2011-09-13 17:44:24 +00:00
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<title>DbEnv::set_alloc()</title>
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<p>Library Version 11.2.5.2</p>
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<table width="100%" summary="Navigation header">
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<th colspan="3" align="center">DbEnv::set_alloc()</th>
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<td width="20%" align="left"><a accesskey="p" href="envremove.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5.
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The DbEnv Handle
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<h2 class="title" style="clear: both"><a id="envset_alloc"></a>DbEnv::set_alloc()</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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extern "C" {
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typedef void *(*db_malloc_fcn_type)(size_t);
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typedef void *(*db_realloc_fcn_type)(void *, size_t);
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typedef void *(*db_free_fcn_type)(void *);
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};
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int
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DbEnv::set_alloc(db_malloc_fcn_type app_malloc,
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db_realloc_fcn_type app_realloc,
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db_free_fcn_type app_free);</pre>
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<p>
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Set the allocation functions used by the <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> and
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<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> methods to allocate or free
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memory owned by the application.
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</p>
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<p>
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There are a number of interfaces in Berkeley DB where memory is
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allocated by the library and then given to the application. For
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example, the <a class="link" href="dbt.html#dbt_DB_DBT_MALLOC">DB_DBT_MALLOC</a>
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flag, when specified in the <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a>
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object, will cause the <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> methods to allocate and
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reallocate memory which then becomes the responsibility of the calling
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application. Other examples are the Berkeley DB interfaces
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which return statistical information to the application:
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<a class="xref" href="dbstat.html" title="Db::stat()">Db::stat()</a>,
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<a class="xref" href="lockstat.html" title="DbEnv::lock_stat()">DbEnv::lock_stat()</a>,
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<a class="xref" href="logarchive.html" title="DbEnv::log_archive()">DbEnv::log_archive()</a>,
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<a class="xref" href="logstat.html" title="DbEnv::log_stat()">DbEnv::log_stat()</a>,
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<a class="xref" href="mempstat.html" title="DbEnv::memp_stat()">DbEnv::memp_stat()</a>, and
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<a class="xref" href="txnstat.html" title="DbEnv::txn_stat()">DbEnv::txn_stat()</a>. There is
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one method in Berkeley DB where memory is allocated by the application
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and then given to the library: the callback specified to
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<a class="xref" href="dbassociate.html" title="Db::associate()">Db::associate()</a>.
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</p>
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<p>
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On systems in which there may be multiple library versions of the
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standard allocation routines (notably Windows NT), transferring memory
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between the library and the application will fail because the Berkeley
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DB library allocates memory from a different heap than the application
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uses to free it. To avoid this problem, the <code class="methodname">DbEnv::set_alloc()</code> and
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<a class="xref" href="dbset_alloc.html" title="Db::set_alloc()">Db::set_alloc()</a>
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methods can be used to pass Berkeley DB references to the
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application's allocation routines.
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</p>
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<p>
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It is not an error to specify only one or two of the possible
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allocation function parameters to these interfaces; however, in that
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case the specified interfaces must be compatible with the standard
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library interfaces, as they will be used together. The functions
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specified must match the calling conventions of the ANSI C X3.159-1989
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(ANSI C) library routines of the same name.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_alloc()</code> method configures operations performed using
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the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
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handle, not all operations performed on the underlying database
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environment.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_alloc()</code> method may not be called after the
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<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_alloc()</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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3599790"></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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3599693"></a>app_malloc</h4>
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2011-09-13 17:44:24 +00:00
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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>app_malloc</strong></span> parameter is the
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application-specified malloc function.
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</p>
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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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3599786"></a>app_realloc</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>app_realloc</strong></span> parameter is the
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application-specified realloc function.
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</p>
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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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3599502"></a>app_free</h4>
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2011-09-13 17:44:24 +00:00
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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>app_free</strong></span> parameter is the
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application-specified free function.
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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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3600117"></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">DbEnv::set_alloc()</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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3600249"></a>EINVAL</h4>
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2011-09-13 17:44:24 +00:00
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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="envopen.html" title="DbEnv::open()">DbEnv::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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3600269"></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="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3598245"></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="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a>
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</p>
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</div>
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<td width="40%" align="left" valign="top">DbEnv::remove() </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 width="40%" align="right" valign="top"> DbEnv::set_app_dispatch()</td>
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