1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>DbEnv</title> 7 <link rel="stylesheet" href="apiReference.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> 10 <link rel="up" href="env.html" title="Chapter��5.�� The DbEnv Handle" /> 11 <link rel="prev" href="envclose.html" title="DbEnv::close()" /> 12 <link rel="next" href="envdbremove.html" title="DbEnv::dbremove()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">DbEnv</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="envclose.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��5.�� 23 The DbEnv Handle 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="envdbremove.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="envcreate"></a>DbEnv</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db_cxx.h> 39 40class DbEnv { 41public: 42 DbEnv(u_int32 flags); 43 ~DbEnv(); 44 45 DB_ENV *DbEnv::get_DB_ENV(); 46 const DB_ENV *DbEnv::get_const_DB_ENV() const; 47 static DbEnv *DbEnv::get_DbEnv(DB_ENV *dbenv); 48 static const DbEnv *DbEnv::get_const_DbEnv(const DB_ENV *dbenv); 49 ... 50}; </pre> 51 <p> 52 The <code class="classname">DbEnv</code> object is the handle for a Berkeley DB environment ��� 53 a collection including support for some or all of caching, locking, logging and transaction subsystems, as well as 54 databases and log files. Methods of the <code class="classname">DbEnv</code> handle are used to configure the environment 55 as well as to operate on subsystems and databases in the environment. 56 </p> 57 <p> 58 <code class="classname">DbEnv</code> handles are free-threaded if the 59 <a class="link" href="envopen.html#envopen_DB_THREAD">DB_THREAD</a> flag is specified to the 60 <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method when the environment is opened. 61 The <code class="classname">DbEnv</code> handle should not be closed while any other handle 62 remains open that is using it as a reference (for example, 63 <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>). 64 Once either the 65 <a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or 66 <a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a> 67 methods are called, the handle may not be accessed again, regardless of the method's return. 68 </p> 69 <p> 70 The constructor creates the <code class="classname">DbEnv</code> object. 71 The constructor allocates memory internally; calling the 72 <a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or 73 <a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a> 74 methods will free that memory. 75 </p> 76 <p> 77 Before the handle may be used, you must open it using the 78 <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> 79 method. 80 </p> 81 <p> 82 The <span class="bold"><strong>flags</strong></span> parameter must be set to 0. 83 </p> 84 <div class="itemizedlist"> 85 <ul type="disc"> 86 <li> 87 <p><a id="env_DB_CXX_NO_EXCEPTIONS"></a> 88 <code class="literal">DB_CXX_NO_EXCEPTIONS</code> 89 </p> 90 <p> 91 The Berkeley DB C++ API supports two different error behaviors. By default, whenever an error 92 occurs, an exception is thrown that encapsulates the error information. This 93 generally allows for cleaner logic for transaction processing because a try block can 94 surround a single transaction. However, if 95 <code class="literal">DB_CXX_NO_EXCEPTIONS</code> is specified, exceptions 96 are not thrown; instead, each individual function returns an error code. 97 </p> 98 </li> 99 </ul> 100 </div> 101 <p> 102 Each <code class="classname">DbEnv</code> object has an associated <code class="literal">DB_ENV</code> 103 structure, which is used by the underlying implementation of Berkeley DB and its C-language 104 API. The <code class="methodname">DbEnv::get_DB_ENV()</code> method returns a pointer to this 105 struct. Given a <code class="literal">const DbEnv</code> object, 106 <code class="methodname">DbEnv::get_const_DB_ENV()</code> returns a const pointer to the same 107 struct. 108 </p> 109 <p> 110 Given a <code class="literal">DB_ENV</code> struct, the <code class="methodname">DbEnv::get_DbEnv()</code> 111 method returns the corresponding <code class="classname">DbEnv</code> object, 112 if there is one. If the <code class="literal">DB_ENV</code> struct was not associated with a 113 <code class="classname">DbEnv</code> (that is, it was not 114 returned from a call to <code class="methodname">DbEnv::get_DB_ENV()</code>), then the result of 115 <code class="methodname">DbEnv::get_DbEnv()</code> is 116 undefined. Given a <code class="literal">const DB_ENV</code> struct, 117 <code class="methodname">DbEnv::get_const_Db_Env()</code> returns the associated 118 <code class="literal">const DbEnv</code> object, if there is one. 119 </p> 120 <p> 121 These methods may be useful for Berkeley DB applications including both C and C++ language 122 software. It should not be necessary to use these calls in a purely C++ application. 123 </p> 124 <div class="sect2" lang="en" xml:lang="en"> 125 <div class="titlepage"> 126 <div> 127 <div> 128 <h3 class="title"><a id="id1663125"></a>Class</h3> 129 </div> 130 </div> 131 </div> 132 <p> 133 <a class="link" href="env.html" title="Chapter��5.�� The DbEnv Handle">DbEnv</a> 134 </p> 135 </div> 136 <div class="sect2" lang="en" xml:lang="en"> 137 <div class="titlepage"> 138 <div> 139 <div> 140 <h3 class="title"><a id="id1663348"></a>See Also</h3> 141 </div> 142 </div> 143 </div> 144 <p> 145 <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> 146 </p> 147 </div> 148 </div> 149 <div class="navfooter"> 150 <hr /> 151 <table width="100%" summary="Navigation footer"> 152 <tr> 153 <td width="40%" align="left"><a accesskey="p" href="envclose.html">Prev</a>��</td> 154 <td width="20%" align="center"> 155 <a accesskey="u" href="env.html">Up</a> 156 </td> 157 <td width="40%" align="right">��<a accesskey="n" href="envdbremove.html">Next</a></td> 158 </tr> 159 <tr> 160 <td width="40%" align="left" valign="top">DbEnv::close()��</td> 161 <td width="20%" align="center"> 162 <a accesskey="h" href="index.html">Home</a> 163 </td> 164 <td width="40%" align="right" valign="top">��DbEnv::dbremove()</td> 165 </tr> 166 </table> 167 </div> 168 </body> 169</html> 170