1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Integer Traits</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="Boost.Integer"> 8<link rel="up" href="../index.html" title="Boost.Integer"> 9<link rel="prev" href="../index.html" title="Boost.Integer"> 10<link rel="next" href="integer.html" title="Integer Type Selection"> 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="../index.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="integer.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="boost_integer.traits"></a><a class="link" href="traits.html" title="Integer Traits">Integer Traits</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="traits.html#boost_integer.traits.motivation">Motivation</a></span></dt> 31<dt><span class="section"><a href="traits.html#boost_integer.traits.synopsis">Synopsis</a></span></dt> 32<dt><span class="section"><a href="traits.html#boost_integer.traits.description">Description</a></span></dt> 33<dt><span class="section"><a href="traits.html#boost_integer.traits.test_program">Test Program</a></span></dt> 34<dt><span class="section"><a href="traits.html#boost_integer.traits.acknowledgements">Acknowledgements</a></span></dt> 35</dl></div> 36<div class="section"> 37<div class="titlepage"><div><div><h3 class="title"> 38<a name="boost_integer.traits.motivation"></a><a class="link" href="traits.html#boost_integer.traits.motivation" title="Motivation">Motivation</a> 39</h3></div></div></div> 40<p> 41 The C++ Standard Library <limits> header supplies a class template 42 <code class="computeroutput"><span class="identifier">numeric_limits</span><span class="special"><></span></code> 43 with specializations for each fundamental type. 44 </p> 45<p> 46 For integer types, the interesting members of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><></span></code> are: 47 </p> 48<pre class="programlisting"><span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_specialized</span><span class="special">;</span> <span class="comment">// Will be true for integer types.</span> 49<span class="keyword">static</span> <span class="identifier">T</span> <span class="identifier">min</span><span class="special">()</span> <span class="keyword">throw</span><span class="special">();</span> <span class="comment">// Smallest representable value.</span> 50<span class="keyword">static</span> <span class="identifier">T</span> <span class="identifier">max</span><span class="special">()</span> <span class="keyword">throw</span><span class="special">();</span> <span class="comment">// Largest representable value.</span> 51<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">digits</span><span class="special">;</span> <span class="comment">// For integers, the number of value bits.</span> 52<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">digits10</span><span class="special">;</span> <span class="comment">// The number of base 10 digits that can be represented.</span> 53<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_signed</span><span class="special">;</span> <span class="comment">// True if the type is signed.</span> 54<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_integer</span><span class="special">;</span> <span class="comment">// Will be true for all integer types.</span> 55</pre> 56<p> 57 For many uses, these are sufficient. But min() and max() are problematical 58 because they are not constant expressions (std::5.19), yet some usages require 59 constant expressions. 60 </p> 61<p> 62 The template class <code class="literal">integer_traits</code> addresses this problem. 63 </p> 64</div> 65<div class="section"> 66<div class="titlepage"><div><div><h3 class="title"> 67<a name="boost_integer.traits.synopsis"></a><a class="link" href="traits.html#boost_integer.traits.synopsis" title="Synopsis">Synopsis</a> 68</h3></div></div></div> 69<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 70 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 71 <span class="keyword">class</span> <span class="identifier">integer_traits</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> 72 <span class="special">{</span> 73 <span class="keyword">public</span><span class="special">:</span> 74 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_integral</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span> 75 <span class="comment">//</span> 76 <span class="comment">// These members are defined only if T is a built-in</span> 77 <span class="comment">// integal type:</span> 78 <span class="comment">//</span> 79 <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">const_min</span> <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span> 80 <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">const_max</span> <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span> 81 <span class="special">};</span> 82<span class="special">}</span> 83</pre> 84</div> 85<div class="section"> 86<div class="titlepage"><div><div><h3 class="title"> 87<a name="boost_integer.traits.description"></a><a class="link" href="traits.html#boost_integer.traits.description" title="Description">Description</a> 88</h3></div></div></div> 89<p> 90 Template class <code class="literal">integer_traits</code> is derived from <code class="literal">std::numeric_limits</code>. 91 The primary specialization adds the single <code class="literal">bool</code> member 92 <code class="literal">is_integral</code> with the compile-time constant value <code class="literal">false</code>. 93 However, for all integral types <code class="literal">T</code> (std::3.9.1/7 [basic.fundamental]), 94 there are specializations provided with the following compile-time constants 95 defined: 96 </p> 97<div class="informaltable"><table class="table"> 98<colgroup> 99<col> 100<col> 101<col> 102</colgroup> 103<thead><tr> 104<th> 105 <p> 106 member 107 </p> 108 </th> 109<th> 110 <p> 111 type 112 </p> 113 </th> 114<th> 115 <p> 116 value 117 </p> 118 </th> 119</tr></thead> 120<tbody> 121<tr> 122<td> 123 <p> 124 <code class="literal">is_integral</code> 125 </p> 126 </td> 127<td> 128 <p> 129 bool 130 </p> 131 </td> 132<td> 133 <p> 134 <code class="literal">true</code> 135 </p> 136 </td> 137</tr> 138<tr> 139<td> 140 <p> 141 <code class="literal">const_min</code> 142 </p> 143 </td> 144<td> 145 <p> 146 <code class="literal">T</code> 147 </p> 148 </td> 149<td> 150 <p> 151 equivalent to <code class="literal">std::numeric_limits<T>::min()</code> 152 </p> 153 </td> 154</tr> 155<tr> 156<td> 157 <p> 158 <code class="literal">const_max</code> 159 </p> 160 </td> 161<td> 162 <p> 163 <code class="literal">T</code> 164 </p> 165 </td> 166<td> 167 <p> 168 equivalent to <code class="literal">std::numeric_limits<T>::max()</code> 169 </p> 170 </td> 171</tr> 172</tbody> 173</table></div> 174<p> 175 Note: The <span class="emphasis"><em>is_integral</em></span> flag is provided, because a user-defined 176 integer class should specialize <code class="literal">std::numeric_limits<>::is_integer 177 = true</code>, while compile-time constants <code class="literal">const_min</code> 178 and <code class="literal">const_max</code> are not provided for that user-defined class, 179 unless boost::integer_traits is also specialized. 180 </p> 181</div> 182<div class="section"> 183<div class="titlepage"><div><div><h3 class="title"> 184<a name="boost_integer.traits.test_program"></a><a class="link" href="traits.html#boost_integer.traits.test_program" title="Test Program">Test Program</a> 185</h3></div></div></div> 186<p> 187 The program <code class="literal"><a href="../../../test/integer_traits_test.cpp" target="_top">integer_traits_test.cpp</a></code> 188 exercises the <code class="literal">integer_traits</code> class. 189 </p> 190</div> 191<div class="section"> 192<div class="titlepage"><div><div><h3 class="title"> 193<a name="boost_integer.traits.acknowledgements"></a><a class="link" href="traits.html#boost_integer.traits.acknowledgements" title="Acknowledgements">Acknowledgements</a> 194</h3></div></div></div> 195<p> 196 Beman Dawes, Ed Brey, Steve Cleary, and Nathan Myers discussed the integer 197 traits idea on the boost mailing list in August 1999. 198 </p> 199</div> 200</div> 201<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 202<td align="left"></td> 203<td align="right"><div class="copyright-footer">Copyright © 2001-2009 Beman 204 Dawes, Daryle Walker, Gennaro Prota, John Maddock<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="../index.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="integer.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 213</div> 214</body> 215</html> 216
