NAME¶

mq_getattr — get message queue attributes (REALTIME)

LIBRARY¶

POSIX Real-time Library (librt, -lrt)

SYNOPSIS¶

#include <mqueue.h>

int
mq_getattr(mqd_t mqdes, struct mq_attr *mqstat);

DESCRIPTION¶

The mq_getattr() system call obtains status information and attributes of the message queue and the open message queue description associated with the message queue descriptor.

The mqdes argument specifies a message queue descriptor.

The results are returned in the mq_attr structure referenced by the mqstat argument.

Upon return, the following members will have the values associated with the open message queue description as set when the message queue was opened and as modified by subsequent mq_setattr() calls: mq_flags.

The following attributes of the message queue will be returned as set at message queue creation: mq_maxmsg, mq_msgsize.

Upon return, the following members within the mq_attr structure referenced by the mqstat argument will be set to the current state of the message queue:

mq_curmsgs

The number of messages currently on the queue.

RETURN VALUES¶

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS¶

The mq_getattr() system call will fail if:

[EBADF]

The mqdes argument is not a valid message queue descriptor.

SEE ALSO¶

mq_open(2), mq_send(2), mq_setattr(2), mq_timedsend(2)

STANDARDS¶

The mq_getattr() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

HISTORY¶

Support for POSIX message queues first appeared in FreeBSD 7.0.

COPYRIGHT¶

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 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.