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MSGGET (3) | C library functions | Unix Manual Pages | :man▋

NAME

msgget - get message queue

CONTENTS

Library
Synopsis
Description
Return Values
Errors
See Also
History

LIBRARY


.Lb libc

SYNOPSIS


.In sys/types.h
.In sys/ipc.h
.In 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 associated with it (the msqid_ds structure, see msgctl(3)) is initialized as follows:

  • msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process.
  • msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process.
  • msg_perm.mode is set to the lower 9 bits of msgflg.
  • msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.
  • msg_qbytes is set to the system wide maximum value for the number of bytes in a queue ( MSGMNB).
  • msg_ctime is set to the current time.

RETURN VALUES

Upon successful completion a positive message queue identifier 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

 
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