Socket-Addresses.html

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<h3 class="section">16.3 Socket Addresses</h3>

<p><a name="index-address-of-socket-1651"></a><a name="index-name-of-socket-1652"></a><a name="index-binding-a-socket-address-1653"></a><a name="index-socket-address-_0028name_0029-binding-1654"></a>The name of a socket is normally called an <dfn>address</dfn>.  The
functions and symbols for dealing with socket addresses were named
inconsistently, sometimes using the term &ldquo;name&rdquo; and sometimes using
&ldquo;address&rdquo;.  You can regard these terms as synonymous where sockets
are concerned.

   <p>A socket newly created with the <code>socket</code> function has no
address.  Other processes can find it for communication only if you
give it an address.  We call this <dfn>binding</dfn> the address to the
socket, and the way to do it is with the <code>bind</code> function.

   <p>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.

   <p>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 <code>IPPORT_RESERVED</code> (see <a href="Ports.html#Ports">Ports</a>).

   <p>The details of socket addresses vary depending on what namespace you are
using.  See <a href="Local-Namespace.html#Local-Namespace">Local Namespace</a>, or <a href="Internet-Namespace.html#Internet-Namespace">Internet Namespace</a>, for specific
information.

   <p>Regardless of the namespace, you use the same functions <code>bind</code> and
<code>getsockname</code> to set and examine a socket's address.  These
functions use a phony data type, <code>struct sockaddr *</code>, 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 <code>struct sockaddr *</code> when you pass it to
<code>bind</code>.

<ul class="menu">
<li><a accesskey="1" href="Address-Formats.html#Address-Formats">Address Formats</a>: 		About <code>struct sockaddr</code>. 
<li><a accesskey="2" href="Setting-Address.html#Setting-Address">Setting Address</a>: 		Binding an address to a socket. 
<li><a accesskey="3" href="Reading-Address.html#Reading-Address">Reading Address</a>: 		Reading the address of a socket. 
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