'\" et
.TH SOCKETPAIR "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
socketpair
\(em create a pair of connected sockets
.SH SYNOPSIS
.LP
.nf
#include <sys/socket.h>
.P
int socketpair(int \fIdomain\fP, int \fItype\fP, int \fIprotocol\fP,
    int \fIsocket_vector\fP[2]);
.fi
.SH DESCRIPTION
The
\fIsocketpair\fR()
function shall create an unbound pair of connected sockets in a
specified
.IR domain ,
of a specified
.IR type ,
under the protocol optionally specified by the
.IR protocol
argument. The two sockets shall be identical. The file descriptors
used in referencing the created sockets shall be returned in
.IR socket_vector [0]
and
.IR socket_vector [1].
.P
The
\fIsocketpair\fR()
function takes the following arguments:
.IP "\fIdomain\fR" 12
Specifies the communications domain in which the sockets are to be
created.
.IP "\fItype\fR" 12
Specifies the type of sockets to be created.
.IP "\fIprotocol\fR" 12
Specifies a particular protocol to be used with the sockets.
Specifying a
.IR protocol
of 0 causes
\fIsocketpair\fR()
to use an unspecified default protocol appropriate for the requested
socket type.
.IP "\fIsocket_vector\fR" 12
Specifies a 2-integer array to hold the file descriptors of the created
socket pair.
.P
The
.IR type
argument specifies the socket type, which determines the semantics of
communications over the socket. The following socket types are defined;
implementations may specify additional socket types:
.IP SOCK_STREAM 14
Provides sequenced, reliable, bidirectional, connection-mode byte
streams, and may provide a transmission mechanism for out-of-band
data.
.IP SOCK_DGRAM 14
Provides datagrams, which are connectionless-mode, unreliable messages
of fixed maximum length.
.IP SOCK_SEQPACKET 14
Provides sequenced, reliable, bidirectional, connection-mode
transmission paths for records. A record can be sent using one or more
output operations and received using one or more input operations, but
a single operation never transfers part of more than one record. Record
boundaries are visible to the receiver via the MSG_EOR flag.
.P
If the
.IR protocol
argument is non-zero, it shall specify a protocol that is supported by
the address family. If the
.IR protocol
argument is zero, the default protocol for this address family and type
shall be used. The protocols supported by the system are
implementation-defined.
.P
The process may need to have appropriate privileges to use the
\fIsocketpair\fR()
function or to create some sockets.
.SH "RETURN VALUE"
Upon successful completion, this function shall return 0; otherwise,
\(mi1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
The
\fIsocketpair\fR()
function shall fail if:
.TP
.BR EAFNOSUPPORT
.br
The implementation does not support the specified address family.
.TP
.BR EMFILE
All, or all but one, of the file descriptors available to the
process are currently open.
.TP
.BR ENFILE
No more file descriptors are available for the system.
.TP
.BR EOPNOTSUPP
The specified protocol does not permit creation of socket pairs.
.TP
.BR EPROTONOSUPPORT
.br
The protocol is not supported by the address family, or the protocol is
not supported by the implementation.
.TP
.BR EPROTOTYPE
The socket type is not supported by the protocol.
.P
The
\fIsocketpair\fR()
function may fail if:
.TP
.BR EACCES
The process does not have appropriate privileges.
.TP
.BR ENOBUFS
Insufficient resources were available in the system to perform the
operation.
.TP
.BR ENOMEM
Insufficient memory was available to fulfill the request.
.LP
.IR "The following sections are informative."
.SH "EXAMPLES"
None.
.SH "APPLICATION USAGE"
The documentation for specific address families specifies which
protocols each address family supports. The documentation for specific
protocols specifies which socket types each protocol supports.
.P
The
\fIsocketpair\fR()
function is used primarily with UNIX domain sockets and need not be
supported for other domains.
.SH "RATIONALE"
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIsocket\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<sys_socket.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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