libs/spirit/doc/html/spirit/karma/reference/directive/buffer.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Generator Directive for Temporary Output Buffering (buffer[])</title>
   5 <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
   7 <link rel="home" href="../../../../index.html" title="Spirit 2.5.2">
   8 <link rel="up" href="../directive.html" title="Generator Directives">
   9 <link rel="prev" href="maxwidth.html" title="Generator Directives Controlling the Maximum Field Width (maxwidth[])">
  10 <link rel="next" href="omit.html" title="Generator Directives Consuming Attributes (omit[] and skip[])">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td>
  15 <td align="center"><a href="../../../../../../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="maxwidth.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../directive.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="omit.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="spirit.karma.reference.directive.buffer"></a><a class="link" href="buffer.html" title="Generator Directive for Temporary Output Buffering (buffer[])">Generator
  28           Directive for Temporary Output Buffering (<code class="computeroutput"><span class="identifier">buffer</span><span class="special">[]</span></code>)</a>
  29 </h5></div></div></div>
  30 <h6>
  31 <a name="spirit.karma.reference.directive.buffer.h0"></a>
  32             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.description"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.description">Description</a>
  33           </h6>
  34 <p>
  35             All generator components (except the <a class="link" href="../operator/alternative.html" title="Alternative Generator (a | b)">Alternative
  36             (<code class="computeroutput"><span class="special">|</span></code>)</a> generator) pass
  37             their generated output directly to the underlying output stream. If a
  38             generator fails halfway through, the output generated so far is not 'rolled
  39             back'. The buffering generator directive allows to avoid this unwanted
  40             output to be generated. It temporarily redirects the output produced
  41             by the embedded generator into a buffer. This buffer is flushed to the
  42             underlying stream only after the embedded generator succeeded, but is
  43             discarded otherwise.
  44           </p>
  45 <h6>
  46 <a name="spirit.karma.reference.directive.buffer.h1"></a>
  47             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.header"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.header">Header</a>
  48           </h6>
  49 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/directive/buffer.hpp&gt;</span>
  50 <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">karma_buffer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  51 </pre>
  52 <p>
  53             Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
  54           </p>
  55 <div class="informaltable"><table class="table">
  56 <colgroup><col></colgroup>
  57 <thead><tr><th>
  58                     <p>
  59                       Name
  60                     </p>
  61                   </th></tr></thead>
  62 <tbody><tr><td>
  63                     <p>
  64                       <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">//
  65                       alias: boost::spirit::karma::buffer</span></code>
  66                     </p>
  67                   </td></tr></tbody>
  68 </table></div>
  69 <h6>
  70 <a name="spirit.karma.reference.directive.buffer.h2"></a>
  71             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.model_of"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.model_of">Model of</a>
  72           </h6>
  73 <div class="blockquote"><blockquote class="blockquote"><p>
  74               <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>
  75             </p></blockquote></div>
  76 <div class="variablelist">
  77 <p class="title"><b>Notation</b></p>
  78 <dl class="variablelist">
  79 <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt>
  80 <dd><p>
  81                   A generator object
  82                 </p></dd>
  83 <dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt>
  84 <dd><p>
  85                   Attribute type of generator <code class="computeroutput"><span class="identifier">a</span></code>
  86                 </p></dd>
  87 </dl>
  88 </div>
  89 <h6>
  90 <a name="spirit.karma.reference.directive.buffer.h3"></a>
  91             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.expression_semantics"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.expression_semantics">Expression
  92             Semantics</a>
  93           </h6>
  94 <p>
  95             Semantics of an expression is defined only where it differs from, or
  96             is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>.
  97           </p>
  98 <div class="informaltable"><table class="table">
  99 <colgroup>
 100 <col>
 101 <col>
 102 </colgroup>
 103 <thead><tr>
 104 <th>
 105                     <p>
 106                       Expression
 107                     </p>
 108                   </th>
 109 <th>
 110                     <p>
 111                       Semantics
 112                     </p>
 113                   </th>
 114 </tr></thead>
 115 <tbody><tr>
 116 <td>
 117                     <p>
 118                       <code class="computeroutput"><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
 119                     </p>
 120                   </td>
 121 <td>
 122                     <p>
 123                       The embedded generator <code class="computeroutput"><span class="identifier">a</span></code>
 124                       is invoked but its output is temporarily intercepted and stored
 125                       in an internal buffer. If <code class="computeroutput"><span class="identifier">a</span></code>
 126                       succeeds the buffer content is flushed to the underlying output
 127                       stream, otherwise the buffer content is discarded. The buffer
 128                       directive succeeds as long as the embedded generator succeeded
 129                       (unless the underlying output stream reports an error).
