//server

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/msg.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <errno.h>

#include <unistd.h>

#define ERR_EXIT(m) \

	do \

	{ \

		perror(m); \

	} \

	while(0);

struct msgbuf {

   long mtype;       /* message type, must be > 0 */

   char mtext[1024];    /* message data */

};

int main()

{

	struct msgbuf revbuf;

	int key 	= 0;

	int msgid   = 0;

	int ret 	= 0;

	int pid		= 0;

	key = ftok("./", '2');

	if (key < 0)

		ERR_EXIT("ftok");

	//获取消息队列

	ret = msgget(key, 0666 | IPC_CREAT | IPC_EXCL);

	if (ret < 0)

	{

		if (errno == EEXIST) //如果消息队列已存在

			msgid = msgget(key, 0666);

		else

			ERR_EXIT("msgget:");

	}

	else

		msgid = ret;

	//设置发送buf

	memset(&revbuf, 0, sizeof(revbuf));

	revbuf.mtype = 1; //接收方总是接收类型1

	while (1)

	{

		ret = msgrcv(msgid, &revbuf, sizeof(revbuf.mtext), 1, 0);

		if (ret < 0)

			ERR_EXIT("msgrcv:");

		fputs(revbuf.mtext + 4, stdout);

		pid = *((int *)(revbuf.mtext));

		revbuf.mtype = pid;

		ret = msgsnd(msgid, &revbuf, ret, IPC_NOWAIT);

		if (ret < 0)

			ERR_EXIT("msgsnd");

	}

	return 0;

}

//clt

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/msg.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <errno.h>

#include <unistd.h>

#define ERR_EXIT(m) \

	do \

	{ \

		perror(m); \

	} \

	while(0);

struct msgbuf {

   long mtype;       /* message type, must be > 0 */

   char mtext[1024];    /* message data */

};

int main()

{

	struct msgbuf sndbuf;

	struct msgbuf revbuf;

	int key 	= 0;

	int msgid   = 0;

	int ret 	= 0;

	int pid		= 0;

	key = ftok("./", '2');

	if (key < 0)

		ERR_EXIT("ftok");

	//获取消息队列

	ret = msgget(key, 0666 | IPC_CREAT | IPC_EXCL);

	if (ret < 0)

	{

		if (errno == EEXIST) //如果消息队列已存在

			msgid = msgget(key, 0666);

		else

			ERR_EXIT("msgget:");

	}

	else

		msgid = ret;

	//设置发送buf

	memset(&sndbuf, 0, sizeof(sndbuf));

	memset(&revbuf, 0, sizeof(revbuf));

	pid = getpid(); //获取pid作为包头发出去

	while (fgets(sndbuf.mtext + 4, sizeof(sndbuf.mtext), stdin) != NULL)

	{

		sndbuf.mtype = 1; //发送方总是发送类型1

		memcpy(sndbuf.mtext, &pid, 4);

		//*((int*)sndbuf.mtext) = pid; //这句话是指将sndbuf.mtext最前面四个字节指向一个int类型指针

		ret = msgsnd(msgid, &sndbuf, strlen(sndbuf.mtext + 4) + 4, IPC_NOWAIT);

		if (ret < 0)

			ERR_EXIT("msgsnd");

		sleep(1);

		//读取

		ret = msgrcv(msgid, &revbuf, sizeof(revbuf.mtext), pid, IPC_NOWAIT);

		if (ret < 0)

			ERR_EXIT("msgrcv:");

		fputs(revbuf.mtext + 4, stdout);

		memset(&sndbuf, 0, sizeof(sndbuf));

		memset(&revbuf, 0, sizeof(revbuf));

	}

	return 0;

}