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<h2><span class="refentrytitle">Function template skip</span></h2>
<p>boost::xpressive::skip — Specify which characters to skip when matching a regex. </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>>
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<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Skip<span class="special">></span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="identifier">skip</span><span class="special">(</span><span class="identifier">Skip</span> <span class="keyword">const</span> <span class="special">&</span> skip<span class="special">)</span><span class="special">;</span></pre></div>
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<a name="idm45555016880592"></a><h2>Description</h2>
<p><code class="computeroutput">skip()</code> instructs the regex engine to skip certain characters when matching a regex. It is most useful for writing regexes that ignore whitespace. For instance, the following specifies a regex that skips whitespace and punctuation:</p>
<pre class="programlisting"><span class="comment">// A sentence is one or more words separated by whitespace</span>
<span class="comment">// and punctuation.</span>
<span class="identifier">sregex</span> <span class="identifier">word</span> <span class="special">=</span> <span class="special">+</span><span class="identifier">alpha</span><span class="special">;</span>
<span class="identifier">sregex</span> <span class="identifier">sentence</span> <span class="special">=</span> <span class="identifier">skip</span><span class="special">(</span><span class="identifier">set</span><span class="special">[</span><span class="identifier">_s</span> <span class="special">|</span> <span class="identifier">punct</span><span class="special">]</span><span class="special">)</span><span class="special">(</span> <span class="special">+</span><span class="identifier">word</span> <span class="special">)</span><span class="special">;</span>
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<p>The way it works in the above example is to insert <code class="computeroutput">keep(*set[_s | punct])</code> before each primitive within the regex. A "primitive" includes terminals like strings, character sets and nested regexes. A final <code class="computeroutput">*set[_s | punct]</code> is added to the end of the regex. The regex <code class="computeroutput">sentence</code> specified above is equivalent to the following:</p>
<pre class="programlisting"><span class="identifier">sregex</span> <span class="identifier">sentence</span> <span class="special">=</span> <span class="special">+</span><span class="special">(</span> <span class="identifier">keep</span><span class="special">(</span><span class="special">*</span><span class="identifier">set</span><span class="special">[</span><span class="identifier">_s</span> <span class="special">|</span> <span class="identifier">punct</span><span class="special">]</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">word</span> <span class="special">)</span>
<span class="special">>></span> <span class="special">*</span><span class="identifier">set</span><span class="special">[</span><span class="identifier">_s</span> <span class="special">|</span> <span class="identifier">punct</span><span class="special">]</span><span class="special">;</span>
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<th align="left">Note</th>
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<tr><td align="left" valign="top"><p>Skipping does not affect how nested regexes are handled because they are treated atomically. String literals are also treated atomically; that is, no skipping is done within a string literal. So <code class="computeroutput">skip(_s)("this that")</code> is not the same as <code class="computeroutput">skip(_s)("this" >> as_xpr("that"))</code>. The first will only match when there is only one space between "this" and "that". The second will skip any and all whitespace between "this" and "that".</p></td></tr>
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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">skip</code></span></p></td>
<td><p>A regex that specifies which characters to skip. </p></td>
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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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