creating a queue message returns zero in id

Question

I can't figure out what I missed. The first time that I run this msgget() retuns 0 but msgctl() can remove it. The second time still having 0 and msgctl() aborts with invalid argument error.

Already tried to use some key instead of IPC_PRIVATE

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <sys/msg.h>
#include <time.h>

#define DEBUG

int main(){
    int queue_id;

    if(queue_id = msgget(IPC_PRIVATE, IPC_CREAT | IPC_EXCL | 0600) == -1){
         perror("queue");
         return -1;
    }

    if(msgctl(queue_id, IPC_RMID, NULL) == -1) {
         perror("queue rmid:");
    }

             return 0;
}

nmichaels · Accepted Answer · 2019-04-03 16:49:44Z

1

== binds more tightly than =. Try putting parentheses around the assignment of queue_id, or put it on its own line:

queue_id = msgget(IPC_PRIVATE, IPC_CREAT | IPC_EXCL | 0600);
if(queue_id == -1) {
         perror("queue");
         return -1;
}

Running your compiler with -Wall -Wextra -Werror will help with this kind of thing.

answered Apr 3, 2019 at 16:49

nmichaels

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