MSGGET(S) UNIX System V MSGGET(S)
Name
msgget - get message queue
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgget (key, msgflg)
key_t key;
int msgflg;
Description
The msgget system call returns the message queue identifier
associated with key.
A message queue identifier and associated message queue and
data structure (see intro(S)) 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 will fail if one or more of the
following is true:
[EACCES] A message queue identifier exists for key,
but operation permission (see intro(S)) as
specified by the low-order 9 bits of msgflg
would not be granted.
[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.
[EEXIST] A message queue identifier exists for key but
[(msgflg & IPC_CREAT) & (msgflg & IPC_EXCL)]
is ``true''.
See Also
intro(S), msgctl(S), msgop(S)
Diagnostics
Upon successful completion, a non-negative integer, namely a
message queue identifier, is returned. Otherwise, a value
of -1 is returned, and errno is set to indicate the error.
Standards Conformance
msgget is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 6/20/89)