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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit_repository.qi_components.directives.seek"></a><a class="link" href="seek.html" title="Qi Seek Parser Directive">Qi |
| Seek Parser Directive </a> |
| </h4></div></div></div> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h0"></a> |
| <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> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">seek</span><span class="special">[]</span></code> |
| parser-directive skips all input until the subject parser matches. |
| </p> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h1"></a> |
| <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> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/repository/home/qi/directive/seek.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">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">></span> |
| </pre> |
| <p> |
| Also, see <a href="../../../../../../doc/html/spirit/structure/include.html" target="_top">Include |
| Structure</a>. |
| </p> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h2"></a> |
| <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> |
| </h6> |
| <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">repository</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">seek</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h3"></a> |
| <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 |
| of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a href="../../../../../../doc/html/spirit/qi/reference/parser_concepts/unaryparser.html" target="_top"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a> |
| </p></blockquote></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl class="variablelist"> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt> |
| <dd><p> |
| A <a href="../../../../../../doc/html/spirit/qi/reference/parser_concepts/parser.html" target="_top"><code class="computeroutput"><span class="identifier">Parser</span></code></a>. |
| </p></dd> |
| </dl> |
| </div> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h4"></a> |
| <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 |
| Semantics</a> |
| </h6> |
| <p> |
| Semantics of an expression is defined only where it differs from, or is |
| 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>. |
| </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">seek</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Advances until the parser <code class="computeroutput"><span class="identifier">a</span></code> |
| matches. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h5"></a> |
| <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> |
| </h6> |
| <p> |
| See <a href="../../../../../../doc/html/spirit/qi/quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation" target="_top">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">seek</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">seek</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">seek</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> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h6"></a> |
| <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> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The overall complexity is defined by the complexity of its subject parser. |
| The complexity of <code class="computeroutput"><span class="identifier">seek</span></code> |
| itself is O(N), where N is the number of unsuccessful matches. |
| </p></blockquote></div> |
| <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> |
| <span class="bold"><strong>seeking sequence with skipping</strong></span> |
| </p> |
| <p> |
| Using <code class="computeroutput"><span class="identifier">seek</span><span class="special">[</span><span class="identifier">a</span> <span class="special">>></span> |
| <span class="identifier">b</span><span class="special">]</span></code> |
| with skipping is inefficient, because when sequence fails, the backtracked |
| position is non-skipped. The solution is to ensure the input will always |
| be pre-skipped, for example: |
| </p> |
| <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">>></span> <span class="identifier">b</span><span class="special">]]]</span> |
| </pre> |
| <p> |
| does the trick. |
| </p> |
| </td></tr> |
| </table></div> |
| <h6> |
| <a name="spirit_repository.qi_components.directives.seek.h7"></a> |
| <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> |
| </h6> |
| <p> |
| 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 |
| the full source of the example, see <a href="../../../../../example/qi/seek.cpp" target="_top">seek.cpp</a>) |
| </p> |
| <p> |
| Some namespace aliases: |
| </p> |
| <p> |
| </p> |
| <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> |
| <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> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The input string and its iterators: |
| </p> |
| <p> |
| </p> |
| <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> |
| <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> |
| <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> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Parsing and showing the result: |
| </p> |
| <p> |
| </p> |
| <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">>></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> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing succeeded.\n"</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"---------------------------------\n"</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="keyword">else</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Unterminated /* comment.\n"</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------------- \n"</span><span class="special">;</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> |
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| <td align="right"><div class="copyright-footer">Copyright © 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>) |
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