478 lines
17 KiB
HTML
478 lines
17 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<!--
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- Copyright (C) 2001, 2004, 2005, 2007, 2014-2016 Internet Systems Consortium, Inc. ("ISC")
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-
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- This Source Code Form is subject to the terms of the Mozilla Public
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- License, v. 2.0. If a copy of the MPL was not distributed with this
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- file, You can obtain one at http://mozilla.org/MPL/2.0/.
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-->
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<html lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>lwres_gethostent</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry">
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<a name="id-1"></a><div class="titlepage"></div>
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<div class="refnamediv">
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<h2>Name</h2>
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<p>
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lwres_gethostbyname,
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lwres_gethostbyname2,
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lwres_gethostbyaddr,
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lwres_gethostent,
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lwres_sethostent,
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lwres_endhostent,
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lwres_gethostbyname_r,
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lwres_gethostbyaddr_r,
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lwres_gethostent_r,
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lwres_sethostent_r,
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lwres_endhostent_r
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— lightweight resolver get network host entry
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</p>
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</div>
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<div class="refsynopsisdiv">
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<h2>Synopsis</h2>
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<div class="funcsynopsis">
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<pre class="funcsynopsisinfo">#include <lwres/netdb.h></pre>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostbyname</b>(</code></td>
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<td>const char *<var class="pdparam">name</var><code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
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<tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostbyname2</b>(</code></td>
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<td>const char *<var class="pdparam">name</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">af</var><code>)</code>;</td>
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</tr>
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</table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
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<tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostbyaddr</b>(</code></td>
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<td>const char *<var class="pdparam">addr</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">len</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">type</var><code>)</code>;</td>
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</tr>
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</table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostent</b>(</code></td>
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<td>void<code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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void
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<b class="fsfunc">lwres_sethostent</b>(</code></td>
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<td>int <var class="pdparam">stayopen</var><code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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void
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<b class="fsfunc">lwres_endhostent</b>(</code></td>
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<td>void<code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
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<tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostbyname_r</b>(</code></td>
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<td>const char *<var class="pdparam">name</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>char *<var class="pdparam">buf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">buflen</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int *<var class="pdparam">error</var><code>)</code>;</td>
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</tr>
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</table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
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<tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostbyaddr_r</b>(</code></td>
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<td>const char *<var class="pdparam">addr</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">len</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">type</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>char *<var class="pdparam">buf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">buflen</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int *<var class="pdparam">error</var><code>)</code>;</td>
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</tr>
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</table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;">
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<tr>
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<td><code class="funcdef">
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struct hostent *
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<b class="fsfunc">lwres_gethostent_r</b>(</code></td>
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<td>struct hostent *<var class="pdparam">resbuf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>char *<var class="pdparam">buf</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int <var class="pdparam">buflen</var>, </td>
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</tr>
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<tr>
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<td> </td>
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<td>int *<var class="pdparam">error</var><code>)</code>;</td>
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</tr>
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</table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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void
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<b class="fsfunc">lwres_sethostent_r</b>(</code></td>
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<td>int <var class="pdparam">stayopen</var><code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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<table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr>
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<td><code class="funcdef">
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void
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<b class="fsfunc">lwres_endhostent_r</b>(</code></td>
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<td>void<code>)</code>;</td>
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</tr></table>
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<div class="funcprototype-spacer"> </div>
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</div>
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</div>
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<div class="refsection">
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<a name="id-1.7"></a><h2>DESCRIPTION</h2>
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<p>
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These functions provide hostname-to-address and
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address-to-hostname lookups by means of the lightweight resolver.
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They are similar to the standard
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<span class="citerefentry">
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<span class="refentrytitle">gethostent</span>(3)
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</span>
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functions provided by most operating systems.
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They use a
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<span class="type">struct hostent</span>
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which is usually defined in
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<code class="filename"><namedb.h></code>.
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</p>
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<pre class="programlisting">
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struct hostent {
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char *h_name; /* official name of host */
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char **h_aliases; /* alias list */
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int h_addrtype; /* host address type */
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int h_length; /* length of address */
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char **h_addr_list; /* list of addresses from name server */
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};
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#define h_addr h_addr_list[0] /* address, for backward compatibility */
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</pre>
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<p>
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</p>
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<p>
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The members of this structure are:
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</p>
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<div class="variablelist"><dl class="variablelist">
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<dt><span class="term"><code class="constant">h_name</code></span></dt>
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<dd>
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<p>
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The official (canonical) name of the host.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">h_aliases</code></span></dt>
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<dd>
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<p>
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A NULL-terminated array of alternate names (nicknames) for the
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host.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">h_addrtype</code></span></dt>
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<dd>
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<p>
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The type of address being returned —
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<span class="type">PF_INET</span>
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or
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<span class="type">PF_INET6</span>.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">h_length</code></span></dt>
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<dd>
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<p>
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The length of the address in bytes.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">h_addr_list</code></span></dt>
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<dd>
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<p>
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A <span class="type">NULL</span>
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terminated array of network addresses for the host.
