#include <mqueue.h> int mq_setattr(mqd_t mqdes, const struct mq_attr *mqstat, struct mq_attr *omqstat);
The mq_setattr() function is used to set attributes associated with the open message queue description referenced by the message queue descriptor specified by mqdes.
The message queue attributes corresponding to the following members defined in the mq_attr structure are set to the specified values upon successful completion of mq_setattr():
The value of this member is either 0 or O_NONBLOCK.
The values of mq_maxmsg, mq_msgsize, and mq_curmsgs are ignored by mq_setattr().
If omqstat is non-NULL, mq_setattr() stores, in the location referenced by omqstat, the previous message queue attributes and the current queue status. These values are the same as would be returned by a call to mq_getattr() at that point.
Upon successful completion, mq_setattr() returns 0 and the attributes of the message queue will have been changed as specified. Otherwise, the message queue attributes are unchanged, and the function returns −1 and sets errno to indicate the error.
The mq_setattr() function will fail if:
The mqdes argument is not a valid message queue descriptor.
The mq_setattr() function is not supported by the system.
See attributes(5) for descriptions of the following attributes: