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| <title>Attribute (attr)</title> |
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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.auxiliary.attr"></a><a class="link" href="attr.html" title="Attribute (attr)">Attribute (<code class="computeroutput"><span class="identifier">attr</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.auxiliary.attr.description"></a><h6> |
| <a name="id861507"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.description">Description</a> |
| </h6> |
| <p> |
| The Attribute parser does not consume any input, for this reason it always |
| matches an empty string and always succeeds. It's purpose is to expose |
| its specified parameter as an attribute. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.attr.header"></a><h6> |
| <a name="id861524"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/auxiliary/attr.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_attr</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.auxiliary.attr.namespace"></a><h6> |
| <a name="id861598"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.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">attr</span> <span class="comment">// alias: |
| boost::spirit::qi::attr</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr.model_of"></a><h6> |
| <a name="id861676"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.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">a</span></code></span></dt> |
| <dd><p> |
| A arbitrary typed constant value, e.g. 0.0, "Hello", |
| or a variable of arbitrary type or a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy |
| Argument</a> that evaluates to an arbitrary type. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt> |
| <dd><p> |
| The type of <code class="computeroutput"><span class="identifier">a</span></code> or |
| if it is a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy |
| Argument</a>, its return type. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.auxiliary.attr.expression_semantics"></a><h6> |
| <a name="id861769"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.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">attr</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a pseudo parser exposing the current value of <code class="computeroutput"><span class="identifier">a</span></code> as its attribute without |
| consuming any input at parse time. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr.attributes"></a><h6> |
| <a name="id861873"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.attributes">Attributes</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Attribute |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">A</span></code> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr.complexity"></a><h6> |
| <a name="id861964"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| O(1) |
| </p></blockquote></div> |
| <p> |
| The complexity is constant as no input is consumed and no matching is |
| done. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.attr.example"></a><h6> |
| <a name="id861988"></a> |
| <a class="link" href="attr.html#spirit.qi.reference.auxiliary.attr.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">namespace</span> <span class="identifier">phx</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</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">attr</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Using <code class="computeroutput"><span class="identifier">attr</span></code> with literals: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><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="identifier">test_parser_attr</span><span class="special">(</span><span class="string">""</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">(</span><span class="string">"boost"</span><span class="special">),</span> <span class="identifier">str</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">str</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// will print 'boost' |
| </span> |
| <span class="keyword">double</span> <span class="identifier">d</span><span class="special">;</span> |
| <span class="identifier">test_parser_attr</span><span class="special">(</span><span class="string">""</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">(</span><span class="number">1.0</span><span class="special">),</span> <span class="identifier">d</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">d</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// will print '1.0' |
| </span></pre> |
| <p> |
| </p> |
| <p> |
| Using <code class="computeroutput"><span class="identifier">attr</span></code> with <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> function objects: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">d</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">d1</span> <span class="special">=</span> <span class="number">1.2</span><span class="special">;</span> |
| <span class="identifier">test_parser_attr</span><span class="special">(</span><span class="string">""</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">(</span><span class="identifier">phx</span><span class="special">::</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">d1</span><span class="special">)),</span> <span class="identifier">d</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">d</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// will print '1.2' |
| </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> |
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