| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Function template let</title> |
| <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> |
| <link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> |
| <link rel="up" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp" title="Header <boost/xpressive/regex_actions.hpp>"> |
| <link rel="prev" href="check.html" title="Function template check"> |
| <link rel="next" href="construct_idp353112864.html" title="Function template construct"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> |
| <td align="center"><a href="../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="check.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="construct_idp353112864.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="refentry"> |
| <a name="boost.xpressive.let"></a><div class="titlepage"></div> |
| <div class="refnamediv"> |
| <h2><span class="refentrytitle">Function template let</span></h2> |
| <p>boost::xpressive::let — For binding local variables to placeholders in semantic actions when constructing a <code class="computeroutput"><a class="link" href="regex_iterator.html" title="Struct template regex_iterator">regex_iterator</a></code> or a <code class="computeroutput"><a class="link" href="regex_token_iterator.html" title="Struct template regex_token_iterator">regex_token_iterator</a></code>. </p> |
| </div> |
| <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_actions_hpp" title="Header <boost/xpressive/regex_actions.hpp>">boost/xpressive/regex_actions.hpp</a>> |
| |
| </span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span><span class="special">...</span> ArgBindings<span class="special">></span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="identifier">let</span><span class="special">(</span><span class="identifier">ArgBindings</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">...</span> args<span class="special">)</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="idp531949024"></a><h2>Description</h2> |
| <p> |
| <code class="computeroutput">xpressive::let()</code> serves the same purpose as <code class="computeroutput">match_results::let()</code>; that is, it binds a placeholder to a local value. The purpose is to allow a regex with semantic actions to be defined that refers to objects that do not yet exist. Rather than referring directly to an object, a semantic action can refer to a placeholder, and the value of the placeholder can be specified later with a <span class="emphasis"><em>let expression</em></span>. The <span class="emphasis"><em>let expression</em></span> created with <code class="computeroutput">let()</code> is passed to the constructor of either <code class="computeroutput"><code class="computeroutput"><a class="link" href="regex_iterator.html" title="Struct template regex_iterator">regex_iterator</a></code></code> or <code class="computeroutput"><code class="computeroutput"><a class="link" href="regex_token_iterator.html" title="Struct template regex_token_iterator">regex_token_iterator</a></code></code>.</p> |
| <p>See the section <a class="link" href="../../xpressive/user_s_guide.html#boost_xpressive.user_s_guide.semantic_actions_and_user_defined_assertions.referring_to_non_local_variables"> "Referring to Non-Local Variables"</a> in the Users' Guide for more discussion.</p> |
| <p><span class="emphasis"><em>Example:</em></span> </p> |
| <pre class="programlisting"><span class="comment">// Define a placeholder for a map object:</span> |
| <span class="identifier">placeholder</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">_map</span><span class="special">;</span> |
| |
| <span class="comment">// Match a word and an integer, separated by =>,</span> |
| <span class="comment">// and then stuff the result into a std::map<></span> |
| <span class="identifier">sregex</span> <span class="identifier">pair</span> <span class="special">=</span> <span class="special">(</span> <span class="special">(</span><span class="identifier">s1</span><span class="special">=</span> <span class="special">+</span><span class="identifier">_w</span><span class="special">)</span> <span class="special">>></span> <span class="string">"=>"</span> <span class="special">>></span> <span class="special">(</span><span class="identifier">s2</span><span class="special">=</span> <span class="special">+</span><span class="identifier">_d</span><span class="special">)</span> <span class="special">)</span> |
| <span class="special">[</span> <span class="identifier">_map</span><span class="special">[</span><span class="identifier">s1</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">as</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span><span class="special">(</span><span class="identifier">s2</span><span class="special">)</span> <span class="special">]</span><span class="special">;</span> |
| |
| <span class="comment">// The string to parse</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"aaa=>1 bbb=>23 ccc=>456"</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="comment">// Here is the actual map to fill in:</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="identifier">result</span><span class="special">;</span> |
| |
| <span class="comment">// Create a regex_iterator to find all the matches</span> |
| <span class="identifier">sregex_iterator</span> <span class="identifier">it</span><span class="special">(</span><span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">pair</span><span class="special">,</span> <span class="identifier">let</span><span class="special">(</span><span class="identifier">_map</span><span class="special">=</span><span class="identifier">result</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> |
| <span class="identifier">sregex_iterator</span> <span class="identifier">end</span><span class="special">;</span> |
| |
| <span class="comment">// step through all the matches, and fill in</span> |
| <span class="comment">// the result map</span> |
| <span class="keyword">while</span><span class="special">(</span><span class="identifier">it</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">)</span> |
| <span class="special">++</span><span class="identifier">it</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">result</span><span class="special">[</span><span class="string">"aaa"</span><span class="special">]</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">result</span><span class="special">[</span><span class="string">"bbb"</span><span class="special">]</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">result</span><span class="special">[</span><span class="string">"ccc"</span><span class="special">]</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| </pre> |
| <p> The above code displays:</p> |
| <pre class="programlisting"><span class="number">1</span> |
| <span class="number">23</span> |
| <span class="number">456</span> |
| </pre> |
| <p> </p> |
| <div class="variablelist"><table border="0" class="variablelist compact"> |
| <colgroup> |
| <col align="left" valign="top"> |
| <col> |
| </colgroup> |
| <tbody><tr> |
| <td><p><span class="term">Parameters:</span></p></td> |
| <td><div class="variablelist"><table border="0" class="variablelist compact"> |
| <colgroup> |
| <col align="left" valign="top"> |
| <col> |
| </colgroup> |
| <tbody><tr> |
| <td><p><span class="term"><code class="computeroutput">args</code></span></p></td> |
| <td><p>A set of argument bindings, where each argument binding is an assignment expression, the left hand side of which must be an instance of <code class="computeroutput">placeholder<X></code> for some <code class="computeroutput">X</code>, and the right hand side is an lvalue of type <code class="computeroutput">X</code>.</p></td> |
| </tr></tbody> |
| </table></div></td> |
| </tr></tbody> |
| </table></div> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <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>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="check.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="construct_idp353112864.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
