; see @ref{Socket Options}.
@pindex sys/socket.h
You can also shut down only reception or transmission on a
connection by calling @code{shutdown}, which is declared in
@file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypefun int shutdown (int @var{socket}, int @var{how})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{shutdown} function shuts down the connection of socket
@var{socket}. The argument @var{how} specifies what action to
perform:
@table @code
@item 0
Stop receiving data for this socket. If further data arrives,
reject it.
@item 1
Stop trying to transmit data from this socket. Discard any data
waiting to be sent. Stop looking for acknowledgement of data already
sent; don't retransmit it if it is lost.
@item 2
Stop both reception and transmission.
@end table
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
@var{socket} is not a valid file descriptor.
@item ENOTSOCK
@var{socket} is not a socket.
@item ENOTCONN
@var{socket} is not connected.
@end table
@end deftypefun
@node Socket Pairs
@subsection Socket Pairs
@cindex creating a socket pair
@cindex socket pair
@cindex opening a socket pair
@pindex sys/socket.h
A @dfn{socket pair} consists of a pair of connected (but unnamed)
sockets. It is very similar to a pipe and is used in much the same
way. Socket pairs are created with the @code{socketpair} function,
declared in @file{sys/socket.h}. A socket pair is much like a pipe; the
main difference is that the socket pair is bidirectional, whereas the
pipe has one input-only end and one output-only end (@pxref{Pipes and
FIFOs}).
@comment sys/socket.h
@comment BSD
@deftypefun int socketpair (int @var{namespace}, int @var{style}, int @var{protocol}, int @var{filedes}@t{[2]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function creates a socket pair, returning the file descriptors in
@code{@var{filedes}[0]} and @code{@var{filedes}[1]}. The socket pair
is a full-duplex communications channel, so that both reading and writing
may be performed at either end.
The @var{namespace}, @var{style} and @var{protocol} arguments are
interpreted as for the @code{socket} function. @var{style} should be
one of the communication styles listed in @ref{Communication Styles}.
The @var{namespace} argument specifies the namespace, which must be
@code{AF_LOCAL} (@pxref{Local Namespace}); @var{protocol} specifies the
communications protocol, but zero is the only meaningful value.
If @var{style} specifies a connectionless communication style, then
the two sockets you get are not @emph{connected}, strictly speaking,
but each of them knows the other as the default destination address,
so they can send packets to each other.
The @code{socketpair} function returns @code{0} on success and @code{-1}
on failure. The following @code{errno} error conditions are defined
for this function:
@table @code
@item EMFILE
The process has too many file descriptors open.
@item EAFNOSUPPORT
The specified namespace is not supported.
@item EPROTONOSUPPORT
The specified protocol is not supported.
@item EOPNOTSUPP
The specified protocol does not support the creation of socket pairs.
@end table
@end deftypefun
@node Connections
@section Using Sockets with Connections
@cindex connection
@cindex client
@cindex server
The most common communication styles involve making a connection to a
particular other socket, and then exchanging data with that socket
over and over. Making a connection is asymmetric; one side (the
@dfn{client}) acts to request a connection, while the other side (the
@dfn{server}) makes a socket and waits for the connection request.
@iftex
@itemize @bullet
@item
@ref{Connecting}, describes what the client program must do to
initiate a connection with a server.
@item
@ref{Listening} and @ref{Accepting Connections} describe what the
server program must do to wait for and act upon connection requests
from clients.
@item
@ref{Transferring Data}, describes how data are transferred through the
connected socket.
@end itemize
@end iftex
@menu
* Connecting:: What the client program must do.
* Listening:: How a server program waits for requests.
* Accepting Connections:: What the server does when it gets a request.
* Who is Connected:: Getting the address of the
other side of a connection.
* Transferring Data:: How to send and receive data.
* Byte Stream Example:: An example program: a client for communicating
over a byte stream socket in the Internet namespace.
* Server Example:: A corresponding server program.
* Out-of-Band Data:: This is an advanced feature.
@end menu
@node Connecting
@subsection Making a Connection
@cindex connecting a socket
@cindex socket, connecting
@cindex socket, initiating a connection
@cindex socket, client actions
In making a connection, the client makes a connection while the server
waits for and accepts the connection. Here we discuss what the client
program must do with the @code{connect} function, which is declared in
@file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypefun int connect (int @var{socket}, struct sockaddr *@var{addr}, socklen_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{connect} function initiates a connection from the socket
with file descriptor @var{socket} to the socket whose address is
specified by the @var{addr} and @var{length} arguments. (This socket
is typically on another machine, and it must be already set up as a
server.) @xref{Socket Addresses}, for information about how these
arguments are interpreted.
Normally, @code{connect} waits until the server responds to the request
before it returns. You can set nonblocking mode on the socket
@var{socket} to make @code{connect} return immediately without waiting
for the response. @xref{File Status Flags}, for information about
nonblocking mode.
@c !!! how do you tell when it has finished connecting? I suspect the
@c way you do it is select for writing.
The normal return value from @code{connect} is @code{0}. If an error
occurs, @code{connect} returns @code{-1}. The following @code{errno}
error conditions are defined for this function:
@table @code
@item EBADF
The socket @var{socket} is not a valid file descriptor.
@item ENOTSOCK
File descriptor @var{socket} is not a socket.
@item EADDRNOTAVAIL
The specified address is not available on the remote machine.
@item EAFNOSUPPORT
The namespace of the @var{addr} is not supported by this socket.
@item EISCONN
The socket @var{socket} is already connected.
@item ETIMEDOUT
The attempt to establish the connection timed out.
@item ECONNREFUSED
The server has actively refused to establish the connection.
@item ENETUNREACH
The network of the given @var{addr} isn't reachable from this host.
@item EADDRINUSE
The socket address of the given @var{addr} is already in use.
@item EINPROGRESS
The socket @var{socket} is non-blocking and the connection could not be
established immediately. You can determine when the connection is
completely established with @code{select}; @pxref{Waiting for I/O}.
Another @code{connect} call on the same socket, before the connection is
completely established, will fail with @code{EALREADY}.
@item EALREADY
The socket @var{socket} is non-blocking and already has a pending
connection in progress (see @code{EINPROGRESS} above).
@end table
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@node Listening
@subsection Listening for Connections
@cindex listening (sockets)
@cindex sockets, server actions
@cindex sockets, listening
Now let us consider what the server process must do to accept
connections on a socket. First it must use the @code{listen} function
to enable connection requests on the socket, and then accept each
incoming connection with a call to @code{accept} (@pxref{Accepting
Connections}). Once connection requests are enabled on a server socket,
the @code{select} function reports when the socket has a connection
ready to be accepted (@pxref{Waiting for I/O}).
The @code{listen} function is not allowed for sockets using
connectionless communication styles.
You can write a network server that does not even start running until a
connection to it is requested. @xref{Inetd Servers}.
In the Internet namespace, there are no special protection mechanisms
for controlling access to a port; any process on any machine
can make a connection to your server. If you want to restrict access to
your server, make it examine the addresses associated with connection
requests or implement some other handshaking or identification
protocol.
In the local namespace, the ordinary file protection bits control who has
access to connect to the socket.
@comment sys/socket.h
@comment BSD
@deftypefun int listen (int @var{socket}, int @var{n})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
The @code{listen} function enables the socket @var{socket} to accept
connections, thus making it a server socket.
The argument @var{n} specifies the length of the queue for pending
connections. When the queue fills, new clients attempting to connect
fail with @code{ECONNREFUSED} until the server calls @code{accept} to
accept a connection from the queue.
The @code{listen} function returns @code{0} on success and @code{-1}
on failure. The following @code{errno} error conditions are defined
for this function:
@table @code
@item EBADF
The argument @var{socket} is not a valid file descriptor.
@item ENOTSOCK
The argument @var{socket} is not a socket.
@item EOPNOTSUPP
The socket @var{socket} does not support this operation.
@end table
@end deftypefun
@node Accepting Connections
@subsection Accepting Connections
@cindex sockets, accepting connections
@cindex accepting connections
When a server receives a connection request, it can complete the
connection by accepting the request. Use the function @code{accept}
to do this.
A socket that has been established as a server can accept connection
requests from multiple clients. The server's original socket
@emph{does not become part of the connection}; instead, @code{accept}
makes a new socket which participates in the connection.
@code{accept} returns the descriptor for this socket. The server's
original socket remains available for listening for further connection
requests.
The number of pending connection requests on a server socket is finite.
If connection requests arrive from clients faster than the server can
act upon them, the queue can fill up and additional requests are refused
with an @code{ECONNREFUSED} error. You can specify the maximum length of
this queue as an argument to the @code{listen} function, although the
system may also impose its own internal limit on the length of this
queue.
@comment sys/socket.h
@comment BSD
@deftypefun int accept (int @var{socket}, struct sockaddr *@var{addr}, socklen_t *@var{length_ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
This function is used to accept a connection request on the server
socket @var{socket}.
The @code{accept} function waits if there are no connections pending,
unless the socket @var{socket} has nonblocking mode set. (You can use
@code{select} to wait for a pending connection, with a nonblocking
socket.) @xref{File Status Flags}, for information about nonblocking
mode.
The @var{addr} and @var{length-ptr} arguments are used to return
information about the name of the client socket that initiated the
connection. @xref{Socket Addresses}, for information about the format
of the information.
Accepting a connection does not make @var{socket} part of the
connection. Instead, it creates a new socket which becomes
connected. The normal return value of @code{accept} is the file
descriptor for the new socket.
After @code{accept}, the original socket @var{socket} remains open and
unconnected, and continues listening until you close it. You can
accept further connections with @var{socket} by calling @code{accept}
again.
If an error occurs, @code{accept} returns @code{-1}. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} argument is not a socket.
@item EOPNOTSUPP
The descriptor @var{socket} does not support this operation.
@item EWOULDBLOCK
@var{socket} has nonblocking mode set, and there are no pending
connections immediately available.
@end table
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
The @code{accept} function is not allowed for sockets using
connectionless communication styles.
@node Who is Connected
@subsection Who is Connected to Me?
@comment sys/socket.h
@comment BSD
@deftypefun int getpeername (int @var{socket}, struct sockaddr *@var{addr}, socklen_t *@var{length-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getpeername} function returns the address of the socket that
@var{socket} is connected to; it stores the address in the memory space
specified by @var{addr} and @var{length-ptr}. It stores the length of
the address in @code{*@var{length-ptr}}.
@xref{Socket Addresses}, for information about the format of the
address. In some operating systems, @code{getpeername} works only for
sockets in the Internet domain.
The return value is @code{0} on success and @code{-1} on error. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The argument @var{socket} is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item ENOTCONN
The socket @var{socket} is not connected.
@item ENOBUFS
There are not enough internal buffers available.
@end table
@end deftypefun
@node Transferring Data
@subsection Transferring Data
@cindex reading from a socket
@cindex writing to a socket
Once a socket has been connected to a peer, you can use the ordinary
@code{read} and @code{write} operations (@pxref{I/O Primitives}) to
transfer data. A socket is a two-way communications channel, so read
and write operations can be performed at either end.
There are also some I/O modes that are specific to socket operations.
In order to specify these modes, you must use the @code{recv} and
@code{send} functions instead of the more generic @code{read} and
@code{write} functions. The @code{recv} and @code{send} functions take
an additional argument which you can use to specify various flags to
control special I/O modes. For example, you can specify the
@code{MSG_OOB} flag to read or write out-of-band data, the
@code{MSG_PEEK} flag to peek at input, or the @code{MSG_DONTROUTE} flag
to control inclusion of routing information on output.
@menu
* Sending Data:: Sending data with @code{send}.
* Receiving Data:: Reading data with @code{recv}.
* Socket Data Options:: Using @code{send} and @code{recv}.
@end menu
@node Sending Data
@subsubsection Sending Data
@pindex sys/socket.h
The @code{send} function is declared in the header file
@file{sys/socket.h}. If your @var{flags} argument is zero, you can just
as well use @code{write} instead of @code{send}; see @ref{I/O
Primitives}. If the socket was connected but the connection has broken,
you get a @code{SIGPIPE} signal for any use of @code{send} or
@code{write} (@pxref{Miscellaneous Signals}).
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t send (int @var{socket}, const void *@var{buffer}, size_t @var{size}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{send} function is like @code{write}, but with the additional
flags @var{flags}. The possible values of @var{flags} are described
in @ref{Socket Data Options}.
This function returns the number of bytes transmitted, or @code{-1} on
failure. If the socket is nonblocking, then @code{send} (like
@code{write}) can return after sending just part of the data.
@xref{File Status Flags}, for information about nonblocking mode.
Note, however, that a successful return value merely indicates that
the message has been sent without error, not necessarily that it has
been received without error.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item EINTR
The operation was interrupted by a signal before any data was sent.
@xref{Interrupted Primitives}.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item EMSGSIZE
The socket type requires that the message be sent atomically, but the
message is too large for this to be possible.
@item EWOULDBLOCK
Nonblocking mode has been set on the socket, and the write operation
would block. (Normally @code{send} blocks until the operation can be
completed.)
@item ENOBUFS
There is not enough internal buffer space available.
@item ENOTCONN
You never connected this socket.
@item EPIPE
This socket was connected but the connection is now broken. In this
case, @code{send} generates a @code{SIGPIPE} signal first; if that
signal is ignored or blocked, or if its handler returns, then
@code{send} fails with @code{EPIPE}.
@end table
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@node Receiving Data
@subsubsection Receiving Data
@pindex sys/socket.h
The @code{recv} function is declared in the header file
@file{sys/socket.h}. If your @var{flags} argument is zero, you can
just as well use @code{read} instead of @code{recv}; see @ref{I/O
Primitives}.
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t recv (int @var{socket}, void *@var{buffer}, size_t @var{size}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{recv} function is like @code{read}, but with the additional
flags @var{flags}. The possible values of @var{flags} are described
in @ref{Socket Data Options}.
If nonblocking mode is set for @var{socket}, and no data are available to
be read, @code{recv} fails immediately rather than waiting. @xref{File
Status Flags}, for information about nonblocking mode.
This function returns the number of bytes received, or @code{-1} on failure.
The following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item EWOULDBLOCK
Nonblocking mode has been set on the socket, and the read operation
would block. (Normally, @code{recv} blocks until there is input
available to be read.)
@item EINTR
The operation was interrupted by a signal before any data was read.
@xref{Interrupted Primitives}.
@item ENOTCONN
You never connected this socket.
@end table
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@node Socket Data Options
@subsubsection Socket Data Options
@pindex sys/socket.h
The @var{flags} argument to @code{send} and @code{recv} is a bit
mask. You can bitwise-OR the values of the following macros together
to obtain a value for this argument. All are defined in the header
file @file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypevr Macro int MSG_OOB
Send or receive out-of-band data. @xref{Out-of-Band Data}.
@end deftypevr
@comment sys/socket.h
@comment BSD
@deftypevr Macro int MSG_PEEK
Look at the data but don't remove it from the input queue. This is
only meaningful with input functions such as @code{recv}, not with
@code{send}.
@end deftypevr
@comment sys/socket.h
@comment BSD
@deftypevr Macro int MSG_DONTROUTE
Don't include routing information in the message. This is only
meaningful with output operations, and is usually only of interest for
diagnostic or routing programs. We don't try to explain it here.
@end deftypevr
@node Byte Stream Example
@subsection Byte Stream Socket Example
Here is an example client program that makes a connection for a byte
stream socket in the Internet namespace. It doesn't do anything
particularly interesting once it has connected to the server; it just
sends a text string to the server and exits.
This program uses @code{init_sockaddr} to set up the socket address; see
@ref{Inet Example}.
@smallexample
@include inetcli.c.texi
@end smallexample
@node Server Example
@subsection Byte Stream Connection Server Example
The server end is much more complicated. Since we want to allow
multiple clients to be connected to the server at the same time, it
would be incorrect to wait for input from a single client by simply
calling @code{read} or @code{recv}. Instead, the right thing to do is
to use @code{select} (@pxref{Waiting for I/O}) to wait for input on
all of the open sockets. This also allows the server to deal with
additional connection requests.
This particular server doesn't do anything interesting once it has
gotten a message from a client. It does close the socket for that
client when it detects an end-of-file condition (resulting from the
client shutting down its end of the connection).
This program uses @code{make_socket} to set up the socket address; see
@ref{Inet Example}.
@smallexample
@include inetsrv.c.texi
@end smallexample
@node Out-of-Band Data
@subsection Out-of-Band Data
@cindex out-of-band data
@cindex high-priority data
Streams with connections permit @dfn{out-of-band} data that is
delivered with higher priority than ordinary data. Typically the
reason for sending out-of-band data is to send notice of an
exceptional condition. To send out-of-band data use
@code{send}, specifying the flag @code{MSG_OOB} (@pxref{Sending
Data}).
Out-of-band data are received with higher priority because the
receiving process need not read it in sequence; to read the next
available out-of-band data, use @code{recv} with the @code{MSG_OOB}
flag (@pxref{Receiving Data}). Ordinary read operations do not read
out-of-band data; they read only ordinary data.
@cindex urgent socket condition
When a socket finds that out-of-band data are on their way, it sends a
@code{SIGURG} signal to the owner process or process group of the
socket. You can specify the owner using the @code{F_SETOWN} command
to the @code{fcntl} function; see @ref{Interrupt Input}. You must
also establish a handler for this signal, as described in @ref{Signal
Handling}, in order to take appropriate action such as reading the
out-of-band data.
Alternatively, you can test for pending out-of-band data, or wait
until there is out-of-band data, using the @code{select} function; it
can wait for an exceptional condition on the socket. @xref{Waiting
for I/O}, for more information about @code{select}.
Notification of out-of-band data (whether with @code{SIGURG} or with
@code{select}) indicates that out-of-band data are on the way; the data
may not actually arrive until later. If you try to read the
out-of-band data before it arrives, @code{recv} fails with an
@code{EWOULDBLOCK} error.
Sending out-of-band data automatically places a ``mark'' in the stream
of ordinary data, showing where in the sequence the out-of-band data
``would have been''. This is useful when the meaning of out-of-band
data is ``cancel everything sent so far''. Here is how you can test,
in the receiving process, whether any ordinary data was sent before
the mark:
@smallexample
success = ioctl (socket, SIOCATMARK, &atmark);
@end smallexample
The @code{integer} variable @var{atmark} is set to a nonzero value if
the socket's read pointer has reached the ``mark''.
@c Posix 1.g specifies sockatmark for this ioctl. sockatmark is not
@c implemented yet.
Here's a function to discard any ordinary data preceding the
out-of-band mark:
@smallexample
int
discard_until_mark (int socket)
@{
while (1)
@{
/* @r{This is not an arbitrary limit; any size will do.} */
char buffer[1024];
int atmark, success;
/* @r{If we have reached the mark, return.} */
success = ioctl (socket, SIOCATMARK, &atmark);
if (success < 0)
perror ("ioctl");
if (result)
return;
/* @r{Otherwise, read a bunch of ordinary data and discard it.}
@r{This is guaranteed not to read past the mark}
@r{if it starts before the mark.} */
success = read (socket, buffer, sizeof buffer);
if (success < 0)
perror ("read");
@}
@}
@end smallexample
If you don't want to discard the ordinary data preceding the mark, you
may need to read some of it anyway, to make room in internal system
buffers for the out-of-band data. If you try to read out-of-band data
and get an @code{EWOULDBLOCK} error, try reading some ordinary data
(saving it so that you can use it when you want it) and see if that
makes room. Here is an example:
@smallexample
struct buffer
@{
char *buf;
int size;
struct buffer *next;
@};
/* @r{Read the out-of-band data from SOCKET and return it}
@r{as a `struct buffer', which records the address of the data}
@r{and its size.}
@r{It may be necessary to read some ordinary data}
@r{in order to make room for the out-of-band data.}
@r{If so, the ordinary data are saved as a chain of buffers}
@r{found in the `next' field of the value.} */
struct buffer *
read_oob (int socket)
@{
struct buffer *tail = 0;
struct buffer *list = 0;
while (1)
@{
/* @r{This is an arbitrary limit.}
@r{Does anyone know how to do this without a limit?} */
#define BUF_SZ 1024
char *buf = (char *) xmalloc (BUF_SZ);
int success;
int atmark;
/* @r{Try again to read the out-of-band data.} */
success = recv (socket, buf, BUF_SZ, MSG_OOB);
if (success >= 0)
@{
/* @r{We got it, so return it.} */
struct buffer *link
= (struct buffer *) xmalloc (sizeof (struct buffer));
link->buf = buf;
link->size = success;
link->next = list;
return link;
@}
/* @r{If we fail, see if we are at the mark.} */
success = ioctl (socket, SIOCATMARK, &atmark);
if (success < 0)
perror ("ioctl");
if (atmark)
@{
/* @r{At the mark; skipping past more ordinary data cannot help.}
@r{So just wait a while.} */
sleep (1);
continue;
@}
/* @r{Otherwise, read a bunch of ordinary data and save it.}
@r{This is guaranteed not to read past the mark}
@r{if it starts before the mark.} */
success = read (socket, buf, BUF_SZ);
if (success < 0)
perror ("read");
/* @r{Save this data in the buffer list.} */
@{
struct buffer *link
= (struct buffer *) xmalloc (sizeof (struct buffer));
link->buf = buf;
link->size = success;
/* @r{Add the new link to the end of the list.} */
if (tail)
tail->next = link;
else
list = link;
tail = link;
@}
@}
@}
@end smallexample
@node Datagrams
@section Datagram Socket Operations
@cindex datagram socket
This section describes how to use communication styles that don't use
connections (styles @code{SOCK_DGRAM} and @code{SOCK_RDM}). Using
these styles, you group data into packets and each packet is an
independent communication. You specify the destination for each
packet individually.
Datagram packets are like letters: you send each one independently
with its own destination address, and they may arrive in the wrong
order or not at all.
The @code{listen} and @code{accept} functions are not allowed for
sockets using connectionless communication styles.
@menu
* Sending Datagrams:: Sending packets on a datagram socket.
* Receiving Datagrams:: Receiving packets on a datagram socket.
* Datagram Example:: An example program: packets sent over a
datagram socket in the local namespace.
* Example Receiver:: Another program, that receives those packets.
@end menu
@node Sending Datagrams
@subsection Sending Datagrams
@cindex sending a datagram
@cindex transmitting datagrams
@cindex datagrams, transmitting
@pindex sys/socket.h
The normal way of sending data on a datagram socket is by using the
@code{sendto} function, declared in @file{sys/socket.h}.
You can call @code{connect} on a datagram socket, but this only
specifies a default destination for further data transmission on the
socket. When a socket has a default destination you can use
@code{send} (@pxref{Sending Data}) or even @code{write} (@pxref{I/O
Primitives}) to send a packet there. You can cancel the default
destination by calling @code{connect} using an address format of
@code{AF_UNSPEC} in the @var{addr} argument. @xref{Connecting}, for
more information about the @code{connect} function.
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t sendto (int @var{socket}, const void *@var{buffer}, size_t @var{size}, int @var{flags}, struct sockaddr *@var{addr}, socklen_t @var{length})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{sendto} function transmits the data in the @var{buffer}
through the socket @var{socket} to the destination address specified
by the @var{addr} and @var{length} arguments. The @var{size} argument
specifies the number of bytes to be transmitted.
The @var{flags} are interpreted the same way as for @code{send}; see
@ref{Socket Data Options}.
The return value and error conditions are also the same as for
@code{send}, but you cannot rely on the system to detect errors and
report them; the most common error is that the packet is lost or there
is no-one at the specified address to receive it, and the operating
system on your machine usually does not know this.
It is also possible for one call to @code{sendto} to report an error
owing to a problem related to a previous call.
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@node Receiving Datagrams
@subsection Receiving Datagrams
@cindex receiving datagrams
The @code{recvfrom} function reads a packet from a datagram socket and
also tells you where it was sent from. This function is declared in
@file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t recvfrom (int @var{socket}, void *@var{buffer}, size_t @var{size}, int @var{flags}, struct sockaddr *@var{addr}, socklen_t *@var{length-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{recvfrom} function reads one packet from the socket
@var{socket} into the buffer @var{buffer}. The @var{size} argument
specifies the maximum number of bytes to be read.
If the packet is longer than @var{size} bytes, then you get the first
@var{size} bytes of the packet and the rest of the packet is lost.
There's no way to read the rest of the packet. Thus, when you use a
packet protocol, you must always know how long a packet to expect.
The @var{addr} and @var{length-ptr} arguments are used to return the
address where the packet came from. @xref{Socket Addresses}. For a
socket in the local domain the address information won't be meaningful,
since you can't read the address of such a socket (@pxref{Local
Namespace}). You can specify a null pointer as the @var{addr} argument
if you are not interested in this information.
The @var{flags} are interpreted the same way as for @code{recv}
(@pxref{Socket Data Options}). The return value and error conditions
are also the same as for @code{recv}.
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
You can use plain @code{recv} (@pxref{Receiving Data}) instead of
@code{recvfrom} if you don't need to find out who sent the packet
(either because you know where it should come from or because you
treat all possible senders alike). Even @code{read} can be used if
you don't want to specify @var{flags} (@pxref{I/O Primitives}).
@ignore
@c sendmsg and recvmsg are like readv and writev in that they
@c use a series of buffers. It's not clear this is worth
@c supporting or that we support them.
@c !!! they can do more; it is hairy
@comment sys/socket.h
@comment BSD
@deftp {Data Type} {struct msghdr}
@end deftp
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t sendmsg (int @var{socket}, const struct msghdr *@var{message}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is cancel.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@comment sys/socket.h
@comment BSD
@deftypefun ssize_t recvmsg (int @var{socket}, struct msghdr *@var{message}, int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is defined as a cancellation point in multi-threaded
programs, so one has to be prepared for this and make sure that
allocated resources (like memory, files descriptors, semaphores or
whatever) are freed even if the thread is canceled.
@c @xref{pthread_cleanup_push}, for a method how to do this.
@end deftypefun
@end ignore
@node Datagram Example
@subsection Datagram Socket Example
Here is a set of example programs that send messages over a datagram
stream in the local namespace. Both the client and server programs use
the @code{make_named_socket} function that was presented in @ref{Local
Socket Example}, to create and name their sockets.
First, here is the server program. It sits in a loop waiting for
messages to arrive, bouncing each message back to the sender.
Obviously this isn't a particularly useful program, but it does show
the general ideas involved.
@smallexample
@include filesrv.c.texi
@end smallexample
@node Example Receiver
@subsection Example of Reading Datagrams
Here is the client program corresponding to the server above.
It sends a datagram to the server and then waits for a reply. Notice
that the socket for the client (as well as for the server) in this
example has to be given a name. This is so that the server can direct
a message back to the client. Since the socket has no associated
connection state, the only way the server can do this is by
referencing the name of the client.
@smallexample
@include filecli.c.texi
@end smallexample
Keep in mind that datagram socket communications are unreliable. In
this example, the client program waits indefinitely if the message
never reaches the server or if the server's response never comes
back. It's up to the user running the program to kill and restart
it if desired. A more automatic solution could be to use
@code{select} (@pxref{Waiting for I/O}) to establish a timeout period
for the reply, and in case of timeout either re-send the message or
shut down the socket and exit.
@node Inetd
@section The @code{inetd} Daemon
We've explained above how to write a server program that does its own
listening. Such a server must already be running in order for anyone
to connect to it.
Another way to provide a service on an Internet port is to let the daemon
program @code{inetd} do the listening. @code{inetd} is a program that
runs all the time and waits (using @code{select}) for messages on a
specified set of ports. When it receives a message, it accepts the
connection (if the socket style calls for connections) and then forks a
child process to run the corresponding server program. You specify the
ports and their programs in the file @file{/etc/inetd.conf}.
@menu
* Inetd Servers::
* Configuring Inetd::
@end menu
@node Inetd Servers
@subsection @code{inetd} Servers
Writing a server program to be run by @code{inetd} is very simple. Each time
someone requests a connection to the appropriate port, a new server
process starts. The connection already exists at this time; the
socket is available as the standard input descriptor and as the
standard output descriptor (descriptors 0 and 1) in the server
process. Thus the server program can begin reading and writing data
right away. Often the program needs only the ordinary I/O facilities;
in fact, a general-purpose filter program that knows nothing about
sockets can work as a byte stream server run by @code{inetd}.
You can also use @code{inetd} for servers that use connectionless
communication styles. For these servers, @code{inetd} does not try to accept
a connection since no connection is possible. It just starts the
server program, which can read the incoming datagram packet from
descriptor 0. The server program can handle one request and then
exit, or you can choose to write it to keep reading more requests
until no more arrive, and then exit. You must specify which of these
two techniques the server uses when you configure @code{inetd}.
@node Configuring Inetd
@subsection Configuring @code{inetd}
The file @file{/etc/inetd.conf} tells @code{inetd} which ports to listen to
and what server programs to run for them. Normally each entry in the
file is one line, but you can split it onto multiple lines provided
all but the first line of the entry start with whitespace. Lines that
start with @samp{#} are comments.
Here are two standard entries in @file{/etc/inetd.conf}:
@smallexample
ftp stream tcp nowait root /libexec/ftpd ftpd
talk dgram udp wait root /libexec/talkd talkd
@end smallexample
An entry has this format:
@smallexample
@var{service} @var{style} @var{protocol} @var{wait} @var{username} @var{program} @var{arguments}
@end smallexample
The @var{service} field says which service this program provides. It
should be the name of a service defined in @file{/etc/services}.
@code{inetd} uses @var{service} to decide which port to listen on for
this entry.
The fields @var{style} and @var{protocol} specify the communication
style and the protocol to use for the listening socket. The style
should be the name of a communication style, converted to lower case
and with @samp{SOCK_} deleted---for example, @samp{stream} or
@samp{dgram}. @var{protocol} should be one of the protocols listed in
@file{/etc/protocols}. The typical protocol names are @samp{tcp} for
byte stream connections and @samp{udp} for unreliable datagrams.
The @var{wait} field should be either @samp{wait} or @samp{nowait}.
Use @samp{wait} if @var{style} is a connectionless style and the
server, once started, handles multiple requests as they come in.
Use @samp{nowait} if @code{inetd} should start a new process for each message
or request that comes in. If @var{style} uses connections, then
@var{wait} @strong{must} be @samp{nowait}.
@var{user} is the user name that the server should run as. @code{inetd} runs
as root, so it can set the user ID of its children arbitrarily. It's
best to avoid using @samp{root} for @var{user} if you can; but some
servers, such as Telnet and FTP, read a username and password
themselves. These servers need to be root initially so they can log
in as commanded by the data coming over the network.
@var{program} together with @var{arguments} specifies the command to
run to start the server. @var{program} should be an absolute file
name specifying the executable file to run. @var{arguments} consists
of any number of whitespace-separated words, which become the
command-line arguments of @var{program}. The first word in
@var{arguments} is argument zero, which should by convention be the
program name itself (sans directories).
If you edit @file{/etc/inetd.conf}, you can tell @code{inetd} to reread the
file and obey its new contents by sending the @code{inetd} process the
@code{SIGHUP} signal. You'll have to use @code{ps} to determine the
process ID of the @code{inetd} process as it is not fixed.
@c !!! could document /etc/inetd.sec
@node Socket Options
@section Socket Options
@cindex socket options
This section describes how to read or set various options that modify
the behavior of sockets and their underlying communications protocols.
@cindex level, for socket options
@cindex socket option level
When you are manipulating a socket option, you must specify which
@dfn{level} the option pertains to. This describes whether the option
applies to the socket interface, or to a lower-level communications
protocol interface.
@menu
* Socket Option Functions:: The basic functions for setting and getting
socket options.
* Socket-Level Options:: Details of the options at the socket level.
@end menu
@node Socket Option Functions
@subsection Socket Option Functions
@pindex sys/socket.h
Here are the functions for examining and modifying socket options.
They are declared in @file{sys/socket.h}.
@comment sys/socket.h
@comment BSD
@deftypefun int getsockopt (int @var{socket}, int @var{level}, int @var{optname}, void *@var{optval}, socklen_t *@var{optlen-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getsockopt} function gets information about the value of
option @var{optname} at level @var{level} for socket @var{socket}.
The option value is stored in a buffer that @var{optval} points to.
Before the call, you should supply in @code{*@var{optlen-ptr}} the
size of this buffer; on return, it contains the number of bytes of
information actually stored in the buffer.
Most options interpret the @var{optval} buffer as a single @code{int}
value.
The actual return value of @code{getsockopt} is @code{0} on success
and @code{-1} on failure. The following @code{errno} error conditions
are defined:
@table @code
@item EBADF
The @var{socket} argument is not a valid file descriptor.
@item ENOTSOCK
The descriptor @var{socket} is not a socket.
@item ENOPROTOOPT
The @var{optname} doesn't make sense for the given @var{level}.
@end table
@end deftypefun
@comment sys/socket.h
@comment BSD
@deftypefun int setsockopt (int @var{socket}, int @var{level}, int @var{optname}, const void *@var{optval}, socklen_t @var{optlen})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is used to set the socket option @var{optname} at level
@var{level} for socket @var{socket}. The value of the option is passed
in the buffer @var{optval} of size @var{optlen}.
@c Argh. -zw
@iftex
@hfuzz 6pt
The return value and error codes for @code{setsockopt} are the same as
for @code{getsockopt}.
@end iftex
@ifinfo
The return value and error codes for @code{setsockopt} are the same as
for @code{getsockopt}.
@end ifinfo
@end deftypefun
@node Socket-Level Options
@subsection Socket-Level Options
@comment sys/socket.h
@comment BSD
@deftypevr Constant int SOL_SOCKET
Use this constant as the @var{level} argument to @code{getsockopt} or
@code{setsockopt} to manipulate the socket-level options described in
this section.
@end deftypevr
@pindex sys/socket.h
@noindent
Here is a table of socket-level option names; all are defined in the
header file @file{sys/socket.h}.
@table @code
@comment sys/socket.h
@comment BSD
@item SO_DEBUG
@c Extra blank line here makes the table look better.
This option toggles recording of debugging information in the underlying
protocol modules. The value has type @code{int}; a nonzero value means
``yes''.
@c !!! should say how this is used
@c OK, anyone who knows, please explain.
@comment sys/socket.h
@comment BSD
@item SO_REUSEADDR
This option controls whether @code{bind} (@pxref{Setting Address})
should permit reuse of local addresses for this socket. If you enable
this option, you can actually have two sockets with the same Internet
port number; but the system won't allow you to use the two
identically-named sockets in a way that would confuse the Internet. The
reason for this option is that some higher-level Internet protocols,
including FTP, require you to keep reusing the same port number.
The value has type @code{int}; a nonzero value means ``yes''.
@comment sys/socket.h
@comment BSD
@item SO_KEEPALIVE
This option controls whether the underlying protocol should
periodically transmit messages on a connected socket. If the peer
fails to respond to these messages, the connection is considered
broken. The value has type @code{int}; a nonzero value means
``yes''.
@comment sys/socket.h
@comment BSD
@item SO_DONTROUTE
This option controls whether outgoing messages bypass the normal
message routing facilities. If set, messages are sent directly to the
network interface instead. The value has type @code{int}; a nonzero
value means ``yes''.
@comment sys/socket.h
@comment BSD
@item SO_LINGER
This option specifies what should happen when the socket of a type
that promises reliable delivery still has untransmitted messages when
it is closed; see @ref{Closing a Socket}. The value has type
@code{struct linger}.
@comment sys/socket.h
@comment BSD
@deftp {Data Type} {struct linger}
This structure type has the following members:
@table @code
@item int l_onoff
This field is interpreted as a boolean. If nonzero, @code{close}
blocks until the data are transmitted or the timeout period has expired.
@item int l_linger
This specifies the timeout period, in seconds.
@end table
@end deftp
@comment sys/socket.h
@comment BSD
@item SO_BROADCAST
This option controls whether datagrams may be broadcast from the socket.
The value has type @code{int}; a nonzero value means ``yes''.
@comment sys/socket.h
@comment BSD
@item SO_OOBINLINE
If this option is set, out-of-band data received on the socket is
placed in the normal input queue. This permits it to be read using
@code{read} or @code{recv} without specifying the @code{MSG_OOB}
flag. @xref{Out-of-Band Data}. The value has type @code{int}; a
nonzero value means ``yes''.
@comment sys/socket.h
@comment BSD
@item SO_SNDBUF
This option gets or sets the size of the output buffer. The value is a
@code{size_t}, which is the size in bytes.
@comment sys/socket.h
@comment BSD
@item SO_RCVBUF
This option gets or sets the size of the input buffer. The value is a
@code{size_t}, which is the size in bytes.
@comment sys/socket.h
@comment GNU
@item SO_STYLE
@comment sys/socket.h
@comment BSD
@itemx SO_TYPE
This option can be used with @code{getsockopt} only. It is used to
get the socket's communication style. @code{SO_TYPE} is the
historical name, and @code{SO_STYLE} is the preferred name in GNU.
The value has type @code{int} and its value designates a communication
style; see @ref{Communication Styles}.
@comment sys/socket.h
@comment BSD
@item SO_ERROR
@c Extra blank line here makes the table look better.
This option can be used with @code{getsockopt} only. It is used to reset
the error status of the socket. The value is an @code{int}, which represents
the previous error status.
@c !!! what is "socket error status"? this is never defined.
@end table
@node Networks Database
@section Networks Database
@cindex networks database
@cindex converting network number to network name
@cindex converting network name to network number
@pindex /etc/networks
@pindex netdb.h
Many systems come with a database that records a list of networks known
to the system developer. This is usually kept either in the file
@file{/etc/networks} or in an equivalent from a name server. This data
base is useful for routing programs such as @code{route}, but it is not
useful for programs that simply communicate over the network. We
provide functions to access this database, which are declared in
@file{netdb.h}.
@comment netdb.h
@comment BSD
@deftp {Data Type} {struct netent}
This data type is used to represent information about entries in the
networks database. It has the following members:
@table @code
@item char *n_name
This is the ``official'' name of the network.
@item char **n_aliases
These are alternative names for the network, represented as a vector
of strings. A null pointer terminates the array.
@item int n_addrtype
This is the type of the network number; this is always equal to
@code{AF_INET} for Internet networks.
@item unsigned long int n_net
This is the network number. Network numbers are returned in host
byte order; see @ref{Byte Order}.
@end table
@end deftp
Use the @code{getnetbyname} or @code{getnetbyaddr} functions to search
the networks database for information about a specific network. The
information is returned in a statically-allocated structure; you must
copy the information if you need to save it.
@comment netdb.h
@comment BSD
@deftypefun {struct netent *} getnetbyname (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasurace{:netbyname} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getnetbyname =~ getpwuid @mtasurace:netbyname @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getnetbyname_r dup @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getnetbyname_r =~ getpwuid_r @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c no nscd support
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c nss_networks_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getnetbyname_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getnetbyname} function returns information about the network
named @var{name}. It returns a null pointer if there is no such
network.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct netent *} getnetbyaddr (uint32_t @var{net}, int @var{type})
@safety{@prelim{}@mtunsafe{@mtasurace{:netbyaddr} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getnetbyaddr =~ getpwuid @mtasurace:netbyaddr @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c malloc dup @ascuheap @acsmem
@c getnetbyaddr_r dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getnetbyaddr_r =~ getpwuid_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c no nscd support
@c nss_networks_lookup2 =~ nss_passwd_lookup2 @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.l -> _nss_*_getnetbyaddr_r @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
The @code{getnetbyaddr} function returns information about the network
of type @var{type} with number @var{net}. You should specify a value of
@code{AF_INET} for the @var{type} argument for Internet networks.
@code{getnetbyaddr} returns a null pointer if there is no such
network.
@end deftypefun
You can also scan the networks database using @code{setnetent},
@code{getnetent} and @code{endnetent}. Be careful when using these
functions because they are not reentrant.
@comment netdb.h
@comment BSD
@deftypefun void setnetent (int @var{stayopen})
@safety{@prelim{}@mtunsafe{@mtasurace{:netent} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c setnetent @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_setent(nss_networks_lookup2) @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c setup(nss_networks_lookup2) @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *lookup_fct = nss_networks_lookup2 dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:netent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock dup @aculock
This function opens and rewinds the networks database.
If the @var{stayopen} argument is nonzero, this sets a flag so that
subsequent calls to @code{getnetbyname} or @code{getnetbyaddr} will
not close the database (as they usually would). This makes for more
efficiency if you call those functions several times, by avoiding
reopening the database for each call.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun {struct netent *} getnetent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:netent} @mtasurace{:netentbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c getnetent @mtasurace:netent @mtasurace:netentbuf @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent(getnetent_r) @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c malloc dup @ascuheap @acsmem
@c *func = getnetent_r dup @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c realloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c libc_lock_unlock dup @aculock
@c
@c getnetent_r @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock dup @asulock @aculock
@c nss_getent_r(nss_networks_lookup2) @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c setup(nss_networks_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:servent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c nss_lookup dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *sfct.f @mtasurace:netent @ascuplugin
@c libc_lock_unlock dup @aculock
This function returns the next entry in the networks database. It
returns a null pointer if there are no more entries.
@end deftypefun
@comment netdb.h
@comment BSD
@deftypefun void endnetent (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:netent} @mtsenv{} @mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c endnetent @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_lock @asulock @aculock
@c nss_endent(nss_networks_lookup2) @mtasurace:netent @mtsenv @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c res_maybe_init(!preinit) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
@c setup(nss_networks_lookup2) dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c *fct.f @mtasurace:netent @ascuplugin
@c nss_next2 dup @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c libc_lock_unlock @aculock
This function closes the networks database.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/errno.texi 0000664 0001750 0001750 00000162650 12275120646 021611 0 ustar adconrad adconrad @node Error Reporting, Memory, Introduction, Top
@chapter Error Reporting
@c %MENU% How library functions report errors
@cindex error reporting
@cindex reporting errors
@cindex error codes
@cindex status codes
Many functions in @theglibc{} detect and report error conditions,
and sometimes your programs need to check for these error conditions.
For example, when you open an input file, you should verify that the
file was actually opened correctly, and print an error message or take
other appropriate action if the call to the library function failed.
This chapter describes how the error reporting facility works. Your
program should include the header file @file{errno.h} to use this
facility.
@pindex errno.h
@menu
* Checking for Errors:: How errors are reported by library functions.
* Error Codes:: Error code macros; all of these expand
into integer constant values.
* Error Messages:: Mapping error codes onto error messages.
@end menu
@node Checking for Errors, Error Codes, , Error Reporting
@section Checking for Errors
Most library functions return a special value to indicate that they have
failed. The special value is typically @code{-1}, a null pointer, or a
constant such as @code{EOF} that is defined for that purpose. But this
return value tells you only that an error has occurred. To find out
what kind of error it was, you need to look at the error code stored in the
variable @code{errno}. This variable is declared in the header file
@file{errno.h}.
@pindex errno.h
@comment errno.h
@comment ISO
@deftypevr {Variable} {volatile int} errno
The variable @code{errno} contains the system error number. You can
change the value of @code{errno}.
Since @code{errno} is declared @code{volatile}, it might be changed
asynchronously by a signal handler; see @ref{Defining Handlers}.
However, a properly written signal handler saves and restores the value
of @code{errno}, so you generally do not need to worry about this
possibility except when writing signal handlers.
The initial value of @code{errno} at program startup is zero. Many
library functions are guaranteed to set it to certain nonzero values
when they encounter certain kinds of errors. These error conditions are
listed for each function. These functions do not change @code{errno}
when they succeed; thus, the value of @code{errno} after a successful
call is not necessarily zero, and you should not use @code{errno} to
determine @emph{whether} a call failed. The proper way to do that is
documented for each function. @emph{If} the call failed, you can
examine @code{errno}.
Many library functions can set @code{errno} to a nonzero value as a
result of calling other library functions which might fail. You should
assume that any library function might alter @code{errno} when the
function returns an error.
@strong{Portability Note:} @w{ISO C} specifies @code{errno} as a
``modifiable lvalue'' rather than as a variable, permitting it to be
implemented as a macro. For example, its expansion might involve a
function call, like @w{@code{*__errno_location ()}}. In fact, that is
what it is
on @gnulinuxhurdsystems{}. @Theglibc{}, on each system, does
whatever is right for the particular system.
There are a few library functions, like @code{sqrt} and @code{atan},
that return a perfectly legitimate value in case of an error, but also
set @code{errno}. For these functions, if you want to check to see
whether an error occurred, the recommended method is to set @code{errno}
to zero before calling the function, and then check its value afterward.
@end deftypevr
@pindex errno.h
All the error codes have symbolic names; they are macros defined in
@file{errno.h}. The names start with @samp{E} and an upper-case
letter or digit; you should consider names of this form to be
reserved names. @xref{Reserved Names}.
The error code values are all positive integers and are all distinct,
with one exception: @code{EWOULDBLOCK} and @code{EAGAIN} are the same.
Since the values are distinct, you can use them as labels in a
@code{switch} statement; just don't use both @code{EWOULDBLOCK} and
@code{EAGAIN}. Your program should not make any other assumptions about
the specific values of these symbolic constants.
The value of @code{errno} doesn't necessarily have to correspond to any
of these macros, since some library functions might return other error
codes of their own for other situations. The only values that are
guaranteed to be meaningful for a particular library function are the
ones that this manual lists for that function.
Except on @gnuhurdsystems{}, almost any system call can return @code{EFAULT} if
it is given an invalid pointer as an argument. Since this could only
happen as a result of a bug in your program, and since it will not
happen on @gnuhurdsystems{}, we have saved space by not mentioning
@code{EFAULT} in the descriptions of individual functions.
In some Unix systems, many system calls can also return @code{EFAULT} if
given as an argument a pointer into the stack, and the kernel for some
obscure reason fails in its attempt to extend the stack. If this ever
happens, you should probably try using statically or dynamically
allocated memory instead of stack memory on that system.
@node Error Codes, Error Messages, Checking for Errors, Error Reporting
@section Error Codes
@pindex errno.h
The error code macros are defined in the header file @file{errno.h}.
All of them expand into integer constant values. Some of these error
codes can't occur on @gnusystems{}, but they can occur using @theglibc{}
on other systems.
@comment errno.h
@comment POSIX.1: Operation not permitted
@deftypevr Macro int EPERM
@comment errno 1 @c DO NOT REMOVE
Operation not permitted; only the owner of the file (or other resource)
or processes with special privileges can perform the operation.
@end deftypevr
@comment errno.h
@comment POSIX.1: No such file or directory
@deftypevr Macro int ENOENT
@comment errno 2 @c DO NOT REMOVE
No such file or directory. This is a ``file doesn't exist'' error
for ordinary files that are referenced in contexts where they are
expected to already exist.
@end deftypevr
@comment errno.h
@comment POSIX.1: No such process
@deftypevr Macro int ESRCH
@comment errno 3 @c DO NOT REMOVE
No process matches the specified process ID.
@end deftypevr
@comment errno.h
@comment POSIX.1: Interrupted system call
@deftypevr Macro int EINTR
@comment errno 4 @c DO NOT REMOVE
Interrupted function call; an asynchronous signal occurred and prevented
completion of the call. When this happens, you should try the call
again.
You can choose to have functions resume after a signal that is handled,
rather than failing with @code{EINTR}; see @ref{Interrupted
Primitives}.
@end deftypevr
@comment errno.h
@comment POSIX.1: Input/output error
@deftypevr Macro int EIO
@comment errno 5 @c DO NOT REMOVE
Input/output error; usually used for physical read or write errors.
@end deftypevr
@comment errno.h
@comment POSIX.1: No such device or address
@deftypevr Macro int ENXIO
@comment errno 6 @c DO NOT REMOVE
No such device or address. The system tried to use the device
represented by a file you specified, and it couldn't find the device.
This can mean that the device file was installed incorrectly, or that
the physical device is missing or not correctly attached to the
computer.
@end deftypevr
@comment errno.h
@comment POSIX.1: Argument list too long
@deftypevr Macro int E2BIG
@comment errno 7 @c DO NOT REMOVE
Argument list too long; used when the arguments passed to a new program
being executed with one of the @code{exec} functions (@pxref{Executing a
File}) occupy too much memory space. This condition never arises on
@gnuhurdsystems{}.
@end deftypevr
@comment errno.h
@comment POSIX.1: Exec format error
@deftypevr Macro int ENOEXEC
@comment errno 8 @c DO NOT REMOVE
Invalid executable file format. This condition is detected by the
@code{exec} functions; see @ref{Executing a File}.
@end deftypevr
@comment errno.h
@comment POSIX.1: Bad file descriptor
@deftypevr Macro int EBADF
@comment errno 9 @c DO NOT REMOVE
Bad file descriptor; for example, I/O on a descriptor that has been
closed or reading from a descriptor open only for writing (or vice
versa).
@end deftypevr
@comment errno.h
@comment POSIX.1: No child processes
@deftypevr Macro int ECHILD
@comment errno 10 @c DO NOT REMOVE
There are no child processes. This error happens on operations that are
supposed to manipulate child processes, when there aren't any processes
to manipulate.
@end deftypevr
@comment errno.h
@comment POSIX.1: Resource deadlock avoided
@deftypevr Macro int EDEADLK
@comment errno 11 @c DO NOT REMOVE
Deadlock avoided; allocating a system resource would have resulted in a
deadlock situation. The system does not guarantee that it will notice
all such situations. This error means you got lucky and the system
noticed; it might just hang. @xref{File Locks}, for an example.
@end deftypevr
@comment errno.h
@comment POSIX.1: Cannot allocate memory
@deftypevr Macro int ENOMEM
@comment errno 12 @c DO NOT REMOVE
No memory available. The system cannot allocate more virtual memory
because its capacity is full.
@end deftypevr
@comment errno.h
@comment POSIX.1: Permission denied
@deftypevr Macro int EACCES
@comment errno 13 @c DO NOT REMOVE
Permission denied; the file permissions do not allow the attempted operation.
@end deftypevr
@comment errno.h
@comment POSIX.1: Bad address
@deftypevr Macro int EFAULT
@comment errno 14 @c DO NOT REMOVE
Bad address; an invalid pointer was detected.
On @gnuhurdsystems{}, this error never happens; you get a signal instead.
@end deftypevr
@comment errno.h
@comment BSD: Block device required
@deftypevr Macro int ENOTBLK
@comment errno 15 @c DO NOT REMOVE
A file that isn't a block special file was given in a situation that
requires one. For example, trying to mount an ordinary file as a file
system in Unix gives this error.
@end deftypevr
@comment errno.h
@comment POSIX.1: Device or resource busy
@deftypevr Macro int EBUSY
@comment errno 16 @c DO NOT REMOVE
Resource busy; a system resource that can't be shared is already in use.
For example, if you try to delete a file that is the root of a currently
mounted filesystem, you get this error.
@end deftypevr
@comment errno.h
@comment POSIX.1: File exists
@deftypevr Macro int EEXIST
@comment errno 17 @c DO NOT REMOVE
File exists; an existing file was specified in a context where it only
makes sense to specify a new file.
@end deftypevr
@comment errno.h
@comment POSIX.1: Invalid cross-device link
@deftypevr Macro int EXDEV
@comment errno 18 @c DO NOT REMOVE
An attempt to make an improper link across file systems was detected.
This happens not only when you use @code{link} (@pxref{Hard Links}) but
also when you rename a file with @code{rename} (@pxref{Renaming Files}).
@end deftypevr
@comment errno.h
@comment POSIX.1: No such device
@deftypevr Macro int ENODEV
@comment errno 19 @c DO NOT REMOVE
The wrong type of device was given to a function that expects a
particular sort of device.
@end deftypevr
@comment errno.h
@comment POSIX.1: Not a directory
@deftypevr Macro int ENOTDIR
@comment errno 20 @c DO NOT REMOVE
A file that isn't a directory was specified when a directory is required.
@end deftypevr
@comment errno.h
@comment POSIX.1: Is a directory
@deftypevr Macro int EISDIR
@comment errno 21 @c DO NOT REMOVE
File is a directory; you cannot open a directory for writing,
or create or remove hard links to it.
@end deftypevr
@comment errno.h
@comment POSIX.1: Invalid argument
@deftypevr Macro int EINVAL
@comment errno 22 @c DO NOT REMOVE
Invalid argument. This is used to indicate various kinds of problems
with passing the wrong argument to a library function.
@end deftypevr
@comment errno.h
@comment POSIX.1: Too many open files
@deftypevr Macro int EMFILE
@comment errno 24 @c DO NOT REMOVE
The current process has too many files open and can't open any more.
Duplicate descriptors do count toward this limit.
In BSD and GNU, the number of open files is controlled by a resource
limit that can usually be increased. If you get this error, you might
want to increase the @code{RLIMIT_NOFILE} limit or make it unlimited;
@pxref{Limits on Resources}.
@end deftypevr
@comment errno.h
@comment POSIX.1: Too many open files in system
@deftypevr Macro int ENFILE
@comment errno 23 @c DO NOT REMOVE
There are too many distinct file openings in the entire system. Note
that any number of linked channels count as just one file opening; see
@ref{Linked Channels}. This error never occurs on @gnuhurdsystems{}.
