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Full Discussion: Msgget(2) returns 0 - a workaround fix
Top Forums Programming Msgget(2) returns 0 - a workaround fix Post 302907107 by mr_bandit on Wednesday 25th of June 2014 07:43:38 PM
Old 06-25-2014
Quote:
using msgid as a message and NOT as message queue id. Which it is. They are not the same thing. Period.
I do not understand why you make this statement, I have consistently used msgget() to get the ID of the queue, never as a message itself. the msgq_id is a parameter to msgsnd() and msgrcv() to specify the queue for the message.

Now, my confusion was over a msgq_id == 0 as a valid number. It is, in both practice and theory.

@Don is absolutely correct stating

Quote:
Unless the man page explicitly states otherwise, the value of errno after a call to a function that completes successfully is meaningless.
Again, my confusion was that what seemed to be a successful return from msgget() (according to the man page), but not having success. I actually had two bugs that were subtle and misleading, but that is the life of a programmer. (Especially when dealing with *really* bad code.) My searches for information found scant help. The collected wisdom of the community have helped me many times (Thanks, Google!) in finding the obscure information on forums. (If one programs Atmel chips, I recommend avrfreaks.net.)

AND - my purpose in this post was to try to help provide some more information to the next person who had this issue at 3am. The helpful replies have added to that goal, and I thank the posters for their time and attention.
 

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LEARN ABOUT SUSE

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  a  few  architectures,  for	example ia64, 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 3.25 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								    2007-06-28								    IPC(2)
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