1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Boolean Parser (bool_)</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="../numeric.html" title="Numeric Parsers"> 9<link rel="prev" href="real.html" title="Real Number Parsers (float_, double_, etc.)"> 10<link rel="next" href="../operator.html" title="Parser Operators"> 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="real.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../numeric.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="../operator.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.qi.reference.numeric.boolean"></a><a class="link" href="boolean.html" title="Boolean Parser (bool_)">Boolean Parser 28 (<code class="computeroutput"><span class="identifier">bool_</span></code>)</a> 29</h5></div></div></div> 30<h6> 31<a name="spirit.qi.reference.numeric.boolean.h0"></a> 32 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.description"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.description">Description</a> 33 </h6> 34<p> 35 The <code class="computeroutput"><span class="identifier">bool_parser</span></code> can parse 36 booleans of arbitrary type, <code class="computeroutput"><span class="identifier">B</span></code>. 37 The boolean base type <code class="computeroutput"><span class="identifier">T</span></code> 38 can be a user defined boolean type as long as the type follows certain 39 expression requirements (documented below). 40 </p> 41<h6> 42<a name="spirit.qi.reference.numeric.boolean.h1"></a> 43 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.header"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.header">Header</a> 44 </h6> 45<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/numeric/bool.hpp></span> 46<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">qi_bool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 47</pre> 48<p> 49 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 50 </p> 51<h6> 52<a name="spirit.qi.reference.numeric.boolean.h2"></a> 53 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.namespace"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.namespace">Namespace</a> 54 </h6> 55<div class="informaltable"><table class="table"> 56<colgroup><col></colgroup> 57<thead><tr><th> 58 <p> 59 Name 60 </p> 61 </th></tr></thead> 62<tbody> 63<tr><td> 64 <p> 65 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">bool_</span> <span class="comment">// 66 alias: boost::spirit::qi::bool_</span></code> 67 </p> 68 </td></tr> 69<tr><td> 70 <p> 71 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">true_</span> <span class="comment">// 72 alias: boost::spirit::qi::true_</span></code> 73 </p> 74 </td></tr> 75<tr><td> 76 <p> 77 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">false_</span> <span class="comment">// 78 alias: boost::spirit::qi::false_</span></code> 79 </p> 80 </td></tr> 81</tbody> 82</table></div> 83<h6> 84<a name="spirit.qi.reference.numeric.boolean.h3"></a> 85 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.synopsis"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.synopsis">Synopsis</a> 86 </h6> 87<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BooleanPolicies</span><span class="special">></span> 88<span class="keyword">struct</span> <span class="identifier">bool_parser</span><span class="special">;</span> 89</pre> 90<h6> 91<a name="spirit.qi.reference.numeric.boolean.h4"></a> 92 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.template_parameters"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.template_parameters">Template 93 parameters</a> 94 </h6> 95<div class="informaltable"><table class="table"> 96<colgroup> 97<col> 98<col> 99<col> 100</colgroup> 101<thead><tr> 102<th> 103 <p> 104 Parameter 105 </p> 106 </th> 107<th> 108 <p> 109 Description 110 </p> 111 </th> 112<th> 113 <p> 114 Default 115 </p> 116 </th> 117</tr></thead> 118<tbody> 119<tr> 120<td> 121 <p> 122 <code class="computeroutput"><span class="identifier">B</span></code> 123 </p> 124 </td> 125<td> 126 <p> 127 The boolean type of the boolean parser. 128 </p> 129 </td> 130<td> 131 <p> 132 <code class="computeroutput"><span class="keyword">bool</span></code> 133 </p> 134 </td> 135</tr> 136<tr> 137<td> 138 <p> 139 <code class="computeroutput"><span class="identifier">BooleanPolicies</span></code> 140 </p> 141 </td> 142<td> 143 <p> 144 Policies control the parser's behavior. 145 </p> 146 </td> 147<td> 148 <p> 149 <code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span></code> 150 </p> 151 </td> 152</tr> 153</tbody> 154</table></div> 155<h6> 156<a name="spirit.qi.reference.numeric.boolean.h5"></a> 157 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.model_of"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.model_of">Model 158 of</a> 159 </h6> 160<div class="blockquote"><blockquote class="blockquote"><p> 161 <a class="link" href="../parser_concepts/primitiveparser.html" title="PrimitiveParser"><code class="computeroutput"><span class="identifier">PrimitiveParser</span></code></a> 162 </p></blockquote></div> 163<div class="variablelist"> 164<p class="title"><b>Notation</b></p> 165<dl class="variablelist"> 166<dt><span class="term"><code class="computeroutput"><span class="identifier">BP</span></code></span></dt> 167<dd><p> 168 A boolean <code class="computeroutput"><span class="identifier">Policies</span></code> 169 (type). 