@end deftypevr
@comment errno.h
@comment POSIX.1: Inappropriate ioctl for device
@deftypevr Macro int ENOTTY
@comment errno 25 @c DO NOT REMOVE
Inappropriate I/O control operation, such as trying to set terminal
modes on an ordinary file.
@end deftypevr
@comment errno.h
@comment BSD: Text file busy
@deftypevr Macro int ETXTBSY
@comment errno 26 @c DO NOT REMOVE
An attempt to execute a file that is currently open for writing, or
write to a file that is currently being executed. Often using a
debugger to run a program is considered having it open for writing and
will cause this error. (The name stands for ``text file busy''.) This
is not an error on @gnuhurdsystems{}; the text is copied as necessary.
@end deftypevr
@comment errno.h
@comment POSIX.1: File too large
@deftypevr Macro int EFBIG
@comment errno 27 @c DO NOT REMOVE
File too big; the size of a file would be larger than allowed by the system.
@end deftypevr
@comment errno.h
@comment POSIX.1: No space left on device
@deftypevr Macro int ENOSPC
@comment errno 28 @c DO NOT REMOVE
No space left on device; write operation on a file failed because the
disk is full.
@end deftypevr
@comment errno.h
@comment POSIX.1: Illegal seek
@deftypevr Macro int ESPIPE
@comment errno 29 @c DO NOT REMOVE
Invalid seek operation (such as on a pipe).
@end deftypevr
@comment errno.h
@comment POSIX.1: Read-only file system
@deftypevr Macro int EROFS
@comment errno 30 @c DO NOT REMOVE
An attempt was made to modify something on a read-only file system.
@end deftypevr
@comment errno.h
@comment POSIX.1: Too many links
@deftypevr Macro int EMLINK
@comment errno 31 @c DO NOT REMOVE
Too many links; the link count of a single file would become too large.
@code{rename} can cause this error if the file being renamed already has
as many links as it can take (@pxref{Renaming Files}).
@end deftypevr
@comment errno.h
@comment POSIX.1: Broken pipe
@deftypevr Macro int EPIPE
@comment errno 32 @c DO NOT REMOVE
Broken pipe; there is no process reading from the other end of a pipe.
Every library function that returns this error code also generates a
@code{SIGPIPE} signal; this signal terminates the program if not handled
or blocked. Thus, your program will never actually see @code{EPIPE}
unless it has handled or blocked @code{SIGPIPE}.
@end deftypevr
@comment errno.h
@comment ISO: Numerical argument out of domain
@deftypevr Macro int EDOM
@comment errno 33 @c DO NOT REMOVE
Domain error; used by mathematical functions when an argument value does
not fall into the domain over which the function is defined.
@end deftypevr
@comment errno.h
@comment ISO: Numerical result out of range
@deftypevr Macro int ERANGE
@comment errno 34 @c DO NOT REMOVE
Range error; used by mathematical functions when the result value is
not representable because of overflow or underflow.
@end deftypevr
@comment errno.h
@comment POSIX.1: Resource temporarily unavailable
@deftypevr Macro int EAGAIN
@comment errno 35 @c DO NOT REMOVE
Resource temporarily unavailable; the call might work if you try again
later. The macro @code{EWOULDBLOCK} is another name for @code{EAGAIN};
they are always the same in @theglibc{}.
This error can happen in a few different situations:
@itemize @bullet
@item
An operation that would block was attempted on an object that has
non-blocking mode selected. Trying the same operation again will block
until some external condition makes it possible to read, write, or
connect (whatever the operation). You can use @code{select} to find out
when the operation will be possible; @pxref{Waiting for I/O}.
@strong{Portability Note:} In many older Unix systems, this condition
was indicated by @code{EWOULDBLOCK}, which was a distinct error code
different from @code{EAGAIN}. To make your program portable, you should
check for both codes and treat them the same.
@item
A temporary resource shortage made an operation impossible. @code{fork}
can return this error. It indicates that the shortage is expected to
pass, so your program can try the call again later and it may succeed.
It is probably a good idea to delay for a few seconds before trying it
again, to allow time for other processes to release scarce resources.
Such shortages are usually fairly serious and affect the whole system,
so usually an interactive program should report the error to the user
and return to its command loop.
@end itemize
@end deftypevr
@comment errno.h
@comment BSD: Operation would block
@deftypevr Macro int EWOULDBLOCK
@comment errno EAGAIN @c DO NOT REMOVE
In @theglibc{}, this is another name for @code{EAGAIN} (above).
The values are always the same, on every operating system.
C libraries in many older Unix systems have @code{EWOULDBLOCK} as a
separate error code.
@end deftypevr
@comment errno.h
@comment BSD: Operation now in progress
@deftypevr Macro int EINPROGRESS
@comment errno 36 @c DO NOT REMOVE
An operation that cannot complete immediately was initiated on an object
that has non-blocking mode selected. Some functions that must always
block (such as @code{connect}; @pxref{Connecting}) never return
@code{EAGAIN}. Instead, they return @code{EINPROGRESS} to indicate that
the operation has begun and will take some time. Attempts to manipulate
the object before the call completes return @code{EALREADY}. You can
use the @code{select} function to find out when the pending operation
has completed; @pxref{Waiting for I/O}.
@end deftypevr
@comment errno.h
@comment BSD: Operation already in progress
@deftypevr Macro int EALREADY
@comment errno 37 @c DO NOT REMOVE
An operation is already in progress on an object that has non-blocking
mode selected.
@end deftypevr
@comment errno.h
@comment BSD: Socket operation on non-socket
@deftypevr Macro int ENOTSOCK
@comment errno 38 @c DO NOT REMOVE
A file that isn't a socket was specified when a socket is required.
@end deftypevr
@comment errno.h
@comment BSD: Message too long
@deftypevr Macro int EMSGSIZE
@comment errno 40 @c DO NOT REMOVE
The size of a message sent on a socket was larger than the supported
maximum size.
@end deftypevr
@comment errno.h
@comment BSD: Protocol wrong type for socket
@deftypevr Macro int EPROTOTYPE
@comment errno 41 @c DO NOT REMOVE
The socket type does not support the requested communications protocol.
@end deftypevr
@comment errno.h
@comment BSD: Protocol not available
@deftypevr Macro int ENOPROTOOPT
@comment errno 42 @c DO NOT REMOVE
You specified a socket option that doesn't make sense for the
particular protocol being used by the socket. @xref{Socket Options}.
@end deftypevr
@comment errno.h
@comment BSD: Protocol not supported
@deftypevr Macro int EPROTONOSUPPORT
@comment errno 43 @c DO NOT REMOVE
The socket domain does not support the requested communications protocol
(perhaps because the requested protocol is completely invalid).
@xref{Creating a Socket}.
@end deftypevr
@comment errno.h
@comment BSD: Socket type not supported
@deftypevr Macro int ESOCKTNOSUPPORT
@comment errno 44 @c DO NOT REMOVE
The socket type is not supported.
@end deftypevr
@comment errno.h
@comment BSD: Operation not supported
@deftypevr Macro int EOPNOTSUPP
@comment errno 45 @c DO NOT REMOVE
The operation you requested is not supported. Some socket functions
don't make sense for all types of sockets, and others may not be
implemented for all communications protocols. On @gnuhurdsystems{}, this
error can happen for many calls when the object does not support the
particular operation; it is a generic indication that the server knows
nothing to do for that call.
@end deftypevr
@comment errno.h
@comment BSD: Protocol family not supported
@deftypevr Macro int EPFNOSUPPORT
@comment errno 46 @c DO NOT REMOVE
The socket communications protocol family you requested is not supported.
@end deftypevr
@comment errno.h
@comment BSD: Address family not supported by protocol
@deftypevr Macro int EAFNOSUPPORT
@comment errno 47 @c DO NOT REMOVE
The address family specified for a socket is not supported; it is
inconsistent with the protocol being used on the socket. @xref{Sockets}.
@end deftypevr
@comment errno.h
@comment BSD: Address already in use
@deftypevr Macro int EADDRINUSE
@comment errno 48 @c DO NOT REMOVE
The requested socket address is already in use. @xref{Socket Addresses}.
@end deftypevr
@comment errno.h
@comment BSD: Cannot assign requested address
@deftypevr Macro int EADDRNOTAVAIL
@comment errno 49 @c DO NOT REMOVE
The requested socket address is not available; for example, you tried
to give a socket a name that doesn't match the local host name.
@xref{Socket Addresses}.
@end deftypevr
@comment errno.h
@comment BSD: Network is down
@deftypevr Macro int ENETDOWN
@comment errno 50 @c DO NOT REMOVE
A socket operation failed because the network was down.
@end deftypevr
@comment errno.h
@comment BSD: Network is unreachable
@deftypevr Macro int ENETUNREACH
@comment errno 51 @c DO NOT REMOVE
A socket operation failed because the subnet containing the remote host
was unreachable.
@end deftypevr
@comment errno.h
@comment BSD: Network dropped connection on reset
@deftypevr Macro int ENETRESET
@comment errno 52 @c DO NOT REMOVE
A network connection was reset because the remote host crashed.
@end deftypevr
@comment errno.h
@comment BSD: Software caused connection abort
@deftypevr Macro int ECONNABORTED
@comment errno 53 @c DO NOT REMOVE
A network connection was aborted locally.
@end deftypevr
@comment errno.h
@comment BSD: Connection reset by peer
@deftypevr Macro int ECONNRESET
@comment errno 54 @c DO NOT REMOVE
A network connection was closed for reasons outside the control of the
local host, such as by the remote machine rebooting or an unrecoverable
protocol violation.
@end deftypevr
@comment errno.h
@comment BSD: No buffer space available
@deftypevr Macro int ENOBUFS
@comment errno 55 @c DO NOT REMOVE
The kernel's buffers for I/O operations are all in use. In GNU, this
error is always synonymous with @code{ENOMEM}; you may get one or the
other from network operations.
@end deftypevr
@comment errno.h
@comment BSD: Transport endpoint is already connected
@deftypevr Macro int EISCONN
@comment errno 56 @c DO NOT REMOVE
You tried to connect a socket that is already connected.
@xref{Connecting}.
@end deftypevr
@comment errno.h
@comment BSD: Transport endpoint is not connected
@deftypevr Macro int ENOTCONN
@comment errno 57 @c DO NOT REMOVE
The socket is not connected to anything. You get this error when you
try to transmit data over a socket, without first specifying a
destination for the data. For a connectionless socket (for datagram
protocols, such as UDP), you get @code{EDESTADDRREQ} instead.
@end deftypevr
@comment errno.h
@comment BSD: Destination address required
@deftypevr Macro int EDESTADDRREQ
@comment errno 39 @c DO NOT REMOVE
No default destination address was set for the socket. You get this
error when you try to transmit data over a connectionless socket,
without first specifying a destination for the data with @code{connect}.
@end deftypevr
@comment errno.h
@comment BSD: Cannot send after transport endpoint shutdown
@deftypevr Macro int ESHUTDOWN
@comment errno 58 @c DO NOT REMOVE
The socket has already been shut down.
@end deftypevr
@comment errno.h
@comment BSD: Too many references: cannot splice
@deftypevr Macro int ETOOMANYREFS
@comment errno 59 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: Connection timed out
@deftypevr Macro int ETIMEDOUT
@comment errno 60 @c DO NOT REMOVE
A socket operation with a specified timeout received no response during
the timeout period.
@end deftypevr
@comment errno.h
@comment BSD: Connection refused
@deftypevr Macro int ECONNREFUSED
@comment errno 61 @c DO NOT REMOVE
A remote host refused to allow the network connection (typically because
it is not running the requested service).
@end deftypevr
@comment errno.h
@comment BSD: Too many levels of symbolic links
@deftypevr Macro int ELOOP
@comment errno 62 @c DO NOT REMOVE
Too many levels of symbolic links were encountered in looking up a file name.
This often indicates a cycle of symbolic links.
@end deftypevr
@comment errno.h
@comment POSIX.1: File name too long
@deftypevr Macro int ENAMETOOLONG
@comment errno 63 @c DO NOT REMOVE
Filename too long (longer than @code{PATH_MAX}; @pxref{Limits for
Files}) or host name too long (in @code{gethostname} or
@code{sethostname}; @pxref{Host Identification}).
@end deftypevr
@comment errno.h
@comment BSD: Host is down
@deftypevr Macro int EHOSTDOWN
@comment errno 64 @c DO NOT REMOVE
The remote host for a requested network connection is down.
@end deftypevr
@comment errno.h
@comment BSD: No route to host
@deftypevr Macro int EHOSTUNREACH
@comment errno 65 @c DO NOT REMOVE
The remote host for a requested network connection is not reachable.
@end deftypevr
@comment errno.h
@comment POSIX.1: Directory not empty
@deftypevr Macro int ENOTEMPTY
@comment errno 66 @c DO NOT REMOVE
Directory not empty, where an empty directory was expected. Typically,
this error occurs when you are trying to delete a directory.
@end deftypevr
@comment errno.h
@comment BSD: Too many processes
@deftypevr Macro int EPROCLIM
@comment errno 67 @c DO NOT REMOVE
This means that the per-user limit on new process would be exceeded by
an attempted @code{fork}. @xref{Limits on Resources}, for details on
the @code{RLIMIT_NPROC} limit.
@end deftypevr
@comment errno.h
@comment BSD: Too many users
@deftypevr Macro int EUSERS
@comment errno 68 @c DO NOT REMOVE
The file quota system is confused because there are too many users.
@c This can probably happen in a GNU system when using NFS.
@end deftypevr
@comment errno.h
@comment BSD: Disk quota exceeded
@deftypevr Macro int EDQUOT
@comment errno 69 @c DO NOT REMOVE
The user's disk quota was exceeded.
@end deftypevr
@comment errno.h
@comment BSD: Stale file handle
@deftypevr Macro int ESTALE
@comment errno 70 @c DO NOT REMOVE
Stale file handle. This indicates an internal confusion in the
file system which is due to file system rearrangements on the server host
for NFS file systems or corruption in other file systems.
Repairing this condition usually requires unmounting, possibly repairing
and remounting the file system.
@end deftypevr
@comment errno.h
@comment BSD: Object is remote
@deftypevr Macro int EREMOTE
@comment errno 71 @c DO NOT REMOVE
An attempt was made to NFS-mount a remote file system with a file name that
already specifies an NFS-mounted file.
(This is an error on some operating systems, but we expect it to work
properly on @gnuhurdsystems{}, making this error code impossible.)
@end deftypevr
@comment errno.h
@comment BSD: RPC struct is bad
@deftypevr Macro int EBADRPC
@comment errno 72 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: RPC version wrong
@deftypevr Macro int ERPCMISMATCH
@comment errno 73 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: RPC program not available
@deftypevr Macro int EPROGUNAVAIL
@comment errno 74 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: RPC program version wrong
@deftypevr Macro int EPROGMISMATCH
@comment errno 75 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: RPC bad procedure for program
@deftypevr Macro int EPROCUNAVAIL
@comment errno 76 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment POSIX.1: No locks available
@deftypevr Macro int ENOLCK
@comment errno 77 @c DO NOT REMOVE
No locks available. This is used by the file locking facilities; see
@ref{File Locks}. This error is never generated by @gnuhurdsystems{}, but
it can result from an operation to an NFS server running another
operating system.
@end deftypevr
@comment errno.h
@comment BSD: Inappropriate file type or format
@deftypevr Macro int EFTYPE
@comment errno 79 @c DO NOT REMOVE
Inappropriate file type or format. The file was the wrong type for the
operation, or a data file had the wrong format.
On some systems @code{chmod} returns this error if you try to set the
sticky bit on a non-directory file; @pxref{Setting Permissions}.
@end deftypevr
@comment errno.h
@comment BSD: Authentication error
@deftypevr Macro int EAUTH
@comment errno 80 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment BSD: Need authenticator
@deftypevr Macro int ENEEDAUTH
@comment errno 81 @c DO NOT REMOVE
???
@end deftypevr
@comment errno.h
@comment POSIX.1: Function not implemented
@deftypevr Macro int ENOSYS
@comment errno 78 @c DO NOT REMOVE
Function not implemented. This indicates that the function called is
not implemented at all, either in the C library itself or in the
operating system. When you get this error, you can be sure that this
particular function will always fail with @code{ENOSYS} unless you
install a new version of the C library or the operating system.
@end deftypevr
@comment errno.h
@comment POSIX.1: Not supported
@deftypevr Macro int ENOTSUP
@comment errno 118 @c DO NOT REMOVE
Not supported. A function returns this error when certain parameter
values are valid, but the functionality they request is not available.
This can mean that the function does not implement a particular command
or option value or flag bit at all. For functions that operate on some
object given in a parameter, such as a file descriptor or a port, it
might instead mean that only @emph{that specific object} (file
descriptor, port, etc.) is unable to support the other parameters given;
different file descriptors might support different ranges of parameter
values.
If the entire function is not available at all in the implementation,
it returns @code{ENOSYS} instead.
@end deftypevr
@comment errno.h
@comment ISO: Invalid or incomplete multibyte or wide character
@deftypevr Macro int EILSEQ
@comment errno 106 @c DO NOT REMOVE
While decoding a multibyte character the function came along an invalid
or an incomplete sequence of bytes or the given wide character is invalid.
@end deftypevr
@comment errno.h
@comment GNU: Inappropriate operation for background process
@deftypevr Macro int EBACKGROUND
@comment errno 100 @c DO NOT REMOVE
On @gnuhurdsystems{}, servers supporting the @code{term} protocol return
this error for certain operations when the caller is not in the
foreground process group of the terminal. Users do not usually see this
error because functions such as @code{read} and @code{write} translate
it into a @code{SIGTTIN} or @code{SIGTTOU} signal. @xref{Job Control},
for information on process groups and these signals.
@end deftypevr
@comment errno.h
@comment GNU: Translator died
@deftypevr Macro int EDIED
@comment errno 101 @c DO NOT REMOVE
On @gnuhurdsystems{}, opening a file returns this error when the file is
translated by a program and the translator program dies while starting
up, before it has connected to the file.
@end deftypevr
@comment errno.h
@comment GNU: ?
@deftypevr Macro int ED
@comment errno 102 @c DO NOT REMOVE
The experienced user will know what is wrong.
@c This error code is a joke. Its perror text is part of the joke.
@c Don't change it.
@end deftypevr
@comment errno.h
@comment GNU: You really blew it this time
@deftypevr Macro int EGREGIOUS
@comment errno 103 @c DO NOT REMOVE
You did @strong{what}?
@end deftypevr
@comment errno.h
@comment GNU: Computer bought the farm
@deftypevr Macro int EIEIO
@comment errno 104 @c DO NOT REMOVE
Go home and have a glass of warm, dairy-fresh milk.
@end deftypevr
@comment errno.h
@comment GNU: Gratuitous error
@deftypevr Macro int EGRATUITOUS
@comment errno 105 @c DO NOT REMOVE
This error code has no purpose.
@end deftypevr
@comment errno.h
@comment XOPEN: Bad message
@deftypevr Macro int EBADMSG
@comment errno 107
@end deftypevr
@comment errno.h
@comment XOPEN: Identifier removed
@deftypevr Macro int EIDRM
@comment errno 108
@end deftypevr
@comment errno.h
@comment XOPEN: Multihop attempted
@deftypevr Macro int EMULTIHOP
@comment errno 109
@end deftypevr
@comment errno.h
@comment XOPEN: No data available
@deftypevr Macro int ENODATA
@comment errno 110
@end deftypevr
@comment errno.h
@comment XOPEN: Link has been severed
@deftypevr Macro int ENOLINK
@comment errno 111
@end deftypevr
@comment errno.h
@comment XOPEN: No message of desired type
@deftypevr Macro int ENOMSG
@comment errno 112
@end deftypevr
@comment errno.h
@comment XOPEN: Out of streams resources
@deftypevr Macro int ENOSR
@comment errno 113
@end deftypevr
@comment errno.h
@comment XOPEN: Device not a stream
@deftypevr Macro int ENOSTR
@comment errno 114
@end deftypevr
@comment errno.h
@comment XOPEN: Value too large for defined data type
@deftypevr Macro int EOVERFLOW
@comment errno 115
@end deftypevr
@comment errno.h
@comment XOPEN: Protocol error
@deftypevr Macro int EPROTO
@comment errno 116
@end deftypevr
@comment errno.h
@comment XOPEN: Timer expired
@deftypevr Macro int ETIME
@comment errno 117
@end deftypevr
@comment errno.h
@comment POSIX.1: Operation canceled
@deftypevr Macro int ECANCELED
@comment errno 119
Operation canceled; an asynchronous operation was canceled before it
completed. @xref{Asynchronous I/O}. When you call @code{aio_cancel},
the normal result is for the operations affected to complete with this
error; @pxref{Cancel AIO Operations}.
@end deftypevr
@emph{The following error codes are defined by the Linux/i386 kernel.
They are not yet documented.}
@comment errno.h
@comment Linux???: Interrupted system call should be restarted
@deftypevr Macro int ERESTART
@comment errno ???/85
@end deftypevr
@comment errno.h
@comment Linux???: Channel number out of range
@deftypevr Macro int ECHRNG
@comment errno ???/44
@end deftypevr
@comment errno.h
@comment Obsolete: Level 2 not synchronized
@deftypevr Macro int EL2NSYNC
@comment errno ???/45
@end deftypevr
@comment errno.h
@comment Obsolete: Level 3 halted
@deftypevr Macro int EL3HLT
@comment errno ???/46
@end deftypevr
@comment errno.h
@comment Obsolete: Level 3 reset
@deftypevr Macro int EL3RST
@comment errno ???/47
@end deftypevr
@comment errno.h
@comment Linux???: Link number out of range
@deftypevr Macro int ELNRNG
@comment errno ???/48
@end deftypevr
@comment errno.h
@comment Linux???: Protocol driver not attached
@deftypevr Macro int EUNATCH
@comment errno ???/49
@end deftypevr
@comment errno.h
@comment Linux???: No CSI structure available
@deftypevr Macro int ENOCSI
@comment errno ???/50
@end deftypevr
@comment errno.h
@comment Obsolete: Level 2 halted
@deftypevr Macro int EL2HLT
@comment errno ???/51
@end deftypevr
@comment errno.h
@comment Linux???: Invalid exchange
@deftypevr Macro int EBADE
@comment errno ???/52
@end deftypevr
@comment errno.h
@comment Linux???: Invalid request descriptor
@deftypevr Macro int EBADR
@comment errno ???/53
@end deftypevr
@comment errno.h
@comment Linux???: Exchange full
@deftypevr Macro int EXFULL
@comment errno ???/54
@end deftypevr
@comment errno.h
@comment Linux???: No anode
@deftypevr Macro int ENOANO
@comment errno ???/55
@end deftypevr
@comment errno.h
@comment Linux???: Invalid request code
@deftypevr Macro int EBADRQC
@comment errno ???/56
@end deftypevr
@comment errno.h
@comment Linux???: Invalid slot
@deftypevr Macro int EBADSLT
@comment errno ???/57
@end deftypevr
@comment errno.h
@comment Linux???: File locking deadlock error
@deftypevr Macro int EDEADLOCK
@comment errno ???/58
@end deftypevr
@comment errno.h
@comment Linux???: Bad font file format
@deftypevr Macro int EBFONT
@comment errno ???/59
@end deftypevr
@comment errno.h
@comment Linux???: Machine is not on the network
@deftypevr Macro int ENONET
@comment errno ???/64
@end deftypevr
@comment errno.h
@comment Linux???: Package not installed
@deftypevr Macro int ENOPKG
@comment errno ???/65
@end deftypevr
@comment errno.h
@comment Linux???: Advertise error
@deftypevr Macro int EADV
@comment errno ???/68
@end deftypevr
@comment errno.h
@comment Linux???: Srmount error
@deftypevr Macro int ESRMNT
@comment errno ???/69
@end deftypevr
@comment errno.h
@comment Linux???: Communication error on send
@deftypevr Macro int ECOMM
@comment errno ???/70
@end deftypevr
@comment errno.h
@comment Linux???: RFS specific error
@deftypevr Macro int EDOTDOT
@comment errno ???/73
@end deftypevr
@comment errno.h
@comment Linux???: Name not unique on network
@deftypevr Macro int ENOTUNIQ
@comment errno ???/76
@end deftypevr
@comment errno.h
@comment Linux???: File descriptor in bad state
@deftypevr Macro int EBADFD
@comment errno ???/77
@end deftypevr
@comment errno.h
@comment Linux???: Remote address changed
@deftypevr Macro int EREMCHG
@comment errno ???/78
@end deftypevr
@comment errno.h
@comment Linux???: Can not access a needed shared library
@deftypevr Macro int ELIBACC
@comment errno ???/79
@end deftypevr
@comment errno.h
@comment Linux???: Accessing a corrupted shared library
@deftypevr Macro int ELIBBAD
@comment errno ???/80
@end deftypevr
@comment errno.h
@comment Linux???: .lib section in a.out corrupted
@deftypevr Macro int ELIBSCN
@comment errno ???/81
@end deftypevr
@comment errno.h
@comment Linux???: Attempting to link in too many shared libraries
@deftypevr Macro int ELIBMAX
@comment errno ???/82
@end deftypevr
@comment errno.h
@comment Linux???: Cannot exec a shared library directly
@deftypevr Macro int ELIBEXEC
@comment errno ???/83
@end deftypevr
@comment errno.h
@comment Linux???: Streams pipe error
@deftypevr Macro int ESTRPIPE
@comment errno ???/86
@end deftypevr
@comment errno.h
@comment Linux???: Structure needs cleaning
@deftypevr Macro int EUCLEAN
@comment errno ???/117
@end deftypevr
@comment errno.h
@comment Linux???: Not a XENIX named type file
@deftypevr Macro int ENOTNAM
@comment errno ???/118
@end deftypevr
@comment errno.h
@comment Linux???: No XENIX semaphores available
@deftypevr Macro int ENAVAIL
@comment errno ???/119
@end deftypevr
@comment errno.h
@comment Linux???: Is a named type file
@deftypevr Macro int EISNAM
@comment errno ???/120
@end deftypevr
@comment errno.h
@comment Linux???: Remote I/O error
@deftypevr Macro int EREMOTEIO
@comment errno ???/121
@end deftypevr
@comment errno.h
@comment Linux???: No medium found
@deftypevr Macro int ENOMEDIUM
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux???: Wrong medium type
@deftypevr Macro int EMEDIUMTYPE
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Required key not available
@deftypevr Macro int ENOKEY
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Key has expired
@deftypevr Macro int EKEYEXPIRED
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Key has been revoked
@deftypevr Macro int EKEYREVOKED
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Key was rejected by service
@deftypevr Macro int EKEYREJECTED
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Owner died
@deftypevr Macro int EOWNERDEAD
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: State not recoverable
@deftypevr Macro int ENOTRECOVERABLE
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Operation not possible due to RF-kill
@deftypevr Macro int ERFKILL
@comment errno ???/???
@end deftypevr
@comment errno.h
@comment Linux: Memory page has hardware error
@deftypevr Macro int EHWPOISON
@comment errno ???/???
@end deftypevr
@node Error Messages, , Error Codes, Error Reporting
@section Error Messages
The library has functions and variables designed to make it easy for
your program to report informative error messages in the customary
format about the failure of a library call. The functions
@code{strerror} and @code{perror} give you the standard error message
for a given error code; the variable
@w{@code{program_invocation_short_name}} gives you convenient access to the
name of the program that encountered the error.
@comment string.h
@comment ISO
@deftypefun {char *} strerror (int @var{errnum})
@safety{@prelim{}@mtunsafe{@mtasurace{:strerror}}@asunsafe{@ascuheap{} @ascuintl{}}@acunsafe{@acsmem{}}}
@c Calls strerror_r with a static buffer allocated with malloc on the
@c first use.
The @code{strerror} function maps the error code (@pxref{Checking for
Errors}) specified by the @var{errnum} argument to a descriptive error
message string. The return value is a pointer to this string.
The value @var{errnum} normally comes from the variable @code{errno}.
You should not modify the string returned by @code{strerror}. Also, if
you make subsequent calls to @code{strerror}, the string might be
overwritten. (But it's guaranteed that no library function ever calls
@code{strerror} behind your back.)
The function @code{strerror} is declared in @file{string.h}.
@end deftypefun
@comment string.h
@comment GNU
@deftypefun {char *} strerror_r (int @var{errnum}, char *@var{buf}, size_t @var{n})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuintl{}}@acunsafe{}}
The @code{strerror_r} function works like @code{strerror} but instead of
returning the error message in a statically allocated buffer shared by
all threads in the process, it returns a private copy for the
thread. This might be either some permanent global data or a message
string in the user supplied buffer starting at @var{buf} with the
length of @var{n} bytes.
At most @var{n} characters are written (including the NUL byte) so it is
up to the user to select the buffer large enough.
This function should always be used in multi-threaded programs since
there is no way to guarantee the string returned by @code{strerror}
really belongs to the last call of the current thread.
This function @code{strerror_r} is a GNU extension and it is declared in
@file{string.h}.
@end deftypefun
@comment stdio.h
@comment ISO
@deftypefun void perror (const char *@var{message})
@safety{@prelim{}@mtsafe{@mtasurace{:stderr}}@asunsafe{@asucorrupt{} @ascuintl{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
@c Besides strerror_r's and some of fprintf's issues, if stderr is not
@c oriented yet, create a new stream with a dup of stderr's fd and write
@c to that instead of stderr, to avoid orienting it.
This function prints an error message to the stream @code{stderr};
see @ref{Standard Streams}. The orientation of @code{stderr} is not
changed.
If you call @code{perror} with a @var{message} that is either a null
pointer or an empty string, @code{perror} just prints the error message
corresponding to @code{errno}, adding a trailing newline.
If you supply a non-null @var{message} argument, then @code{perror}
prefixes its output with this string. It adds a colon and a space
character to separate the @var{message} from the error string corresponding
to @code{errno}.
The function @code{perror} is declared in @file{stdio.h}.
@end deftypefun
@code{strerror} and @code{perror} produce the exact same message for any
given error code; the precise text varies from system to system. With
@theglibc{}, the messages are fairly short; there are no multi-line
messages or embedded newlines. Each error message begins with a capital
letter and does not include any terminating punctuation.
@strong{Compatibility Note:} The @code{strerror} function was introduced
in @w{ISO C89}. Many older C systems do not support this function yet.
@cindex program name
@cindex name of running program
Many programs that don't read input from the terminal are designed to
exit if any system call fails. By convention, the error message from
such a program should start with the program's name, sans directories.
You can find that name in the variable
@code{program_invocation_short_name}; the full file name is stored the
variable @code{program_invocation_name}.
@comment errno.h
@comment GNU
@deftypevar {char *} program_invocation_name
This variable's value is the name that was used to invoke the program
running in the current process. It is the same as @code{argv[0]}. Note
that this is not necessarily a useful file name; often it contains no
directory names. @xref{Program Arguments}.
@end deftypevar
@comment errno.h
@comment GNU
@deftypevar {char *} program_invocation_short_name
This variable's value is the name that was used to invoke the program
running in the current process, with directory names removed. (That is
to say, it is the same as @code{program_invocation_name} minus
everything up to the last slash, if any.)
@end deftypevar
The library initialization code sets up both of these variables before
calling @code{main}.
@strong{Portability Note:} These two variables are GNU extensions. If
you want your program to work with non-GNU libraries, you must save the
value of @code{argv[0]} in @code{main}, and then strip off the directory
names yourself. We added these extensions to make it possible to write
self-contained error-reporting subroutines that require no explicit
cooperation from @code{main}.
Here is an example showing how to handle failure to open a file
correctly. The function @code{open_sesame} tries to open the named file
for reading and returns a stream if successful. The @code{fopen}
library function returns a null pointer if it couldn't open the file for
some reason. In that situation, @code{open_sesame} constructs an
appropriate error message using the @code{strerror} function, and
terminates the program. If we were going to make some other library
calls before passing the error code to @code{strerror}, we'd have to
save it in a local variable instead, because those other library
functions might overwrite @code{errno} in the meantime.
@smallexample
#include
#include
#include
#include
FILE *
open_sesame (char *name)
@{
FILE *stream;
errno = 0;
stream = fopen (name, "r");
if (stream == NULL)
@{
fprintf (stderr, "%s: Couldn't open file %s; %s\n",
program_invocation_short_name, name, strerror (errno));
exit (EXIT_FAILURE);
@}
else
return stream;
@}
@end smallexample
Using @code{perror} has the advantage that the function is portable and
available on all systems implementing @w{ISO C}. But often the text
@code{perror} generates is not what is wanted and there is no way to
extend or change what @code{perror} does. The GNU coding standard, for
instance, requires error messages to be preceded by the program name and
programs which read some input files should provide information
about the input file name and the line number in case an error is
encountered while reading the file. For these occasions there are two
functions available which are widely used throughout the GNU project.
These functions are declared in @file{error.h}.
@comment error.h
@comment GNU
@deftypefun void error (int @var{status}, int @var{errnum}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @asuheap{} @asuintl{}}@acsafe{}}
@c Cancellation is disabled throughout the execution. It flushes stdout
@c and then holds a lock on stderr while printing the program name and
@c then running error_tail. The non-wide case just runs vfprintf; the
@c wide case converts the message to an alloca/malloc-allocated buffer
@c with mbsrtowcs, then prints it with vfwprintf. Afterwards,
@c print_errno_message calls strerror_r and fxprintf.
The @code{error} function can be used to report general problems during
program execution. The @var{format} argument is a format string just
like those given to the @code{printf} family of functions. The
arguments required for the format can follow the @var{format} parameter.
Just like @code{perror}, @code{error} also can report an error code in
textual form. But unlike @code{perror} the error value is explicitly
passed to the function in the @var{errnum} parameter. This eliminates
the problem mentioned above that the error reporting function must be
called immediately after the function causing the error since otherwise
@code{errno} might have a different value.
The @code{error} prints first the program name. If the application
defined a global variable @code{error_print_progname} and points it to a
function this function will be called to print the program name.
Otherwise the string from the global variable @code{program_name} is
used. The program name is followed by a colon and a space which in turn
is followed by the output produced by the format string. If the
@var{errnum} parameter is non-zero the format string output is followed
by a colon and a space, followed by the error message for the error code
@var{errnum}. In any case is the output terminated with a newline.
The output is directed to the @code{stderr} stream. If the
@code{stderr} wasn't oriented before the call it will be narrow-oriented
afterwards.
The function will return unless the @var{status} parameter has a
non-zero value. In this case the function will call @code{exit} with
the @var{status} value for its parameter and therefore never return. If
@code{error} returns the global variable @code{error_message_count} is
incremented by one to keep track of the number of errors reported.
@end deftypefun
@comment error.h
@comment GNU
@deftypefun void error_at_line (int @var{status}, int @var{errnum}, const char *@var{fname}, unsigned int @var{lineno}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtunsafe{@mtasurace{:error_at_line/error_one_per_line} @mtslocale{}}@asunsafe{@asucorrupt{} @asuheap{} @asuintl{}}@acunsafe{@acucorrupt{/error_one_per_line}}}
@c The error_one_per_line variable is accessed (without any form of
@c synchronization, but since it's an int used once, it should be safe
@c enough) and, if this mode is enabled, static variables used to hold
@c the last printed file name and line number are accessed and modified
@c without synchronization; the update is not atomic and it occurs
@c before disabling cancellation, so it can be interrupted after only
@c one of the two variables is modified. After that, it's very much
@c like error.
The @code{error_at_line} function is very similar to the @code{error}
function. The only difference are the additional parameters @var{fname}
and @var{lineno}. The handling of the other parameters is identical to
that of @code{error} except that between the program name and the string
generated by the format string additional text is inserted.
Directly following the program name a colon, followed by the file name
pointer to by @var{fname}, another colon, and a value of @var{lineno} is
printed.
This additional output of course is meant to be used to locate an error
in an input file (like a programming language source code file etc).
If the global variable @code{error_one_per_line} is set to a non-zero
value @code{error_at_line} will avoid printing consecutive messages for
the same file and line. Repetition which are not directly following
each other are not caught.
Just like @code{error} this function only returned if @var{status} is
zero. Otherwise @code{exit} is called with the non-zero value. If
@code{error} returns the global variable @code{error_message_count} is
incremented by one to keep track of the number of errors reported.
@end deftypefun
As mentioned above the @code{error} and @code{error_at_line} functions
can be customized by defining a variable named
@code{error_print_progname}.
@comment error.h
@comment GNU
@deftypevar {void (*error_print_progname)} (void)
If the @code{error_print_progname} variable is defined to a non-zero
value the function pointed to is called by @code{error} or
@code{error_at_line}. It is expected to print the program name or do
something similarly useful.
The function is expected to be print to the @code{stderr} stream and
must be able to handle whatever orientation the stream has.
The variable is global and shared by all threads.
@end deftypevar
@comment error.h
@comment GNU
@deftypevar {unsigned int} error_message_count
The @code{error_message_count} variable is incremented whenever one of
the functions @code{error} or @code{error_at_line} returns. The
variable is global and shared by all threads.
@end deftypevar
@comment error.h
@comment GNU
@deftypevar int error_one_per_line
The @code{error_one_per_line} variable influences only
@code{error_at_line}. Normally the @code{error_at_line} function
creates output for every invocation. If @code{error_one_per_line} is
set to a non-zero value @code{error_at_line} keeps track of the last
file name and line number for which an error was reported and avoid
directly following messages for the same file and line. This variable
is global and shared by all threads.
@end deftypevar
@noindent
A program which read some input file and reports errors in it could look
like this:
@smallexample
@{
char *line = NULL;
size_t len = 0;
unsigned int lineno = 0;
error_message_count = 0;
while (! feof_unlocked (fp))
@{
ssize_t n = getline (&line, &len, fp);
if (n <= 0)
/* @r{End of file or error.} */
break;
++lineno;
/* @r{Process the line.} */
@dots{}
if (@r{Detect error in line})
error_at_line (0, errval, filename, lineno,
"some error text %s", some_variable);
@}
if (error_message_count != 0)
error (EXIT_FAILURE, 0, "%u errors found", error_message_count);
@}
@end smallexample
@code{error} and @code{error_at_line} are clearly the functions of
choice and enable the programmer to write applications which follow the
GNU coding standard. @Theglibc{} additionally contains functions which
are used in BSD for the same purpose. These functions are declared in
@file{err.h}. It is generally advised to not use these functions. They
are included only for compatibility.
@comment err.h
@comment BSD
@deftypefun void warn (const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @ascuintl{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Just calls vwarn with the va_list.
The @code{warn} function is roughly equivalent to a call like
@smallexample
error (0, errno, format, @r{the parameters})
@end smallexample
@noindent
except that the global variables @code{error} respects and modifies
are not used.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void vwarn (const char *@var{format}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @ascuintl{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c While holding stderr's recursive lock, it prints the programname, the
@c given message, and the error string with fw?printf's %m. When the
@c stream is wide, convert_and_print converts the format string to an
@c alloca/malloc-created buffer using mbsrtowcs and then calls fwprintf.
The @code{vwarn} function is just like @code{warn} except that the
parameters for the handling of the format string @var{format} are passed
in as a value of type @code{va_list}.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void warnx (const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as warn, but without the strerror translation issues.
The @code{warnx} function is roughly equivalent to a call like
@smallexample
error (0, 0, format, @r{the parameters})
@end smallexample
@noindent
except that the global variables @code{error} respects and modifies
are not used. The difference to @code{warn} is that no error number
string is printed.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void vwarnx (const char *@var{format}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as vwarn, but without the strerror translation issues.
The @code{vwarnx} function is just like @code{warnx} except that the
parameters for the handling of the format string @var{format} are passed
in as a value of type @code{va_list}.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void err (int @var{status}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @ascuintl{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as warn followed by exit.
The @code{err} function is roughly equivalent to a call like
@smallexample
error (status, errno, format, @r{the parameters})
@end smallexample
@noindent
except that the global variables @code{error} respects and modifies
are not used and that the program is exited even if @var{status} is zero.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void verr (int @var{status}, const char *@var{format}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @ascuintl{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as vwarn followed by exit.
The @code{verr} function is just like @code{err} except that the
parameters for the handling of the format string @var{format} are passed
in as a value of type @code{va_list}.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void errx (int @var{status}, const char *@var{format}, @dots{})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as warnx followed by exit.
The @code{errx} function is roughly equivalent to a call like
@smallexample
error (status, 0, format, @r{the parameters})
@end smallexample
@noindent
except that the global variables @code{error} respects and modifies
are not used and that the program is exited even if @var{status}
is zero. The difference to @code{err} is that no error number
string is printed.
@end deftypefun
@comment err.h
@comment BSD
@deftypefun void verrx (int @var{status}, const char *@var{format}, va_list @var{ap})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c Same as vwarnx followed by exit.
The @code{verrx} function is just like @code{errx} except that the
parameters for the handling of the format string @var{format} are passed
in as a value of type @code{va_list}.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/job.texi 0000664 0001750 0001750 00000134345 12275120646 021236 0 ustar adconrad adconrad @node Job Control, Name Service Switch, Processes, Top
@c %MENU% All about process groups and sessions
@chapter Job Control
@cindex process groups
@cindex job control
@cindex job
@cindex session
@dfn{Job control} refers to the protocol for allowing a user to move
between multiple @dfn{process groups} (or @dfn{jobs}) within a single
@dfn{login session}. The job control facilities are set up so that
appropriate behavior for most programs happens automatically and they
need not do anything special about job control. So you can probably
ignore the material in this chapter unless you are writing a shell or
login program.
You need to be familiar with concepts relating to process creation
(@pxref{Process Creation Concepts}) and signal handling (@pxref{Signal
Handling}) in order to understand this material presented in this
chapter.
@menu
* Concepts of Job Control:: Jobs can be controlled by a shell.
* Job Control is Optional:: Not all POSIX systems support job control.
* Controlling Terminal:: How a process gets its controlling terminal.
* Access to the Terminal:: How processes share the controlling terminal.
* Orphaned Process Groups:: Jobs left after the user logs out.
* Implementing a Shell:: What a shell must do to implement job control.
* Functions for Job Control:: Functions to control process groups.
@end menu
@node Concepts of Job Control, Job Control is Optional, , Job Control
@section Concepts of Job Control
@cindex shell
The fundamental purpose of an interactive shell is to read
commands from the user's terminal and create processes to execute the
programs specified by those commands. It can do this using the
@code{fork} (@pxref{Creating a Process}) and @code{exec}
(@pxref{Executing a File}) functions.
A single command may run just one process---but often one command uses
several processes. If you use the @samp{|} operator in a shell command,
you explicitly request several programs in their own processes. But
even if you run just one program, it can use multiple processes
internally. For example, a single compilation command such as @samp{cc
-c foo.c} typically uses four processes (though normally only two at any
given time). If you run @code{make}, its job is to run other programs
in separate processes.
The processes belonging to a single command are called a @dfn{process
group} or @dfn{job}. This is so that you can operate on all of them at
once. For example, typing @kbd{C-c} sends the signal @code{SIGINT} to
terminate all the processes in the foreground process group.
@cindex session
A @dfn{session} is a larger group of processes. Normally all the
processes that stem from a single login belong to the same session.
Every process belongs to a process group. When a process is created, it
becomes a member of the same process group and session as its parent
process. You can put it in another process group using the
@code{setpgid} function, provided the process group belongs to the same
session.
@cindex session leader
The only way to put a process in a different session is to make it the
initial process of a new session, or a @dfn{session leader}, using the
@code{setsid} function. This also puts the session leader into a new
process group, and you can't move it out of that process group again.
Usually, new sessions are created by the system login program, and the
session leader is the process running the user's login shell.
@cindex controlling terminal
A shell that supports job control must arrange to control which job can
use the terminal at any time. Otherwise there might be multiple jobs
trying to read from the terminal at once, and confusion about which
process should receive the input typed by the user. To prevent this,
the shell must cooperate with the terminal driver using the protocol
described in this chapter.
@cindex foreground job
@cindex background job
The shell can give unlimited access to the controlling terminal to only
one process group at a time. This is called the @dfn{foreground job} on
that controlling terminal. Other process groups managed by the shell
that are executing without such access to the terminal are called
@dfn{background jobs}.
@cindex stopped job
If a background job needs to read from its controlling
terminal, it is @dfn{stopped} by the terminal driver; if the
@code{TOSTOP} mode is set, likewise for writing. The user can stop
a foreground job by typing the SUSP character (@pxref{Special
Characters}) and a program can stop any job by sending it a
@code{SIGSTOP} signal. It's the responsibility of the shell to notice
when jobs stop, to notify the user about them, and to provide mechanisms
for allowing the user to interactively continue stopped jobs and switch
jobs between foreground and background.
@xref{Access to the Terminal}, for more information about I/O to the
controlling terminal,
@node Job Control is Optional, Controlling Terminal, Concepts of Job Control , Job Control
@section Job Control is Optional
@cindex job control is optional
Not all operating systems support job control. @gnusystems{} do
support job control, but if you are using @theglibc{} on some other
system, that system may not support job control itself.
You can use the @code{_POSIX_JOB_CONTROL} macro to test at compile-time
whether the system supports job control. @xref{System Options}.
If job control is not supported, then there can be only one process
group per session, which behaves as if it were always in the foreground.
The functions for creating additional process groups simply fail with
the error code @code{ENOSYS}.
The macros naming the various job control signals (@pxref{Job Control
Signals}) are defined even if job control is not supported. However,
the system never generates these signals, and attempts to send a job
control signal or examine or specify their actions report errors or do
nothing.
@node Controlling Terminal, Access to the Terminal, Job Control is Optional, Job Control
@section Controlling Terminal of a Process
One of the attributes of a process is its controlling terminal. Child
processes created with @code{fork} inherit the controlling terminal from
their parent process. In this way, all the processes in a session
inherit the controlling terminal from the session leader. A session
leader that has control of a terminal is called the @dfn{controlling
process} of that terminal.
@cindex controlling process
You generally do not need to worry about the exact mechanism used to
allocate a controlling terminal to a session, since it is done for you
by the system when you log in.
@c ??? How does GNU system let a process get a ctl terminal.
An individual process disconnects from its controlling terminal when it
calls @code{setsid} to become the leader of a new session.
@xref{Process Group Functions}.
@c !!! explain how it gets a new one (by opening any terminal)
@c ??? How you get a controlling terminal is system-dependent.
@c We should document how this will work in the GNU system when it is decided.
@c What Unix does is not clean and I don't think GNU should use that.
@node Access to the Terminal, Orphaned Process Groups, Controlling Terminal, Job Control
@section Access to the Controlling Terminal
@cindex controlling terminal, access to
Processes in the foreground job of a controlling terminal have
unrestricted access to that terminal; background processes do not. This
section describes in more detail what happens when a process in a
background job tries to access its controlling terminal.
@cindex @code{SIGTTIN}, from background job
When a process in a background job tries to read from its controlling
terminal, the process group is usually sent a @code{SIGTTIN} signal.
This normally causes all of the processes in that group to stop (unless
they handle the signal and don't stop themselves). However, if the
reading process is ignoring or blocking this signal, then @code{read}
fails with an @code{EIO} error instead.
@cindex @code{SIGTTOU}, from background job
Similarly, when a process in a background job tries to write to its
controlling terminal, the default behavior is to send a @code{SIGTTOU}
signal to the process group. However, the behavior is modified by the
@code{TOSTOP} bit of the local modes flags (@pxref{Local Modes}). If
this bit is not set (which is the default), then writing to the
controlling terminal is always permitted without sending a signal.
Writing is also permitted if the @code{SIGTTOU} signal is being ignored
or blocked by the writing process.
Most other terminal operations that a program can do are treated as
reading or as writing. (The description of each operation should say
which.)
For more information about the primitive @code{read} and @code{write}
functions, see @ref{I/O Primitives}.
@node Orphaned Process Groups, Implementing a Shell, Access to the Terminal, Job Control
@section Orphaned Process Groups
@cindex orphaned process group
When a controlling process terminates, its terminal becomes free and a
new session can be established on it. (In fact, another user could log
in on the terminal.) This could cause a problem if any processes from
the old session are still trying to use that terminal.
To prevent problems, process groups that continue running even after the
session leader has terminated are marked as @dfn{orphaned process
groups}.
When a process group becomes an orphan, its processes are sent a
@code{SIGHUP} signal. Ordinarily, this causes the processes to
terminate. However, if a program ignores this signal or establishes a
handler for it (@pxref{Signal Handling}), it can continue running as in
the orphan process group even after its controlling process terminates;
but it still cannot access the terminal any more.
@node Implementing a Shell, Functions for Job Control, Orphaned Process Groups, Job Control
@section Implementing a Job Control Shell
This section describes what a shell must do to implement job control, by
presenting an extensive sample program to illustrate the concepts
involved.
@iftex
@itemize @bullet
@item
@ref{Data Structures}, introduces the example and presents
its primary data structures.
@item
@ref{Initializing the Shell}, discusses actions which the shell must
perform to prepare for job control.
@item
@ref{Launching Jobs}, includes information about how to create jobs
to execute commands.
@item
@ref{Foreground and Background}, discusses what the shell should
do differently when launching a job in the foreground as opposed to
a background job.
@item
@ref{Stopped and Terminated Jobs}, discusses reporting of job status
back to the shell.
@item
@ref{Continuing Stopped Jobs}, tells you how to continue jobs that
have been stopped.
@item
@ref{Missing Pieces}, discusses other parts of the shell.
@end itemize
@end iftex
@menu
* Data Structures:: Introduction to the sample shell.
* Initializing the Shell:: What the shell must do to take
responsibility for job control.
* Launching Jobs:: Creating jobs to execute commands.
* Foreground and Background:: Putting a job in foreground of background.
* Stopped and Terminated Jobs:: Reporting job status.
* Continuing Stopped Jobs:: How to continue a stopped job in
the foreground or background.
* Missing Pieces:: Other parts of the shell.
@end menu
@node Data Structures, Initializing the Shell, , Implementing a Shell
@subsection Data Structures for the Shell
All of the program examples included in this chapter are part of
a simple shell program. This section presents data structures
and utility functions which are used throughout the example.
The sample shell deals mainly with two data structures. The
@code{job} type contains information about a job, which is a
set of subprocesses linked together with pipes. The @code{process} type
holds information about a single subprocess. Here are the relevant
data structure declarations:
@smallexample
@group
/* @r{A process is a single process.} */
typedef struct process
@{
struct process *next; /* @r{next process in pipeline} */
char **argv; /* @r{for exec} */
pid_t pid; /* @r{process ID} */
char completed; /* @r{true if process has completed} */
char stopped; /* @r{true if process has stopped} */
int status; /* @r{reported status value} */
@} process;
@end group
@group
/* @r{A job is a pipeline of processes.} */
typedef struct job
@{
struct job *next; /* @r{next active job} */
char *command; /* @r{command line, used for messages} */
process *first_process; /* @r{list of processes in this job} */
pid_t pgid; /* @r{process group ID} */
char notified; /* @r{true if user told about stopped job} */
struct termios tmodes; /* @r{saved terminal modes} */
int stdin, stdout, stderr; /* @r{standard i/o channels} */
@} job;
/* @r{The active jobs are linked into a list. This is its head.} */
job *first_job = NULL;
@end group
@end smallexample
Here are some utility functions that are used for operating on @code{job}
objects.
@smallexample
@group
/* @r{Find the active job with the indicated @var{pgid}.} */
job *
find_job (pid_t pgid)
@{
job *j;
for (j = first_job; j; j = j->next)
if (j->pgid == pgid)
return j;
return NULL;
@}
@end group
@group
/* @r{Return true if all processes in the job have stopped or completed.} */
int
job_is_stopped (job *j)
@{
process *p;
for (p = j->first_process; p; p = p->next)
if (!p->completed && !p->stopped)
return 0;
return 1;
@}
@end group
@group
/* @r{Return true if all processes in the job have completed.} */
int
job_is_completed (job *j)
@{
process *p;
for (p = j->first_process; p; p = p->next)
if (!p->completed)
return 0;
return 1;
@}
@end group
@end smallexample
@node Initializing the Shell, Launching Jobs, Data Structures, Implementing a Shell
@subsection Initializing the Shell
@cindex job control, enabling
@cindex subshell
When a shell program that normally performs job control is started, it
has to be careful in case it has been invoked from another shell that is
already doing its own job control.
A subshell that runs interactively has to ensure that it has been placed
in the foreground by its parent shell before it can enable job control
itself. It does this by getting its initial process group ID with the
@code{getpgrp} function, and comparing it to the process group ID of the
current foreground job associated with its controlling terminal (which
can be retrieved using the @code{tcgetpgrp} function).
If the subshell is not running as a foreground job, it must stop itself
by sending a @code{SIGTTIN} signal to its own process group. It may not
arbitrarily put itself into the foreground; it must wait for the user to
tell the parent shell to do this. If the subshell is continued again,
it should repeat the check and stop itself again if it is still not in
the foreground.
