消息队列 mq 发送错误错误的文件描述符

问题描述

我正在尝试写入我的消息队列 (mq_send)。

这是我首先打开队列然后写入队列的代码。

开幕：

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         */
}

打开工作正常，但我无法写入消息队列。

mq_send 返回 -1 作为返回值，错误信息为：

errno 的值：9 perror 打印的错误：文件描述符错误 错误：错误的文件描述符

对上述函数的调用发生在这个函数中：

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);
}

有人知道为什么我会收到这种错误吗？我的朋友有完全相同的代码，对他来说它正在工作。

解决方法

您忘记取消引用 MQconnect 中的给定指针。

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*/
}