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| <h4 class="subsection">16.6.4 The Services Database</h4> |
| |
| <p><a name="index-services-database-1736"></a><a name="index-converting-service-name-to-port-number-1737"></a><a name="index-converting-port-number-to-service-name-1738"></a> |
| <a name="index-g_t_002fetc_002fservices-1739"></a>The database that keeps track of “well-known” services is usually |
| either the file <samp><span class="file">/etc/services</span></samp> or an equivalent from a name server. |
| You can use these utilities, declared in <samp><span class="file">netdb.h</span></samp>, to access |
| the services database. |
| <a name="index-netdb_002eh-1740"></a> |
| <!-- netdb.h --> |
| <!-- BSD --> |
| |
| <div class="defun"> |
| — Data Type: <b>struct servent</b><var><a name="index-struct-servent-1741"></a></var><br> |
| <blockquote><p>This data type holds information about entries from the services database. |
| It has the following members: |
| |
| <dl> |
| <dt><code>char *s_name</code><dd>This is the “official” name of the service. |
| |
| <br><dt><code>char **s_aliases</code><dd>These are alternate names for the service, represented as an array of |
| strings. A null pointer terminates the array. |
| |
| <br><dt><code>int s_port</code><dd>This is the port number for the service. Port numbers are given in |
| network byte order; see <a href="Byte-Order.html#Byte-Order">Byte Order</a>. |
| |
| <br><dt><code>char *s_proto</code><dd>This is the name of the protocol to use with this service. |
| See <a href="Protocols-Database.html#Protocols-Database">Protocols Database</a>. |
| </dl> |
| </p></blockquote></div> |
| |
| <p>To get information about a particular service, use the |
| <code>getservbyname</code> or <code>getservbyport</code> functions. The information |
| is returned in a statically-allocated structure; you must copy the |
| information if you need to save it across calls. |
| |
| <!-- netdb.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: struct servent * <b>getservbyname</b> (<var>const char *name, const char *proto</var>)<var><a name="index-getservbyname-1742"></a></var><br> |
| <blockquote><p>The <code>getservbyname</code> function returns information about the |
| service named <var>name</var> using protocol <var>proto</var>. If it can't find |
| such a service, it returns a null pointer. |
| |
| <p>This function is useful for servers as well as for clients; servers |
| use it to determine which port they should listen on (see <a href="Listening.html#Listening">Listening</a>). |
| </p></blockquote></div> |
| |
| <!-- netdb.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: struct servent * <b>getservbyport</b> (<var>int port, const char *proto</var>)<var><a name="index-getservbyport-1743"></a></var><br> |
| <blockquote><p>The <code>getservbyport</code> function returns information about the |
| service at port <var>port</var> using protocol <var>proto</var>. If it can't |
| find such a service, it returns a null pointer. |
| </p></blockquote></div> |
| |
| <p class="noindent">You can also scan the services database using <code>setservent</code>, |
| <code>getservent</code> and <code>endservent</code>. Be careful when using these |
| functions because they are not reentrant. |
| |
| <!-- netdb.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: void <b>setservent</b> (<var>int stayopen</var>)<var><a name="index-setservent-1744"></a></var><br> |
| <blockquote><p>This function opens the services database to begin scanning it. |
| |
| <p>If the <var>stayopen</var> argument is nonzero, this sets a flag so that |
| subsequent calls to <code>getservbyname</code> or <code>getservbyport</code> will |
| not close the database (as they usually would). This makes for more |
| efficiency if you call those functions several times, by avoiding |
| reopening the database for each call. |
| </p></blockquote></div> |
| |
| <!-- netdb.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: struct servent * <b>getservent</b> (<var>void</var>)<var><a name="index-getservent-1745"></a></var><br> |
| <blockquote><p>This function returns the next entry in the services database. If |
| there are no more entries, it returns a null pointer. |
| </p></blockquote></div> |
| |
| <!-- netdb.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: void <b>endservent</b> (<var>void</var>)<var><a name="index-endservent-1746"></a></var><br> |
| <blockquote><p>This function closes the services database. |
| </p></blockquote></div> |
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