@cindex job control, enabling
Once the subshell has been placed into the foreground by its parent
shell, it can enable its own job control. It does this by calling
@code{setpgid} to put itself into its own process group, and then
calling @code{tcsetpgrp} to place this process group into the
foreground.
When a shell enables job control, it should set itself to ignore all the
job control stop signals so that it doesn't accidentally stop itself.
You can do this by setting the action for all the stop signals to
@code{SIG_IGN}.
A subshell that runs non-interactively cannot and should not support job
control. It must leave all processes it creates in the same process
group as the shell itself; this allows the non-interactive shell and its
child processes to be treated as a single job by the parent shell. This
is easy to do---just don't use any of the job control primitives---but
you must remember to make the shell do it.
Here is the initialization code for the sample shell that shows how to
do all of this.
@smallexample
/* @r{Keep track of attributes of the shell.} */
#include
#include
#include
pid_t shell_pgid;
struct termios shell_tmodes;
int shell_terminal;
int shell_is_interactive;
/* @r{Make sure the shell is running interactively as the foreground job}
@r{before proceeding.} */
void
init_shell ()
@{
/* @r{See if we are running interactively.} */
shell_terminal = STDIN_FILENO;
shell_is_interactive = isatty (shell_terminal);
if (shell_is_interactive)
@{
/* @r{Loop until we are in the foreground.} */
while (tcgetpgrp (shell_terminal) != (shell_pgid = getpgrp ()))
kill (- shell_pgid, SIGTTIN);
/* @r{Ignore interactive and job-control signals.} */
signal (SIGINT, SIG_IGN);
signal (SIGQUIT, SIG_IGN);
signal (SIGTSTP, SIG_IGN);
signal (SIGTTIN, SIG_IGN);
signal (SIGTTOU, SIG_IGN);
signal (SIGCHLD, SIG_IGN);
/* @r{Put ourselves in our own process group.} */
shell_pgid = getpid ();
if (setpgid (shell_pgid, shell_pgid) < 0)
@{
perror ("Couldn't put the shell in its own process group");
exit (1);
@}
/* @r{Grab control of the terminal.} */
tcsetpgrp (shell_terminal, shell_pgid);
/* @r{Save default terminal attributes for shell.} */
tcgetattr (shell_terminal, &shell_tmodes);
@}
@}
@end smallexample
@node Launching Jobs, Foreground and Background, Initializing the Shell, Implementing a Shell
@subsection Launching Jobs
@cindex launching jobs
Once the shell has taken responsibility for performing job control on
its controlling terminal, it can launch jobs in response to commands
typed by the user.
To create the processes in a process group, you use the same @code{fork}
and @code{exec} functions described in @ref{Process Creation Concepts}.
Since there are multiple child processes involved, though, things are a
little more complicated and you must be careful to do things in the
right order. Otherwise, nasty race conditions can result.
You have two choices for how to structure the tree of parent-child
relationships among the processes. You can either make all the
processes in the process group be children of the shell process, or you
can make one process in group be the ancestor of all the other processes
in that group. The sample shell program presented in this chapter uses
the first approach because it makes bookkeeping somewhat simpler.
@cindex process group leader
@cindex process group ID
As each process is forked, it should put itself in the new process group
by calling @code{setpgid}; see @ref{Process Group Functions}. The first
process in the new group becomes its @dfn{process group leader}, and its
process ID becomes the @dfn{process group ID} for the group.
@cindex race conditions, relating to job control
The shell should also call @code{setpgid} to put each of its child
processes into the new process group. This is because there is a
potential timing problem: each child process must be put in the process
group before it begins executing a new program, and the shell depends on
having all the child processes in the group before it continues
executing. If both the child processes and the shell call
@code{setpgid}, this ensures that the right things happen no matter which
process gets to it first.
If the job is being launched as a foreground job, the new process group
also needs to be put into the foreground on the controlling terminal
using @code{tcsetpgrp}. Again, this should be done by the shell as well
as by each of its child processes, to avoid race conditions.
The next thing each child process should do is to reset its signal
actions.
During initialization, the shell process set itself to ignore job
control signals; see @ref{Initializing the Shell}. As a result, any child
processes it creates also ignore these signals by inheritance. This is
definitely undesirable, so each child process should explicitly set the
actions for these signals back to @code{SIG_DFL} just after it is forked.
Since shells follow this convention, applications can assume that they
inherit the correct handling of these signals from the parent process.
But every application has a responsibility not to mess up the handling
of stop signals. Applications that disable the normal interpretation of
the SUSP character should provide some other mechanism for the user to
stop the job. When the user invokes this mechanism, the program should
send a @code{SIGTSTP} signal to the process group of the process, not
just to the process itself. @xref{Signaling Another Process}.
Finally, each child process should call @code{exec} in the normal way.
This is also the point at which redirection of the standard input and
output channels should be handled. @xref{Duplicating Descriptors},
for an explanation of how to do this.
Here is the function from the sample shell program that is responsible
for launching a program. The function is executed by each child process
immediately after it has been forked by the shell, and never returns.
@smallexample
void
launch_process (process *p, pid_t pgid,
int infile, int outfile, int errfile,
int foreground)
@{
pid_t pid;
if (shell_is_interactive)
@{
/* @r{Put the process into the process group and give the process group}
@r{the terminal, if appropriate.}
@r{This has to be done both by the shell and in the individual}
@r{child processes because of potential race conditions.} */
pid = getpid ();
if (pgid == 0) pgid = pid;
setpgid (pid, pgid);
if (foreground)
tcsetpgrp (shell_terminal, pgid);
/* @r{Set the handling for job control signals back to the default.} */
signal (SIGINT, SIG_DFL);
signal (SIGQUIT, SIG_DFL);
signal (SIGTSTP, SIG_DFL);
signal (SIGTTIN, SIG_DFL);
signal (SIGTTOU, SIG_DFL);
signal (SIGCHLD, SIG_DFL);
@}
/* @r{Set the standard input/output channels of the new process.} */
if (infile != STDIN_FILENO)
@{
dup2 (infile, STDIN_FILENO);
close (infile);
@}
if (outfile != STDOUT_FILENO)
@{
dup2 (outfile, STDOUT_FILENO);
close (outfile);
@}
if (errfile != STDERR_FILENO)
@{
dup2 (errfile, STDERR_FILENO);
close (errfile);
@}
/* @r{Exec the new process. Make sure we exit.} */
execvp (p->argv[0], p->argv);
perror ("execvp");
exit (1);
@}
@end smallexample
If the shell is not running interactively, this function does not do
anything with process groups or signals. Remember that a shell not
performing job control must keep all of its subprocesses in the same
process group as the shell itself.
Next, here is the function that actually launches a complete job.
After creating the child processes, this function calls some other
functions to put the newly created job into the foreground or background;
these are discussed in @ref{Foreground and Background}.
@smallexample
void
launch_job (job *j, int foreground)
@{
process *p;
pid_t pid;
int mypipe[2], infile, outfile;
infile = j->stdin;
for (p = j->first_process; p; p = p->next)
@{
/* @r{Set up pipes, if necessary.} */
if (p->next)
@{
if (pipe (mypipe) < 0)
@{
perror ("pipe");
exit (1);
@}
outfile = mypipe[1];
@}
else
outfile = j->stdout;
/* @r{Fork the child processes.} */
pid = fork ();
if (pid == 0)
/* @r{This is the child process.} */
launch_process (p, j->pgid, infile,
outfile, j->stderr, foreground);
else if (pid < 0)
@{
/* @r{The fork failed.} */
perror ("fork");
exit (1);
@}
else
@{
/* @r{This is the parent process.} */
p->pid = pid;
if (shell_is_interactive)
@{
if (!j->pgid)
j->pgid = pid;
setpgid (pid, j->pgid);
@}
@}
/* @r{Clean up after pipes.} */
if (infile != j->stdin)
close (infile);
if (outfile != j->stdout)
close (outfile);
infile = mypipe[0];
@}
format_job_info (j, "launched");
if (!shell_is_interactive)
wait_for_job (j);
else if (foreground)
put_job_in_foreground (j, 0);
else
put_job_in_background (j, 0);
@}
@end smallexample
@node Foreground and Background, Stopped and Terminated Jobs, Launching Jobs, Implementing a Shell
@subsection Foreground and Background
Now let's consider what actions must be taken by the shell when it
launches a job into the foreground, and how this differs from what
must be done when a background job is launched.
@cindex foreground job, launching
When a foreground job is launched, the shell must first give it access
to the controlling terminal by calling @code{tcsetpgrp}. Then, the
shell should wait for processes in that process group to terminate or
stop. This is discussed in more detail in @ref{Stopped and Terminated
Jobs}.
When all of the processes in the group have either completed or stopped,
the shell should regain control of the terminal for its own process
group by calling @code{tcsetpgrp} again. Since stop signals caused by
I/O from a background process or a SUSP character typed by the user
are sent to the process group, normally all the processes in the job
stop together.
The foreground job may have left the terminal in a strange state, so the
shell should restore its own saved terminal modes before continuing. In
case the job is merely stopped, the shell should first save the current
terminal modes so that it can restore them later if the job is
continued. The functions for dealing with terminal modes are
@code{tcgetattr} and @code{tcsetattr}; these are described in
@ref{Terminal Modes}.
Here is the sample shell's function for doing all of this.
@smallexample
@group
/* @r{Put job @var{j} in the foreground. If @var{cont} is nonzero,}
@r{restore the saved terminal modes and send the process group a}
@r{@code{SIGCONT} signal to wake it up before we block.} */
void
put_job_in_foreground (job *j, int cont)
@{
/* @r{Put the job into the foreground.} */
tcsetpgrp (shell_terminal, j->pgid);
@end group
@group
/* @r{Send the job a continue signal, if necessary.} */
if (cont)
@{
tcsetattr (shell_terminal, TCSADRAIN, &j->tmodes);
if (kill (- j->pgid, SIGCONT) < 0)
perror ("kill (SIGCONT)");
@}
@end group
/* @r{Wait for it to report.} */
wait_for_job (j);
/* @r{Put the shell back in the foreground.} */
tcsetpgrp (shell_terminal, shell_pgid);
@group
/* @r{Restore the shell's terminal modes.} */
tcgetattr (shell_terminal, &j->tmodes);
tcsetattr (shell_terminal, TCSADRAIN, &shell_tmodes);
@}
@end group
@end smallexample
@cindex background job, launching
If the process group is launched as a background job, the shell should
remain in the foreground itself and continue to read commands from
the terminal.
In the sample shell, there is not much that needs to be done to put
a job into the background. Here is the function it uses:
@smallexample
/* @r{Put a job in the background. If the cont argument is true, send}
@r{the process group a @code{SIGCONT} signal to wake it up.} */
void
put_job_in_background (job *j, int cont)
@{
/* @r{Send the job a continue signal, if necessary.} */
if (cont)
if (kill (-j->pgid, SIGCONT) < 0)
perror ("kill (SIGCONT)");
@}
@end smallexample
@node Stopped and Terminated Jobs, Continuing Stopped Jobs, Foreground and Background, Implementing a Shell
@subsection Stopped and Terminated Jobs
@cindex stopped jobs, detecting
@cindex terminated jobs, detecting
When a foreground process is launched, the shell must block until all of
the processes in that job have either terminated or stopped. It can do
this by calling the @code{waitpid} function; see @ref{Process
Completion}. Use the @code{WUNTRACED} option so that status is reported
for processes that stop as well as processes that terminate.
The shell must also check on the status of background jobs so that it
can report terminated and stopped jobs to the user; this can be done by
calling @code{waitpid} with the @code{WNOHANG} option. A good place to
put a such a check for terminated and stopped jobs is just before
prompting for a new command.
@cindex @code{SIGCHLD}, handling of
The shell can also receive asynchronous notification that there is
status information available for a child process by establishing a
handler for @code{SIGCHLD} signals. @xref{Signal Handling}.
In the sample shell program, the @code{SIGCHLD} signal is normally
ignored. This is to avoid reentrancy problems involving the global data
structures the shell manipulates. But at specific times when the shell
is not using these data structures---such as when it is waiting for
input on the terminal---it makes sense to enable a handler for
@code{SIGCHLD}. The same function that is used to do the synchronous
status checks (@code{do_job_notification}, in this case) can also be
called from within this handler.
Here are the parts of the sample shell program that deal with checking
the status of jobs and reporting the information to the user.
@smallexample
@group
/* @r{Store the status of the process @var{pid} that was returned by waitpid.}
@r{Return 0 if all went well, nonzero otherwise.} */
int
mark_process_status (pid_t pid, int status)
@{
job *j;
process *p;
@end group
@group
if (pid > 0)
@{
/* @r{Update the record for the process.} */
for (j = first_job; j; j = j->next)
for (p = j->first_process; p; p = p->next)
if (p->pid == pid)
@{
p->status = status;
if (WIFSTOPPED (status))
p->stopped = 1;
else
@{
p->completed = 1;
if (WIFSIGNALED (status))
fprintf (stderr, "%d: Terminated by signal %d.\n",
(int) pid, WTERMSIG (p->status));
@}
return 0;
@}
fprintf (stderr, "No child process %d.\n", pid);
return -1;
@}
@end group
@group
else if (pid == 0 || errno == ECHILD)
/* @r{No processes ready to report.} */
return -1;
else @{
/* @r{Other weird errors.} */
perror ("waitpid");
return -1;
@}
@}
@end group
@group
/* @r{Check for processes that have status information available,}
@r{without blocking.} */
void
update_status (void)
@{
int status;
pid_t pid;
do
pid = waitpid (WAIT_ANY, &status, WUNTRACED|WNOHANG);
while (!mark_process_status (pid, status));
@}
@end group
@group
/* @r{Check for processes that have status information available,}
@r{blocking until all processes in the given job have reported.} */
void
wait_for_job (job *j)
@{
int status;
pid_t pid;
do
pid = waitpid (WAIT_ANY, &status, WUNTRACED);
while (!mark_process_status (pid, status)
&& !job_is_stopped (j)
&& !job_is_completed (j));
@}
@end group
@group
/* @r{Format information about job status for the user to look at.} */
void
format_job_info (job *j, const char *status)
@{
fprintf (stderr, "%ld (%s): %s\n", (long)j->pgid, status, j->command);
@}
@end group
@group
/* @r{Notify the user about stopped or terminated jobs.}
@r{Delete terminated jobs from the active job list.} */
void
do_job_notification (void)
@{
job *j, *jlast, *jnext;
process *p;
/* @r{Update status information for child processes.} */
update_status ();
jlast = NULL;
for (j = first_job; j; j = jnext)
@{
jnext = j->next;
/* @r{If all processes have completed, tell the user the job has}
@r{completed and delete it from the list of active jobs.} */
if (job_is_completed (j)) @{
format_job_info (j, "completed");
if (jlast)
jlast->next = jnext;
else
first_job = jnext;
free_job (j);
@}
/* @r{Notify the user about stopped jobs,}
@r{marking them so that we won't do this more than once.} */
else if (job_is_stopped (j) && !j->notified) @{
format_job_info (j, "stopped");
j->notified = 1;
jlast = j;
@}
/* @r{Don't say anything about jobs that are still running.} */
else
jlast = j;
@}
@}
@end group
@end smallexample
@node Continuing Stopped Jobs, Missing Pieces, Stopped and Terminated Jobs, Implementing a Shell
@subsection Continuing Stopped Jobs
@cindex stopped jobs, continuing
The shell can continue a stopped job by sending a @code{SIGCONT} signal
to its process group. If the job is being continued in the foreground,
the shell should first invoke @code{tcsetpgrp} to give the job access to
the terminal, and restore the saved terminal settings. After continuing
a job in the foreground, the shell should wait for the job to stop or
complete, as if the job had just been launched in the foreground.
The sample shell program handles both newly created and continued jobs
with the same pair of functions, @w{@code{put_job_in_foreground}} and
@w{@code{put_job_in_background}}. The definitions of these functions
were given in @ref{Foreground and Background}. When continuing a
stopped job, a nonzero value is passed as the @var{cont} argument to
ensure that the @code{SIGCONT} signal is sent and the terminal modes
reset, as appropriate.
This leaves only a function for updating the shell's internal bookkeeping
about the job being continued:
@smallexample
@group
/* @r{Mark a stopped job J as being running again.} */
void
mark_job_as_running (job *j)
@{
Process *p;
for (p = j->first_process; p; p = p->next)
p->stopped = 0;
j->notified = 0;
@}
@end group
@group
/* @r{Continue the job J.} */
void
continue_job (job *j, int foreground)
@{
mark_job_as_running (j);
if (foreground)
put_job_in_foreground (j, 1);
else
put_job_in_background (j, 1);
@}
@end group
@end smallexample
@node Missing Pieces, , Continuing Stopped Jobs, Implementing a Shell
@subsection The Missing Pieces
The code extracts for the sample shell included in this chapter are only
a part of the entire shell program. In particular, nothing at all has
been said about how @code{job} and @code{program} data structures are
allocated and initialized.
Most real shells provide a complex user interface that has support for
a command language; variables; abbreviations, substitutions, and pattern
matching on file names; and the like. All of this is far too complicated
to explain here! Instead, we have concentrated on showing how to
implement the core process creation and job control functions that can
be called from such a shell.
Here is a table summarizing the major entry points we have presented:
@table @code
@item void init_shell (void)
Initialize the shell's internal state. @xref{Initializing the
Shell}.
@item void launch_job (job *@var{j}, int @var{foreground})
Launch the job @var{j} as either a foreground or background job.
@xref{Launching Jobs}.
@item void do_job_notification (void)
Check for and report any jobs that have terminated or stopped. Can be
called synchronously or within a handler for @code{SIGCHLD} signals.
@xref{Stopped and Terminated Jobs}.
@item void continue_job (job *@var{j}, int @var{foreground})
Continue the job @var{j}. @xref{Continuing Stopped Jobs}.
@end table
Of course, a real shell would also want to provide other functions for
managing jobs. For example, it would be useful to have commands to list
all active jobs or to send a signal (such as @code{SIGKILL}) to a job.
@node Functions for Job Control, , Implementing a Shell, Job Control
@section Functions for Job Control
@cindex process group functions
@cindex job control functions
This section contains detailed descriptions of the functions relating
to job control.
@menu
* Identifying the Terminal:: Determining the controlling terminal's name.
* Process Group Functions:: Functions for manipulating process groups.
* Terminal Access Functions:: Functions for controlling terminal access.
@end menu
@node Identifying the Terminal, Process Group Functions, , Functions for Job Control
@subsection Identifying the Controlling Terminal
@cindex controlling terminal, determining
You can use the @code{ctermid} function to get a file name that you can
use to open the controlling terminal. In @theglibc{}, it returns
the same string all the time: @code{"/dev/tty"}. That is a special
``magic'' file name that refers to the controlling terminal of the
current process (if it has one). To find the name of the specific
terminal device, use @code{ttyname}; @pxref{Is It a Terminal}.
The function @code{ctermid} is declared in the header file
@file{stdio.h}.
@pindex stdio.h
@comment stdio.h
@comment POSIX.1
@deftypefun {char *} ctermid (char *@var{string})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This function is a stub by default; the actual implementation, for
@c posix systems, returns an internal buffer if passed a NULL string,
@c but the internal buffer is always set to /dev/tty.
The @code{ctermid} function returns a string containing the file name of
the controlling terminal for the current process. If @var{string} is
not a null pointer, it should be an array that can hold at least
@code{L_ctermid} characters; the string is returned in this array.
Otherwise, a pointer to a string in a static area is returned, which
might get overwritten on subsequent calls to this function.
An empty string is returned if the file name cannot be determined for
any reason. Even if a file name is returned, access to the file it
represents is not guaranteed.
@end deftypefun
@comment stdio.h
@comment POSIX.1
@deftypevr Macro int L_ctermid
The value of this macro is an integer constant expression that
represents the size of a string large enough to hold the file name
returned by @code{ctermid}.
@end deftypevr
See also the @code{isatty} and @code{ttyname} functions, in
@ref{Is It a Terminal}.
@node Process Group Functions, Terminal Access Functions, Identifying the Terminal, Functions for Job Control
@subsection Process Group Functions
Here are descriptions of the functions for manipulating process groups.
Your program should include the header files @file{sys/types.h} and
@file{unistd.h} to use these functions.
@pindex unistd.h
@pindex sys/types.h
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t setsid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is usually a direct syscall, but if a syscall is not available,
@c we use a stub, or Hurd- and BSD-specific implementations. The former
@c uses a mutex and a hurd critical section, and the latter issues a few
@c syscalls, so both seem safe, the locking on Hurd is safe because of
@c the critical section.
The @code{setsid} function creates a new session. The calling process
becomes the session leader, and is put in a new process group whose
process group ID is the same as the process ID of that process. There
are initially no other processes in the new process group, and no other
process groups in the new session.
This function also makes the calling process have no controlling terminal.
The @code{setsid} function returns the new process group ID of the
calling process if successful. A return value of @code{-1} indicates an
error. The following @code{errno} error conditions are defined for this
function:
@table @code
@item EPERM
The calling process is already a process group leader, or there is
already another process group around that has the same process group ID.
@end table
@end deftypefun
@comment unistd.h
@comment SVID
@deftypefun pid_t getsid (pid_t @var{pid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Stub or direct syscall, except on hurd, where it is equally safe.
The @code{getsid} function returns the process group ID of the session
leader of the specified process. If a @var{pid} is @code{0}, the
process group ID of the session leader of the current process is
returned.
In case of error @code{-1} is returned and @code{errno} is set. The
following @code{errno} error conditions are defined for this function:
@table @code
@item ESRCH
There is no process with the given process ID @var{pid}.
@item EPERM
The calling process and the process specified by @var{pid} are in
different sessions, and the implementation doesn't allow to access the
process group ID of the session leader of the process with ID @var{pid}
from the calling process.
@end table
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t getpgrp (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getpgrp} function returns the process group ID of
the calling process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int getpgid (pid_t @var{pid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Stub or direct syscall, except on hurd, where it is equally safe.
The @code{getpgid} function
returns the process group ID of the process @var{pid}. You can supply a
value of @code{0} for the @var{pid} argument to get information about
the calling process.
In case of error @code{-1} is returned and @code{errno} is set. The
following @code{errno} error conditions are defined for this function:
@table @code
@item ESRCH
There is no process with the given process ID @var{pid}.
The calling process and the process specified by @var{pid} are in
different sessions, and the implementation doesn't allow to access the
process group ID of the process with ID @var{pid} from the calling
process.
@end table
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int setpgid (pid_t @var{pid}, pid_t @var{pgid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Stub or direct syscall, except on hurd, where it is equally safe.
The @code{setpgid} function puts the process @var{pid} into the process
group @var{pgid}. As a special case, either @var{pid} or @var{pgid} can
be zero to indicate the process ID of the calling process.
This function fails on a system that does not support job control.
@xref{Job Control is Optional}, for more information.
If the operation is successful, @code{setpgid} returns zero. Otherwise
it returns @code{-1}. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EACCES
The child process named by @var{pid} has executed an @code{exec}
function since it was forked.
@item EINVAL
The value of the @var{pgid} is not valid.
@item ENOSYS
The system doesn't support job control.
@item EPERM
The process indicated by the @var{pid} argument is a session leader,
or is not in the same session as the calling process, or the value of
the @var{pgid} argument doesn't match a process group ID in the same
session as the calling process.
@item ESRCH
The process indicated by the @var{pid} argument is not the calling
process or a child of the calling process.
@end table
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun int setpgrp (pid_t @var{pid}, pid_t @var{pgid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall or setpgid wrapper.
This is the BSD Unix name for @code{setpgid}. Both functions do exactly
the same thing.
@end deftypefun
@node Terminal Access Functions, , Process Group Functions, Functions for Job Control
@subsection Functions for Controlling Terminal Access
These are the functions for reading or setting the foreground
process group of a terminal. You should include the header files
@file{sys/types.h} and @file{unistd.h} in your application to use
these functions.
@pindex unistd.h
@pindex sys/types.h
Although these functions take a file descriptor argument to specify
the terminal device, the foreground job is associated with the terminal
file itself and not a particular open file descriptor.
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t tcgetpgrp (int @var{filedes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Stub, or ioctl on BSD and GNU/Linux.
This function returns the process group ID of the foreground process
group associated with the terminal open on descriptor @var{filedes}.
If there is no foreground process group, the return value is a number
greater than @code{1} that does not match the process group ID of any
existing process group. This can happen if all of the processes in the
job that was formerly the foreground job have terminated, and no other
job has yet been moved into the foreground.
In case of an error, a value of @code{-1} is returned. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOSYS
The system doesn't support job control.
@item ENOTTY
The terminal file associated with the @var{filedes} argument isn't the
controlling terminal of the calling process.
@end table
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int tcsetpgrp (int @var{filedes}, pid_t @var{pgid})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Stub, or ioctl on BSD and GNU/Linux.
This function is used to set a terminal's foreground process group ID.
The argument @var{filedes} is a descriptor which specifies the terminal;
@var{pgid} specifies the process group. The calling process must be a
member of the same session as @var{pgid} and must have the same
controlling terminal.
For terminal access purposes, this function is treated as output. If it
is called from a background process on its controlling terminal,
normally all processes in the process group are sent a @code{SIGTTOU}
signal. The exception is if the calling process itself is ignoring or
blocking @code{SIGTTOU} signals, in which case the operation is
performed and no signal is sent.
If successful, @code{tcsetpgrp} returns @code{0}. A return value of
@code{-1} indicates an error. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The @var{pgid} argument is not valid.
@item ENOSYS
The system doesn't support job control.
@item ENOTTY
The @var{filedes} isn't the controlling terminal of the calling process.
@item EPERM
The @var{pgid} isn't a process group in the same session as the calling
process.
@end table
@end deftypefun
@comment termios.h
@comment Unix98
@deftypefun pid_t tcgetsid (int @var{fildes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Ioctl call, if available, or tcgetpgrp followed by getsid.
This function is used to obtain the process group ID of the session
for which the terminal specified by @var{fildes} is the controlling terminal.
If the call is successful the group ID is returned. Otherwise the
return value is @code{(pid_t) -1} and the global variable @var{errno}
is set to the following value:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOTTY
The calling process does not have a controlling terminal, or the file
is not the controlling terminal.
@end table
@end deftypefun
glibc-doc-reference-2.19.orig/manual/terminal.texi 0000664 0001750 0001750 00000244135 12275120646 022276 0 ustar adconrad adconrad @node Low-Level Terminal Interface, Syslog, Sockets, Top
@c %MENU% How to change the characteristics of a terminal device
@chapter Low-Level Terminal Interface
This chapter describes functions that are specific to terminal devices.
You can use these functions to do things like turn off input echoing;
set serial line characteristics such as line speed and flow control; and
change which characters are used for end-of-file, command-line editing,
sending signals, and similar control functions.
Most of the functions in this chapter operate on file descriptors.
@xref{Low-Level I/O}, for more information about what a file
descriptor is and how to open a file descriptor for a terminal device.
@menu
* Is It a Terminal:: How to determine if a file is a terminal
device, and what its name is.
* I/O Queues:: About flow control and typeahead.
* Canonical or Not:: Two basic styles of input processing.
* Terminal Modes:: How to examine and modify flags controlling
details of terminal I/O: echoing,
signals, editing. Posix.
* BSD Terminal Modes:: BSD compatible terminal mode setting
* Line Control:: Sending break sequences, clearing
terminal buffers @dots{}
* Noncanon Example:: How to read single characters without echo.
* Pseudo-Terminals:: How to open a pseudo-terminal.
@end menu
@node Is It a Terminal
@section Identifying Terminals
@cindex terminal identification
@cindex identifying terminals
The functions described in this chapter only work on files that
correspond to terminal devices. You can find out whether a file
descriptor is associated with a terminal by using the @code{isatty}
function.
@pindex unistd.h
Prototypes for the functions in this section are declared in the header
file @file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun int isatty (int @var{filedes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c isatty ok
@c tcgetattr dup ok
This function returns @code{1} if @var{filedes} is a file descriptor
associated with an open terminal device, and @math{0} otherwise.
@end deftypefun
If a file descriptor is associated with a terminal, you can get its
associated file name using the @code{ttyname} function. See also the
@code{ctermid} function, described in @ref{Identifying the Terminal}.
@comment unistd.h
@comment POSIX.1
@deftypefun {char *} ttyname (int @var{filedes})
@safety{@prelim{}@mtunsafe{@mtasurace{:ttyname}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c ttyname @mtasurace:ttyname @ascuheap @asulock @aculock @acsmem @acsfd
@c isatty dup ok
@c fstat dup ok
@c memcpy dup ok
@c getttyname @mtasurace:ttyname @ascuheap @asulock @aculock @acsmem @acsfd
@c opendir @ascuheap @acsmem @acsfd
@c readdir ok [protected by exclusive access]
@c strcmp dup ok
@c free dup @asulock @aculock @acsfd @acsmem
@c malloc dup @asulock @aculock @acsfd @acsmem
@c closedir @ascuheap @acsmem @acsfd
@c mempcpy dup ok
@c stat dup ok
If the file descriptor @var{filedes} is associated with a terminal
device, the @code{ttyname} function returns a pointer to a
statically-allocated, null-terminated string containing the file name of
the terminal file. The value is a null pointer if the file descriptor
isn't associated with a terminal, or the file name cannot be determined.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int ttyname_r (int @var{filedes}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
@c ttyname_r @ascuheap @acsmem @acsfd
@c isatty dup ok
@c fstat dup ok
@c memcpy dup ok
@c getttyname_r @ascuheap @acsmem @acsfd
@c opendir @ascuheap @acsmem @acsfd
@c readdir ok [protected by exclusive access]
@c strcmp dup ok
@c closedir @ascuheap @acsmem @acsfd
@c stpncpy dup ok
@c stat dup ok
The @code{ttyname_r} function is similar to the @code{ttyname} function
except that it places its result into the user-specified buffer starting
at @var{buf} with length @var{len}.
The normal return value from @code{ttyname_r} is @math{0}. Otherwise an
error number is returned to indicate the error. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal.
@item ERANGE
The buffer length @var{len} is too small to store the string to be
returned.
@end table
@end deftypefun
@node I/O Queues
@section I/O Queues
Many of the remaining functions in this section refer to the input and
output queues of a terminal device. These queues implement a form of
buffering @emph{within the kernel} independent of the buffering
implemented by I/O streams (@pxref{I/O on Streams}).
@cindex terminal input queue
@cindex typeahead buffer
The @dfn{terminal input queue} is also sometimes referred to as its
@dfn{typeahead buffer}. It holds the characters that have been received
from the terminal but not yet read by any process.
The size of the input queue is described by the @code{MAX_INPUT} and
@w{@code{_POSIX_MAX_INPUT}} parameters; see @ref{Limits for Files}. You
are guaranteed a queue size of at least @code{MAX_INPUT}, but the queue
might be larger, and might even dynamically change size. If input flow
control is enabled by setting the @code{IXOFF} input mode bit
(@pxref{Input Modes}), the terminal driver transmits STOP and START
characters to the terminal when necessary to prevent the queue from
overflowing. Otherwise, input may be lost if it comes in too fast from
the terminal. In canonical mode, all input stays in the queue until a
newline character is received, so the terminal input queue can fill up
when you type a very long line. @xref{Canonical or Not}.
@cindex terminal output queue
The @dfn{terminal output queue} is like the input queue, but for output;
it contains characters that have been written by processes, but not yet
transmitted to the terminal. If output flow control is enabled by
setting the @code{IXON} input mode bit (@pxref{Input Modes}), the
terminal driver obeys START and STOP characters sent by the terminal to
stop and restart transmission of output.
@dfn{Clearing} the terminal input queue means discarding any characters
that have been received but not yet read. Similarly, clearing the
terminal output queue means discarding any characters that have been
written but not yet transmitted.
@node Canonical or Not
@section Two Styles of Input: Canonical or Not
POSIX systems support two basic modes of input: canonical and
noncanonical.
@cindex canonical input processing
In @dfn{canonical input processing} mode, terminal input is processed in
lines terminated by newline (@code{'\n'}), EOF, or EOL characters. No
input can be read until an entire line has been typed by the user, and
the @code{read} function (@pxref{I/O Primitives}) returns at most a
single line of input, no matter how many bytes are requested.
In canonical input mode, the operating system provides input editing
facilities: some characters are interpreted specially to perform editing
operations within the current line of text, such as ERASE and KILL.
@xref{Editing Characters}.
The constants @code{_POSIX_MAX_CANON} and @code{MAX_CANON} parameterize
the maximum number of bytes which may appear in a single line of
canonical input. @xref{Limits for Files}. You are guaranteed a maximum
line length of at least @code{MAX_CANON} bytes, but the maximum might be
larger, and might even dynamically change size.
@cindex noncanonical input processing
In @dfn{noncanonical input processing} mode, characters are not grouped
into lines, and ERASE and KILL processing is not performed. The
granularity with which bytes are read in noncanonical input mode is
controlled by the MIN and TIME settings. @xref{Noncanonical Input}.
Most programs use canonical input mode, because this gives the user a
way to edit input line by line. The usual reason to use noncanonical
mode is when the program accepts single-character commands or provides
its own editing facilities.
The choice of canonical or noncanonical input is controlled by the
@code{ICANON} flag in the @code{c_lflag} member of @code{struct termios}.
@xref{Local Modes}.
@node Terminal Modes
@section Terminal Modes
@pindex termios.h
This section describes the various terminal attributes that control how
input and output are done. The functions, data structures, and symbolic
constants are all declared in the header file @file{termios.h}.
Don't confuse terminal attributes with file attributes. A device special
file which is associated with a terminal has file attributes as described
in @ref{File Attributes}. These are unrelated to the attributes of the
terminal device itself, which are discussed in this section.
@menu
* Mode Data Types:: The data type @code{struct termios} and
related types.
* Mode Functions:: Functions to read and set the terminal
attributes.
* Setting Modes:: The right way to set terminal attributes
reliably.
* Input Modes:: Flags controlling low-level input handling.
* Output Modes:: Flags controlling low-level output handling.
* Control Modes:: Flags controlling serial port behavior.
* Local Modes:: Flags controlling high-level input handling.
* Line Speed:: How to read and set the terminal line speed.
* Special Characters:: Characters that have special effects,
and how to change them.
* Noncanonical Input:: Controlling how long to wait for input.
@end menu
@node Mode Data Types
@subsection Terminal Mode Data Types
@cindex terminal mode data types
The entire collection of attributes of a terminal is stored in a
structure of type @code{struct termios}. This structure is used
with the functions @code{tcgetattr} and @code{tcsetattr} to read
and set the attributes.
@comment termios.h
@comment POSIX.1
@deftp {Data Type} {struct termios}
Structure that records all the I/O attributes of a terminal. The
structure includes at least the following members:
@table @code
@item tcflag_t c_iflag
A bit mask specifying flags for input modes; see @ref{Input Modes}.
@item tcflag_t c_oflag
A bit mask specifying flags for output modes; see @ref{Output Modes}.
@item tcflag_t c_cflag
A bit mask specifying flags for control modes; see @ref{Control Modes}.
@item tcflag_t c_lflag
A bit mask specifying flags for local modes; see @ref{Local Modes}.
@item cc_t c_cc[NCCS]
An array specifying which characters are associated with various
control functions; see @ref{Special Characters}.
@end table
The @code{struct termios} structure also contains members which
encode input and output transmission speeds, but the representation is
not specified. @xref{Line Speed}, for how to examine and store the
speed values.
@end deftp
The following sections describe the details of the members of the
@code{struct termios} structure.
@comment termios.h
@comment POSIX.1
@deftp {Data Type} tcflag_t
This is an unsigned integer type used to represent the various
bit masks for terminal flags.
@end deftp
@comment termios.h
@comment POSIX.1
@deftp {Data Type} cc_t
This is an unsigned integer type used to represent characters associated
with various terminal control functions.
@end deftp
@comment termios.h
@comment POSIX.1
@deftypevr Macro int NCCS
The value of this macro is the number of elements in the @code{c_cc}
array.
@end deftypevr
@node Mode Functions
@subsection Terminal Mode Functions
@cindex terminal mode functions
@comment termios.h
@comment POSIX.1
@deftypefun int tcgetattr (int @var{filedes}, struct termios *@var{termios-p})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Converting the kernel-returned termios data structure to the userland
@c format does not ensure atomic or consistent writing.
This function is used to examine the attributes of the terminal
device with file descriptor @var{filedes}. The attributes are returned
in the structure that @var{termios-p} points to.
If successful, @code{tcgetattr} returns @math{0}. A return value of @math{-1}
indicates an error. The following @code{errno} error conditions are
defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal.
@end table
@end deftypefun
@comment termios.h
@comment POSIX.1
@deftypefun int tcsetattr (int @var{filedes}, int @var{when}, const struct termios *@var{termios-p})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Converting the incoming termios data structure to the kernel format
@c does not ensure atomic or consistent reading.
This function sets the attributes of the terminal device with file
descriptor @var{filedes}. The new attributes are taken from the
structure that @var{termios-p} points to.
The @var{when} argument specifies how to deal with input and output
already queued. It can be one of the following values:
@table @code
@comment termios.h
@comment POSIX.1
@item TCSANOW
@vindex TCSANOW
Make the change immediately.
@comment termios.h
@comment POSIX.1
@item TCSADRAIN
@vindex TCSADRAIN
Make the change after waiting until all queued output has been written.
You should usually use this option when changing parameters that affect
output.
@comment termios.h
@comment POSIX.1
@item TCSAFLUSH
@vindex TCSAFLUSH
This is like @code{TCSADRAIN}, but also discards any queued input.
@comment termios.h
@comment BSD
@item TCSASOFT
@vindex TCSASOFT
This is a flag bit that you can add to any of the above alternatives.
Its meaning is to inhibit alteration of the state of the terminal
hardware. It is a BSD extension; it is only supported on BSD systems
and @gnuhurdsystems{}.
Using @code{TCSASOFT} is exactly the same as setting the @code{CIGNORE}
bit in the @code{c_cflag} member of the structure @var{termios-p} points
to. @xref{Control Modes}, for a description of @code{CIGNORE}.
@end table
If this function is called from a background process on its controlling
terminal, normally all processes in the process group are sent a
@code{SIGTTOU} signal, in the same way as if the process were trying to
write to the terminal. The exception is if the calling process itself
is ignoring or blocking @code{SIGTTOU} signals, in which case the
operation is performed and no signal is sent. @xref{Job Control}.
If successful, @code{tcsetattr} returns @math{0}. A return value of
@math{-1} indicates an error. The following @code{errno} error
conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal.
@item EINVAL
Either the value of the @code{when} argument is not valid, or there is
something wrong with the data in the @var{termios-p} argument.
@end table
@end deftypefun
Although @code{tcgetattr} and @code{tcsetattr} specify the terminal
device with a file descriptor, the attributes are those of the terminal
device itself and not of the file descriptor. This means that the
effects of changing terminal attributes are persistent; if another
process opens the terminal file later on, it will see the changed
attributes even though it doesn't have anything to do with the open file
descriptor you originally specified in changing the attributes.
Similarly, if a single process has multiple or duplicated file
descriptors for the same terminal device, changing the terminal
attributes affects input and output to all of these file
descriptors. This means, for example, that you can't open one file
descriptor or stream to read from a terminal in the normal
line-buffered, echoed mode; and simultaneously have another file
descriptor for the same terminal that you use to read from it in
single-character, non-echoed mode. Instead, you have to explicitly
switch the terminal back and forth between the two modes.
@node Setting Modes
@subsection Setting Terminal Modes Properly
When you set terminal modes, you should call @code{tcgetattr} first to
get the current modes of the particular terminal device, modify only
those modes that you are really interested in, and store the result with
@code{tcsetattr}.
It's a bad idea to simply initialize a @code{struct termios} structure
to a chosen set of attributes and pass it directly to @code{tcsetattr}.
Your program may be run years from now, on systems that support members
not documented in this manual. The way to avoid setting these members
to unreasonable values is to avoid changing them.
What's more, different terminal devices may require different mode
settings in order to function properly. So you should avoid blindly
copying attributes from one terminal device to another.
When a member contains a collection of independent flags, as the
@code{c_iflag}, @code{c_oflag} and @code{c_cflag} members do, even
setting the entire member is a bad idea, because particular operating
systems have their own flags. Instead, you should start with the
current value of the member and alter only the flags whose values matter
in your program, leaving any other flags unchanged.
Here is an example of how to set one flag (@code{ISTRIP}) in the
@code{struct termios} structure while properly preserving all the other
data in the structure:
@smallexample
@group
int
set_istrip (int desc, int value)
@{
struct termios settings;
int result;
@end group
@group
result = tcgetattr (desc, &settings);
if (result < 0)
@{
perror ("error in tcgetattr");
return 0;
@}
@end group
@group
settings.c_iflag &= ~ISTRIP;
if (value)
settings.c_iflag |= ISTRIP;
@end group
@group
result = tcsetattr (desc, TCSANOW, &settings);
if (result < 0)
@{
perror ("error in tcsetattr");
return 0;
@}
return 1;
@}
@end group
@end smallexample
@node Input Modes
@subsection Input Modes
This section describes the terminal attribute flags that control
fairly low-level aspects of input processing: handling of parity errors,
break signals, flow control, and @key{RET} and @key{LFD} characters.
All of these flags are bits in the @code{c_iflag} member of the
@code{struct termios} structure. The member is an integer, and you
change flags using the operators @code{&}, @code{|} and @code{^}. Don't
try to specify the entire value for @code{c_iflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t INPCK
@cindex parity checking
If this bit is set, input parity checking is enabled. If it is not set,
no checking at all is done for parity errors on input; the
characters are simply passed through to the application.
Parity checking on input processing is independent of whether parity
detection and generation on the underlying terminal hardware is enabled;
see @ref{Control Modes}. For example, you could clear the @code{INPCK}
input mode flag and set the @code{PARENB} control mode flag to ignore
parity errors on input, but still generate parity on output.
If this bit is set, what happens when a parity error is detected depends
on whether the @code{IGNPAR} or @code{PARMRK} bits are set. If neither
of these bits are set, a byte with a parity error is passed to the
application as a @code{'\0'} character.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNPAR
If this bit is set, any byte with a framing or parity error is ignored.
This is only useful if @code{INPCK} is also set.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARMRK
If this bit is set, input bytes with parity or framing errors are marked
when passed to the program. This bit is meaningful only when
@code{INPCK} is set and @code{IGNPAR} is not set.
The way erroneous bytes are marked is with two preceding bytes,
@code{377} and @code{0}. Thus, the program actually reads three bytes
for one erroneous byte received from the terminal.
If a valid byte has the value @code{0377}, and @code{ISTRIP} (see below)
is not set, the program might confuse it with the prefix that marks a
parity error. So a valid byte @code{0377} is passed to the program as
two bytes, @code{0377} @code{0377}, in this case.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ISTRIP
If this bit is set, valid input bytes are stripped to seven bits;
otherwise, all eight bits are available for programs to read.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNBRK
If this bit is set, break conditions are ignored.
@cindex break condition, detecting
A @dfn{break condition} is defined in the context of asynchronous
serial data transmission as a series of zero-value bits longer than a
single byte.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t BRKINT
If this bit is set and @code{IGNBRK} is not set, a break condition
clears the terminal input and output queues and raises a @code{SIGINT}
signal for the foreground process group associated with the terminal.
If neither @code{BRKINT} nor @code{IGNBRK} are set, a break condition is
passed to the application as a single @code{'\0'} character if
@code{PARMRK} is not set, or otherwise as a three-character sequence
@code{'\377'}, @code{'\0'}, @code{'\0'}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNCR
If this bit is set, carriage return characters (@code{'\r'}) are
discarded on input. Discarding carriage return may be useful on
terminals that send both carriage return and linefeed when you type the
@key{RET} key.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ICRNL
If this bit is set and @code{IGNCR} is not set, carriage return characters
(@code{'\r'}) received as input are passed to the application as newline
characters (@code{'\n'}).
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t INLCR
If this bit is set, newline characters (@code{'\n'}) received as input
are passed to the application as carriage return characters (@code{'\r'}).
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IXOFF
If this bit is set, start/stop control on input is enabled. In other
words, the computer sends STOP and START characters as necessary to
prevent input from coming in faster than programs are reading it. The
idea is that the actual terminal hardware that is generating the input
data responds to a STOP character by suspending transmission, and to a
START character by resuming transmission. @xref{Start/Stop Characters}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IXON
If this bit is set, start/stop control on output is enabled. In other
words, if the computer receives a STOP character, it suspends output
until a START character is received. In this case, the STOP and START
characters are never passed to the application program. If this bit is
not set, then START and STOP can be read as ordinary characters.
@xref{Start/Stop Characters}.
@c !!! mention this interferes with using C-s and C-q for programs like emacs
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t IXANY
If this bit is set, any input character restarts output when output has
been suspended with the STOP character. Otherwise, only the START
character restarts output.
This is a BSD extension; it exists only on BSD systems and
@gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t IMAXBEL
If this bit is set, then filling up the terminal input buffer sends a
BEL character (code @code{007}) to the terminal to ring the bell.
This is a BSD extension.
@end deftypevr
@node Output Modes
@subsection Output Modes
This section describes the terminal flags and fields that control how
output characters are translated and padded for display. All of these
are contained in the @code{c_oflag} member of the @w{@code{struct termios}}
structure.
The @code{c_oflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}. Don't
try to specify the entire value for @code{c_oflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t OPOST
If this bit is set, output data is processed in some unspecified way so
that it is displayed appropriately on the terminal device. This
typically includes mapping newline characters (@code{'\n'}) onto
carriage return and linefeed pairs.
If this bit isn't set, the characters are transmitted as-is.
@end deftypevr
The following three bits are effective only if @code{OPOST} is set.
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ONLCR
If this bit is set, convert the newline character on output into a pair
of characters, carriage return followed by linefeed.
@end deftypevr
@comment termios.h (optional)
@comment BSD
@deftypevr Macro tcflag_t OXTABS
If this bit is set, convert tab characters on output into the appropriate
number of spaces to emulate a tab stop every eight columns. This bit
exists only on BSD systems and @gnuhurdsystems{}; on
@gnulinuxsystems{} it is available as @code{XTABS}.
@end deftypevr
@comment termios.h (optional)
@comment BSD
@deftypevr Macro tcflag_t ONOEOT
If this bit is set, discard @kbd{C-d} characters (code @code{004}) on
output. These characters cause many dial-up terminals to disconnect.
This bit exists only on BSD systems and @gnuhurdsystems{}.
@end deftypevr
@node Control Modes
@subsection Control Modes
This section describes the terminal flags and fields that control
parameters usually associated with asynchronous serial data
transmission. These flags may not make sense for other kinds of
terminal ports (such as a network connection pseudo-terminal). All of
these are contained in the @code{c_cflag} member of the @code{struct
termios} structure.
The @code{c_cflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}. Don't
try to specify the entire value for @code{c_cflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CLOCAL
If this bit is set, it indicates that the terminal is connected
``locally'' and that the modem status lines (such as carrier detect)
should be ignored.
@cindex modem status lines
@cindex carrier detect
On many systems if this bit is not set and you call @code{open} without
the @code{O_NONBLOCK} flag set, @code{open} blocks until a modem
connection is established.
If this bit is not set and a modem disconnect is detected, a
@code{SIGHUP} signal is sent to the controlling process group for the
terminal (if it has one). Normally, this causes the process to exit;
see @ref{Signal Handling}. Reading from the terminal after a disconnect
causes an end-of-file condition, and writing causes an @code{EIO} error
to be returned. The terminal device must be closed and reopened to
clear the condition.
@cindex modem disconnect
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t HUPCL
If this bit is set, a modem disconnect is generated when all processes
that have the terminal device open have either closed the file or exited.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CREAD
If this bit is set, input can be read from the terminal. Otherwise,
input is discarded when it arrives.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CSTOPB
If this bit is set, two stop bits are used. Otherwise, only one stop bit
is used.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARENB
If this bit is set, generation and detection of a parity bit are enabled.
@xref{Input Modes}, for information on how input parity errors are handled.
If this bit is not set, no parity bit is added to output characters, and
input characters are not checked for correct parity.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARODD
This bit is only useful if @code{PARENB} is set. If @code{PARODD} is set,
odd parity is used, otherwise even parity is used.
@end deftypevr
The control mode flags also includes a field for the number of bits per
character. You can use the @code{CSIZE} macro as a mask to extract the
value, like this: @code{settings.c_cflag & CSIZE}.
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CSIZE
This is a mask for the number of bits per character.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS5
This specifies five bits per byte.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS6
This specifies six bits per byte.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS7
This specifies seven bits per byte.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS8
This specifies eight bits per byte.
@end deftypevr
The following four bits are BSD extensions; these exist only on BSD
systems and @gnuhurdsystems{}.
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CCTS_OFLOW
If this bit is set, enable flow control of output based on the CTS wire
(RS232 protocol).
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CRTS_IFLOW
If this bit is set, enable flow control of input based on the RTS wire
(RS232 protocol).
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t MDMBUF
If this bit is set, enable carrier-based flow control of output.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CIGNORE
If this bit is set, it says to ignore the control modes and line speed
values entirely. This is only meaningful in a call to @code{tcsetattr}.
The @code{c_cflag} member and the line speed values returned by
@code{cfgetispeed} and @code{cfgetospeed} will be unaffected by the
call. @code{CIGNORE} is useful if you want to set all the software
modes in the other members, but leave the hardware details in
@code{c_cflag} unchanged. (This is how the @code{TCSASOFT} flag to
@code{tcsettattr} works.)
This bit is never set in the structure filled in by @code{tcgetattr}.
@end deftypevr
@node Local Modes
@subsection Local Modes
This section describes the flags for the @code{c_lflag} member of the
@code{struct termios} structure. These flags generally control
higher-level aspects of input processing than the input modes flags
described in @ref{Input Modes}, such as echoing, signals, and the choice
of canonical or noncanonical input.
The @code{c_lflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}. Don't
try to specify the entire value for @code{c_lflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ICANON
This bit, if set, enables canonical input processing mode. Otherwise,
input is processed in noncanonical mode. @xref{Canonical or Not}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHO
If this bit is set, echoing of input characters back to the terminal
is enabled.
@cindex echo of terminal input
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHOE
If this bit is set, echoing indicates erasure of input with the ERASE
character by erasing the last character in the current line from the
screen. Otherwise, the character erased is re-echoed to show what has
happened (suitable for a printing terminal).
This bit only controls the display behavior; the @code{ICANON} bit by
itself controls actual recognition of the ERASE character and erasure of
input, without which @code{ECHOE} is simply irrelevant.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOPRT
This bit is like @code{ECHOE}, enables display of the ERASE character in
a way that is geared to a hardcopy terminal. When you type the ERASE
character, a @samp{\} character is printed followed by the first
character erased. Typing the ERASE character again just prints the next
character erased. Then, the next time you type a normal character, a
@samp{/} character is printed before the character echoes.
This is a BSD extension, and exists only in BSD systems and
@gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHOK
This bit enables special display of the KILL character by moving to a
new line after echoing the KILL character normally. The behavior of
@code{ECHOKE} (below) is nicer to look at.
If this bit is not set, the KILL character echoes just as it would if it
were not the KILL character. Then it is up to the user to remember that
the KILL character has erased the preceding input; there is no
indication of this on the screen.
This bit only controls the display behavior; the @code{ICANON} bit by
itself controls actual recognition of the KILL character and erasure of
input, without which @code{ECHOK} is simply irrelevant.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOKE
This bit is similar to @code{ECHOK}. It enables special display of the
KILL character by erasing on the screen the entire line that has been
killed. This is a BSD extension, and exists only in BSD systems and
@gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHONL
If this bit is set and the @code{ICANON} bit is also set, then the
newline (@code{'\n'}) character is echoed even if the @code{ECHO} bit
is not set.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOCTL
If this bit is set and the @code{ECHO} bit is also set, echo control
characters with @samp{^} followed by the corresponding text character.
Thus, control-A echoes as @samp{^A}. This is usually the preferred mode
for interactive input, because echoing a control character back to the
terminal could have some undesired effect on the terminal.
This is a BSD extension, and exists only in BSD systems and
@gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ISIG
This bit controls whether the INTR, QUIT, and SUSP characters are
recognized. The functions associated with these characters are performed
if and only if this bit is set. Being in canonical or noncanonical
input mode has no affect on the interpretation of these characters.
You should use caution when disabling recognition of these characters.
Programs that cannot be interrupted interactively are very
user-unfriendly. If you clear this bit, your program should provide
some alternate interface that allows the user to interactively send the
signals associated with these characters, or to escape from the program.
@cindex interactive signals, from terminal
@xref{Signal Characters}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IEXTEN
POSIX.1 gives @code{IEXTEN} implementation-defined meaning,
so you cannot rely on this interpretation on all systems.
On BSD systems and @gnulinuxhurdsystems{}, it enables the LNEXT and
DISCARD characters.
