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<title>Why my application fails to link with Boost.Log? What's the fuss about library namespaces?</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="log.rationale.namespace_mangling"></a><a class="link" href="namespace_mangling.html" title="Why my application fails to link with Boost.Log? What's the fuss about library namespaces?">Why my application
fails to link with Boost.Log? What's the fuss about library namespaces?</a>
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<p>
The library declares the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">log</span></code> namespace
which should be used in client code to access library components. However,
internally the library uses another nested namespace for actual implementation.
The namespace name is configuration and platform dependent, it can change
between different releases of the library, so it should never be used in
the user side code. This is done in order to make the library configuration
synchronized with the application as much as possible and eliminate problems
caused by configuration mismatch.
</p>
<p>
Most of the time users won't even notice the existence of this internal namespace,
but it often appears in compiler and linker errors and in some cases it is
useful to know how to decode its name. Currently, the namespace name is composed
from the following elements:
</p>
<pre class="programlisting"><version><linkage>_<threading>_<system></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The <code class="computeroutput"><span class="special"><</span><span class="identifier">version</span><span class="special">></span></code> component describes the library major
version. It is currently <code class="computeroutput"><span class="identifier">v2</span></code>.
</li>
<li class="listitem">
The <code class="computeroutput"><span class="special"><</span><span class="identifier">linkage</span><span class="special">></span></code> component tells whether the library
is linked statically or dynamically. It is <code class="computeroutput"><span class="identifier">s</span></code>
if the library is linked statically and empty otherwise.
</li>
<li class="listitem">
The <code class="computeroutput"><span class="special"><</span><span class="identifier">threading</span><span class="special">></span></code> component is <code class="computeroutput"><span class="identifier">st</span></code>
for single-threaded builds and <code class="computeroutput"><span class="identifier">mt</span></code>
for multi-threaded ones.
</li>
<li class="listitem">
The <code class="computeroutput"><span class="special"><</span><span class="identifier">system</span><span class="special">></span></code> component describes the underlying
OS API used by the library. Currently, it is only specified for multi-threaded
builds. Depending on the target platform and configuration, it can be
<code class="computeroutput"><span class="identifier">posix</span></code>, <code class="computeroutput"><span class="identifier">nt5</span></code> or <code class="computeroutput"><span class="identifier">nt6</span></code>.
</li>
</ul></div>
<p>
As a couple quick examples, <code class="computeroutput"><span class="identifier">v2s_st</span></code>
corresponds to v2 static single-threaded build of the library and <code class="computeroutput"><span class="identifier">v2_mt_posix</span></code> - to v2 dynamic multi-threaded
build for POSIX system API.
</p>
<p>
Namespace mangling may lead to linking errors if the application is misconfigured.
One common mistake is to build dynamic version of the library and not define
<code class="computeroutput"><span class="identifier">BOOST_LOG_DYN_LINK</span></code> or <code class="computeroutput"><span class="identifier">BOOST_ALL_DYN_LINK</span></code> when building the application,
so that the library assumes static linking by default. Whenever such linking
errors appear, one can decode the namespace name in the missing symbols and
the exported symbols of Boost.Log library and adjust library or application
<a class="link" href="../installation/config.html" title="Configuring and building the library">configuration</a> accordingly.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2007-2015 Andrey
Semashev<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>).
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