2011-09-13 17:44:24 +00:00
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DbEnv</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="env.html" title="Chapter 5. The DbEnv Handle" />
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<link rel="prev" href="envclose.html" title="DbEnv::close()" />
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<link rel="next" href="envdbremove.html" title="DbEnv::dbremove()" />
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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">DbEnv</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="envclose.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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</th>
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<td width="20%" align="right"> <a accesskey="n" href="envdbremove.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="envcreate"></a>DbEnv</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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class DbEnv {
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public:
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DbEnv(u_int32 flags);
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~DbEnv();
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DB_ENV *DbEnv::get_DB_ENV();
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const DB_ENV *DbEnv::get_const_DB_ENV() const;
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static DbEnv *DbEnv::get_DbEnv(DB_ENV *dbenv);
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static const DbEnv *DbEnv::get_const_DbEnv(const DB_ENV *dbenv);
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...
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}; </pre>
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<p>
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The <code class="classname">DbEnv</code> object is the handle for a Berkeley DB environment —
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a collection including support for some or all of caching, locking, logging and transaction subsystems, as well as
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databases and log files. Methods of the <code class="classname">DbEnv</code> handle are used to configure the environment
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as well as to operate on subsystems and databases in the environment.
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</p>
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<p>
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<code class="classname">DbEnv</code> handles are free-threaded if the
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<a class="link" href="envopen.html#envopen_DB_THREAD">DB_THREAD</a> flag is specified to the
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<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method when the environment is opened.
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The <code class="classname">DbEnv</code> handle should not be closed while any other handle
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remains open that is using it as a reference (for example,
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<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> or <a class="link" href="txn.html" title="Chapter 13. The DbTxn Handle">DbTxn</a>).
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Once either the
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<a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or
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<a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a>
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methods are called, the handle may not be accessed again, regardless of the method's return.
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</p>
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<p>
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The constructor creates the <code class="classname">DbEnv</code> object.
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The constructor allocates memory internally; calling the
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<a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or
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<a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a>
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methods will free that memory.
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</p>
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<p>
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Before the handle may be used, you must open it using the
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<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
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method.
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</p>
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<p>
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The <span class="bold"><strong>flags</strong></span> parameter must be set to 0.
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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><a id="env_DB_CXX_NO_EXCEPTIONS"></a>
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<code class="literal">DB_CXX_NO_EXCEPTIONS</code>
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</p>
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<p>
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The Berkeley DB C++ API supports two different error behaviors. By default, whenever an error
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occurs, an exception is thrown that encapsulates the error information. This
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generally allows for cleaner logic for transaction processing because a try block can
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surround a single transaction. However, if
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<code class="literal">DB_CXX_NO_EXCEPTIONS</code> is specified, exceptions
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are not thrown; instead, each individual function returns an error code.
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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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Each <code class="classname">DbEnv</code> object has an associated <code class="literal">DB_ENV</code>
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structure, which is used by the underlying implementation of Berkeley DB and its C-language
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API. The <code class="methodname">DbEnv::get_DB_ENV()</code> method returns a pointer to this
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struct. Given a <code class="literal">const DbEnv</code> object,
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<code class="methodname">DbEnv::get_const_DB_ENV()</code> returns a const pointer to the same
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struct.
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</p>
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<p>
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Given a <code class="literal">DB_ENV</code> struct, the <code class="methodname">DbEnv::get_DbEnv()</code>
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method returns the corresponding <code class="classname">DbEnv</code> object,
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if there is one. If the <code class="literal">DB_ENV</code> struct was not associated with a
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<code class="classname">DbEnv</code> (that is, it was not
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returned from a call to <code class="methodname">DbEnv::get_DB_ENV()</code>), then the result of
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<code class="methodname">DbEnv::get_DbEnv()</code> is
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undefined. Given a <code class="literal">const DB_ENV</code> struct,
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<code class="methodname">DbEnv::get_const_Db_Env()</code> returns the associated
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<code class="literal">const DbEnv</code> object, if there is one.
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</p>
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<p>
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These methods may be useful for Berkeley DB applications including both C and C++ language
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software. It should not be necessary to use these calls in a purely C++ application.
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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="id3593115"></a>Class</h3>
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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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<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="id3592641"></a>See Also</h3>
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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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<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"><a accesskey="p" href="envclose.html">Prev</a> </td>
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<a accesskey="u" href="env.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="envdbremove.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">DbEnv::close() </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"> DbEnv::dbremove()</td>
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</tr>
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</table>
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</body>
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