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Full Discussion: Msgget(2) returns 0 - a workaround fix
Top Forums Programming Msgget(2) returns 0 - a workaround fix Post 302906930 by jim mcnamara on Tuesday 24th of June 2014 02:55:44 PM
Old 06-24-2014
msgid is NOT a message it is a message queue id. (A shared (IPC) memory object, not an individual message) A return of msgid ==0 means success. Any number >-1 == success.

Since you really did not post much code --
You should be calling msgrcv like this (note infinite loop is NOT required):
Code:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct my_msgbuf 
{
 long mtype;
 char mtext[200];
};

int main(void)
{
   struct my_msgbuf buf;
   int msqid=0;
   key_t key;
   if ((key = ftok("[your key code goes here]", 'B')) =< -1)  /* same key as other program  edit:changed to =< */
   {
     perror("ftok");
     exit(1);
   }
   if ((msqid = msgget(key, 0666)) == -1)  /* connect to the queue */
   {
      perror("msgget");
      exit(1);
   }
   printf("Ready to receive messages\n");
   for(;;) 
   { 
      if (msgrcv(msqid, &buf, sizeof(buf.mtext), 0, 0) == -1)
      {
        perror("msgrcv");
        exit(1);
      }
      printf("%s\n", buf.mtext);
   }
   return 0;
}

The above snippet works correctly, I use it in other code....
Last edited by jim mcnamara; 06-24-2014 at 11:25 PM..
This User Gave Thanks to jim mcnamara For This Post:
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LEARN ABOUT DEBIAN

ipc

IPC(2)							     Linux Programmer's Manual							    IPC(2)

NAME

       ipc - System V IPC system calls

SYNOPSIS

       int ipc(unsigned int call, int first, int second, int third,
	       void *ptr, long fifth);

DESCRIPTION

       ipc()  is  a  common  kernel entry point for the System V IPC calls for messages, semaphores, and shared memory.  call determines which IPC
       function to invoke; the other arguments are passed through to the appropriate call.

       User programs should call the appropriate functions by their usual names.  Only standard library implementors and kernel  hackers  need	to
       know about ipc().

CONFORMING TO

       ipc() is Linux-specific, and should not be used in programs intended to be portable.

NOTES

       On some architectures--for example x86-46 and ARM--there is no ipc() system call; instead msgctl(2), semctl(2), shmctl(2), and so on really
       are implemented as separate system calls.

SEE ALSO

       msgctl(2), msgget(2), msgrcv(2), msgsnd(2), semctl(2), semget(2), semop(2), semtimedop(2), shmat(2), shmctl(2), shmdt(2), shmget(2)

COLOPHON

       This page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-10-16								    IPC(2)
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