@xref{Other Special}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t NOFLSH
Normally, the INTR, QUIT, and SUSP characters cause input and output
queues for the terminal to be cleared. If this bit is set, the queues
are not cleared.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t TOSTOP
If this bit is set and the system supports job control, then
@code{SIGTTOU} signals are generated by background processes that
attempt to write to the terminal. @xref{Access to the Terminal}.
@end deftypevr
The following bits are BSD extensions; they exist only on BSD systems
and @gnuhurdsystems{}.
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ALTWERASE
This bit determines how far the WERASE character should erase. The
WERASE character erases back to the beginning of a word; the question
is, where do words begin?
If this bit is clear, then the beginning of a word is a nonwhitespace
character following a whitespace character. If the bit is set, then the
beginning of a word is an alphanumeric character or underscore following
a character which is none of those.
@xref{Editing Characters}, for more information about the WERASE character.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t FLUSHO
This is the bit that toggles when the user types the DISCARD character.
While this bit is set, all output is discarded. @xref{Other Special}.
@end deftypevr
@comment termios.h (optional)
@comment BSD
@deftypevr Macro tcflag_t NOKERNINFO
Setting this bit disables handling of the STATUS character.
@xref{Other Special}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t PENDIN
If this bit is set, it indicates that there is a line of input that
needs to be reprinted. Typing the REPRINT character sets this bit; the
bit remains set until reprinting is finished. @xref{Editing Characters}.
@end deftypevr
@c EXTPROC is too obscure to document now. --roland
@node Line Speed
@subsection Line Speed
@cindex line speed
@cindex baud rate
@cindex terminal line speed
@cindex terminal line speed
The terminal line speed tells the computer how fast to read and write
data on the terminal.
If the terminal is connected to a real serial line, the terminal speed
you specify actually controls the line---if it doesn't match the
terminal's own idea of the speed, communication does not work. Real
serial ports accept only certain standard speeds. Also, particular
hardware may not support even all the standard speeds. Specifying a
speed of zero hangs up a dialup connection and turns off modem control
signals.
If the terminal is not a real serial line (for example, if it is a
network connection), then the line speed won't really affect data
transmission speed, but some programs will use it to determine the
amount of padding needed. It's best to specify a line speed value that
matches the actual speed of the actual terminal, but you can safely
experiment with different values to vary the amount of padding.
There are actually two line speeds for each terminal, one for input and
one for output. You can set them independently, but most often
terminals use the same speed for both directions.
The speed values are stored in the @code{struct termios} structure, but
don't try to access them in the @code{struct termios} structure
directly. Instead, you should use the following functions to read and
store them:
@comment termios.h
@comment POSIX.1
@deftypefun speed_t cfgetospeed (const struct termios *@var{termios-p})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct access to a single termios field, except on Linux, where
@c multiple accesses may take place. No worries either way, callers
@c must ensure mutual exclusion on such non-opaque types.
This function returns the output line speed stored in the structure
@code{*@var{termios-p}}.
@end deftypefun
@comment termios.h
@comment POSIX.1
@deftypefun speed_t cfgetispeed (const struct termios *@var{termios-p})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function returns the input line speed stored in the structure
@code{*@var{termios-p}}.
@end deftypefun
@comment termios.h
@comment POSIX.1
@deftypefun int cfsetospeed (struct termios *@var{termios-p}, speed_t @var{speed})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function stores @var{speed} in @code{*@var{termios-p}} as the output
speed. The normal return value is @math{0}; a value of @math{-1}
indicates an error. If @var{speed} is not a speed, @code{cfsetospeed}
returns @math{-1}.
@end deftypefun
@comment termios.h
@comment POSIX.1
@deftypefun int cfsetispeed (struct termios *@var{termios-p}, speed_t @var{speed})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function stores @var{speed} in @code{*@var{termios-p}} as the input
speed. The normal return value is @math{0}; a value of @math{-1}
indicates an error. If @var{speed} is not a speed, @code{cfsetospeed}
returns @math{-1}.
@end deftypefun
@comment termios.h
@comment BSD
@deftypefun int cfsetspeed (struct termios *@var{termios-p}, speed_t @var{speed})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c There's no guarantee that the two calls are atomic, but since this is
@c not an opaque type, callers ought to ensure mutual exclusion to the
@c termios object.
@c cfsetspeed ok
@c cfsetispeed ok
@c cfsetospeed ok
This function stores @var{speed} in @code{*@var{termios-p}} as both the
input and output speeds. The normal return value is @math{0}; a value
of @math{-1} indicates an error. If @var{speed} is not a speed,
@code{cfsetspeed} returns @math{-1}. This function is an extension in
4.4 BSD.
@end deftypefun
@comment termios.h
@comment POSIX.1
@deftp {Data Type} speed_t
The @code{speed_t} type is an unsigned integer data type used to
represent line speeds.
@end deftp
The functions @code{cfsetospeed} and @code{cfsetispeed} report errors
only for speed values that the system simply cannot handle. If you
specify a speed value that is basically acceptable, then those functions
will succeed. But they do not check that a particular hardware device
can actually support the specified speeds---in fact, they don't know
which device you plan to set the speed for. If you use @code{tcsetattr}
to set the speed of a particular device to a value that it cannot
handle, @code{tcsetattr} returns @math{-1}.
@strong{Portability note:} In @theglibc{}, the functions above
accept speeds measured in bits per second as input, and return speed
values measured in bits per second. Other libraries require speeds to
be indicated by special codes. For POSIX.1 portability, you must use
one of the following symbols to represent the speed; their precise
numeric values are system-dependent, but each name has a fixed meaning:
@code{B110} stands for 110 bps, @code{B300} for 300 bps, and so on.
There is no portable way to represent any speed but these, but these are
the only speeds that typical serial lines can support.
@comment termios.h
@comment POSIX.1
@vindex B0
@comment termios.h
@comment POSIX.1
@vindex B50
@comment termios.h
@comment POSIX.1
@vindex B75
@comment termios.h
@comment POSIX.1
@vindex B110
@comment termios.h
@comment POSIX.1
@vindex B134
@comment termios.h
@comment POSIX.1
@vindex B150
@comment termios.h
@comment POSIX.1
@vindex B200
@comment termios.h
@comment POSIX.1
@vindex B300
@comment termios.h
@comment POSIX.1
@vindex B600
@comment termios.h
@comment POSIX.1
@vindex B1200
@comment termios.h
@comment POSIX.1
@vindex B1800
@comment termios.h
@comment POSIX.1
@vindex B2400
@comment termios.h
@comment POSIX.1
@vindex B4800
@comment termios.h
@comment POSIX.1
@vindex B9600
@comment termios.h
@comment POSIX.1
@vindex B19200
@comment termios.h
@comment POSIX.1
@vindex B38400
@comment termios.h
@comment GNU
@vindex B57600
@comment termios.h
@comment GNU
@vindex B115200
@comment termios.h
@comment GNU
@vindex B230400
@comment termios.h
@comment GNU
@vindex B460800
@smallexample
B0 B50 B75 B110 B134 B150 B200
B300 B600 B1200 B1800 B2400 B4800
B9600 B19200 B38400 B57600 B115200
B230400 B460800
@end smallexample
@vindex EXTA
@vindex EXTB
BSD defines two additional speed symbols as aliases: @code{EXTA} is an
alias for @code{B19200} and @code{EXTB} is an alias for @code{B38400}.
These aliases are obsolete.
@node Special Characters
@subsection Special Characters
In canonical input, the terminal driver recognizes a number of special
characters which perform various control functions. These include the
ERASE character (usually @key{DEL}) for editing input, and other editing
characters. The INTR character (normally @kbd{C-c}) for sending a
@code{SIGINT} signal, and other signal-raising characters, may be
available in either canonical or noncanonical input mode. All these
characters are described in this section.
The particular characters used are specified in the @code{c_cc} member
of the @code{struct termios} structure. This member is an array; each
element specifies the character for a particular role. Each element has
a symbolic constant that stands for the index of that element---for
example, @code{VINTR} is the index of the element that specifies the INTR
character, so storing @code{'='} in @code{@var{termios}.c_cc[VINTR]}
specifies @samp{=} as the INTR character.
@vindex _POSIX_VDISABLE
On some systems, you can disable a particular special character function
by specifying the value @code{_POSIX_VDISABLE} for that role. This
value is unequal to any possible character code. @xref{Options for
Files}, for more information about how to tell whether the operating
system you are using supports @code{_POSIX_VDISABLE}.
@menu
* Editing Characters:: Special characters that terminate lines and
delete text, and other editing functions.
* Signal Characters:: Special characters that send or raise signals
to or for certain classes of processes.
* Start/Stop Characters:: Special characters that suspend or resume
suspended output.
* Other Special:: Other special characters for BSD systems:
they can discard output, and print status.
@end menu
@node Editing Characters
@subsubsection Characters for Input Editing
These special characters are active only in canonical input mode.
@xref{Canonical or Not}.
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VEOF
@cindex EOF character
This is the subscript for the EOF character in the special control
character array. @code{@var{termios}.c_cc[VEOF]} holds the character
itself.
The EOF character is recognized only in canonical input mode. It acts
as a line terminator in the same way as a newline character, but if the
EOF character is typed at the beginning of a line it causes @code{read}
to return a byte count of zero, indicating end-of-file. The EOF
character itself is discarded.
Usually, the EOF character is @kbd{C-d}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VEOL
@cindex EOL character
This is the subscript for the EOL character in the special control
character array. @code{@var{termios}.c_cc[VEOL]} holds the character
itself.
The EOL character is recognized only in canonical input mode. It acts
as a line terminator, just like a newline character. The EOL character
is not discarded; it is read as the last character in the input line.
@c !!! example: this is set to ESC by 4.3 csh with "set filec" so it can
@c complete partial lines without using cbreak or raw mode.
You don't need to use the EOL character to make @key{RET} end a line.
Just set the ICRNL flag. In fact, this is the default state of
affairs.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro int VEOL2
@cindex EOL2 character
This is the subscript for the EOL2 character in the special control
character array. @code{@var{termios}.c_cc[VEOL2]} holds the character
itself.
The EOL2 character works just like the EOL character (see above), but it
can be a different character. Thus, you can specify two characters to
terminate an input line, by setting EOL to one of them and EOL2 to the
other.
The EOL2 character is a BSD extension; it exists only on BSD systems
and @gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VERASE
@cindex ERASE character
This is the subscript for the ERASE character in the special control
character array. @code{@var{termios}.c_cc[VERASE]} holds the
character itself.
The ERASE character is recognized only in canonical input mode. When
the user types the erase character, the previous character typed is
discarded. (If the terminal generates multibyte character sequences,
this may cause more than one byte of input to be discarded.) This
cannot be used to erase past the beginning of the current line of text.
The ERASE character itself is discarded.
@c !!! mention ECHOE here
Usually, the ERASE character is @key{DEL}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro int VWERASE
@cindex WERASE character
This is the subscript for the WERASE character in the special control
character array. @code{@var{termios}.c_cc[VWERASE]} holds the character
itself.
The WERASE character is recognized only in canonical mode. It erases an
entire word of prior input, and any whitespace after it; whitespace
characters before the word are not erased.
The definition of a ``word'' depends on the setting of the
@code{ALTWERASE} mode; @pxref{Local Modes}.
If the @code{ALTWERASE} mode is not set, a word is defined as a sequence
of any characters except space or tab.
If the @code{ALTWERASE} mode is set, a word is defined as a sequence of
characters containing only letters, numbers, and underscores, optionally
followed by one character that is not a letter, number, or underscore.
The WERASE character is usually @kbd{C-w}.
This is a BSD extension.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VKILL
@cindex KILL character
This is the subscript for the KILL character in the special control
character array. @code{@var{termios}.c_cc[VKILL]} holds the character
itself.
The KILL character is recognized only in canonical input mode. When the
user types the kill character, the entire contents of the current line
of input are discarded. The kill character itself is discarded too.
The KILL character is usually @kbd{C-u}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro int VREPRINT
@cindex REPRINT character
This is the subscript for the REPRINT character in the special control
character array. @code{@var{termios}.c_cc[VREPRINT]} holds the character
itself.
The REPRINT character is recognized only in canonical mode. It reprints
the current input line. If some asynchronous output has come while you
are typing, this lets you see the line you are typing clearly again.
The REPRINT character is usually @kbd{C-r}.
This is a BSD extension.
@end deftypevr
@node Signal Characters
@subsubsection Characters that Cause Signals
These special characters may be active in either canonical or noncanonical
input mode, but only when the @code{ISIG} flag is set (@pxref{Local
Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VINTR
@cindex INTR character
@cindex interrupt character
This is the subscript for the INTR character in the special control
character array. @code{@var{termios}.c_cc[VINTR]} holds the character
itself.
The INTR (interrupt) character raises a @code{SIGINT} signal for all
processes in the foreground job associated with the terminal. The INTR
character itself is then discarded. @xref{Signal Handling}, for more
information about signals.
Typically, the INTR character is @kbd{C-c}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VQUIT
@cindex QUIT character
This is the subscript for the QUIT character in the special control
character array. @code{@var{termios}.c_cc[VQUIT]} holds the character
itself.
The QUIT character raises a @code{SIGQUIT} signal for all processes in
the foreground job associated with the terminal. The QUIT character
itself is then discarded. @xref{Signal Handling}, for more information
about signals.
Typically, the QUIT character is @kbd{C-\}.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VSUSP
@cindex SUSP character
@cindex suspend character
This is the subscript for the SUSP character in the special control
character array. @code{@var{termios}.c_cc[VSUSP]} holds the character
itself.
The SUSP (suspend) character is recognized only if the implementation
supports job control (@pxref{Job Control}). It causes a @code{SIGTSTP}
signal to be sent to all processes in the foreground job associated with
the terminal. The SUSP character itself is then discarded.
@xref{Signal Handling}, for more information about signals.
Typically, the SUSP character is @kbd{C-z}.
@end deftypevr
Few applications disable the normal interpretation of the SUSP
character. If your program does this, it should provide some other
mechanism for the user to stop the job. When the user invokes this
mechanism, the program should send a @code{SIGTSTP} signal to the
process group of the process, not just to the process itself.
@xref{Signaling Another Process}.
@comment termios.h
@comment BSD
@deftypevr Macro int VDSUSP
@cindex DSUSP character
@cindex delayed suspend character
This is the subscript for the DSUSP character in the special control
character array. @code{@var{termios}.c_cc[VDSUSP]} holds the character
itself.
The DSUSP (suspend) character is recognized only if the implementation
supports job control (@pxref{Job Control}). It sends a @code{SIGTSTP}
signal, like the SUSP character, but not right away---only when the
program tries to read it as input. Not all systems with job control
support DSUSP; only BSD-compatible systems (including @gnuhurdsystems{}).
@xref{Signal Handling}, for more information about signals.
Typically, the DSUSP character is @kbd{C-y}.
@end deftypevr
@node Start/Stop Characters
@subsubsection Special Characters for Flow Control
These special characters may be active in either canonical or noncanonical
input mode, but their use is controlled by the flags @code{IXON} and
@code{IXOFF} (@pxref{Input Modes}).
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VSTART
@cindex START character
This is the subscript for the START character in the special control
character array. @code{@var{termios}.c_cc[VSTART]} holds the
character itself.
The START character is used to support the @code{IXON} and @code{IXOFF}
input modes. If @code{IXON} is set, receiving a START character resumes
suspended output; the START character itself is discarded. If
@code{IXANY} is set, receiving any character at all resumes suspended
output; the resuming character is not discarded unless it is the START
character. @code{IXOFF} is set, the system may also transmit START
characters to the terminal.
The usual value for the START character is @kbd{C-q}. You may not be
able to change this value---the hardware may insist on using @kbd{C-q}
regardless of what you specify.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VSTOP
@cindex STOP character
This is the subscript for the STOP character in the special control
character array. @code{@var{termios}.c_cc[VSTOP]} holds the character
itself.
The STOP character is used to support the @code{IXON} and @code{IXOFF}
input modes. If @code{IXON} is set, receiving a STOP character causes
output to be suspended; the STOP character itself is discarded. If
@code{IXOFF} is set, the system may also transmit STOP characters to the
terminal, to prevent the input queue from overflowing.
The usual value for the STOP character is @kbd{C-s}. You may not be
able to change this value---the hardware may insist on using @kbd{C-s}
regardless of what you specify.
@end deftypevr
@node Other Special
@subsubsection Other Special Characters
@comment termios.h
@comment BSD
@deftypevr Macro int VLNEXT
@cindex LNEXT character
This is the subscript for the LNEXT character in the special control
character array. @code{@var{termios}.c_cc[VLNEXT]} holds the character
itself.
The LNEXT character is recognized only when @code{IEXTEN} is set, but in
both canonical and noncanonical mode. It disables any special
significance of the next character the user types. Even if the
character would normally perform some editing function or generate a
signal, it is read as a plain character. This is the analogue of the
@kbd{C-q} command in Emacs. ``LNEXT'' stands for ``literal next.''
The LNEXT character is usually @kbd{C-v}.
This character is available on BSD systems and @gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro int VDISCARD
@cindex DISCARD character
This is the subscript for the DISCARD character in the special control
character array. @code{@var{termios}.c_cc[VDISCARD]} holds the character
itself.
The DISCARD character is recognized only when @code{IEXTEN} is set, but
in both canonical and noncanonical mode. Its effect is to toggle the
discard-output flag. When this flag is set, all program output is
discarded. Setting the flag also discards all output currently in the
output buffer. Typing any other character resets the flag.
This character is available on BSD systems and @gnulinuxhurdsystems{}.
@end deftypevr
@comment termios.h
@comment BSD
@deftypevr Macro int VSTATUS
@cindex STATUS character
This is the subscript for the STATUS character in the special control
character array. @code{@var{termios}.c_cc[VSTATUS]} holds the character
itself.
The STATUS character's effect is to print out a status message about how
the current process is running.
The STATUS character is recognized only in canonical mode, and only if
@code{NOKERNINFO} is not set.
This character is available only on BSD systems and @gnuhurdsystems{}.
@end deftypevr
@node Noncanonical Input
@subsection Noncanonical Input
In noncanonical input mode, the special editing characters such as
ERASE and KILL are ignored. The system facilities for the user to edit
input are disabled in noncanonical mode, so that all input characters
(unless they are special for signal or flow-control purposes) are passed
to the application program exactly as typed. It is up to the
application program to give the user ways to edit the input, if
appropriate.
Noncanonical mode offers special parameters called MIN and TIME for
controlling whether and how long to wait for input to be available. You
can even use them to avoid ever waiting---to return immediately with
whatever input is available, or with no input.
The MIN and TIME are stored in elements of the @code{c_cc} array, which
is a member of the @w{@code{struct termios}} structure. Each element of
this array has a particular role, and each element has a symbolic
constant that stands for the index of that element. @code{VMIN} and
@code{VMAX} are the names for the indices in the array of the MIN and
TIME slots.
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VMIN
@cindex MIN termios slot
This is the subscript for the MIN slot in the @code{c_cc} array. Thus,
@code{@var{termios}.c_cc[VMIN]} is the value itself.
The MIN slot is only meaningful in noncanonical input mode; it
specifies the minimum number of bytes that must be available in the
input queue in order for @code{read} to return.
@end deftypevr
@comment termios.h
@comment POSIX.1
@deftypevr Macro int VTIME
@cindex TIME termios slot
This is the subscript for the TIME slot in the @code{c_cc} array. Thus,
@code{@var{termios}.c_cc[VTIME]} is the value itself.
The TIME slot is only meaningful in noncanonical input mode; it
specifies how long to wait for input before returning, in units of 0.1
seconds.
@end deftypevr
The MIN and TIME values interact to determine the criterion for when
@code{read} should return; their precise meanings depend on which of
them are nonzero. There are four possible cases:
@itemize @bullet
@item
Both TIME and MIN are nonzero.
In this case, TIME specifies how long to wait after each input character
to see if more input arrives. After the first character received,
@code{read} keeps waiting until either MIN bytes have arrived in all, or
TIME elapses with no further input.
@code{read} always blocks until the first character arrives, even if
TIME elapses first. @code{read} can return more than MIN characters if
more than MIN happen to be in the queue.
@item
Both MIN and TIME are zero.
In this case, @code{read} always returns immediately with as many
characters as are available in the queue, up to the number requested.
If no input is immediately available, @code{read} returns a value of
zero.
@item
MIN is zero but TIME has a nonzero value.
In this case, @code{read} waits for time TIME for input to become
available; the availability of a single byte is enough to satisfy the
read request and cause @code{read} to return. When it returns, it
returns as many characters as are available, up to the number requested.
If no input is available before the timer expires, @code{read} returns a
value of zero.
@item
TIME is zero but MIN has a nonzero value.
In this case, @code{read} waits until at least MIN bytes are available
in the queue. At that time, @code{read} returns as many characters as
are available, up to the number requested. @code{read} can return more
than MIN characters if more than MIN happen to be in the queue.
@end itemize
What happens if MIN is 50 and you ask to read just 10 bytes?
Normally, @code{read} waits until there are 50 bytes in the buffer (or,
more generally, the wait condition described above is satisfied), and
then reads 10 of them, leaving the other 40 buffered in the operating
system for a subsequent call to @code{read}.
@strong{Portability note:} On some systems, the MIN and TIME slots are
actually the same as the EOF and EOL slots. This causes no serious
problem because the MIN and TIME slots are used only in noncanonical
input and the EOF and EOL slots are used only in canonical input, but it
isn't very clean. @Theglibc{} allocates separate slots for these
uses.
@comment termios.h
@comment BSD
@deftypefun void cfmakeraw (struct termios *@var{termios-p})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c There's no guarantee the changes are atomic, but since this is not an
@c opaque type, callers ought to ensure mutual exclusion to the termios
@c object.
This function provides an easy way to set up @code{*@var{termios-p}} for
what has traditionally been called ``raw mode'' in BSD. This uses
noncanonical input, and turns off most processing to give an unmodified
channel to the terminal.
It does exactly this:
@smallexample
@var{termios-p}->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP
|INLCR|IGNCR|ICRNL|IXON);
@var{termios-p}->c_oflag &= ~OPOST;
@var{termios-p}->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
@var{termios-p}->c_cflag &= ~(CSIZE|PARENB);
@var{termios-p}->c_cflag |= CS8;
@end smallexample
@end deftypefun
@node BSD Terminal Modes
@section BSD Terminal Modes
@cindex terminal modes, BSD
The usual way to get and set terminal modes is with the functions described
in @ref{Terminal Modes}. However, on some systems you can use the
BSD-derived functions in this section to do some of the same thing. On
many systems, these functions do not exist. Even with @theglibc{},
the functions simply fail with @code{errno} = @code{ENOSYS} with many
kernels, including Linux.
The symbols used in this section are declared in @file{sgtty.h}.
@comment termios.h
@comment BSD
@deftp {Data Type} {struct sgttyb}
This structure is an input or output parameter list for @code{gtty} and
@code{stty}.
@table @code
@item char sg_ispeed
Line speed for input
@item char sg_ospeed
Line speed for output
@item char sg_erase
Erase character
@item char sg_kill
Kill character
@item int sg_flags
Various flags
@end table
@end deftp
@comment sgtty.h
@comment BSD
@deftypefun int gtty (int @var{filedes}, struct sgttyb *@var{attributes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct ioctl, BSD only.
This function gets the attributes of a terminal.
@code{gtty} sets *@var{attributes} to describe the terminal attributes
of the terminal which is open with file descriptor @var{filedes}.
@end deftypefun
@comment sgtty.h
@comment BSD
@deftypefun int stty (int @var{filedes}, const struct sgttyb *@var{attributes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct ioctl, BSD only.
This function sets the attributes of a terminal.
@code{stty} sets the terminal attributes of the terminal which is open with
file descriptor @var{filedes} to those described by *@var{filedes}.
@end deftypefun
@node Line Control
@section Line Control Functions
@cindex terminal line control functions
These functions perform miscellaneous control actions on terminal
devices. As regards terminal access, they are treated like doing
output: if any of these functions is used by a background process on its
controlling terminal, normally all processes in the process group are
sent a @code{SIGTTOU} signal. The exception is if the calling process
itself is ignoring or blocking @code{SIGTTOU} signals, in which case the
operation is performed and no signal is sent. @xref{Job Control}.
@cindex break condition, generating
@comment termios.h
@comment POSIX.1
@deftypefun int tcsendbreak (int @var{filedes}, int @var{duration})
@safety{@prelim{}@mtunsafe{@mtasurace{:tcattr(filedes)/bsd}}@asunsafe{}@acunsafe{@acucorrupt{/bsd}}}
@c On Linux, this calls just one out of two ioctls; on BSD, it's two
@c ioctls with a select (for the delay only) in between, the first
@c setting and the latter clearing the break status. The BSD
@c implementation may leave the break enabled if cancelled, and threads
@c and signals may cause the break to be interrupted before requested.
This function generates a break condition by transmitting a stream of
zero bits on the terminal associated with the file descriptor
@var{filedes}. The duration of the break is controlled by the
@var{duration} argument. If zero, the duration is between 0.25 and 0.5
seconds. The meaning of a nonzero value depends on the operating system.
This function does nothing if the terminal is not an asynchronous serial
data port.
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following @code{errno} error conditions
are defined for this function:
@table @code
@item EBADF
The @var{filedes} is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal device.
@end table
@end deftypefun
@cindex flushing terminal output queue
@cindex terminal output queue, flushing
@comment termios.h
@comment POSIX.1
@deftypefun int tcdrain (int @var{filedes})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct ioctl.
The @code{tcdrain} function waits until all queued
output to the terminal @var{filedes} has been transmitted.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{tcdrain} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{tcdrain} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following @code{errno} error conditions
are defined for this function:
@table @code
@item EBADF
The @var{filedes} is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal device.
@item EINTR
The operation was interrupted by delivery of a signal.
@xref{Interrupted Primitives}.
@end table
@end deftypefun
@cindex clearing terminal input queue
@cindex terminal input queue, clearing
@comment termios.h
@comment POSIX.1
@deftypefun int tcflush (int @var{filedes}, int @var{queue})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct ioctl.
The @code{tcflush} function is used to clear the input and/or output
queues associated with the terminal file @var{filedes}. The @var{queue}
argument specifies which queue(s) to clear, and can be one of the
following values:
@c Extra blank lines here make it look better.
@table @code
@vindex TCIFLUSH
@item TCIFLUSH
Clear any input data received, but not yet read.
@vindex TCOFLUSH
@item TCOFLUSH
Clear any output data written, but not yet transmitted.
@vindex TCIOFLUSH
@item TCIOFLUSH
Clear both queued input and output.
@end table
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following @code{errno} error conditions
are defined for this function:
@table @code
@item EBADF
The @var{filedes} is not a valid file descriptor.
@item ENOTTY
The @var{filedes} is not associated with a terminal device.
@item EINVAL
A bad value was supplied as the @var{queue} argument.
@end table
It is unfortunate that this function is named @code{tcflush}, because
the term ``flush'' is normally used for quite another operation---waiting
until all output is transmitted---and using it for discarding input or
output would be confusing. Unfortunately, the name @code{tcflush} comes
from POSIX and we cannot change it.
@end deftypefun
@cindex flow control, terminal
@cindex terminal flow control
@comment termios.h
@comment POSIX.1
@deftypefun int tcflow (int @var{filedes}, int @var{action})
@safety{@prelim{}@mtunsafe{@mtasurace{:tcattr(filedes)/bsd}}@asunsafe{}@acsafe{}}
@c Direct ioctl on Linux. On BSD, the TCO* actions are a single ioctl,
@c whereas the TCI actions first call tcgetattr and then write to the fd
@c the c_cc character corresponding to the action; there's a window for
@c another thread to change the xon/xoff characters.
The @code{tcflow} function is used to perform operations relating to
XON/XOFF flow control on the terminal file specified by @var{filedes}.
The @var{action} argument specifies what operation to perform, and can
be one of the following values:
@table @code
@vindex TCOOFF
@item TCOOFF
Suspend transmission of output.
@vindex TCOON
@item TCOON
Restart transmission of output.
@vindex TCIOFF
@item TCIOFF
Transmit a STOP character.
@vindex TCION
@item TCION
Transmit a START character.
@end table
For more information about the STOP and START characters, see @ref{Special
Characters}.
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following @code{errno} error conditions
are defined for this function:
@table @code
@vindex EBADF
@item EBADF
The @var{filedes} is not a valid file descriptor.
@vindex ENOTTY
@item ENOTTY
The @var{filedes} is not associated with a terminal device.
@vindex EINVAL
@item EINVAL
A bad value was supplied as the @var{action} argument.
@end table
@end deftypefun
@node Noncanon Example
@section Noncanonical Mode Example
Here is an example program that shows how you can set up a terminal
device to read single characters in noncanonical input mode, without
echo.
@smallexample
@include termios.c.texi
@end smallexample
This program is careful to restore the original terminal modes before
exiting or terminating with a signal. It uses the @code{atexit}
function (@pxref{Cleanups on Exit}) to make sure this is done
by @code{exit}.
@ignore
@c !!!! the example doesn't handle any signals!
The signals handled in the example are the ones that typically occur due
to actions of the user. It might be desirable to handle other signals
such as SIGSEGV that can result from bugs in the program.
@end ignore
The shell is supposed to take care of resetting the terminal modes when
a process is stopped or continued; see @ref{Job Control}. But some
existing shells do not actually do this, so you may wish to establish
handlers for job control signals that reset terminal modes. The above
example does so.
@node Pseudo-Terminals
@section Pseudo-Terminals
@cindex pseudo-terminals
A @dfn{pseudo-terminal} is a special interprocess communication channel
that acts like a terminal. One end of the channel is called the
@dfn{master} side or @dfn{master pseudo-terminal device}, the other side
is called the @dfn{slave} side. Data written to the master side is
received by the slave side as if it was the result of a user typing at
an ordinary terminal, and data written to the slave side is sent to the
master side as if it was written on an ordinary terminal.
Pseudo terminals are the way programs like @code{xterm} and @code{emacs}
implement their terminal emulation functionality.
@menu
* Allocation:: Allocating a pseudo terminal.
* Pseudo-Terminal Pairs:: How to open both sides of a
pseudo-terminal in a single operation.
@end menu
@node Allocation
@subsection Allocating Pseudo-Terminals
@cindex allocating pseudo-terminals
@pindex stdlib.h
This subsection describes functions for allocating a pseudo-terminal,
and for making this pseudo-terminal available for actual use. These
functions are declared in the header file @file{stdlib.h}.
@comment stdlib.h
@comment GNU
@deftypefun int getpt (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
@c On BSD, tries to open multiple potential pty names, returning on the
@c first success. On Linux, try posix_openpt first, then fallback to
@c the BSD implementation. The posix implementation opens the ptmx
@c device, checks with statfs that /dev/pts is a devpts or that /dev is
@c a devfs, and returns the fd; static variables devpts_mounted and
@c have_no_dev_ptmx are safely initialized so as to avoid repeated
@c tests.
The @code{getpt} function returns a new file descriptor for the next
available master pseudo-terminal. The normal return value from
@code{getpt} is a non-negative integer file descriptor. In the case of
an error, a value of @math{-1} is returned instead. The following
@code{errno} conditions are defined for this function:
@table @code
@item ENOENT
There are no free master pseudo-terminals available.
@end table
This function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment SVID, XPG4.2
@deftypefun int grantpt (int @var{filedes})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c grantpt @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c unix/grantpt:pts_name @acsuheap @acsmem
@c ptsname_internal dup ok (but this is Linux-only!)
@c memchr dup ok
@c realloc dup @acsuheap @acsmem
@c malloc dup @acsuheap @acsmem
@c free dup @acsuheap @acsmem
@c fcntl dup ok
@c getuid dup ok
@c chown dup ok
@c sysconf(_SC_GETGR_R_SIZE_MAX) ok
@c getgrnam_r @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getgid dup ok
@c chmod dup ok
@c fork dup @aculock
@c [child]
@c setrlimit
@c dup2
@c CLOSE_ALL_FDS
@c execle
@c _exit
@c waitpid dup ok
@c WIFEXITED dup ok
@c WEXITSTATUS dup ok
@c free dup @ascuheap @acsmem
The @code{grantpt} function changes the ownership and access permission
of the slave pseudo-terminal device corresponding to the master
pseudo-terminal device associated with the file descriptor
@var{filedes}. The owner is set from the real user ID of the calling
process (@pxref{Process Persona}), and the group is set to a special
group (typically @dfn{tty}) or from the real group ID of the calling
process. The access permission is set such that the file is both
readable and writable by the owner and only writable by the group.
On some systems this function is implemented by invoking a special
@code{setuid} root program (@pxref{How Change Persona}). As a
consequence, installing a signal handler for the @code{SIGCHLD} signal
(@pxref{Job Control Signals}) may interfere with a call to
@code{grantpt}.
The normal return value from @code{grantpt} is @math{0}; a value of
@math{-1} is returned in case of failure. The following @code{errno}
error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The @var{filedes} argument is not associated with a master pseudo-terminal
device.
@item EACCES
The slave pseudo-terminal device corresponding to the master associated
with @var{filedes} could not be accessed.
@end table
@end deftypefun
@comment stdlib.h
@comment SVID, XPG4.2
@deftypefun int unlockpt (int @var{filedes})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{/bsd}}@acunsafe{@acsmem{} @acsfd{}}}
@c unlockpt @ascuheap/bsd @acsmem @acsfd
@c /bsd
@c ptsname_r dup @ascuheap @acsmem @acsfd
@c revoke ok (syscall)
@c /linux
@c ioctl dup ok
The @code{unlockpt} function unlocks the slave pseudo-terminal device
corresponding to the master pseudo-terminal device associated with the
file descriptor @var{filedes}. On many systems, the slave can only be
opened after unlocking, so portable applications should always call
@code{unlockpt} before trying to open the slave.
The normal return value from @code{unlockpt} is @math{0}; a value of
@math{-1} is returned in case of failure. The following @code{errno}
error conditions are defined for this function:
@table @code
@item EBADF
The @var{filedes} argument is not a valid file descriptor.
@item EINVAL
The @var{filedes} argument is not associated with a master pseudo-terminal
device.
@end table
@end deftypefun
@comment stdlib.h
@comment SVID, XPG4.2
@deftypefun {char *} ptsname (int @var{filedes})
@safety{@prelim{}@mtunsafe{@mtasurace{:ptsname}}@asunsafe{@ascuheap{/bsd}}@acunsafe{@acsmem{} @acsfd{}}}
@c ptsname @mtasurace:ptsname @ascuheap/bsd @acsmem @acsfd
@c ptsname_r dup @ascuheap/bsd @acsmem @acsfd
If the file descriptor @var{filedes} is associated with a
master pseudo-terminal device, the @code{ptsname} function returns a
pointer to a statically-allocated, null-terminated string containing the
file name of the associated slave pseudo-terminal file. This string
might be overwritten by subsequent calls to @code{ptsname}.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun int ptsname_r (int @var{filedes}, char *@var{buf}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{/bsd}}@acunsafe{@acsmem{} @acsfd{}}}
@c ptsname_r @ascuheap/bsd @acsmem @acsfd
@c /hurd
@c term_get_peername ok
@c strlen dup ok
@c memcpy dup ok
@c /bsd
@c isatty dup ok
@c strlen dup ok
@c ttyname_r dup @ascuheap @acsmem @acsfd
@c stat dup ok
@c /linux
@c ptsname_internal ok
@c isatty dup ok
@c ioctl dup ok
@c strlen dup ok
@c itoa_word dup ok
@c stpcpy dup ok
@c memcpy dup ok
@c fxstat64 dup ok
@c MASTER_P ok
@c major ok
@c gnu_dev_major ok
@c minor ok
@c gnu_dev_minor ok
@c minor dup ok
@c xstat64 dup ok
@c S_ISCHR dup ok
@c SLAVE_P ok
@c major dup ok
@c minor dup ok
The @code{ptsname_r} function is similar to the @code{ptsname} function
except that it places its result into the user-specified buffer starting
at @var{buf} with length @var{len}.
This function is a GNU extension.
@end deftypefun
@strong{Portability Note:} On @w{System V} derived systems, the file
returned by the @code{ptsname} and @code{ptsname_r} functions may be
STREAMS-based, and therefore require additional processing after opening
before it actually behaves as a pseudo terminal.
@c FIXME: xref STREAMS
Typical usage of these functions is illustrated by the following example:
@smallexample
int
open_pty_pair (int *amaster, int *aslave)
@{
int master, slave;
char *name;
master = getpt ();
if (master < 0)
return 0;
if (grantpt (master) < 0 || unlockpt (master) < 0)
goto close_master;
name = ptsname (master);
if (name == NULL)
goto close_master;
slave = open (name, O_RDWR);
if (slave == -1)
goto close_master;
if (isastream (slave))
@{
if (ioctl (slave, I_PUSH, "ptem") < 0
|| ioctl (slave, I_PUSH, "ldterm") < 0)
goto close_slave;
@}
*amaster = master;
*aslave = slave;
return 1;
close_slave:
close (slave);
close_master:
close (master);
return 0;
@}
@end smallexample
@node Pseudo-Terminal Pairs
@subsection Opening a Pseudo-Terminal Pair
@cindex opening a pseudo-terminal pair
These functions, derived from BSD, are available in the separate
@file{libutil} library, and declared in @file{pty.h}.
@comment pty.h
@comment BSD
@deftypefun int openpty (int *@var{amaster}, int *@var{aslave}, char *@var{name}, const struct termios *@var{termp}, const struct winsize *@var{winp})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c openpty @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c getpt @acsfd
@c grantpt @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c unlockpt dup @ascuheap/bsd @acsmem @acsfd
@c openpty:pts_name @acsuheap @acsmem @acsfd
@c ptsname_r dup @ascuheap/bsd @acsmem @acsfd
@c realloc dup @acsuheap @acsmem
@c malloc dup @acsuheap @acsmem
@c free dup @acsuheap @acsmem
@c open dup @acsfd
@c free dup @acsuheap @acsmem
@c tcsetattr dup ok
@c ioctl dup ok
@c strcpy dup ok
@c close dup @acsfd
This function allocates and opens a pseudo-terminal pair, returning the
file descriptor for the master in @var{*amaster}, and the file
descriptor for the slave in @var{*aslave}. If the argument @var{name}
is not a null pointer, the file name of the slave pseudo-terminal
device is stored in @code{*name}. If @var{termp} is not a null pointer,
the terminal attributes of the slave are set to the ones specified in
the structure that @var{termp} points to (@pxref{Terminal Modes}).
Likewise, if the @var{winp} is not a null pointer, the screen size of
the slave is set to the values specified in the structure that
@var{winp} points to.
The normal return value from @code{openpty} is @math{0}; a value of
@math{-1} is returned in case of failure. The following @code{errno}
conditions are defined for this function:
@table @code
@item ENOENT
There are no free pseudo-terminal pairs available.
@end table
@strong{Warning:} Using the @code{openpty} function with @var{name} not
set to @code{NULL} is @strong{very dangerous} because it provides no
protection against overflowing the string @var{name}. You should use
the @code{ttyname} function on the file descriptor returned in
@var{*slave} to find out the file name of the slave pseudo-terminal
device instead.
@end deftypefun
@comment pty.h
@comment BSD
@deftypefun int forkpty (int *@var{amaster}, char *@var{name}, const struct termios *@var{termp}, const struct winsize *@var{winp})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascudlopen{} @ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c forkpty @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c openpty dup @mtslocale @ascudlopen @ascuplugin @ascuheap @asulock @acucorrupt @aculock @acsfd @acsmem
@c fork dup @aculock
@c close dup @acsfd
@c /child
@c close dup @acsfd
@c login_tty dup @mtasurace:ttyname @ascuheap @asulock @aculock @acsmem @acsfd
@c _exit dup ok
@c close dup @acsfd
This function is similar to the @code{openpty} function, but in
addition, forks a new process (@pxref{Creating a Process}) and makes the
newly opened slave pseudo-terminal device the controlling terminal
(@pxref{Controlling Terminal}) for the child process.
If the operation is successful, there are then both parent and child
processes and both see @code{forkpty} return, but with different values:
it returns a value of @math{0} in the child process and returns the child's
process ID in the parent process.
If the allocation of a pseudo-terminal pair or the process creation
failed, @code{forkpty} returns a value of @math{-1} in the parent
process.
@strong{Warning:} The @code{forkpty} function has the same problems with
respect to the @var{name} argument as @code{openpty}.
@end deftypefun
glibc-doc-reference-2.19.orig/manual/texis.awk 0000664 0001750 0001750 00000000474 12275120646 021424 0 ustar adconrad adconrad BEGIN {
print "texis = \\";
for(x = 1; x < ARGC; x++)
{
input[0] = ARGV[x];
print ARGV[x], "\\";
for (s = 0; s >= 0; s--)
{
while ((getline < input[s]) > 0)
{
if ($1 == "@include")
{
input[++s] = $2;
print $2, "\\";
}
}
close(input[s]);
}
}
print "";
}
glibc-doc-reference-2.19.orig/manual/lang.texi 0000664 0001750 0001750 00000134372 12275120646 021405 0 ustar adconrad adconrad @c This node must have no pointers.
@node Language Features
@c @node Language Features, Library Summary, , Top
@c %MENU% C language features provided by the library
@appendix C Language Facilities in the Library
Some of the facilities implemented by the C library really should be
thought of as parts of the C language itself. These facilities ought to
be documented in the C Language Manual, not in the library manual; but
since we don't have the language manual yet, and documentation for these
features has been written, we are publishing it here.
@menu
* Consistency Checking:: Using @code{assert} to abort if
something ``impossible'' happens.
* Variadic Functions:: Defining functions with varying numbers
of args.
* Null Pointer Constant:: The macro @code{NULL}.
* Important Data Types:: Data types for object sizes.
* Data Type Measurements:: Parameters of data type representations.
@end menu
@node Consistency Checking
@section Explicitly Checking Internal Consistency
@cindex consistency checking
@cindex impossible events
@cindex assertions
When you're writing a program, it's often a good idea to put in checks
at strategic places for ``impossible'' errors or violations of basic
assumptions. These kinds of checks are helpful in debugging problems
with the interfaces between different parts of the program, for example.
@pindex assert.h
The @code{assert} macro, defined in the header file @file{assert.h},
provides a convenient way to abort the program while printing a message
about where in the program the error was detected.
@vindex NDEBUG
Once you think your program is debugged, you can disable the error
checks performed by the @code{assert} macro by recompiling with the
macro @code{NDEBUG} defined. This means you don't actually have to
change the program source code to disable these checks.
But disabling these consistency checks is undesirable unless they make
the program significantly slower. All else being equal, more error
checking is good no matter who is running the program. A wise user
would rather have a program crash, visibly, than have it return nonsense
without indicating anything might be wrong.
@comment assert.h
@comment ISO
@deftypefn Macro void assert (int @var{expression})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c assert_fail_base calls asprintf, and fflushes stderr.
Verify the programmer's belief that @var{expression} is nonzero at
this point in the program.
If @code{NDEBUG} is not defined, @code{assert} tests the value of
@var{expression}. If it is false (zero), @code{assert} aborts the
program (@pxref{Aborting a Program}) after printing a message of the
form:
@smallexample
@file{@var{file}}:@var{linenum}: @var{function}: Assertion `@var{expression}' failed.
@end smallexample
@noindent
on the standard error stream @code{stderr} (@pxref{Standard Streams}).
The filename and line number are taken from the C preprocessor macros
@code{__FILE__} and @code{__LINE__} and specify where the call to
@code{assert} was made. When using the GNU C compiler, the name of
the function which calls @code{assert} is taken from the built-in
variable @code{__PRETTY_FUNCTION__}; with older compilers, the function
name and following colon are omitted.
If the preprocessor macro @code{NDEBUG} is defined before
@file{assert.h} is included, the @code{assert} macro is defined to do
absolutely nothing.
@strong{Warning:} Even the argument expression @var{expression} is not
evaluated if @code{NDEBUG} is in effect. So never use @code{assert}
with arguments that involve side effects. For example, @code{assert
(++i > 0);} is a bad idea, because @code{i} will not be incremented if
@code{NDEBUG} is defined.
@end deftypefn
Sometimes the ``impossible'' condition you want to check for is an error
return from an operating system function. Then it is useful to display
not only where the program crashes, but also what error was returned.
The @code{assert_perror} macro makes this easy.
@comment assert.h
@comment GNU
@deftypefn Macro void assert_perror (int @var{errnum})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
@c assert_fail_base calls asprintf, and fflushes stderr.
Similar to @code{assert}, but verifies that @var{errnum} is zero.
If @code{NDEBUG} is not defined, @code{assert_perror} tests the value of
@var{errnum}. If it is nonzero, @code{assert_perror} aborts the program
after printing a message of the form:
@smallexample
@file{@var{file}}:@var{linenum}: @var{function}: @var{error text}
@end smallexample
@noindent
on the standard error stream. The file name, line number, and function
name are as for @code{assert}. The error text is the result of
@w{@code{strerror (@var{errnum})}}. @xref{Error Messages}.
Like @code{assert}, if @code{NDEBUG} is defined before @file{assert.h}
is included, the @code{assert_perror} macro does absolutely nothing. It
does not evaluate the argument, so @var{errnum} should not have any side
effects. It is best for @var{errnum} to be just a simple variable
reference; often it will be @code{errno}.
This macro is a GNU extension.
@end deftypefn
@strong{Usage note:} The @code{assert} facility is designed for
detecting @emph{internal inconsistency}; it is not suitable for
reporting invalid input or improper usage by the @emph{user} of the
program.
The information in the diagnostic messages printed by the @code{assert}
and @code{assert_perror} macro is intended to help you, the programmer,
track down the cause of a bug, but is not really useful for telling a user
of your program why his or her input was invalid or why a command could not
be carried out. What's more, your program should not abort when given
invalid input, as @code{assert} would do---it should exit with nonzero
status (@pxref{Exit Status}) after printing its error messages, or perhaps
read another command or move on to the next input file.
@xref{Error Messages}, for information on printing error messages for
problems that @emph{do not} represent bugs in the program.
@node Variadic Functions
@section Variadic Functions
@cindex variable number of arguments
@cindex variadic functions
@cindex optional arguments
@w{ISO C} defines a syntax for declaring a function to take a variable
number or type of arguments. (Such functions are referred to as
@dfn{varargs functions} or @dfn{variadic functions}.) However, the
language itself provides no mechanism for such functions to access their
non-required arguments; instead, you use the variable arguments macros
defined in @file{stdarg.h}.
This section describes how to declare variadic functions, how to write
them, and how to call them properly.
@strong{Compatibility Note:} Many older C dialects provide a similar,
but incompatible, mechanism for defining functions with variable numbers
of arguments, using @file{varargs.h}.
@menu
* Why Variadic:: Reasons for making functions take
variable arguments.
* How Variadic:: How to define and call variadic functions.
* Variadic Example:: A complete example.
@end menu
@node Why Variadic
@subsection Why Variadic Functions are Used
Ordinary C functions take a fixed number of arguments. When you define
a function, you specify the data type for each argument. Every call to
the function should supply the expected number of arguments, with types
that can be converted to the specified ones. Thus, if the function
@samp{foo} is declared with @code{int foo (int, char *);} then you must
call it with two arguments, a number (any kind will do) and a string
pointer.
But some functions perform operations that can meaningfully accept an
unlimited number of arguments.
In some cases a function can handle any number of values by operating on
all of them as a block. For example, consider a function that allocates
a one-dimensional array with @code{malloc} to hold a specified set of
values. This operation makes sense for any number of values, as long as
the length of the array corresponds to that number. Without facilities
for variable arguments, you would have to define a separate function for
each possible array size.
The library function @code{printf} (@pxref{Formatted Output}) is an
example of another class of function where variable arguments are
useful. This function prints its arguments (which can vary in type as
well as number) under the control of a format template string.
These are good reasons to define a @dfn{variadic} function which can
handle as many arguments as the caller chooses to pass.
Some functions such as @code{open} take a fixed set of arguments, but
occasionally ignore the last few. Strict adherence to @w{ISO C} requires
these functions to be defined as variadic; in practice, however, the GNU
C compiler and most other C compilers let you define such a function to
take a fixed set of arguments---the most it can ever use---and then only
@emph{declare} the function as variadic (or not declare its arguments
at all!).
@node How Variadic
@subsection How Variadic Functions are Defined and Used
Defining and using a variadic function involves three steps:
@itemize @bullet
@item
@emph{Define} the function as variadic, using an ellipsis
(@samp{@dots{}}) in the argument list, and using special macros to
access the variable arguments. @xref{Receiving Arguments}.
@item
@emph{Declare} the function as variadic, using a prototype with an
ellipsis (@samp{@dots{}}), in all the files which call it.
@xref{Variadic Prototypes}.
@item
@emph{Call} the function by writing the fixed arguments followed by the
additional variable arguments. @xref{Calling Variadics}.
@end itemize
@menu
* Variadic Prototypes:: How to make a prototype for a function
with variable arguments.
* Receiving Arguments:: Steps you must follow to access the
optional argument values.
* How Many Arguments:: How to decide whether there are more arguments.
* Calling Variadics:: Things you need to know about calling
variable arguments functions.
* Argument Macros:: Detailed specification of the macros
for accessing variable arguments.
@end menu
@node Variadic Prototypes
@subsubsection Syntax for Variable Arguments
@cindex function prototypes (variadic)
@cindex prototypes for variadic functions
@cindex variadic function prototypes
A function that accepts a variable number of arguments must be declared
with a prototype that says so. You write the fixed arguments as usual,
and then tack on @samp{@dots{}} to indicate the possibility of
additional arguments. The syntax of @w{ISO C} requires at least one fixed
argument before the @samp{@dots{}}. For example,
@smallexample
int
func (const char *a, int b, @dots{})
@{
@dots{}
@}
@end smallexample
@noindent
defines a function @code{func} which returns an @code{int} and takes two
required arguments, a @code{const char *} and an @code{int}. These are
followed by any number of anonymous arguments.
@strong{Portability note:} For some C compilers, the last required
argument must not be declared @code{register} in the function
definition. Furthermore, this argument's type must be
@dfn{self-promoting}: that is, the default promotions must not change
its type. This rules out array and function types, as well as
@code{float}, @code{char} (whether signed or not) and @w{@code{short int}}
(whether signed or not). This is actually an @w{ISO C} requirement.
@node Receiving Arguments
@subsubsection Receiving the Argument Values
@cindex variadic function argument access
@cindex arguments (variadic functions)
Ordinary fixed arguments have individual names, and you can use these
names to access their values. But optional arguments have no
names---nothing but @samp{@dots{}}. How can you access them?
@pindex stdarg.h
The only way to access them is sequentially, in the order they were
written, and you must use special macros from @file{stdarg.h} in the
following three step process:
@enumerate
@item
You initialize an argument pointer variable of type @code{va_list} using
@code{va_start}. The argument pointer when initialized points to the
first optional argument.
@item
You access the optional arguments by successive calls to @code{va_arg}.
The first call to @code{va_arg} gives you the first optional argument,
the next call gives you the second, and so on.
You can stop at any time if you wish to ignore any remaining optional
arguments. It is perfectly all right for a function to access fewer
arguments than were supplied in the call, but you will get garbage
values if you try to access too many arguments.
@item
You indicate that you are finished with the argument pointer variable by
calling @code{va_end}.
(In practice, with most C compilers, calling @code{va_end} does nothing.
This is always true in the GNU C compiler. But you might as well call
@code{va_end} just in case your program is someday compiled with a peculiar
compiler.)
@end enumerate
@xref{Argument Macros}, for the full definitions of @code{va_start},
@code{va_arg} and @code{va_end}.
Steps 1 and 3 must be performed in the function that accepts the
optional arguments. However, you can pass the @code{va_list} variable
as an argument to another function and perform all or part of step 2
there.
You can perform the entire sequence of three steps multiple times
within a single function invocation. If you want to ignore the optional
arguments, you can do these steps zero times.
You can have more than one argument pointer variable if you like. You
can initialize each variable with @code{va_start} when you wish, and
then you can fetch arguments with each argument pointer as you wish.
Each argument pointer variable will sequence through the same set of
argument values, but at its own pace.
@strong{Portability note:} With some compilers, once you pass an
argument pointer value to a subroutine, you must not keep using the same
argument pointer value after that subroutine returns. For full
portability, you should just pass it to @code{va_end}. This is actually
an @w{ISO C} requirement, but most ANSI C compilers work happily
regardless.
@node How Many Arguments
@subsubsection How Many Arguments Were Supplied
@cindex number of arguments passed
@cindex how many arguments
@cindex arguments, how many
There is no general way for a function to determine the number and type
of the optional arguments it was called with. So whoever designs the
function typically designs a convention for the caller to specify the number
and type of arguments. It is up to you to define an appropriate calling
convention for each variadic function, and write all calls accordingly.
