1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Qi advance Parser</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 Repository 0.2"> 8<link rel="up" href="../primitive.html" title="Qi Parser Primitives"> 9<link rel="prev" href="../primitive.html" title="Qi Parser Primitives"> 10<link rel="next" href="flush_multi_pass.html" title="Qi flush_multi_pass parser"> 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="../primitive.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../primitive.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="flush_multi_pass.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="spirit_repository.qi_components.primitive.advance"></a><a class="link" href="advance.html" title="Qi advance Parser">Qi 28 advance Parser</a> 29</h4></div></div></div> 30<h6> 31<a name="spirit_repository.qi_components.primitive.advance.h0"></a> 32 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.description"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.description">Description</a> 33 </h6> 34<p> 35 The <span class="emphasis"><em>Spirit.Qi</em></span> <code class="computeroutput"><span class="identifier">advance</span></code> 36 is a primitive parser component allowing the parser to skip (advance) through 37 a specified number of iterations without performing unnecessary work: 38 </p> 39<pre class="programlisting"><span class="identifier">advance</span><span class="special">(</span><span class="identifier">distance</span><span class="special">)</span> 40</pre> 41<p> 42 The most obvious existing alternative to this, the <code class="computeroutput"><span class="identifier">repeat</span></code> 43 directive, will cause the parser to advance one iterator at a time while 44 usually performing operations at each step. In some cases that work is 45 unnecessary, as in the case where large binary objects are being parsed. 46 Take, for example, the following binary data: 47 </p> 48<pre class="programlisting">00 00 00 01 77 fc b4 51 0a b3 b7 ... 1e 60 70 b6 00 00 01 00 49</pre> 50<p> 51 If the first 4 bytes are a little-endian 32-bit integer describing the 52 length of the subsequent data, but the data itself is not relevant to parsing, 53 then the repeat directive would cause all of the subsequent 16 MB of data 54 to be consumed one byte at a time while generating page faults or other 55 superfluous I/O. If the value is large, as it is in this case, the parser 56 becomes very slow. 57 </p> 58<pre class="programlisting"><span class="identifier">little_dword</span><span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</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">byte_</span><span class="special">]</span> <span class="special">>></span> <span class="identifier">little_dword</span><span class="special">...</span> 59</pre> 60<p> 61 The <code class="computeroutput"><span class="identifier">advance</span></code> parser component 62 solves this problem by performing as little work as possible to advance 63 the parser's iterator, and will optimize for the case of random-access 64 iterators by advancing directly to the desired relative iterator position. 65 </p> 66<pre class="programlisting"><span class="identifier">little_dword</span><span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> <span class="special">>></span> <span class="identifier">advance</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">little_dword</span><span class="special">...</span> 67</pre> 68<h6> 69<a name="spirit_repository.qi_components.primitive.advance.h1"></a> 70 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.header"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.header">Header</a> 71 </h6> 72<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/repository/home/qi/primitive/advance.hpp></span> 73<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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_advance</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 74</pre> 75<h6> 76<a name="spirit_repository.qi_components.primitive.advance.h2"></a> 77 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.synopsis"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.synopsis">Synopsis</a> 78 </h6> 79<pre class="programlisting"><span class="identifier">advance</span><span class="special">(</span><span class="identifier">distance</span><span class="special">)</span> 80</pre> 81<h6> 82<a name="spirit_repository.qi_components.primitive.advance.h3"></a> 83 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.parameters"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.parameters">Parameters</a> 84 </h6> 85<div class="informaltable"><table class="table"> 86<colgroup> 87<col> 88<col> 89</colgroup> 90<thead><tr> 91<th> 92 <p> 93 Parameter 94 </p> 95 </th> 96<th> 97 <p> 98 Description 99 </p> 100 </th> 101</tr></thead> 102<tbody><tr> 103<td> 104 <p> 105 'distance' 106 </p> 107 </td> 108<td> 109 <p> 110 The distance that the iterator shall be advanced 111 </p> 112 </td> 113</tr></tbody> 114</table></div> 115<h6> 116<a name="spirit_repository.qi_components.primitive.advance.h4"></a> 117 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.attribute"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.attribute">Attribute</a> 118 </h6> 119<p> 120 The <code class="computeroutput"><span class="identifier">advance</span></code> component exposes 121 no attribute (the exposed attribute type is <code class="computeroutput"><span class="identifier">unused_type</span></code>): 122 </p> 123<pre class="programlisting"><span class="identifier">advance</span> <span class="special">--></span> <span class="identifier">unused</span> 124</pre> 125<h6> 126<a name="spirit_repository.qi_components.primitive.advance.h5"></a> 127 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.example"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.example">Example</a> 128 </h6> 129<p> 130 The following example shows simple use cases of the <code class="computeroutput"><span class="identifier">advance</span></code> 131 component. We will illustrate its usage by generating parsers for some 132 binary data (for the full example code see <a href="../../../../../example/qi/advance.cpp" target="_top">advance.cpp</a>) 133 </p> 134<h6> 135<a name="spirit_repository.qi_components.primitive.advance.h6"></a> 136 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.prerequisites"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.prerequisites">Prerequisites</a> 137 </h6> 138<p> 139 In addition to the main header file needed to include the core components 140 implemented in <span class="emphasis"><em>Spirit.Qi</em></span> we add the header file needed 141 for the new <code class="computeroutput"><span class="identifier">advance</span></code> component. 