 130                     </p>
 131                   </td>
 132 </tr></tbody>
 133 </table></div>
 134 <div class="tip"><table border="0" summary="Tip">
 135 <tr>
 136 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td>
 137 <th align="left">Tip</th>
 138 </tr>
 139 <tr><td align="left" valign="top"><p>
 140               If you want to make the buffered generator succeed regardless of the
 141               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 Generator (-a)">Optional
 142               (unary <code class="computeroutput"><span class="special">-</span></code>)</a>).
 143             </p></td></tr>
 144 </table></div>
 145 <h6>
 146 <a name="spirit.karma.reference.directive.buffer.h4"></a>
 147             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.attributes"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.attributes">Attributes</a>
 148           </h6>
 149 <p>
 150             See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound
 151             Attribute Notation</a>.
 152           </p>
 153 <div class="informaltable"><table class="table">
 154 <colgroup>
 155 <col>
 156 <col>
 157 </colgroup>
 158 <thead><tr>
 159 <th>
 160                     <p>
 161                       Expression
 162                     </p>
 163                   </th>
 164 <th>
 165                     <p>
 166                       Attribute
 167                     </p>
 168                   </th>
 169 </tr></thead>
 170 <tbody><tr>
 171 <td>
 172                     <p>
 173                       <code class="computeroutput"><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
 174                     </p>
 175                   </td>
 176 <td>
 177                     <p>
 178 </p>
 179 <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">--&gt;</span> <span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
 180 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</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>
 181 <p>
 182                     </p>
 183                   </td>
 184 </tr></tbody>
 185 </table></div>
 186 <h6>
 187 <a name="spirit.karma.reference.directive.buffer.h5"></a>
 188             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.complexity"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.complexity">Complexity</a>
 189           </h6>
 190 <div class="blockquote"><blockquote class="blockquote"><p>
 191               The overall complexity of the buffering generator directive is defined
 192               by the complexity of its embedded generator. The complexity of the
 193               buffering directive generator itself is O(N), where N is the number
 194               of characters buffered.
 195             </p></blockquote></div>
 196 <h6>
 197 <a name="spirit.karma.reference.directive.buffer.h6"></a>
 198             <span class="phrase"><a name="spirit.karma.reference.directive.buffer.example"></a></span><a class="link" href="buffer.html#spirit.karma.reference.directive.buffer.example">Example</a>
 199           </h6>
 200 <div class="note"><table border="0" summary="Note">
 201 <tr>
 202 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
 203 <th align="left">Note</th>
 204 </tr>
 205 <tr><td align="left" valign="top"><p>
 206               The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.karma.reference.basics.examples">Basics Examples</a>
 207               section.
 208             </p></td></tr>
 209 </table></div>
 210 <p>
 211             Some includes:
 212           </p>
 213 <p>
 214 </p>
 215 <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">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 216 <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">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 217 <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">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 218 <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">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 219 <span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
 220 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 221 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
 222 </pre>
 223 <p>
 224           </p>
 225 <p>
 226             Some using declarations:
 227           </p>
 228 <p>
 229 </p>
 230 <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>
 231 <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>
 232 </pre>
 233 <p>
 234           </p>
 235 <p>
 236             Basic usage of a buffering generator directive. It shows how the partial
 237             output generated in the first example does not show up in the generated
 238             output as the plus generator fails (no data is available, see <a class="link" href="../operator/plus.html" title="Plus Generator (+a)">Plus
 239             (unary <code class="computeroutput"><span class="special">+</span></code>)</a>).
 240           </p>
 241 <p>
 242 </p>
 243 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">;</span>                <span class="comment">// empty container</span>
 244 <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">&lt;&lt;</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">']'</span><span class="special">],</span> <span class="identifier">v</span><span class="special">);</span>
 245
 246 <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>
 247 <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>
 248 <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">&lt;&lt;</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">']'</span><span class="special">],</span> <span class="identifier">v</span><span class="special">);</span>
 249 </pre>
 250 <p>
 251           </p>
 252 </div>
 253 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 254 <td align="left"></td>
 255 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 256         Distributed under the Boost Software License, Version 1.0. (See accompanying
 257         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>)
 258       </p>
 259 </div></td>
 260 </tr></table>
 261 <hr>
 262 <div class="spirit-nav">
 263 <a accesskey="p" href="maxwidth.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../directive.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="omit.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a>
 264 </div>
 265 </body>
 266 </html>