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21 <h2><span class="refentrytitle">Function template extract</span></h2>
22 <p>boost::log::extract</p>
24 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
25 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../attributes.html#header.boost.log.attributes.value_extraction_hpp" title="Header <boost/log/attributes/value_extraction.hpp>">boost/log/attributes/value_extraction.hpp</a>>
28 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> DescriptorT<span class="special">,</span> <span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="special">></span> <span class="keyword">class</span> ActorT<span class="special">></span>
29 <a class="link" href="result_of/extract.html" title="Struct template extract">result_of::extract</a><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">DescriptorT</span><span class="special">::</span><span class="identifier">value_type</span><span class="special">,</span> <span class="identifier">DescriptorT</span> <span class="special">></span><span class="special">::</span><span class="identifier">type</span>
30 <span class="identifier">extract</span><span class="special">(</span><span class="identifier">expressions</span><span class="special">::</span><span class="identifier">attribute_keyword</span><span class="special"><</span> <span class="identifier">DescriptorT</span><span class="special">,</span> <span class="identifier">ActorT</span> <span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> keyword<span class="special">,</span>
31 <span class="identifier">record</span> <span class="keyword">const</span> <span class="special">&</span> rec<span class="special">)</span><span class="special">;</span></pre></div>
32 <div class="refsect1">
33 <a name="idp93182368"></a><h2>Description</h2>
34 <p>The function extracts an attribute value from the view. The user has to explicitly specify the type or set of possible types of the attribute value to be extracted.</p>
38 <div class="variablelist"><table border="0" class="variablelist compact">
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45 <td><p><span class="term">Parameters:</span></p></td>
46 <td><div class="variablelist"><table border="0" class="variablelist compact">
48 <col align="left" valign="top">
53 <td><p><span class="term"><code class="computeroutput">keyword</code></span></p></td>
54 <td><p>The keyword of the attribute value to extract. </p></td>
57 <td><p><span class="term"><code class="computeroutput">rec</code></span></p></td>
58 <td><p>A log record. The attribute value will be sought among those associated with the record. </p></td>
64 <td><p><span class="term">Returns:</span></p></td>
65 <td><p>A <code class="computeroutput">value_ref</code> that refers to the extracted value, if found. An empty value otherwise. </p></td>
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73 <td align="right"><div class="copyright-footer">Copyright © 2007-2014 Andrey Semashev<p>
74 Distributed under the Boost Software License, Version 1.0. (See accompanying
75 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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