CODEWITHSUNDEEP
cmessage-queueshared-memorymsgrcvmsgsend
user69514
user69514

Reputation: 27629

IPC message queue. msgrcv system call. System V. how to get out of loop

I have a message queue from which I am getting messages in a loop. The problem is that I don't know how to exit the loop. msgrcv returns type size_t so it keeps going. What value should I compare the return value so I can exit the loop?

while(msgrcv(msqid, &msgreceived, sizeof(msgreceived), BUFFER_CHANGED, 0) != -1){
    printf("%d %d %d %d ",msgreceived.value0,msgreceived.value1,msgreceived.value2,msgreceived.value3);

Upvotes: 0

Views: 2290

Answers (1)

ephemient
ephemient

Reputation: 204678

Because your last parameter does not include IPC_NOWAIT, msgrcv blocks while waiting for future messages.

If there is no message to be read immediately, msgrcv(..., ... | IPC_NOWAIT) will return (size_t)-1 and set errno = ENOMSG.

Upvotes: 1

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