CODEWITHSUNDEEP
cfork
haunted85
haunted85

Reputation: 1671

After forking parent never executes

I'm trying to get acquainted with pipes and I have written a pretty stupid parrot program that basically takes in the input from the keyboard and then displays the exact same thing: 

if (pipe(fd) < 0) {
        perror("Pipe");
        exit(1);
    }

    if ( ( pid = fork() < 0 ) ) {
        perror("Fork");
        exit(1);
    }

    if ( pid > 0 ) //If I'm the parent...
    {
        printf("Parent!");
        close(fd[0]);
        //as long as something is typed in and that something isn't 
        // the word "stop"
        while (((n = read(STDIN_FILENO, buffer, BUFFERSIZE)) > 0) && 
               (strncmp(buffer, "stop", 4) != 0))
        {
            //shove all the buffer content into the pipe
            write(fd[1], buffer, BUFFERSIZE);
        }
    }
    else //If I am the child...
    {
        printf("Child!");
        close(fd[1]);

        //as long as there's something to read
        while (pipe_read = read(fd[0], buf, sizeof(buf)) > 0)
        {
            //display on the screen!
            write(STDOUT_FILENO, buf, pipe_read);
        }
    }

I get why this program doesn't get engaged in the loop, that is because the parent never executes and as a result I get Child! Child! as output and I can't figure out why.

Upvotes: 1

Views: 75

Answers (1)

blue
blue

Reputation: 2793

Change

if ( ( pid = fork() < 0 ) )

with

if ( (pid = fork()) < 0 )

Without the right parentheses pid was being set to (fork() < 0), which was 0.

Upvotes: 7

Related Questions