1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Generator Directives Controlling the Maximum Field Width (maxwidth[])</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="../directive.html" title="Generator Directives"> 9<link rel="prev" href="upperlower.html" title="Generator Directives Controlling Case Sensitivity (upper[], lower[])"> 10<link rel="next" href="buffer.html" title="Generator Directive for Temporary Output Buffering (buffer[])"> 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 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name="spirit.karma.reference.directive.maxwidth"></a><a class="link" href="maxwidth.html" title="Generator Directives Controlling the Maximum Field Width (maxwidth[])">Generator 28 Directives Controlling the Maximum Field Width (<code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[]</span></code>)</a> 29</h5></div></div></div> 30<h6> 31<a name="spirit.karma.reference.directive.maxwidth.h0"></a> 32 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.description"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.description">Description</a> 33 </h6> 34<p> 35 The <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[]</span></code> 36 directive allows to limit (truncate) the overall length of the output 37 generated by the embedded generator. 38 </p> 39<h6> 40<a name="spirit.karma.reference.directive.maxwidth.h1"></a> 41 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.header"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.header">Header</a> 42 </h6> 43<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/directive/maxwidth.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_maxwidth</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<div class="informaltable"><table class="table"> 50<colgroup><col></colgroup> 51<thead><tr><th> 52 <p> 53 Name 54 </p> 55 </th></tr></thead> 56<tbody><tr><td> 57 <p> 58 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">maxwidth</span> <span class="comment">// 59 alias: boost::spirit::karma::maxwidth</span></code> 60 </p> 61 </td></tr></tbody> 62</table></div> 63<h6> 64<a name="spirit.karma.reference.directive.maxwidth.h2"></a> 65 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.model_of"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.model_of">Model of</a> 66 </h6> 67<div class="blockquote"><blockquote class="blockquote"><p> 68 <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a> 69 </p></blockquote></div> 70<div class="variablelist"> 71<p class="title"><b>Notation</b></p> 72<dl class="variablelist"> 73<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt> 74<dd><p> 75 A generator object 76 </p></dd> 77<dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt> 78<dd><p> 79 Attribute type of the generator <code class="computeroutput"><span class="identifier">a</span></code> 80 </p></dd> 81<dt><span class="term"><code class="computeroutput"><span class="identifier">num</span></code></span></dt> 82<dd><p> 83 Numeric literal, any unsigned integer value, or a <a class="link" href="../basics.html#spirit.karma.reference.basics.lazy_argument">Lazy 84 Argument</a> that evaluates to an unsigned integer value 85 </p></dd> 86</dl> 87</div> 88<h6> 89<a name="spirit.karma.reference.directive.maxwidth.h3"></a> 90 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.expression_semantics"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.expression_semantics">Expression 91 Semantics</a> 92 </h6> 93<p> 94 Semantics of an expression is defined only where it differs from, or 95 is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>. 96 </p> 97<div class="informaltable"><table class="table"> 98<colgroup> 99<col> 100<col> 101</colgroup> 102<thead><tr> 103<th> 104 <p> 105 Expression 106 </p> 107 </th> 108<th> 109 <p> 110 Semantics 111 </p> 112 </th> 113</tr></thead> 114<tbody> 115<tr> 116<td> 117 <p> 118 <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> 119 </p> 120 </td> 121<td> 122 <p> 123 Limit the overall length of the emitted output of the embedded 124 generator (including characters generated by automatic delimiting) 125 to the number of characters as defined by the preprocessor 126 constant <code class="computeroutput"><span class="identifier">BOOST_KARMA_DEFAULT_FIELD_MAXWIDTH</span></code>. 127 Any additional output is truncated. The directive succeeds 128 as long as the embedded generator succeeded (unless the underlying 129 output stream reports an error). 130 </p> 131 </td> 132</tr> 133<tr> 134<td> 135 <p> 136 <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code> 137 </p> 138 </td> 139<td> 140 <p> 141 Limit the overall length of the emitted output of the embedded 142 generator (including characters generated by automatic delimiting) 143 to the number of characters as defined by <code class="computeroutput"><span class="identifier">num</span></code>. 144 Any additional output is truncated. The directive succeeds 145 as long as the embedded generator succeeded (unless the underlying 146 output stream reports an error). 147 </p> 148 </td> 149</tr> 150</tbody> 151</table></div> 152<div class="note"><table border="0" summary="Note"> 153<tr> 154<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 155<th align="left">Note</th> 156</tr> 157<tr><td align="left" valign="top"> 158<p> 159 The <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[]</span></code> 160 generator directive does not pad the generated output to fill the specified 161 column width. If the emitted output is shorter than the specified (or 162 implied) column width, the generated output will be more narrow than 163 the column width. 164 </p> 165<p> 166 If the output needs to always be equal to a specified column width, 167 use one of the alignment directives <code class="computeroutput"><span class="identifier">left</span><span class="special">-</span><span class="identifier">align</span><span class="special">[]</span></code>, <code class="computeroutput"><span class="identifier">center</span><span class="special">[]</span></code>, or <code class="computeroutput"><span class="identifier">right_align</span><span class="special">[]</span></code>, for instance: 168</p> 169<pre class="programlisting"><span class="identifier">maxwidth</span><span class="special">(</span><span class="number">8</span><span class="special">)[</span><span class="identifier">left_align</span><span class="special">(</span><span class="number">8</span><span class="special">)[</span><span class="string">"1234"</span><span class="special">]]</span> 170</pre> 171<p> 172 which will output: <code class="computeroutput"><span class="string">"1234 "</span></code> 173 (without the quotes). 