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<a name="boost.xpressive.mark_tag"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct mark_tag</span></h2>
<p>boost::xpressive::mark_tag — Sub-match placeholder type, used to create named captures in static regexes. </p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<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="../../xpressive/reference.html#header.boost.xpressive.regex_primitives_hpp" title="Header <boost/xpressive/regex_primitives.hpp>">boost/xpressive/regex_primitives.hpp</a>>
</span>
<span class="keyword">struct</span> <a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a> <span class="special">{</span>
<span class="comment">// <a class="link" href="mark_tag.html#boost.xpressive.mark_tagconstruct-copy-destruct">construct/copy/destruct</a></span>
<a class="link" href="mark_tag.html#idm45506839611952-bb"><span class="identifier">mark_tag</span></a><span class="special">(</span><span class="keyword">int</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="mark_tag.html#idm45506839615344-bb">private static functions</a></span>
<span class="keyword">static</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <a class="link" href="mark_tag.html#idm45506839614768-bb"><span class="identifier">make_tag</span></a><span class="special">(</span><span class="keyword">int</span><span class="special">)</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555017447536"></a><h2>Description</h2>
<p><code class="computeroutput"><a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a></code> is the type of the global sub-match placeholders <code class="computeroutput">s0</code>, <code class="computeroutput">s1</code>, etc.. You can use the <code class="computeroutput"><a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a></code> type to create your own sub-match placeholders with more meaningful names. This is roughly equivalent to the "named capture" feature of dynamic regular expressions.</p>
<p>To create a named sub-match placeholder, initialize it with a unique integer. The integer must only be unique within the regex in which the placeholder is used. Then you can use it within static regexes to created sub-matches by assigning a sub-expression to it, or to refer back to already created sub-matches.</p>
<pre class="programlisting"><span class="identifier">mark_tag</span> <span class="identifier">number</span><span class="special">(</span><span class="number">1</span><span class="special">)</span><span class="special">;</span> <span class="comment">// "number" is now equivalent to "s1"</span>
<span class="comment">// Match a number, followed by a space and the same number again</span>
<span class="identifier">sregex</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">number</span> <span class="special">=</span> <span class="special">+</span><span class="identifier">_d</span><span class="special">)</span> <span class="special">>></span> <span class="char">' '</span> <span class="special">>></span> <span class="identifier">number</span><span class="special">;</span>
</pre>
<p>After a successful <code class="computeroutput">regex_match()</code> or <code class="computeroutput">regex_search()</code>, the sub-match placeholder can be used to index into the <code class="computeroutput"><a class="link" href="match_results.html" title="Struct template match_results">match_results</a><></code> object to retrieve the corresponding sub-match. </p>
<div class="refsect2">
<a name="idm45555017424784"></a><h3>
<a name="boost.xpressive.mark_tagconstruct-copy-destruct"></a><code class="computeroutput">mark_tag</code>
public
construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><a name="idm45506839611952-bb"></a><span class="identifier">mark_tag</span><span class="special">(</span><span class="keyword">int</span> mark_nbr<span class="special">)</span><span class="special">;</span></pre>Initialize a <code class="computeroutput"><a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a></code> placeholder. <p>
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<td><p><span class="term">Parameters:</span></p></td>
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<td><p><span class="term"><code class="computeroutput">mark_nbr</code></span></p></td>
<td><p>An integer that uniquely identifies this <code class="computeroutput"><code class="computeroutput"><a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a></code></code> within the static regexes in which this <code class="computeroutput"><code class="computeroutput"><a class="link" href="mark_tag.html" title="Struct mark_tag">mark_tag</a></code></code> will be used. </p></td>
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<td><p><span class="term">Requires:</span></p></td>
<td><p><code class="computeroutput">mark_nbr > 0</code> </p></td>
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</li></ol></div>
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<div class="refsect2">
<a name="idm45555017408848"></a><h3>
<a name="idm45506839615344-bb"></a><code class="computeroutput">mark_tag</code> private static functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><pre class="literallayout"><span class="keyword">static</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <a name="idm45506839614768-bb"></a><span class="identifier">make_tag</span><span class="special">(</span><span class="keyword">int</span> mark_nbr<span class="special">)</span><span class="special">;</span></pre></li></ol></div>
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<td align="right"><div class="copyright-footer">Copyright © 2007 Eric Niebler<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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