.\"	$NetBSD: sockatmark.3,v 1.10 2022/06/28 20:12:52 rillig Exp $
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.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Klaus Klein.
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.Dd June 28, 2022
.Dt SOCKATMARK 3
.Os
.Sh NAME
.Nm sockatmark
.Nd determine whether a socket is at the out-of-band mark
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn sockatmark "int s"
.Sh DESCRIPTION
The
.Nm sockatmark
function determines whether the socket referenced by the file descriptor
.Fa s
is at the out-of-band mark.
.Sh RETURN VALUES
If successful, the
.Nm sockatmark
function returns 1 to indicate that the socket is at an out-of-band mark;
0 is returned if there is no out-of-band mark or the mark is preceded
by in-band data.
Otherwise, -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Nm sockatmark
function will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The argument
.Fa s
is not a valid file descriptor.
.It Bq Er ENOTTY
The file descriptor
.Fa s
does not refer to a socket.
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr recv 2 ,
.Xr socket 2
.Rs
.%T "An Introductory 4.4BSD Interprocess Communication Tutorial"
.%A Stuart Sechrest
.Re
.Pq see Pa /usr/share/doc/reference/ref3/sockets
.Rs
.%T "Advanced 4.4BSD IPC Tutorial"
.%A Samuel J. Leffler
.%A Robert S. Fabry
.%A William N. Joy
.%A Phil Lapsley
.%A Steve Miller
.%A Chris Torek
.Re
.Pq see Pa /usr/share/doc/reference/ref3/sockets-advanced
.Sh STANDARDS
The
.Nm sockatmark
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Nm sockatmark
function appeared in
.St -p1003.1g-2000
as a replacement for the
.Dv SIOCATMARK
.Xr ioctl 2
interface.