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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 “name” and sometimes using |
| “address”. 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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