170 </p></dd> 171<dt><span class="term"><code class="computeroutput"><span class="identifier">b</span></code></span></dt> 172<dd><p> 173 An object of <code class="computeroutput"><span class="identifier">B</span></code>, 174 the numeric base type. 175 </p></dd> 176<dt><span class="term"><code class="computeroutput"><span class="identifier">boolean</span></code></span></dt> 177<dd><p> 178 Numeric literal, any boolean value, or a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy 179 Argument</a> that evaluates to a boolean value. 180 </p></dd> 181<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code>, <code class="computeroutput"><span class="identifier">l</span></code></span></dt> 182<dd><p> 183 <a href="http://en.cppreference.com/w/cpp/named_req/ForwardIterator" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a>. first/last 184 iterator pair. 185 </p></dd> 186<dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt> 187<dd><p> 188 An attribute value. 189 </p></dd> 190<dt><span class="term"><code class="computeroutput"><span class="identifier">Context</span></code></span></dt> 191<dd><p> 192 The type of the parse context of the current invocation of the 193 <code class="computeroutput"><span class="identifier">bool_</span></code> parser. 194 </p></dd> 195<dt><span class="term"><code class="computeroutput"><span class="identifier">ctx</span></code></span></dt> 196<dd><p> 197 An instance of the parse context, <code class="computeroutput"><span class="identifier">Context</span></code>. 198 </p></dd> 199</dl> 200</div> 201<h6> 202<a name="spirit.qi.reference.numeric.boolean.h6"></a> 203 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.expression_semantics"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.expression_semantics">Expression 204 Semantics</a> 205 </h6> 206<p> 207 Semantics of an expression is defined only where it differs from, or 208 is not defined in <a class="link" href="../parser_concepts/primitiveparser.html" title="PrimitiveParser"><code class="computeroutput"><span class="identifier">PrimitiveParser</span></code></a>. 209 </p> 210<div class="informaltable"><table class="table"> 211<colgroup> 212<col> 213<col> 214</colgroup> 215<thead><tr> 216<th> 217 <p> 218 Expression 219 </p> 220 </th> 221<th> 222 <p> 223 Semantics 224 </p> 225 </th> 226</tr></thead> 227<tbody> 228<tr> 229<td> 230 <p> 231</p> 232<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">bool_</span> 233</pre> 234<p> 235 </p> 236 </td> 237<td> 238 <p> 239 Parse a boolean using the default policies (<code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>). 240 </p> 241 </td> 242</tr> 243<tr> 244<td> 245 <p> 246</p> 247<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">lit</span><span class="special">(</span><span class="identifier">boolean</span><span class="special">)</span> 248<span class="identifier">bool_</span><span class="special">(</span><span class="identifier">boolean</span><span class="special">)</span> 249</pre> 250<p> 251 </p> 252 </td> 253<td> 254 <p> 255 Match the literal <code class="computeroutput"><span class="identifier">boolean</span></code> 256 using the default policies (<code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>). The parser will fail 257 if the parsed value is not equal to the specified value. 258 </p> 259 </td> 260</tr> 261<tr> 262<td> 263 <p> 264</p> 265<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">true_</span> 266<span class="identifier">false_</span> 267</pre> 268<p> 269 </p> 270 </td> 271<td> 272 <p> 273 Match <code class="computeroutput"><span class="string">"true"</span></code> 274 and <code class="computeroutput"><span class="string">"false"</span></code>, 275 respectively. 276 </p> 277 </td> 278</tr> 279<tr> 280<td> 281 <p> 282</p> 283<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">bool_parser</span><span class="special"><</span> 284 <span class="identifier">T</span><span class="special">,</span> <span class="identifier">BoolPolicies</span> 285<span class="special">>()</span> 286</pre> 287<p> 288 </p> 289 </td> 290<td> 291 <p> 292 Parse a real of type <code class="computeroutput"><span class="identifier">T</span></code> 293 using <code class="computeroutput"><span class="identifier">BoolPolicies</span></code>. 294 </p> 295 </td> 296</tr> 297<tr> 298<td> 299 <p> 300</p> 301<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">bool_parser</span><span class="special"><</span> 302 <span class="identifier">T</span><span class="special">,</span> <span class="identifier">BoolPolicies</span> 303<span class="special">>()(</span><span class="identifier">boolean</span><span class="special">)</span> 304</pre> 305<p> 306 </p> 307 </td> 308<td> 309 <p> 310 Match the literal <code class="computeroutput"><span class="identifier">boolean</span></code> 311 of type <code class="computeroutput"><span class="identifier">T</span></code> using 312 <code class="computeroutput"><span class="identifier">BoolPolicies</span></code>. 313 The parser will fail if the parsed value is not equal to the 314 specified value. 315 </p> 316 </td> 317</tr> 318</tbody> 319</table></div> 320<div class="note"><table border="0" summary="Note"> 321<tr> 322<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 323<th align="left">Note</th> 324</tr> 325<tr><td align="left" valign="top"><p> 326 All boolean parsers properly respect the <a class="link" href="../directive/no_case.html" title="Parser Directive Inhibiting Case Sensitivity (no_case[])"><code class="computeroutput"><span class="identifier">no_case</span></code></a><code class="computeroutput"><span class="special">[]</span></code> 327 directive. 