Programming Interfaces Guide

Socket Creation

The socket(3SOCKET) call creates a socket in the specified family and of the specified type.

s = socket(family, type, protocol);

If the protocol is unspecified, the system selects a protocol that supports the requested socket type. The socket handle is returned. The socket handle is a file descriptor.

The family is specified by one of the constants that are defined in sys/socket.h. Constants that are named AF_suite specify the address format to use in interpreting names:


Apple Computer Inc. Appletalk network


Internet family for IPv6 and IPv4


Internet family for IPv4 only


Xerox Corporation PUP internet


UNIX file system

Socket types are defined in sys/socket.h. These types, SOCK_STREAM, SOCK_DGRAM, or SOCK_RAW, are supported by AF_INET6, AF_INET, and AF_UNIX. The following example creates a stream socket in the Internet family:

s = socket(AF_INET6, SOCK_STREAM, 0);

This call results in a stream socket. The TCP protocol provides the underlying communication. Set the protocol argument to 0, the default, in most situations. You can specify a protocol other than the default, as described in Advanced Socket Topics.