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// gcc main.c -lrt -Wall
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mqueue.h>
#include <unistd.h>


const char MQ_NAME[] = "/somename";     // Muss mit / beginnen, siehe https://man7.org/linux/man-pages/man7/mq_overview.7.html
const long MQ_MAX_MESSAGES = 10;
const long MQ_MAX_MESSAGE_SIZE = 64;


int child_stuff(const unsigned int id)
{
    printf("[%u] Started child\n", id);

    mqd_t mq = mq_open(MQ_NAME, O_RDONLY);
    if (mq == -1)
    {
        fprintf(stderr, "[%u] Error opening message queue: %s\n", id, strerror(errno));
        return 1;
    }

    printf("[%u] Ready to receive\n", id);
    char buffer[MQ_MAX_MESSAGE_SIZE];
    while(1)
    {
        ssize_t bytes_received = mq_receive(mq, buffer, MQ_MAX_MESSAGE_SIZE, NULL);
        if (bytes_received == -1)
        {
            fprintf(stderr, "[%u] Error receiving message: %s\n", id, strerror(errno));
            return 1;
        }

        printf("[%u] %s\n", id, buffer);
    }

    return 0;
}


int parent_stuff()
{
    char buffer[MQ_MAX_MESSAGE_SIZE];

    struct mq_attr attr;
    attr.mq_flags = 0;
    attr.mq_maxmsg = MQ_MAX_MESSAGES;
    attr.mq_msgsize = MQ_MAX_MESSAGE_SIZE;
    attr.mq_curmsgs = 0;

    mqd_t mq = mq_open(MQ_NAME, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR, &attr);
    if (mq == -1)
    {
        fprintf(stderr, "Error creating message queue: %s\n", strerror(errno));
        return 1;
    }

    while(1)
    {
        printf("Enter message:\n");
        fgets(buffer, MQ_MAX_MESSAGE_SIZE, stdin);
        buffer[strlen(buffer) - 1] = '\0';

        printf("Sending message %s\n", buffer);
        int bytes_sent = mq_send(mq, buffer, MQ_MAX_MESSAGE_SIZE, 0);
        if (bytes_sent == -1)
        {
            fprintf(stderr, "Error sending message: %s\n", strerror(errno));
            return 1;
        }
    }
}


int main()
{
    const unsigned int NUM_CHILDREN = 2;
    for (unsigned int i = 0; i < NUM_CHILDREN; i++)
    {
        pid_t child_pid = fork();
        if (child_pid == 0)
            return child_stuff(i + 1);
        else
            continue;
    }
    return parent_stuff();
}