| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Boolean Parser (bool_)</title> |
| <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> |
| <link rel="home" href="../../../../index.html" title="Spirit 2.4.1"> |
| <link rel="up" href="../numeric.html" title="Numeric"> |
| <link rel="prev" href="real.html" title="Real Numbers (float_, double_, etc.)"> |
| <link rel="next" href="../operator.html" title="Operator"> |
| </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="real.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../numeric.html"><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="../operator.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.numeric.boolean"></a><a class="link" href="boolean.html" title="Boolean Parser (bool_)">Boolean Parser |
| (<code class="computeroutput"><span class="identifier">bool_</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.numeric.boolean.description"></a><h6> |
| <a name="id916460"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.description">Description</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">bool_parser</span></code> can parse |
| booleans of arbitrary type, <code class="computeroutput"><span class="identifier">B</span></code>. |
| The boolean base type <code class="computeroutput"><span class="identifier">T</span></code> |
| can be a user defined boolean type as long as the type follows certain |
| expression requirements (documented below). |
| </p> |
| <a name="spirit.qi.reference.numeric.boolean.header"></a><h6> |
| <a name="id916499"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/numeric/bool.hpp> |
| </span><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_bool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. |
| </p> |
| <a name="spirit.qi.reference.numeric.boolean.namespace"></a><h6> |
| <a name="id916573"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.namespace">Namespace</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup><col></colgroup> |
| <thead><tr><th> |
| <p> |
| Name |
| </p> |
| </th></tr></thead> |
| <tbody> |
| <tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">bool_</span> <span class="comment">// |
| alias: boost::spirit::qi::bool_</span></code> |
| </p> |
| </td></tr> |
| <tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">true_</span> <span class="comment">// |
| alias: boost::spirit::qi::true_</span></code> |
| </p> |
| </td></tr> |
| <tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">false_</span> <span class="comment">// |
| alias: boost::spirit::qi::false_</span></code> |
| </p> |
| </td></tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.numeric.boolean.synopsis"></a><h6> |
| <a name="id916729"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BooleanPolicies</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">bool_parser</span><span class="special">;</span> |
| </pre> |
| <a name="spirit.qi.reference.numeric.boolean.template_parameters"></a><h6> |
| <a name="id916794"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.template_parameters">Template |
| parameters</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| <th> |
| <p> |
| Default |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">B</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The boolean type of the boolean parser. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">bool</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">BooleanPolicies</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Policies control the parser's behavior. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.numeric.boolean.model_of"></a><h6> |
| <a name="id916939"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../parser_concepts/primitiveparser.html" title="PrimitiveParser"><code class="computeroutput"><span class="identifier">PrimitiveParser</span></code></a> |
| </p></blockquote></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">BP</span></code></span></dt> |
| <dd><p> |
| An instance of <code class="computeroutput"><span class="identifier">bool_parser</span></code> |
| (type). |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">BP</span></code></span></dt> |
| <dd><p> |
| A boolean <code class="computeroutput"><span class="identifier">Policies</span></code> |
| (type). |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">b</span></code></span></dt> |
| <dd><p> |
| An object of <code class="computeroutput"><span class="identifier">B</span></code>, |
| the numeric base type. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code>, <code class="computeroutput"><span class="identifier">l</span></code></span></dt> |
| <dd><p> |
| <a href="http://www.sgi.com/tech/stl/ForwardIterator.html" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a>. first/last |
| iterator pair. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt> |
| <dd><p> |
| An attribute value. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Context</span></code></span></dt> |
| <dd><p> |
| The type of the parse context of the current invocation of the |
| <code class="computeroutput"><span class="identifier">bool_</span></code> parser. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">ctx</span></code></span></dt> |
| <dd><p> |
| An instance of the parse context, <code class="computeroutput"><span class="identifier">Context</span></code>. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.numeric.boolean.expression_semantics"></a><h6> |
| <a name="id917168"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.expression_semantics">Expression |
| Semantics</a> |
| </h6> |
| <p> |
| Semantics of an expression is defined only where it differs from, or |
| is not defined in <a class="link" href="../parser_concepts/primitiveparser.html" title="PrimitiveParser"><code class="computeroutput"><span class="identifier">PrimitiveParser</span></code></a>. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">BP</span><span class="special">()</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Instantiate and (default) construct a <code class="computeroutput"><span class="identifier">bool_parser</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">bool_</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a <code class="computeroutput"><span class="identifier">bool_parser</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">bool_policies</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="special">></span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">true_</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a <code class="computeroutput"><span class="identifier">bool_parser</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">bool_policies</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="special">></span></code> |
| which is succeeding only after matching <code class="computeroutput"><span class="string">"true"</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">false_</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a <code class="computeroutput"><span class="identifier">bool_parser</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">bool_policies</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="special">></span></code> |
| which is succeeding only after matching <code class="computeroutput"><span class="string">"false"</span></code>. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| All boolean parsers properly respect the <a class="link" href="../directive/no_case.html" title="Inhibiting Case Sensitivity (no_case[])"><code class="computeroutput"><span class="identifier">no_case</span></code></a><code class="computeroutput"><span class="special">[]</span></code> |
| directive. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.qi.reference.numeric.boolean.attributes"></a><h6> |
| <a name="id917501"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.attributes">Attributes</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">B</span></code>, The boolean type |
| of the boolean parser. |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.numeric.boolean.complexity"></a><h6> |
| <a name="id917528"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| O(N), where N is the number of characters being parsed. |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.numeric.boolean.minimum_expression_requirements_for__code__phrase_role__identifier__b__phrase___code_"></a><h6> |
| <a name="id917549"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.minimum_expression_requirements_for__code__phrase_role__identifier__b__phrase___code_">Minimum |
| Expression Requirements for <code class="computeroutput"><span class="identifier">B</span></code></a> |
| </h6> |
| <p> |
| The boolean type, <code class="computeroutput"><span class="identifier">B</span></code>, |
| the minimum expression requirements listed below must be valid. Take |
