消息队列创建流程及代码示例

消息队列是消息的链接表，存放在内核中并由消息队列标示符标识。

1. 创建或打开一个队列

    int msgget(key_t key, int flag);

    key: 键 由ftok()生成

        key_t ftok(const char* path, int id);

    flag: IPC_CREAT 或 IPC_EXCL 

2. 发送消息

    int msgsnd(int msgid, const void* ptr, size_t nbyte, int flag);

    msgid: 消息队列标识

    ptr: 发送的消息，一般格式为：

        struct _msg{

            long mtype;

            char _msg[512];

            . . . 

        };

    nbyte:消息大小，一般为sizeof(struct _msg)-sizeof(long)

    flag: 0                     默认阻塞方式

            IPC_NOWAIT  非阻塞

3. 接收消息

    int msgrcv(int msgid, void* ptr, size_t nbyte, long mtype, int flag);

msgQueue.h

#ifndef _MSGQUEUE_H_

#define _MSGQUEUE_H_

#include

#include

#include

#include

#include

using namespace std;

#define KEYPATH "/tmp/count"

#define KEYPROJ 'a'

#define NAMESIZE 16

#define MTYPE 2

typedef struct {

long mtype;

char name[NAMESIZE];

int iChiScore;

int iEngScore;

int iMathScore;

} S_SCORE_ST;

#endif

send.c

#include "msgQueue.h"

int main()

{

int iRet = 0;

key_t key;

int msgid;

S_SCORE_ST score_st;

do {

key = ftok(KEYPATH, KEYPROJ);

if (key < 0) {

iRet = -1;

cout << "ftok() error : " << key <<  endl;

break;

}

msgid = msgget(key, IPC_CREAT);

if (msgid < 0) {

iRet = -1;

cout << "msgget() error : " << msgid << endl;

break;

}

strcpy(score_st.name, "leex");

score_st.iChiScore = 100;

score_st.iEngScore = 100;

score_st.iMathScore = 100;

score_st.mtype = MTYPE;

iRet = msgsnd(msgid, &score_st, sizeof(score_st)-sizeof(long),  0);

if (iRet < 0) {

cout << "msgsnd() error : " << iRet << endl;

break;

}

} while(false);

return iRet;

}

recv.c

        

#include "msgQueue.h"

int main()

{

int iRet = 0;

key_t key;

int msgid;

S_SCORE_ST score_st;

do {

key = ftok(KEYPATH, KEYPROJ);

if (key < 0) {

iRet = -1;

cout << "ftok() error : " << key <<  endl;

break;

}

msgid = msgget(key, IPC_CREAT);

if (msgid < 0) {

iRet = -1;

cout << "msgget() error : " << msgid << endl;

break;

}

while (1) {

iRet = msgrcv(msgid, &score_st, sizeof(score_st)-sizeof(long), MTYPE, 0);

if (iRet < 0) {

cout << "msgrcv() error : " << iRet << endl;

break;

}

cout << "name:\t" << score_st.name << endl;

cout << "chinese score:\t" << score_st.iChiScore << endl;

cout << "english score:\t" << score_st.iEngScore << endl;

cout << "math score:\t" << score_st.iMathScore << endl;

}

} while(false);

return iRet;

}