# socketpair

## 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.
    


## NAME



           socketpair — create a pair of connected sockets
    


## SYNOPSIS



           #include <sys/socket.h>
    
           int socketpair(int _domain_ , int _type_ , int _protocol_ ,
               int _socket_vector_[2]);
    


## DESCRIPTION



           The _socketpair_() function shall create 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 shall be identical. The file descriptors used in
           referencing the created sockets shall be returned in
           _socket_vector_[0] and _socket_vector_[1].  The file descriptors shall
           be allocated as described in _Section 2.14_ , _File Descriptor_
           _Allocation_.
    
           The _socketpair_() function takes the following arguments:
    
           _domain_      Specifies the communications domain in which the
                       sockets are to be created.
    
           _type_        Specifies the type of sockets to be created.
    
           _protocol_    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.
    
           _socket_vector_
                       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 following socket
           types are defined; implementations may specify additional socket
           types:
    
           SOCK_STREAM   Provides sequenced, reliable, bidirectional,
                         connection-mode byte streams, and may provide a
                         transmission mechanism for out-of-band data.
    
           SOCK_DGRAM    Provides datagrams, which are connectionless-mode,
                         unreliable messages of fixed maximum length.
    
           SOCK_SEQPACKET
                         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.
    
           If the _protocol_ argument is non-zero, it shall specify a protocol
           that is supported by the address family. If the _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.
    
           The process may need to have appropriate privileges to use the
           _socketpair_() function or to create some sockets.
    


## RETURN VALUE



           Upon successful completion, this function shall return 0;
           otherwise, -1 shall be returned and _errno_ set to indicate the
           error, no file descriptors shall be allocated, and the contents of
           _socket_vector_ shall be left unmodified.
    


## ERRORS



           The _socketpair_() function shall fail if:
    
           **EAFNOSUPPORT**
                  The implementation does not support the specified address
                  family.
    
           **EMFILE** All, or all but one, of the file descriptors available to
                  the process are currently open.
    
           **ENFILE** No more file descriptors are available for the system.
    
           **EOPNOTSUPP**
                  The specified protocol does not permit creation of socket
                  pairs.
    
           **EPROTONOSUPPORT**
                  The protocol is not supported by the address family, or the
                  protocol is not supported by the implementation.
    
           **EPROTOTYPE**
                  The socket type is not supported by the protocol.
    
           The _socketpair_() function may fail if:
    
           **EACCES** The process does not have appropriate privileges.
    
           **ENOBUFS**
                  Insufficient resources were available in the system to
                  perform the operation.
    
           **ENOMEM** Insufficient memory was available to fulfill the request.
    
           _The following sections are informative._
    


## EXAMPLES



           None.
    


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


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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