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Host addresses are returned in network byte order.
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</p>
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</dd>
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</dl></div>
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<p>
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</p>
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<p>
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For backward compatibility with very old software,
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<code class="constant">h_addr</code>
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is the first address in
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<code class="constant">h_addr_list.</code>
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</p>
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<p><code class="function">lwres_gethostent()</code>,
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<code class="function">lwres_sethostent()</code>,
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<code class="function">lwres_endhostent()</code>,
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<code class="function">lwres_gethostent_r()</code>,
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<code class="function">lwres_sethostent_r()</code>
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and
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<code class="function">lwres_endhostent_r()</code>
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provide iteration over the known host entries on systems that
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provide such functionality through facilities like
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<code class="filename">/etc/hosts</code>
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or NIS. The lightweight resolver does not currently implement
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these functions; it only provides them as stub functions that always
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return failure.
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</p>
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<p><code class="function">lwres_gethostbyname()</code>
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and <code class="function">lwres_gethostbyname2()</code> look up the
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hostname <em class="parameter"><code>name</code></em>.
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<code class="function">lwres_gethostbyname()</code> always looks for an
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IPv4 address while <code class="function">lwres_gethostbyname2()</code>
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looks for an address of protocol family
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<em class="parameter"><code>af</code></em>: either <span class="type">PF_INET</span> or
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<span class="type">PF_INET6</span> — IPv4 or IPV6 addresses
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respectively. Successful calls of the functions return a
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<span class="type">struct hostent</span>for the name that was looked up.
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<span class="type">NULL</span> is returned if the lookups by
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<code class="function">lwres_gethostbyname()</code> or
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<code class="function">lwres_gethostbyname2()</code> fail.
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</p>
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<p>
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Reverse lookups of addresses are performed by
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<code class="function">lwres_gethostbyaddr()</code>.
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<em class="parameter"><code>addr</code></em> is an address of length
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<em class="parameter"><code>len</code></em> bytes and protocol family
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<em class="parameter"><code>type</code></em> — <span class="type">PF_INET</span> or
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<span class="type">PF_INET6</span>.
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<code class="function">lwres_gethostbyname_r()</code> is a
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thread-safe function
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for forward lookups. If an error occurs, an error code is returned in
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<em class="parameter"><code>*error</code></em>.
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<em class="parameter"><code>resbuf</code></em> is a pointer to a
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<span class="type">struct hostent</span> which is initialised by a successful call to
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<code class="function">lwres_gethostbyname_r()</code>.
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<em class="parameter"><code>buf</code></em> is a buffer of length
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<em class="parameter"><code>len</code></em> bytes which is used to store the
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<code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
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<code class="constant">h_addr_list</code> elements of the
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<span class="type">struct hostent</span> returned in <em class="parameter"><code>resbuf</code></em>.
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Successful calls to <code class="function">lwres_gethostbyname_r()</code>
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return <em class="parameter"><code>resbuf</code></em>,
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which is a pointer to the <span class="type">struct hostent</span> it created.
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</p>
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<p><code class="function">lwres_gethostbyaddr_r()</code>
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is a thread-safe function
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that performs a reverse lookup of address <em class="parameter"><code>addr</code></em>
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which is <em class="parameter"><code>len</code></em> bytes long and is of
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protocol
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family <em class="parameter"><code>type</code></em> — <span class="type">PF_INET</span> or
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<span class="type">PF_INET6</span>. If an error occurs, the error code is returned
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in <em class="parameter"><code>*error</code></em>. The other function
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parameters are
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identical to those in <code class="function">lwres_gethostbyname_r()</code>.
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<em class="parameter"><code>resbuf</code></em> is a pointer to a
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<span class="type">struct hostent</span> which is initialised by a successful call to
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<code class="function">lwres_gethostbyaddr_r()</code>.
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<em class="parameter"><code>buf</code></em> is a buffer of length
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<em class="parameter"><code>len</code></em> bytes which is used to store the
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<code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
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<code class="constant">h_addr_list</code> elements of the
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<span class="type">struct hostent</span> returned in <em class="parameter"><code>resbuf</code></em>.
