glibc/manual/examples/select.c

/* Waiting for Input or Output
   Copyright (C) 1991-2019 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, see <http://www.gnu.org/licenses/>.
*/

/*@group*/
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>
/*@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*/