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

       int
       main(void)
       {
           fd_set rfds;
           struct timeval tv;
           int retval;

           /* Watch stdin (fd 0) to see when it has input. */
           FD_ZERO(&rfds);
           FD_SET(0, &rfds);

           /* Wait up to five seconds. */
           tv.tv_sec = 5;
           tv.tv_usec = 0;

           retval = select(1, &rfds, NULL, NULL, &tv);
           /* Don't rely on the value of tv now! */

           if (retval == -1)
               perror("select()");
           else if (retval)
               printf("Data is available now.\n");
               /* FD_ISSET(0, &rfds) will be true. */
           else
               printf("No data within five seconds.\n");

           exit(EXIT_SUCCESS);
       }

bogon:/home/jackxiang/com/com118 # ./a.out
dir
Data is available now.
bogon:/home/jackxiang/com/com118 # dir
total 24
-rwxr-xr-x 1 root root 7534 Aug 28 13:42 a.out
-rw-r--r-- 1 root root 4980 Aug 28 13:30 com118.c
-rw-r--r-- 1 root root 4056 Aug 27 23:05 com118.c.bak.jackxiang
-rw-r--r-- 1 root root  890 Aug 28 13:42 selectexample.cpp