The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> sys/msg.h - XSI message queue structures

#### SYNOPSIS

> `[XSI] #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>

> XSH msgctl, msgget, msgrcv, msgsnd

#### CHANGE HISTORY

> First released in Issue 2. Derived from System V Release 2.0.

#### Issue 7

> Austin Group Interpretation 1003.1-2001 #179 is applied.

> This reference page is clarified with respect to macros and symbolic constants.

End of informative text.

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