.\"	$OpenBSD: socketpair.2,v 1.12 2003/06/02 20:18:39 millert Exp $
.\"	$NetBSD: socketpair.2,v 1.5 1995/02/27 12:38:00 cgd Exp $
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.\"     @(#)socketpair.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt SOCKETPAIR 2
.Os
.Sh NAME
.Nm socketpair
.Nd create a pair of connected sockets
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Ft int
.Fn socketpair "int d" "int type" "int protocol" "int *sv"
.Sh DESCRIPTION
The
.Fn socketpair
call creates an unnamed pair of connected sockets in
the specified domain
.Fa d ,
of the specified
.Fa type ,
and using the optionally specified
.Fa protocol .
The descriptors used in referencing the new sockets
are returned in
.Fa sv Ns [0]
and
.Fa sv Ns [1] .
The two sockets are indistinguishable.
.Sh RETURN VALUES
A 0 is returned if the call succeeds, \-1 if it fails.
.Sh ERRORS
The call succeeds unless:
.Bl -tag -width Er
.It Bq Er EMFILE
Too many descriptors are in use by this process.
.It Bq Er EAFNOSUPPORT
The specified address family is not supported on this machine.
.It Bq Er EPROTONOSUPPORT
The specified protocol is not supported on this machine.
.It Bq Er EOPNOTSUPP
The specified protocol does not support creation of socket pairs.
.It Bq Er EFAULT
The address
.Fa sv
does not specify a valid part of the
process address space.
.It Bq Er ENFILE
The system file table is full.
.El
.Sh SEE ALSO
.Xr pipe 2 ,
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The
.Fn socketpair
function conforms to
.St -xpg4.2 .
.Sh HISTORY
The
.Fn socketpair
function call appeared in
.Bx 4.2 .
.Sh BUGS
This call is currently implemented only for the
.Tn LOCAL
domain.
Many operating systems only accept a
.Ar protocol
of
.Ev PF_UNSPEC ,
so that should be used instead of
.Ev PF_LOCAL
for maximal portability.