1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Plus Generator (+a)</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Spirit 2.5.8"> 8<link rel="up" href="../operator.html" title="Generator Operators"> 9<link rel="prev" href="kleene.html" title="Kleene Star Generator (*a)"> 10<link rel="next" href="list.html" title="List Generator (a % b)"> 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="kleene.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="list.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.operator.plus"></a><a class="link" href="plus.html" title="Plus Generator (+a)">Plus Generator 28 (<code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>)</a> 29</h5></div></div></div> 30<h6> 31<a name="spirit.karma.reference.operator.plus.h0"></a> 32 <span class="phrase"><a name="spirit.karma.reference.operator.plus.description"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.description">Description</a> 33 </h6> 34<p> 35 The Plus generator is used to repeat the execution of an embedded generator 36 one or more times. It succeeds if the embedded generator has been successfully 37 executed at least once. 38 </p> 39<h6> 40<a name="spirit.karma.reference.operator.plus.h1"></a> 41 <span class="phrase"><a name="spirit.karma.reference.operator.plus.header"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.header">Header</a> 42 </h6> 43<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/operator/plus.hpp></span> 44<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_plus</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 45</pre> 46<p> 47 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 48 </p> 49<h6> 50<a name="spirit.karma.reference.operator.plus.h2"></a> 51 <span class="phrase"><a name="spirit.karma.reference.operator.plus.model_of"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.model_of">Model 52 of</a> 53 </h6> 54<div class="blockquote"><blockquote class="blockquote"><p> 55 <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a> 56 </p></blockquote></div> 57<h6> 58<a name="spirit.karma.reference.operator.plus.h3"></a> 59 <span class="phrase"><a name="spirit.karma.reference.operator.plus.expression_semantics"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.expression_semantics">Expression 60 Semantics</a> 61 </h6> 62<p> 63 Semantics of an expression is defined only where it differs from, or 64 is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>. 65 </p> 66<div class="informaltable"><table class="table"> 67<colgroup> 68<col> 69<col> 70</colgroup> 71<thead><tr> 72<th> 73 <p> 74 Expression 75 </p> 76 </th> 77<th> 78 <p> 79 Semantics 80 </p> 81 </th> 82</tr></thead> 83<tbody><tr> 84<td> 85 <p> 86 <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> 87 </p> 88 </td> 89<td> 90 <p> 91 The generator <code class="computeroutput"><span class="identifier">a</span></code> 92 is executed one or more times depending on the availability 93 of an attribute. The execution of <code class="computeroutput"><span class="identifier">a</span></code> 94 stops after the attribute values passed to the plus generator 95 are exhausted. The plus generator succeeds as long as its embedded 96 generator has been successfully executed at least once (unless 97 the underlying output stream reports an error). 98 </p> 99 </td> 100</tr></tbody> 101</table></div> 102<div class="note"><table border="0" summary="Note"> 103<tr> 104<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 105<th align="left">Note</th> 106</tr> 107<tr><td align="left" valign="top"><p> 108 All failing iterations of the embedded generator will consume one element 109 from the supplied attribute. The overall <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> will succeed as long as at least 110 one invocation of the embedded generator will succeed (unless the underlying 111 output stream reports an error). 112 </p></td></tr> 113</table></div> 114<h6> 115<a name="spirit.karma.reference.operator.plus.h4"></a> 116 <span class="phrase"><a name="spirit.karma.reference.operator.plus.attributes"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.attributes">Attributes</a> 117 </h6> 118<p> 119 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound 120 Attribute Notation</a>. 121 </p> 122<div class="informaltable"><table class="table"> 123<colgroup> 124<col> 125<col> 126</colgroup> 127<thead><tr> 128<th> 129 <p> 130 Expression 131 </p> 132 </th> 133<th> 134 <p> 135 Attribute 136 </p> 137 </th> 138</tr></thead> 139<tbody><tr> 140<td> 141 <p> 142 <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> 143 (unary <code class="computeroutput"><span class="special">+</span></code>) 144 </p> 145 </td> 146<td> 147 <p> 148</p> 149<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> 150<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> 151<p> 152 </p> 153 </td> 154</tr></tbody> 155</table></div> 156<div class="important"><table border="0" summary="Important"> 157<tr> 158<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../images/important.png"></td> 159<th align="left">Important</th> 160</tr> 161<tr><td align="left" valign="top"><p> 162 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 163 of <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> 164 stands for <span class="emphasis"><em>any STL container</em></span> holding elements 165 of type <code class="computeroutput"><span class="identifier">A</span></code>. 