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 (a value of 0), the system selects a protocol that supports the requested socket type. The socket handle (a file descriptor) is returned.

The family is specified by one of the constants defined in sys/socket.h. Constants named AF_suite specify the address format to use in interpreting names, as shown in Table 2-1.

Table 2-1 Protocol Family

AF_APPLETALK	Apple Computer Inc. Appletalk network
AF_INET6	Internet family for IPv6 and IPv4
AF_INET	Internet family for IPv4 only
AF_PUP	Xerox Corporation PUP internet
AF_UNIX	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 creates a stream socket in the Internet family:

s = socket(AF_INET6, SOCK_STREAM, 0);

This call results in a stream socket with the TCP protocol providing the underlying communication. Use the default protocol (the protocol argument is 0) in most situations. You can specify a protocol other than the default, as described in "Advanced Topics".