sockatmark(3N)															    sockatmark(3N)

NAME

       sockatmark() - determine whether a socket is at the out-of-band mark

SYNOPSIS

DESCRIPTION

       The function determines whether the socket specified by the descriptor is at the out-of-band data mark.

       If  the	protocol  for the socket supports out-of-band data by marking the stream with an out-of-band mark, the function returns 1 when all
       data preceding the mark has been read and the out-of-band mark is the first element in the receive queue.  The function does not remove the
       mark from the stream.

   X/Open Sockets Only
       is new in

RETURN VALUES

       Upon successful completion, the function returns a value indicating whether the socket is at an out-of-band data mark:

	  If the protocol has marked the data stream and all data preceding the mark has
	       been read.

	  If there is no mark, or if data
	       precedes the mark in the receive queue.

       On failure, returns and sets to indicate the error.

ERRORS

       If fails, is set to one of the following values:

       The	   argument is not a valid file descriptor.

       The	   argument does not specify a descriptor for a socket.

APPLICATION USAGE

       The  use  of  this function between receive operations allows an application to determine which received data precedes the out-of-band data
       and which follows the out-of-band data.

       There is an inherent race condition in the use of this function.  On an empty receive queue, the current read of the location might  be	at
       the  "mark".   However,	the  system has no way of knowing that the next data segment arriving from the network is carrying the mark.  Then
       returns false, and the next read operation silently consumes the mark.

       Hence, this function can only be used reliably in one or both ways:

       o      when the application already knows that the out-of-band data has been seen by the system

       o      and that it knows data is waiting to be read at the socket (by using or

AUTHOR

       was developed by HP and IEEE.

SEE ALSO

       ioctl(2), pselect(2), recv(2), recvmsg(2), socket(7).

STANDARDS CONFORMANCE

																    sockatmark(3N)