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<h2 class="title" style="clear: both"><a id="envset_alloc"></a>DbEnv::set_alloc()</h2>
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<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">
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<h3 class="title"><a id="id1669213"></a>Parameters</h3>
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<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1669219"></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="id1669339"></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>
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<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
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<div>
<h4 class="title"><a id="id1669353"></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>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
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<div>
<h3 class="title"><a id="id1669369"></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="id1668897"></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">
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<div>
<h3 class="title"><a id="id1669274"></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">
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<div>
<h3 class="title"><a id="id1669239"></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>
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