libs/spirit/repository/doc/html/spirit_repository/qi_components/directives/seek.html

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   4 <title>Qi Seek Parser Directive</title>
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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="spirit_repository.qi_components.directives.seek"></a><a class="link" href="seek.html" title="Qi Seek Parser Directive">Qi
  28         Seek Parser Directive </a>
  29 </h4></div></div></div>
  30 <h6>
  31 <a name="spirit_repository.qi_components.directives.seek.h0"></a>
  32           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.description"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.description">Description</a>
  33         </h6>
  34 <p>
  35           The <code class="computeroutput"><span class="identifier">seek</span><span class="special">[]</span></code>
  36           parser-directive skips all input until the subject parser matches.
  37         </p>
  38 <h6>
  39 <a name="spirit_repository.qi_components.directives.seek.h1"></a>
  40           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.header"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.header">Header</a>
  41         </h6>
  42 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/repository/home/qi/directive/seek.hpp&gt;</span>
  43 <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_seek</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  44 </pre>
  45 <p>
  46           Also, see <a href="../../../../../../doc/html/spirit/structure/include.html" target="_top">Include
  47           Structure</a>.
  48         </p>
  49 <h6>
  50 <a name="spirit_repository.qi_components.directives.seek.h2"></a>
  51           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.namespace"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.namespace">Namespace</a>
  52         </h6>
  53 <div class="informaltable"><table class="table">
  54 <colgroup><col></colgroup>
  55 <thead><tr><th>
  56                   <p>
  57                     Name
  58                   </p>
  59                 </th></tr></thead>
  60 <tbody><tr><td>
  61                   <p>
  62                     <code class="computeroutput"><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">qi</span><span class="special">::</span><span class="identifier">seek</span></code>
  63                   </p>
  64                 </td></tr></tbody>
  65 </table></div>
  66 <h6>
  67 <a name="spirit_repository.qi_components.directives.seek.h3"></a>
  68           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.model_of"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.model_of">Model
  69           of</a>
  70         </h6>
  71 <div class="blockquote"><blockquote class="blockquote"><p>
  72             <a href="../../../../../../doc/html/spirit/qi/reference/parser_concepts/unaryparser.html" target="_top"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>
  73           </p></blockquote></div>
  74 <div class="variablelist">
  75 <p class="title"><b>Notation</b></p>
  76 <dl class="variablelist">
  77 <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt>
  78 <dd><p>
  79                 A <a href="../../../../../../doc/html/spirit/qi/reference/parser_concepts/parser.html" target="_top"><code class="computeroutput"><span class="identifier">Parser</span></code></a>.
  80               </p></dd>
  81 </dl>
  82 </div>
  83 <h6>
  84 <a name="spirit_repository.qi_components.directives.seek.h4"></a>
  85           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.expression_semantics"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.expression_semantics">Expression
  86           Semantics</a>
  87         </h6>
  88 <p>
  89           Semantics of an expression is defined only where it differs from, or is
  90           not defined in <a href="../../../../../../doc/html/spirit/qi/reference/parser_concepts/unaryparser.html" target="_top"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>.
  91         </p>
  92 <div class="informaltable"><table class="table">
  93 <colgroup>
  94 <col>
  95 <col>
  96 </colgroup>
  97 <thead><tr>
  98 <th>
  99                   <p>
 100                     Expression
 101                   </p>
 102                 </th>
 103 <th>
 104                   <p>
 105                     Semantics
 106                   </p>
 107                 </th>
 108 </tr></thead>
 109 <tbody><tr>
 110 <td>
 111                   <p>
 112                     <code class="computeroutput"><span class="identifier">seek</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
 113                   </p>
 114                 </td>
 115 <td>
 116                   <p>
 117                     Advances until the parser <code class="computeroutput"><span class="identifier">a</span></code>
 118                     matches.
 119                   </p>
 120                 </td>
 121 </tr></tbody>
 122 </table></div>
 123 <h6>
 124 <a name="spirit_repository.qi_components.directives.seek.h5"></a>
 125           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.attributes"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.attributes">Attributes</a>
 126         </h6>
 127 <p>
 128           See <a href="../../../../../../doc/html/spirit/qi/quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation" target="_top">Compound
