msgget(S)

Syntax

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int msgget (key, msgflg)
key_t key;
int msgflg;

Description

A message queue identifier and associated message queue and data structure are created for key if one of the following is true:

• The key argument is equal to IPC_PRIVATE.

• The key argument does not already have a message queue identifier associated with it, and (msgflg & IPC_CREAT) is ``true''.

Upon creation, the data structure associated with the new message queue identifier is initialized as follows:

• msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.

• The low-order 9 bits of msg_perm.mode are set equal to the low-order 9 bits of msgflg.

• msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set equal to 0.

• msg_ctime is set equal to the current time.

• msg_qbytes is set equal to the system limit.

The msgget system call fails if one or more of the following is true:

[EACCES]

A message queue identifier exists for key, but operation permission as specified by the low-order 9 bits of msgflg would not be granted.

[EEXIST]

A message queue identifier exists for key but [(msgflg & IPC_CREAT) & (msgflg & IPC_EXCL)] is ``true''.

[ENOENT]

A message queue identifier does not exist for key and (msgflg & IPC_CREAT) is ``false''.

[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.

Diagnostics

See also

Standards conformance

X/Open Portability Guide, Issue 3, 1989 .