<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Kleene Star (*a)</title> <link rel="stylesheet" href="../../../../../../../../doc/html/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> <link rel="home" href="../../../../index.html" title="Spirit 2.2"> <link rel="up" href="../operator.html" title="Operator"> <link rel="prev" href="alternative.html" title="Alternative (a | b)"> <link rel="next" href="plus.html" title="Plus (+a)"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="alternative.html"><img src="../../../../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.html"><img src="../../../../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="plus.html"><img src="../../../../../../../../doc/html/images/next.png" alt="Next"></a> </div> <div class="section" title="Kleene Star (*a)"> <div class="titlepage"><div><div><h5 class="title"> <a name="spirit.karma.reference.operator.kleene"></a><a class="link" href="kleene.html" title="Kleene Star (*a)"> Kleene Star (<code class="computeroutput"><span class="special">*</span><span class="identifier">a</span></code>)</a> </h5></div></div></div> <a name="spirit.karma.reference.operator.kleene.description"></a><h6> <a name="id907184"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.description">Description</a> </h6> <p> Kleene star generators are used to repeat the execution of an embedded generator zero or more times. Regardless of the success of the embedded generator, the Kleene star generator always succeeds. </p> <a name="spirit.karma.reference.operator.kleene.header"></a><h6> <a name="id907201"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.header">Header</a> </h6> <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/operator/kleene.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_kleene</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> <a name="spirit.karma.reference.operator.kleene.model_of"></a><h6> <a name="id907275"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.model_of">Model of</a> </h6> <div class="blockquote"><blockquote class="blockquote"> <p> </p> <p> <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a> </p> <p> </p> </blockquote></div> <a name="spirit.karma.reference.operator.kleene.expression_semantics"></a><h6> <a name="id907314"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.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="special">*</span><span class="identifier">a</span></code> </p> </td> <td> <p> The generator <code class="computeroutput"><span class="identifier">a</span></code> is executed zero or more times depending on the availability of an attribute. The execution of <code class="computeroutput"><span class="identifier">a</span></code> stops after the attribute values passed to the Kleene star generator are exhausted. The Kleene star always succeeds (unless the underlying output stream reports an error). </p> </td> </tr></tbody> </table></div> <div class="note" title="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> All failing iterations of the embedded generator will consume one element from the supplied attribute. </p></td></tr> </table></div> <a name="spirit.karma.reference.operator.kleene.attributes"></a><h6> <a name="id907428"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.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="special">*</span><span class="identifier">a</span></code> (Kleene star, unary <code class="computeroutput"><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="special">*</span><span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></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> <div class="important" title="Important"><table border="0" summary="Important"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../images/important.png"></td> <th align="left">Important</th> </tr> <tr><td align="left" valign="top"><p> The table above uses <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> as a placeholder only. The notation of <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> stands for <span class="emphasis"><em>any STL container</em></span> holding elements of type <code class="computeroutput"><span class="identifier">A</span></code>. </p></td></tr> </table></div> <p> The Kleene star generator will execute its embedded generator once for each element in the provided container attribute as long as the embedded generator succeeds. On each iteration it will pass the next consecutive element from the container attribute to the embedded generator. Therefore the number of iterations will not be larger than the number of elements in the container passed as its attribute. An empty container will make the Kleene star generate no output at all. </p> <p> It is important to note, that the Kleene star does not perform any buffering of the output generated by its embedded elements. That means that any failing element generator might have already generated some output, which is <span class="emphasis"><em>not</em></span> rolled back. </p> <div class="tip" title="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> The simplest way to force a Kleene star to behave as if it did buffering is to wrap it into a buffering directive (see <a class="link" href="../directive/buffer.html" title="Temporary Output Buffering (buffer[])"><code class="computeroutput"><span class="identifier">buffer</span></code></a>): </p> <p> </p> <pre class="programlisting"><span class="identifier">buffer</span><span class="special">[*</span><span class="identifier">a</span><span class="special">]</span></pre> <p> </p> <p> which will <span class="emphasis"><em>not</em></span> generate any output in case of a failing generator <code class="computeroutput"><span class="special">*</span><span class="identifier">a</span></code>. The expression: </p> <p> </p> <pre class="programlisting"><span class="special">*(</span><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">])</span></pre> <p> </p> <p> will not generate any partial output from a generator <code class="computeroutput"><span class="identifier">a</span></code> if it fails generating in the middle of its output. The overall expression will still generate the output as produced by all successful invocations of the generator <code class="computeroutput"><span class="identifier">a</span></code>. </p> </td></tr> </table></div> <a name="spirit.karma.reference.operator.kleene.complexity"></a><h6> <a name="id907767"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.complexity">Complexity</a> </h6> <div class="blockquote"><blockquote class="blockquote"> <p> </p> <p> The overall complexity of the Kleene star generator is defined by the complexity of its embedded generator multiplied by the number of executed iterations. The complexity of the Kleene star itself is O(N), where N is the number of elements in the container passed as its attribute. </p> <p> </p> </blockquote></div> <a name="spirit.karma.reference.operator.kleene.example"></a><h6> <a name="id907791"></a> <a class="link" href="kleene.html#spirit.karma.reference.operator.kleene.example">Example</a> </h6> <div class="note" title="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> <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> </p> <p> Some using declarations: </p> <p> </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">space</span><span class="special">;</span> </pre> <p> </p> <p> </p> <p> Basic usage of a Kleene star generator: </p> <p> </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="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="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">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">3.0</span><span class="special">);</span> <span class="identifier">test_generator_attr_delim</span><span class="special">(</span><span class="string">"1.0 2.0 3.0 "</span><span class="special">,</span> <span class="special">*</span><span class="identifier">double_</span><span class="special">,</span> <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span> </pre> <p> </p> <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> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="alternative.html"><img src="../../../../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.html"><img src="../../../../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="plus.html"><img src="../../../../../../../../doc/html/images/next.png" alt="Next"></a> </div> </body> </html>