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11 KiB
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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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Db::set_re_source()</title>
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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_re_pad.html" title="Db::set_re_pad()" />
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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_re_source()</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_re_pad.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="dbstat.html">Next</a></td>
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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_re_source"></a>Db::set_re_source()</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_cxx.h>
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int
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Db::set_re_source(char *source); </pre>
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<p>
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Set the underlying source file for the Recno access method. The
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purpose of the <span class="bold"><strong>source</strong></span> value is to
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provide fast access and modification to databases that are normally
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stored as flat text files.
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</p>
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<p>
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The <span class="bold"><strong>source</strong></span> parameter specifies an
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underlying flat text database file that is read to initialize a
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transient record number index. In the case of variable length
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records, the records are separated, as specified by
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<a class="xref" href="dbset_re_delim.html" title="Db::set_re_delim()">Db::set_re_delim()</a>. For
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example, standard UNIX byte stream files can be interpreted as a
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sequence of variable length records separated by <newline>
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characters.
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</p>
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<p>
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In addition, when cached data would normally be written back to the
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underlying database file (for example, the
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<a class="xref" href="dbclose.html" title="Db::close()">Db::close()</a> or
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<a class="xref" href="dbsync.html" title="Db::sync()">Db::sync()</a> methods are called),
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the in-memory copy of the database will be written back to the
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<span class="bold"><strong>source</strong></span> file.
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</p>
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<p>
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By default, the backing source file is read lazily; that is, records
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are not read from the file until they are requested by the
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application. <span class="bold"><strong>If multiple processes (not threads)
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are accessing a Recno database concurrently, and are either inserting
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or deleting records, the backing source file must be read in its
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entirety before more than a single process accesses the database, and
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only that process should specify the backing source file as part of
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the <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> call. See the
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<a class="link" href="dbset_flags.html#dbset_flags_DB_SNAPSHOT">DB_SNAPSHOT</a> flag
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for more information.</strong></span>
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</p>
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<p>
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<span class="bold"><strong>Reading and writing the backing source file
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specified by <span class="bold"><strong>source</strong></span> cannot be
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transaction-protected because it involves filesystem operations that
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are not part of the Db transaction methodology.</strong></span> For this
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reason, if a temporary database is used to hold the records, it is
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possible to lose the contents of the <span class="bold"><strong>source</strong></span> file, for example, if the system crashes
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at the right instant. If a file is used to hold the database, normal
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database recovery on that file can be used to prevent information
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loss, although it is still possible that the contents of <span class="bold"><strong>source</strong></span> will be lost if the system crashes.
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</p>
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<p>
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The <span class="bold"><strong>source</strong></span> file must already exist
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(but may be zero-length) when <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> is called.
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</p>
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<p>
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It is not an error to specify a read-only <span class="bold"><strong>source</strong></span> file when creating a database, nor is it
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an error to modify the resulting database. However, any attempt to
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write the changes to the backing source file using either the
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<a class="xref" href="dbsync.html" title="Db::sync()">Db::sync()</a> or
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<a class="xref" href="dbclose.html" title="Db::close()">Db::close()</a> methods will fail,
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of course. Specify the
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<a class="link" href="dbclose.html#dbclose_DB_NOSYNC">DB_NOSYNC</a> flag to the
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<a class="xref" href="dbclose.html" title="Db::close()">Db::close()</a> method to
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stop it from attempting to write the changes to the backing file;
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instead, they will be silently discarded.
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</p>
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<p>
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For all of the previous reasons, the <span class="bold"><strong>source</strong></span> field is generally used to specify
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databases that are read-only for Berkeley DB applications; and that
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are either generated on the fly by software tools or modified using a
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different mechanism — for example, a text editor.
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</p>
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<p>
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The <code class="methodname">Db::set_re_source()</code> method configures operations performed using
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the specified <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> handle,
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not all operations performed on the underlying database.
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</p>
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<p>
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The <code class="methodname">Db::set_re_source()</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
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<a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> is called, the
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information specified to <code class="methodname">Db::set_re_source()</code> must be the same as that
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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_re_source()</code> <span>
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<span>
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method either returns a non-zero error value or throws an
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exception that encapsulates a non-zero error value on
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failure, and returns 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="id3600063"></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="id3600074"></a>source</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 backing flat text database file for a Recno database.
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</p>
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<p>
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When using a Unicode build on Windows (the default), the
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<span class="bold"><strong>source</strong></span>
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argument will be interpreted as a UTF-8 string, which is equivalent to
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ASCII for Latin characters.
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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="id3599842"></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_re_source()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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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="id3600483"></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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If the method was called after <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a>
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was called; or if 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="id3600505"></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="id3600223"></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_re_pad.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="dbstat.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_re_pad() </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::stat()</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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