<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Repetition Directive (repeat[])</title> <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> <link rel="home" href="../../../../index.html" title="Spirit 2.4"> <link rel="up" href="../directive.html" title="Directive"> <link rel="prev" href="alignment.html" title="Alignment Directives (left_align[], center[], right_align[])"> <link rel="next" href="delimit.html" title="Directives Controlling Automatic Delimiting (verbatim[], no_delimit[], delimit[])"> </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="../../../../../../../../libs/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="alignment.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="delimit.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h5 class="title"> <a name="spirit.karma.reference.directive.repeat"></a><a class="link" href="repeat.html" title="Repetition Directive (repeat[])"> Repetition Directive (<code class="computeroutput"><span class="identifier">repeat</span><span class="special">[]</span></code>)</a> </h5></div></div></div> <a name="spirit.karma.reference.directive.repeat.description"></a><h6> <a name="id1082586"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.description">Description</a> </h6> <p> The repetition directive allows to repeat an arbitrary generator expression while optionally specifying the lower and upper repetition counts. It provides a more powerful and flexible mechanism for repeating a generator. There are grammars that are impractical and cumbersome, if not impossible, for the basic EBNF iteration syntax ( <a class="link" href="../operator/kleene.html" title="Kleene Star (*a)">unary <code class="computeroutput"><span class="char">'*'</span></code></a> and the <a class="link" href="../operator/plus.html" title="Plus (+a)">unary <code class="computeroutput"><span class="char">'+'</span></code></a>) to specify. Examples: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> A file name may have a maximum of 255 characters only. </li> <li class="listitem"> A specific bitmap file format has exactly 4096 RGB color information. </li> <li class="listitem"> A 256 bit binary string (1..256 1s or 0s). </li> </ul></div> <a name="spirit.karma.reference.directive.repeat.header"></a><h6> <a name="id1082649"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.header">Header</a> </h6> <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/directive/repeat.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_repeat</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.directive.repeat.namespace"></a><h6> <a name="id1082724"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.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">repeat</span> <span class="comment">// alias: boost::spirit::karma::repeat</span></code> </p> </td></tr> <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">inf</span> <span class="comment">// alias: boost::spirit::karma::inf</span></code> </p> </td></tr> </tbody> </table></div> <a name="spirit.karma.reference.directive.repeat.model_of"></a><h6> <a name="id1082848"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.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">num</span><span class="special">,</span> <span class="identifier">num1</span><span class="special">,</span> <span class="identifier">num2</span></code></span></dt> <dd><p> Numeric literals, any unsigned integer value, or a <a class="link" href="../karma_basics.html#spirit.karma.reference.karma_basics.lazy_argument">Lazy Argument</a> that evaluates to an unsigned integer value </p></dd> <dt><span class="term"><code class="computeroutput"><span class="identifier">inf</span></code></span></dt> <dd><p> Placeholder expression standing for 'no upper repeat limit' </p></dd> </dl> </div> <a name="spirit.karma.reference.directive.repeat.expression_semantics"></a><h6> <a name="id1082970"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.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">repeat</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> </p> </td> <td> <p> Repeat the generator <code class="computeroutput"><span class="identifier">a</span></code> zero or more times. This generator succeeds as long as its embedded generator <code class="computeroutput"><span class="identifier">a</span></code> does not fail (except if the underlying output stream reports an error). This variant of <code class="computeroutput"><span class="identifier">repeat</span><span class="special">[]</span></code> is semantically equivalent to the <a class="link" href="../operator/kleene.html" title="Kleene Star (*a)">Kleene Star operator <code class="computeroutput"><span class="special">*</span><span class="identifier">a</span></code></a> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code> </p> </td> <td> <p> Repeat the generator <code class="computeroutput"><span class="identifier">a</span></code> exactly <code class="computeroutput"><span class="identifier">num</span></code> times. This generator succeeds as long as its embedded generator <code class="computeroutput"><span class="identifier">a</span></code> does not fail and as long as the associated attribute (container) contains at least <code class="computeroutput"><span class="identifier">num</span></code> elements (unless the underlying output stream reports an error). </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num1</span><span class="special">,</span> <span class="identifier">num2</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code> </p> </td> <td> <p> Repeat the generator <code class="computeroutput"><span class="identifier">a</span></code> at least <code class="computeroutput"><span class="identifier">num1</span></code> times but not more than <code class="computeroutput"><span class="identifier">num2</span></code> times. This generator succeeds as long as its embedded generator <code class="computeroutput"><span class="identifier">a</span></code> does not fail and as long as the associated attribute (container) contains at least <code class="computeroutput"><span class="identifier">num1</span></code> elements (unless the underlying output stream reports an error). If the associated attribute (container) does contain more than <code