328 </p></td></tr> 329</table></div> 330<h6> 331<a name="spirit.qi.reference.numeric.boolean.h7"></a> 332 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.attributes"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.attributes">Attributes</a> 333 </h6> 334<div class="informaltable"><table class="table"> 335<colgroup> 336<col> 337<col> 338</colgroup> 339<thead><tr> 340<th> 341 <p> 342 Expression 343 </p> 344 </th> 345<th> 346 <p> 347 Attribute 348 </p> 349 </th> 350</tr></thead> 351<tbody> 352<tr> 353<td> 354 <p> 355</p> 356<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">lit</span><span class="special">(</span><span class="identifier">boolean</span><span class="special">)</span> 357</pre> 358<p> 359 </p> 360 </td> 361<td> 362 <p> 363 <code class="computeroutput"><span class="identifier">unused</span></code> 364 </p> 365 </td> 366</tr> 367<tr> 368<td> 369 <p> 370</p> 371<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">true_</span> 372<span class="identifier">false_</span> 373<span class="identifier">bool_</span> 374<span class="identifier">bool_</span><span class="special">(</span><span class="identifier">boolean</span><span class="special">)</span> 375</pre> 376<p> 377 </p> 378 </td> 379<td> 380 <p> 381 <code class="computeroutput"><span class="keyword">bool</span></code> 382 </p> 383 </td> 384</tr> 385<tr> 386<td> 387 <p> 388</p> 389<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">bool_parser</span><span class="special"><</span> 390 <span class="identifier">T</span><span class="special">,</span> <span class="identifier">BoolPolicies</span> 391<span class="special">>()</span> 392<span class="identifier">bool_parser</span><span class="special"><</span> 393 <span class="identifier">T</span><span class="special">,</span> <span class="identifier">BoolPolicies</span> 394<span class="special">>()(</span><span class="identifier">num</span><span class="special">)</span> 395</pre> 396<p> 397 </p> 398 </td> 399<td> 400 <p> 401 <code class="computeroutput"><span class="identifier">T</span></code> 402 </p> 403 </td> 404</tr> 405</tbody> 406</table></div> 407<h6> 408<a name="spirit.qi.reference.numeric.boolean.h8"></a> 409 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.complexity"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.complexity">Complexity</a> 410 </h6> 411<div class="blockquote"><blockquote class="blockquote"><p> 412 O(N), where N is the number of characters being parsed. 413 </p></blockquote></div> 414<h6> 415<a name="spirit.qi.reference.numeric.boolean.h9"></a> 416 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.minimum_expression_requirements_for__code__phrase_role__identifier__b__phrase___code_"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.minimum_expression_requirements_for__code__phrase_role__identifier__b__phrase___code_">Minimum 417 Expression Requirements for <code class="computeroutput"><span class="identifier">B</span></code></a> 418 </h6> 419<p> 420 The boolean type, <code class="computeroutput"><span class="identifier">B</span></code>, 421 the minimum expression requirements listed below must be valid. Take 422 note that additional requirements may be imposed by custom policies. 423 </p> 424<div class="informaltable"><table class="table"> 425<colgroup> 426<col> 427<col> 428</colgroup> 429<thead><tr> 430<th> 431 <p> 432 Expression 433 </p> 434 </th> 435<th> 436 <p> 437 Semantics 438 </p> 439 </th> 440</tr></thead> 441<tbody><tr> 442<td> 443 <p> 444 <code class="computeroutput"><span class="identifier">B</span><span class="special">(</span><span class="keyword">bool</span><span class="special">)</span></code> 445 </p> 446 </td> 447<td> 448 <p> 449 Constructible from a <code class="computeroutput"><span class="keyword">bool</span></code>. 450 </p> 451 </td> 452</tr></tbody> 453</table></div> 454<h6> 455<a name="spirit.qi.reference.numeric.boolean.h10"></a> 456 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code_"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code_">Boolean 457 <code class="computeroutput"><span class="identifier">Policies</span></code></a> 458 </h6> 459<p> 460 The boolean <code class="computeroutput"><span class="identifier">Policies</span></code> 461 template parameter is a class that groups all the policies that control 462 the parser's behavior. Policies control the boolean parsers' behavior. 463 </p> 464<p> 465 The default is <code class="computeroutput"><span class="identifier">bool_policies</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>. The default is provided to take 466 care of the most common case (there are many ways to represent, and hence 467 parse, boolean numbers). In most cases, the default policies are sufficient 468 and can be used straight out of the box. They are designed to parse boolean 469 value of the form <code class="computeroutput"><span class="string">"true"</span></code> 470 and <code class="computeroutput"><span class="string">"false"</span></code>. 