fig15.31

Unix Advanced Programming Source Code Unix1-7

#include "apue.h"
#include <sys/shm.h>

#define	ARRAY_SIZE	40000
#define	MALLOC_SIZE	100000
#define	SHM_SIZE	100000
#define	SHM_MODE	0600	/* user read/write */

char	array[ARRAY_SIZE];	/* uninitialized data = bss */

int
main(void)
{
	int		shmid;
	char	*ptr, *shmptr;

	printf("array[] from %lx to %lx\n", (unsigned long)&array[0],
	  (unsigned long)&array[ARRAY_SIZE]);
	printf("stack around %lx\n", (unsigned long)&shmid);

	if ((ptr = malloc(MALLOC_SIZE)) == NULL)
		err_sys("malloc error");
	printf("malloced from %lx to %lx\n", (unsigned long)ptr,
	  (unsigned long)ptr+MALLOC_SIZE);

	if ((shmid = shmget(IPC_PRIVATE, SHM_SIZE, SHM_MODE)) < 0)
		err_sys("shmget error");
	if ((shmptr = shmat(shmid, 0, 0)) == (void *)-1)
		err_sys("shmat error");
	printf("shared memory attached from %lx to %lx\n",
	  (unsigned long)shmptr, (unsigned long)shmptr+SHM_SIZE);

	if (shmctl(shmid, IPC_RMID, 0) < 0)
		err_sys("shmctl error");

	exit(0);
}