msgget(3)

NAME

msgget - get message queue

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int
msgget(key_t key, int msgflg);

DESCRIPTION

The msgget() function returns the message queue identifier

associated
with key. A message queue identifier is a unique integer

greater than
zero.

A message queue is created if either key is equal to

IPC_PRIVATE, or key
does not have a message queue identifier associated with it,

and the
IPC_CREAT bit is set in msgflg.

If a new message queue is created, the data structure asso

ciated with it
(the msqid_ds structure, see msgctl(3)) is initialized as

follows:

+o msg_perm.cuid and msg_perm.uid are set to the effective

uid of the

calling process.

+o msg_perm.gid and msg_perm.cgid are set to the effective

gid of the

calling process.

+o msg_perm.mode is set to the lower 9 bits of msgflg.

+o msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime,

and msg_stime

are set to 0.

+o msg_qbytes is set to the system wide maximum value for

the number of

bytes in a queue (MSGMNB).

+o msg_ctime is set to the current time.

RETURN VALUES

Upon successful completion a positive message queue identi

fier is
returned. Otherwise, -1 is returned and the global variable

errno is set
to indicate the error.

ERRORS

[EACCES] A message queue is already associated

with key and the

caller has no permission to access it.

[EEXIST] Both IPC_CREAT and IPC_EXCL are set in

msgflg, and a

message queue is already associated with

key.

[ENOSPC] A new message queue could not be created

because the

system limit for the number of message

queues has been
reached.

[ENOENT] IPC_CREAT was not set in msgflg and no

message queue

associated with key was found.

SEE ALSO

msgctl(3), msgrcv(3), msgsnd(3)

HISTORY

Message queues appeared in the first release of AT&T System

V UNIX.

BSD August 17, 1995

BSD