471 </p> 472<h6> 473<a name="spirit.qi.reference.numeric.boolean.h11"></a> 474 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__expression_requirements"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__expression_requirements">Boolean 475 <code class="computeroutput"><span class="identifier">Policies</span></code> Expression Requirements</a> 476 </h6> 477<p> 478 For models of boolean <code class="computeroutput"><span class="identifier">Policies</span></code> 479 the following expressions must be valid: 480 </p> 481<div class="informaltable"><table class="table"> 482<colgroup> 483<col> 484<col> 485</colgroup> 486<thead><tr> 487<th> 488 <p> 489 Expression 490 </p> 491 </th> 492<th> 493 <p> 494 Semantics 495 </p> 496 </th> 497</tr></thead> 498<tbody> 499<tr> 500<td> 501 <p> 502 <code class="computeroutput"><span class="identifier">BP</span><span class="special">::</span><span class="identifier">parse_true</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> 503 <span class="identifier">l</span><span class="special">,</span> 504 <span class="identifier">attr</span><span class="special">)</span></code> 505 </p> 506 </td> 507<td> 508 <p> 509 Parse a <code class="computeroutput"><span class="keyword">true</span></code> value. 510 </p> 511 </td> 512</tr> 513<tr> 514<td> 515 <p> 516 <code class="computeroutput"><span class="identifier">BP</span><span class="special">::</span><span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> 517 <span class="identifier">l</span><span class="special">,</span> 518 <span class="identifier">attr</span><span class="special">)</span></code> 519 </p> 520 </td> 521<td> 522 <p> 523 Parse a <code class="computeroutput"><span class="keyword">false</span></code> 524 value. 525 </p> 526 </td> 527</tr> 528</tbody> 529</table></div> 530<p> 531 The functions should return true if the required representations of 532 <code class="computeroutput"><span class="keyword">true</span></code> or <code class="computeroutput"><span class="keyword">false</span></code> 533 have been found. In this case the attribute <code class="computeroutput"><span class="identifier">n</span></code> 534 should be set to the matched value (<code class="computeroutput"><span class="keyword">true</span></code> 535 or <code class="computeroutput"><span class="keyword">false</span></code>). 536 </p> 537<h6> 538<a name="spirit.qi.reference.numeric.boolean.h12"></a> 539 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__specializations"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.boolean__code__phrase_role__identifier__policies__phrase___code__specializations">Boolean 540 <code class="computeroutput"><span class="identifier">Policies</span></code> Specializations</a> 541 </h6> 542<p> 543 The easiest way to implement a proper boolean parsing policy is to derive 544 a new type from the type <code class="computeroutput"><span class="identifier">bool_policies</span></code> 545 while overriding the aspects of the parsing which need to be changed. 546 For example, here's the implementation of a boolean parsing policy interpreting 547 the string <code class="computeroutput"><span class="string">"eurt"</span></code> 548 (i.e. "true" spelled backwards) as <code class="computeroutput"><span class="keyword">false</span></code>: 549 </p> 550<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">backwards_bool_policies</span> <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">bool_policies</span><span class="special"><></span> 551<span class="special">{</span> 552 <span class="comment">// we want to interpret a 'true' spelled backwards as 'false'</span> 553 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attribute</span><span class="special">></span> 554 <span class="keyword">static</span> <span class="keyword">bool</span> 555 <span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">Iterator</span><span class="special">&</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">)</span> 556 <span class="special">{</span> 557 <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> 558 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">string_parse</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">unused</span><span class="special">))</span> 559 <span class="special">{</span> 560 <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span><span class="special">::</span><span class="identifier">assign_to</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">);</span> <span class="comment">// result is false</span> 561 <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 562 <span class="special">}</span> 563 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 564 <span class="special">}</span> 565<span class="special">};</span> 566</pre> 567<h6> 568<a name="spirit.qi.reference.numeric.boolean.h13"></a> 569 <span class="phrase"><a name="spirit.qi.reference.numeric.boolean.example"></a></span><a class="link" href="boolean.html#spirit.qi.reference.numeric.boolean.example">Example</a> 570 </h6> 571<div class="note"><table border="0" summary="Note"> 572<tr> 573<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 574<th align="left">Note</th> 575</tr> 576<tr><td align="left" valign="top"><p> 577 The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> 578 section. 