class="computeroutput"><span class="identifier">num2</span></code> elements, this directive limits the repeat count to <code class="computeroutput"><span class="identifier">num2</span></code>. </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">inf</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code> </p> </td> <td> <p> Repeat the generator <code class="computeroutput"><span class="identifier">a</span></code> at least <code class="computeroutput"><span class="identifier">num1</span></code> times. No upper limit for the repeat count is set. This generator succeeds as long as its embedded generator <code class="computeroutput"><span class="identifier">a</span></code> does not fail and as long as the associated attribute (container) contains at least <code class="computeroutput"><span class="identifier">num</span></code> elements (unless the underlying output stream reports an error). </p> </td> </tr> </tbody> </table></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> All failing iterations of the embedded generator will consume one element from the supplied attribute. The overall <code class="computeroutput"><span class="identifier">repeat</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> will succeed as long as the iteration criteria (number of successful invocations of the embedded generator) is fullfilled (unless the underlying output stream reports an error). </p></td></tr> </table></div> <a name="spirit.karma.reference.directive.repeat.attributes"></a><h6> <a name="id1083393"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.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">repeat</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">repeat</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="identifier">repeat</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> <p> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num</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">repeat</span><span class="special">(</span><span class="identifier">num</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="identifier">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> <p> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num1</span><span class="special">,</span> <span class="identifier">num2</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">repeat</span><span class="special">(</span><span class="identifier">num1</span><span class="special">,</span> <span class="identifier">num2</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="identifier">repeat</span><span class="special">(</span><span class="identifier">num1</span><span class="special">,</span> <span class="identifier">num2</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> <p> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">inf</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">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">inf</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="identifier">repeat</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">inf</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"><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 placeholders only. </p> <p> 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> It is important to note, that the <code class="computeroutput"><span class="identifier">repeat</span><span class="special">[]</span></code> directive 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"><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 <code class="computeroutput"><span class="identifier">repeat</span><span class="special">[]</span></code> directive to behave as if it did buffering is to wrap it into a buffering directive (see <a class="link" href="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">repeat</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="identifier">repeat</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>. The expression: </p> <p> </p> <pre class="programlisting"><span class="identifier">repeat</span><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 succeeded invocations of the generator <code class="computeroutput"><span class="identifier">a</span></code>. </p> </td></tr> </table></div> <a name="spirit.karma.reference.directive.repeat.complexity"></a><h6> <a name="id1084275"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.complexity">Complexity</a> </h6> <div class="blockquote"><blockquote class="blockquote"><p> The overall complexity of the repetition generator is defined by the complexity of its embedded generator. The complexity of the repeat itself is O(N), where N is the number of repetitions to execute. </p></blockquote></div> <a name="spirit.karma.reference.directive.repeat.example"></a><h6> <a name="id1084295"></a> <a class="link" href="repeat.html#spirit.karma.reference.directive.repeat.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">repeat</span><span class="special">;</span> </pre> <p> </p> <p> Basic usage of <code class="computeroutput"><span class="identifier">repeat</span></code> generator directive: </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</span><span class="special">(</span><span class="string">"[1.0][2.0][3.0]"</span><span class="special">,</span> <span class="identifier">repeat</span><span class="special">[</span><span class="char">'['</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">test_generator_attr</span><span class="special">(</span><span class="string">"[1.0][2.0]"</span><span class="special">,</span> <span class="identifier">repeat</span><span class="special">(</span><span class="number">2</span><span class="special">)[</span><span class="char">'['</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="comment">// fails because of insufficient number of items </span><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">""</span><span class="special">,</span> <span class="identifier">repeat</span><span class="special">(</span><span class="number">4</span><span class="special">)[</span><span class="char">'['</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> <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="alignment.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="delimit.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>