libs/integer/doc/html/boost_integer/traits.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   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 V1.75.2">
   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="cstdint.html" title="Standard Integer Types">
  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="cstdint.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>
  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 &lt;limits&gt; header supplies a class template
  42         <code class="computeroutput"><span class="identifier">numeric_limits</span><span class="special">&lt;&gt;</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">&lt;&gt;</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.
  49 </span><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.
  50 </span><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.
  51 </span><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.
  52 </span><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.
  53 </span><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.
  54 </span><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.
  55 </span></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">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;</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">//
  76 </span>     <span class="comment">// These members are defined only if T is a built-in
  77 </span>     <span class="comment">// integal type:
  78 </span>     <span class="comment">//
  79 </span>     <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&lt;T&gt;::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&lt;T&gt;::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&lt;&gt;::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 &#169; 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota,
 204       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="cstdint.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>