mq_setattr()

set the flags for a message queue

Synopsis:

#include <mqueue.h>
int mq_setattr( mqd_t mqdes, 
                const struct mq_attr *mqstat,
                struct mq_attr *omqstat );

Description:

The mq_setattr() function is used to set the mq_flags field of the structure pointed to by mqstat for the queue specified by mqdes. If omqstat isn't NULL, then the location it references is used to store the old attribute structure.

The mq_maxmsg and mq_msgsize fields of mqstat are ignored.

For information on the bits in the mq_flags field, see "Message-queue structures" in the chapter on POSIX.4 message queues.

Returns:

If the attributes are successfully changed, then 0 is returned. If not, -1 is returned, the attributes aren't changed, and errno is set.

Errors:

EBADF

mqdes doesn't represent a valid message queue.

EINVAL

This value indicates one of the following:

• mq_attr is NULL.
• MQ_MULT_NOTIFY had been set for this queue, and the given mq_flags includes a 0 in the MQ_MULT_NOTIFY bit. Once MQ_MULT_NOTIFY has been turned on, it may never be turned off.

Classification:

POSIX 1003.4, with extensions

Caveats:

In order to use the mq_... functions, you must:

• Link your application with the mqueue library (specify -lmqueue in your cc command).
• Start the message queue server, Mqueue. For more information, see the QNX Utilities Reference.

See also:

errno, mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(), mq_send(), mq_unlink()

chapter on POSIX.4 message queues