消息队列mq发送错误。错误的文件描述符

Question

我正在尝试写入我的消息队列(mq_send)。

下面是我的代码，用于先打开队列，然后再写入队列。

打开：

int MQconnect (mqd_t * mq, char * name)
{
    //printf("hello from MQconnect\n");
    do{
        mq=mq_open(name, O_WRONLY);  //O_RDONLY
    }while(mq==-1);

    if(mq== -1){
        return 0;
    }
    else
        return 1;
    // Connects to an existing mailslot for writing Uses mq as reference pointer, so that you can     reach the handle from anywhere/
    // Should return 1 on success and 0 on fail*/
}

写作：

int MQwrite (mqd_t mq, void * sendBuffer) // (const char) sendBuffer
{
    int nrOfBytes = mq_send(mq, (const char)sendBuffer, 1024, 10);

    printf("\n%d", nrOfBytes);

    return nrOfBytes; //nrOfBytes;

    // Write a msg to a mailslot, return nr Uses mq as reference pointer, so that you can reach the handle from anywhere
    // should return number of bytes read         */
}

打开可以正常工作，但我不能写入消息队列。

mq_send返回-1作为返回值，错误消息为：

errno: 9的值错误输出错误:错误文件描述符错误:文件描述符错误

对上述函数的调用是从这个函数中进行的：

void * mqClient(void * arg){
    pthread_mutex_lock(&mutex);

    char answer[20];
    mqd_t mq_on_server;
    usleep(1000);
    int response = MQconnect(&mq_on_server, "/servermq");
    if(response==0){
        printf("something went wrong with MQconnect\n");
    }
    else{
        //This loop continously scans planets given by the user
        //while(!(0)){
    printf("\nWrite to mailbox: ");
    scanf("%s", answer);


    MQwrite (mq_on_server, &answer);
    int c;
    while ( (c = getchar()) != '\n' && c != EOF);
    //fflush(stdout);
        //}

    }

    pthread_mutex_unlock(&mutex);
}

有谁知道为什么我会得到这样的错误？我的朋友有完全相同的代码，对他来说，它是有效的。

Answer 1

您忘记在MQconnect中取消对给定指针的引用。

int MQconnect (mqd_t * mq, char * name)
{
    //printf("hello from MQconnect\n");
#if 0
    /* wrong part */
    do{
        mq=mq_open(name, O_WRONLY);  //O_RDONLY
    }while(mq==-1);

    if(mq== -1){
#else
    /* fixed code */
    do{
        *mq=mq_open(name, O_WRONLY);  //O_RDONLY
    }while(*mq==-1);

    if(*mq== -1){
#endif
        return 0;
    }
    else
        return 1;
    // Connects to an existing mailslot for writing Uses mq as reference pointer, so that you can     reach the handle from anywhere/
    // Should return 1 on success and 0 on fail*/
}