Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_cxx/env_class.html
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<!--$Id: env_class.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DbEnv</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>DbEnv</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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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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<p>
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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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};
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbEnv</b>
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<p>The DbEnv object is the handle for a Berkeley DB environment -- a
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collection including support for some or all of caching, locking,
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logging and transaction subsystems, as well as databases and log files.
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Methods of the DbEnv handle are used to configure the
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environment as well as to operate on subsystems and databases in the
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environment.</p>
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<p>DbEnv handles are free-threaded if the <a href="../api_cxx/env_open.html#DB_THREAD">DB_THREAD</a> flag
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is specified to the <a href="../api_cxx/env_open.html">DbEnv::open</a> method when the environment is opened.
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The DbEnv handle should not be closed while any other handle
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remains open that is using it as a reference (for example, <a href="../api_cxx/db_class.html">Db</a>
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or <a href="../api_cxx/txn_class.html">DbTxn</a>). Once either the <a href="../api_cxx/env_close.html">DbEnv::close</a> or
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<a href="../api_cxx/env_remove.html">DbEnv::remove</a> methods are called, the handle may not be accessed again,
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regardless of the method's return.</p>
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<p>The constructor creates the DbEnv object. The constructor
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allocates memory internally; calling the <a href="../api_cxx/env_close.html">DbEnv::close</a> or
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<a href="../api_cxx/env_remove.html">DbEnv::remove</a> methods will free that memory.</p>
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<p>The following <b>flags</b> value may be specified:</p>
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<br>
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<b><a name="DB_CXX_NO_EXCEPTIONS">DB_CXX_NO_EXCEPTIONS</a></b><ul compact><li>The Berkeley DB C++ API supports two different error behaviors. By default,
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whenever an error occurs, an exception is thrown that encapsulates the
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error information. This generally allows for cleaner logic for
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transaction processing because a try block can surround a single
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transaction. However, if DB_CXX_NO_EXCEPTIONS is specified,
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exceptions are not thrown; instead, each individual function returns an
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error code.</ul>
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<b><a name="DB_RPCCLIENT">DB_RPCCLIENT</a></b><ul compact><li>Create a client environment to connect to a server.</ul>
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<p>The DB_RPCCLIENT flag indicates to the system that this environment
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is remote on a server. The use of this flag causes the environment
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methods to use functions that call a server instead of local functions.
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Prior to making any environment or database method calls, the application
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must call the <a href="../api_cxx/env_set_rpc_server.html">DbEnv::set_rpc_server</a> function to establish the
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connection to the server.</p>
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<br>
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<p>Each DbEnv object has an associated DB_ENV structure,
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which is used by the underlying implementation of Berkeley DB and its
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C-language API. The DbEnv::get_DB_ENV method returns a pointer to this
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struct. Given a const DbEnv object, DbEnv::get_const_DB_ENV
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returns a const pointer to the same struct.</p>
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<p>Given a DB_ENV struct, the DbEnv::get_DbEnv method returns the
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corresponding DbEnv object, if there is one. If the
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DB_ENV object was not associated with a DbEnv (that is,
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it was not returned from a call to DbEnv::get_DB_ENV), then the result
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of DbEnv::get_DbEnv is undefined. Given a const DB_ENV struct,
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DbEnv::get_const_Db_Env returns the associated const DbEnv
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object, if there is one.</p>
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<p>These methods may be useful for Berkeley DB applications including both C
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and C++ language software. It should not be necessary to use these
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calls in a purely C++ application.</p>
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<hr size=1 noshade>
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<br><b>Class</b>
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DbEnv
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<br><b>See Also</b>
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<a href="../api_cxx/env_list.html">Database Environments and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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