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

void myexit(int ret);

struct shared {
	char data[256];
};
struct shared *s = (void *)-1;
int shm_id = -1;


int main()
{
	pid_t pid;

	if ((shm_id = shmget(IPC_PRIVATE, sizeof(struct shared), 0777)) == -1) {
		perror("shmget");
		myexit(5);
	}
	printf("Shared memory id %d\n",shm_id);
	if ( (s = shmat(shm_id, NULL , 0)) == (void *)-1) {
		perror("shmat");
		myexit(5);
	}
	printf("Shared memory attached at %p\n",s);
	if ( (pid = fork()) == -1 ) {
		perror("fork");
		myexit(5);
	}
	if (pid == 0) { /* child -> process 0 */
		sprintf(s->data,"Message from child");
		printf("Child: Message sent\n");
		myexit(0);
	} else { /* parent */
		sleep(1);
		printf("Parent: s->data == %s\n",s->data);
		myexit(0);
	}
}

void myexit(int ret)
{
	struct shmid_ds shds;

	/* detach shared memory (exit() do this automatically) */
	if (s != (void *)-1) shmdt(s);
	/* mark shared memory segment as destroyed */
	if (shm_id != -1) { shmctl(shm_id,IPC_RMID,&shds); }

	exit(ret);
}