sys_msg.h man page


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.

sys/msg.h — XSI message queue structures


#include <sys/msg.h>


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

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

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.

See Also

<sys_ipc.h>, <sys_types.h>

The System Interfaces volume of POSIX.1‐2008, msgctl(), msgget(), msgrcv(), msgsnd()