302 lines
8.5 KiB
HTML
302 lines
8.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>res_send()--Send Buffered Domain Query</title>
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<!-- Begin Header Records ========================================== -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!-- Edited by Kersten Feb 02 -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<a name="Top_Of_Page"></a>
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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</script>
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<h2>res_send()--Send Buffered Domain Query or Update</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax<br>
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<pre>
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#include <sys/types.h>
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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#include <resolv.h>
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int res_send(char *<em>query_buffer</em>,
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int <em>query_buffer_length</em>,
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char *<em>answer_buffer</em>,
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int <em>answer_buffer_length</em>)
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</pre>
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<br>
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Service Program Name: QSOSRV2<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <em>res_send()</em> function is used to send a query or update message
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to a name server and retrieve a response.</p>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>query_buffer</strong></dt>
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<dd>(Input) The pointer to the query or update message.<br>
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<br>
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</dd>
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<dt><strong>query_buffer_length</strong></dt>
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<dd>(Input) The length of <em>query_buffer</em>.<br>
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<br>
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</dd>
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<dt><strong>answer_buffer</strong></dt>
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<dd>(Output) The pointer to where the response is stored.<br>
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<br>
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</dd>
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<dt><strong>answer_buffer_length</strong></dt>
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<dd>(Input) The size of the answer_buffer.</dd>
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</dl>
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<br>
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<h3>Authorities:</h3>
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<p>No authorization is required.</p>
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<br>
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<h3>Return Value</h3>
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<p><em>res_send()</em> returns an integer. Possible values are:</p>
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<ul>
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<li>-1 (unsuccessful)<br>
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<br>
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</li>
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<li>n (successful), where n is the actual size of the answer returned.</li>
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</ul>
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<br>
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<h3>Error Conditions</h3>
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<p>When the <em>res_send()</em> function fails, <em>res_send()</em> can set
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<em>errno</em> to one of the following:</p>
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<dl>
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<dt><em>[ECONNREFUSED]</em></dt>
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<dd><p>Not able to connect to a server.</p></dd>
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<dt><em>[ECONVERT]</em></dt>
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<dd><p>Either the input packet could not be translated
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to ASCII or the answer received could not be translated to the coded character
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set identifier (CCSID) currently in effect for the job.</p></dd>
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<dt><em>[EINVAL]</em></dt>
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<dd><p>One of the following reasons:</p>
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<p>An invalid length or NULL pointer was passed to <em>res_send()</em> or
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The <strong>_res</strong> could not be initialized properly or
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The <strong>_res</strong> appears to be initialized but the reserved field
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is not set to zeros.</p>
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<p><strong>Note:</strong> No attempt is made to initialize the
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<strong>_res</strong> structure if it was initialized previous to the
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<em>res_send()</em> being issued.</p></dd>
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<dt><em>[ESRCH]</em></dt>
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<dd><p>No DNS servers were specified in
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<em>nsaddr</em>.</p></dd>
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<dt><em>[ETIMEDOUT]</em></dt>
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<dd><p>A timeout received from a connected server.</p></dd>
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<dd><p>When the <em>res_send()</em> function fails, <em>h_errno</em> (defined in
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<strong><netdb.h></strong>) can also be set to one of the following:</p>
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<dl>
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<dt><em>HOST_NOT_FOUND</em></dt>
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<dd><p>Either the input packet could not be translated
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to ASCII or the answer received could not be translated to the coded character
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set identifier (CCSID) currently in effect for the job.</p></dd>
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<dt><em>NO_RECOVERY</em></dt>
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<dd><p>An invalid length or NULL pointer was passed to
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<em>res_send()</em> or the <strong>_res</strong> could not be initialized
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properly.</p></dd>
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</dl></dd></dl>
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<p><strong>Notes:</strong>
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<ul>
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<li>No attempt is made to initialize the
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<strong>_res</strong> structure if it was initialized previous to the
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<em>res_send()</em> being issued.<br><br></li>
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<li>There are numerous other values that <em>errno</em>
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can be set to by the sockets functions that <em>res_send()</em> calls. The
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above values are the only values that <em>res_send()</em> can specifically set.
