select.c

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>

int max(int a, int b) {
    return a > b ? a : b;
}

int main()
{
    int fd1, fd2;
    fd_set readfs;
    struct timeval tv;
    int maxfd, result;
    char buf[BUFSIZ];

    fd1 = fileno(stdin);
    fd2 = fileno(stdin); // socket(...);
    maxfd = max (fd1, fd2) + 1;
    tv.tv_sec = 5;
    tv.tv_usec = 0;

    /* loop for input */
    while (1) {
        FD_ZERO(&readfs);
        FD_SET(fd1, &readfs);
        FD_SET(fd2, &readfs);

        /* block until input becomes available */
        result = select(maxfd, &readfs, NULL, NULL, &tv);

        switch(result)
        {
            case -1:
                perror("select()");
                break;
            case 0:
                printf("Timeout\n");
                break;
            default:
                if (FD_ISSET(fd1, &readfs))
                {
                    read(fd1, buf, sizeof(buf));
                    printf("%s", buf);
                }

                if (FD_ISSET(fd2, &readfs))
                {
                    read(fd2, buf, sizeof(buf));
                    printf("%s", buf);
                }
                break;
        }
    }
}