| note that additional requirements may be imposed by custom policies. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">B</span><span class="special">(</span><span class="keyword">bool</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Constructible from a <code class="computeroutput"><span class="keyword">bool</span></code>. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code_"></a><h6> |
| <a name="id917657"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code_">Boolean |
| <code class="computeroutput"><span class="identifier">Policies</span></code></a> |
| </h6> |
| <p> |
| The boolean <code class="computeroutput"><span class="identifier">Policies</span></code> |
| template parameter is a class that groups all the policies that control |
| the parser's behavior. Policies control the boolean parsers' behavior. |
| </p> |
| <p> |
| The default is <code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>. The default is provided to take |
| care of the most common case (there are many ways to represent, and hence |
| parse, boolean numbers). In most cases, the default policies are sufficient |
| and can be used straight out of the box. They are designed to parse boolean |
| value of the form <code class="computeroutput"><span class="string">"true"</span></code> |
| and <code class="computeroutput"><span class="string">"false"</span></code>. |
| </p> |
| <a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__expression_requirements"></a><h6> |
| <a name="id917723"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__expression_requirements">Boolean |
| <code class="computeroutput"><span class="identifier">Policies</span></code> Expression Requirements</a> |
| </h6> |
| <p> |
| For models of boolean <code class="computeroutput"><span class="identifier">Policies</span></code> |
| the following expressions must be valid: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">BP</span><span class="special">::</span><span class="identifier">parse_true</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> |
| <span class="identifier">l</span><span class="special">,</span> |
| <span class="identifier">attr</span><span class="special">,</span> |
| <span class="identifier">ctx</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Parse a <code class="computeroutput"><span class="keyword">true</span></code> value. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">BP</span><span class="special">::</span><span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> |
| <span class="identifier">l</span><span class="special">,</span> |
| <span class="identifier">attr</span><span class="special">,</span> |
| <span class="identifier">ctx</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Parse a <code class="computeroutput"><span class="keyword">false</span></code> |
| value. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| The functions should return true if the required representations of |
| <code class="computeroutput"><span class="keyword">true</span></code> or <code class="computeroutput"><span class="keyword">false</span></code> |
| have been found. In this case the attribute <code class="computeroutput"><span class="identifier">n</span></code> |
| should be set to the matched value (<code class="computeroutput"><span class="keyword">true</span></code> |
| or <code class="computeroutput"><span class="keyword">false</span></code>). |
| </p> |
| <a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__specializations"></a><h6> |
| <a name="id917981"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__specializations">Boolean |
| <code class="computeroutput"><span class="identifier">Policies</span></code> Specializations</a> |
| </h6> |
| <p> |
| The easiest way to implement a proper boolean parsing policy is to derive |
| a new type from the the type <code class="computeroutput"><span class="identifier">bool_policies</span></code> |
| while overriding the aspects of the parsing which need to be changed. |
| For example, here's the implementation of a boolean parsing policy interpreting |
| the string <code class="computeroutput"><span class="string">"eurt"</span></code> |
| (i.e. "true" spelled backwards) as <code class="computeroutput"><span class="keyword">false</span></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">backwards_bool_policies</span> <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">bool_policies</span><span class="special"><></span> |
| <span class="special">{</span> |
| <span class="comment">// we want to interpret a 'true' spelled backwards as 'false' |
| </span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attribute</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> |
| <span class="keyword">static</span> <span class="keyword">bool</span> |
| <span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">Iterator</span><span class="special">&</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">,</span> <span class="identifier">Context</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">qi</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">;</span> |
| <span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">string_parse</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">unused</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">unused</span><span class="special">))</span> |
| <span class="special">{</span> |
| <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span><span class="special">::</span><span class="identifier">assign_to</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">,</span> <span class="identifier">ctx</span><span class="special">);</span> <span class="comment">// result is false |
| </span> <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| </pre> |
| <a name="spirit.qi.reference.numeric.boolean.example"></a><h6> |
| <a name="id919548"></a> |
| <a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.example">Example</a> |
| </h6> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some using declarations: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">bool_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">bool_parser</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Basic real number parsing: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">);</span> |
| <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| A custom real number policy: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">/////////////////////////////////////////////////////////////////////////////// |
| </span><span class="comment">// These policies can be used to parse "eurt" (i.e. "true" spelled backwards) |
| </span><span class="comment">// as `false` |
| </span><span class="comment">/////////////////////////////////////////////////////////////////////////////// |
| </span><span class="keyword">struct</span> <span class="identifier">backwards_bool_policies</span> <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">bool_policies</span><span class="special"><></span> |
| <span class="special">{</span> |
| <span class="comment">// we want to interpret a 'true' spelled backwards as 'false' |
| </span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attribute</span><span class="special">></span> |
| <span class="keyword">static</span> <span class="keyword">bool</span> |
| <span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">Iterator</span><span class="special">&</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">qi</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">;</span> |
| <span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">string_parse</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">unused</span><span class="special">))</span> |
| <span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">traits</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span><span class="special">;</span> |
| <span class="identifier">traits</span><span class="special">::</span><span class="identifier">assign_to</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">);</span> <span class="comment">// result is false |
| </span> <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| And its use: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">bool_parser</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">backwards_bool_policies</span><span class="special">></span> <span class="identifier">backwards_bool</span><span class="special">;</span> |
| <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">);</span> |
| <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </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 © 2001-2010 Joel de Guzman, Hartmut Kaiser<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="real.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../numeric.html"><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="../operator.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