One kind of calling convention is to pass the number of optional
arguments as one of the fixed arguments. This convention works provided
all of the optional arguments are of the same type.
A similar alternative is to have one of the required arguments be a bit
mask, with a bit for each possible purpose for which an optional
argument might be supplied. You would test the bits in a predefined
sequence; if the bit is set, fetch the value of the next argument,
otherwise use a default value.
A required argument can be used as a pattern to specify both the number
and types of the optional arguments. The format string argument to
@code{printf} is one example of this (@pxref{Formatted Output Functions}).
Another possibility is to pass an ``end marker'' value as the last
optional argument. For example, for a function that manipulates an
arbitrary number of pointer arguments, a null pointer might indicate the
end of the argument list. (This assumes that a null pointer isn't
otherwise meaningful to the function.) The @code{execl} function works
in just this way; see @ref{Executing a File}.
@node Calling Variadics
@subsubsection Calling Variadic Functions
@cindex variadic functions, calling
@cindex calling variadic functions
@cindex declaring variadic functions
You don't have to do anything special to call a variadic function.
Just put the arguments (required arguments, followed by optional ones)
inside parentheses, separated by commas, as usual. But you must declare
the function with a prototype and know how the argument values are converted.
In principle, functions that are @emph{defined} to be variadic must also
be @emph{declared} to be variadic using a function prototype whenever
you call them. (@xref{Variadic Prototypes}, for how.) This is because
some C compilers use a different calling convention to pass the same set
of argument values to a function depending on whether that function
takes variable arguments or fixed arguments.
In practice, the GNU C compiler always passes a given set of argument
types in the same way regardless of whether they are optional or
required. So, as long as the argument types are self-promoting, you can
safely omit declaring them. Usually it is a good idea to declare the
argument types for variadic functions, and indeed for all functions.
But there are a few functions which it is extremely convenient not to
have to declare as variadic---for example, @code{open} and
@code{printf}.
@cindex default argument promotions
@cindex argument promotion
Since the prototype doesn't specify types for optional arguments, in a
call to a variadic function the @dfn{default argument promotions} are
performed on the optional argument values. This means the objects of
type @code{char} or @w{@code{short int}} (whether signed or not) are
promoted to either @code{int} or @w{@code{unsigned int}}, as
appropriate; and that objects of type @code{float} are promoted to type
@code{double}. So, if the caller passes a @code{char} as an optional
argument, it is promoted to an @code{int}, and the function can access
it with @code{va_arg (@var{ap}, int)}.
Conversion of the required arguments is controlled by the function
prototype in the usual way: the argument expression is converted to the
declared argument type as if it were being assigned to a variable of
that type.
@node Argument Macros
@subsubsection Argument Access Macros
Here are descriptions of the macros used to retrieve variable arguments.
These macros are defined in the header file @file{stdarg.h}.
@pindex stdarg.h
@comment stdarg.h
@comment ISO
@deftp {Data Type} va_list
The type @code{va_list} is used for argument pointer variables.
@end deftp
@comment stdarg.h
@comment ISO
@deftypefn {Macro} void va_start (va_list @var{ap}, @var{last-required})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is no longer provided by glibc, but rather by the compiler.
This macro initializes the argument pointer variable @var{ap} to point
to the first of the optional arguments of the current function;
@var{last-required} must be the last required argument to the function.
@end deftypefn
@comment stdarg.h
@comment ISO
@deftypefn {Macro} @var{type} va_arg (va_list @var{ap}, @var{type})
@safety{@prelim{}@mtsafe{@mtsrace{:ap}}@assafe{}@acunsafe{@acucorrupt{}}}
@c This is no longer provided by glibc, but rather by the compiler.
@c Unlike the other va_ macros, that either start/end the lifetime of
@c the va_list object or don't modify it, this one modifies ap, and it
@c may leave it in a partially updated state.
The @code{va_arg} macro returns the value of the next optional argument,
and modifies the value of @var{ap} to point to the subsequent argument.
Thus, successive uses of @code{va_arg} return successive optional
arguments.
The type of the value returned by @code{va_arg} is @var{type} as
specified in the call. @var{type} must be a self-promoting type (not
@code{char} or @code{short int} or @code{float}) that matches the type
of the actual argument.
@end deftypefn
@comment stdarg.h
@comment ISO
@deftypefn {Macro} void va_end (va_list @var{ap})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is no longer provided by glibc, but rather by the compiler.
This ends the use of @var{ap}. After a @code{va_end} call, further
@code{va_arg} calls with the same @var{ap} may not work. You should invoke
@code{va_end} before returning from the function in which @code{va_start}
was invoked with the same @var{ap} argument.
In @theglibc{}, @code{va_end} does nothing, and you need not ever
use it except for reasons of portability.
@refill
@end deftypefn
Sometimes it is necessary to parse the list of parameters more than once
or one wants to remember a certain position in the parameter list. To
do this, one will have to make a copy of the current value of the
argument. But @code{va_list} is an opaque type and one cannot necessarily
assign the value of one variable of type @code{va_list} to another variable
of the same type.
@comment stdarg.h
@comment ISO
@deftypefn {Macro} void va_copy (va_list @var{dest}, va_list @var{src})
@deftypefnx {Macro} void __va_copy (va_list @var{dest}, va_list @var{src})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is no longer provided by glibc, but rather by the compiler.
The @code{va_copy} macro allows copying of objects of type
@code{va_list} even if this is not an integral type. The argument pointer
in @var{dest} is initialized to point to the same argument as the
pointer in @var{src}.
This macro was added in ISO C99. When building for strict conformance
to ISO C90 (@samp{gcc -ansi}), it is not available. The macro
@code{__va_copy} is available as a GNU extension in any standards
mode; before GCC 3.0, it was the only macro for this functionality.
@end deftypefn
If you want to use @code{va_copy} and be portable to pre-C99 systems,
you should always be prepared for the
possibility that this macro will not be available. On architectures where a
simple assignment is invalid, hopefully @code{va_copy} @emph{will} be available,
so one should always write something like this if concerned about
pre-C99 portability:
@smallexample
@{
va_list ap, save;
@dots{}
#ifdef va_copy
va_copy (save, ap);
#else
save = ap;
#endif
@dots{}
@}
@end smallexample
@node Variadic Example
@subsection Example of a Variadic Function
Here is a complete sample function that accepts a variable number of
arguments. The first argument to the function is the count of remaining
arguments, which are added up and the result returned. While trivial,
this function is sufficient to illustrate how to use the variable
arguments facility.
@comment Yes, this example has been tested.
@smallexample
@include add.c.texi
@end smallexample
@node Null Pointer Constant
@section Null Pointer Constant
@cindex null pointer constant
The null pointer constant is guaranteed not to point to any real object.
You can assign it to any pointer variable since it has type @code{void
*}. The preferred way to write a null pointer constant is with
@code{NULL}.
@comment stddef.h
@comment ISO
@deftypevr Macro {void *} NULL
This is a null pointer constant.
@end deftypevr
You can also use @code{0} or @code{(void *)0} as a null pointer
constant, but using @code{NULL} is cleaner because it makes the purpose
of the constant more evident.
If you use the null pointer constant as a function argument, then for
complete portability you should make sure that the function has a
prototype declaration. Otherwise, if the target machine has two
different pointer representations, the compiler won't know which
representation to use for that argument. You can avoid the problem by
explicitly casting the constant to the proper pointer type, but we
recommend instead adding a prototype for the function you are calling.
@node Important Data Types
@section Important Data Types
The result of subtracting two pointers in C is always an integer, but the
precise data type varies from C compiler to C compiler. Likewise, the
data type of the result of @code{sizeof} also varies between compilers.
ISO defines standard aliases for these two types, so you can refer to
them in a portable fashion. They are defined in the header file
@file{stddef.h}.
@pindex stddef.h
@comment stddef.h
@comment ISO
@deftp {Data Type} ptrdiff_t
This is the signed integer type of the result of subtracting two
pointers. For example, with the declaration @code{char *p1, *p2;}, the
expression @code{p2 - p1} is of type @code{ptrdiff_t}. This will
probably be one of the standard signed integer types (@w{@code{short
int}}, @code{int} or @w{@code{long int}}), but might be a nonstandard
type that exists only for this purpose.
@end deftp
@comment stddef.h
@comment ISO
@deftp {Data Type} size_t
This is an unsigned integer type used to represent the sizes of objects.
The result of the @code{sizeof} operator is of this type, and functions
such as @code{malloc} (@pxref{Unconstrained Allocation}) and
@code{memcpy} (@pxref{Copying and Concatenation}) accept arguments of
this type to specify object sizes. On systems using @theglibc{}, this
will be @w{@code{unsigned int}} or @w{@code{unsigned long int}}.
@strong{Usage Note:} @code{size_t} is the preferred way to declare any
arguments or variables that hold the size of an object.
@end deftp
@strong{Compatibility Note:} Implementations of C before the advent of
@w{ISO C} generally used @code{unsigned int} for representing object sizes
and @code{int} for pointer subtraction results. They did not
necessarily define either @code{size_t} or @code{ptrdiff_t}. Unix
systems did define @code{size_t}, in @file{sys/types.h}, but the
definition was usually a signed type.
@node Data Type Measurements
@section Data Type Measurements
Most of the time, if you choose the proper C data type for each object
in your program, you need not be concerned with just how it is
represented or how many bits it uses. When you do need such
information, the C language itself does not provide a way to get it.
The header files @file{limits.h} and @file{float.h} contain macros
which give you this information in full detail.
@menu
* Width of Type:: How many bits does an integer type hold?
* Range of Type:: What are the largest and smallest values
that an integer type can hold?
* Floating Type Macros:: Parameters that measure the floating point types.
* Structure Measurement:: Getting measurements on structure types.
@end menu
@node Width of Type
@subsection Computing the Width of an Integer Data Type
@cindex integer type width
@cindex width of integer type
@cindex type measurements, integer
The most common reason that a program needs to know how many bits are in
an integer type is for using an array of @code{long int} as a bit vector.
You can access the bit at index @var{n} with
@smallexample
vector[@var{n} / LONGBITS] & (1 << (@var{n} % LONGBITS))
@end smallexample
@noindent
provided you define @code{LONGBITS} as the number of bits in a
@code{long int}.
@pindex limits.h
There is no operator in the C language that can give you the number of
bits in an integer data type. But you can compute it from the macro
@code{CHAR_BIT}, defined in the header file @file{limits.h}.
@table @code
@comment limits.h
@comment ISO
@item CHAR_BIT
This is the number of bits in a @code{char}---eight, on most systems.
The value has type @code{int}.
You can compute the number of bits in any data type @var{type} like
this:
@smallexample
sizeof (@var{type}) * CHAR_BIT
@end smallexample
@end table
@node Range of Type
@subsection Range of an Integer Type
@cindex integer type range
@cindex range of integer type
@cindex limits, integer types
Suppose you need to store an integer value which can range from zero to
one million. Which is the smallest type you can use? There is no
general rule; it depends on the C compiler and target machine. You can
use the @samp{MIN} and @samp{MAX} macros in @file{limits.h} to determine
which type will work.
Each signed integer type has a pair of macros which give the smallest
and largest values that it can hold. Each unsigned integer type has one
such macro, for the maximum value; the minimum value is, of course,
zero.
The values of these macros are all integer constant expressions. The
@samp{MAX} and @samp{MIN} macros for @code{char} and @w{@code{short
int}} types have values of type @code{int}. The @samp{MAX} and
@samp{MIN} macros for the other types have values of the same type
described by the macro---thus, @code{ULONG_MAX} has type
@w{@code{unsigned long int}}.
@comment Extra blank lines make it look better.
@vtable @code
@comment limits.h
@comment ISO
@item SCHAR_MIN
This is the minimum value that can be represented by a @w{@code{signed char}}.
@comment limits.h
@comment ISO
@item SCHAR_MAX
@comment limits.h
@comment ISO
@itemx UCHAR_MAX
These are the maximum values that can be represented by a
@w{@code{signed char}} and @w{@code{unsigned char}}, respectively.
@comment limits.h
@comment ISO
@item CHAR_MIN
This is the minimum value that can be represented by a @code{char}.
It's equal to @code{SCHAR_MIN} if @code{char} is signed, or zero
otherwise.
@comment limits.h
@comment ISO
@item CHAR_MAX
This is the maximum value that can be represented by a @code{char}.
It's equal to @code{SCHAR_MAX} if @code{char} is signed, or
@code{UCHAR_MAX} otherwise.
@comment limits.h
@comment ISO
@item SHRT_MIN
This is the minimum value that can be represented by a @w{@code{signed
short int}}. On most machines that @theglibc{} runs on,
@code{short} integers are 16-bit quantities.
@comment limits.h
@comment ISO
@item SHRT_MAX
@comment limits.h
@comment ISO
@itemx USHRT_MAX
These are the maximum values that can be represented by a
@w{@code{signed short int}} and @w{@code{unsigned short int}},
respectively.
@comment limits.h
@comment ISO
@item INT_MIN
This is the minimum value that can be represented by a @w{@code{signed
int}}. On most machines that @theglibc{} runs on, an @code{int} is
a 32-bit quantity.
@comment limits.h
@comment ISO
@item INT_MAX
@comment limits.h
@comment ISO
@itemx UINT_MAX
These are the maximum values that can be represented by, respectively,
the type @w{@code{signed int}} and the type @w{@code{unsigned int}}.
@comment limits.h
@comment ISO
@item LONG_MIN
This is the minimum value that can be represented by a @w{@code{signed
long int}}. On most machines that @theglibc{} runs on, @code{long}
integers are 32-bit quantities, the same size as @code{int}.
@comment limits.h
@comment ISO
@item LONG_MAX
@comment limits.h
@comment ISO
@itemx ULONG_MAX
These are the maximum values that can be represented by a
@w{@code{signed long int}} and @code{unsigned long int}, respectively.
@comment limits.h
@comment ISO
@item LLONG_MIN
This is the minimum value that can be represented by a @w{@code{signed
long long int}}. On most machines that @theglibc{} runs on,
@w{@code{long long}} integers are 64-bit quantities.
@comment limits.h
@comment ISO
@item LLONG_MAX
@comment limits.h
@comment ISO
@itemx ULLONG_MAX
These are the maximum values that can be represented by a @code{signed
long long int} and @code{unsigned long long int}, respectively.
@comment limits.h
@comment GNU
@item LONG_LONG_MIN
@comment limits.h
@comment GNU
@itemx LONG_LONG_MAX
@comment limits.h
@comment GNU
@itemx ULONG_LONG_MAX
These are obsolete names for @code{LLONG_MIN}, @code{LLONG_MAX}, and
@code{ULLONG_MAX}. They are only available if @code{_GNU_SOURCE} is
defined (@pxref{Feature Test Macros}). In GCC versions prior to 3.0,
these were the only names available.
@comment limits.h
@comment GNU
@item WCHAR_MAX
This is the maximum value that can be represented by a @code{wchar_t}.
@xref{Extended Char Intro}.
@end vtable
The header file @file{limits.h} also defines some additional constants
that parameterize various operating system and file system limits. These
constants are described in @ref{System Configuration}.
@node Floating Type Macros
@subsection Floating Type Macros
@cindex floating type measurements
@cindex measurements of floating types
@cindex type measurements, floating
@cindex limits, floating types
The specific representation of floating point numbers varies from
machine to machine. Because floating point numbers are represented
internally as approximate quantities, algorithms for manipulating
floating point data often need to take account of the precise details of
the machine's floating point representation.
Some of the functions in the C library itself need this information; for
example, the algorithms for printing and reading floating point numbers
(@pxref{I/O on Streams}) and for calculating trigonometric and
irrational functions (@pxref{Mathematics}) use it to avoid round-off
error and loss of accuracy. User programs that implement numerical
analysis techniques also often need this information in order to
minimize or compute error bounds.
The header file @file{float.h} describes the format used by your
machine.
@menu
* Floating Point Concepts:: Definitions of terminology.
* Floating Point Parameters:: Details of specific macros.
* IEEE Floating Point:: The measurements for one common
representation.
@end menu
@node Floating Point Concepts
@subsubsection Floating Point Representation Concepts
This section introduces the terminology for describing floating point
representations.
You are probably already familiar with most of these concepts in terms
of scientific or exponential notation for floating point numbers. For
example, the number @code{123456.0} could be expressed in exponential
notation as @code{1.23456e+05}, a shorthand notation indicating that the
mantissa @code{1.23456} is multiplied by the base @code{10} raised to
power @code{5}.
More formally, the internal representation of a floating point number
can be characterized in terms of the following parameters:
@itemize @bullet
@item
@cindex sign (of floating point number)
The @dfn{sign} is either @code{-1} or @code{1}.
@item
@cindex base (of floating point number)
@cindex radix (of floating point number)
The @dfn{base} or @dfn{radix} for exponentiation, an integer greater
than @code{1}. This is a constant for a particular representation.
@item
@cindex exponent (of floating point number)
The @dfn{exponent} to which the base is raised. The upper and lower
bounds of the exponent value are constants for a particular
representation.
@cindex bias (of floating point number exponent)
Sometimes, in the actual bits representing the floating point number,
the exponent is @dfn{biased} by adding a constant to it, to make it
always be represented as an unsigned quantity. This is only important
if you have some reason to pick apart the bit fields making up the
floating point number by hand, which is something for which @theglibc{}
provides no support. So this is ignored in the discussion that
follows.
@item
@cindex mantissa (of floating point number)
@cindex significand (of floating point number)
The @dfn{mantissa} or @dfn{significand} is an unsigned integer which is a
part of each floating point number.
@item
@cindex precision (of floating point number)
The @dfn{precision} of the mantissa. If the base of the representation
is @var{b}, then the precision is the number of base-@var{b} digits in
the mantissa. This is a constant for a particular representation.
@cindex hidden bit (of floating point number mantissa)
Many floating point representations have an implicit @dfn{hidden bit} in
the mantissa. This is a bit which is present virtually in the mantissa,
but not stored in memory because its value is always 1 in a normalized
number. The precision figure (see above) includes any hidden bits.
Again, @theglibc{} provides no facilities for dealing with such
low-level aspects of the representation.
@end itemize
The mantissa of a floating point number represents an implicit fraction
whose denominator is the base raised to the power of the precision. Since
the largest representable mantissa is one less than this denominator, the
value of the fraction is always strictly less than @code{1}. The
mathematical value of a floating point number is then the product of this
fraction, the sign, and the base raised to the exponent.
@cindex normalized floating point number
We say that the floating point number is @dfn{normalized} if the
fraction is at least @code{1/@var{b}}, where @var{b} is the base. In
other words, the mantissa would be too large to fit if it were
multiplied by the base. Non-normalized numbers are sometimes called
@dfn{denormal}; they contain less precision than the representation
normally can hold.
If the number is not normalized, then you can subtract @code{1} from the
exponent while multiplying the mantissa by the base, and get another
floating point number with the same value. @dfn{Normalization} consists
of doing this repeatedly until the number is normalized. Two distinct
normalized floating point numbers cannot be equal in value.
(There is an exception to this rule: if the mantissa is zero, it is
considered normalized. Another exception happens on certain machines
where the exponent is as small as the representation can hold. Then
it is impossible to subtract @code{1} from the exponent, so a number
may be normalized even if its fraction is less than @code{1/@var{b}}.)
@node Floating Point Parameters
@subsubsection Floating Point Parameters
@pindex float.h
These macro definitions can be accessed by including the header file
@file{float.h} in your program.
Macro names starting with @samp{FLT_} refer to the @code{float} type,
while names beginning with @samp{DBL_} refer to the @code{double} type
and names beginning with @samp{LDBL_} refer to the @code{long double}
type. (If GCC does not support @code{long double} as a distinct data
type on a target machine then the values for the @samp{LDBL_} constants
are equal to the corresponding constants for the @code{double} type.)
Of these macros, only @code{FLT_RADIX} is guaranteed to be a constant
expression. The other macros listed here cannot be reliably used in
places that require constant expressions, such as @samp{#if}
preprocessing directives or in the dimensions of static arrays.
Although the @w{ISO C} standard specifies minimum and maximum values for
most of these parameters, the GNU C implementation uses whatever values
describe the floating point representation of the target machine. So in
principle GNU C actually satisfies the @w{ISO C} requirements only if the
target machine is suitable. In practice, all the machines currently
supported are suitable.
@vtable @code
@comment float.h
@comment ISO
@item FLT_ROUNDS
This value characterizes the rounding mode for floating point addition.
The following values indicate standard rounding modes:
@need 750
@table @code
@item -1
The mode is indeterminable.
@item 0
Rounding is towards zero.
@item 1
Rounding is to the nearest number.
@item 2
Rounding is towards positive infinity.
@item 3
Rounding is towards negative infinity.
@end table
@noindent
Any other value represents a machine-dependent nonstandard rounding
mode.
On most machines, the value is @code{1}, in accordance with the IEEE
standard for floating point.
Here is a table showing how certain values round for each possible value
of @code{FLT_ROUNDS}, if the other aspects of the representation match
the IEEE single-precision standard.
@smallexample
0 1 2 3
1.00000003 1.0 1.0 1.00000012 1.0
1.00000007 1.0 1.00000012 1.00000012 1.0
-1.00000003 -1.0 -1.0 -1.0 -1.00000012
-1.00000007 -1.0 -1.00000012 -1.0 -1.00000012
@end smallexample
@comment float.h
@comment ISO
@item FLT_RADIX
This is the value of the base, or radix, of the exponent representation.
This is guaranteed to be a constant expression, unlike the other macros
described in this section. The value is 2 on all machines we know of
except the IBM 360 and derivatives.
@comment float.h
@comment ISO
@item FLT_MANT_DIG
This is the number of base-@code{FLT_RADIX} digits in the floating point
mantissa for the @code{float} data type. The following expression
yields @code{1.0} (even though mathematically it should not) due to the
limited number of mantissa digits:
@smallexample
float radix = FLT_RADIX;
1.0f + 1.0f / radix / radix / @dots{} / radix
@end smallexample
@noindent
where @code{radix} appears @code{FLT_MANT_DIG} times.
@comment float.h
@comment ISO
@item DBL_MANT_DIG
@itemx LDBL_MANT_DIG
This is the number of base-@code{FLT_RADIX} digits in the floating point
mantissa for the data types @code{double} and @code{long double},
respectively.
@comment Extra blank lines make it look better.
@comment float.h
@comment ISO
@item FLT_DIG
This is the number of decimal digits of precision for the @code{float}
data type. Technically, if @var{p} and @var{b} are the precision and
base (respectively) for the representation, then the decimal precision
@var{q} is the maximum number of decimal digits such that any floating
point number with @var{q} base 10 digits can be rounded to a floating
point number with @var{p} base @var{b} digits and back again, without
change to the @var{q} decimal digits.
The value of this macro is supposed to be at least @code{6}, to satisfy
@w{ISO C}.
@comment float.h
@comment ISO
@item DBL_DIG
@itemx LDBL_DIG
These are similar to @code{FLT_DIG}, but for the data types
@code{double} and @code{long double}, respectively. The values of these
macros are supposed to be at least @code{10}.
@comment float.h
@comment ISO
@item FLT_MIN_EXP
This is the smallest possible exponent value for type @code{float}.
More precisely, is the minimum negative integer such that the value
@code{FLT_RADIX} raised to this power minus 1 can be represented as a
normalized floating point number of type @code{float}.
@comment float.h
@comment ISO
@item DBL_MIN_EXP
@itemx LDBL_MIN_EXP
These are similar to @code{FLT_MIN_EXP}, but for the data types
@code{double} and @code{long double}, respectively.
@comment float.h
@comment ISO
@item FLT_MIN_10_EXP
This is the minimum negative integer such that @code{10} raised to this
power minus 1 can be represented as a normalized floating point number
of type @code{float}. This is supposed to be @code{-37} or even less.
@comment float.h
@comment ISO
@item DBL_MIN_10_EXP
@itemx LDBL_MIN_10_EXP
These are similar to @code{FLT_MIN_10_EXP}, but for the data types
@code{double} and @code{long double}, respectively.
@comment float.h
@comment ISO
@item FLT_MAX_EXP
This is the largest possible exponent value for type @code{float}. More
precisely, this is the maximum positive integer such that value
@code{FLT_RADIX} raised to this power minus 1 can be represented as a
floating point number of type @code{float}.
@comment float.h
@comment ISO
@item DBL_MAX_EXP
@itemx LDBL_MAX_EXP
These are similar to @code{FLT_MAX_EXP}, but for the data types
@code{double} and @code{long double}, respectively.
@comment float.h
@comment ISO
@item FLT_MAX_10_EXP
This is the maximum positive integer such that @code{10} raised to this
power minus 1 can be represented as a normalized floating point number
of type @code{float}. This is supposed to be at least @code{37}.
@comment float.h
@comment ISO
@item DBL_MAX_10_EXP
@itemx LDBL_MAX_10_EXP
These are similar to @code{FLT_MAX_10_EXP}, but for the data types
@code{double} and @code{long double}, respectively.
@comment float.h
@comment ISO
@item FLT_MAX
The value of this macro is the maximum number representable in type
@code{float}. It is supposed to be at least @code{1E+37}. The value
has type @code{float}.
The smallest representable number is @code{- FLT_MAX}.
@comment float.h
@comment ISO
@item DBL_MAX
@itemx LDBL_MAX
These are similar to @code{FLT_MAX}, but for the data types
@code{double} and @code{long double}, respectively. The type of the
macro's value is the same as the type it describes.
@comment float.h
@comment ISO
@item FLT_MIN
The value of this macro is the minimum normalized positive floating
point number that is representable in type @code{float}. It is supposed
to be no more than @code{1E-37}.
@comment float.h
@comment ISO
@item DBL_MIN
@itemx LDBL_MIN
These are similar to @code{FLT_MIN}, but for the data types
@code{double} and @code{long double}, respectively. The type of the
macro's value is the same as the type it describes.
@comment float.h
@comment ISO
@item FLT_EPSILON
This is the difference between 1 and the smallest floating point
number of type @code{float} that is greater than 1. It's supposed to
be no greater than @code{1E-5}.
@comment float.h
@comment ISO
@item DBL_EPSILON
@itemx LDBL_EPSILON
These are similar to @code{FLT_EPSILON}, but for the data types
@code{double} and @code{long double}, respectively. The type of the
macro's value is the same as the type it describes. The values are not
supposed to be greater than @code{1E-9}.
@end vtable
@node IEEE Floating Point
@subsubsection IEEE Floating Point
@cindex IEEE floating point representation
@cindex floating point, IEEE
Here is an example showing how the floating type measurements come out
for the most common floating point representation, specified by the
@cite{IEEE Standard for Binary Floating Point Arithmetic (ANSI/IEEE Std
754-1985)}. Nearly all computers designed since the 1980s use this
format.
The IEEE single-precision float representation uses a base of 2. There
is a sign bit, a mantissa with 23 bits plus one hidden bit (so the total
precision is 24 base-2 digits), and an 8-bit exponent that can represent
values in the range -125 to 128, inclusive.
So, for an implementation that uses this representation for the
@code{float} data type, appropriate values for the corresponding
parameters are:
@smallexample
FLT_RADIX 2
FLT_MANT_DIG 24
FLT_DIG 6
FLT_MIN_EXP -125
FLT_MIN_10_EXP -37
FLT_MAX_EXP 128
FLT_MAX_10_EXP +38
FLT_MIN 1.17549435E-38F
FLT_MAX 3.40282347E+38F
FLT_EPSILON 1.19209290E-07F
@end smallexample
Here are the values for the @code{double} data type:
@smallexample
DBL_MANT_DIG 53
DBL_DIG 15
DBL_MIN_EXP -1021
DBL_MIN_10_EXP -307
DBL_MAX_EXP 1024
DBL_MAX_10_EXP 308
DBL_MAX 1.7976931348623157E+308
DBL_MIN 2.2250738585072014E-308
DBL_EPSILON 2.2204460492503131E-016
@end smallexample
@node Structure Measurement
@subsection Structure Field Offset Measurement
You can use @code{offsetof} to measure the location within a structure
type of a particular structure member.
@comment stddef.h
@comment ISO
@deftypefn {Macro} size_t offsetof (@var{type}, @var{member})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is no longer provided by glibc, but rather by the compiler.
This expands to an integer constant expression that is the offset of the
structure member named @var{member} in the structure type @var{type}.
For example, @code{offsetof (struct s, elem)} is the offset, in bytes,
of the member @code{elem} in a @code{struct s}.
This macro won't work if @var{member} is a bit field; you get an error
from the C compiler in that case.
@end deftypefn
glibc-doc-reference-2.19.orig/manual/process.texi 0000664 0001750 0001750 00000103310 12275120646 022126 0 ustar adconrad adconrad @node Processes, Job Control, Program Basics, Top
@c %MENU% How to create processes and run other programs
@chapter Processes
@cindex process
@dfn{Processes} are the primitive units for allocation of system
resources. Each process has its own address space and (usually) one
thread of control. A process executes a program; you can have multiple
processes executing the same program, but each process has its own copy
of the program within its own address space and executes it
independently of the other copies.
@cindex child process
@cindex parent process
Processes are organized hierarchically. Each process has a @dfn{parent
process} which explicitly arranged to create it. The processes created
by a given parent are called its @dfn{child processes}. A child
inherits many of its attributes from the parent process.
This chapter describes how a program can create, terminate, and control
child processes. Actually, there are three distinct operations
involved: creating a new child process, causing the new process to
execute a program, and coordinating the completion of the child process
with the original program.
The @code{system} function provides a simple, portable mechanism for
running another program; it does all three steps automatically. If you
need more control over the details of how this is done, you can use the
primitive functions to do each step individually instead.
@menu
* Running a Command:: The easy way to run another program.
* Process Creation Concepts:: An overview of the hard way to do it.
* Process Identification:: How to get the process ID of a process.
* Creating a Process:: How to fork a child process.
* Executing a File:: How to make a process execute another program.
* Process Completion:: How to tell when a child process has completed.
* Process Completion Status:: How to interpret the status value
returned from a child process.
* BSD Wait Functions:: More functions, for backward compatibility.
* Process Creation Example:: A complete example program.
@end menu
@node Running a Command
@section Running a Command
@cindex running a command
The easy way to run another program is to use the @code{system}
function. This function does all the work of running a subprogram, but
it doesn't give you much control over the details: you have to wait
until the subprogram terminates before you can do anything else.
@comment stdlib.h
@comment ISO
@deftypefun int system (const char *@var{command})
@pindex sh
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{} @ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
@c system @ascuplugin @ascuheap @asulock @aculock @acsmem
@c do_system @ascuplugin @ascuheap @asulock @aculock @acsmem
@c sigemptyset dup ok
@c libc_lock_lock @asulock @aculock
@c ADD_REF ok
@c sigaction dup ok
@c SUB_REF ok
@c libc_lock_unlock @aculock
@c sigaddset dup ok
@c sigprocmask dup ok
@c CLEANUP_HANDLER @ascuplugin @ascuheap @acsmem
@c libc_cleanup_region_start @ascuplugin @ascuheap @acsmem
@c pthread_cleanup_push_defer @ascuplugin @ascuheap @acsmem
@c CANCELLATION_P @ascuplugin @ascuheap @acsmem
@c CANCEL_ENABLED_AND_CANCELED ok
@c do_cancel @ascuplugin @ascuheap @acsmem
@c cancel_handler ok
@c kill syscall ok
@c waitpid dup ok
@c libc_lock_lock ok
@c sigaction dup ok
@c libc_lock_unlock ok
@c FORK ok
@c clone syscall ok
@c waitpid dup ok
@c CLEANUP_RESET ok
@c libc_cleanup_region_end ok
@c pthread_cleanup_pop_restore ok
@c SINGLE_THREAD_P ok
@c LIBC_CANCEL_ASYNC @ascuplugin @ascuheap @acsmem
@c libc_enable_asynccancel @ascuplugin @ascuheap @acsmem
@c CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS dup ok
@c do_cancel dup @ascuplugin @ascuheap @acsmem
@c LIBC_CANCEL_RESET ok
@c libc_disable_asynccancel ok
@c lll_futex_wait dup ok
This function executes @var{command} as a shell command. In @theglibc{},
it always uses the default shell @code{sh} to run the command.
In particular, it searches the directories in @code{PATH} to find
programs to execute. The return value is @code{-1} if it wasn't
possible to create the shell process, and otherwise is the status of the
shell process. @xref{Process Completion}, for details on how this
status code can be interpreted.
If the @var{command} argument is a null pointer, a return value of zero
indicates that no command processor is available.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{system} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{system} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
@pindex stdlib.h
The @code{system} function is declared in the header file
@file{stdlib.h}.
@end deftypefun
@strong{Portability Note:} Some C implementations may not have any
notion of a command processor that can execute other programs. You can
determine whether a command processor exists by executing
@w{@code{system (NULL)}}; if the return value is nonzero, a command
processor is available.
The @code{popen} and @code{pclose} functions (@pxref{Pipe to a
Subprocess}) are closely related to the @code{system} function. They
allow the parent process to communicate with the standard input and
output channels of the command being executed.
@node Process Creation Concepts
@section Process Creation Concepts
This section gives an overview of processes and of the steps involved in
creating a process and making it run another program.
@cindex process ID
@cindex process lifetime
Each process is named by a @dfn{process ID} number. A unique process ID
is allocated to each process when it is created. The @dfn{lifetime} of
a process ends when its termination is reported to its parent process;
at that time, all of the process resources, including its process ID,
are freed.
@cindex creating a process
@cindex forking a process
@cindex child process
@cindex parent process
Processes are created with the @code{fork} system call (so the operation
of creating a new process is sometimes called @dfn{forking} a process).
The @dfn{child process} created by @code{fork} is a copy of the original
@dfn{parent process}, except that it has its own process ID.
After forking a child process, both the parent and child processes
continue to execute normally. If you want your program to wait for a
child process to finish executing before continuing, you must do this
explicitly after the fork operation, by calling @code{wait} or
@code{waitpid} (@pxref{Process Completion}). These functions give you
limited information about why the child terminated---for example, its
exit status code.
A newly forked child process continues to execute the same program as
its parent process, at the point where the @code{fork} call returns.
You can use the return value from @code{fork} to tell whether the program
is running in the parent process or the child.
@cindex process image
Having several processes run the same program is only occasionally
useful. But the child can execute another program using one of the
@code{exec} functions; see @ref{Executing a File}. The program that the
process is executing is called its @dfn{process image}. Starting
execution of a new program causes the process to forget all about its
previous process image; when the new program exits, the process exits
too, instead of returning to the previous process image.
@node Process Identification
@section Process Identification
The @code{pid_t} data type represents process IDs. You can get the
process ID of a process by calling @code{getpid}. The function
@code{getppid} returns the process ID of the parent of the current
process (this is also known as the @dfn{parent process ID}). Your
program should include the header files @file{unistd.h} and
@file{sys/types.h} to use these functions.
@pindex sys/types.h
@pindex unistd.h
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} pid_t
The @code{pid_t} data type is a signed integer type which is capable
of representing a process ID. In @theglibc{}, this is an @code{int}.
@end deftp
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t getpid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getpid} function returns the process ID of the current process.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t getppid (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getppid} function returns the process ID of the parent of the
current process.
@end deftypefun
@node Creating a Process
@section Creating a Process
The @code{fork} function is the primitive for creating a process.
It is declared in the header file @file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun pid_t fork (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{}}@acunsafe{@aculock{}}}
@c The nptl/.../linux implementation safely collects fork_handlers into
@c an alloca()ed linked list and increments ref counters; it uses atomic
@c ops and retries, avoiding locking altogether. It then takes the
@c IO_list lock, resets the thread-local pid, and runs fork. The parent
@c restores the thread-local pid, releases the lock, and runs parent
@c handlers, decrementing the ref count and signaling futex wait if
@c requested by unregister_atfork. The child bumps the fork generation,
@c sets the thread-local pid, resets cpu clocks, initializes the robust
@c mutex list, the stream locks, the IO_list lock, the dynamic loader
@c lock, runs the child handlers, reseting ref counters to 1, and
@c initializes the fork lock. These are all safe, unless atfork
@c handlers themselves are unsafe.
The @code{fork} function creates a new process.
If the operation is successful, there are then both parent and child
processes and both see @code{fork} return, but with different values: it
returns a value of @code{0} in the child process and returns the child's
process ID in the parent process.
If process creation failed, @code{fork} returns a value of @code{-1} in
the parent process. The following @code{errno} error conditions are
defined for @code{fork}:
@table @code
@item EAGAIN
There aren't enough system resources to create another process, or the
user already has too many processes running. This means exceeding the
@code{RLIMIT_NPROC} resource limit, which can usually be increased;
@pxref{Limits on Resources}.
@item ENOMEM
The process requires more space than the system can supply.
@end table
@end deftypefun
The specific attributes of the child process that differ from the
parent process are:
@itemize @bullet
@item
The child process has its own unique process ID.
@item
The parent process ID of the child process is the process ID of its
parent process.
@item
The child process gets its own copies of the parent process's open file
descriptors. Subsequently changing attributes of the file descriptors
in the parent process won't affect the file descriptors in the child,
and vice versa. @xref{Control Operations}. However, the file position
associated with each descriptor is shared by both processes;
@pxref{File Position}.
@item
The elapsed processor times for the child process are set to zero;
see @ref{Processor Time}.
@item
The child doesn't inherit file locks set by the parent process.
@c !!! flock locks shared
@xref{Control Operations}.
@item
The child doesn't inherit alarms set by the parent process.
@xref{Setting an Alarm}.
@item
The set of pending signals (@pxref{Delivery of Signal}) for the child
process is cleared. (The child process inherits its mask of blocked
signals and signal actions from the parent process.)
@end itemize
@comment unistd.h
@comment BSD
@deftypefun pid_t vfork (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{}}@acunsafe{@aculock{}}}
@c The vfork implementation proper is a safe syscall, but it may fall
@c back to fork if the vfork syscall is not available.
The @code{vfork} function is similar to @code{fork} but on some systems
it is more efficient; however, there are restrictions you must follow to
use it safely.
While @code{fork} makes a complete copy of the calling process's address
space and allows both the parent and child to execute independently,
@code{vfork} does not make this copy. Instead, the child process
created with @code{vfork} shares its parent's address space until it
calls @code{_exit} or one of the @code{exec} functions. In the
meantime, the parent process suspends execution.
You must be very careful not to allow the child process created with
@code{vfork} to modify any global data or even local variables shared
with the parent. Furthermore, the child process cannot return from (or
do a long jump out of) the function that called @code{vfork}! This
would leave the parent process's control information very confused. If
in doubt, use @code{fork} instead.
Some operating systems don't really implement @code{vfork}. @Theglibc{}
permits you to use @code{vfork} on all systems, but actually
executes @code{fork} if @code{vfork} isn't available. If you follow
the proper precautions for using @code{vfork}, your program will still
work even if the system uses @code{fork} instead.
@end deftypefun
@node Executing a File
@section Executing a File
@cindex executing a file
@cindex @code{exec} functions
This section describes the @code{exec} family of functions, for executing
a file as a process image. You can use these functions to make a child
process execute a new program after it has been forked.
To see the effects of @code{exec} from the point of view of the called
program, see @ref{Program Basics}.
@pindex unistd.h
The functions in this family differ in how you specify the arguments,
but otherwise they all do the same thing. They are declared in the
header file @file{unistd.h}.
@comment unistd.h
@comment POSIX.1
@deftypefun int execv (const char *@var{filename}, char *const @var{argv}@t{[]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{execv} function executes the file named by @var{filename} as a
new process image.
The @var{argv} argument is an array of null-terminated strings that is
used to provide a value for the @code{argv} argument to the @code{main}
function of the program to be executed. The last element of this array
must be a null pointer. By convention, the first element of this array
is the file name of the program sans directory names. @xref{Program
Arguments}, for full details on how programs can access these arguments.
The environment for the new process image is taken from the
@code{environ} variable of the current process image; see
@ref{Environment Variables}, for information about environments.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int execl (const char *@var{filename}, const char *@var{arg0}, @dots{})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is similar to @code{execv}, but the @var{argv} strings are
specified individually instead of as an array. A null pointer must be
passed as the last such argument.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int execve (const char *@var{filename}, char *const @var{argv}@t{[]}, char *const @var{env}@t{[]})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is similar to @code{execv}, but permits you to specify the environment
for the new program explicitly as the @var{env} argument. This should
be an array of strings in the same format as for the @code{environ}
variable; see @ref{Environment Access}.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int execle (const char *@var{filename}, const char *@var{arg0}, @dots{}, char *const @var{env}@t{[]})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This is similar to @code{execl}, but permits you to specify the
environment for the new program explicitly. The environment argument is
passed following the null pointer that marks the last @var{argv}
argument, and should be an array of strings in the same format as for
the @code{environ} variable.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int execvp (const char *@var{filename}, char *const @var{argv}@t{[]})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{execvp} function is similar to @code{execv}, except that it
searches the directories listed in the @code{PATH} environment variable
(@pxref{Standard Environment}) to find the full file name of a
file from @var{filename} if @var{filename} does not contain a slash.
This function is useful for executing system utility programs, because
it looks for them in the places that the user has chosen. Shells use it
to run the commands that users type.
@end deftypefun
@comment unistd.h
@comment POSIX.1
@deftypefun int execlp (const char *@var{filename}, const char *@var{arg0}, @dots{})
@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function is like @code{execl}, except that it performs the same
file name searching as the @code{execvp} function.
@end deftypefun
The size of the argument list and environment list taken together must
not be greater than @code{ARG_MAX} bytes. @xref{General Limits}. On
@gnuhurdsystems{}, the size (which compares against @code{ARG_MAX})
includes, for each string, the number of characters in the string, plus
the size of a @code{char *}, plus one, rounded up to a multiple of the
size of a @code{char *}. Other systems may have somewhat different
rules for counting.
These functions normally don't return, since execution of a new program
causes the currently executing program to go away completely. A value
of @code{-1} is returned in the event of a failure. In addition to the
usual file name errors (@pxref{File Name Errors}), the following
@code{errno} error conditions are defined for these functions:
@table @code
@item E2BIG
The combined size of the new program's argument list and environment
list is larger than @code{ARG_MAX} bytes. @gnuhurdsystems{} have no
specific limit on the argument list size, so this error code cannot
result, but you may get @code{ENOMEM} instead if the arguments are too
big for available memory.
@item ENOEXEC
The specified file can't be executed because it isn't in the right format.
@item ENOMEM
Executing the specified file requires more storage than is available.
@end table
If execution of the new file succeeds, it updates the access time field
of the file as if the file had been read. @xref{File Times}, for more
details about access times of files.
The point at which the file is closed again is not specified, but
is at some point before the process exits or before another process
image is executed.
Executing a new process image completely changes the contents of memory,
copying only the argument and environment strings to new locations. But
many other attributes of the process are unchanged:
@itemize @bullet
@item
The process ID and the parent process ID. @xref{Process Creation Concepts}.
@item
Session and process group membership. @xref{Concepts of Job Control}.
@item
Real user ID and group ID, and supplementary group IDs. @xref{Process
Persona}.
@item
Pending alarms. @xref{Setting an Alarm}.
@item
Current working directory and root directory. @xref{Working
Directory}. On @gnuhurdsystems{}, the root directory is not copied when
executing a setuid program; instead the system default root directory
is used for the new program.
@item
File mode creation mask. @xref{Setting Permissions}.
@item
Process signal mask; see @ref{Process Signal Mask}.
@item
Pending signals; see @ref{Blocking Signals}.
@item
Elapsed processor time associated with the process; see @ref{Processor Time}.
@end itemize
If the set-user-ID and set-group-ID mode bits of the process image file
are set, this affects the effective user ID and effective group ID
(respectively) of the process. These concepts are discussed in detail
in @ref{Process Persona}.
Signals that are set to be ignored in the existing process image are
also set to be ignored in the new process image. All other signals are
set to the default action in the new process image. For more
information about signals, see @ref{Signal Handling}.
File descriptors open in the existing process image remain open in the
new process image, unless they have the @code{FD_CLOEXEC}
(close-on-exec) flag set. The files that remain open inherit all
attributes of the open file description from the existing process image,
including file locks. File descriptors are discussed in @ref{Low-Level I/O}.
Streams, by contrast, cannot survive through @code{exec} functions,
because they are located in the memory of the process itself. The new
process image has no streams except those it creates afresh. Each of
the streams in the pre-@code{exec} process image has a descriptor inside
it, and these descriptors do survive through @code{exec} (provided that
they do not have @code{FD_CLOEXEC} set). The new process image can
reconnect these to new streams using @code{fdopen} (@pxref{Descriptors
and Streams}).
@node Process Completion
@section Process Completion
@cindex process completion
@cindex waiting for completion of child process
@cindex testing exit status of child process
The functions described in this section are used to wait for a child
process to terminate or stop, and determine its status. These functions
are declared in the header file @file{sys/wait.h}.
@pindex sys/wait.h
@comment sys/wait.h
@comment POSIX.1
@deftypefun pid_t waitpid (pid_t @var{pid}, int *@var{status-ptr}, int @var{options})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{waitpid} function is used to request status information from a
child process whose process ID is @var{pid}. Normally, the calling
process is suspended until the child process makes status information
available by terminating.
Other values for the @var{pid} argument have special interpretations. A
value of @code{-1} or @code{WAIT_ANY} requests status information for
any child process; a value of @code{0} or @code{WAIT_MYPGRP} requests
information for any child process in the same process group as the
calling process; and any other negative value @minus{} @var{pgid}
requests information for any child process whose process group ID is
@var{pgid}.
If status information for a child process is available immediately, this
function returns immediately without waiting. If more than one eligible
child process has status information available, one of them is chosen
randomly, and its status is returned immediately. To get the status
from the other eligible child processes, you need to call @code{waitpid}
again.
The @var{options} argument is a bit mask. Its value should be the
bitwise OR (that is, the @samp{|} operator) of zero or more of the
@code{WNOHANG} and @code{WUNTRACED} flags. You can use the
@code{WNOHANG} flag to indicate that the parent process shouldn't wait;
and the @code{WUNTRACED} flag to request status information from stopped
processes as well as processes that have terminated.
The status information from the child process is stored in the object
that @var{status-ptr} points to, unless @var{status-ptr} is a null pointer.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{waitpid} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{waitpid} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
The return value is normally the process ID of the child process whose
status is reported. If there are child processes but none of them is
waiting to be noticed, @code{waitpid} will block until one is. However,
if the @code{WNOHANG} option was specified, @code{waitpid} will return
zero instead of blocking.
If a specific PID to wait for was given to @code{waitpid}, it will
ignore all other children (if any). Therefore if there are children
waiting to be noticed but the child whose PID was specified is not one
of them, @code{waitpid} will block or return zero as described above.
A value of @code{-1} is returned in case of error. The following
@code{errno} error conditions are defined for this function:
@table @code
@item EINTR
The function was interrupted by delivery of a signal to the calling
process. @xref{Interrupted Primitives}.
@item ECHILD
There are no child processes to wait for, or the specified @var{pid}
is not a child of the calling process.
@item EINVAL
An invalid value was provided for the @var{options} argument.
@end table
@end deftypefun
These symbolic constants are defined as values for the @var{pid} argument
to the @code{waitpid} function.
@comment Extra blank lines make it look better.
@table @code
@item WAIT_ANY
This constant macro (whose value is @code{-1}) specifies that
@code{waitpid} should return status information about any child process.
@item WAIT_MYPGRP
This constant (with value @code{0}) specifies that @code{waitpid} should
return status information about any child process in the same process
group as the calling process.
@end table
These symbolic constants are defined as flags for the @var{options}
argument to the @code{waitpid} function. You can bitwise-OR the flags
together to obtain a value to use as the argument.
@table @code
@item WNOHANG
This flag specifies that @code{waitpid} should return immediately
instead of waiting, if there is no child process ready to be noticed.
@item WUNTRACED
This flag specifies that @code{waitpid} should report the status of any
child processes that have been stopped as well as those that have
terminated.
@end table
@comment sys/wait.h
@comment POSIX.1
@deftypefun pid_t wait (int *@var{status-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is a simplified version of @code{waitpid}, and is used to wait
until any one child process terminates. The call:
@smallexample
wait (&status)
@end smallexample
@noindent
is exactly equivalent to:
@smallexample
waitpid (-1, &status, 0)
@end smallexample
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time @code{wait} is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to @code{wait} should be
protected using cancellation handlers.
@c ref pthread_cleanup_push / pthread_cleanup_pop
@end deftypefun
@comment sys/wait.h
@comment BSD
@deftypefun pid_t wait4 (pid_t @var{pid}, int *@var{status-ptr}, int @var{options}, struct rusage *@var{usage})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @var{usage} is a null pointer, @code{wait4} is equivalent to
@code{waitpid (@var{pid}, @var{status-ptr}, @var{options})}.
If @var{usage} is not null, @code{wait4} stores usage figures for the
child process in @code{*@var{rusage}} (but only if the child has
terminated, not if it has stopped). @xref{Resource Usage}.
This function is a BSD extension.
@end deftypefun
Here's an example of how to use @code{waitpid} to get the status from
all child processes that have terminated, without ever waiting. This
function is designed to be a handler for @code{SIGCHLD}, the signal that
indicates that at least one child process has terminated.
@smallexample
@group
void
sigchld_handler (int signum)
@{
int pid, status, serrno;
serrno = errno;
while (1)
@{
pid = waitpid (WAIT_ANY, &status, WNOHANG);
if (pid < 0)
@{
perror ("waitpid");
break;
@}
if (pid == 0)
break;
notice_termination (pid, status);
@}
errno = serrno;
@}
@end group
@end smallexample
@node Process Completion Status
@section Process Completion Status
If the exit status value (@pxref{Program Termination}) of the child
process is zero, then the status value reported by @code{waitpid} or
@code{wait} is also zero. You can test for other kinds of information
encoded in the returned status value using the following macros.
These macros are defined in the header file @file{sys/wait.h}.
@pindex sys/wait.h
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WIFEXITED (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if the child process terminated
normally with @code{exit} or @code{_exit}.
@end deftypefn
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WEXITSTATUS (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @code{WIFEXITED} is true of @var{status}, this macro returns the
low-order 8 bits of the exit status value from the child process.
@xref{Exit Status}.
@end deftypefn
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WIFSIGNALED (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if the child process terminated
because it received a signal that was not handled.
@xref{Signal Handling}.
@end deftypefn
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WTERMSIG (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @code{WIFSIGNALED} is true of @var{status}, this macro returns the
signal number of the signal that terminated the child process.
@end deftypefn
@comment sys/wait.h
@comment BSD
@deftypefn Macro int WCOREDUMP (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if the child process terminated
and produced a core dump.
@end deftypefn
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WIFSTOPPED (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro returns a nonzero value if the child process is stopped.
@end deftypefn
@comment sys/wait.h
@comment POSIX.1
@deftypefn Macro int WSTOPSIG (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @code{WIFSTOPPED} is true of @var{status}, this macro returns the
signal number of the signal that caused the child process to stop.
@end deftypefn
@node BSD Wait Functions
@section BSD Process Wait Functions
@Theglibc{} also provides these related facilities for compatibility
with BSD Unix. BSD uses the @code{union wait} data type to represent
status values rather than an @code{int}. The two representations are
actually interchangeable; they describe the same bit patterns. @Theglibc{}
defines macros such as @code{WEXITSTATUS} so that they will
work on either kind of object, and the @code{wait} function is defined
to accept either type of pointer as its @var{status-ptr} argument.
These functions are declared in @file{sys/wait.h}.
@pindex sys/wait.h
@comment sys/wait.h
@comment BSD
@deftp {Data Type} {union wait}
This data type represents program termination status values. It has
the following members:
@table @code
@item int w_termsig
The value of this member is the same as that of the
@code{WTERMSIG} macro.
@item int w_coredump
The value of this member is the same as that of the
@code{WCOREDUMP} macro.
@item int w_retcode
The value of this member is the same as that of the
@code{WEXITSTATUS} macro.
@item int w_stopsig
The value of this member is the same as that of the
@code{WSTOPSIG} macro.
@end table
Instead of accessing these members directly, you should use the
equivalent macros.
@end deftp
The @code{wait3} function is the predecessor to @code{wait4}, which is
more flexible. @code{wait3} is now obsolete.
@comment sys/wait.h
@comment BSD
@deftypefun pid_t wait3 (union wait *@var{status-ptr}, int @var{options}, struct rusage *@var{usage})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
If @var{usage} is a null pointer, @code{wait3} is equivalent to
@code{waitpid (-1, @var{status-ptr}, @var{options})}.
If @var{usage} is not null, @code{wait3} stores usage figures for the
child process in @code{*@var{rusage}} (but only if the child has
terminated, not if it has stopped). @xref{Resource Usage}.
@end deftypefun
@node Process Creation Example
@section Process Creation Example
Here is an example program showing how you might write a function
similar to the built-in @code{system}. It executes its @var{command}
argument using the equivalent of @samp{sh -c @var{command}}.
@smallexample
#include
#include
#include
#include
#include
/* @r{Execute the command using this shell program.} */
#define SHELL "/bin/sh"
@group
int
my_system (const char *command)
@{
int status;
pid_t pid;
@end group
pid = fork ();
if (pid == 0)
@{
/* @r{This is the child process. Execute the shell command.} */
execl (SHELL, SHELL, "-c", command, NULL);
_exit (EXIT_FAILURE);
@}
else if (pid < 0)
/* @r{The fork failed. Report failure.} */
status = -1;
else
/* @r{This is the parent process. Wait for the child to complete.} */
if (waitpid (pid, &status, 0) != pid)
status = -1;
return status;
@}
@end smallexample
@comment Yes, this example has been tested.
There are a couple of things you should pay attention to in this
example.
Remember that the first @code{argv} argument supplied to the program
represents the name of the program being executed. That is why, in the
call to @code{execl}, @code{SHELL} is supplied once to name the program
to execute and a second time to supply a value for @code{argv[0]}.
The @code{execl} call in the child process doesn't return if it is
successful. If it fails, you must do something to make the child
process terminate. Just returning a bad status code with @code{return}
would leave two processes running the original program. Instead, the
right behavior is for the child process to report failure to its parent
process.
Call @code{_exit} to accomplish this. The reason for using @code{_exit}
instead of @code{exit} is to avoid flushing fully buffered streams such
as @code{stdout}. The buffers of these streams probably contain data
that was copied from the parent process by the @code{fork}, data that
will be output eventually by the parent process. Calling @code{exit} in
the child would output the data twice. @xref{Termination Internals}.
glibc-doc-reference-2.19.orig/manual/nsswitch.texi 0000664 0001750 0001750 00000000624 12275120646 022316 0 ustar adconrad adconrad # /etc/nsswitch.conf
#
# Name Service Switch configuration file.
#
passwd: db files nis
shadow: files
group: db files nis
hosts: files nisplus nis dns
networks: nisplus [NOTFOUND=return] files
ethers: nisplus [NOTFOUND=return] db files
protocols: nisplus [NOTFOUND=return] db files
rpc: nisplus [NOTFOUND=return] db files
services: nisplus [NOTFOUND=return] db files
glibc-doc-reference-2.19.orig/manual/startup.texi 0000664 0001750 0001750 00000125331 12275120646 022161 0 ustar adconrad adconrad @node Program Basics, Processes, Signal Handling, Top
@c %MENU% Writing the beginning and end of your program
@chapter The Basic Program/System Interface
@cindex process
@cindex program
@cindex address space
@cindex thread of control
@dfn{Processes} are the primitive units for allocation of system
resources. Each process has its own address space and (usually) one
thread of control. A process executes a program; you can have multiple
processes executing the same program, but each process has its own copy
of the program within its own address space and executes it
independently of the other copies. Though it may have multiple threads
of control within the same program and a program may be composed of
multiple logically separate modules, a process always executes exactly
one program.
Note that we are using a specific definition of ``program'' for the
purposes of this manual, which corresponds to a common definition in the
context of Unix system. In popular usage, ``program'' enjoys a much
broader definition; it can refer for example to a system's kernel, an
editor macro, a complex package of software, or a discrete section of
code executing within a process.
Writing the program is what this manual is all about. This chapter
explains the most basic interface between your program and the system
that runs, or calls, it. This includes passing of parameters (arguments
and environment) from the system, requesting basic services from the
system, and telling the system the program is done.
A program starts another program with the @code{exec} family of system calls.
This chapter looks at program startup from the execee's point of view. To
see the event from the execor's point of view, see @ref{Executing a File}.
@menu
* Program Arguments:: Parsing your program's command-line arguments
* Environment Variables:: Less direct parameters affecting your program
* Auxiliary Vector:: Least direct parameters affecting your program
* System Calls:: Requesting service from the system
* Program Termination:: Telling the system you're done; return status
@end menu
@node Program Arguments, Environment Variables, , Program Basics
@section Program Arguments
@cindex program arguments
@cindex command line arguments
@cindex arguments, to program
@cindex program startup
@cindex startup of program
@cindex invocation of program
@cindex @code{main} function
@findex main
The system starts a C program by calling the function @code{main}. It
is up to you to write a function named @code{main}---otherwise, you
won't even be able to link your program without errors.
In @w{ISO C} you can define @code{main} either to take no arguments, or to
take two arguments that represent the command line arguments to the
program, like this:
@smallexample
int main (int @var{argc}, char *@var{argv}[])
@end smallexample
@cindex argc (program argument count)
@cindex argv (program argument vector)
The command line arguments are the whitespace-separated tokens given in
the shell command used to invoke the program; thus, in @samp{cat foo
bar}, the arguments are @samp{foo} and @samp{bar}. The only way a
program can look at its command line arguments is via the arguments of
@code{main}. If @code{main} doesn't take arguments, then you cannot get
at the command line.
The value of the @var{argc} argument is the number of command line
arguments. The @var{argv} argument is a vector of C strings; its
elements are the individual command line argument strings. The file
name of the program being run is also included in the vector as the
first element; the value of @var{argc} counts this element. A null
pointer always follows the last element: @code{@var{argv}[@var{argc}]}
is this null pointer.
For the command @samp{cat foo bar}, @var{argc} is 3 and @var{argv} has
three elements, @code{"cat"}, @code{"foo"} and @code{"bar"}.
In Unix systems you can define @code{main} a third way, using three arguments:
@smallexample
int main (int @var{argc}, char *@var{argv}[], char *@var{envp}[])
@end smallexample
The first two arguments are just the same. The third argument
@var{envp} gives the program's environment; it is the same as the value
of @code{environ}. @xref{Environment Variables}. POSIX.1 does not
allow this three-argument form, so to be portable it is best to write
@code{main} to take two arguments, and use the value of @code{environ}.
@menu
* Argument Syntax:: By convention, options start with a hyphen.
* Parsing Program Arguments:: Ways to parse program options and arguments.
@end menu
@node Argument Syntax, Parsing Program Arguments, , Program Arguments
@subsection Program Argument Syntax Conventions
@cindex program argument syntax
@cindex syntax, for program arguments
@cindex command argument syntax
POSIX recommends these conventions for command line arguments.
@code{getopt} (@pxref{Getopt}) and @code{argp_parse} (@pxref{Argp}) make
it easy to implement them.
@itemize @bullet
@item
Arguments are options if they begin with a hyphen delimiter (@samp{-}).
@item
Multiple options may follow a hyphen delimiter in a single token if
the options do not take arguments. Thus, @samp{-abc} is equivalent to
@samp{-a -b -c}.
@item
Option names are single alphanumeric characters (as for @code{isalnum};
@pxref{Classification of Characters}).
@item
Certain options require an argument. For example, the @samp{-o} command
of the @code{ld} command requires an argument---an output file name.
@item
An option and its argument may or may not appear as separate tokens. (In
other words, the whitespace separating them is optional.) Thus,
@w{@samp{-o foo}} and @samp{-ofoo} are equivalent.
@item
Options typically precede other non-option arguments.
The implementations of @code{getopt} and @code{argp_parse} in @theglibc{}
normally make it appear as if all the option arguments were
specified before all the non-option arguments for the purposes of
parsing, even if the user of your program intermixed option and
non-option arguments. They do this by reordering the elements of the
@var{argv} array. This behavior is nonstandard; if you want to suppress
it, define the @code{_POSIX_OPTION_ORDER} environment variable.
@xref{Standard Environment}.
@item
The argument @samp{--} terminates all options; any following arguments
are treated as non-option arguments, even if they begin with a hyphen.
@item
A token consisting of a single hyphen character is interpreted as an
ordinary non-option argument. By convention, it is used to specify
input from or output to the standard input and output streams.
@item
Options may be supplied in any order, or appear multiple times. The
interpretation is left up to the particular application program.
@end itemize
@cindex long-named options
GNU adds @dfn{long options} to these conventions. Long options consist
of @samp{--} followed by a name made of alphanumeric characters and
dashes. Option names are typically one to three words long, with
hyphens to separate words. Users can abbreviate the option names as
long as the abbreviations are unique.
To specify an argument for a long option, write
@samp{--@var{name}=@var{value}}. This syntax enables a long option to
accept an argument that is itself optional.
Eventually, @gnusystems{} will provide completion for long option names
in the shell.
@node Parsing Program Arguments, , Argument Syntax, Program Arguments
@subsection Parsing Program Arguments
@cindex program arguments, parsing
@cindex command arguments, parsing
@cindex parsing program arguments
If the syntax for the command line arguments to your program is simple
enough, you can simply pick the arguments off from @var{argv} by hand.
But unless your program takes a fixed number of arguments, or all of the
arguments are interpreted in the same way (as file names, for example),
you are usually better off using @code{getopt} (@pxref{Getopt}) or
@code{argp_parse} (@pxref{Argp}) to do the parsing.
@code{getopt} is more standard (the short-option only version of it is a
part of the POSIX standard), but using @code{argp_parse} is often
easier, both for very simple and very complex option structures, because
it does more of the dirty work for you.
@menu
* Getopt:: Parsing program options using @code{getopt}.
* Argp:: Parsing program options using @code{argp_parse}.
* Suboptions:: Some programs need more detailed options.
* Suboptions Example:: This shows how it could be done for @code{mount}.
@end menu
@c Getopt and argp start at the @section level so that there's
@c enough room for their internal hierarchy (mostly a problem with
@c argp). -Miles
@include getopt.texi
@include argp.texi
@node Suboptions, Suboptions Example, Argp, Parsing Program Arguments
@c This is a @section so that it's at the same level as getopt and argp
@subsubsection Parsing of Suboptions
Having a single level of options is sometimes not enough. There might
be too many options which have to be available or a set of options is
closely related.
For this case some programs use suboptions. One of the most prominent
programs is certainly @code{mount}(8). The @code{-o} option take one
argument which itself is a comma separated list of options. To ease the
programming of code like this the function @code{getsubopt} is
available.
@comment stdlib.h
@deftypefun int getsubopt (char **@var{optionp}, char *const *@var{tokens}, char **@var{valuep})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c getsubopt ok
@c strchrnul dup ok
@c memchr dup ok
@c strncmp dup ok
The @var{optionp} parameter must be a pointer to a variable containing
the address of the string to process. When the function returns the
reference is updated to point to the next suboption or to the
terminating @samp{\0} character if there is no more suboption available.
The @var{tokens} parameter references an array of strings containing the
known suboptions. All strings must be @samp{\0} terminated and to mark
the end a null pointer must be stored. When @code{getsubopt} finds a
possible legal suboption it compares it with all strings available in
the @var{tokens} array and returns the index in the string as the
indicator.
In case the suboption has an associated value introduced by a @samp{=}
character, a pointer to the value is returned in @var{valuep}. The
string is @samp{\0} terminated. If no argument is available
@var{valuep} is set to the null pointer. By doing this the caller can
check whether a necessary value is given or whether no unexpected value
is present.
In case the next suboption in the string is not mentioned in the
@var{tokens} array the starting address of the suboption including a
possible value is returned in @var{valuep} and the return value of the
function is @samp{-1}.
@end deftypefun
@node Suboptions Example, , Suboptions, Parsing Program Arguments
@subsection Parsing of Suboptions Example
The code which might appear in the @code{mount}(8) program is a perfect
example of the use of @code{getsubopt}:
@smallexample
@include subopt.c.texi
@end smallexample
@node Environment Variables, Auxiliary Vector, Program Arguments, Program Basics
@section Environment Variables
@cindex environment variable
When a program is executed, it receives information about the context in
which it was invoked in two ways. The first mechanism uses the
@var{argv} and @var{argc} arguments to its @code{main} function, and is
discussed in @ref{Program Arguments}. The second mechanism uses
@dfn{environment variables} and is discussed in this section.
The @var{argv} mechanism is typically used to pass command-line
arguments specific to the particular program being invoked. The
environment, on the other hand, keeps track of information that is
shared by many programs, changes infrequently, and that is less
frequently used.
The environment variables discussed in this section are the same
environment variables that you set using assignments and the
@code{export} command in the shell. Programs executed from the shell
inherit all of the environment variables from the shell.
@c !!! xref to right part of bash manual when it exists
@cindex environment
Standard environment variables are used for information about the user's
home directory, terminal type, current locale, and so on; you can define
additional variables for other purposes. The set of all environment
variables that have values is collectively known as the
@dfn{environment}.
Names of environment variables are case-sensitive and must not contain
the character @samp{=}. System-defined environment variables are
invariably uppercase.
The values of environment variables can be anything that can be
represented as a string. A value must not contain an embedded null
character, since this is assumed to terminate the string.
@menu
* Environment Access:: How to get and set the values of
environment variables.
* Standard Environment:: These environment variables have
standard interpretations.
@end menu
@node Environment Access
@subsection Environment Access
@cindex environment access
@cindex environment representation
The value of an environment variable can be accessed with the
@code{getenv} function. This is declared in the header file
@file{stdlib.h}.
@pindex stdlib.h
Libraries should use @code{secure_getenv} instead of @code{getenv}, so
that they do not accidentally use untrusted environment variables.
Modifications of environment variables are not allowed in
multi-threaded programs. The @code{getenv} and @code{secure_getenv}
functions can be safely used in multi-threaded programs.
@comment stdlib.h
@comment ISO
@deftypefun {char *} getenv (const char *@var{name})
@safety{@prelim{}@mtsafe{@mtsenv{}}@assafe{}@acsafe{}}
@c Unguarded access to __environ.
This function returns a string that is the value of the environment
variable @var{name}. You must not modify this string. In some non-Unix
systems not using @theglibc{}, it might be overwritten by subsequent
calls to @code{getenv} (but not by any other library function). If the
environment variable @var{name} is not defined, the value is a null
pointer.
@end deftypefun
@comment stdlib.h
@comment GNU
@deftypefun {char *} secure_getenv (const char *@var{name})
@safety{@prelim{}@mtsafe{@mtsenv{}}@assafe{}@acsafe{}}
@c Calls getenv unless secure mode is enabled.
This function is similar to @code{getenv}, but it returns a null
pointer if the environment is untrusted. This happens when the
program file has SUID or SGID bits set. General-purpose libraries
should always prefer this function over @code{getenv} to avoid
vulnerabilities if the library is referenced from a SUID/SGID program.
This function is a GNU extension.
@end deftypefun
@comment stdlib.h
@comment SVID
@deftypefun int putenv (char *@var{string})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtsenv{}}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c putenv @mtasuconst:@mtsenv @ascuheap @asulock @acucorrupt @aculock @acsmem
@c strchr dup ok
@c strndup dup @ascuheap @acsmem
@c add_to_environ dup @mtasuconst:@mtsenv @ascuheap @asulock @acucorrupt @aculock @acsmem
@c free dup @ascuheap @acsmem
@c unsetenv dup @mtasuconst:@mtsenv @asulock @aculock
The @code{putenv} function adds or removes definitions from the environment.
If the @var{string} is of the form @samp{@var{name}=@var{value}}, the
definition is added to the environment. Otherwise, the @var{string} is
interpreted as the name of an environment variable, and any definition
for this variable in the environment is removed.
If the function is successful it returns @code{0}. Otherwise the return
value is nonzero and @code{errno} is set to indicate the error.
The difference to the @code{setenv} function is that the exact string
given as the parameter @var{string} is put into the environment. If the
user should change the string after the @code{putenv} call this will
reflect automatically in the environment. This also requires that
@var{string} not be an automatic variable whose scope is left before the
variable is removed from the environment. The same applies of course to
dynamically allocated variables which are freed later.
This function is part of the extended Unix interface. Since it was also
available in old SVID libraries you should define either
@var{_XOPEN_SOURCE} or @var{_SVID_SOURCE} before including any header.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun int setenv (const char *@var{name}, const char *@var{value}, int @var{replace})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtsenv{}}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{}}}
@c setenv @mtasuconst:@mtsenv @ascuheap @asulock @acucorrupt @aculock @acsmem
@c add_to_environ @mtasuconst:@mtsenv @ascuheap @asulock @acucorrupt @aculock @acsmem
@c strlen dup ok
@c libc_lock_lock @asulock @aculock
@c strncmp dup ok
@c realloc dup @ascuheap @acsmem
@c libc_lock_unlock @aculock
@c malloc dup @ascuheap @acsmem
@c free dup @ascuheap @acsmem
@c mempcpy dup ok
@c memcpy dup ok
@c KNOWN_VALUE ok
@c tfind(strcmp) [no @mtsrace guarded access]
@c strcmp dup ok
@c STORE_VALUE @ascuheap @acucorrupt @acsmem
@c tsearch(strcmp) @ascuheap @acucorrupt @acsmem [no @mtsrace or @asucorrupt guarded access makes for mtsafe and @asulock]
@c strcmp dup ok
The @code{setenv} function can be used to add a new definition to the
environment. The entry with the name @var{name} is replaced by the
value @samp{@var{name}=@var{value}}. Please note that this is also true
if @var{value} is the empty string. To do this a new string is created
and the strings @var{name} and @var{value} are copied. A null pointer
for the @var{value} parameter is illegal. If the environment already
contains an entry with key @var{name} the @var{replace} parameter
controls the action. If replace is zero, nothing happens. Otherwise
the old entry is replaced by the new one.
Please note that you cannot remove an entry completely using this function.
If the function is successful it returns @code{0}. Otherwise the
environment is unchanged and the return value is @code{-1} and
@code{errno} is set.
This function was originally part of the BSD library but is now part of
the Unix standard.
@end deftypefun
@comment stdlib.h
@comment BSD
@deftypefun int unsetenv (const char *@var{name})
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtsenv{}}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
@c unsetenv @mtasuconst:@mtsenv @asulock @aculock
@c strchr dup ok
@c strlen dup ok
@c libc_lock_lock @asulock @aculock
@c strncmp dup ok
@c libc_lock_unlock @aculock
Using this function one can remove an entry completely from the
environment. If the environment contains an entry with the key
@var{name} this whole entry is removed. A call to this function is
equivalent to a call to @code{putenv} when the @var{value} part of the
string is empty.
The function return @code{-1} if @var{name} is a null pointer, points to
an empty string, or points to a string containing a @code{=} character.
It returns @code{0} if the call succeeded.
This function was originally part of the BSD library but is now part of
the Unix standard. The BSD version had no return value, though.
@end deftypefun
There is one more function to modify the whole environment. This
function is said to be used in the POSIX.9 (POSIX bindings for Fortran
77) and so one should expect it did made it into POSIX.1. But this
never happened. But we still provide this function as a GNU extension
to enable writing standard compliant Fortran environments.
@comment stdlib.h
@comment GNU
@deftypefun int clearenv (void)
@safety{@prelim{}@mtunsafe{@mtasuconst{:@mtsenv{}}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
@c clearenv @mtasuconst:@mtsenv @ascuheap @asulock @aculock @acsmem
@c libc_lock_lock @asulock @aculock
@c free dup @ascuheap @acsmem
@c libc_lock_unlock @aculock
The @code{clearenv} function removes all entries from the environment.
Using @code{putenv} and @code{setenv} new entries can be added again
later.
If the function is successful it returns @code{0}. Otherwise the return
value is nonzero.
@end deftypefun
You can deal directly with the underlying representation of environment
objects to add more variables to the environment (for example, to
communicate with another program you are about to execute;
@pxref{Executing a File}).
@comment unistd.h
@comment POSIX.1
@deftypevar {char **} environ
The environment is represented as an array of strings. Each string is
of the format @samp{@var{name}=@var{value}}. The order in which
strings appear in the environment is not significant, but the same
@var{name} must not appear more than once. The last element of the
array is a null pointer.
This variable is declared in the header file @file{unistd.h}.
If you just want to get the value of an environment variable, use
@code{getenv}.
@end deftypevar
Unix systems, and @gnusystems{}, pass the initial value of
@code{environ} as the third argument to @code{main}.
@xref{Program Arguments}.
@node Standard Environment
@subsection Standard Environment Variables
@cindex standard environment variables
These environment variables have standard meanings. This doesn't mean
that they are always present in the environment; but if these variables
@emph{are} present, they have these meanings. You shouldn't try to use
these environment variable names for some other purpose.
@comment Extra blank lines make it look better.
@table @code
@item HOME
@cindex @code{HOME} environment variable
@cindex home directory
This is a string representing the user's @dfn{home directory}, or
initial default working directory.
The user can set @code{HOME} to any value.
If you need to make sure to obtain the proper home directory
for a particular user, you should not use @code{HOME}; instead,
look up the user's name in the user database (@pxref{User Database}).
For most purposes, it is better to use @code{HOME}, precisely because
this lets the user specify the value.
@c !!! also USER
@item LOGNAME
@cindex @code{LOGNAME} environment variable
This is the name that the user used to log in. Since the value in the
environment can be tweaked arbitrarily, this is not a reliable way to
identify the user who is running a program; a function like
@code{getlogin} (@pxref{Who Logged In}) is better for that purpose.
For most purposes, it is better to use @code{LOGNAME}, precisely because
this lets the user specify the value.
@item PATH
@cindex @code{PATH} environment variable
A @dfn{path} is a sequence of directory names which is used for
searching for a file. The variable @code{PATH} holds a path used
for searching for programs to be run.
The @code{execlp} and @code{execvp} functions (@pxref{Executing a File})
use this environment variable, as do many shells and other utilities
which are implemented in terms of those functions.
The syntax of a path is a sequence of directory names separated by
colons. An empty string instead of a directory name stands for the
current directory (@pxref{Working Directory}).
A typical value for this environment variable might be a string like:
@smallexample
:/bin:/etc:/usr/bin:/usr/new/X11:/usr/new:/usr/local/bin
@end smallexample
This means that if the user tries to execute a program named @code{foo},
the system will look for files named @file{foo}, @file{/bin/foo},
@file{/etc/foo}, and so on. The first of these files that exists is
the one that is executed.
@c !!! also TERMCAP
@item TERM
@cindex @code{TERM} environment variable
This specifies the kind of terminal that is receiving program output.
Some programs can make use of this information to take advantage of
special escape sequences or terminal modes supported by particular kinds
of terminals. Many programs which use the termcap library
(@pxref{Finding a Terminal Description,Find,,termcap,The Termcap Library
Manual}) use the @code{TERM} environment variable, for example.
@item TZ
@cindex @code{TZ} environment variable
This specifies the time zone. @xref{TZ Variable}, for information about
the format of this string and how it is used.
@item LANG
@cindex @code{LANG} environment variable
This specifies the default locale to use for attribute categories where
neither @code{LC_ALL} nor the specific environment variable for that
category is set. @xref{Locales}, for more information about
locales.
@ignore
@c I doubt this really exists
@item LC_ALL
@cindex @code{LC_ALL} environment variable
This is similar to the @code{LANG} environment variable. However, its
value takes precedence over any values provided for the individual
attribute category environment variables, or for the @code{LANG}
environment variable.
@end ignore
@item LC_ALL
@cindex @code{LC_ALL} environment variable
If this environment variable is set it overrides the selection for all
the locales done using the other @code{LC_*} environment variables. The
value of the other @code{LC_*} environment variables is simply ignored
in this case.
@item LC_COLLATE
@cindex @code{LC_COLLATE} environment variable
This specifies what locale to use for string sorting.
@item LC_CTYPE
@cindex @code{LC_CTYPE} environment variable
This specifies what locale to use for character sets and character
classification.
@item LC_MESSAGES
@cindex @code{LC_MESSAGES} environment variable
This specifies what locale to use for printing messages and to parse
responses.
@item LC_MONETARY
@cindex @code{LC_MONETARY} environment variable
This specifies what locale to use for formatting monetary values.
@item LC_NUMERIC
@cindex @code{LC_NUMERIC} environment variable
This specifies what locale to use for formatting numbers.
@item LC_TIME
@cindex @code{LC_TIME} environment variable
This specifies what locale to use for formatting date/time values.
@item NLSPATH
@cindex @code{NLSPATH} environment variable
This specifies the directories in which the @code{catopen} function
looks for message translation catalogs.
@item _POSIX_OPTION_ORDER
@cindex @code{_POSIX_OPTION_ORDER} environment variable.
If this environment variable is defined, it suppresses the usual
reordering of command line arguments by @code{getopt} and
@code{argp_parse}. @xref{Argument Syntax}.
@c !!! GNU also has COREFILE, CORESERVER, EXECSERVERS
@end table
@node Auxiliary Vector
@section Auxiliary Vector
@cindex auxiliary vector
When a program is executed, it receives information from the operating
system about the environment in which it is operating. The form of this
information is a table of key-value pairs, where the keys are from the
set of @samp{AT_} values in @file{elf.h}. Some of the data is provided
by the kernel for libc consumption, and may be obtained by ordinary
interfaces, such as @code{sysconf}. However, on a platform-by-platform
basis there may be information that is not available any other way.
@subsection Definition of @code{getauxval}
@comment sys/auxv.h
@deftypefun {unsigned long int} getauxval (unsigned long int @var{type})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Reads from hwcap or iterates over constant auxv.
This function is used to inquire about the entries in the auxiliary
vector. The @var{type} argument should be one of the @samp{AT_} symbols
defined in @file{elf.h}. If a matching entry is found, the value is
returned; if the entry is not found, zero is returned and @code{errno} is
set to @code{ENOENT}.
@end deftypefun
For some platforms, the key @code{AT_HWCAP} is the easiest way to inquire
about any instruction set extensions available at runtime. In this case,
there will (of necessity) be a platform-specific set of @samp{HWCAP_}
values masked together that describe the capabilities of the cpu on which
the program is being executed.
@node System Calls
@section System Calls
@cindex system call
A system call is a request for service that a program makes of the
kernel. The service is generally something that only the kernel has
the privilege to do, such as doing I/O. Programmers don't normally
need to be concerned with system calls because there are functions in
@theglibc{} to do virtually everything that system calls do.
These functions work by making system calls themselves. For example,
there is a system call that changes the permissions of a file, but
you don't need to know about it because you can just use @theglibc{}'s
@code{chmod} function.
@cindex kernel call
System calls are sometimes called kernel calls.
However, there are times when you want to make a system call explicitly,
and for that, @theglibc{} provides the @code{syscall} function.
@code{syscall} is harder to use and less portable than functions like
@code{chmod}, but easier and more portable than coding the system call
in assembler instructions.
@code{syscall} is most useful when you are working with a system call
which is special to your system or is newer than @theglibc{} you
are using. @code{syscall} is implemented in an entirely generic way;
the function does not know anything about what a particular system
call does or even if it is valid.
The description of @code{syscall} in this section assumes a certain
protocol for system calls on the various platforms on which @theglibc{}
runs. That protocol is not defined by any strong authority, but
we won't describe it here either because anyone who is coding
@code{syscall} probably won't accept anything less than kernel and C
library source code as a specification of the interface between them
anyway.
@code{syscall} is declared in @file{unistd.h}.
@comment unistd.h
@comment ???
@deftypefun {long int} syscall (long int @var{sysno}, @dots{})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{syscall} performs a generic system call.
@cindex system call number
@var{sysno} is the system call number. Each kind of system call is
identified by a number. Macros for all the possible system call numbers
are defined in @file{sys/syscall.h}
The remaining arguments are the arguments for the system call, in
order, and their meanings depend on the kind of system call. Each kind
of system call has a definite number of arguments, from zero to five.
If you code more arguments than the system call takes, the extra ones to
the right are ignored.
The return value is the return value from the system call, unless the
system call failed. In that case, @code{syscall} returns @code{-1} and
sets @code{errno} to an error code that the system call returned. Note
that system calls do not return @code{-1} when they succeed.
@cindex errno
If you specify an invalid @var{sysno}, @code{syscall} returns @code{-1}
with @code{errno} = @code{ENOSYS}.
Example:
@smallexample
#include
#include
#include
@dots{}
int rc;
rc = syscall(SYS_chmod, "/etc/passwd", 0444);
if (rc == -1)
fprintf(stderr, "chmod failed, errno = %d\n", errno);
@end smallexample
This, if all the compatibility stars are aligned, is equivalent to the
following preferable code:
@smallexample
#include
#include
#include
@dots{}
int rc;
rc = chmod("/etc/passwd", 0444);
if (rc == -1)
fprintf(stderr, "chmod failed, errno = %d\n", errno);
@end smallexample
@end deftypefun
@node Program Termination
@section Program Termination
@cindex program termination
@cindex process termination
@cindex exit status value
The usual way for a program to terminate is simply for its @code{main}
function to return. The @dfn{exit status value} returned from the
@code{main} function is used to report information back to the process's
parent process or shell.
A program can also terminate normally by calling the @code{exit}
function.
In addition, programs can be terminated by signals; this is discussed in
more detail in @ref{Signal Handling}. The @code{abort} function causes
a signal that kills the program.
@menu
* Normal Termination:: If a program calls @code{exit}, a
process terminates normally.
* Exit Status:: The @code{exit status} provides information
about why the process terminated.
* Cleanups on Exit:: A process can run its own cleanup
functions upon normal termination.
* Aborting a Program:: The @code{abort} function causes
abnormal program termination.
* Termination Internals:: What happens when a process terminates.
@end menu
@node Normal Termination
@subsection Normal Termination
A process terminates normally when its program signals it is done by
calling @code{exit}. Returning from @code{main} is equivalent to
calling @code{exit}, and the value that @code{main} returns is used as
the argument to @code{exit}.
@comment stdlib.h
@comment ISO
@deftypefun void exit (int @var{status})
@safety{@prelim{}@mtunsafe{@mtasurace{:exit}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
@c Access to the atexit/on_exit list, the libc_atexit hook and tls dtors
@c is not guarded. Streams must be flushed, and that triggers the usual
@c AS and AC issues with streams.
The @code{exit} function tells the system that the program is done, which
causes it to terminate the process.
@var{status} is the program's exit status, which becomes part of the
process' termination status. This function does not return.
@end deftypefun
Normal termination causes the following actions:
@enumerate
@item
Functions that were registered with the @code{atexit} or @code{on_exit}
functions are called in the reverse order of their registration. This
mechanism allows your application to specify its own ``cleanup'' actions
to be performed at program termination. Typically, this is used to do
things like saving program state information in a file, or unlocking
locks in shared data bases.
@item
All open streams are closed, writing out any buffered output data. See
@ref{Closing Streams}. In addition, temporary files opened
with the @code{tmpfile} function are removed; see @ref{Temporary Files}.
@item
@code{_exit} is called, terminating the program. @xref{Termination Internals}.
@end enumerate
@node Exit Status
@subsection Exit Status
@cindex exit status
When a program exits, it can return to the parent process a small
amount of information about the cause of termination, using the
@dfn{exit status}. This is a value between 0 and 255 that the exiting
process passes as an argument to @code{exit}.
Normally you should use the exit status to report very broad information
about success or failure. You can't provide a lot of detail about the
reasons for the failure, and most parent processes would not want much
detail anyway.
There are conventions for what sorts of status values certain programs
should return. The most common convention is simply 0 for success and 1
for failure. Programs that perform comparison use a different
convention: they use status 1 to indicate a mismatch, and status 2 to
indicate an inability to compare. Your program should follow an
existing convention if an existing convention makes sense for it.
A general convention reserves status values 128 and up for special
purposes. In particular, the value 128 is used to indicate failure to
execute another program in a subprocess. This convention is not
universally obeyed, but it is a good idea to follow it in your programs.
@strong{Warning:} Don't try to use the number of errors as the exit
status. This is actually not very useful; a parent process would
generally not care how many errors occurred. Worse than that, it does
not work, because the status value is truncated to eight bits.
Thus, if the program tried to report 256 errors, the parent would
receive a report of 0 errors---that is, success.
For the same reason, it does not work to use the value of @code{errno}
as the exit status---these can exceed 255.
@strong{Portability note:} Some non-POSIX systems use different
conventions for exit status values. For greater portability, you can
use the macros @code{EXIT_SUCCESS} and @code{EXIT_FAILURE} for the
conventional status value for success and failure, respectively. They
are declared in the file @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment ISO
@deftypevr Macro int EXIT_SUCCESS
This macro can be used with the @code{exit} function to indicate
successful program completion.
On POSIX systems, the value of this macro is @code{0}. On other
systems, the value might be some other (possibly non-constant) integer
expression.
@end deftypevr
@comment stdlib.h
@comment ISO
@deftypevr Macro int EXIT_FAILURE
This macro can be used with the @code{exit} function to indicate
unsuccessful program completion in a general sense.
On POSIX systems, the value of this macro is @code{1}. On other
systems, the value might be some other (possibly non-constant) integer
expression. Other nonzero status values also indicate failures. Certain
programs use different nonzero status values to indicate particular
kinds of "non-success". For example, @code{diff} uses status value
@code{1} to mean that the files are different, and @code{2} or more to
mean that there was difficulty in opening the files.
@end deftypevr
Don't confuse a program's exit status with a process' termination status.
There are lots of ways a process can terminate besides having its program
finish. In the event that the process termination @emph{is} caused by program
termination (i.e., @code{exit}), though, the program's exit status becomes
part of the process' termination status.
@node Cleanups on Exit
@subsection Cleanups on Exit
Your program can arrange to run its own cleanup functions if normal
termination happens. If you are writing a library for use in various
application programs, then it is unreliable to insist that all
applications call the library's cleanup functions explicitly before
exiting. It is much more robust to make the cleanup invisible to the
application, by setting up a cleanup function in the library itself
using @code{atexit} or @code{on_exit}.
@comment stdlib.h
@comment ISO
@deftypefun int atexit (void (*@var{function}) (void))
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
@c atexit @ascuheap @asulock @aculock @acsmem
@c cxa_atexit @ascuheap @asulock @aculock @acsmem
@c __internal_atexit @ascuheap @asulock @aculock @acsmem
@c __new_exitfn @ascuheap @asulock @aculock @acsmem
@c __libc_lock_lock @asulock @aculock
@c calloc dup @ascuheap @acsmem
@c __libc_lock_unlock @aculock
@c atomic_write_barrier dup ok
The @code{atexit} function registers the function @var{function} to be
called at normal program termination. The @var{function} is called with
no arguments.
The return value from @code{atexit} is zero on success and nonzero if
the function cannot be registered.
@end deftypefun
@comment stdlib.h
@comment SunOS
@deftypefun int on_exit (void (*@var{function})(int @var{status}, void *@var{arg}), void *@var{arg})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{}}}
@c on_exit @ascuheap @asulock @aculock @acsmem
@c new_exitfn dup @ascuheap @asulock @aculock @acsmem
@c atomic_write_barrier dup ok
This function is a somewhat more powerful variant of @code{atexit}. It
accepts two arguments, a function @var{function} and an arbitrary
pointer @var{arg}. At normal program termination, the @var{function} is
called with two arguments: the @var{status} value passed to @code{exit},
and the @var{arg}.
This function is included in @theglibc{} only for compatibility
for SunOS, and may not be supported by other implementations.
@end deftypefun
Here's a trivial program that illustrates the use of @code{exit} and
@code{atexit}:
@smallexample
@include atexit.c.texi
@end smallexample
@noindent
When this program is executed, it just prints the message and exits.
@node Aborting a Program
@subsection Aborting a Program
@cindex aborting a program
You can abort your program using the @code{abort} function. The prototype
for this function is in @file{stdlib.h}.
@pindex stdlib.h
@comment stdlib.h
@comment ISO
@deftypefun void abort (void)
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}}
@c The implementation takes a recursive lock and attempts to support
@c calls from signal handlers, but if we're in the middle of flushing or
@c using streams, we may encounter them in inconsistent states.
The @code{abort} function causes abnormal program termination. This
does not execute cleanup functions registered with @code{atexit} or
@code{on_exit}.
This function actually terminates the process by raising a
@code{SIGABRT} signal, and your program can include a handler to
intercept this signal; see @ref{Signal Handling}.
@end deftypefun
@c Put in by rms. Don't remove.
@cartouche
@strong{Future Change Warning:} Proposed Federal censorship regulations
may prohibit us from giving you information about the possibility of
calling this function. We would be required to say that this is not an
acceptable way of terminating a program.
@end cartouche
@node Termination Internals
@subsection Termination Internals
The @code{_exit} function is the primitive used for process termination
by @code{exit}. It is declared in the header file @file{unistd.h}.
@pindex unistd.h
@comment unistd.h
@comment POSIX.1
@deftypefun void _exit (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Direct syscall (exit_group or exit); calls __task_terminate on hurd,
@c and abort in the generic posix implementation.
The @code{_exit} function is the primitive for causing a process to
terminate with status @var{status}. Calling this function does not
execute cleanup functions registered with @code{atexit} or
@code{on_exit}.
@end deftypefun
@comment stdlib.h
@comment ISO
@deftypefun void _Exit (int @var{status})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c Alias for _exit.
The @code{_Exit} function is the @w{ISO C} equivalent to @code{_exit}.
The @w{ISO C} committee members were not sure whether the definitions of
@code{_exit} and @code{_Exit} were compatible so they have not used the
POSIX name.
This function was introduced in @w{ISO C99} and is declared in
@file{stdlib.h}.
@end deftypefun
When a process terminates for any reason---either because the program
terminates, or as a result of a signal---the
following things happen:
@itemize @bullet
@item
All open file descriptors in the process are closed. @xref{Low-Level I/O}.
Note that streams are not flushed automatically when the process
terminates; see @ref{I/O on Streams}.
@item
A process exit status is saved to be reported back to the parent process
via @code{wait} or @code{waitpid}; see @ref{Process Completion}. If the
program exited, this status includes as its low-order 8 bits the program
exit status.
@item
Any child processes of the process being terminated are assigned a new
parent process. (On most systems, including GNU, this is the @code{init}
process, with process ID 1.)
@item
A @code{SIGCHLD} signal is sent to the parent process.
@item
If the process is a session leader that has a controlling terminal, then
a @code{SIGHUP} signal is sent to each process in the foreground job,
and the controlling terminal is disassociated from that session.
@xref{Job Control}.
@item
If termination of a process causes a process group to become orphaned,
and any member of that process group is stopped, then a @code{SIGHUP}
signal and a @code{SIGCONT} signal are sent to each process in the
group. @xref{Job Control}.
@end itemize
glibc-doc-reference-2.19.orig/manual/memory.texi 0000664 0001750 0001750 00000403356 12275120646 021775 0 ustar adconrad adconrad @node Memory, Character Handling, Error Reporting, Top
@chapter Virtual Memory Allocation And Paging
@c %MENU% Allocating virtual memory and controlling paging
@cindex memory allocation
@cindex storage allocation
This chapter describes how processes manage and use memory in a system
that uses @theglibc{}.
@Theglibc{} has several functions for dynamically allocating
virtual memory in various ways. They vary in generality and in
efficiency. The library also provides functions for controlling paging
and allocation of real memory.
@menu
* Memory Concepts:: An introduction to concepts and terminology.
* Memory Allocation:: Allocating storage for your program data
* Resizing the Data Segment:: @code{brk}, @code{sbrk}
* Locking Pages:: Preventing page faults
@end menu
Memory mapped I/O is not discussed in this chapter. @xref{Memory-mapped I/O}.
@node Memory Concepts
@section Process Memory Concepts
One of the most basic resources a process has available to it is memory.
There are a lot of different ways systems organize memory, but in a
typical one, each process has one linear virtual address space, with
addresses running from zero to some huge maximum. It need not be
contiguous; i.e., not all of these addresses actually can be used to
store data.
The virtual memory is divided into pages (4 kilobytes is typical).
Backing each page of virtual memory is a page of real memory (called a
@dfn{frame}) or some secondary storage, usually disk space. The disk
space might be swap space or just some ordinary disk file. Actually, a
page of all zeroes sometimes has nothing at all backing it -- there's
just a flag saying it is all zeroes.
@cindex page frame
@cindex frame, real memory
@cindex swap space
@cindex page, virtual memory
The same frame of real memory or backing store can back multiple virtual
pages belonging to multiple processes. This is normally the case, for
example, with virtual memory occupied by @glibcadj{} code. The same
real memory frame containing the @code{printf} function backs a virtual
memory page in each of the existing processes that has a @code{printf}
call in its program.
In order for a program to access any part of a virtual page, the page
must at that moment be backed by (``connected to'') a real frame. But
because there is usually a lot more virtual memory than real memory, the
pages must move back and forth between real memory and backing store
regularly, coming into real memory when a process needs to access them
and then retreating to backing store when not needed anymore. This
movement is called @dfn{paging}.
When a program attempts to access a page which is not at that moment
backed by real memory, this is known as a @dfn{page fault}. When a page
fault occurs, the kernel suspends the process, places the page into a
real page frame (this is called ``paging in'' or ``faulting in''), then
resumes the process so that from the process' point of view, the page
was in real memory all along. In fact, to the process, all pages always
seem to be in real memory. Except for one thing: the elapsed execution
time of an instruction that would normally be a few nanoseconds is
suddenly much, much, longer (because the kernel normally has to do I/O
to complete the page-in). For programs sensitive to that, the functions
described in @ref{Locking Pages} can control it.
@cindex page fault
@cindex paging
Within each virtual address space, a process has to keep track of what
is at which addresses, and that process is called memory allocation.
Allocation usually brings to mind meting out scarce resources, but in
the case of virtual memory, that's not a major goal, because there is
generally much more of it than anyone needs. Memory allocation within a
process is mainly just a matter of making sure that the same byte of
memory isn't used to store two different things.
Processes allocate memory in two major ways: by exec and
programmatically. Actually, forking is a third way, but it's not very
interesting. @xref{Creating a Process}.
Exec is the operation of creating a virtual address space for a process,
loading its basic program into it, and executing the program. It is
done by the ``exec'' family of functions (e.g. @code{execl}). The
operation takes a program file (an executable), it allocates space to
load all the data in the executable, loads it, and transfers control to
it. That data is most notably the instructions of the program (the
@dfn{text}), but also literals and constants in the program and even
some variables: C variables with the static storage class (@pxref{Memory
Allocation and C}).
@cindex executable
@cindex literals
@cindex constants
Once that program begins to execute, it uses programmatic allocation to
gain additional memory. In a C program with @theglibc{}, there
are two kinds of programmatic allocation: automatic and dynamic.
@xref{Memory Allocation and C}.
Memory-mapped I/O is another form of dynamic virtual memory allocation.
Mapping memory to a file means declaring that the contents of certain
range of a process' addresses shall be identical to the contents of a
specified regular file. The system makes the virtual memory initially
contain the contents of the file, and if you modify the memory, the
system writes the same modification to the file. Note that due to the
magic of virtual memory and page faults, there is no reason for the
system to do I/O to read the file, or allocate real memory for its
contents, until the program accesses the virtual memory.
@xref{Memory-mapped I/O}.
@cindex memory mapped I/O
@cindex memory mapped file
@cindex files, accessing
Just as it programmatically allocates memory, the program can
programmatically deallocate (@dfn{free}) it. You can't free the memory
that was allocated by exec. When the program exits or execs, you might
say that all its memory gets freed, but since in both cases the address
space ceases to exist, the point is really moot. @xref{Program
Termination}.
@cindex execing a program
@cindex freeing memory
@cindex exiting a program
A process' virtual address space is divided into segments. A segment is
a contiguous range of virtual addresses. Three important segments are:
@itemize @bullet
@item
The @dfn{text segment} contains a program's instructions and literals and
static constants. It is allocated by exec and stays the same size for
the life of the virtual address space.
@item
The @dfn{data segment} is working storage for the program. It can be
preallocated and preloaded by exec and the process can extend or shrink
it by calling functions as described in @xref{Resizing the Data
Segment}. Its lower end is fixed.
@item
The @dfn{stack segment} contains a program stack. It grows as the stack
grows, but doesn't shrink when the stack shrinks.
@end itemize
@node Memory Allocation
@section Allocating Storage For Program Data
This section covers how ordinary programs manage storage for their data,
including the famous @code{malloc} function and some fancier facilities
special @theglibc{} and GNU Compiler.
@menu
* Memory Allocation and C:: How to get different kinds of allocation in C.
* Unconstrained Allocation:: The @code{malloc} facility allows fully general
dynamic allocation.
* Allocation Debugging:: Finding memory leaks and not freed memory.
* Obstacks:: Obstacks are less general than malloc
but more efficient and convenient.
* Variable Size Automatic:: Allocation of variable-sized blocks
of automatic storage that are freed when the
calling function returns.
@end menu
@node Memory Allocation and C
@subsection Memory Allocation in C Programs
The C language supports two kinds of memory allocation through the
variables in C programs:
@itemize @bullet
@item
@dfn{Static allocation} is what happens when you declare a static or
global variable. Each static or global variable defines one block of
space, of a fixed size. The space is allocated once, when your program
is started (part of the exec operation), and is never freed.
@cindex static memory allocation
@cindex static storage class
@item
@dfn{Automatic allocation} happens when you declare an automatic
variable, such as a function argument or a local variable. The space
for an automatic variable is allocated when the compound statement
containing the declaration is entered, and is freed when that
compound statement is exited.
@cindex automatic memory allocation
@cindex automatic storage class
In GNU C, the size of the automatic storage can be an expression
that varies. In other C implementations, it must be a constant.
@end itemize
A third important kind of memory allocation, @dfn{dynamic allocation},
is not supported by C variables but is available via @glibcadj{}
functions.
@cindex dynamic memory allocation
@subsubsection Dynamic Memory Allocation
@cindex dynamic memory allocation
@dfn{Dynamic memory allocation} is a technique in which programs
determine as they are running where to store some information. You need
dynamic allocation when the amount of memory you need, or how long you
continue to need it, depends on factors that are not known before the
program runs.
For example, you may need a block to store a line read from an input
file; since there is no limit to how long a line can be, you must
allocate the memory dynamically and make it dynamically larger as you
read more of the line.
Or, you may need a block for each record or each definition in the input
data; since you can't know in advance how many there will be, you must
allocate a new block for each record or definition as you read it.
When you use dynamic allocation, the allocation of a block of memory is
an action that the program requests explicitly. You call a function or
macro when you want to allocate space, and specify the size with an
argument. If you want to free the space, you do so by calling another
function or macro. You can do these things whenever you want, as often
as you want.
Dynamic allocation is not supported by C variables; there is no storage
class ``dynamic'', and there can never be a C variable whose value is
stored in dynamically allocated space. The only way to get dynamically
allocated memory is via a system call (which is generally via a @glibcadj{}
function call), and the only way to refer to dynamically
allocated space is through a pointer. Because it is less convenient,
and because the actual process of dynamic allocation requires more
computation time, programmers generally use dynamic allocation only when
neither static nor automatic allocation will serve.
For example, if you want to allocate dynamically some space to hold a
@code{struct foobar}, you cannot declare a variable of type @code{struct
foobar} whose contents are the dynamically allocated space. But you can
declare a variable of pointer type @code{struct foobar *} and assign it the
address of the space. Then you can use the operators @samp{*} and
@samp{->} on this pointer variable to refer to the contents of the space:
@smallexample
@{
struct foobar *ptr
= (struct foobar *) malloc (sizeof (struct foobar));
ptr->name = x;
ptr->next = current_foobar;
current_foobar = ptr;
@}
@end smallexample
@node Unconstrained Allocation
@subsection Unconstrained Allocation
@cindex unconstrained memory allocation
@cindex @code{malloc} function
@cindex heap, dynamic allocation from
The most general dynamic allocation facility is @code{malloc}. It
allows you to allocate blocks of memory of any size at any time, make
them bigger or smaller at any time, and free the blocks individually at
any time (or never).
@menu
* Basic Allocation:: Simple use of @code{malloc}.
* Malloc Examples:: Examples of @code{malloc}. @code{xmalloc}.
* Freeing after Malloc:: Use @code{free} to free a block you
got with @code{malloc}.
* Changing Block Size:: Use @code{realloc} to make a block
bigger or smaller.
* Allocating Cleared Space:: Use @code{calloc} to allocate a
block and clear it.
* Efficiency and Malloc:: Efficiency considerations in use of
these functions.
* Aligned Memory Blocks:: Allocating specially aligned memory.
* Malloc Tunable Parameters:: Use @code{mallopt} to adjust allocation
parameters.
* Heap Consistency Checking:: Automatic checking for errors.
* Hooks for Malloc:: You can use these hooks for debugging
programs that use @code{malloc}.
* Statistics of Malloc:: Getting information about how much
memory your program is using.
* Summary of Malloc:: Summary of @code{malloc} and related functions.
@end menu
@node Basic Allocation
@subsubsection Basic Memory Allocation
@cindex allocation of memory with @code{malloc}
To allocate a block of memory, call @code{malloc}. The prototype for
this function is in @file{stdlib.h}.
@pindex stdlib.h
@comment malloc.h stdlib.h
@comment ISO
@deftypefun {void *} malloc (size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Malloc hooks and __morecore pointers, as well as such parameters as
@c max_n_mmaps and max_mmapped_mem, are accessed without guards, so they
@c could pose a thread safety issue; in order to not declare malloc
@c MT-unsafe, it's modifying the hooks and parameters while multiple
@c threads are active that is regarded as unsafe. An arena's next field
@c is initialized and never changed again, except for main_arena's,
@c that's protected by list_lock; next_free is only modified while
@c list_lock is held too. All other data members of an arena, as well
@c as the metadata of the memory areas assigned to it, are only modified
@c while holding the arena's mutex (fastbin pointers use catomic ops
@c because they may be modified by free without taking the arena's
@c lock). Some reassurance was needed for fastbins, for it wasn't clear
@c how they were initialized. It turns out they are always
@c zero-initialized: main_arena's, for being static data, and other
@c arena's, for being just-mmapped memory.
@c Leaking file descriptors and memory in case of cancellation is
@c unavoidable without disabling cancellation, but the lock situation is
@c a bit more complicated: we don't have fallback arenas for malloc to
@c be safe to call from within signal handlers. Error-checking mutexes
@c or trylock could enable us to try and use alternate arenas, even with
@c -DPER_THREAD (enabled by default), but supporting interruption
@c (cancellation or signal handling) while holding the arena list mutex
@c would require more work; maybe blocking signals and disabling async
@c cancellation while manipulating the arena lists?
@c __libc_malloc @asulock @aculock @acsfd @acsmem
@c force_reg ok
@c *malloc_hook unguarded
@c arena_lookup ok
@c tsd_getspecific ok, TLS
@c arena_lock @asulock @aculock @acsfd @acsmem
@c mutex_lock @asulock @aculock
@c arena_get2 @asulock @aculock @acsfd @acsmem
@c get_free_list @asulock @aculock
@c mutex_lock (list_lock) dup @asulock @aculock
@c mutex_unlock (list_lock) dup @aculock
@c mutex_lock (arena lock) dup @asulock @aculock [returns locked]
@c tsd_setspecific ok, TLS
@c __get_nprocs ext ok @acsfd
@c NARENAS_FROM_NCORES ok
@c catomic_compare_and_exchange_bool_acq ok
@c _int_new_arena ok @asulock @aculock @acsmem
@c new_heap ok @acsmem
@c mmap ok @acsmem
@c munmap ok @acsmem
@c mprotect ok
@c chunk2mem ok
@c set_head ok
@c tsd_setspecific dup ok
@c mutex_init ok
@c mutex_lock (just-created mutex) ok, returns locked
@c mutex_lock (list_lock) dup @asulock @aculock
@c atomic_write_barrier ok
@c mutex_unlock (list_lock) @aculock
@c catomic_decrement ok
@c reused_arena @asulock @aculock
@c reads&writes next_to_use and iterates over arena next without guards
@c those are harmless as long as we don't drop arenas from the
@c NEXT list, and we never do; when a thread terminates,
@c arena_thread_freeres prepends the arena to the free_list
@c NEXT_FREE list, but NEXT is never modified, so it's safe!
