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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass"></a><a class="link" href="flush_multi_pass.html" title="Qi flush_multi_pass parser"> |
| Qi flush_multi_pass parser</a> |
| </h4></div></div></div> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.description"></a><h6> |
| <a name="id760277"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.description">Description</a> |
| </h6> |
| <p> |
| The <span class="emphasis"><em>Spirit.Qi</em></span> <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> |
| parser is a primitive (pseudo) parser component allowing to clear the internal |
| buffer of a <code class="computeroutput"><span class="identifier">multi_pass</span></code> |
| iterator. Clearing the buffer of a <code class="computeroutput"><span class="identifier">multi_pass</span></code> |
| might be beneficial for grammars where it is clear that no backtracking |
| can occur. The general syntax for using the <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> |
| is: |
| </p> |
| <pre class="programlisting"><span class="identifier">flush_multi_pass</span> |
| </pre> |
| <p> |
| which will call the <code class="computeroutput"><span class="identifier">clear_queue</span><span class="special">()</span></code> member function if the current iterators |
| are of the type <code class="computeroutput"><span class="identifier">multi_pass</span></code>. |
| This will cause any buffered data to be erased. This also will invalidate |
| all other copies of multi_pass and they should not be used. If they are, |
| an <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">illegal_backtracking</span></code> exception will be |
| thrown. For all other iterator types this is a no-op. The <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> generates a parser component |
| which always succeeds and which does not consume any input (very much like |
| <code class="computeroutput"><span class="identifier">eps</span></code>). |
| </p> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.header"></a><h6> |
| <a name="id760413"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/repository/home/qi/primitive/flush_multi_pass.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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_flush_multi_pass</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.synopsis"></a><h6> |
| <a name="id760502"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="identifier">flush_multi_pass</span> |
| </pre> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.parameters"></a><h6> |
| <a name="id760531"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.parameters">Parameters</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> does |
| not require any parameters. |
| </p> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.attribute"></a><h6> |
| <a name="id760563"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.attribute">Attribute</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> component |
| exposes no attribute (the exposed attribute type is <code class="computeroutput"><span class="identifier">unused_type</span></code>): |
| </p> |
| <pre class="programlisting"><span class="identifier">flush_multi_pass</span> <span class="special">--></span> <span class="identifier">unused</span> |
| </pre> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.example"></a><h6> |
| <a name="id760623"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.example">Example</a> |
| </h6> |
| <p> |
| The following example shows a simple use case of the <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> |
| parser. |
| </p> |
| <p> |
| We will illustrate its usage by generating different comment styles and |
| a function prototype (for the full example code see here: <a href="../../../../../example/qi/flush_multi_pass.cpp" target="_top">flush_multi_pass.cpp</a>) |
| </p> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.prerequisites"></a><h6> |
| <a name="id760666"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.prerequisites">Prerequisites</a> |
| </h6> |
| <p> |
| In addition to the main header file needed to include the core components |
| implemented in <span class="emphasis"><em>Spirit.Qi</em></span> we add the header file needed |
| for the new <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> |
| parser. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><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</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_flush_multi_pass</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| To make all the code below more readable we introduce the following namespaces. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">spirit</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="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">repository</span><span class="special">::</span><span class="identifier">flush_multi_pass</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <a name="spirit_repository.qi_components.primitive.flush_multi_pass.clearing_the_internal_buffer"></a><h6> |
| <a name="id760902"></a> |
| <a class="link" href="flush_multi_pass.html#spirit_repository.qi_components.primitive.flush_multi_pass.clearing_the_internal_buffer">Clearing |
| the internal buffer</a> |
| </h6> |
| <p> |
| The example grammar recognizes the (simplified) preprocessor commands |
| <code class="computeroutput"><span class="preprocessor">#define</span></code> and <code class="computeroutput"><span class="preprocessor">#undef</span></code> both of which are constraint |
| to a single line. This makes it possible to delete all internal iterator |
| buffers on each detected line break. This is safe as no backtracking will |
| occur after any line end. The following code snippet shows the usage of |
| <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> for this |
| purpose. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><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">Skipper</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">preprocessor</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">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">Skipper</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="comment">// This is a simplified preprocessor grammar recognizing |
| </span> <span class="comment">// |
| </span> <span class="comment">// #define MACRONAME something |
| </span> <span class="comment">// #undef MACRONAME |
| </span> <span class="comment">// |
| </span> <span class="comment">// Its sole purpose is to show an example how to use the |
| </span> <span class="comment">// flush_multi_pass parser. At the end of each line no backtracking can |
| </span> <span class="comment">// occur anymore so that it's safe to clear all internal buffers in the |
| </span> <span class="comment">// multi_pass. |
| </span> <span class="identifier">preprocessor</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">preprocessor</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">file</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">using</span> <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">eol</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> |
| |
| <span class="identifier">file</span> <span class="special">=</span> |
| <span class="special">*</span><span class="identifier">line</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">line</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">command</span> <span class="special">|</span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span> <span class="special">)</span> |
| <span class="special">>></span> <span class="identifier">eol</span> |
| <span class="special">>></span> <span class="identifier">flush_multi_pass</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">command</span> <span class="special">=</span> |
| <span class="string">"#define"</span> <span class="special">>></span> <span class="special">*</span><span class="identifier">lit</span><span class="special">(</span><span class="char">' '</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">' '</span><span class="special">)</span> <span class="special">>></span> <span class="special">*</span><span class="identifier">lit</span><span class="special">(</span><span class="char">' '</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span> |
| <span class="special">|</span> <span class="string">"#undef"</span> <span class="special">>></span> <span class="special">*</span><span class="identifier">lit</span><span class="special">(</span><span class="char">' '</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span> |
| <span class="special">;</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">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">Skipper</span><span class="special">></span> <span class="identifier">file</span><span class="special">,</span> <span class="identifier">line</span><span class="special">,</span> <span class="identifier">command</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <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> |
| Using the <code class="computeroutput"><span class="identifier">flush_multi_pass</span></code> |
| parser component with iterators other than <code class="computeroutput"><span class="identifier">multi_pass</span></code> |
| is safe as it has no effect on the parsing. |
| </p></td></tr> |
| </table></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 © 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> |
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