int SP_poll( mailbox mbox);
DESCRIPTIONSP_poll is a way to poll a mailbox to see if any messages are available for receiving. The value returned will be < 0 if error, 0 if nothing is available, and the number of bytes waiting if something is there.
RETURN VALUESReturns 0 if nothing is available or the number of bytes available, or one of the following errors ( < 0 ):
- The session specified by mbox is illegal. Usually because it is not active.