@c mutex_trylock (arena lock) @asulock @aculock
@c mutex_lock (arena lock) dup @asulock @aculock
@c tsd_setspecific dup ok
@c _int_malloc @acsfd @acsmem
@c checked_request2size ok
@c REQUEST_OUT_OF_RANGE ok
@c request2size ok
@c get_max_fast ok
@c fastbin_index ok
@c fastbin ok
@c catomic_compare_and_exhange_val_acq ok
@c malloc_printerr dup @mtsenv
@c if we get to it, we're toast already, undefined behavior must have
@c been invoked before
@c libc_message @mtsenv [no leaks with cancellation disabled]
@c FATAL_PREPARE ok
@c pthread_setcancelstate disable ok
@c libc_secure_getenv @mtsenv
@c getenv @mtsenv
@c open_not_cancel_2 dup @acsfd
@c strchrnul ok
@c WRITEV_FOR_FATAL ok
@c writev ok
@c mmap ok @acsmem
@c munmap ok @acsmem
@c BEFORE_ABORT @acsfd
@c backtrace ok
@c write_not_cancel dup ok
@c backtrace_symbols_fd @aculock
@c open_not_cancel_2 dup @acsfd
@c read_not_cancel dup ok
@c close_not_cancel_no_status dup @acsfd
@c abort ok
@c itoa_word ok
@c abort ok
@c check_remalloced_chunk ok/disabled
@c chunk2mem dup ok
@c alloc_perturb ok
@c in_smallbin_range ok
@c smallbin_index ok
@c bin_at ok
@c last ok
@c malloc_consolidate ok
@c get_max_fast dup ok
@c clear_fastchunks ok
@c unsorted_chunks dup ok
@c fastbin dup ok
@c atomic_exchange_acq ok
@c check_inuse_chunk dup ok/disabled
@c chunk_at_offset dup ok
@c chunksize dup ok
@c inuse_bit_at_offset dup ok
@c unlink dup ok
@c clear_inuse_bit_at_offset dup ok
@c in_smallbin_range dup ok
@c set_head dup ok
@c malloc_init_state ok
@c bin_at dup ok
@c set_noncontiguous dup ok
@c set_max_fast dup ok
@c initial_top ok
@c unsorted_chunks dup ok
@c check_malloc_state ok/disabled
@c set_inuse_bit_at_offset ok
@c check_malloced_chunk ok/disabled
@c largebin_index ok
@c have_fastchunks ok
@c unsorted_chunks ok
@c bin_at ok
@c chunksize ok
@c chunk_at_offset ok
@c set_head ok
@c set_foot ok
@c mark_bin ok
@c idx2bit ok
@c first ok
@c unlink ok
@c malloc_printerr dup ok
@c in_smallbin_range dup ok
@c idx2block ok
@c idx2bit dup ok
@c next_bin ok
@c sysmalloc @acsfd @acsmem
@c MMAP @acsmem
@c set_head dup ok
@c check_chunk ok/disabled
@c chunk2mem dup ok
@c chunksize dup ok
@c chunk_at_offset dup ok
@c heap_for_ptr ok
@c grow_heap ok
@c mprotect ok
@c set_head dup ok
@c new_heap @acsmem
@c MMAP dup @acsmem
@c munmap @acsmem
@c top ok
@c set_foot dup ok
@c contiguous ok
@c MORECORE ok
@c *__morecore ok unguarded
@c __default_morecore
@c sbrk ok
@c force_reg dup ok
@c *__after_morecore_hook unguarded
@c set_noncontiguous ok
@c malloc_printerr dup ok
@c _int_free (have_lock) @acsfd @acsmem [@asulock @aculock]
@c chunksize dup ok
@c mutex_unlock dup @aculock/!have_lock
@c malloc_printerr dup ok
@c check_inuse_chunk ok/disabled
@c chunk_at_offset dup ok
@c mutex_lock dup @asulock @aculock/@have_lock
@c chunk2mem dup ok
@c free_perturb ok
@c set_fastchunks ok
@c catomic_and ok
@c fastbin_index dup ok
@c fastbin dup ok
@c catomic_compare_and_exchange_val_rel ok
@c chunk_is_mmapped ok
@c contiguous dup ok
@c prev_inuse ok
@c unlink dup ok
@c inuse_bit_at_offset dup ok
@c clear_inuse_bit_at_offset ok
@c unsorted_chunks dup ok
@c in_smallbin_range dup ok
@c set_head dup ok
@c set_foot dup ok
@c check_free_chunk ok/disabled
@c check_chunk dup ok/disabled
@c have_fastchunks dup ok
@c malloc_consolidate dup ok
@c systrim ok
@c MORECORE dup ok
@c *__after_morecore_hook dup unguarded
@c set_head dup ok
@c check_malloc_state ok/disabled
@c top dup ok
@c heap_for_ptr dup ok
@c heap_trim @acsfd @acsmem
@c top dup ok
@c chunk_at_offset dup ok
@c prev_chunk ok
@c chunksize dup ok
@c prev_inuse dup ok
@c delete_heap @acsmem
@c munmap dup @acsmem
@c unlink dup ok
@c set_head dup ok
@c shrink_heap @acsfd
@c check_may_shrink_heap @acsfd
@c open_not_cancel_2 @acsfd
@c read_not_cancel ok
@c close_not_cancel_no_status @acsfd
@c MMAP dup ok
@c madvise ok
@c munmap_chunk @acsmem
@c chunksize dup ok
@c chunk_is_mmapped dup ok
@c chunk2mem dup ok
@c malloc_printerr dup ok
@c munmap dup @acsmem
@c check_malloc_state ok/disabled
@c arena_get_retry @asulock @aculock @acsfd @acsmem
@c mutex_unlock dup @aculock
@c mutex_lock dup @asulock @aculock
@c arena_get2 dup @asulock @aculock @acsfd @acsmem
@c mutex_unlock @aculock
@c mem2chunk ok
@c chunk_is_mmapped ok
@c arena_for_chunk ok
@c chunk_non_main_arena ok
@c heap_for_ptr ok
This function returns a pointer to a newly allocated block @var{size}
bytes long, or a null pointer if the block could not be allocated.
@end deftypefun
The contents of the block are undefined; you must initialize it yourself
(or use @code{calloc} instead; @pxref{Allocating Cleared Space}).
Normally you would cast the value as a pointer to the kind of object
that you want to store in the block. Here we show an example of doing
so, and of initializing the space with zeros using the library function
@code{memset} (@pxref{Copying and Concatenation}):
@smallexample
struct foo *ptr;
@dots{}
ptr = (struct foo *) malloc (sizeof (struct foo));
if (ptr == 0) abort ();
memset (ptr, 0, sizeof (struct foo));
@end smallexample
You can store the result of @code{malloc} into any pointer variable
without a cast, because @w{ISO C} automatically converts the type
@code{void *} to another type of pointer when necessary. But the cast
is necessary in contexts other than assignment operators or if you might
want your code to run in traditional C.
Remember that when allocating space for a string, the argument to
@code{malloc} must be one plus the length of the string. This is
because a string is terminated with a null character that doesn't count
in the ``length'' of the string but does need space. For example:
@smallexample
char *ptr;
@dots{}
ptr = (char *) malloc (length + 1);
@end smallexample
@noindent
@xref{Representation of Strings}, for more information about this.
@node Malloc Examples
@subsubsection Examples of @code{malloc}
If no more space is available, @code{malloc} returns a null pointer.
You should check the value of @emph{every} call to @code{malloc}. It is
useful to write a subroutine that calls @code{malloc} and reports an
error if the value is a null pointer, returning only if the value is
nonzero. This function is conventionally called @code{xmalloc}. Here
it is:
@smallexample
void *
xmalloc (size_t size)
@{
void *value = malloc (size);
if (value == 0)
fatal ("virtual memory exhausted");
return value;
@}
@end smallexample
Here is a real example of using @code{malloc} (by way of @code{xmalloc}).
The function @code{savestring} will copy a sequence of characters into
a newly allocated null-terminated string:
@smallexample
@group
char *
savestring (const char *ptr, size_t len)
@{
char *value = (char *) xmalloc (len + 1);
value[len] = '\0';
return (char *) memcpy (value, ptr, len);
@}
@end group
@end smallexample
The block that @code{malloc} gives you is guaranteed to be aligned so
that it can hold any type of data. On @gnusystems{}, the address is
always a multiple of eight on 32-bit systems, and a multiple of 16 on
64-bit systems. Only rarely is any higher boundary (such as a page
boundary) necessary; for those cases, use @code{aligned_alloc} or
@code{posix_memalign} (@pxref{Aligned Memory Blocks}).
Note that the memory located after the end of the block is likely to be
in use for something else; perhaps a block already allocated by another
call to @code{malloc}. If you attempt to treat the block as longer than
you asked for it to be, you are liable to destroy the data that
@code{malloc} uses to keep track of its blocks, or you may destroy the
contents of another block. If you have already allocated a block and
discover you want it to be bigger, use @code{realloc} (@pxref{Changing
Block Size}).
@node Freeing after Malloc
@subsubsection Freeing Memory Allocated with @code{malloc}
@cindex freeing memory allocated with @code{malloc}
@cindex heap, freeing memory from
When you no longer need a block that you got with @code{malloc}, use the
function @code{free} to make the block available to be allocated again.
The prototype for this function is in @file{stdlib.h}.
@pindex stdlib.h
@comment malloc.h stdlib.h
@comment ISO
@deftypefun void free (void *@var{ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c __libc_free @asulock @aculock @acsfd @acsmem
@c releasing memory into fastbins modifies the arena without taking
@c its mutex, but catomic operations ensure safety. If two (or more)
@c threads are running malloc and have their own arenas locked when
@c each gets a signal whose handler free()s large (non-fastbin-able)
@c blocks from each other's arena, we deadlock; this is a more general
@c case of @asulock.
@c *__free_hook unguarded
@c mem2chunk ok
@c chunk_is_mmapped ok, chunk bits not modified after allocation
@c chunksize ok
@c munmap_chunk dup @acsmem
@c arena_for_chunk dup ok
@c _int_free (!have_lock) dup @asulock @aculock @acsfd @acsmem
The @code{free} function deallocates the block of memory pointed at
by @var{ptr}.
@end deftypefun
@comment stdlib.h
@comment Sun
@deftypefun void cfree (void *@var{ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c alias to free
This function does the same thing as @code{free}. It's provided for
backward compatibility with SunOS; you should use @code{free} instead.
@end deftypefun
Freeing a block alters the contents of the block. @strong{Do not expect to
find any data (such as a pointer to the next block in a chain of blocks) in
the block after freeing it.} Copy whatever you need out of the block before
freeing it! Here is an example of the proper way to free all the blocks in
a chain, and the strings that they point to:
@smallexample
struct chain
@{
struct chain *next;
char *name;
@}
void
free_chain (struct chain *chain)
@{
while (chain != 0)
@{
struct chain *next = chain->next;
free (chain->name);
free (chain);
chain = next;
@}
@}
@end smallexample
Occasionally, @code{free} can actually return memory to the operating
system and make the process smaller. Usually, all it can do is allow a
later call to @code{malloc} to reuse the space. In the meantime, the
space remains in your program as part of a free-list used internally by
@code{malloc}.
There is no point in freeing blocks at the end of a program, because all
of the program's space is given back to the system when the process
terminates.
@node Changing Block Size
@subsubsection Changing the Size of a Block
@cindex changing the size of a block (@code{malloc})
Often you do not know for certain how big a block you will ultimately need
at the time you must begin to use the block. For example, the block might
be a buffer that you use to hold a line being read from a file; no matter
how long you make the buffer initially, you may encounter a line that is
longer.
You can make the block longer by calling @code{realloc}. This function
is declared in @file{stdlib.h}.
@pindex stdlib.h
@comment malloc.h stdlib.h
@comment ISO
@deftypefun {void *} realloc (void *@var{ptr}, size_t @var{newsize})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c It may call the implementations of malloc and free, so all of their
@c issues arise, plus the realloc hook, also accessed without guards.
@c __libc_realloc @asulock @aculock @acsfd @acsmem
@c *__realloc_hook unguarded
@c __libc_free dup @asulock @aculock @acsfd @acsmem
@c __libc_malloc dup @asulock @aculock @acsfd @acsmem
@c mem2chunk dup ok
@c chunksize dup ok
@c malloc_printerr dup ok
@c checked_request2size dup ok
@c chunk_is_mmapped dup ok
@c mremap_chunk
@c chunksize dup ok
@c __mremap ok
@c set_head dup ok
@c MALLOC_COPY ok
@c memcpy ok
@c munmap_chunk dup @acsmem
@c arena_for_chunk dup ok
@c mutex_lock (arena mutex) dup @asulock @aculock
@c _int_realloc @acsfd @acsmem
@c malloc_printerr dup ok
@c check_inuse_chunk dup ok/disabled
@c chunk_at_offset dup ok
@c chunksize dup ok
@c set_head_size dup ok
@c chunk_at_offset dup ok
@c set_head dup ok
@c chunk2mem dup ok
@c inuse dup ok
@c unlink dup ok
@c _int_malloc dup @acsfd @acsmem
@c mem2chunk dup ok
@c MALLOC_COPY dup ok
@c _int_free (have_lock) dup @acsfd @acsmem
@c set_inuse_bit_at_offset dup ok
@c set_head dup ok
@c mutex_unlock (arena mutex) dup @aculock
@c _int_free (!have_lock) dup @asulock @aculock @acsfd @acsmem
The @code{realloc} function changes the size of the block whose address is
@var{ptr} to be @var{newsize}.
Since the space after the end of the block may be in use, @code{realloc}
may find it necessary to copy the block to a new address where more free
space is available. The value of @code{realloc} is the new address of the
block. If the block needs to be moved, @code{realloc} copies the old
contents.
If you pass a null pointer for @var{ptr}, @code{realloc} behaves just
like @samp{malloc (@var{newsize})}. This can be convenient, but beware
that older implementations (before @w{ISO C}) may not support this
behavior, and will probably crash when @code{realloc} is passed a null
pointer.
@end deftypefun
Like @code{malloc}, @code{realloc} may return a null pointer if no
memory space is available to make the block bigger. When this happens,
the original block is untouched; it has not been modified or relocated.
In most cases it makes no difference what happens to the original block
when @code{realloc} fails, because the application program cannot continue
when it is out of memory, and the only thing to do is to give a fatal error
message. Often it is convenient to write and use a subroutine,
conventionally called @code{xrealloc}, that takes care of the error message
as @code{xmalloc} does for @code{malloc}:
@smallexample
void *
xrealloc (void *ptr, size_t size)
@{
void *value = realloc (ptr, size);
if (value == 0)
fatal ("Virtual memory exhausted");
return value;
@}
@end smallexample
You can also use @code{realloc} to make a block smaller. The reason you
would do this is to avoid tying up a lot of memory space when only a little
is needed.
@comment The following is no longer true with the new malloc.
@comment But it seems wise to keep the warning for other implementations.
In several allocation implementations, making a block smaller sometimes
necessitates copying it, so it can fail if no other space is available.
If the new size you specify is the same as the old size, @code{realloc}
is guaranteed to change nothing and return the same address that you gave.
@node Allocating Cleared Space
@subsubsection Allocating Cleared Space
The function @code{calloc} allocates memory and clears it to zero. It
is declared in @file{stdlib.h}.
@pindex stdlib.h
@comment malloc.h stdlib.h
@comment ISO
@deftypefun {void *} calloc (size_t @var{count}, size_t @var{eltsize})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Same caveats as malloc.
@c __libc_calloc @asulock @aculock @acsfd @acsmem
@c *__malloc_hook dup unguarded
@c memset dup ok
@c arena_get @asulock @aculock @acsfd @acsmem
@c arena_lookup dup ok
@c arena_lock dup @asulock @aculock @acsfd @acsmem
@c top dup ok
@c chunksize dup ok
@c heap_for_ptr dup ok
@c _int_malloc dup @acsfd @acsmem
@c arena_get_retry dup @asulock @aculock @acsfd @acsmem
@c mutex_unlock dup @aculock
@c mem2chunk dup ok
@c chunk_is_mmapped dup ok
@c MALLOC_ZERO ok
@c memset dup ok
This function allocates a block long enough to contain a vector of
@var{count} elements, each of size @var{eltsize}. Its contents are
cleared to zero before @code{calloc} returns.
@end deftypefun
You could define @code{calloc} as follows:
@smallexample
void *
calloc (size_t count, size_t eltsize)
@{
size_t size = count * eltsize;
void *value = malloc (size);
if (value != 0)
memset (value, 0, size);
return value;
@}
@end smallexample
But in general, it is not guaranteed that @code{calloc} calls
@code{malloc} internally. Therefore, if an application provides its own
@code{malloc}/@code{realloc}/@code{free} outside the C library, it
should always define @code{calloc}, too.
@node Efficiency and Malloc
@subsubsection Efficiency Considerations for @code{malloc}
@cindex efficiency and @code{malloc}
@ignore
@c No longer true, see below instead.
To make the best use of @code{malloc}, it helps to know that the GNU
version of @code{malloc} always dispenses small amounts of memory in
blocks whose sizes are powers of two. It keeps separate pools for each
power of two. This holds for sizes up to a page size. Therefore, if
you are free to choose the size of a small block in order to make
@code{malloc} more efficient, make it a power of two.
@c !!! xref getpagesize
Once a page is split up for a particular block size, it can't be reused
for another size unless all the blocks in it are freed. In many
programs, this is unlikely to happen. Thus, you can sometimes make a
program use memory more efficiently by using blocks of the same size for
many different purposes.
When you ask for memory blocks of a page or larger, @code{malloc} uses a
different strategy; it rounds the size up to a multiple of a page, and
it can coalesce and split blocks as needed.
The reason for the two strategies is that it is important to allocate
and free small blocks as fast as possible, but speed is less important
for a large block since the program normally spends a fair amount of
time using it. Also, large blocks are normally fewer in number.
Therefore, for large blocks, it makes sense to use a method which takes
more time to minimize the wasted space.
@end ignore
As opposed to other versions, the @code{malloc} in @theglibc{}
does not round up block sizes to powers of two, neither for large nor
for small sizes. Neighboring chunks can be coalesced on a @code{free}
no matter what their size is. This makes the implementation suitable
for all kinds of allocation patterns without generally incurring high
memory waste through fragmentation.
Very large blocks (much larger than a page) are allocated with
@code{mmap} (anonymous or via @code{/dev/zero}) by this implementation.
This has the great advantage that these chunks are returned to the
system immediately when they are freed. Therefore, it cannot happen
that a large chunk becomes ``locked'' in between smaller ones and even
after calling @code{free} wastes memory. The size threshold for
@code{mmap} to be used can be adjusted with @code{mallopt}. The use of
@code{mmap} can also be disabled completely.
@node Aligned Memory Blocks
@subsubsection Allocating Aligned Memory Blocks
@cindex page boundary
@cindex alignment (with @code{malloc})
@pindex stdlib.h
The address of a block returned by @code{malloc} or @code{realloc} in
@gnusystems{} is always a multiple of eight (or sixteen on 64-bit
systems). If you need a block whose address is a multiple of a higher
power of two than that, use @code{aligned_alloc} or @code{posix_memalign}.
@code{aligned_alloc} and @code{posix_memalign} are declared in
@file{stdlib.h}.
@comment stdlib.h
@deftypefun {void *} aligned_alloc (size_t @var{alignment}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Alias to memalign.
The @code{aligned_alloc} function allocates a block of @var{size} bytes whose
address is a multiple of @var{alignment}. The @var{alignment} must be a
power of two and @var{size} must be a multiple of @var{alignment}.
The @code{aligned_alloc} function returns a null pointer on error and sets
@code{errno} to one of the following values:
@table @code
@item ENOMEM
There was insufficient memory available to satisfy the request.
@item EINVAL
@var{alignment} is not a power of two.
This function was introduced in @w{ISO C11} and hence may have better
portability to modern non-POSIX systems than @code{posix_memalign}.
@end table
@end deftypefun
@comment malloc.h
@comment BSD
@deftypefun {void *} memalign (size_t @var{boundary}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Same issues as malloc. The padding bytes are safely freed in
@c _int_memalign, with the arena still locked.
@c __libc_memalign @asulock @aculock @acsfd @acsmem
@c *__memalign_hook dup unguarded
@c __libc_malloc dup @asulock @aculock @acsfd @acsmem
@c arena_get dup @asulock @aculock @acsfd @acsmem
@c _int_memalign @acsfd @acsmem
@c _int_malloc dup @acsfd @acsmem
@c checked_request2size dup ok
@c mem2chunk dup ok
@c chunksize dup ok
@c chunk_is_mmapped dup ok
@c set_head dup ok
@c chunk2mem dup ok
@c set_inuse_bit_at_offset dup ok
@c set_head_size dup ok
@c _int_free (have_lock) dup @acsfd @acsmem
@c chunk_at_offset dup ok
@c check_inuse_chunk dup ok
@c arena_get_retry dup @asulock @aculock @acsfd @acsmem
@c mutex_unlock dup @aculock
The @code{memalign} function allocates a block of @var{size} bytes whose
address is a multiple of @var{boundary}. The @var{boundary} must be a
power of two! The function @code{memalign} works by allocating a
somewhat larger block, and then returning an address within the block
that is on the specified boundary.
The @code{memalign} function returns a null pointer on error and sets
@code{errno} to one of the following values:
@table @code
@item ENOMEM
There was insufficient memory available to satisfy the request.
@item EINVAL
@var{alignment} is not a power of two.
@end table
The @code{memalign} function is obsolete and @code{aligned_alloc} or
@code{posix_memalign} should be used instead.
@end deftypefun
@comment stdlib.h
@comment POSIX
@deftypefun int posix_memalign (void **@var{memptr}, size_t @var{alignment}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
@c Calls memalign unless the requirements are not met (powerof2 macro is
@c safe given an automatic variable as an argument) or there's a
@c memalign hook (accessed unguarded, but safely).
The @code{posix_memalign} function is similar to the @code{memalign}
function in that it returns a buffer of @var{size} bytes aligned to a
multiple of @var{alignment}. But it adds one requirement to the
parameter @var{alignment}: the value must be a power of two multiple of
@code{sizeof (void *)}.
If the function succeeds in allocation memory a pointer to the allocated
memory is returned in @code{*@var{memptr}} and the return value is zero.
Otherwise the function returns an error value indicating the problem.
The possible error values returned are:
@table @code
@item ENOMEM
There was insufficient memory available to satisfy the request.
@item EINVAL
@var{alignment} is not a power of two multiple of @code{sizeof (void *)}.
@end table
This function was introduced in POSIX 1003.1d. Although this function is
superseded by @code{aligned_alloc}, it is more portable to older POSIX
systems that do not support @w{ISO C11}.
@end deftypefun
@comment malloc.h stdlib.h
@comment BSD
@deftypefun {void *} valloc (size_t @var{size})
@safety{@prelim{}@mtunsafe{@mtuinit{}}@asunsafe{@asuinit{} @asulock{}}@acunsafe{@acuinit{} @aculock{} @acsfd{} @acsmem{}}}
@c __libc_valloc @mtuinit @asuinit @asulock @aculock @acsfd @acsmem
@c ptmalloc_init (once) @mtsenv @asulock @aculock @acsfd @acsmem
@c _dl_addr @asucorrupt? @aculock
@c __rtld_lock_lock_recursive (dl_load_lock) @asucorrupt? @aculock
@c _dl_find_dso_for_object ok, iterates over dl_ns and its _ns_loaded objs
@c the ok above assumes no partial updates on dl_ns and _ns_loaded
@c that could confuse a _dl_addr call in a signal handler
@c _dl_addr_inside_object ok
@c determine_info ok
@c __rtld_lock_unlock_recursive (dl_load_lock) @aculock
@c thread_atfork @asulock @aculock @acsfd @acsmem
@c __register_atfork @asulock @aculock @acsfd @acsmem
@c lll_lock (__fork_lock) @asulock @aculock
@c fork_handler_alloc @asulock @aculock @acsfd @acsmem
@c calloc dup @asulock @aculock @acsfd @acsmem
@c __linkin_atfork ok
@c catomic_compare_and_exchange_bool_acq ok
@c lll_unlock (__fork_lock) @aculock
@c *_environ @mtsenv
@c next_env_entry ok
@c strcspn dup ok
@c __libc_mallopt dup @mtasuconst:mallopt [setting mp_]
@c __malloc_check_init @mtasuconst:malloc_hooks [setting hooks]
@c *__malloc_initialize_hook unguarded, ok
@c *__memalign_hook dup ok, unguarded
@c arena_get dup @asulock @aculock @acsfd @acsmem
@c _int_valloc @acsfd @acsmem
@c malloc_consolidate dup ok
@c _int_memalign dup @acsfd @acsmem
@c arena_get_retry dup @asulock @aculock @acsfd @acsmem
@c _int_memalign dup @acsfd @acsmem
@c mutex_unlock dup @aculock
Using @code{valloc} is like using @code{memalign} and passing the page size
as the value of the second argument. It is implemented like this:
@smallexample
void *
valloc (size_t size)
@{
return memalign (getpagesize (), size);
@}
@end smallexample
@ref{Query Memory Parameters} for more information about the memory
subsystem.
The @code{valloc} function is obsolete and @code{aligned_alloc} or
@code{posix_memalign} should be used instead.
@end deftypefun
@node Malloc Tunable Parameters
@subsubsection Malloc Tunable Parameters
You can adjust some parameters for dynamic memory allocation with the
@code{mallopt} function. This function is the general SVID/XPG
interface, defined in @file{malloc.h}.
@pindex malloc.h
@deftypefun int mallopt (int @var{param}, int @var{value})
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasuconst{:mallopt}}@asunsafe{@asuinit{} @asulock{}}@acunsafe{@acuinit{} @aculock{}}}
@c __libc_mallopt @mtuinit @mtasuconst:mallopt @asuinit @asulock @aculock
@c ptmalloc_init (once) dup @mtsenv @asulock @aculock @acsfd @acsmem
@c mutex_lock (main_arena->mutex) @asulock @aculock
@c malloc_consolidate dup ok
@c set_max_fast ok
@c mutex_unlock dup @aculock
When calling @code{mallopt}, the @var{param} argument specifies the
parameter to be set, and @var{value} the new value to be set. Possible
choices for @var{param}, as defined in @file{malloc.h}, are:
@table @code
@comment TODO: @item M_ARENA_MAX
@comment - Document ARENA_MAX env var.
@comment TODO: @item M_ARENA_TEST
@comment - Document ARENA_TEST env var.
@comment TODO: @item M_CHECK_ACTION
@item M_MMAP_MAX
The maximum number of chunks to allocate with @code{mmap}. Setting this
to zero disables all use of @code{mmap}.
@item M_MMAP_THRESHOLD
All chunks larger than this value are allocated outside the normal
heap, using the @code{mmap} system call. This way it is guaranteed
that the memory for these chunks can be returned to the system on
@code{free}. Note that requests smaller than this threshold might still
be allocated via @code{mmap}.
@comment TODO: @item M_MXFAST
@item M_PERTURB
If non-zero, memory blocks are filled with values depending on some
low order bits of this parameter when they are allocated (except when
allocated by @code{calloc}) and freed. This can be used to debug the
use of uninitialized or freed heap memory. Note that this option does not
guarantee that the freed block will have any specific values. It only
guarantees that the content the block had before it was freed will be
overwritten.
@item M_TOP_PAD
This parameter determines the amount of extra memory to obtain from the
system when a call to @code{sbrk} is required. It also specifies the
number of bytes to retain when shrinking the heap by calling @code{sbrk}
with a negative argument. This provides the necessary hysteresis in
heap size such that excessive amounts of system calls can be avoided.
@item M_TRIM_THRESHOLD
This is the minimum size (in bytes) of the top-most, releasable chunk
that will cause @code{sbrk} to be called with a negative argument in
order to return memory to the system.
@end table
@end deftypefun
@node Heap Consistency Checking
@subsubsection Heap Consistency Checking
@cindex heap consistency checking
@cindex consistency checking, of heap
You can ask @code{malloc} to check the consistency of dynamic memory by
using the @code{mcheck} function. This function is a GNU extension,
declared in @file{mcheck.h}.
@pindex mcheck.h
@comment mcheck.h
@comment GNU
@deftypefun int mcheck (void (*@var{abortfn}) (enum mcheck_status @var{status}))
@safety{@prelim{}@mtunsafe{@mtasurace{:mcheck} @mtasuconst{:malloc_hooks}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c The hooks must be set up before malloc is first used, which sort of
@c implies @mtuinit/@asuinit but since the function is a no-op if malloc
@c was already used, that doesn't pose any safety issues. The actual
@c problem is with the hooks, designed for single-threaded
@c fully-synchronous operation: they manage an unguarded linked list of
@c allocated blocks, and get temporarily overwritten before calling the
@c allocation functions recursively while holding the old hooks. There
@c are no guards for thread safety, and inconsistent hooks may be found
@c within signal handlers or left behind in case of cancellation.
Calling @code{mcheck} tells @code{malloc} to perform occasional
consistency checks. These will catch things such as writing
past the end of a block that was allocated with @code{malloc}.
The @var{abortfn} argument is the function to call when an inconsistency
is found. If you supply a null pointer, then @code{mcheck} uses a
default function which prints a message and calls @code{abort}
(@pxref{Aborting a Program}). The function you supply is called with
one argument, which says what sort of inconsistency was detected; its
type is described below.
It is too late to begin allocation checking once you have allocated
anything with @code{malloc}. So @code{mcheck} does nothing in that
case. The function returns @code{-1} if you call it too late, and
@code{0} otherwise (when it is successful).
The easiest way to arrange to call @code{mcheck} early enough is to use
the option @samp{-lmcheck} when you link your program; then you don't
need to modify your program source at all. Alternatively you might use
a debugger to insert a call to @code{mcheck} whenever the program is
started, for example these gdb commands will automatically call @code{mcheck}
whenever the program starts:
@smallexample
(gdb) break main
Breakpoint 1, main (argc=2, argv=0xbffff964) at whatever.c:10
(gdb) command 1
Type commands for when breakpoint 1 is hit, one per line.
End with a line saying just "end".
>call mcheck(0)
>continue
>end
(gdb) @dots{}
@end smallexample
This will however only work if no initialization function of any object
involved calls any of the @code{malloc} functions since @code{mcheck}
must be called before the first such function.
@end deftypefun
@deftypefun {enum mcheck_status} mprobe (void *@var{pointer})
@safety{@prelim{}@mtunsafe{@mtasurace{:mcheck} @mtasuconst{:malloc_hooks}}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{}}}
@c The linked list of headers may be modified concurrently by other
@c threads, and it may find a partial update if called from a signal
@c handler. It's mostly read only, so cancelling it might be safe, but
@c it will modify global state that, if cancellation hits at just the
@c right spot, may be left behind inconsistent. This path is only taken
@c if checkhdr finds an inconsistency. If the inconsistency could only
@c occur because of earlier undefined behavior, that wouldn't be an
@c additional safety issue problem, but because of the other concurrency
@c issues in the mcheck hooks, the apparent inconsistency could be the
@c result of mcheck's own internal data race. So, AC-Unsafe it is.
The @code{mprobe} function lets you explicitly check for inconsistencies
in a particular allocated block. You must have already called
@code{mcheck} at the beginning of the program, to do its occasional
checks; calling @code{mprobe} requests an additional consistency check
to be done at the time of the call.
The argument @var{pointer} must be a pointer returned by @code{malloc}
or @code{realloc}. @code{mprobe} returns a value that says what
inconsistency, if any, was found. The values are described below.
@end deftypefun
@deftp {Data Type} {enum mcheck_status}
This enumerated type describes what kind of inconsistency was detected
in an allocated block, if any. Here are the possible values:
@table @code
@item MCHECK_DISABLED
@code{mcheck} was not called before the first allocation.
No consistency checking can be done.
@item MCHECK_OK
No inconsistency detected.
@item MCHECK_HEAD
The data immediately before the block was modified.
This commonly happens when an array index or pointer
is decremented too far.
@item MCHECK_TAIL
The data immediately after the block was modified.
This commonly happens when an array index or pointer
is incremented too far.
@item MCHECK_FREE
The block was already freed.
@end table
@end deftp
Another possibility to check for and guard against bugs in the use of
@code{malloc}, @code{realloc} and @code{free} is to set the environment
variable @code{MALLOC_CHECK_}. When @code{MALLOC_CHECK_} is set, a
special (less efficient) implementation is used which is designed to be
tolerant against simple errors, such as double calls of @code{free} with
the same argument, or overruns of a single byte (off-by-one bugs). Not
all such errors can be protected against, however, and memory leaks can
result. If @code{MALLOC_CHECK_} is set to @code{0}, any detected heap
corruption is silently ignored; if set to @code{1}, a diagnostic is
printed on @code{stderr}; if set to @code{2}, @code{abort} is called
immediately. This can be useful because otherwise a crash may happen
much later, and the true cause for the problem is then very hard to
track down.
There is one problem with @code{MALLOC_CHECK_}: in SUID or SGID binaries
it could possibly be exploited since diverging from the normal programs
behavior it now writes something to the standard error descriptor.
Therefore the use of @code{MALLOC_CHECK_} is disabled by default for
SUID and SGID binaries. It can be enabled again by the system
administrator by adding a file @file{/etc/suid-debug} (the content is
not important it could be empty).
So, what's the difference between using @code{MALLOC_CHECK_} and linking
with @samp{-lmcheck}? @code{MALLOC_CHECK_} is orthogonal with respect to
@samp{-lmcheck}. @samp{-lmcheck} has been added for backward
compatibility. Both @code{MALLOC_CHECK_} and @samp{-lmcheck} should
uncover the same bugs - but using @code{MALLOC_CHECK_} you don't need to
recompile your application.
@node Hooks for Malloc
@subsubsection Memory Allocation Hooks
@cindex allocation hooks, for @code{malloc}
@Theglibc{} lets you modify the behavior of @code{malloc},
@code{realloc}, and @code{free} by specifying appropriate hook
functions. You can use these hooks to help you debug programs that use
dynamic memory allocation, for example.
The hook variables are declared in @file{malloc.h}.
@pindex malloc.h
@comment malloc.h
@comment GNU
@defvar __malloc_hook
The value of this variable is a pointer to the function that
@code{malloc} uses whenever it is called. You should define this
function to look like @code{malloc}; that is, like:
@smallexample
void *@var{function} (size_t @var{size}, const void *@var{caller})
@end smallexample
The value of @var{caller} is the return address found on the stack when
the @code{malloc} function was called. This value allows you to trace
the memory consumption of the program.
@end defvar
@comment malloc.h
@comment GNU
@defvar __realloc_hook
The value of this variable is a pointer to function that @code{realloc}
uses whenever it is called. You should define this function to look
like @code{realloc}; that is, like:
@smallexample
void *@var{function} (void *@var{ptr}, size_t @var{size}, const void *@var{caller})
@end smallexample
The value of @var{caller} is the return address found on the stack when
the @code{realloc} function was called. This value allows you to trace the
memory consumption of the program.
@end defvar
@comment malloc.h
@comment GNU
@defvar __free_hook
The value of this variable is a pointer to function that @code{free}
uses whenever it is called. You should define this function to look
like @code{free}; that is, like:
@smallexample
void @var{function} (void *@var{ptr}, const void *@var{caller})
@end smallexample
The value of @var{caller} is the return address found on the stack when
the @code{free} function was called. This value allows you to trace the
memory consumption of the program.
@end defvar
@comment malloc.h
@comment GNU
@defvar __memalign_hook
The value of this variable is a pointer to function that @code{aligned_alloc},
@code{memalign}, @code{posix_memalign} and @code{valloc} use whenever they
are called. You should define this function to look like @code{aligned_alloc};
that is, like:
@smallexample
void *@var{function} (size_t @var{alignment}, size_t @var{size}, const void *@var{caller})
@end smallexample
The value of @var{caller} is the return address found on the stack when
the @code{aligned_alloc}, @code{memalign}, @code{posix_memalign} or
@code{valloc} functions are called. This value allows you to trace the
memory consumption of the program.
@end defvar
You must make sure that the function you install as a hook for one of
these functions does not call that function recursively without restoring
the old value of the hook first! Otherwise, your program will get stuck
in an infinite recursion. Before calling the function recursively, one
should make sure to restore all the hooks to their previous value. When
coming back from the recursive call, all the hooks should be resaved
since a hook might modify itself.
@comment malloc.h
@comment GNU
@defvar __malloc_initialize_hook
The value of this variable is a pointer to a function that is called
once when the malloc implementation is initialized. This is a weak
variable, so it can be overridden in the application with a definition
like the following:
@smallexample
void (*@var{__malloc_initialize_hook}) (void) = my_init_hook;
@end smallexample
@end defvar
An issue to look out for is the time at which the malloc hook functions
can be safely installed. If the hook functions call the malloc-related
functions recursively, it is necessary that malloc has already properly
initialized itself at the time when @code{__malloc_hook} etc. is
assigned to. On the other hand, if the hook functions provide a
complete malloc implementation of their own, it is vital that the hooks
are assigned to @emph{before} the very first @code{malloc} call has
completed, because otherwise a chunk obtained from the ordinary,
un-hooked malloc may later be handed to @code{__free_hook}, for example.
In both cases, the problem can be solved by setting up the hooks from
within a user-defined function pointed to by
@code{__malloc_initialize_hook}---then the hooks will be set up safely
at the right time.
Here is an example showing how to use @code{__malloc_hook} and
@code{__free_hook} properly. It installs a function that prints out
information every time @code{malloc} or @code{free} is called. We just
assume here that @code{realloc} and @code{memalign} are not used in our
program.
@smallexample
/* Prototypes for __malloc_hook, __free_hook */
#include
/* Prototypes for our hooks. */
static void my_init_hook (void);
static void *my_malloc_hook (size_t, const void *);
static void my_free_hook (void*, const void *);
/* Override initializing hook from the C library. */
void (*__malloc_initialize_hook) (void) = my_init_hook;
static void
my_init_hook (void)
@{
old_malloc_hook = __malloc_hook;
old_free_hook = __free_hook;
__malloc_hook = my_malloc_hook;
__free_hook = my_free_hook;
@}
static void *
my_malloc_hook (size_t size, const void *caller)
@{
void *result;
/* Restore all old hooks */
__malloc_hook = old_malloc_hook;
__free_hook = old_free_hook;
/* Call recursively */
result = malloc (size);
/* Save underlying hooks */
old_malloc_hook = __malloc_hook;
old_free_hook = __free_hook;
/* @r{@code{printf} might call @code{malloc}, so protect it too.} */
printf ("malloc (%u) returns %p\n", (unsigned int) size, result);
/* Restore our own hooks */
__malloc_hook = my_malloc_hook;
__free_hook = my_free_hook;
return result;
@}
static void
my_free_hook (void *ptr, const void *caller)
@{
/* Restore all old hooks */
__malloc_hook = old_malloc_hook;
__free_hook = old_free_hook;
/* Call recursively */
free (ptr);
/* Save underlying hooks */
old_malloc_hook = __malloc_hook;
old_free_hook = __free_hook;
/* @r{@code{printf} might call @code{free}, so protect it too.} */
printf ("freed pointer %p\n", ptr);
/* Restore our own hooks */
__malloc_hook = my_malloc_hook;
__free_hook = my_free_hook;
@}
main ()
@{
@dots{}
@}
@end smallexample
The @code{mcheck} function (@pxref{Heap Consistency Checking}) works by
installing such hooks.
@c __morecore, __after_morecore_hook are undocumented
@c It's not clear whether to document them.
@node Statistics of Malloc
@subsubsection Statistics for Memory Allocation with @code{malloc}
@cindex allocation statistics
You can get information about dynamic memory allocation by calling the
@code{mallinfo} function. This function and its associated data type
are declared in @file{malloc.h}; they are an extension of the standard
SVID/XPG version.
@pindex malloc.h
@comment malloc.h
@comment GNU
@deftp {Data Type} {struct mallinfo}
This structure type is used to return information about the dynamic
memory allocator. It contains the following members:
@table @code
@item int arena
This is the total size of memory allocated with @code{sbrk} by
@code{malloc}, in bytes.
@item int ordblks
This is the number of chunks not in use. (The memory allocator
internally gets chunks of memory from the operating system, and then
carves them up to satisfy individual @code{malloc} requests; see
@ref{Efficiency and Malloc}.)
@item int smblks
This field is unused.
@item int hblks
This is the total number of chunks allocated with @code{mmap}.
@item int hblkhd
This is the total size of memory allocated with @code{mmap}, in bytes.
@item int usmblks
This field is unused.
@item int fsmblks
This field is unused.
@item int uordblks
This is the total size of memory occupied by chunks handed out by
@code{malloc}.
@item int fordblks
This is the total size of memory occupied by free (not in use) chunks.
@item int keepcost
This is the size of the top-most releasable chunk that normally
borders the end of the heap (i.e., the high end of the virtual address
space's data segment).
@end table
@end deftp
@comment malloc.h
@comment SVID
@deftypefun {struct mallinfo} mallinfo (void)
@safety{@prelim{}@mtunsafe{@mtuinit{} @mtasuconst{:mallopt}}@asunsafe{@asuinit{} @asulock{}}@acunsafe{@acuinit{} @aculock{}}}
@c Accessing mp_.n_mmaps and mp_.max_mmapped_mem, modified with atomics
@c but non-atomically elsewhere, may get us inconsistent results. We
@c mark the statistics as unsafe, rather than the fast-path functions
@c that collect the possibly inconsistent data.
@c __libc_mallinfo @mtuinit @mtasuconst:mallopt @asuinit @asulock @aculock
@c ptmalloc_init (once) dup @mtsenv @asulock @aculock @acsfd @acsmem
@c mutex_lock dup @asulock @aculock
@c int_mallinfo @mtasuconst:mallopt [mp_ access on main_arena]
@c malloc_consolidate dup ok
@c check_malloc_state dup ok/disabled
@c chunksize dup ok
@c fastbin dupo ok
@c bin_at dup ok
@c last dup ok
@c mutex_unlock @aculock
This function returns information about the current dynamic memory usage
in a structure of type @code{struct mallinfo}.
@end deftypefun
@node Summary of Malloc
@subsubsection Summary of @code{malloc}-Related Functions
Here is a summary of the functions that work with @code{malloc}:
@table @code
@item void *malloc (size_t @var{size})
Allocate a block of @var{size} bytes. @xref{Basic Allocation}.
@item void free (void *@var{addr})
Free a block previously allocated by @code{malloc}. @xref{Freeing after
Malloc}.
@item void *realloc (void *@var{addr}, size_t @var{size})
Make a block previously allocated by @code{malloc} larger or smaller,
possibly by copying it to a new location. @xref{Changing Block Size}.
@item void *calloc (size_t @var{count}, size_t @var{eltsize})
Allocate a block of @var{count} * @var{eltsize} bytes using
@code{malloc}, and set its contents to zero. @xref{Allocating Cleared
Space}.
@item void *valloc (size_t @var{size})
Allocate a block of @var{size} bytes, starting on a page boundary.
@xref{Aligned Memory Blocks}.
@item void *aligned_alloc (size_t @var{size}, size_t @var{alignment})
Allocate a block of @var{size} bytes, starting on an address that is a
multiple of @var{alignment}. @xref{Aligned Memory Blocks}.
@item int posix_memalign (void **@var{memptr}, size_t @var{alignment}, size_t @var{size})
Allocate a block of @var{size} bytes, starting on an address that is a
multiple of @var{alignment}. @xref{Aligned Memory Blocks}.
@item void *memalign (size_t @var{size}, size_t @var{boundary})
Allocate a block of @var{size} bytes, starting on an address that is a
multiple of @var{boundary}. @xref{Aligned Memory Blocks}.
@item int mallopt (int @var{param}, int @var{value})
Adjust a tunable parameter. @xref{Malloc Tunable Parameters}.
@item int mcheck (void (*@var{abortfn}) (void))
Tell @code{malloc} to perform occasional consistency checks on
dynamically allocated memory, and to call @var{abortfn} when an
inconsistency is found. @xref{Heap Consistency Checking}.
@item void *(*__malloc_hook) (size_t @var{size}, const void *@var{caller})
A pointer to a function that @code{malloc} uses whenever it is called.
@item void *(*__realloc_hook) (void *@var{ptr}, size_t @var{size}, const void *@var{caller})
A pointer to a function that @code{realloc} uses whenever it is called.
@item void (*__free_hook) (void *@var{ptr}, const void *@var{caller})
A pointer to a function that @code{free} uses whenever it is called.
@item void (*__memalign_hook) (size_t @var{size}, size_t @var{alignment}, const void *@var{caller})
A pointer to a function that @code{aligned_alloc}, @code{memalign},
@code{posix_memalign} and @code{valloc} use whenever they are called.
@item struct mallinfo mallinfo (void)
Return information about the current dynamic memory usage.
@xref{Statistics of Malloc}.
@end table
@node Allocation Debugging
@subsection Allocation Debugging
@cindex allocation debugging
@cindex malloc debugger
A complicated task when programming with languages which do not use
garbage collected dynamic memory allocation is to find memory leaks.
Long running programs must assure that dynamically allocated objects are
freed at the end of their lifetime. If this does not happen the system
runs out of memory, sooner or later.
The @code{malloc} implementation in @theglibc{} provides some
simple means to detect such leaks and obtain some information to find
the location. To do this the application must be started in a special
mode which is enabled by an environment variable. There are no speed
penalties for the program if the debugging mode is not enabled.
@menu
* Tracing malloc:: How to install the tracing functionality.
* Using the Memory Debugger:: Example programs excerpts.
* Tips for the Memory Debugger:: Some more or less clever ideas.
* Interpreting the traces:: What do all these lines mean?
@end menu
@node Tracing malloc
@subsubsection How to install the tracing functionality
@comment mcheck.h
@comment GNU
@deftypefun void mtrace (void)
@safety{@prelim{}@mtunsafe{@mtsenv{} @mtasurace{:mtrace} @mtasuconst{:malloc_hooks} @mtuinit{}}@asunsafe{@asuinit{} @ascuheap{} @asucorrupt{} @asulock{}}@acunsafe{@acuinit{} @acucorrupt{} @aculock{} @acsfd{} @acsmem{}}}
@c Like the mcheck hooks, these are not designed with thread safety in
@c mind, because the hook pointers are temporarily modified without
@c regard to other threads, signals or cancellation.
@c mtrace @mtuinit @mtasurace:mtrace @mtsenv @asuinit @ascuheap @asucorrupt @acuinit @acucorrupt @aculock @acsfd @acsmem
@c __libc_secure_getenv dup @mtsenv
@c malloc dup @ascuheap @acsmem
@c fopen dup @ascuheap @asulock @aculock @acsmem @acsfd
@c fcntl dup ok
@c setvbuf dup @aculock
@c fprintf dup (on newly-created stream) @aculock
@c __cxa_atexit (once) dup @asulock @aculock @acsmem
@c free dup @ascuheap @acsmem
When the @code{mtrace} function is called it looks for an environment
variable named @code{MALLOC_TRACE}. This variable is supposed to
contain a valid file name. The user must have write access. If the
file already exists it is truncated. If the environment variable is not
set or it does not name a valid file which can be opened for writing
nothing is done. The behavior of @code{malloc} etc. is not changed.
For obvious reasons this also happens if the application is installed
with the SUID or SGID bit set.
If the named file is successfully opened, @code{mtrace} installs special
handlers for the functions @code{malloc}, @code{realloc}, and
@code{free} (@pxref{Hooks for Malloc}). From then on, all uses of these
functions are traced and protocolled into the file. There is now of
course a speed penalty for all calls to the traced functions so tracing
should not be enabled during normal use.
This function is a GNU extension and generally not available on other
systems. The prototype can be found in @file{mcheck.h}.
@end deftypefun
@comment mcheck.h
@comment GNU
@deftypefun void muntrace (void)
@safety{@prelim{}@mtunsafe{@mtasurace{:mtrace} @mtasuconst{:malloc_hooks} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{} @aculock{} @acsfd{}}}
@c muntrace @mtasurace:mtrace @mtslocale @asucorrupt @ascuheap @acucorrupt @acsmem @aculock @acsfd
@c fprintf (fputs) dup @mtslocale @asucorrupt @ascuheap @acsmem @aculock @acucorrupt
@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
The @code{muntrace} function can be called after @code{mtrace} was used
to enable tracing the @code{malloc} calls. If no (successful) call of
@code{mtrace} was made @code{muntrace} does nothing.
Otherwise it deinstalls the handlers for @code{malloc}, @code{realloc},
and @code{free} and then closes the protocol file. No calls are
protocolled anymore and the program runs again at full speed.
This function is a GNU extension and generally not available on other
systems. The prototype can be found in @file{mcheck.h}.
@end deftypefun
@node Using the Memory Debugger
@subsubsection Example program excerpts
Even though the tracing functionality does not influence the runtime
behavior of the program it is not a good idea to call @code{mtrace} in
all programs. Just imagine that you debug a program using @code{mtrace}
and all other programs used in the debugging session also trace their
@code{malloc} calls. The output file would be the same for all programs
and thus is unusable. Therefore one should call @code{mtrace} only if
compiled for debugging. A program could therefore start like this:
@example
#include
int
main (int argc, char *argv[])
@{
#ifdef DEBUGGING
mtrace ();
#endif
@dots{}
@}
@end example
This is all what is needed if you want to trace the calls during the
whole runtime of the program. Alternatively you can stop the tracing at
any time with a call to @code{muntrace}. It is even possible to restart
the tracing again with a new call to @code{mtrace}. But this can cause
unreliable results since there may be calls of the functions which are
not called. Please note that not only the application uses the traced
functions, also libraries (including the C library itself) use these
functions.
This last point is also why it is no good idea to call @code{muntrace}
before the program terminated. The libraries are informed about the
termination of the program only after the program returns from
@code{main} or calls @code{exit} and so cannot free the memory they use
before this time.
So the best thing one can do is to call @code{mtrace} as the very first
function in the program and never call @code{muntrace}. So the program
traces almost all uses of the @code{malloc} functions (except those
calls which are executed by constructors of the program or used
libraries).
@node Tips for the Memory Debugger
@subsubsection Some more or less clever ideas
You know the situation. The program is prepared for debugging and in
all debugging sessions it runs well. But once it is started without
debugging the error shows up. A typical example is a memory leak that
becomes visible only when we turn off the debugging. If you foresee
such situations you can still win. Simply use something equivalent to
the following little program:
@example
#include
#include
static void
enable (int sig)
@{
mtrace ();
signal (SIGUSR1, enable);
@}
static void
disable (int sig)
@{
muntrace ();
signal (SIGUSR2, disable);
@}
int
main (int argc, char *argv[])
@{
@dots{}
signal (SIGUSR1, enable);
signal (SIGUSR2, disable);
@dots{}
@}
@end example
I.e., the user can start the memory debugger any time s/he wants if the
program was started with @code{MALLOC_TRACE} set in the environment.
The output will of course not show the allocations which happened before
the first signal but if there is a memory leak this will show up
nevertheless.
@node Interpreting the traces
@subsubsection Interpreting the traces
If you take a look at the output it will look similar to this:
@example
= Start
@ [0x8048209] - 0x8064cc8
@ [0x8048209] - 0x8064ce0
@ [0x8048209] - 0x8064cf8
@ [0x80481eb] + 0x8064c48 0x14
@ [0x80481eb] + 0x8064c60 0x14
@ [0x80481eb] + 0x8064c78 0x14
@ [0x80481eb] + 0x8064c90 0x14
= End
@end example
What this all means is not really important since the trace file is not
meant to be read by a human. Therefore no attention is given to
readability. Instead there is a program which comes with @theglibc{}
which interprets the traces and outputs a summary in an
user-friendly way. The program is called @code{mtrace} (it is in fact a
Perl script) and it takes one or two arguments. In any case the name of
the file with the trace output must be specified. If an optional
argument precedes the name of the trace file this must be the name of
the program which generated the trace.
@example
drepper$ mtrace tst-mtrace log
No memory leaks.
@end example
In this case the program @code{tst-mtrace} was run and it produced a
trace file @file{log}. The message printed by @code{mtrace} shows there
are no problems with the code, all allocated memory was freed
afterwards.
If we call @code{mtrace} on the example trace given above we would get a
different outout:
@example
drepper$ mtrace errlog
- 0x08064cc8 Free 2 was never alloc'd 0x8048209
- 0x08064ce0 Free 3 was never alloc'd 0x8048209
- 0x08064cf8 Free 4 was never alloc'd 0x8048209
Memory not freed:
-----------------
Address Size Caller
0x08064c48 0x14 at 0x80481eb
0x08064c60 0x14 at 0x80481eb
0x08064c78 0x14 at 0x80481eb
0x08064c90 0x14 at 0x80481eb
@end example
We have called @code{mtrace} with only one argument and so the script
has no chance to find out what is meant with the addresses given in the
trace. We can do better:
@example
drepper$ mtrace tst errlog
- 0x08064cc8 Free 2 was never alloc'd /home/drepper/tst.c:39
- 0x08064ce0 Free 3 was never alloc'd /home/drepper/tst.c:39
- 0x08064cf8 Free 4 was never alloc'd /home/drepper/tst.c:39
Memory not freed:
-----------------
Address Size Caller
0x08064c48 0x14 at /home/drepper/tst.c:33
0x08064c60 0x14 at /home/drepper/tst.c:33
0x08064c78 0x14 at /home/drepper/tst.c:33
0x08064c90 0x14 at /home/drepper/tst.c:33
@end example
Suddenly the output makes much more sense and the user can see
immediately where the function calls causing the trouble can be found.
Interpreting this output is not complicated. There are at most two
different situations being detected. First, @code{free} was called for
pointers which were never returned by one of the allocation functions.
This is usually a very bad problem and what this looks like is shown in
the first three lines of the output. Situations like this are quite
rare and if they appear they show up very drastically: the program
normally crashes.
The other situation which is much harder to detect are memory leaks. As
you can see in the output the @code{mtrace} function collects all this
information and so can say that the program calls an allocation function
from line 33 in the source file @file{/home/drepper/tst-mtrace.c} four
times without freeing this memory before the program terminates.
Whether this is a real problem remains to be investigated.
@node Obstacks
@subsection Obstacks
@cindex obstacks
An @dfn{obstack} is a pool of memory containing a stack of objects. You
can create any number of separate obstacks, and then allocate objects in
specified obstacks. Within each obstack, the last object allocated must
always be the first one freed, but distinct obstacks are independent of
each other.
