NAME

mq_getattr − Returns the status and attributes of a message queue (P1003.1b)

SYNOPSIS

#include <mqueue.h>
 
int mq_getattr (
mqd_t mqdes,
struct mq_attr ∗mqstat);

LIBRARY

Realtime Library (librt.so, librt.a)

PARAMETERS

mqdes
Specifies the message queue descriptor whose attributes are obtained.

∗mqstat
Specifies a pointer to a structure that is updated to contain the values that were set when the message queue was created or modified by a call to the mq_setattr function. 

When the mq_getattr function returns, the following three members of the mq_attr structure specified by mqstat will have the values that were set when the message queue was created, but with modifications made by subsequent calls to the mq_setattr function:

       •The mq_maxmsg member specifies the maximum number of messages that can be held in the queue specified by the mqdes argument. 

       •The mq_msgsize member specifies the maximum size of any message in the queue. 

       •The mq_options member specifies whether the message operation is blocking or nonblocking (MQ_NONBLOCK). 

The mq_curmsgs member of the mq_attr structure indicates the number of messages currently on the queue. 

DESCRIPTION

The mq_getattr function returns the status and attributes of a message queue. Use the mq_setattr function to set message queue attributes. 

RETURN VALUES

On successful completion, the function returns the value 0 (zero); otherwise, the function returns the value −1 and sets errno to indicate the error. 

ERRORS

The mq_getattr function fails under the following conditions:

[EBADF]
The fildes argument is an invalid file descriptor. 

[EINVAL]
The mqstat argument is a null pointer. 

SEE ALSO

Functions: mq_open(3), mq_receive(3), mq_send(3), mq_setattr(3)

Guide to Realtime Programming