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.TH SOCKETPAIR 3XNET "Jun 10, 2002"
.SH NAME
socketpair \- create a pair of connected sockets
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lxnet\fR [ \fIlibrary\fR ... ]
#include <sys/socket.h>

\fBint\fR \fBsocketpair\fR(\fBint\fR \fIdomain\fR, \fBint\fR \fItype\fR, \fBint\fR \fIprotocol\fR, \fBint\fR \fIsocket_vector\fR\fB[2]\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsocketpair()\fR function creates an unbound pair of connected sockets in
a specified \fIdomain\fR, of a specified \fBtype\fR, under the protocol
optionally specified by the \fIprotocol\fR argument.  The two sockets are
identical. The file descriptors used in referencing the created sockets are
returned in \fIsocket_vector\fR\fB0\fR and \fIsocket_vector\fR\fB1\fR.
.sp
.LP
The \fItype\fR argument specifies the socket type, which determines the
semantics of communications over the socket.  The socket types supported by the
system are implementation-dependent.  Possible socket types include:
.sp
.ne 2
.na
\fB\fBSOCK_STREAM\fR\fR
.ad
.RS 18n
Provides sequenced, reliable, bidirectional, connection-mode byte streams, and
may provide a transmission mechanism for out-of-band data.
.RE

.sp
.ne 2
.na
\fB\fBSOCK_DGRAM\fR\fR
.ad
.RS 18n
Provides datagrams, which are connectionless-mode, unreliable messages of fixed
maximum length.
.RE

.sp
.ne 2
.na
\fB\fBSOCK_SEQPACKET\fR\fR
.ad
.RS 18n
Provides sequenced, reliable, bidirectional, connection-mode transmission path
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.
.RE

.sp
.LP
If the \fIprotocol\fR argument is non-zero, it must specify a protocol that is
supported by the address family.  The protocols supported by the system are
implementation-dependent.
.sp
.LP
The process may need to have appropriate privileges to use the
\fBsocketpair()\fR function or to create some sockets.
.SH PARAMETERS
.sp
.ne 2
.na
\fB\fIdomain\fR\fR
.ad
.RS 17n
Specifies the communications domain in which the sockets are to be created.
.RE

.sp
.ne 2
.na
\fB\fItype\fR\fR
.ad
.RS 17n
Specifies the type of sockets to be created.
.RE

.sp
.ne 2
.na
\fB\fIprotocol\fR\fR
.ad
.RS 17n
Specifies a particular protocol to be used with the sockets. Specifying a
\fIprotocol\fR of 0 causes \fBsocketpair()\fR to use an unspecified default
protocol appropriate for the requested socket type.
.RE

.sp
.ne 2
.na
\fB\fIsocket_vector\fR\fR
.ad
.RS 17n
Specifies a 2-integer array to hold the file descriptors of the created socket
pair.
.RE

.SH USAGE
.sp
.LP
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.
.sp
.LP
The \fBsocketpair()\fR function is used primarily with UNIX domain sockets and
need not be supported for other domains.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, this function returns 0.  Otherwise, \(mi1 is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.sp
.LP
The \fBsocketpair()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAFNOSUPPORT\fR\fR
.ad
.RS 19n
The implementation does not support the specified address family.
.RE

.sp
.ne 2
.na
\fB\fBEMFILE\fR\fR
.ad
.RS 19n
No more file descriptors are available for this process.
.RE

.sp
.ne 2
.na
\fB\fBENFILE\fR\fR
.ad
.RS 19n
No more file descriptors are available for the system.
.RE

.sp
.ne 2
.na
\fB\fBEOPNOTSUPP\fR\fR
.ad
.RS 19n
The specified protocol does not permit creation of socket pairs.
.RE

.sp
.ne 2
.na
\fB\fBEPROTONOSUPPORT\fR\fR
.ad
.RS 19n
The protocol is not supported by the address family, or the protocol is not
supported by the implementation.
.RE

.sp
.ne 2
.na
\fB\fBEPROTOTYPE\fR\fR
.ad
.RS 19n
The socket type is not supported by the protocol.
.RE

.sp
.LP
The \fBsocketpair()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 11n
The process does not have appropriate privileges.
.RE

.sp
.ne 2
.na
\fB\fBENOBUFS\fR\fR
.ad
.RS 11n
Insufficient resources were available in the system to perform the operation.
.RE

.sp
.ne 2
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 11n
Insufficient memory was available to fulfill the request.
.RE

.sp
.ne 2
.na
\fB\fBENOSR\fR\fR
.ad
.RS 11n
There were insufficient STREAMS resources available for the operation to
complete.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
\fBsocket\fR(3XNET), \fBattributes\fR(5), \fBstandards\fR(5)