1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Difference Parser (a - b)</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="Parser Operators"> 9<link rel="prev" href="and_predicate.html" title="And-Predicate Parser (&a)"> 10<link rel="next" href="expect.html" title="Expectation Operator (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 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href="difference.html" title="Difference Parser (a - b)">Difference 28 Parser (<code class="computeroutput"><span class="identifier">a</span> <span class="special">-</span> 29 <span class="identifier">b</span></code>)</a> 30</h5></div></div></div> 31<h6> 32<a name="spirit.qi.reference.operator.difference.h0"></a> 33 <span class="phrase"><a name="spirit.qi.reference.operator.difference.description"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.description">Description</a> 34 </h6> 35<p> 36 The difference operator, <code class="computeroutput"><span class="identifier">a</span> 37 <span class="special">-</span> <span class="identifier">b</span></code>, 38 is a binary operator that matches the first (LHS) operand but not the 39 second (RHS). <a href="#ftn.spirit.qi.reference.operator.difference.f0" class="footnote" name="spirit.qi.reference.operator.difference.f0"><sup class="footnote">[8]</sup></a> 40 </p> 41<h6> 42<a name="spirit.qi.reference.operator.difference.h1"></a> 43 <span class="phrase"><a name="spirit.qi.reference.operator.difference.header"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.header">Header</a> 44 </h6> 45<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/difference.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_difference</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.operator.difference.h2"></a> 53 <span class="phrase"><a name="spirit.qi.reference.operator.difference.model_of"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.model_of">Model of</a> 54 </h6> 55<div class="blockquote"><blockquote class="blockquote"><p> 56 <a class="link" href="../parser_concepts/binaryparser.html" title="BinaryParser"><code class="computeroutput"><span class="identifier">BinaryParser</span></code></a> 57 </p></blockquote></div> 58<div class="variablelist"> 59<p class="title"><b>Notation</b></p> 60<dl class="variablelist"> 61<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code></span></dt> 62<dd><p> 63 A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> 64 </p></dd> 65</dl> 66</div> 67<h6> 68<a name="spirit.qi.reference.operator.difference.h3"></a> 69 <span class="phrase"><a name="spirit.qi.reference.operator.difference.expression_semantics"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.expression_semantics">Expression 70 Semantics</a> 71 </h6> 72<p> 73 Semantics of an expression is defined only where it differs from, or 74 is not defined in <a class="link" href="../parser_concepts/binaryparser.html" title="BinaryParser"><code class="computeroutput"><span class="identifier">BinaryParser</span></code></a>. 75 </p> 76<div class="informaltable"><table class="table"> 77<colgroup> 78<col> 79<col> 80</colgroup> 81<thead><tr> 82<th> 83 <p> 84 Expression 85 </p> 86 </th> 87<th> 88 <p> 89 Semantics 90 </p> 91 </th> 92</tr></thead> 93<tbody><tr> 94<td> 95 <p> 96 <code class="computeroutput"><span class="identifier">a</span> <span class="special">-</span> 97 <span class="identifier">b</span></code> 98 </p> 99 </td> 100<td> 101 <p> 102 Parse <code class="computeroutput"><span class="identifier">a</span></code> but 103 not <code class="computeroutput"><span class="identifier">b</span></code>. 104 </p> 105 </td> 106</tr></tbody> 107</table></div> 108<h6> 109<a name="spirit.qi.reference.operator.difference.h4"></a> 110 <span class="phrase"><a name="spirit.qi.reference.operator.difference.attributes"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.attributes">Attributes</a> 111 </h6> 112<p> 113 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound 114 Attribute Notation</a>. 115 </p> 116<div class="informaltable"><table class="table"> 117<colgroup> 118<col> 119<col> 120</colgroup> 121<thead><tr> 122<th> 123 <p> 124 Expression 125 </p> 126 </th> 127<th> 128 <p> 129 Attribute 130 </p> 131 </th> 132</tr></thead> 133<tbody><tr> 134<td> 135 <p> 136 <code class="computeroutput"><span class="identifier">a</span> <span class="special">-</span> 137 <span class="identifier">b</span></code> 138 </p> 139 </td> 140<td> 141 <p> 142</p> 143<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">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">-</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">A</span> 144<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">-</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">Unused</span></pre> 145<p> 146 </p> 147 </td> 148</tr></tbody> 149</table></div> 150<h6> 151<a name="spirit.qi.reference.operator.difference.h5"></a> 152 <span class="phrase"><a name="spirit.qi.reference.operator.difference.complexity"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.complexity">Complexity</a> 153 </h6> 154<div class="blockquote"><blockquote class="blockquote"><p> 155 The complexity of the difference parser is defined by the sum of the 156 complexities of both operands. 157 </p></blockquote></div> 158<h6> 159<a name="spirit.qi.reference.operator.difference.h6"></a> 160 <span class="phrase"><a name="spirit.qi.reference.operator.difference.example"></a></span><a class="link" href="difference.html#spirit.qi.reference.operator.difference.example">Example</a> 161 </h6> 162<div class="note"><table border="0" summary="Note"> 163<tr> 164<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 165<th align="left">Note</th> 166</tr> 167<tr><td align="left" valign="top"><p> 168 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> 169 section. 170 </p></td></tr> 171</table></div> 172<p> 173 Some using declarations: 174 </p> 175<p> 176</p> 177<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">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> 178</pre> 179<p> 180 </p> 181<p> 182 Parse a C/C++ style comment: 183 </p> 184<p> 185</p> 186<pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"/*A Comment*/"</span><span class="special">,</span> <span class="string">"/*"</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="string">"*/"</span><span class="special">)</span> <span class="special">>></span> <span class="string">"*/"</span><span class="special">);</span> 187</pre> 188<p> 189 </p> 190<div class="footnotes"> 191<br><hr style="width:100; text-align:left;margin-left: 0"> 192<div id="ftn.spirit.qi.reference.operator.difference.f0" class="footnote"><p><a href="#spirit.qi.reference.operator.difference.f0" class="para"><sup class="para">[8] </sup></a> 193 Unlike classic Spirit, with Spirit2, the expression will always fail 194 if the RHS is a successful match regardless if the RHS matches less 195 characters. For example, the rule <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"policeman"</span><span class="special">)</span> <span class="special">-</span> <span class="string">"police"</span></code> will always fail to 196 match. Spirit2 does not count the matching chars while parsing and 197 there is no reliable and fast way to check if the LHS matches more 198 than the RHS. 199 </p></div> 200</div> 201</div> 202<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 203<td align="left"></td> 204<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 205 Distributed under the Boost Software License, Version 1.0. (See accompanying 206 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>) 207 </p> 208</div></td> 209</tr></table> 210<hr> 211<div class="spirit-nav"> 212<a accesskey="p" href="and_predicate.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="expect.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 213</div> 214</body> 215</html> 216
