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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 &lt;boost/spirit/repository/home/qi/primitive/flush_multi_pass.hpp&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</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">--&gt;</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">&lt;</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">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</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">&lt;</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">&gt;</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">&lt;</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">Skipper</span><span class="special">&gt;</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">&gt;&gt;</span>  <span class="identifier">eol</span>
            <span class="special">&gt;&gt;</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">&gt;&gt;</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">&gt;&gt;</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">&gt;&gt;</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">&gt;&gt;</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">&gt;&gt;</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">&gt;&gt;</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">&lt;</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">Skipper</span><span class="special">&gt;</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>
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<td align="right"><div class="copyright-footer">Copyright &#169; 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>
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