<!--$Id: env_class.so,v 10.45 2005/11/30 19:09:47 bostic Exp $--> <!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB: DbEnv</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <table width="100%"><tr valign=top> <td> <b>DbEnv</b> </td> <td align=right> <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></td> </tr></table> <hr size=1 noshade> <tt> <b><pre> #include <db_cxx.h> <p> class DbEnv { public: DbEnv(u_int32 flags); ~DbEnv(); <p> DB_ENV *DbEnv::get_DB_ENV(); const DB_ENV *DbEnv::get_const_DB_ENV() const; static DbEnv *DbEnv::get_DbEnv(DB_ENV *dbenv); static const DbEnv *DbEnv::get_const_DbEnv(const DB_ENV *dbenv); ... }; </pre></b> <hr size=1 noshade> <b>Description: DbEnv</b> <p>The DbEnv object is the handle for a Berkeley DB environment -- a collection including support for some or all of caching, locking, logging and transaction subsystems, as well as databases and log files. Methods of the DbEnv handle are used to configure the environment as well as to operate on subsystems and databases in the environment.</p> <p>DbEnv handles are free-threaded if the <a href="../api_cxx/env_open.html#DB_THREAD">DB_THREAD</a> flag is specified to the <a href="../api_cxx/env_open.html">DbEnv::open</a> method when the environment is opened. The DbEnv handle should not be closed while any other handle remains open that is using it as a reference (for example, <a href="../api_cxx/db_class.html">Db</a> or <a href="../api_cxx/txn_class.html">DbTxn</a>). Once either the <a href="../api_cxx/env_close.html">DbEnv::close</a> or <a href="../api_cxx/env_remove.html">DbEnv::remove</a> methods are called, the handle may not be accessed again, regardless of the method's return.</p> <p>The constructor creates the DbEnv object. The constructor allocates memory internally; calling the <a href="../api_cxx/env_close.html">DbEnv::close</a> or <a href="../api_cxx/env_remove.html">DbEnv::remove</a> methods will free that memory.</p> <p>The following <b>flags</b> value may be specified:</p> <br> <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, whenever an error occurs, an exception is thrown that encapsulates the error information. This generally allows for cleaner logic for transaction processing because a try block can surround a single transaction. However, if DB_CXX_NO_EXCEPTIONS is specified, exceptions are not thrown; instead, each individual function returns an error code.</ul> <b><a name="DB_RPCCLIENT">DB_RPCCLIENT</a></b><ul compact><li>Create a client environment to connect to a server.</ul> <p>The DB_RPCCLIENT flag indicates to the system that this environment is remote on a server. The use of this flag causes the environment methods to use functions that call a server instead of local functions. Prior to making any environment or database method calls, the application must call the <a href="../api_cxx/env_set_rpc_server.html">DbEnv::set_rpc_server</a> function to establish the connection to the server.</p> <br> <p>Each DbEnv object has an associated DB_ENV structure, which is used by the underlying implementation of Berkeley DB and its C-language API. The DbEnv::get_DB_ENV method returns a pointer to this struct. Given a const DbEnv object, DbEnv::get_const_DB_ENV returns a const pointer to the same struct.</p> <p>Given a DB_ENV struct, the DbEnv::get_DbEnv method returns the corresponding DbEnv object, if there is one. If the DB_ENV object was not associated with a DbEnv (that is, it was not returned from a call to DbEnv::get_DB_ENV), then the result of DbEnv::get_DbEnv is undefined. Given a const DB_ENV struct, DbEnv::get_const_Db_Env returns the associated const DbEnv object, if there is one.</p> <p>These methods may be useful for Berkeley DB applications including both C and C++ language software. It should not be necessary to use these calls in a purely C++ application.</p> <hr size=1 noshade> <br><b>Class</b> DbEnv <br><b>See Also</b> <a href="../api_cxx/env_list.html">Database Environments and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <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> </td></tr></table> <p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> </body> </html>