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SOCKATMARK(3)		 BSD Library Functions Manual		 SOCKATMARK(3)

NAME
     sockatmark	-- determine whether the read pointer is at the	OOB mark

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/socket.h>

     int
     sockatmark(int s);

DESCRIPTION
     To	find out if the	read pointer is	currently pointing at the mark in the
     data stream, the sockatmark() function is provided.  If sockatmark() re-
     turns 1, the next read will return	data after the mark.  Otherwise	(as-
     suming out	of band	data has arrived), the next read will provide data
     sent by the client	prior to transmission of the out of band signal.  The
     routine used in the remote	login process to flush output on receipt of an
     interrupt or quit signal is shown below.  It reads	the normal data	up to
     the mark (to discard it), then reads the out-of-band byte.

	   #include <sys/socket.h>
	   ...
	   oob()
	   {
		   int out = FWRITE, mark;
		   char	waste[BUFSIZ];

		   /* flush local terminal output */
		   ioctl(1, TIOCFLUSH, (char *)&out);
		   for (;;) {
			   if ((mark = sockatmark(rem))	< 0) {
				   perror("sockatmark");
				   break;
			   }
			   if (mark)
				   break;
			   (void) read(rem, waste, sizeof (waste));
		   }
		   if (recv(rem, &mark,	1, MSG_OOB) < 0) {
			   perror("recv");
			   ...
		   }
		   ...
	   }

RETURN VALUES
     Upon successful completion, the sockatmark() function returns the value 1
     if	the read pointer is pointing at	the OOB	mark, 0	if it is not.  Other-
     wise the value -1 is returned and the global variable errno is set	to in-
     dicate the	error.

ERRORS
     The sockatmark() call fails if:

     [EBADF]		The s argument is not a	valid descriptor.

     [ENOTTY]		The s argument is a descriptor for a file, not a
			socket.

SEE ALSO
     recv(2), send(2)

HISTORY
     The sockatmark() function was introduced by IEEE Std 1003.1-2001
     ("POSIX.1"), to standardize the historical	SIOCATMARK ioctl(2).  The
     ENOTTY error instead of the usual ENOTSOCK	is to match the	historical be-
     havior of SIOCATMARK.

BSD			       October 13, 2002				   BSD
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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