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Refer to other sockets functions for the other values. <em>errno</em> is always
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set in an error condition, but <em>h_errno</em> is not necessarily set.</li>
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</ul>
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<p>After receiving an error reply packet, <em>res_send()</em> will set the
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<em>extended_error</em> field in the <em>state</em> structure to the last reply
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return code from the DNS server. See <arpa/nameser.h> for all possible
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values of <em>ns_rcode</em>.</p>
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<br>
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<h3>Usage Notes</h3>
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<ol>
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<li><em>res_send()</em> sends the query or update to the local name server and
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handles all timeouts and retries. The response packet is stored in
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<em>answer_buffer</em>.<br>
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<br>
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</li>
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<li><em>res_send()</em> calls <em>res_init()</em> if the <strong>_res</strong>
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structure has not been initialized.<br>
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<br>
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</li>
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<li><em>res_send()</em> uses the UDP protocol, except for the following cases
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in which it uses TCP to send the packet.
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<ul>
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<li>If the RES_USEVC or RES_STAYOPEN bits are set in the options field of the
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<strong>_res</strong> structure.<br>
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<br>
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</li>
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<li>If the configuration from Change TCP/IP Domain (CHGTCPDMN) specifies that
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the server protocol is TCP.<br>
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<br>
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</li>
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<li>If the truncation bit is set in the packet header on the response from a
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UDP packet, and RES_IGNTC is not set in the <strong>_res</strong>
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structure.</li>
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</ul>
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<br>
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</li>
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<li><em>res_send()</em> does not perform interactive queries and expects the
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name server to handle recursion.<br>
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<br>
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</li>
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<li><em>res_send()</em> assumes that the data passed to it is EBCDIC and is in
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the default coded character set identifier (CCSID) currently in effect for the
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job. It translates the data from the default CCSID currently in effect for the
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job to ASCII (CCSID 819) before the data is sent out to a name server. The
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response that it receives from the name server is returned in the default CCSID
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currently in effect for the job.<br>
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<br>
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</li>
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<li>Unless RES_NOCACHE was specified, <em>res_send()</em> checks the cached
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data for the answer to the query (but not for updates). If the answer is found
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and the time to live has not expired, it is returned to the calling program in
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<em>answer_buffer</em> and no attempt is made to send it on the network. If the
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time to live has expired, the entry is deleted from the cache, and the query is
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sent on the network. If the answer is not found in the cache,
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<em>res_send()</em> also sends the query on the network. When an answer is
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received from the network, it is placed in cache if it is an authoritative
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answer and is not the result of an inverse query. RES_NOCACHE does not stop
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answers from being cached. Authoritative negative replies, indicating the data
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does not exist, will also be cached.<br>
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<br>
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</li>
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<li>In a thread-enabled environment, the <strong>_res</strong> structure is
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shared among all threads within a process.</li>
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</ol>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li><a href="hstrerror.htm">hstrerror()</a>--Retrieve Resolver Error
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Message<br>
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<br>
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</li>
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<li><a href="resnsend.htm">res_nsend()</a>--Send Buffered Domain Query<br>
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<br>
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</li>
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<li><a href="reshostalias.htm">res_hostalias()</a>--Retrieve the host alias<br>
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<br>
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</li>
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<li><a href="resini.htm">res_init()</a>--Initialize _res Structure<br>
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<br>
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</li>
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<li><a href="resmkq.htm">res_mkquery()</a>--Place Domain Query in Buffer<br>
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<br>
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</li>
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<li><a href="resqry.htm">res_query()</a>--Send Domain Query<br>
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<br>
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</li>
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<li><a href="ressch.htm">res_search()</a>--Search for Domain Name<br>
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<br>
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</li>
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<li><a href="resclo.htm">res_close()</a>--Close Socket and Reset _res
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Structure<br>
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<br>
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</li>
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<li><a href="resxlt.htm">res_xlate()</a>--Translate DNS Packets</li>
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</ul>
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<br>
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<hr>
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API introduced: V3R1
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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