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HTML
219 lines
9.2 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DB->set_dup_compare()</title>
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<link rel="stylesheet" href="apiReference.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB C API Reference" />
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<link rel="up" href="db.html" title="Chapter 2. The DB Handle" />
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<link rel="prev" href="dbset_create_dir.html" title="DB->set_create_dir()" />
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<link rel="next" href="dbset_encrypt.html" title="DB->set_encrypt()" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DB->set_dup_compare()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbset_create_dir.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The DB Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbset_encrypt.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="dbset_dup_compare"></a>DB->set_dup_compare()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB->set_dup_compare(DB *db,
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int (*dup_compare_fcn)(DB *db, const DBT *dbt1, const DBT *dbt2)); </pre>
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<p>
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Set the duplicate data item comparison function. The comparison
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function is called whenever it is necessary to compare a data item
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specified by the application with a data item currently stored in the
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database. Calling <code class="methodname">DB->set_dup_compare()</code> implies calling
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<a class="xref" href="dbset_flags.html" title="DB->set_flags()">DB->set_flags()</a> with the
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<a class="link" href="dbset_flags.html#dbset_flags_DB_DUPSORT">DB_DUPSORT</a>
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flag.
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</p>
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<p>
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If no comparison function is specified, the data items are compared
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lexically, with shorter data items collating before longer data items.
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</p>
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<p>
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The <code class="methodname">DB->set_dup_compare()</code> method may not be called after the
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<a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called. If
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the database already exists when <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a>
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is called, the information specified to <code class="methodname">DB->set_dup_compare()</code> must be the same as
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that historically used to create the database or corruption can occur.
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</p>
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<p>
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The <code class="methodname">DB->set_dup_compare()</code> <span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3866741"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3866876"></a>dup_compare_fcn</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>dup_compare_fcn</strong></span> function is the
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application-specified duplicate data item comparison function. The
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function takes three arguments:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">db</code>
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</p>
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<p>
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The <span class="bold"><strong>db</strong></span> parameter is the enclosing
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database handle.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">dbt1</code>
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</p>
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<p>
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The <span class="bold"><strong>dbt1</strong></span> parameter is a
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<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the application
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supplied data item.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">dbt2</code>
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</p>
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<p>
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The <span class="bold"><strong>dbt2</strong></span> parameter is a
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<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the current
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tree's data item.
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</p>
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</li>
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</ul>
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</div>
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<p>
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The <span class="bold"><strong>dup_compare_fcn</strong></span> function must return an
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integer value less than, equal to, or greater than zero if the first data item
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parameter is considered to be respectively less than, equal to, or greater than
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the second data item parameter. In addition, the comparison function must cause
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the data items in the set to be <span class="emphasis"><em>well-ordered</em></span>. The
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comparison function must correctly handle any data item values used by the
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application (possibly including zero-length data items). The
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<span class="bold"><strong>data</strong></span> and <span class="bold"><strong>size</strong></span>
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fields of the <a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> are the only fields
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that may be used for the purposes of this comparison, and no particular
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alignment of the memory to which the <span class="bold"><strong>data</strong></span> field
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refers may be assumed.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3867065"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DB->set_dup_compare()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3867265"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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An invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3867241"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3867283"></a>See Also</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="dbset_create_dir.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="db.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dbset_encrypt.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">DB->set_create_dir() </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> DB->set_encrypt()</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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