166 </p></td></tr> 167</table></div> 168<p> 169 The Plus generator will execute its embedded generator once for each 170 element in the provided container attribute as long as the embedded generator 171 succeeds. On each iteration it will pass the next consecutive element 172 from the container attribute to the embedded generator. Therefore the 173 number of iterations will not be larger than the number of elements in 174 the container passed as its attribute. An empty container will make the 175 plus generator fail. 176 </p> 177<p> 178 It is important to note, that the plus generator does not perform any 179 buffering of the output generated by its embedded elements. That means 180 that any failing element generator might have already generated some 181 output, which is <span class="emphasis"><em>not</em></span> rolled back. 182 </p> 183<div class="tip"><table border="0" summary="Tip"> 184<tr> 185<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td> 186<th align="left">Tip</th> 187</tr> 188<tr><td align="left" valign="top"> 189<p> 190 The simplest way to force a plus generator to behave as if it did buffering 191 is to wrap it into a buffering directive (see <a class="link" href="../directive/buffer.html" title="Generator Directive for Temporary Output Buffering (buffer[])"><code class="computeroutput"><span class="identifier">buffer</span></code></a>): 192 </p> 193<p> 194</p> 195<pre class="programlisting"><span class="identifier">buffer</span><span class="special">[+</span><span class="identifier">a</span><span class="special">]</span></pre> 196<p> 197 </p> 198<p> 199 which will <span class="emphasis"><em>not</em></span> generate any output in case of 200 a failing generator <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>. The expression: 201 </p> 202<p> 203</p> 204<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> 205<p> 206 </p> 207<p> 208 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 209 of its output. The overall expression will still generate the output 210 as produced by all successful invocations of the generator <code class="computeroutput"><span class="identifier">a</span></code>. 211 </p> 212</td></tr> 213</table></div> 214<h6> 215<a name="spirit.karma.reference.operator.plus.h5"></a> 216 <span class="phrase"><a name="spirit.karma.reference.operator.plus.complexity"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.complexity">Complexity</a> 217 </h6> 218<div class="blockquote"><blockquote class="blockquote"><p> 219 The overall complexity of the plus generator is defined by the complexity 220 of its embedded generator multiplied by the number of executed iterations. 221 The complexity of the plus generator itself is O(N), where N is the 222 number of elements in the container passed as its attribute. 223 </p></blockquote></div> 224<h6> 225<a name="spirit.karma.reference.operator.plus.h6"></a> 226 <span class="phrase"><a name="spirit.karma.reference.operator.plus.example"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.example">Example</a> 227 </h6> 228<div class="note"><table border="0" summary="Note"> 229<tr> 230<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 231<th align="left">Note</th> 232</tr> 233<tr><td align="left" valign="top"><p> 234 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> 235 section. 236 </p></td></tr> 237</table></div> 238<p> 239 Some includes: 240 </p> 241<p> 242</p> 243<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> 244<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">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 245<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> 246<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> 247<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> 248<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 249<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> 250</pre> 251<p> 252 </p> 253<p> 254 Some using declarations: 255 </p> 256<p> 257</p> 258<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> 259<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> 260</pre> 261<p> 262 </p> 263<p> 264 Basic usage of a plus generator: 265 </p> 266<p> 267</p> 268<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">v1</span><span class="special">;</span> 269<span class="identifier">v1</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> 270<span class="identifier">v1</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> 271<span class="identifier">v1</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> 272<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">v1</span><span class="special">);</span> 273</pre> 274<p> 275 </p> 276<p> 277 A more sophisticated use case showing how to leverage the fact that plus 278 is failing for empty containers passed as its attribute: 279 </p> 280<p> 281</p> 282<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">v2</span><span class="special">;</span> <span class="comment">// empty container</span> 283<span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"empty"</span><span class="special">,</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special">|</span> <span class="string">"empty"</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">);</span> 284</pre> 285<p> 286 </p> 287</div> 288<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 289<td align="left"></td> 290<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 291 Distributed under the Boost Software License, Version 1.0. (See accompanying 292 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>) 293 </p> 294</div></td> 295</tr></table> 296<hr> 297<div class="spirit-nav"> 298<a accesskey="p" href="kleene.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="list.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 299</div> 300</body> 301</html> 302
