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 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.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

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

CHANGE HISTORY

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