c - 为什么msgrcv返回ENOMSG

Question

System V消息队列创建成功，命令ipcs -q输出:

 ------ Message Queues --------<
 key        msqid      owner      perms      used-bytes   messages    
 0x080b2fb4 0          hel         600        0            0          

但是接收消息的程序返回:

exit: msgrcv error, No message of desired type

这是我的代码:

/* create key for message queue */
key = ftok("/home/hel/messageQueueSystemV", 8);
if (key == -1) {
    printf("exit: ftok error, %s\n", strerror(errno)); // error
    exit(0);
}

/* open existed message queue */
mqFd = msgget(key, 0600);
if (mqFd < 0) {
    printf("exit: msgget error, %s\n", strerror(errno)); // error
    exit(0);
}

/* receive a message */
if (msgrcv(mqFd, &buf, 1 + sizeof(short), 0, IPC_NOWAIT) < 0) { // type is 0
    printf("exit: msgrcv error, %s\n", strerror(errno)); // error
    exit(0);
}

Answer 1

^{将评论转移到答案。}

我建议:

Maybe there isn't a message waiting? Where did you write the code to send the message to the queue?

响应是:

Firstly, I run a program to create message queue and send a message. Then use command ipcs -q to check whether it succeeds. Then I start another process to receive that message.

狡辩开始了:

The output of ipcs says there are no messages queued. You told msgrcv() not to wait, so it didn't, so it returned "there are no messages queued". What am I not understanding?

而且，看来，这是正确的诊断。