The name of a socket is normally called an address. The
functions and symbols for dealing with socket addresses were named
inconsistently, sometimes using the term “name” and sometimes using
“address”. You can regard these terms as synonymous where sockets
are concerned.
A socket newly created with the socket function has no
address. Other processes can find it for communication only if you
give it an address. We call this binding the address to the
socket, and the way to do it is with the bind function.
You need be concerned with the address of a socket if other processes
are to find it and start communicating with it. You can specify an
address for other sockets, but this is usually pointless; the first time
you send data from a socket, or use it to initiate a connection, the
system assigns an address automatically if you have not specified one.
Occasionally a client needs to specify an address because the server
discriminates based on address; for example, the rsh and rlogin
protocols look at the client's socket address and only bypass password
checking if it is less than IPPORT_RESERVED (see Ports).
The details of socket addresses vary depending on what namespace you are
using. See Local Namespace, or Internet Namespace, for specific
information.
Regardless of the namespace, you use the same functions bind and
getsockname to set and examine a socket's address. These
functions use a phony data type, struct sockaddr *, to accept the
address. In practice, the address lives in a structure of some other
data type appropriate to the address format you are using, but you cast
its address to struct sockaddr * when you pass it to
bind.
