Linux Application Development

Michael K. Johnson Erik W. Troan

mpx-blocks.c

/* mpx-blocks.c -- reads input from pipes p1, p2 alternately */

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

int main(void) {
    int fds[2];
    char buf[4096];
    int i;
    int fd;

    if ((fds[0] = open("p1", O_RDONLY)) < 0) {
        perror("open p1");
        return 1;
    }

    if ((fds[1] = open("p2", O_RDONLY)) < 0) {
        perror("open p2");
        return 1;
    }

    fd = 0;
    while (1) {
	/* if data is available read it and display it */
        i = read(fds[fd], buf, sizeof(buf) - 1);
        if (i < 0) {
            perror("read");
            return 1;
        } else if (!i) {
            printf("pipe closed\n");
            return 0;
        } 

        buf[i] = '\0';
        printf("read: %s", buf);

	/* read from the other file descriptor */
        fd = (fd + 1) % 2;
    }
}