sys_msg.h(0P)		   POSIX Programmer's Manual		 sys_msg.h(0P)

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.

NAME
       sys/msg.h — XSI message queue structures

SYNOPSIS
       #include <sys/msg.h>

DESCRIPTION
       The <sys/msg.h> header shall define the following data types through
       typedef:

       msgqnum_t     Used for the number of messages in the message queue.

       msglen_t	     Used for the number of bytes allowed in a message queue.

       These types shall be unsigned integer types that are able to store
       values at least as large as a type unsigned short.

       The <sys/msg.h> header shall define the following symbolic constant as
       a message operation flag:

       MSG_NOERROR   No error if big message.

       The <sys/msg.h> header shall define the msqid_ds structure, which shall
       include the following members:


	   struct ipc_perm msg_perm   Operation permission structure.
	   msgqnum_t	   msg_qnum   Number of messages currently on queue.
	   msglen_t	   msg_qbytes Maximum number of bytes allowed on queue.
	   pid_t	   msg_lspid  Process ID of last msgsnd().
	   pid_t	   msg_lrpid  Process ID of last msgrcv().
	   time_t	   msg_stime  Time of last msgsnd().
	   time_t	   msg_rtime  Time of last msgrcv().
	   time_t	   msg_ctime  Time of last change.

       The <sys/msg.h> header shall define the pid_t, size_t, ssize_t, and
       time_t types as described in <sys/types.h>.

       The following shall be declared as functions and may also be defined as
       macros. Function prototypes shall be provided.


	   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);

       In addition, the <sys/msg.h> header shall include the <sys/ipc.h>
       header.

       The following sections are informative.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, msgctl(), msgget(),
       msgrcv(), msgsnd()

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 .

       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 .

IEEE/The Open Group		     2017			 sys_msg.h(0P)