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Successful calls to <code class="function">lwres_gethostbyaddr_r()</code> return
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<em class="parameter"><code>resbuf</code></em>, which is a pointer to the
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<code class="function">struct hostent()</code> it created.
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</p>
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</div>
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<div class="refsection">
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<a name="id-1.8"></a><h2>RETURN VALUES</h2>
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<p>
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The functions
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<code class="function">lwres_gethostbyname()</code>,
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<code class="function">lwres_gethostbyname2()</code>,
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<code class="function">lwres_gethostbyaddr()</code>,
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and
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<code class="function">lwres_gethostent()</code>
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return NULL to indicate an error. In this case the global variable
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<span class="type">lwres_h_errno</span>
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will contain one of the following error codes defined in
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<code class="filename"><lwres/netdb.h></code>:
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</p>
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<div class="variablelist"><dl class="variablelist">
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<dt><span class="term"><code class="constant">HOST_NOT_FOUND</code></span></dt>
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<dd>
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<p>
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The host or address was not found.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">TRY_AGAIN</code></span></dt>
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<dd>
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<p>
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A recoverable error occurred, e.g., a timeout.
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Retrying the lookup may succeed.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">NO_RECOVERY</code></span></dt>
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<dd>
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<p>
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A non-recoverable error occurred.
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</p>
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</dd>
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<dt><span class="term"><code class="constant">NO_DATA</code></span></dt>
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<dd>
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<p>
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The name exists, but has no address information
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associated with it (or vice versa in the case
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of a reverse lookup). The code NO_ADDRESS
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is accepted as a synonym for NO_DATA for backwards
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compatibility.
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</p>
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</dd>
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</dl></div>
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<p>
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</p>
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<p><span class="citerefentry">
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<span class="refentrytitle">lwres_hstrerror</span>(3)
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</span>
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translates these error codes to suitable error messages.
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</p>
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<p><code class="function">lwres_gethostent()</code>
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and <code class="function">lwres_gethostent_r()</code>
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always return <span class="type">NULL</span>.
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</p>
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<p>
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Successful calls to <code class="function">lwres_gethostbyname_r()</code> and
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<code class="function">lwres_gethostbyaddr_r()</code> return
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<em class="parameter"><code>resbuf</code></em>, a pointer to the
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<span class="type">struct hostent</span> that was initialised by these functions. They return
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<span class="type">NULL</span> if the lookups fail or if <em class="parameter"><code>buf</code></em>
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was too small to hold the list of addresses and names referenced by
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the <code class="constant">h_name</code>, <code class="constant">h_aliases</code>, and
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<code class="constant">h_addr_list</code> elements of the
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<span class="type">struct hostent</span>.
|
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If <em class="parameter"><code>buf</code></em> was too small, both
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<code class="function">lwres_gethostbyname_r()</code> and
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<code class="function">lwres_gethostbyaddr_r()</code> set the global
|
||
variable
|
||
<span class="type">errno</span> to <span class="errorcode">ERANGE</span>.
|
||
</p>
|
||
|
||
</div>
|
||
<div class="refsection">
|
||
<a name="id-1.9"></a><h2>SEE ALSO</h2>
|
||
|
||
<p><span class="citerefentry">
|
||
<span class="refentrytitle">gethostent</span>(3)
|
||
</span>,
|
||
|
||
<span class="citerefentry">
|
||
<span class="refentrytitle">lwres_getipnode</span>(3)
|
||
</span>,
|
||
|
||
<span class="citerefentry">
|
||
<span class="refentrytitle">lwres_hstrerror</span>(3)
|
||
</span>
|
||
</p>
|
||
</div>
|
||
|
||
<div class="refsection">
|
||
<a name="id-1.10"></a><h2>BUGS</h2>
|
||
|
||
<p><code class="function">lwres_gethostbyname()</code>,
|
||
<code class="function">lwres_gethostbyname2()</code>,
|
||
<code class="function">lwres_gethostbyaddr()</code>
|
||
and
|
||
<code class="function">lwres_endhostent()</code>
|
||
are not thread safe; they return pointers to static data and
|
||
provide error codes through a global variable.
|
||
Thread-safe versions for name and address lookup are provided by
|
||
<code class="function">lwres_gethostbyname_r()</code>,
|
||
and
|
||
<code class="function">lwres_gethostbyaddr_r()</code>
|
||
respectively.
|
||
</p>
|
||
<p>
|
||
The resolver daemon does not currently support any non-DNS
|
||
name services such as
|
||
<code class="filename">/etc/hosts</code>
|
||
or
|
||
<span class="type">NIS</span>,
|
||
consequently the above functions don't, either.
|
||
</p>
|
||
</div>
|
||
</div></body>
|
||
</html>
|