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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.karma.reference.directive.buffer"></a><a class="link" href="buffer.html" title="Temporary Output Buffering (buffer[])">Temporary |
| Output Buffering (<code class="computeroutput"><span class="identifier">buffer</span><span class="special">[]</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.karma.reference.directive.buffer.description"></a><h6> |
| <a name="id1050046"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.description">Description</a> |
| </h6> |
| <p> |
| All generator components (except the <a class="link" href="../operator/alternative.html" title="Alternative (a | b)">Alternative |
| (<code class="computeroutput"><span class="special">|</span></code>)</a> generator) pass |
| their generated output directly to the underlying output stream. If a |
| generator fails halfway through, the output generated so far is not 'rolled |
| back'. The buffering generator directive allows to avoid this unwanted |
| output to be generated. It temporarily redirects the output produced |
| by the embedded generator into a buffer. This buffer is flushed to the |
| underlying stream only after the embedded generator succeeded, but is |
| discarded otherwise. |
| </p> |
| <a name="spirit.karma.reference.directive.buffer.header"></a><h6> |
| <a name="id1050075"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/directive/buffer.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">karma_buffer</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> |
| <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">buffer</span> <span class="comment">// |
| alias: boost::spirit::karma::buffer</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.buffer.model_of"></a><h6> |
| <a name="id1050216"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.model_of">Model |
| of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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 generator object |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt> |
| <dd><p> |
| Attribute type of generator <code class="computeroutput"><span class="identifier">a</span></code> |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.karma.reference.directive.buffer.expression_semantics"></a><h6> |
| <a name="id1050303"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.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="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The embedded generator <code class="computeroutput"><span class="identifier">a</span></code> |
| is invoked but its output is temporarily intercepted and stored |
| in an internal buffer. If <code class="computeroutput"><span class="identifier">a</span></code> |
| succeeds the buffer content is flushed to the underlying output |
| stream, otherwise the buffer content is discarded. The buffer |
| directive succeeds as long as the embedded generator succeeded |
| (unless the underlying output stream reports an error). |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <div class="tip"><table border="0" summary="Tip"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td> |
| <th align="left">Tip</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| If you want to make the buffered generator succeed regardless of the |
| outcome of the embedded generator, simply wrap the <code class="computeroutput"><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> into an additional optional: <code class="computeroutput"><span class="special">-</span><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> (see <a class="link" href="../operator/optional.html" title="Optional (-a)">Optional |
| (unary <code class="computeroutput"><span class="special">-</span></code>)</a>). |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.karma.reference.directive.buffer.attributes"></a><h6> |
| <a name="id1050478"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.attributes">Attributes</a> |
| </h6> |
| <p> |
| See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound |
| Attribute Notation</a>. |
| </p> |
| <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">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--></span> <span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> |
| <p> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.buffer.complexity"></a><h6> |
| <a name="id1050652"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The overall complexity of the buffering generator directive is defined |
| by the complexity of its embedded generator. The complexity of the |
| buffering directive generator itself is O(N), where N is the number |
| of characters buffered. |
| </p></blockquote></div> |
| <a name="spirit.karma.reference.directive.buffer.example"></a><h6> |
| <a name="id1050673"></a> |
| <a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.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="../karma_basics.html#spirit.karma.reference.karma_basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some includes: |
| </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">karma</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">include</span><span class="special">/</span><span class="identifier">phoenix_core</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">include</span><span class="special">/</span><span class="identifier">phoenix_operator</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">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</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">iostream</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> |
| </pre> |
| <p> |
| </p> |
| <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">karma</span><span class="special">::</span><span class="identifier">double_</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">karma</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Basic usage of a buffering generator directive. It shows how the partial |
| output generated in the first example does not show up in the generated |
| output as the plus generator fails (no data is available, see <a class="link" href="../operator/plus.html" title="Plus (+a)">Plus |
| (unary <code class="computeroutput"><span class="special">+</span></code>)</a>). |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span> <span class="comment">// empty container |
| </span><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">""</span><span class="special">,</span> <span class="special">-</span><span class="identifier">buffer</span><span class="special">[</span><span class="char">'['</span> <span class="special"><<</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special"><<</span> <span class="char">']'</span><span class="special">],</span> <span class="identifier">v</span><span class="special">);</span> |
| |
| <span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.0</span><span class="special">);</span> <span class="comment">// now, fill the container |
| </span><span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">2.0</span><span class="special">);</span> |
| <span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"[1.02.0]"</span><span class="special">,</span> <span class="identifier">buffer</span><span class="special">[</span><span class="char">'['</span> <span class="special"><<</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special"><<</span> <span class="char">']'</span><span class="special">],</span> <span class="identifier">v</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> |
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