'\" et
.TH sys_msg.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sys/msg.h
\(em XSI message queue structures
.SH SYNOPSIS
.LP
.nf
#include <sys/msg.h>
.fi
.SH DESCRIPTION
The
.IR <sys/msg.h> 
header shall define the following data types through
.BR typedef :
.IP "\fBmsgqnum_t\fP" 14
Used for the number of messages in the message queue.
.IP "\fBmsglen_t\fP" 14
Used for the number of bytes allowed in a message queue.
.P
These types shall be unsigned integer types that are able to store
values at least as large as a type
.BR "unsigned short" .
.P
The
.IR <sys/msg.h> 
header shall define the following symbolic constant as a message
operation flag:
.IP MSG_NOERROR 14
No error if big message.
.P
The
.IR <sys/msg.h> 
header shall define the
.BR msqid_ds
structure, which shall include the following members:
.sp
.RS 4
.nf

struct ipc_perm msg_perm   \fROperation permission structure.\fR
msgqnum_t       msg_qnum   \fRNumber of messages currently on queue.\fR
msglen_t        msg_qbytes \fRMaximum number of bytes allowed on queue.\fR
pid_t           msg_lspid  \fRProcess ID of last \fImsgsnd\fP\^(\|).\fR
pid_t           msg_lrpid  \fRProcess ID of last \fImsgrcv\fP\^(\|).\fR
time_t          msg_stime  \fRTime of last \fImsgsnd\fP\^(\|).\fR
time_t          msg_rtime  \fRTime of last \fImsgrcv\fP\^(\|).\fR
time_t          msg_ctime  \fRTime of last change.\fR
.fi
.P
.RE
.P
The
.IR <sys/msg.h> 
header shall define the
.BR pid_t ,
.BR size_t ,
.BR ssize_t ,
and
.BR time_t
types as described in
.IR <sys/types.h> .
.P
The following shall be declared as functions and may also be defined
as macros. Function prototypes shall be provided.
.sp
.RS 4
.nf

int       msgctl(int, int, struct msqid_ds *);
int       msgget(key_t, int);
ssize_t   msgrcv(int, void *, size_t, long, int);
int       msgsnd(int, const void *, size_t, int);
.fi
.P
.RE
.P
In addition, the
.IR <sys/msg.h> 
header shall include the
.IR <sys/ipc.h> 
header.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fB<sys_ipc.h>\fP",
.IR "\fB<sys_types.h>\fP"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fImsgctl\fR\^(\|)",
.IR "\fImsgget\fR\^(\|)",
.IR "\fImsgrcv\fR\^(\|)",
.IR "\fImsgsnd\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .