Pipes between processes in C

A pipe is a pair of descriptors: the child writes, the parent reads.

#include <stdio.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

int main(void) {
    int fds[2];
    if (pipe(fds) != 0) {
        perror("pipe");
        return 1;
    }

    pid_t pid = fork();
    if (pid == 0) {
        close(fds[0]);
        const char *message = "from the child\n";
        write(fds[1], message, strlen(message));
        close(fds[1]);
        _exit(0);
    }

    close(fds[1]);
    char buffer[64];
    ssize_t n = read(fds[0], buffer, sizeof buffer - 1);
    if (n > 0) {
        buffer[n] = '\0';
        printf("parent read: %s", buffer);
    }
    close(fds[0]);
    wait(NULL);
    return 0;
}

How it works

1. Each side closes the end it does not use.
2. The reader sees end of file once every writer has closed.
3. Forgetting to close is the classic reason a read hangs.

Keywords and builtins used here

• NULL
• char
• const
• if
• int
• main
• pid_t
• return
• sizeof
• ssize_t
• void

The run, in numbers

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32

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515

Tokens

183

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 105 seconds.

Type this snippet

Step 3 of 4 in Processes & signals, step 9 of 14 in Systems programming.

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