MSGGET(P) POSIX Programmer's Manual MSGGET(P)
msgget - get the XSI message queue identifier
int msgget(key_t key, int msgflg);
The msgget() function operates on XSI message queues (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.224, Message
Queue). It is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in Realtime .
The msgget() function shall return the message queue identifier associated with the argument key.
A message queue identifier, associated message queue, and data structure (see <sys/msg.h>), shall be created for the argument key if one of
the following is true:
* The argument key is equal to IPC_PRIVATE.
* The argument key does not already have a message queue identifier associated with it, and (msgflg & IPC_CREAT) is non-zero.
Upon creation, the data structure associated with the new message queue identifier shall be initialized as follows:
* msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid shall be set equal to the effective user ID and effective group ID, respec-
tively, of the calling process.
* The low-order 9 bits of msg_perm.mode shall be set equal to the low-order 9 bits of msgflg.
* msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime shall be set equal to 0.
* msg_ctime shall be set equal to the current time.
* msg_qbytes shall be set equal to the system limit.
Upon successful completion, msgget() shall return a non-negative integer, namely a message queue identifier. Otherwise, it shall return -1
and set errno to indicate the error.
The msgget() function shall fail if:
EACCES A message queue identifier exists for the argument key, but operation permission as specified by the low-order 9 bits of msgflg
would not be granted; see XSI Interprocess Communication .
EEXIST A message queue identifier exists for the argument key but ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
ENOENT A message queue identifier does not exist for the argument key and (msgflg & IPC_CREAT) is 0.
ENOSPC A message queue identifier is to be created but the system-imposed limit on the maximum number of allowed message queue identifiers
system-wide would be exceeded.
The following sections are informative.
The POSIX Realtime Extension defines alternative interfaces for interprocess communication (IPC). Application developers who need to use
IPC should design their applications so that modules using the IPC routines described in XSI Interprocess Communication can be easily modi-
fied to use the alternative interfaces.
XSI Interprocess Communication , Realtime , mq_close() , mq_getattr() , mq_notify() , mq_open() , mq_receive() , mq_send() , mq_setattr() ,
mq_unlink() , msgctl() , msgrcv() , msgsnd() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/msg.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 MSGGET(P)