Here is an example to get started:

    1   
    2   int main(int argc, char * argv[]) {
    3     fd_set rfds;
    4     struct timeval tv;
    5     int seconds = 5;
    6     int retval;
    7     const int MAXBUF = 120;
    8     char buf[MAXBUF];
    9     char magic[] = "select";
   10   
   11   
   12     /* Get timeout seconds */
   13     if ( argc > 1 ) {
   14       seconds = atoi(argv[1]);
   15       if ( seconds == 0 ) {
   16         seconds = 5;
   17       }
   18     }
   19     /* Watch stdin (fd 0) to see when it has input. */
   20     FD_ZERO(&rfds);
   21     FD_SET(0, &rfds);
   22   
   23     /* Wait up to ? seconds. */
   24     tv.tv_sec = seconds;
   25     tv.tv_usec = 0;
   26   
   27     setbuf(stdout, NULL);
   28     printf("You have %d seconds to enter the magic word.\n", seconds);
   29     printf("> ");
   30     retval = select(1, &rfds, NULL, NULL, &tv);
   31     /* Donb
   32   t rely on the value of tv now! */
   33   
   34   
   35     if (retval == -1)
   36       perror("select()");
   37     else if (retval) {
   38       fgets(buf, MAXBUF, stdin);
   39       buf[strlen(buf) - 1] = 0;
   40       if (!strcmp(buf, magic)) {
   41         printf("Correct!\n");
   42       } else {
   43         printf("Sorry, '%s' is not the magic word.\n", buf);
   44       }
   45     }
   46   
   47     /* FD_ISSET(0, &rfds) will be true. */
   48     else {
   49       printf("\nSorry, %d seconds expired with no guess entered.\n",
   50     seconds);
   51     }
   52   
   53     return 0;
   54   }