16.c

/*
============================================================================
Name : 16
Author : Piyush Singh
Description : Write a program to send and receive data from parent to child vice versa. Use two way
communication.
Date: 19th Sep, 2025.
============================================================================
*/


#include <stdio.h>      // For printf(), perror()
#include <stdlib.h>     // For exit()
#include <unistd.h>     // For pipe(), fork(), read(), write()
#include <string.h>     // For strlen()
#include <sys/wait.h>   // For wait()

int main() 
{
    int pipe_parent_to_child[2]; // Pipe 1: parent writes, child reads
    int pipe_child_to_parent[2]; // Pipe 2: child writes, parent reads
    pid_t pid;

    char parent_msg[] = "👨‍👦 Hi child, how are you?";
    char child_msg[]  = "👶 I'm good, thanks for asking!";
    char buffer[100];

    // Step 1: Create both pipes
    if (pipe(pipe_parent_to_child) == -1 || pipe(pipe_child_to_parent) == -1) 
    {
        perror("❌ Failed to create pipes");
        exit(1);
    }

    // Step 2: Fork the process
    pid = fork();

    if (pid < 0) 
    {
        perror("❌ Fork failed");
        exit(1);
    }

    if (pid == 0) 
    {
        // 👶 Child process

        // Close unused ends
        close(pipe_parent_to_child[1]); // Child doesn't write to parent pipe
        close(pipe_child_to_parent[0]); // Child doesn't read from its own pipe

        // Step 3a: Read message from parent
        ssize_t bytes_read = read(pipe_parent_to_child[0], buffer, sizeof(buffer));
        if (bytes_read < 0) 
        {
            perror("❌ Child failed to read");
            exit(1);
        }
        buffer[bytes_read] = '\0'; // Null-terminate
        printf("👶 Child received: %s\n", buffer);

        // Step 3b: Send reply to parent
        ssize_t bytes_written = write(pipe_child_to_parent[1], child_msg, strlen(child_msg));
        if (bytes_written < 0) 
        {
            perror("❌ Child failed to write");
            exit(1);
        }

        // Close used ends
        close(pipe_parent_to_child[0]);
        close(pipe_child_to_parent[1]);
    } 
    else 
    {
        // 👨‍👦 Parent process

        // Close unused ends
        close(pipe_parent_to_child[0]); // Parent doesn't read from its own pipe
        close(pipe_child_to_parent[1]); // Parent doesn't write to child pipe

        // Step 4a: Send message to child
        ssize_t bytes_written = write(pipe_parent_to_child[1], parent_msg, strlen(parent_msg));
        if (bytes_written < 0) 
        {
            perror("❌ Parent failed to write");
            exit(1);
        }

        // Step 4b: Read reply from child
        ssize_t bytes_read = read(pipe_child_to_parent[0], buffer, sizeof(buffer));
        if (bytes_read < 0) 
        {
            perror("❌ Parent failed to read");
            exit(1);
        }
        buffer[bytes_read] = '\0'; // Null-terminate
        printf("👨‍👦 Parent received: %s\n", buffer);

        // Close used ends
        close(pipe_parent_to_child[1]);
        close(pipe_child_to_parent[0]);

        // Wait for child to finish
        wait(NULL);
        printf("✅ Parent: Child has exited. Communication complete.\n");
    }

    return 0;
}

/*
Output:
╰─ ./16                                                                       ─╯
👶 Child received: 👨‍👦 Hi child, how are you?
👨‍👦 Parent received: 👶 I'm good, thanks for asking!
✅ Parent: Child has exited. Communication complete.
*/