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- <title>Qi flush_multi_pass parser</title>
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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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h0"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.description"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h1"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.header"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h2"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.synopsis"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h3"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.parameters"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h4"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.attribute"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h5"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.example"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h6"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.prerequisites"></a></span><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>
- <h6>
- <a name="spirit_repository.qi_components.primitive.flush_multi_pass.h7"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.primitive.flush_multi_pass.clearing_the_internal_buffer"></a></span><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 © 2001-2011 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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