The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


socketpair - create a pair of connected sockets


#include <sys/socket.h>

int socketpair(int domain, int type, int protocol,
               int socket_vector[2]);


The socketpair() function creates an unbound pair of connected sockets in a specified domain, of a specified type, under the protocol optionally specified by the protocol argument. The two sockets are identical. The file descriptors used in referencing the created sockets are returned in socket_vector[0] and socket_vector[1].

Specifies the communications domain in which the sockets are to be created.
Specifies the type of sockets to be created.
Specifies a particular protocol to be used with the sockets. Specifying a protocol of 0 causes socketpair() to use an unspecified default protocol appropriate for the requested socket type.
Specifies a 2-integer array to hold the file descriptors of the created socket pair.

The type 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:

Provides sequenced, reliable, bidirectional, connection-mode byte streams, and may provide a transmission mechanism for out-of-band data.
Provides datagrams, which are connectionless-mode, unreliable messages of fixed maximum length.
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.

If the protocol 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.

The process may need to have appropriate privileges to use the socketpair() function or to create some sockets.


Upon successful completion, this function returns 0. Otherwise, -1 is returned and errno is set to indicate the error.


The socketpair() function will fail if:
The implementation does not support the specified address family.
No more file descriptors are available for this process.
No more file descriptors are available for the system.
The specified protocol does not permit creation of socket pairs.

The protocol is not supported by the address family, or the protocol is not supported by the implementation.
The socket type is not supported by the protocol.

The socketpair() function may fail if:

The process does not have appropriate privileges.
Insufficient resources were available in the system to perform the operation.
Insufficient memory was available to fulfill the request.
There were insufficient STREAMS resources available for the operation to complete.


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.

The socketpair() function is used primarily with UNIX domain sockets and need not be supported for other domains.


socket(), <sys/socket.h>.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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