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 constant as a message operation flag:

       MSG_NOERROR
              No error if big message.

       The msqid_ds structure shall contain 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 pid_t, time_t, key_t, size_t, and ssize_t types  shall  be  defined  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, all of the symbols from <sys/ipc.h> shall be  defined  when  this  header  is
       included.

       The following sections are informative.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <sys/ipc.h> , <sys/types.h> , msgctl(), msgget(), msgrcv(), msgsnd()

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .