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

int input_timeout (int filedes, unsigned int seconds)
    {
    fd_set set;
    struct timeval timeout;

    // Initialize the file descriptor set.
    FD_ZERO (&set);                  // clears a file descriptor set
    FD_SET (filedes, &set);          // adds fd to the set
    // FD_CLR(int fd, fd_set *set)   // removes fd from the set
    // FD_ISSET(int fd, fd_set *set) // tests to see if fd is in the set

    // Initialize the timeout data structure.
    timeout.tv_sec = seconds;  // seconds
    timeout.tv_usec = 0;       // microseconds

    // select returns 0 if timeout, 1 if input available, -1 if error.
    return TEMP_FAILURE_RETRY (select (FD_SETSIZE,
                                       &set, NULL, NULL,
                                       &timeout));
    }

int main (void)
    {
    fprintf (stderr, "select returned %d.\n",
             input_timeout (STDIN_FILENO, 5));
    return 0;
    }