sockatmark(3XNET)				   X/Open Networking Services Library Functions 				 sockatmark(3XNET)

NAME

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

SYNOPSIS

       cc [ flag ... ] file ... -lxnet [ library ... ]
       #include <sys/socket.h>

       int sockatmark(int s);

DESCRIPTION

       The  sockatmark() function determines whether the socket specified by the descriptor s 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 data mark, the sockatmark() function returns 1 when all data
       preceding  the  mark  has been read and the out-of-band data mark is the first element in the receive queue. The sockatmark() function does
       not remove the mark from the stream.

RETURN VALUES

       Upon successful completion, the sockatmark() 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, the return value is 1. If there is no mark, or if data
       precedes the mark in the receive queue, the sockatmark() function returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

       The sockatmark() function will fail if:

       EBADF	 The s argument is not a valid file descriptor.

       ENOTTY	 The s argument does not specify a descriptor for a socket.

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 well be
       at the "mark", but the system has no way of knowing that the next data segment that will arrive from the network will carry the	mark,  and
       sockatmark() will return false, and the next read operation will silently consume the mark.

       Hence,  this function can only be used reliably when the application already knows that the out-of-band data has been seen by the system or
       that it is known that there is data waiting to be read at the socket, either by SIGURG or select(3C).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       recv(3XNET), recvmsg(3XNET), select(3C), attributes(5), standards(5)

SunOS 5.11							    1 Oct 2003							 sockatmark(3XNET)