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<h2 class="title" style="clear: both"><a id="envset_errcall"></a>DbEnv::set_errcall()</h2>
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<pre class="programlisting">#include <db_cxx.h>
void DbEnv::set_errcall(void (*db_errcall_fcn)
(const Dbenv *dbenv, const char *errpfx, const char *msg));</pre>
<p>
When an error occurs in the Berkeley DB library,
<span>
an exception is thrown
</span>
or an error return value is returned by the interface. In some cases,
however, the <span class="bold"><strong>errno</strong></span> value may be
insufficient to completely describe the cause of the error, especially
during initial application debugging.
</p>
<p>
The <code class="methodname">DbEnv::set_errcall()</code> and
<a class="xref" href="envset_errcall.html" title="DbEnv::set_errcall()">DbEnv::set_errcall()</a> methods
are used to enhance the mechanism for reporting error messages to the
application. In some cases, when an error occurs, Berkeley DB will
call <span class="bold"><strong>db_errcall_fcn</strong></span> with additional
error information. It is up to the <span class="bold"><strong>db_errcall_fcn</strong></span> function to display the error
message in an appropriate manner.
</p>
<p>
Setting <span class="bold"><strong>db_errcall_fcn</strong></span> to NULL
unconfigures the callback interface.
</p>
<p>
Alternatively, you can use the
<span>
<a class="xref" href="envset_error_stream.html" title="DbEnv::set_error_stream()">DbEnv::set_error_stream()</a>
and
<a class="xref" href="dbset_error_stream.html" title="Db::set_error_stream()">Db::set_error_stream()</a>
methods to display the additional information via an output stream, or the
</span>
<a class="xref" href="dbset_errfile.html" title="Db::set_errfile()">Db::set_errfile()</a> or
<a class="xref" href="envset_errfile.html" title="DbEnv::set_errfile()">Db::set_errfile()</a>
methods to display the additional information via a C library <code class="literal">FILE *</code>.
<span>You should not mix these approaches.</span>
</p>
<p>
This error-logging enhancement does not slow performance or
significantly increase application size, and may be run during normal
operation as well as during application debugging.
</p>
<p>
The <code class="methodname">DbEnv::set_errcall()</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_errcall()</code> method may be called at any time during the
life of the application.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Berkeley DB is not re-entrant. Callback functions should not attempt to make library
calls (for example, to release locks or close open handles). Re-entering Berkeley DB is
not guaranteed to work correctly, and the results are undefined.
</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div>
<h3 class="title"><a id="id1670569"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1670301"></a>db_errcall_fcn</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>db_errcall_fcn</strong></span> parameter is the
application-specified error reporting function. The function takes
three parameters:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">dbenv</code>
</p>
<p>
The <span class="bold"><strong>dbenv</strong></span> parameter is the enclosing
database environment.
</p>
</li>
<li>
<p>
<code class="literal">errpfx</code>
</p>
<p>
The <span class="bold"><strong>errpfx</strong></span> parameter is the prefix
string (as previously set by
<a class="xref" href="dbset_errpfx.html" title="Db::set_errpfx()">Db::set_errpfx()</a> or
<a class="xref" href="envset_errpfx.html" title="DbEnv::set_errpfx()">DbEnv::set_errpfx()</a>).
</p>
</li>
<li>
<p>
<code class="literal">msg</code>
</p>
<p>
The <span class="bold"><strong>msg</strong></span> parameter is the error
message string.
</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1671195"></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="id1670298"></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>
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