// man ftruncate

// pass any message between two processes using shared memory

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>

int main(int argc, char *argv[]) {

    const char *memory_name = "/memory";
    char message[] = "Hello there";

    int fd = shm_open(memory_name, O_CREAT | O_RDWR, 0777);
    if (fd < 0) {
        fprintf(stderr, "shm_open: ");
        exit(EXIT_FAILURE);
    }
    printf("Shred memory file descriptor: %d\n", fd);

    if (ftruncate(fd, sizeof(message)) < 0) {
        fprintf(stderr, "ftruncate: \n");
        exit(EXIT_FAILURE);
    }


    pid_t pid;

    pid = fork();
    if (pid == -1) {
        perror("fork: ");
        exit(EXIT_FAILURE);
    }
    if (pid == 0) {
        char *addr = mmap(NULL, sizeof(message), PROT_READ, MAP_SHARED, fd, 0);
        printf("Value: %s\n", addr);
        if (addr == MAP_FAILED) {
            fprintf(stderr, "mmap: ");
            exit(EXIT_FAILURE);
        }
        exit(EXIT_SUCCESS);
    }

    char *addr = mmap(NULL, sizeof(message), PROT_WRITE, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED) {
        fprintf(stderr, "mmap: ");
        exit(EXIT_FAILURE);
    }
    strcpy(addr, message);

    shm_unlink(memory_name);

    int status;
    wait(&status);

    munmap(addr, sizeof(message));

    return 0;
}