#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/shm.h>

int main() {
    int shmid, *shm;

    shmid = shmget(IPC_PRIVATE, 4, IPC_CREAT | 0600);

    if (shmid == -1) {
        printf("Cannot create shared memory!\n");
        exit(1);
    } else {
        printf("Shared memory ID = %d\n", shmid);
    }
    shm = (int*) shmat(shmid, NULL, 0);
    if (shm == (int*) -1) {
        printf("Cannot attach shared memory!\n");
        exit(1);
    }
    shm[0] = 0;
    while(shm[0] == 0) {
        sleep(3);
    }
    for(int i = 0; i < 3; i++) {
        printf("Read %d from shared memory. \n", shm[i+1]);
    }
    shmdt((char*) shm);
    shmctl(shmid, IPC_RMID, 0);
}