#include <unistd.h>		// Defines fork system call
#include <stdlib.h>		// Defines exit system call
#include <stdio.h>		// Defines prinf and sprintf
#include <sys/shm.h>	// Defines the shared memory API
#include <sys/stat.h> 	// Defines the flags IR_USR and IW_USR
#include <sys/wait.h> 	// Defines the wait system call


int main() {
	int segment_id;
	char *parent_shared_memory;
	const int size=4096;
	pid_t child;

	// Create the shared memory segment of size size bytes for Read/Write
	segment_id = shmget(IPC_PRIVATE, size, S_IRUSR | S_IWUSR);

	// Attach the shared memory segment to this process
	parent_shared_memory = shmat(segment_id, NULL, 0);

	// Write a message to shared memory
	sprintf(parent_shared_memory, "%s", "Hello there!");

	child = fork();
	if (child < 0) {
		fprintf(stderr, "Error forking child process: %d\n", child);
		exit(1);
	}
	else if (child == 0) {
		// Attach the shared memory segment to this process
		char *child_shared_memory = shmat(segment_id, NULL, 0);

		// Read the message and write to the terminal
		printf("*%s", child_shared_memory);

		// Detach shared memory
		shmdt(child_shared_memory);
	}
	else {
		wait(NULL);
	
		// Detach shared memory
		shmdt(parent_shared_memory);

		// Release the shared memory segment
		shmctl(segment_id, IPC_RMID, NULL);
	}

	return(0);
}