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<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="id1092407"></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="id1092436"></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="id1092576"></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="id1092664"></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="id1092839"></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="id1093013"></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="id1093033"></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>
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<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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