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Name

msgget - get message queue

Synopsis


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

int msgget(key_t key, int msgflg);

Description

msgget() returns the message queue identifier associated with key.

A message queue identifier and associated message queue and data structure (see intro(2) ) are created for key if one of the following are true:

key
is IPC_PRIVATE.
key
does not already have a message queue identifier associated with it, and (msgflg&IPC_CREAT) is true.

On 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 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 to the low-order 9 bits of msgflg.
msg_qnum, msg_lspid, msg_lrpid,
msg_stime, and msg_rtime are set to 0.
msg_ctime
is set to the current time.
msg_qbytes
is set to the system limit.

Return Values

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.

Errors

msgget() fails if one or more of the following are true:

EACCES
A message queue identifier exists for key, but operation permission (see intro(2) ) 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) and (msgflg&IPC_EXCL) are both 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.

See Also

intro(2) , msgctl(2) , msgop(2) , stdipc(3C)

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