174 </p> 175</td></tr> 176</table></div> 177<h6> 178<a name="spirit.karma.reference.directive.maxwidth.h4"></a> 179 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.attributes"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.attributes">Attributes</a> 180 </h6> 181<p> 182 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound 183 Attribute Notation</a>. 184 </p> 185<div class="informaltable"><table class="table"> 186<colgroup> 187<col> 188<col> 189</colgroup> 190<thead><tr> 191<th> 192 <p> 193 Expression 194 </p> 195 </th> 196<th> 197 <p> 198 Attribute 199 </p> 200 </th> 201</tr></thead> 202<tbody> 203<tr> 204<td> 205 <p> 206 <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> 207 </p> 208 </td> 209<td> 210 <p> 211</p> 212<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">maxwidth</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span> 213<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="identifier">maxwidth</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> 214<p> 215 </p> 216 </td> 217</tr> 218<tr> 219<td> 220 <p> 221 <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code> 222 </p> 223 </td> 224<td> 225 <p> 226</p> 227<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">maxwidth</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span> 228<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="identifier">maxwidth</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre> 229<p> 230 </p> 231 </td> 232</tr> 233</tbody> 234</table></div> 235<h6> 236<a name="spirit.karma.reference.directive.maxwidth.h5"></a> 237 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.complexity"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.complexity">Complexity</a> 238 </h6> 239<div class="blockquote"><blockquote class="blockquote"><p> 240 The overall complexity of the generator directive <code class="computeroutput"><span class="identifier">maxwidth</span><span class="special">[]</span></code> is defined by the complexity of its 241 embedded generator. The complexity of the directive itself is O(N), 242 where <code class="computeroutput"><span class="identifier">N</span></code> is the number 243 of characters generated by the maxwidth directive. 244 </p></blockquote></div> 245<h6> 246<a name="spirit.karma.reference.directive.maxwidth.h6"></a> 247 <span class="phrase"><a name="spirit.karma.reference.directive.maxwidth.example"></a></span><a class="link" href="maxwidth.html#spirit.karma.reference.directive.maxwidth.example">Example</a> 248 </h6> 249<div class="note"><table border="0" summary="Note"> 250<tr> 251<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 252<th align="left">Note</th> 253</tr> 254<tr><td align="left" valign="top"><p> 255 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> 256 section. 257 </p></td></tr> 258</table></div> 259<p> 260 Some includes: 261 </p> 262<p> 263</p> 264<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> 265<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 266<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> 267</pre> 268<p> 269 </p> 270<p> 271 Some using declarations: 272 </p> 273<p> 274</p> 275<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> 276<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">maxwidth</span><span class="special">;</span> 277<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">left_align</span><span class="special">;</span> 278<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">right_align</span><span class="special">;</span> 279</pre> 280<p> 281 </p> 282<p> 283 Basic usage of <code class="computeroutput"><span class="identifier">maxwidth</span></code> 284 generator directive: 285 </p> 286<p> 287</p> 288<pre class="programlisting"><span class="identifier">test_generator</span><span class="special">(</span><span class="string">"01234"</span><span class="special">,</span> <span class="identifier">maxwidth</span><span class="special">(</span><span class="number">5</span><span class="special">)[</span><span class="string">"0123456789"</span><span class="special">]);</span> 289<span class="identifier">test_generator</span><span class="special">(</span><span class="string">" 012"</span><span class="special">,</span> <span class="identifier">maxwidth</span><span class="special">(</span><span class="number">5</span><span class="special">)[</span><span class="identifier">right_align</span><span class="special">(</span><span class="number">12</span><span class="special">)[</span><span class="string">"0123456789"</span><span class="special">]]);</span> 290<span class="identifier">test_generator</span><span class="special">(</span><span class="string">"0123 "</span><span class="special">,</span> <span class="identifier">maxwidth</span><span class="special">(</span><span class="number">8</span><span class="special">)[</span><span class="identifier">left_align</span><span class="special">(</span><span class="number">8</span><span class="special">)[</span><span class="string">"0123"</span><span class="special">]]);</span> 291</pre> 292<p> 293 </p> 294</div> 295<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 296<td align="left"></td> 297<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 298 Distributed under the Boost Software License, Version 1.0. (See accompanying 299 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>) 300 </p> 301</div></td> 302</tr></table> 303<hr> 304<div class="spirit-nav"> 305<a accesskey="p" href="upperlower.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../directive.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="buffer.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 306</div> 307</body> 308</html> 309