142 </p> 143<p> 144</p> 145<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">qi</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 146<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> 147<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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_advance</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 148</pre> 149<p> 150 </p> 151<p> 152 In order to make the examples below more readable we introduce or use the 153 following namespaces. 154 </p> 155<p> 156</p> 157<pre class="programlisting"><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> 158<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">repository</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">advance</span><span class="special">;</span> 159</pre> 160<p> 161 </p> 162<h6> 163<a name="spirit_repository.qi_components.primitive.advance.h7"></a> 164 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.setting_up_the_grammar"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.setting_up_the_grammar">Setting 165 up the Grammar</a> 166 </h6> 167<p> 168 This is a very simple grammar that recognizes several fields of a binary 169 stream of data. There are two fields explicitly delimited by a field indicating 170 the number of bytes that are spanned. They are separated by a literal string. 171 </p> 172<p> 173</p> 174<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> 175<span class="keyword">struct</span> <span class="identifier">advance_grammar</span> <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">locals</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> 176<span class="special">{</span> 177 <span class="identifier">advance_grammar</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">advance_grammar</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">start</span><span class="special">)</span> 178 <span class="special">{</span> 179 <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">byte_</span><span class="special">;</span> 180 <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">eoi</span><span class="special">;</span> 181 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">labels</span><span class="special">;</span> 182 183 <span class="identifier">start</span> 184 <span class="special">=</span> <span class="identifier">byte_</span> <span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> 185 <span class="special">>></span> <span class="identifier">advance</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span> 186 <span class="special">>></span> <span class="string">"boost"</span> 187 <span class="special">>></span> <span class="identifier">byte_</span> <span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> 188 <span class="special">>></span> <span class="special">(</span><span class="identifier">advance</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span> <span class="special">|</span> <span class="string">"qi"</span><span class="special">)</span> <span class="comment">// note alternative when advance fails</span> 189 <span class="special">>></span> <span class="identifier">eoi</span> 190 <span class="special">;</span> 191 <span class="special">}</span> 192 193 <span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">locals</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">start</span><span class="special">;</span> 194<span class="special">};</span> 195</pre> 196<p> 197 </p> 198<p> 199 Note that the second binary field may either contain the number of specified 200 bytes, or the word "qi". If the <code class="computeroutput"><span class="identifier">advance</span></code> 201 parser component fails to advance the specified number of bytes before 202 reaching the end of input, it will fail and the parser will attempt to 203 descend into alternatives. 204 </p> 205<h6> 206<a name="spirit_repository.qi_components.primitive.advance.h8"></a> 207 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.parsing_a_correctly_delimited_string_of_data"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.parsing_a_correctly_delimited_string_of_data">Parsing 208 a Correctly-delimited String of Data</a> 209 </h6> 210<p> 211 The data below is correctly delimited and will thus result in a valid parse. 212 Note that both random-access and bidirectional iterators are used here. 213 </p> 214<p> 215</p> 216<pre class="programlisting"><span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="keyword">const</span> <span class="identifier">alt1</span><span class="special">[]</span> <span class="special">=</span> 217<span class="special">{</span> 218 <span class="number">5</span><span class="special">,</span> <span class="comment">// number of bytes to advance</span> 219 <span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">5</span><span class="special">,</span> <span class="comment">// data to advance through</span> 220 <span class="char">'b'</span><span class="special">,</span> <span class="char">'o'</span><span class="special">,</span> <span class="char">'o'</span><span class="special">,</span> <span class="char">'s'</span><span class="special">,</span> <span class="char">'t'</span><span class="special">,</span> <span class="comment">// word to parse</span> 221 <span class="number">2</span><span class="special">,</span> <span class="comment">// number of bytes to advance</span> 222 <span class="number">11</span><span class="special">,</span> <span class="number">12</span> <span class="comment">// more data to advance through</span> 223 <span class="comment">// eoi</span> 224<span class="special">};</span> 225 226<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span> <span class="identifier">alt1_string</span><span class="special">(</span><span class="identifier">alt1</span><span class="special">,</span> <span class="identifier">alt1</span> <span class="special">+</span> <span class="keyword">sizeof</span> <span class="identifier">alt1</span><span class="special">);</span> 227<span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">alt1_list</span><span class="special">(</span><span class="identifier">alt1</span><span class="special">,</span> <span class="identifier">alt1</span> <span class="special">+</span> <span class="keyword">sizeof</span> <span class="identifier">alt1</span><span class="special">);</span> 228 229<span class="identifier">result</span> <span class="special">=</span> 230 <span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">alt1_string</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">alt1_string</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> 231 <span class="special">,</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">advance_grammar</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">const_iterator</span><span class="special">>())</span> 232 <span class="special">?