<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>DbEnv::set_alloc()</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> <link rel="up" href="env.html" title="Chapter 5. The DbEnv Handle" /> <link rel="prev" href="envremove.html" title="DbEnv::remove()" /> <link rel="next" href="envset_app_dispatch.html" title="DbEnv::set_app_dispatch()" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 11.2.5.3</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DbEnv::set_alloc()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="envremove.html">Prev</a> </td> <th width="60%" align="center">Chapter 5. The DbEnv Handle </th> <td width="20%" align="right"> <a accesskey="n" href="envset_app_dispatch.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="envset_alloc"></a>DbEnv::set_alloc()</h2> </div> </div> </div> <pre class="programlisting">#include <db_cxx.h> extern "C" { typedef void *(*db_malloc_fcn_type)(size_t); typedef void *(*db_realloc_fcn_type)(void *, size_t); typedef void *(*db_free_fcn_type)(void *); }; int DbEnv::set_alloc(db_malloc_fcn_type app_malloc, db_realloc_fcn_type app_realloc, db_free_fcn_type app_free);</pre> <p> Set the allocation functions used by the <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> and <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> methods to allocate or free memory owned by the application. </p> <p> There are a number of interfaces in Berkeley DB where memory is allocated by the library and then given to the application. For example, the <a class="link" href="dbt.html#dbt_DB_DBT_MALLOC">DB_DBT_MALLOC</a> flag, when specified in the <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a> object, will cause the <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> methods to allocate and reallocate memory which then becomes the responsibility of the calling application. Other examples are the Berkeley DB interfaces which return statistical information to the application: <a class="xref" href="dbstat.html" title="Db::stat()">Db::stat()</a>, <a class="xref" href="lockstat.html" title="DbEnv::lock_stat()">DbEnv::lock_stat()</a>, <a class="xref" href="logarchive.html" title="DbEnv::log_archive()">DbEnv::log_archive()</a>, <a class="xref" href="logstat.html" title="DbEnv::log_stat()">DbEnv::log_stat()</a>, <a class="xref" href="mempstat.html" title="DbEnv::memp_stat()">DbEnv::memp_stat()</a>, and <a class="xref" href="txnstat.html" title="DbEnv::txn_stat()">DbEnv::txn_stat()</a>. There is one method in Berkeley DB where memory is allocated by the application and then given to the library: the callback specified to <a class="xref" href="dbassociate.html" title="Db::associate()">Db::associate()</a>. </p> <p> On systems in which there may be multiple library versions of the standard allocation routines (notably Windows NT), transferring memory between the library and the application will fail because the Berkeley DB library allocates memory from a different heap than the application uses to free it. To avoid this problem, the <code class="methodname">DbEnv::set_alloc()</code> and <a class="xref" href="dbset_alloc.html" title="Db::set_alloc()">Db::set_alloc()</a> methods can be used to pass Berkeley DB references to the application's allocation routines. </p> <p> It is not an error to specify only one or two of the possible allocation function parameters to these interfaces; however, in that case the specified interfaces must be compatible with the standard library interfaces, as they will be used together. The functions specified must match the calling conventions of the ANSI C X3.159-1989 (ANSI C) library routines of the same name. </p> <p> The <code class="methodname">DbEnv::set_alloc()</code> method configures operations performed using the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle, not all operations performed on the underlying database environment. </p> <p> The <code class="methodname">DbEnv::set_alloc()</code> method may not be called after the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called. </p> <p> The <code class="methodname">DbEnv::set_alloc()</code> <span> <span> method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp7108152"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp7103800"></a>app_malloc</h4> </div> </div> </div> <p> The <span class="bold"><strong>app_malloc</strong></span> parameter is the application-specified malloc function. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp7108008"></a>app_realloc</h4> </div> </div> </div> <p> The <span class="bold"><strong>app_realloc</strong></span> parameter is the application-specified realloc function. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp7034512"></a>app_free</h4> </div> </div> </div> <p> The <span class="bold"><strong>app_free</strong></span> parameter is the application-specified free function. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp7127640"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DbEnv::set_alloc()</code> <span> <span> method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> exception, encapsulating one of the following non-zero errors, or return one of the following non-zero errors: </span> </span> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp7135520"></a>EINVAL</h4> </div> </div> </div> <p> If the method was called after <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> was called; or if an invalid flag value or parameter was specified. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp7136568"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp7045824"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="envremove.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="env.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="envset_app_dispatch.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DbEnv::remove() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DbEnv::set_app_dispatch()</td> </tr> </table> </div> </body> </html>