manual/examples/select.c

   1 /* Waiting for Input or Output
   2    Copyright (C) 1991-2015 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU General Public License
   6    as published by the Free Software Foundation; either version 2
   7    of the License, or (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, if not, see <http://www.gnu.org/licenses/>.
  16 */
  17
  18 /*@group*/
  19 #include <errno.h>
  20 #include <stdio.h>
  21 #include <unistd.h>
  22 #include <sys/types.h>
  23 #include <sys/time.h>
  24 /*@end group*/
  25
  26 /*@group*/
  27 int
  28 input_timeout (int filedes, unsigned int seconds)
  29 {
  30   fd_set set;
  31   struct timeval timeout;
  32 /*@end group*/
  33
  34   /* Initialize the file descriptor set. */
  35   FD_ZERO (&set);
  36   FD_SET (filedes, &set);
  37
  38   /* Initialize the timeout data structure. */
  39   timeout.tv_sec = seconds;
  40   timeout.tv_usec = 0;
  41
  42 /*@group*/
  43   /* @code{select} returns 0 if timeout, 1 if input available, -1 if error. */
  44   return TEMP_FAILURE_RETRY (select (FD_SETSIZE,
  45                                      &set, NULL, NULL,
  46                                      &timeout));
  47 }
  48 /*@end group*/
  49
  50 /*@group*/
  51 int
  52 main (void)
  53 {
  54   fprintf (stderr, "select returned %d.\n",
  55            input_timeout (STDIN_FILENO, 5));
  56   return 0;
  57 }
  58 /*@end group*/