Aside from this one constraint of order of freeing, obstacks are totally
general: an obstack can contain any number of objects of any size. They
are implemented with macros, so allocation is usually very fast as long as
the objects are usually small. And the only space overhead per object is
the padding needed to start each object on a suitable boundary.
@menu
* Creating Obstacks:: How to declare an obstack in your program.
* Preparing for Obstacks:: Preparations needed before you can
use obstacks.
* Allocation in an Obstack:: Allocating objects in an obstack.
* Freeing Obstack Objects:: Freeing objects in an obstack.
* Obstack Functions:: The obstack functions are both
functions and macros.
* Growing Objects:: Making an object bigger by stages.
* Extra Fast Growing:: Extra-high-efficiency (though more
complicated) growing objects.
* Status of an Obstack:: Inquiries about the status of an obstack.
* Obstacks Data Alignment:: Controlling alignment of objects in obstacks.
* Obstack Chunks:: How obstacks obtain and release chunks;
efficiency considerations.
* Summary of Obstacks::
@end menu
@node Creating Obstacks
@subsubsection Creating Obstacks
The utilities for manipulating obstacks are declared in the header
file @file{obstack.h}.
@pindex obstack.h
@comment obstack.h
@comment GNU
@deftp {Data Type} {struct obstack}
An obstack is represented by a data structure of type @code{struct
obstack}. This structure has a small fixed size; it records the status
of the obstack and how to find the space in which objects are allocated.
It does not contain any of the objects themselves. You should not try
to access the contents of the structure directly; use only the functions
described in this chapter.
@end deftp
You can declare variables of type @code{struct obstack} and use them as
obstacks, or you can allocate obstacks dynamically like any other kind
of object. Dynamic allocation of obstacks allows your program to have a
variable number of different stacks. (You can even allocate an
obstack structure in another obstack, but this is rarely useful.)
All the functions that work with obstacks require you to specify which
obstack to use. You do this with a pointer of type @code{struct obstack
*}. In the following, we often say ``an obstack'' when strictly
speaking the object at hand is such a pointer.
The objects in the obstack are packed into large blocks called
@dfn{chunks}. The @code{struct obstack} structure points to a chain of
the chunks currently in use.
The obstack library obtains a new chunk whenever you allocate an object
that won't fit in the previous chunk. Since the obstack library manages
chunks automatically, you don't need to pay much attention to them, but
you do need to supply a function which the obstack library should use to
get a chunk. Usually you supply a function which uses @code{malloc}
directly or indirectly. You must also supply a function to free a chunk.
These matters are described in the following section.
@node Preparing for Obstacks
@subsubsection Preparing for Using Obstacks
Each source file in which you plan to use the obstack functions
must include the header file @file{obstack.h}, like this:
@smallexample
#include
@end smallexample
@findex obstack_chunk_alloc
@findex obstack_chunk_free
Also, if the source file uses the macro @code{obstack_init}, it must
declare or define two functions or macros that will be called by the
obstack library. One, @code{obstack_chunk_alloc}, is used to allocate
the chunks of memory into which objects are packed. The other,
@code{obstack_chunk_free}, is used to return chunks when the objects in
them are freed. These macros should appear before any use of obstacks
in the source file.
Usually these are defined to use @code{malloc} via the intermediary
@code{xmalloc} (@pxref{Unconstrained Allocation}). This is done with
the following pair of macro definitions:
@smallexample
#define obstack_chunk_alloc xmalloc
#define obstack_chunk_free free
@end smallexample
@noindent
Though the memory you get using obstacks really comes from @code{malloc},
using obstacks is faster because @code{malloc} is called less often, for
larger blocks of memory. @xref{Obstack Chunks}, for full details.
At run time, before the program can use a @code{struct obstack} object
as an obstack, it must initialize the obstack by calling
@code{obstack_init}.
@comment obstack.h
@comment GNU
@deftypefun int obstack_init (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{@acsmem{}}}
@c obstack_init @mtsrace:obstack-ptr @acsmem
@c _obstack_begin @acsmem
@c chunkfun = obstack_chunk_alloc (suggested malloc)
@c freefun = obstack_chunk_free (suggested free)
@c *chunkfun @acsmem
@c obstack_chunk_alloc user-supplied
@c *obstack_alloc_failed_handler user-supplied
@c -> print_and_abort (default)
@c
@c print_and_abort
@c _ dup @ascuintl
@c fxprintf dup @asucorrupt @aculock @acucorrupt
@c exit @acucorrupt?
Initialize obstack @var{obstack-ptr} for allocation of objects. This
function calls the obstack's @code{obstack_chunk_alloc} function. If
allocation of memory fails, the function pointed to by
@code{obstack_alloc_failed_handler} is called. The @code{obstack_init}
function always returns 1 (Compatibility notice: Former versions of
obstack returned 0 if allocation failed).
@end deftypefun
Here are two examples of how to allocate the space for an obstack and
initialize it. First, an obstack that is a static variable:
@smallexample
static struct obstack myobstack;
@dots{}
obstack_init (&myobstack);
@end smallexample
@noindent
Second, an obstack that is itself dynamically allocated:
@smallexample
struct obstack *myobstack_ptr
= (struct obstack *) xmalloc (sizeof (struct obstack));
obstack_init (myobstack_ptr);
@end smallexample
@comment obstack.h
@comment GNU
@defvar obstack_alloc_failed_handler
The value of this variable is a pointer to a function that
@code{obstack} uses when @code{obstack_chunk_alloc} fails to allocate
memory. The default action is to print a message and abort.
You should supply a function that either calls @code{exit}
(@pxref{Program Termination}) or @code{longjmp} (@pxref{Non-Local
Exits}) and doesn't return.
@smallexample
void my_obstack_alloc_failed (void)
@dots{}
obstack_alloc_failed_handler = &my_obstack_alloc_failed;
@end smallexample
@end defvar
@node Allocation in an Obstack
@subsubsection Allocation in an Obstack
@cindex allocation (obstacks)
The most direct way to allocate an object in an obstack is with
@code{obstack_alloc}, which is invoked almost like @code{malloc}.
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_alloc (struct obstack *@var{obstack-ptr}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_alloc @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_blank dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_finish dup @mtsrace:obstack-ptr @acucorrupt
This allocates an uninitialized block of @var{size} bytes in an obstack
and returns its address. Here @var{obstack-ptr} specifies which obstack
to allocate the block in; it is the address of the @code{struct obstack}
object which represents the obstack. Each obstack function or macro
requires you to specify an @var{obstack-ptr} as the first argument.
This function calls the obstack's @code{obstack_chunk_alloc} function if
it needs to allocate a new chunk of memory; it calls
@code{obstack_alloc_failed_handler} if allocation of memory by
@code{obstack_chunk_alloc} failed.
@end deftypefun
For example, here is a function that allocates a copy of a string @var{str}
in a specific obstack, which is in the variable @code{string_obstack}:
@smallexample
struct obstack string_obstack;
char *
copystring (char *string)
@{
size_t len = strlen (string) + 1;
char *s = (char *) obstack_alloc (&string_obstack, len);
memcpy (s, string, len);
return s;
@}
@end smallexample
To allocate a block with specified contents, use the function
@code{obstack_copy}, declared like this:
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_copy (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_copy @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_grow dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_finish dup @mtsrace:obstack-ptr @acucorrupt
This allocates a block and initializes it by copying @var{size}
bytes of data starting at @var{address}. It calls
@code{obstack_alloc_failed_handler} if allocation of memory by
@code{obstack_chunk_alloc} failed.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_copy0 (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_copy0 @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_grow0 dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_finish dup @mtsrace:obstack-ptr @acucorrupt
Like @code{obstack_copy}, but appends an extra byte containing a null
character. This extra byte is not counted in the argument @var{size}.
@end deftypefun
The @code{obstack_copy0} function is convenient for copying a sequence
of characters into an obstack as a null-terminated string. Here is an
example of its use:
@smallexample
char *
obstack_savestring (char *addr, int size)
@{
return obstack_copy0 (&myobstack, addr, size);
@}
@end smallexample
@noindent
Contrast this with the previous example of @code{savestring} using
@code{malloc} (@pxref{Basic Allocation}).
@node Freeing Obstack Objects
@subsubsection Freeing Objects in an Obstack
@cindex freeing (obstacks)
To free an object allocated in an obstack, use the function
@code{obstack_free}. Since the obstack is a stack of objects, freeing
one object automatically frees all other objects allocated more recently
in the same obstack.
@comment obstack.h
@comment GNU
@deftypefun void obstack_free (struct obstack *@var{obstack-ptr}, void *@var{object})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{}}}
@c obstack_free @mtsrace:obstack-ptr @acucorrupt
@c (obstack_free) @mtsrace:obstack-ptr @acucorrupt
@c *freefun dup user-supplied
If @var{object} is a null pointer, everything allocated in the obstack
is freed. Otherwise, @var{object} must be the address of an object
allocated in the obstack. Then @var{object} is freed, along with
everything allocated in @var{obstack} since @var{object}.
@end deftypefun
Note that if @var{object} is a null pointer, the result is an
uninitialized obstack. To free all memory in an obstack but leave it
valid for further allocation, call @code{obstack_free} with the address
of the first object allocated on the obstack:
@smallexample
obstack_free (obstack_ptr, first_object_allocated_ptr);
@end smallexample
Recall that the objects in an obstack are grouped into chunks. When all
the objects in a chunk become free, the obstack library automatically
frees the chunk (@pxref{Preparing for Obstacks}). Then other
obstacks, or non-obstack allocation, can reuse the space of the chunk.
@node Obstack Functions
@subsubsection Obstack Functions and Macros
@cindex macros
The interfaces for using obstacks may be defined either as functions or
as macros, depending on the compiler. The obstack facility works with
all C compilers, including both @w{ISO C} and traditional C, but there are
precautions you must take if you plan to use compilers other than GNU C.
If you are using an old-fashioned @w{non-ISO C} compiler, all the obstack
``functions'' are actually defined only as macros. You can call these
macros like functions, but you cannot use them in any other way (for
example, you cannot take their address).
Calling the macros requires a special precaution: namely, the first
operand (the obstack pointer) may not contain any side effects, because
it may be computed more than once. For example, if you write this:
@smallexample
obstack_alloc (get_obstack (), 4);
@end smallexample
@noindent
you will find that @code{get_obstack} may be called several times.
If you use @code{*obstack_list_ptr++} as the obstack pointer argument,
you will get very strange results since the incrementation may occur
several times.
In @w{ISO C}, each function has both a macro definition and a function
definition. The function definition is used if you take the address of the
function without calling it. An ordinary call uses the macro definition by
default, but you can request the function definition instead by writing the
function name in parentheses, as shown here:
@smallexample
char *x;
void *(*funcp) ();
/* @r{Use the macro}. */
x = (char *) obstack_alloc (obptr, size);
/* @r{Call the function}. */
x = (char *) (obstack_alloc) (obptr, size);
/* @r{Take the address of the function}. */
funcp = obstack_alloc;
@end smallexample
@noindent
This is the same situation that exists in @w{ISO C} for the standard library
functions. @xref{Macro Definitions}.
@strong{Warning:} When you do use the macros, you must observe the
precaution of avoiding side effects in the first operand, even in @w{ISO C}.
If you use the GNU C compiler, this precaution is not necessary, because
various language extensions in GNU C permit defining the macros so as to
compute each argument only once.
@node Growing Objects
@subsubsection Growing Objects
@cindex growing objects (in obstacks)
@cindex changing the size of a block (obstacks)
Because memory in obstack chunks is used sequentially, it is possible to
build up an object step by step, adding one or more bytes at a time to the
end of the object. With this technique, you do not need to know how much
data you will put in the object until you come to the end of it. We call
this the technique of @dfn{growing objects}. The special functions
for adding data to the growing object are described in this section.
You don't need to do anything special when you start to grow an object.
Using one of the functions to add data to the object automatically
starts it. However, it is necessary to say explicitly when the object is
finished. This is done with the function @code{obstack_finish}.
The actual address of the object thus built up is not known until the
object is finished. Until then, it always remains possible that you will
add so much data that the object must be copied into a new chunk.
While the obstack is in use for a growing object, you cannot use it for
ordinary allocation of another object. If you try to do so, the space
already added to the growing object will become part of the other object.
@comment obstack.h
@comment GNU
@deftypefun void obstack_blank (struct obstack *@var{obstack-ptr}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_blank @mtsrace:obstack-ptr @acucorrupt @acsmem
@c _obstack_newchunk @mtsrace:obstack-ptr @acucorrupt @acsmem
@c *chunkfun dup @acsmem
@c *obstack_alloc_failed_handler dup user-supplied
@c *freefun
@c obstack_blank_fast dup @mtsrace:obstack-ptr
The most basic function for adding to a growing object is
@code{obstack_blank}, which adds space without initializing it.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_grow (struct obstack *@var{obstack-ptr}, void *@var{data}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_grow @mtsrace:obstack-ptr @acucorrupt @acsmem
@c _obstack_newchunk dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c memcpy ok
To add a block of initialized space, use @code{obstack_grow}, which is
the growing-object analogue of @code{obstack_copy}. It adds @var{size}
bytes of data to the growing object, copying the contents from
@var{data}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_grow0 (struct obstack *@var{obstack-ptr}, void *@var{data}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_grow0 @mtsrace:obstack-ptr @acucorrupt @acsmem
@c (no sequence point between storing NUL and incrementing next_free)
@c (multiple changes to next_free => @acucorrupt)
@c _obstack_newchunk dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c memcpy ok
This is the growing-object analogue of @code{obstack_copy0}. It adds
@var{size} bytes copied from @var{data}, followed by an additional null
character.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_1grow (struct obstack *@var{obstack-ptr}, char @var{c})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_1grow @mtsrace:obstack-ptr @acucorrupt @acsmem
@c _obstack_newchunk dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_1grow_fast dup @mtsrace:obstack-ptr @acucorrupt @acsmem
To add one character at a time, use the function @code{obstack_1grow}.
It adds a single byte containing @var{c} to the growing object.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_ptr_grow (struct obstack *@var{obstack-ptr}, void *@var{data})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_ptr_grow @mtsrace:obstack-ptr @acucorrupt @acsmem
@c _obstack_newchunk dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_ptr_grow_fast dup @mtsrace:obstack-ptr
Adding the value of a pointer one can use the function
@code{obstack_ptr_grow}. It adds @code{sizeof (void *)} bytes
containing the value of @var{data}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_int_grow (struct obstack *@var{obstack-ptr}, int @var{data})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_int_grow @mtsrace:obstack-ptr @acucorrupt @acsmem
@c _obstack_newchunk dup @mtsrace:obstack-ptr @acucorrupt @acsmem
@c obstack_int_grow_fast dup @mtsrace:obstack-ptr
A single value of type @code{int} can be added by using the
@code{obstack_int_grow} function. It adds @code{sizeof (int)} bytes to
the growing object and initializes them with the value of @var{data}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_finish (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{}}}
@c obstack_finish @mtsrace:obstack-ptr @acucorrupt
When you are finished growing the object, use the function
@code{obstack_finish} to close it off and return its final address.
Once you have finished the object, the obstack is available for ordinary
allocation or for growing another object.
This function can return a null pointer under the same conditions as
@code{obstack_alloc} (@pxref{Allocation in an Obstack}).
@end deftypefun
When you build an object by growing it, you will probably need to know
afterward how long it became. You need not keep track of this as you grow
the object, because you can find out the length from the obstack just
before finishing the object with the function @code{obstack_object_size},
declared as follows:
@comment obstack.h
@comment GNU
@deftypefun int obstack_object_size (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
This function returns the current size of the growing object, in bytes.
Remember to call this function @emph{before} finishing the object.
After it is finished, @code{obstack_object_size} will return zero.
@end deftypefun
If you have started growing an object and wish to cancel it, you should
finish it and then free it, like this:
@smallexample
obstack_free (obstack_ptr, obstack_finish (obstack_ptr));
@end smallexample
@noindent
This has no effect if no object was growing.
@cindex shrinking objects
You can use @code{obstack_blank} with a negative size argument to make
the current object smaller. Just don't try to shrink it beyond zero
length---there's no telling what will happen if you do that.
@node Extra Fast Growing
@subsubsection Extra Fast Growing Objects
@cindex efficiency and obstacks
The usual functions for growing objects incur overhead for checking
whether there is room for the new growth in the current chunk. If you
are frequently constructing objects in small steps of growth, this
overhead can be significant.
You can reduce the overhead by using special ``fast growth''
functions that grow the object without checking. In order to have a
robust program, you must do the checking yourself. If you do this checking
in the simplest way each time you are about to add data to the object, you
have not saved anything, because that is what the ordinary growth
functions do. But if you can arrange to check less often, or check
more efficiently, then you make the program faster.
The function @code{obstack_room} returns the amount of room available
in the current chunk. It is declared as follows:
@comment obstack.h
@comment GNU
@deftypefun int obstack_room (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
This returns the number of bytes that can be added safely to the current
growing object (or to an object about to be started) in obstack
@var{obstack} using the fast growth functions.
@end deftypefun
While you know there is room, you can use these fast growth functions
for adding data to a growing object:
@comment obstack.h
@comment GNU
@deftypefun void obstack_1grow_fast (struct obstack *@var{obstack-ptr}, char @var{c})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acunsafe{@acucorrupt{} @acsmem{}}}
@c obstack_1grow_fast @mtsrace:obstack-ptr @acucorrupt @acsmem
@c (no sequence point between copying c and incrementing next_free)
The function @code{obstack_1grow_fast} adds one byte containing the
character @var{c} to the growing object in obstack @var{obstack-ptr}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_ptr_grow_fast (struct obstack *@var{obstack-ptr}, void *@var{data})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
@c obstack_ptr_grow_fast @mtsrace:obstack-ptr
The function @code{obstack_ptr_grow_fast} adds @code{sizeof (void *)}
bytes containing the value of @var{data} to the growing object in
obstack @var{obstack-ptr}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_int_grow_fast (struct obstack *@var{obstack-ptr}, int @var{data})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
@c obstack_int_grow_fast @mtsrace:obstack-ptr
The function @code{obstack_int_grow_fast} adds @code{sizeof (int)} bytes
containing the value of @var{data} to the growing object in obstack
@var{obstack-ptr}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun void obstack_blank_fast (struct obstack *@var{obstack-ptr}, int @var{size})
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
@c obstack_blank_fast @mtsrace:obstack-ptr
The function @code{obstack_blank_fast} adds @var{size} bytes to the
growing object in obstack @var{obstack-ptr} without initializing them.
@end deftypefun
When you check for space using @code{obstack_room} and there is not
enough room for what you want to add, the fast growth functions
are not safe. In this case, simply use the corresponding ordinary
growth function instead. Very soon this will copy the object to a
new chunk; then there will be lots of room available again.
So, each time you use an ordinary growth function, check afterward for
sufficient space using @code{obstack_room}. Once the object is copied
to a new chunk, there will be plenty of space again, so the program will
start using the fast growth functions again.
Here is an example:
@smallexample
@group
void
add_string (struct obstack *obstack, const char *ptr, int len)
@{
while (len > 0)
@{
int room = obstack_room (obstack);
if (room == 0)
@{
/* @r{Not enough room. Add one character slowly,}
@r{which may copy to a new chunk and make room.} */
obstack_1grow (obstack, *ptr++);
len--;
@}
else
@{
if (room > len)
room = len;
/* @r{Add fast as much as we have room for.} */
len -= room;
while (room-- > 0)
obstack_1grow_fast (obstack, *ptr++);
@}
@}
@}
@end group
@end smallexample
@node Status of an Obstack
@subsubsection Status of an Obstack
@cindex obstack status
@cindex status of obstack
Here are functions that provide information on the current status of
allocation in an obstack. You can use them to learn about an object while
still growing it.
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_base (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
This function returns the tentative address of the beginning of the
currently growing object in @var{obstack-ptr}. If you finish the object
immediately, it will have that address. If you make it larger first, it
may outgrow the current chunk---then its address will change!
If no object is growing, this value says where the next object you
allocate will start (once again assuming it fits in the current
chunk).
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun {void *} obstack_next_free (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
This function returns the address of the first free byte in the current
chunk of obstack @var{obstack-ptr}. This is the end of the currently
growing object. If no object is growing, @code{obstack_next_free}
returns the same value as @code{obstack_base}.
@end deftypefun
@comment obstack.h
@comment GNU
@deftypefun int obstack_object_size (struct obstack *@var{obstack-ptr})
@c dup
@safety{@prelim{}@mtsafe{@mtsrace{:obstack-ptr}}@assafe{}@acsafe{}}
This function returns the size in bytes of the currently growing object.
This is equivalent to
@smallexample
obstack_next_free (@var{obstack-ptr}) - obstack_base (@var{obstack-ptr})
@end smallexample
@end deftypefun
@node Obstacks Data Alignment
@subsubsection Alignment of Data in Obstacks
@cindex alignment (in obstacks)
Each obstack has an @dfn{alignment boundary}; each object allocated in
the obstack automatically starts on an address that is a multiple of the
specified boundary. By default, this boundary is aligned so that
the object can hold any type of data.
To access an obstack's alignment boundary, use the macro
@code{obstack_alignment_mask}, whose function prototype looks like
this:
@comment obstack.h
@comment GNU
@deftypefn Macro int obstack_alignment_mask (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The value is a bit mask; a bit that is 1 indicates that the corresponding
bit in the address of an object should be 0. The mask value should be one
less than a power of 2; the effect is that all object addresses are
multiples of that power of 2. The default value of the mask is a value
that allows aligned objects to hold any type of data: for example, if
its value is 3, any type of data can be stored at locations whose
addresses are multiples of 4. A mask value of 0 means an object can start
on any multiple of 1 (that is, no alignment is required).
The expansion of the macro @code{obstack_alignment_mask} is an lvalue,
so you can alter the mask by assignment. For example, this statement:
@smallexample
obstack_alignment_mask (obstack_ptr) = 0;
@end smallexample
@noindent
has the effect of turning off alignment processing in the specified obstack.
@end deftypefn
Note that a change in alignment mask does not take effect until
@emph{after} the next time an object is allocated or finished in the
obstack. If you are not growing an object, you can make the new
alignment mask take effect immediately by calling @code{obstack_finish}.
This will finish a zero-length object and then do proper alignment for
the next object.
@node Obstack Chunks
@subsubsection Obstack Chunks
@cindex efficiency of chunks
@cindex chunks
Obstacks work by allocating space for themselves in large chunks, and
then parceling out space in the chunks to satisfy your requests. Chunks
are normally 4096 bytes long unless you specify a different chunk size.
The chunk size includes 8 bytes of overhead that are not actually used
for storing objects. Regardless of the specified size, longer chunks
will be allocated when necessary for long objects.
The obstack library allocates chunks by calling the function
@code{obstack_chunk_alloc}, which you must define. When a chunk is no
longer needed because you have freed all the objects in it, the obstack
library frees the chunk by calling @code{obstack_chunk_free}, which you
must also define.
These two must be defined (as macros) or declared (as functions) in each
source file that uses @code{obstack_init} (@pxref{Creating Obstacks}).
Most often they are defined as macros like this:
@smallexample
#define obstack_chunk_alloc malloc
#define obstack_chunk_free free
@end smallexample
Note that these are simple macros (no arguments). Macro definitions with
arguments will not work! It is necessary that @code{obstack_chunk_alloc}
or @code{obstack_chunk_free}, alone, expand into a function name if it is
not itself a function name.
If you allocate chunks with @code{malloc}, the chunk size should be a
power of 2. The default chunk size, 4096, was chosen because it is long
enough to satisfy many typical requests on the obstack yet short enough
not to waste too much memory in the portion of the last chunk not yet used.
@comment obstack.h
@comment GNU
@deftypefn Macro int obstack_chunk_size (struct obstack *@var{obstack-ptr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This returns the chunk size of the given obstack.
@end deftypefn
Since this macro expands to an lvalue, you can specify a new chunk size by
assigning it a new value. Doing so does not affect the chunks already
allocated, but will change the size of chunks allocated for that particular
obstack in the future. It is unlikely to be useful to make the chunk size
smaller, but making it larger might improve efficiency if you are
allocating many objects whose size is comparable to the chunk size. Here
is how to do so cleanly:
@smallexample
if (obstack_chunk_size (obstack_ptr) < @var{new-chunk-size})
obstack_chunk_size (obstack_ptr) = @var{new-chunk-size};
@end smallexample
@node Summary of Obstacks
@subsubsection Summary of Obstack Functions
Here is a summary of all the functions associated with obstacks. Each
takes the address of an obstack (@code{struct obstack *}) as its first
argument.
@table @code
@item void obstack_init (struct obstack *@var{obstack-ptr})
Initialize use of an obstack. @xref{Creating Obstacks}.
@item void *obstack_alloc (struct obstack *@var{obstack-ptr}, int @var{size})
Allocate an object of @var{size} uninitialized bytes.
@xref{Allocation in an Obstack}.
@item void *obstack_copy (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
Allocate an object of @var{size} bytes, with contents copied from
@var{address}. @xref{Allocation in an Obstack}.
@item void *obstack_copy0 (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
Allocate an object of @var{size}+1 bytes, with @var{size} of them copied
from @var{address}, followed by a null character at the end.
@xref{Allocation in an Obstack}.
@item void obstack_free (struct obstack *@var{obstack-ptr}, void *@var{object})
Free @var{object} (and everything allocated in the specified obstack
more recently than @var{object}). @xref{Freeing Obstack Objects}.
@item void obstack_blank (struct obstack *@var{obstack-ptr}, int @var{size})
Add @var{size} uninitialized bytes to a growing object.
@xref{Growing Objects}.
@item void obstack_grow (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
Add @var{size} bytes, copied from @var{address}, to a growing object.
@xref{Growing Objects}.
@item void obstack_grow0 (struct obstack *@var{obstack-ptr}, void *@var{address}, int @var{size})
Add @var{size} bytes, copied from @var{address}, to a growing object,
and then add another byte containing a null character. @xref{Growing
Objects}.
@item void obstack_1grow (struct obstack *@var{obstack-ptr}, char @var{data-char})
Add one byte containing @var{data-char} to a growing object.
@xref{Growing Objects}.
@item void *obstack_finish (struct obstack *@var{obstack-ptr})
Finalize the object that is growing and return its permanent address.
@xref{Growing Objects}.
@item int obstack_object_size (struct obstack *@var{obstack-ptr})
Get the current size of the currently growing object. @xref{Growing
Objects}.
@item void obstack_blank_fast (struct obstack *@var{obstack-ptr}, int @var{size})
Add @var{size} uninitialized bytes to a growing object without checking
that there is enough room. @xref{Extra Fast Growing}.
@item void obstack_1grow_fast (struct obstack *@var{obstack-ptr}, char @var{data-char})
Add one byte containing @var{data-char} to a growing object without
checking that there is enough room. @xref{Extra Fast Growing}.
@item int obstack_room (struct obstack *@var{obstack-ptr})
Get the amount of room now available for growing the current object.
@xref{Extra Fast Growing}.
@item int obstack_alignment_mask (struct obstack *@var{obstack-ptr})
The mask used for aligning the beginning of an object. This is an
lvalue. @xref{Obstacks Data Alignment}.
@item int obstack_chunk_size (struct obstack *@var{obstack-ptr})
The size for allocating chunks. This is an lvalue. @xref{Obstack Chunks}.
@item void *obstack_base (struct obstack *@var{obstack-ptr})
Tentative starting address of the currently growing object.
@xref{Status of an Obstack}.
@item void *obstack_next_free (struct obstack *@var{obstack-ptr})
Address just after the end of the currently growing object.
@xref{Status of an Obstack}.
@end table
@node Variable Size Automatic
@subsection Automatic Storage with Variable Size
@cindex automatic freeing
@cindex @code{alloca} function
@cindex automatic storage with variable size
The function @code{alloca} supports a kind of half-dynamic allocation in
which blocks are allocated dynamically but freed automatically.
Allocating a block with @code{alloca} is an explicit action; you can
allocate as many blocks as you wish, and compute the size at run time. But
all the blocks are freed when you exit the function that @code{alloca} was
called from, just as if they were automatic variables declared in that
function. There is no way to free the space explicitly.
The prototype for @code{alloca} is in @file{stdlib.h}. This function is
a BSD extension.
@pindex stdlib.h
@comment stdlib.h
@comment GNU, BSD
@deftypefun {void *} alloca (size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The return value of @code{alloca} is the address of a block of @var{size}
bytes of memory, allocated in the stack frame of the calling function.
@end deftypefun
Do not use @code{alloca} inside the arguments of a function call---you
will get unpredictable results, because the stack space for the
@code{alloca} would appear on the stack in the middle of the space for
the function arguments. An example of what to avoid is @code{foo (x,
alloca (4), y)}.
@c This might get fixed in future versions of GCC, but that won't make
@c it safe with compilers generally.
@menu
* Alloca Example:: Example of using @code{alloca}.
* Advantages of Alloca:: Reasons to use @code{alloca}.
* Disadvantages of Alloca:: Reasons to avoid @code{alloca}.
* GNU C Variable-Size Arrays:: Only in GNU C, here is an alternative
method of allocating dynamically and
freeing automatically.
@end menu
@node Alloca Example
@subsubsection @code{alloca} Example
As an example of the use of @code{alloca}, here is a function that opens
a file name made from concatenating two argument strings, and returns a
file descriptor or minus one signifying failure:
@smallexample
int
open2 (char *str1, char *str2, int flags, int mode)
@{
char *name = (char *) alloca (strlen (str1) + strlen (str2) + 1);
stpcpy (stpcpy (name, str1), str2);
return open (name, flags, mode);
@}
@end smallexample
@noindent
Here is how you would get the same results with @code{malloc} and
@code{free}:
@smallexample
int
open2 (char *str1, char *str2, int flags, int mode)
@{
char *name = (char *) malloc (strlen (str1) + strlen (str2) + 1);
int desc;
if (name == 0)
fatal ("virtual memory exceeded");
stpcpy (stpcpy (name, str1), str2);
desc = open (name, flags, mode);
free (name);
return desc;
@}
@end smallexample
As you can see, it is simpler with @code{alloca}. But @code{alloca} has
other, more important advantages, and some disadvantages.
@node Advantages of Alloca
@subsubsection Advantages of @code{alloca}
Here are the reasons why @code{alloca} may be preferable to @code{malloc}:
@itemize @bullet
@item
Using @code{alloca} wastes very little space and is very fast. (It is
open-coded by the GNU C compiler.)
@item
Since @code{alloca} does not have separate pools for different sizes of
block, space used for any size block can be reused for any other size.
@code{alloca} does not cause memory fragmentation.
@item
@cindex longjmp
Nonlocal exits done with @code{longjmp} (@pxref{Non-Local Exits})
automatically free the space allocated with @code{alloca} when they exit
through the function that called @code{alloca}. This is the most
important reason to use @code{alloca}.
To illustrate this, suppose you have a function
@code{open_or_report_error} which returns a descriptor, like
@code{open}, if it succeeds, but does not return to its caller if it
fails. If the file cannot be opened, it prints an error message and
jumps out to the command level of your program using @code{longjmp}.
Let's change @code{open2} (@pxref{Alloca Example}) to use this
subroutine:@refill
@smallexample
int
open2 (char *str1, char *str2, int flags, int mode)
@{
char *name = (char *) alloca (strlen (str1) + strlen (str2) + 1);
stpcpy (stpcpy (name, str1), str2);
return open_or_report_error (name, flags, mode);
@}
@end smallexample
@noindent
Because of the way @code{alloca} works, the memory it allocates is
freed even when an error occurs, with no special effort required.
By contrast, the previous definition of @code{open2} (which uses
@code{malloc} and @code{free}) would develop a memory leak if it were
changed in this way. Even if you are willing to make more changes to
fix it, there is no easy way to do so.
@end itemize
@node Disadvantages of Alloca
@subsubsection Disadvantages of @code{alloca}
@cindex @code{alloca} disadvantages
@cindex disadvantages of @code{alloca}
These are the disadvantages of @code{alloca} in comparison with
@code{malloc}:
@itemize @bullet
@item
If you try to allocate more memory than the machine can provide, you
don't get a clean error message. Instead you get a fatal signal like
the one you would get from an infinite recursion; probably a
segmentation violation (@pxref{Program Error Signals}).
@item
Some @nongnusystems{} fail to support @code{alloca}, so it is less
portable. However, a slower emulation of @code{alloca} written in C
is available for use on systems with this deficiency.
@end itemize
@node GNU C Variable-Size Arrays
@subsubsection GNU C Variable-Size Arrays
@cindex variable-sized arrays
In GNU C, you can replace most uses of @code{alloca} with an array of
variable size. Here is how @code{open2} would look then:
@smallexample
int open2 (char *str1, char *str2, int flags, int mode)
@{
char name[strlen (str1) + strlen (str2) + 1];
stpcpy (stpcpy (name, str1), str2);
return open (name, flags, mode);
@}
@end smallexample
But @code{alloca} is not always equivalent to a variable-sized array, for
several reasons:
@itemize @bullet
@item
A variable size array's space is freed at the end of the scope of the
name of the array. The space allocated with @code{alloca}
remains until the end of the function.
@item
It is possible to use @code{alloca} within a loop, allocating an
additional block on each iteration. This is impossible with
variable-sized arrays.
@end itemize
@strong{NB:} If you mix use of @code{alloca} and variable-sized arrays
within one function, exiting a scope in which a variable-sized array was
declared frees all blocks allocated with @code{alloca} during the
execution of that scope.
@node Resizing the Data Segment
@section Resizing the Data Segment
The symbols in this section are declared in @file{unistd.h}.
You will not normally use the functions in this section, because the
functions described in @ref{Memory Allocation} are easier to use. Those
are interfaces to a @glibcadj{} memory allocator that uses the
functions below itself. The functions below are simple interfaces to
system calls.
@comment unistd.h
@comment BSD
@deftypefun int brk (void *@var{addr})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{brk} sets the high end of the calling process' data segment to
@var{addr}.
The address of the end of a segment is defined to be the address of the
last byte in the segment plus 1.
The function has no effect if @var{addr} is lower than the low end of
the data segment. (This is considered success, by the way).
The function fails if it would cause the data segment to overlap another
segment or exceed the process' data storage limit (@pxref{Limits on
Resources}).
The function is named for a common historical case where data storage
and the stack are in the same segment. Data storage allocation grows
upward from the bottom of the segment while the stack grows downward
toward it from the top of the segment and the curtain between them is
called the @dfn{break}.
The return value is zero on success. On failure, the return value is
@code{-1} and @code{errno} is set accordingly. The following @code{errno}
values are specific to this function:
@table @code
@item ENOMEM
The request would cause the data segment to overlap another segment or
exceed the process' data storage limit.
@end table
@c The Brk system call in Linux (as opposed to the GNU C Library function)
@c is considerably different. It always returns the new end of the data
@c segment, whether it succeeds or fails. The GNU C library Brk determines
@c it's a failure if and only if the system call returns an address less
@c than the address requested.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun void *sbrk (ptrdiff_t @var{delta})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is the same as @code{brk} except that you specify the new
end of the data segment as an offset @var{delta} from the current end
and on success the return value is the address of the resulting end of
the data segment instead of zero.
This means you can use @samp{sbrk(0)} to find out what the current end
of the data segment is.
@end deftypefun
@node Locking Pages
@section Locking Pages
@cindex locking pages
@cindex memory lock
@cindex paging
You can tell the system to associate a particular virtual memory page
with a real page frame and keep it that way --- i.e., cause the page to
be paged in if it isn't already and mark it so it will never be paged
out and consequently will never cause a page fault. This is called
@dfn{locking} a page.
The functions in this chapter lock and unlock the calling process'
pages.
@menu
* Why Lock Pages:: Reasons to read this section.
* Locked Memory Details:: Everything you need to know locked
memory
* Page Lock Functions:: Here's how to do it.
@end menu
@node Why Lock Pages
@subsection Why Lock Pages
Because page faults cause paged out pages to be paged in transparently,
a process rarely needs to be concerned about locking pages. However,
there are two reasons people sometimes are:
@itemize @bullet
@item
Speed. A page fault is transparent only insofar as the process is not
sensitive to how long it takes to do a simple memory access. Time-critical
processes, especially realtime processes, may not be able to wait or
may not be able to tolerate variance in execution speed.
@cindex realtime processing
@cindex speed of execution
A process that needs to lock pages for this reason probably also needs
priority among other processes for use of the CPU. @xref{Priority}.
In some cases, the programmer knows better than the system's demand
paging allocator which pages should remain in real memory to optimize
system performance. In this case, locking pages can help.
@item
Privacy. If you keep secrets in virtual memory and that virtual memory
gets paged out, that increases the chance that the secrets will get out.
If a password gets written out to disk swap space, for example, it might
still be there long after virtual and real memory have been wiped clean.
@end itemize
Be aware that when you lock a page, that's one fewer page frame that can
be used to back other virtual memory (by the same or other processes),
which can mean more page faults, which means the system runs more
slowly. In fact, if you lock enough memory, some programs may not be
able to run at all for lack of real memory.
@node Locked Memory Details
@subsection Locked Memory Details
A memory lock is associated with a virtual page, not a real frame. The
paging rule is: If a frame backs at least one locked page, don't page it
out.
Memory locks do not stack. I.e., you can't lock a particular page twice
so that it has to be unlocked twice before it is truly unlocked. It is
either locked or it isn't.
A memory lock persists until the process that owns the memory explicitly
unlocks it. (But process termination and exec cause the virtual memory
to cease to exist, which you might say means it isn't locked any more).
Memory locks are not inherited by child processes. (But note that on a
modern Unix system, immediately after a fork, the parent's and the
child's virtual address space are backed by the same real page frames,
so the child enjoys the parent's locks). @xref{Creating a Process}.
Because of its ability to impact other processes, only the superuser can
lock a page. Any process can unlock its own page.
The system sets limits on the amount of memory a process can have locked
and the amount of real memory it can have dedicated to it. @xref{Limits
on Resources}.
In Linux, locked pages aren't as locked as you might think.
Two virtual pages that are not shared memory can nonetheless be backed
by the same real frame. The kernel does this in the name of efficiency
when it knows both virtual pages contain identical data, and does it
even if one or both of the virtual pages are locked.
But when a process modifies one of those pages, the kernel must get it a
separate frame and fill it with the page's data. This is known as a
@dfn{copy-on-write page fault}. It takes a small amount of time and in
a pathological case, getting that frame may require I/O.
@cindex copy-on-write page fault
@cindex page fault, copy-on-write
To make sure this doesn't happen to your program, don't just lock the
pages. Write to them as well, unless you know you won't write to them
ever. And to make sure you have pre-allocated frames for your stack,
enter a scope that declares a C automatic variable larger than the
maximum stack size you will need, set it to something, then return from
its scope.
@node Page Lock Functions
@subsection Functions To Lock And Unlock Pages
The symbols in this section are declared in @file{sys/mman.h}. These
functions are defined by POSIX.1b, but their availability depends on
your kernel. If your kernel doesn't allow these functions, they exist
but always fail. They @emph{are} available with a Linux kernel.
@strong{Portability Note:} POSIX.1b requires that when the @code{mlock}
and @code{munlock} functions are available, the file @file{unistd.h}
define the macro @code{_POSIX_MEMLOCK_RANGE} and the file
@code{limits.h} define the macro @code{PAGESIZE} to be the size of a
memory page in bytes. It requires that when the @code{mlockall} and
@code{munlockall} functions are available, the @file{unistd.h} file
define the macro @code{_POSIX_MEMLOCK}. @Theglibc{} conforms to
this requirement.
@comment sys/mman.h
@comment POSIX.1b
@deftypefun int mlock (const void *@var{addr}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{mlock} locks a range of the calling process' virtual pages.
The range of memory starts at address @var{addr} and is @var{len} bytes
long. Actually, since you must lock whole pages, it is the range of
pages that include any part of the specified range.
When the function returns successfully, each of those pages is backed by
(connected to) a real frame (is resident) and is marked to stay that
way. This means the function may cause page-ins and have to wait for
them.
When the function fails, it does not affect the lock status of any
pages.
The return value is zero if the function succeeds. Otherwise, it is
@code{-1} and @code{errno} is set accordingly. @code{errno} values
specific to this function are:
@table @code
@item ENOMEM
@itemize @bullet
@item
At least some of the specified address range does not exist in the
calling process' virtual address space.
@item
The locking would cause the process to exceed its locked page limit.
@end itemize
@item EPERM
The calling process is not superuser.
@item EINVAL
@var{len} is not positive.
@item ENOSYS
The kernel does not provide @code{mlock} capability.
@end table
You can lock @emph{all} a process' memory with @code{mlockall}. You
unlock memory with @code{munlock} or @code{munlockall}.
To avoid all page faults in a C program, you have to use
@code{mlockall}, because some of the memory a program uses is hidden
from the C code, e.g. the stack and automatic variables, and you
wouldn't know what address to tell @code{mlock}.
@end deftypefun
@comment sys/mman.h
@comment POSIX.1b
@deftypefun int munlock (const void *@var{addr}, size_t @var{len})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{munlock} unlocks a range of the calling process' virtual pages.
@code{munlock} is the inverse of @code{mlock} and functions completely
analogously to @code{mlock}, except that there is no @code{EPERM}
failure.
@end deftypefun
@comment sys/mman.h
@comment POSIX.1b
@deftypefun int mlockall (int @var{flags})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{mlockall} locks all the pages in a process' virtual memory address
space, and/or any that are added to it in the future. This includes the
pages of the code, data and stack segment, as well as shared libraries,
user space kernel data, shared memory, and memory mapped files.
@var{flags} is a string of single bit flags represented by the following
macros. They tell @code{mlockall} which of its functions you want. All
other bits must be zero.
@table @code
@item MCL_CURRENT
Lock all pages which currently exist in the calling process' virtual
address space.
@item MCL_FUTURE
Set a mode such that any pages added to the process' virtual address
space in the future will be locked from birth. This mode does not
affect future address spaces owned by the same process so exec, which
replaces a process' address space, wipes out @code{MCL_FUTURE}.
@xref{Executing a File}.
@end table
When the function returns successfully, and you specified
@code{MCL_CURRENT}, all of the process' pages are backed by (connected
to) real frames (they are resident) and are marked to stay that way.
This means the function may cause page-ins and have to wait for them.
When the process is in @code{MCL_FUTURE} mode because it successfully
executed this function and specified @code{MCL_CURRENT}, any system call
by the process that requires space be added to its virtual address space
fails with @code{errno} = @code{ENOMEM} if locking the additional space
would cause the process to exceed its locked page limit. In the case
that the address space addition that can't be accommodated is stack
expansion, the stack expansion fails and the kernel sends a
@code{SIGSEGV} signal to the process.
When the function fails, it does not affect the lock status of any pages
or the future locking mode.
The return value is zero if the function succeeds. Otherwise, it is
@code{-1} and @code{errno} is set accordingly. @code{errno} values
specific to this function are:
@table @code
@item ENOMEM
@itemize @bullet
@item
At least some of the specified address range does not exist in the
calling process' virtual address space.
@item
The locking would cause the process to exceed its locked page limit.
@end itemize
@item EPERM
The calling process is not superuser.
@item EINVAL
Undefined bits in @var{flags} are not zero.
@item ENOSYS
The kernel does not provide @code{mlockall} capability.
@end table
You can lock just specific pages with @code{mlock}. You unlock pages
with @code{munlockall} and @code{munlock}.
@end deftypefun
@comment sys/mman.h
@comment POSIX.1b
@deftypefun int munlockall (void)
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{munlockall} unlocks every page in the calling process' virtual
address space and turn off @code{MCL_FUTURE} future locking mode.
The return value is zero if the function succeeds. Otherwise, it is
@code{-1} and @code{errno} is set accordingly. The only way this
function can fail is for generic reasons that all functions and system
calls can fail, so there are no specific @code{errno} values.
@end deftypefun
@ignore
@c This was never actually implemented. -zw
@node Relocating Allocator
@section Relocating Allocator
@cindex relocating memory allocator
Any system of dynamic memory allocation has overhead: the amount of
space it uses is more than the amount the program asks for. The
@dfn{relocating memory allocator} achieves very low overhead by moving
blocks in memory as necessary, on its own initiative.
@c @menu
@c * Relocator Concepts:: How to understand relocating allocation.
@c * Using Relocator:: Functions for relocating allocation.
@c @end menu
@node Relocator Concepts
@subsection Concepts of Relocating Allocation
@ifinfo
The @dfn{relocating memory allocator} achieves very low overhead by
moving blocks in memory as necessary, on its own initiative.
@end ifinfo
When you allocate a block with @code{malloc}, the address of the block
never changes unless you use @code{realloc} to change its size. Thus,
you can safely store the address in various places, temporarily or
permanently, as you like. This is not safe when you use the relocating
memory allocator, because any and all relocatable blocks can move
whenever you allocate memory in any fashion. Even calling @code{malloc}
or @code{realloc} can move the relocatable blocks.
@cindex handle
For each relocatable block, you must make a @dfn{handle}---a pointer
object in memory, designated to store the address of that block. The
relocating allocator knows where each block's handle is, and updates the
address stored there whenever it moves the block, so that the handle
always points to the block. Each time you access the contents of the
block, you should fetch its address anew from the handle.
To call any of the relocating allocator functions from a signal handler
is almost certainly incorrect, because the signal could happen at any
time and relocate all the blocks. The only way to make this safe is to
block the signal around any access to the contents of any relocatable
block---not a convenient mode of operation. @xref{Nonreentrancy}.
@node Using Relocator
@subsection Allocating and Freeing Relocatable Blocks
@pindex malloc.h
In the descriptions below, @var{handleptr} designates the address of the
handle. All the functions are declared in @file{malloc.h}; all are GNU
extensions.
@comment malloc.h
@comment GNU
@c @deftypefun {void *} r_alloc (void **@var{handleptr}, size_t @var{size})
This function allocates a relocatable block of size @var{size}. It
stores the block's address in @code{*@var{handleptr}} and returns
a non-null pointer to indicate success.
If @code{r_alloc} can't get the space needed, it stores a null pointer
in @code{*@var{handleptr}}, and returns a null pointer.
@end deftypefun
@comment malloc.h
@comment GNU
@c @deftypefun void r_alloc_free (void **@var{handleptr})
This function is the way to free a relocatable block. It frees the
block that @code{*@var{handleptr}} points to, and stores a null pointer
in @code{*@var{handleptr}} to show it doesn't point to an allocated
block any more.
@end deftypefun
@comment malloc.h
@comment GNU
@c @deftypefun {void *} r_re_alloc (void **@var{handleptr}, size_t @var{size})
The function @code{r_re_alloc} adjusts the size of the block that
@code{*@var{handleptr}} points to, making it @var{size} bytes long. It
stores the address of the resized block in @code{*@var{handleptr}} and
returns a non-null pointer to indicate success.
If enough memory is not available, this function returns a null pointer
and does not modify @code{*@var{handleptr}}.
@end deftypefun
@end ignore
@ignore
@comment No longer available...
@comment @node Memory Warnings
@comment @section Memory Usage Warnings
@comment @cindex memory usage warnings
@comment @cindex warnings of memory almost full
@pindex malloc.c
You can ask for warnings as the program approaches running out of memory
space, by calling @code{memory_warnings}. This tells @code{malloc} to
check memory usage every time it asks for more memory from the operating
system. This is a GNU extension declared in @file{malloc.h}.
@comment malloc.h
@comment GNU
@comment @deftypefun void memory_warnings (void *@var{start}, void (*@var{warn-func}) (const char *))
Call this function to request warnings for nearing exhaustion of virtual
memory.
The argument @var{start} says where data space begins, in memory. The
allocator compares this against the last address used and against the
limit of data space, to determine the fraction of available memory in
use. If you supply zero for @var{start}, then a default value is used
which is right in most circumstances.
For @var{warn-func}, supply a function that @code{malloc} can call to
warn you. It is called with a string (a warning message) as argument.
Normally it ought to display the string for the user to read.
@end deftypefun
The warnings come when memory becomes 75% full, when it becomes 85%
full, and when it becomes 95% full. Above 95% you get another warning
each time memory usage increases.
@end ignore
glibc-doc-reference-2.19.orig/manual/libc.texinfo 0000664 0001750 0001750 00000010160 12275120646 022064 0 ustar adconrad adconrad \input texinfo @c -*- Texinfo -*-
@comment %**start of header (This is for running Texinfo on a region.)
@setfilename libc.info
@settitle The GNU C Library
@c setchapternewpage odd
@include macros.texi
@comment Tell install-info what to do.
@dircategory Software libraries
@direntry
* Libc: (libc). C library.
@end direntry
@include dir-add.texi
@include pkgvers.texi
@c This tells texinfo.tex to use the real section titles in xrefs in
@c place of the node name, when no section title is explicitly given.
@set xref-automatic-section-title
@c @smallbook
@comment %**end of header (This is for running Texinfo on a region.)
@c Everything related to printed editions is disabled until we have
@c resolved how to keep them in sync with the master sources of the
@c manual.
@c sold 0.06/1.09, print run out 21may96
@c @set EDITION 0.13
@c @set ISBN 1-882114-55-8
@include version.texi
@set FDL_VERSION 1.3
@copying
This file documents @theglibc{}.
This is
@c Disabled (printed editions, see above).
@c Edition @value{EDITION} of
@cite{The GNU C Library Reference Manual}, for version
@ifset PKGVERSION_DEFAULT
@value{VERSION}.
@end ifset
@ifclear PKGVERSION_DEFAULT
@value{VERSION} @value{PKGVERSION}.
@end ifclear
Copyright @copyright{} 1993--2014 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version
@value{FDL_VERSION} or any later version published by the Free
Software Foundation; with the Invariant Sections being ``Free Software
Needs Free Documentation'' and ``GNU Lesser General Public License'',
the Front-Cover texts being ``A GNU Manual'', and with the Back-Cover
Texts as in (a) below. A copy of the license is included in the
section entitled "GNU Free Documentation License".
(a) The FSF's Back-Cover Text is: ``You have the freedom to
copy and modify this GNU manual. Buying copies from the FSF
supports it in developing GNU and promoting software freedom.''
@end copying
@iftex
@shorttitlepage The GNU C Library Reference Manual
@end iftex
@titlepage
@center @titlefont{The GNU C Library}
@sp 1
@center @titlefont{Reference Manual}
@sp 2
@center Sandra Loosemore
@center with
@center Richard M. Stallman, Roland McGrath, Andrew Oram, and Ulrich Drepper
@sp 3
@c Disabled (printed editions, see above).
@c @center Edition @value{EDITION}
@c @sp 1
@center for version @value{VERSION}
@ifclear PKGVERSION_DEFAULT
@sp 1
@center @value{PKGVERSION}
@end ifclear
@page
@vskip 0pt plus 1filll
@insertcopying
@c Disabled (printed editions, see above).
@c @sp 2
@c Published by the @uref{http://www.fsf.org/, Free Software Foundation} @*
@c ISBN @value{ISBN} @*
@c Disabled (printed editions, see above).
@c @sp 2
@c Cover art for the Free Software Foundation's printed edition
@c by Etienne Suvasa.
@end titlepage
@shortcontents
@contents
@ifnottex
@node Top, Introduction, (dir), (dir)
@top Main Menu
This is
@c Disabled (printed editions, see above).
@c Edition @value{EDITION} of
@cite{The GNU C Library Reference Manual}, for Version @value{VERSION}
@ifclear PKGVERSION_DEFAULT
@value{PKGVERSION}
@end ifclear
of @theglibc{}.
@end ifnottex
@include top-menu.texi
@include chapters.texi
@node Free Manuals, Copying, Contributors, Top
@appendix Free Software Needs Free Documentation
@include freemanuals.texi
@node Copying, Documentation License, Free Manuals, Top
@appendix GNU Lesser General Public License
@include lgpl-2.1.texi
@node Documentation License, Concept Index, Copying, Top
@appendix GNU Free Documentation License
@cindex FDL, GNU Free Documentation License
@include fdl-@value{FDL_VERSION}.texi
@node Concept Index, Type Index, Documentation License, Top
@unnumbered Concept Index
@printindex cp
@node Type Index, Function Index, Concept Index, Top
@unnumbered Type Index
@printindex tp
@node Function Index, Variable Index, Type Index, Top
@unnumbered Function and Macro Index
@printindex fn
@node Variable Index, File Index, Function Index, Top
@unnumbered Variable and Constant Macro Index
@printindex vr
@node File Index, , Variable Index, Top
@unnumbered Program and File Index
@printindex pg
@bye
glibc-doc-reference-2.19.orig/manual/install-plain.texi 0000664 0001750 0001750 00000000267 12275120646 023226 0 ustar adconrad adconrad @c This is for making the `INSTALL' file for the distribution.
@c Makeinfo ignores it when processing the file from the include.
@setfilename INSTALL
@set plain
@include install.texi