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<b>DbEnv::set_alloc</b>
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<b><pre>
#include <db_cxx.h>
<p>
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 *);
};
<p>
int
DbEnv::set_alloc(db_malloc_fcn_type app_malloc,
db_realloc_fcn_type app_realloc,
db_free_fcn_type app_free);
</pre></b>
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<b>Description: DbEnv::set_alloc</b>
<p>Set the allocation functions used by the <a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a> and <a href="../../db4-devel-4.7.25/api_cxx/db_class.html">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 href="../../db4-devel-4.7.25/api_cxx/dbt_class.html#DB_DBT_MALLOC">DB_DBT_MALLOC</a> flag, when specified in the <a href="../../db4-devel-4.7.25/api_cxx/dbt_class.html">Dbt</a> object,
will cause the <a href="../../db4-devel-4.7.25/api_cxx/db_class.html">Db</a> methods to allocate and reallocate memory
which then becomes the responsibility of the calling application. (See
<a href="../../db4-devel-4.7.25/api_cxx/dbt_class.html">Dbt</a> for more information.) Other examples are the Berkeley DB
interfaces which return statistical information to the application:
<a href="../../db4-devel-4.7.25/api_cxx/db_stat.html">Db::stat</a>, <a href="../../db4-devel-4.7.25/api_cxx/lock_stat.html">DbEnv::lock_stat</a>, <a href="../../db4-devel-4.7.25/api_cxx/log_archive.html">DbEnv::log_archive</a>,
<a href="../../db4-devel-4.7.25/api_cxx/log_stat.html">DbEnv::log_stat</a>, <a href="../../db4-devel-4.7.25/api_cxx/memp_stat.html">DbEnv::memp_stat</a>, and <a href="../../db4-devel-4.7.25/api_cxx/txn_stat.html">DbEnv::txn_stat</a>. There is one
method in Berkeley DB where memory is allocated by the application and then
given to the library: <a href="../../db4-devel-4.7.25/api_cxx/db_associate.html">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 DbEnv::set_alloc and
<a href="../../db4-devel-4.7.25/api_cxx/db_set_alloc.html">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 DbEnv::set_alloc method configures operations performed using the specified
<a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a> handle, not all operations performed on the underlying
database environment.</p>
<p>The DbEnv::set_alloc method may not be called after the <a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> method is
called.
</p>
<p>The DbEnv::set_alloc 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.
</p>
<b>Parameters</b> <br>
<b>app_malloc</b><ul compact><li>The <b>app_malloc</b> parameter is the application-specified malloc
function.</ul>
<b>app_realloc</b><ul compact><li>The <b>app_realloc</b> parameter is the application-specified realloc
function.</ul>
<b>app_free</b><ul compact><li>The <b>app_free</b> parameter is the application-specified free function.</ul>
<br>
<br><b>Errors</b>
<p>The DbEnv::set_alloc method
may fail and throw
<a href="../../db4-devel-4.7.25/api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:</p>
<br>
<b>EINVAL</b><ul compact><li>If the method was called after <a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> was called; or if an
invalid flag value or parameter was specified.</ul>
<br>
<hr size=1 noshade>
<br><b>Class</b>
<a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a>
<br><b>See Also</b>
<a href="../../db4-devel-4.7.25/api_cxx/env_list.html">Database Environments and Related Methods</a>
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