</span> <span class="string">"succeeded"</span> <span class="special">:</span> <span class="string">"failed"</span><span class="special">;</span> 233<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing alt1 using random access iterator "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 234 235<span class="identifier">result</span> <span class="special">=</span> 236 <span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">alt1_list</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">alt1_list</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> 237 <span class="special">,</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">advance_grammar</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">const_iterator</span><span class="special">>())</span> 238 <span class="special">?</span> <span class="string">"succeeded"</span> <span class="special">:</span> <span class="string">"failed"</span><span class="special">;</span> 239<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing alt1 using bidirectional iterator "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 240</pre> 241<p> 242 </p> 243<h6> 244<a name="spirit_repository.qi_components.primitive.advance.h9"></a> 245 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.parsing_the_alternative_representation"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.parsing_the_alternative_representation">Parsing 246 the Alternative Representation</a> 247 </h6> 248<p> 249 The data below is not correctly delimited, but will correctly parse because 250 the alternative word "qi" is available. 251 </p> 252<p> 253</p> 254<pre class="programlisting"><span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="keyword">const</span> <span class="identifier">alt2</span><span class="special">[]</span> <span class="special">=</span> 255<span class="special">{</span> 256 <span class="number">2</span><span class="special">,</span> <span class="comment">// number of bytes to advance</span> 257 <span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="comment">// data to advance through</span> 258 <span class="char">'b'</span><span class="special">,</span> <span class="char">'o'</span><span class="special">,</span> <span class="char">'o'</span><span class="special">,</span> <span class="char">'s'</span><span class="special">,</span> <span class="char">'t'</span><span class="special">,</span> <span class="comment">// word to parse</span> 259 <span class="number">4</span><span class="special">,</span> <span class="comment">// number of bytes to advance</span> 260 <span class="char">'q'</span><span class="special">,</span> <span class="char">'i'</span> <span class="comment">// alternative (advance won't work)</span> 261 <span class="comment">// eoi</span> 262<span class="special">};</span> 263 264<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span> <span class="identifier">alt2_string</span><span class="special">(</span><span class="identifier">alt2</span><span class="special">,</span> <span class="identifier">alt2</span> <span class="special">+</span> <span class="keyword">sizeof</span> <span class="identifier">alt2</span><span class="special">);</span> 265<span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">alt2_list</span><span class="special">(</span><span class="identifier">alt2</span><span class="special">,</span> <span class="identifier">alt2</span> <span class="special">+</span> <span class="keyword">sizeof</span> <span class="identifier">alt2</span><span class="special">);</span> 266 267<span class="identifier">result</span> <span class="special">=</span> 268 <span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">alt2_string</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">alt2_string</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> 269 <span class="special">,</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">advance_grammar</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">const_iterator</span><span class="special">>())</span> 270 <span class="special">?</span> <span class="string">"succeeded"</span> <span class="special">:</span> <span class="string">"failed"</span><span class="special">;</span> 271<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing alt2 using random access iterator "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 272 273<span class="identifier">result</span> <span class="special">=</span> 274 <span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">alt2_list</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">alt2_list</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> 275 <span class="special">,</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">advance_grammar</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">const_iterator</span><span class="special">>())</span> 276 <span class="special">?</span> <span class="string">"succeeded"</span> <span class="special">:</span> <span class="string">"failed"</span><span class="special">;</span> 277<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing alt2 using bidirectional iterator "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 278</pre> 279<p> 280 </p> 281<h6> 282<a name="spirit_repository.qi_components.primitive.advance.h10"></a> 283 <span class="phrase"><a name="spirit_repository.qi_components.primitive.advance.notes"></a></span><a class="link" href="advance.html#spirit_repository.qi_components.primitive.advance.notes">Notes</a> 284 </h6> 285<p> 286 The <code class="computeroutput"><span class="identifier">advance</span></code> parser component 287 will fail unconditionally on negative values. It will never attempt to 288 advance the iterator in the reverse direction. 289 </p> 290</div> 291<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 292<td align="left"></td> 293<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 294 Distributed under the Boost Software License, Version 1.0. (See accompanying 295 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>) 296 </p> 297</div></td> 298</tr></table> 299<hr> 300<div class="spirit-nav"> 301<a accesskey="p" href="../primitive.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../primitive.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="flush_multi_pass.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 302</div> 303</body> 304</html> 305
