C共享記憶體讀寫結構體中的内容

myshm.h

#ifndef __MYSHM_H__
#define __MYSHM_H__

#define N 			(1)
#define PAGESIZE    (4096)

struct mydata{
	int a;
	int b;
};

#endif


           

shm_write.c

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <errno.h>
#include "myshm.h"

int main(int argc, char const *argv[])
{
	int shmid;
	struct mydata *p;

	struct mydata data[3] = {
		[0] = {
			.a = 1,
			.b = 2,
		},
		[1] = {
			.a = 3,
			.b = 4,
		},
		[2] = {
			.a = 5,
			.b = 6,
		},
	};

	key_t keyval = ftok("/",'A');
	
	shmid = shmget(keyval,N*PAGESIZE,IPC_CREAT | IPC_EXCL | 0777);
	if(shmid < 0)
	{
		if(errno == EEXIST)
		{
			shmid = shmget(keyval,0,0);
		}
		else
		{
			perror("shmget");
			return -1;
		}
	}

	p = shmat(shmid, NULL, 0);
	if(p == (struct mydata*)(-1))
	{
		perror("shmat");
		return -2;
	}
#if 0
	strcpy(p, "hello world");
#else
	printf("sizeof(data)=%lu\n", sizeof(data));
	memcpy(p, data, sizeof(data));  
#endif

	shmdt(p);
	
	return 0;
}


           

shm_read.c

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include "myshm.h"

int main(int argc, char const *argv[])
{
	int shmid = 0;
	int i;
	struct mydata *p;

	key_t keyval = ftok("/",'A');
	
	shmid = shmget(keyval, N*PAGESIZE, IPC_CREAT|IPC_EXCL|0777);
	if(shmid < 0)
	{
		if(errno == EEXIST)
		{
			shmid = shmget(keyval,0,0);
		}
		else
		{
			perror("shmget");
			return -1;
		}
	}

	p = shmat(shmid, NULL, 0);
	if(p == (struct mydata *)(-1))
	{
		perror("shmat");
		return -2;
	}
	
#if 0	
	printf("share memry :%s\n", p);
#else
	for(i=0; i<3;++i)
		printf("share mem :p[%d]=%d,p[%d]=%d\n", i, p[i].a, i, p[i].b);

#endif
	shmdt(p);

	return 0;
}

           

測試結果