 129           Attribute Notation</a>.
 130         </p>
 131 <div class="informaltable"><table class="table">
 132 <colgroup>
 133 <col>
 134 <col>
 135 </colgroup>
 136 <thead><tr>
 137 <th>
 138                   <p>
 139                     Expression
 140                   </p>
 141                 </th>
 142 <th>
 143                   <p>
 144                     Attribute
 145                   </p>
 146                 </th>
 147 </tr></thead>
 148 <tbody><tr>
 149 <td>
 150                   <p>
 151                     <code class="computeroutput"><span class="identifier">seek</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
 152                   </p>
 153                 </td>
 154 <td>
 155                   <p>
 156 </p>
 157 <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">seek</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
 158 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">seek</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
 159 <p>
 160                   </p>
 161                 </td>
 162 </tr></tbody>
 163 </table></div>
 164 <h6>
 165 <a name="spirit_repository.qi_components.directives.seek.h6"></a>
 166           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.complexity"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.complexity">Complexity</a>
 167         </h6>
 168 <div class="blockquote"><blockquote class="blockquote"><p>
 169             The overall complexity is defined by the complexity of its subject parser.
 170             The complexity of <code class="computeroutput"><span class="identifier">seek</span></code>
 171             itself is O(N), where N is the number of unsuccessful matches.
 172           </p></blockquote></div>
 173 <div class="note"><table border="0" summary="Note">
 174 <tr>
 175 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td>
 176 <th align="left">Note</th>
 177 </tr>
 178 <tr><td align="left" valign="top">
 179 <p>
 180             <span class="bold"><strong>seeking sequence with skipping</strong></span>
 181           </p>
 182 <p>
 183             Using <code class="computeroutput"><span class="identifier">seek</span><span class="special">[</span><span class="identifier">a</span> <span class="special">&gt;&gt;</span>
 184             <span class="identifier">b</span><span class="special">]</span></code>
 185             with skipping is inefficient, because when sequence fails, the backtracked
 186             position is non-skipped. The solution is to ensure the input will always
 187             be pre-skipped, for example:
 188 </p>
 189 <pre class="programlisting"><span class="identifier">seek</span><span class="special">[</span><span class="identifier">lexeme</span><span class="special">[</span><span class="identifier">skip</span><span class="special">[</span><span class="identifier">a</span> <span class="special">&gt;&gt;</span> <span class="identifier">b</span><span class="special">]]]</span>
 190 </pre>
 191 <p>
 192             does the trick.
 193           </p>
 194 </td></tr>
 195 </table></div>
 196 <h6>
 197 <a name="spirit_repository.qi_components.directives.seek.h7"></a>
 198           <span class="phrase"><a name="spirit_repository.qi_components.directives.seek.example"></a></span><a class="link" href="seek.html#spirit_repository.qi_components.directives.seek.example">Example</a>
 199         </h6>
 200 <p>
 201           The following example shows a simple use case of the <code class="computeroutput"><span class="identifier">seek</span><span class="special">[]</span></code> directive, parsing C-style comment. (For
 202           the full source of the example, see <a href="../../../../../example/qi/seek.cpp" target="_top">seek.cpp</a>)
 203         </p>
 204 <p>
 205           Some namespace aliases:
 206         </p>
 207 <p>
 208 </p>
 209 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">qi</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">qi</span><span class="special">;</span>
 210 <span class="keyword">namespace</span> <span class="identifier">repo</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>
 211 </pre>
 212 <p>
 213         </p>
 214 <p>
 215           The input string and its iterators:
 216         </p>
 217 <p>
 218 </p>
 219 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"/*C-style comment*/"</span><span class="special">);</span>
 220 <span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
 221 <span class="identifier">iterator</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span>
 222 </pre>
 223 <p>
 224         </p>
 225 <p>
 226           Parsing and showing the result:
 227         </p>
 228 <p>
 229 </p>
 230 <pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">it</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span> <span class="string">"/*"</span> <span class="special">&gt;&gt;</span> <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">seek</span><span class="special">[</span><span class="string">"*/"</span><span class="special">]))</span>
 231 <span class="special">{</span>
 232     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</span>
 233     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Parsing succeeded.\n"</span><span class="special">;</span>
 234     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"---------------------------------\n"</span><span class="special">;</span>
 235 <span class="special">}</span>
 236 <span class="keyword">else</span>
 237 <span class="special">{</span>
 238     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</span>
 239     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Unterminated /* comment.\n"</span><span class="special">;</span>
 240     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</span>
 241 <span class="special">}</span>
 242 </pre>
 243 <p>
 244         </p>
 245 </div>
 246 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 247 <td align="left"></td>
 248 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 249         Distributed under the Boost Software License, Version 1.0. (See accompanying
 250         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>)
 251       </p>
 252 </div></td>
 253 </tr></table>
 254 <hr>
 255 <div class="spirit-nav">
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