shm.h

/*
  this is the pathname of the server executable 
  remember to change it when the executable is moved to
  other directory
*/
#define PATHNAME "/home/valletta/provecpp/shm/shmServer"
#define PROJECT 1

struct shared {
	char data[256];
};

shmServer.c

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

#include "shm.h"

struct shared *s = (void *)-1;
int shm_id = -1;

void server_exit(int ret);

int main()
{
	key_t k;
	
	if ( (k = ftok(PATHNAME,PROJECT)) == -1) {
		perror("ftok");
		server_exit(5);
	}
	shm_id = shmget( k , sizeof(struct shared), IPC_CREAT | IPC_EXCL | 0777);
	if (shm_id == -1) {
		perror("shmget");
		server_exit(5);
	}
	printf("Shared memory id %d\n",shm_id);
	if ( (s = shmat(shm_id, NULL , 0)) == (void *)-1) {
		perror("shmat");
		server_exit(5);
	}
	printf("Shared memory attached at %p\n",s);

	sprintf(s->data,"Message from Server");
	printf("Message put into shared memory\n");

	server_exit(0);
}

void server_exit(int ret)
{
	exit(ret); /* exit automatically detach any shm segment attached */
	/* but we don't destroy it: we leave it for the client */
}

shmClient.c

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

#include "shm.h"

struct shared *s = (void *)-1;
int shm_id = -1;

void client_exit(int ret);

int main()
{
	key_t k;
	
	if ( (k = ftok(PATHNAME,PROJECT)) == -1) {
		perror("ftok");
		client_exit(5);
	}
	if ((shm_id = shmget( k , sizeof(struct shared), 0777)) == -1) {
		perror("shmget");
		client_exit(5);
	}
	printf("Shared memory id %d\n",shm_id);
	if ( (s = shmat(shm_id, NULL , 0)) == (void *)-1) {
		perror("shmat");
		client_exit(5);
	}
	printf("Shared memory attached at %p\n",s);

	printf("s->data == %s\n",s->data);

	client_exit(0);
}

void client_exit(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);
}

-- AntonioValletta - 10 Dec 2001