1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
|
<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_idp163632632.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_idp163632632.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="idp255920280"></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">// Define a placeholder for a map object:
placeholder<std::map<std::string, int> > _map;
// Match a word and an integer, separated by =>,
// and then stuff the result into a std::map<>
sregex pair = ( (s1= +_w) >> "=>" >> (s2= +_d) )
[ _map[s1] = as<int>(s2) ];
// The string to parse
std::string str("aaa=>1 bbb=>23 ccc=>456");
// Here is the actual map to fill in:
std::map<std::string, int> result;
// Create a regex_iterator to find all the matches
sregex_iterator it(str.begin(), str.end(), pair, let(_map=result));
sregex_iterator end;
// step through all the matches, and fill in
// the result map
while(it != end)
++it;
std::cout << result["aaa"] << '\n';
std::cout << result["bbb"] << '\n';
std::cout << result["ccc"] << '\n';
</pre>
<p> The above code displays:</p>
<pre class="programlisting">1
23
456
</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_idp163632632.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|
