msgget.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)msgget.2	8.2	3/28/91
.TH msgget 2
.SH Name
msgget \- get message queue
.SH Syntax
.nf
.ft B
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
.PP
.ft B
int msgget (key, msgflg)
key_t key;
int msgflg;
.fi
.SH Description
.NXR "msgget system call" 
.NXA "msgget system call" "ftok subroutine"
.NXA "msgget system call" "msgsnd system call"
.NXR "message" "getting queue identifier"
The
.PN msgget
system call
returns the message queue identifier associated with
.I key.
.PP
A message queue identifier and associated message queue and data
structure 
are created for
.I key 
if one of the following is true:
.IP \(bu 5
The
.I key
is equal to IPC_PRIVATE
.IP \(bu 5
The
.I key
does not already have a message queue identifier associated with it,
and
.IR (msgflg
& IPC_CREAT)
is true.
For further information, see 
.MS intro 2 . 
.PP
Upon creation, the data structure associated with the new message queue
identifier is initialized as follows:
.IP \(bu 5
The
.IR msg_perm.cuid,
.IR msg_perm.uid,
.I msg_perm.cgid
and 
.I msg_perm.gid
members
are set equal to the effective user ID and effective group ID,
respectively, of the calling process.
.IP \(bu 5
The low-order nine bits of
.I msg_perm.mode
are set equal to the low-order nine bits of
.I msgflg.
.IP \(bu 5
The
.IR msg_qnum ,
.IR msg_lspid ,
.IR msg_lrpid ,
.IR msg_stime ,
and
.I mgs_rtime
members are set equal to 0.
.IP \(bu 5
The
.I msg_ctime
is set equal to the current time.
.IP \(bu 5
The
.I msg_qbytes
is set equal to the system limit.
.SH Return Values
Upon successful completion, a non-negative integer, which is a message
queue identifier, is returned.  Otherwise, a value of \-1 is returned, and
.I errno
is set to indicate the error.
.SH Diagnostics
.NXR "msgget system call" "diagnostics"
The
.PN msgget
system call
fails under the following conditions: 
.TP 15
[EACCES]
A message queue identifier exists for
.I key
but operations permission, 
as specified by the low-order nine bits of
.I msgflg,
would not be granted. 
For further information, see 
.MS intro 2 .
.TP 15
[ENOENT]
A message queue identifier does not exist for
.I key
and the logical operation
.IR (msgflg
& IPC_CREAT)
is false. 
.TP 15
[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. 
.TP 15
[EEXIST]
A message queue identifier exists for
.I key
but the logical operation 
.RI (( msgflg
&
IPC_CREAT )
&
.RI ( msgflg
& 
IPC_EXCL ))
is true. 
.SH See Also
msgctl(2), msgop(2), ftok(3)