579 </p></td></tr> 580</table></div> 581<p> 582 Some using declarations: 583 </p> 584<p> 585</p> 586<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">val</span><span class="special">;</span> 587<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">qi</span><span class="special">::</span><span class="identifier">bool_</span><span class="special">;</span> 588<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">qi</span><span class="special">::</span><span class="identifier">bool_parser</span><span class="special">;</span> 589<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">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> 590</pre> 591<p> 592 </p> 593<p> 594 Basic real number parsing: 595 </p> 596<p> 597</p> 598<pre class="programlisting"><span class="comment">// bool</span> 599<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">);</span> 600<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">);</span> 601<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">(</span><span class="keyword">true</span><span class="special">));</span> 602<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">(</span><span class="keyword">false</span><span class="special">));</span> 603<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">(</span><span class="identifier">val</span><span class="special">(</span><span class="keyword">true</span><span class="special">)));</span> 604<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">bool_</span><span class="special">(</span><span class="identifier">val</span><span class="special">(</span><span class="keyword">false</span><span class="special">)));</span> 605 606<span class="comment">// literals</span> 607<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">lit</span><span class="special">(</span><span class="keyword">true</span><span class="special">));</span> 608<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">lit</span><span class="special">(</span><span class="keyword">false</span><span class="special">));</span> 609<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">lit</span><span class="special">(</span><span class="identifier">val</span><span class="special">(</span><span class="keyword">true</span><span class="special">)));</span> 610<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"false"</span><span class="special">,</span> <span class="identifier">lit</span><span class="special">(</span><span class="identifier">val</span><span class="special">(</span><span class="keyword">false</span><span class="special">)));</span> 611</pre> 612<p> 613 </p> 614<p> 615 A custom real number policy: 616 </p> 617<p> 618</p> 619<pre class="programlisting"><span class="comment">///////////////////////////////////////////////////////////////////////////////</span> 620<span class="comment">// These policies can be used to parse "eurt" (i.e. "true" spelled backwards)</span> 621<span class="comment">// as `false`</span> 622<span class="comment">///////////////////////////////////////////////////////////////////////////////</span> 623<span class="keyword">struct</span> <span class="identifier">backwards_bool_policies</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="identifier">bool_policies</span><span class="special"><></span> 624<span class="special">{</span> 625 <span class="comment">// we want to interpret a 'true' spelled backwards as 'false'</span> 626 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attribute</span><span class="special">></span> 627 <span class="keyword">static</span> <span class="keyword">bool</span> 628 <span class="identifier">parse_false</span><span class="special">(</span><span class="identifier">Iterator</span><span class="special">&</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">)</span> 629 <span class="special">{</span> 630 <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> 631 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">string_parse</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">unused</span><span class="special">))</span> 632 <span class="special">{</span> 633 <span class="keyword">namespace</span> <span class="identifier">traits</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">traits</span><span class="special">;</span> 634 <span class="identifier">traits</span><span class="special">::</span><span class="identifier">assign_to</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">);</span> <span class="comment">// result is false</span> 635 <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 636 <span class="special">}</span> 637 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 638 <span class="special">}</span> 639<span class="special">};</span> 640</pre> 641<p> 642 </p> 643<p> 644 And its use: 645 </p> 646<p> 647</p> 648<pre class="programlisting"><span class="identifier">bool_parser</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">backwards_bool_policies</span><span class="special">></span> <span class="identifier">backwards_bool</span><span class="special">;</span> 649<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">);</span> 650<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">);</span> 651<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"true"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">(</span><span class="keyword">true</span><span class="special">));</span> 652<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"eurt"</span><span class="special">,</span> <span class="identifier">backwards_bool</span><span class="special">(</span><span class="keyword">false</span><span class="special">));</span> 653</pre> 654<p> 655 </p> 656</div> 657<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 658<td align="left"></td> 659<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 660 Distributed under the Boost Software License, Version 1.0. (See accompanying 661 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>) 662 </p> 663</div></td> 664</tr></table> 665<hr> 666<div class="spirit-nav"> 667<a accesskey="p" href="real.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../numeric.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="../operator.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 668</div> 669</body> 670</html> 671
