<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Integer Traits</title> <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../index.html" title="Boost.Integer"> <link rel="up" href="../index.html" title="Boost.Integer"> <link rel="prev" href="cstdint.html" title="Standard Integer Types"> <link rel="next" href="integer.html" title="Integer Type Selection"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <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> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="boost_integer.traits"></a><a class="link" href="traits.html" title="Integer Traits"> Integer Traits</a> </h2></div></div></div> <div class="toc"><dl> <dt><span class="section"><a href="traits.html#boost_integer.traits.motivation">Motivation</a></span></dt> <dt><span class="section"><a href="traits.html#boost_integer.traits.synopsis">Synopsis</a></span></dt> <dt><span class="section"><a href="traits.html#boost_integer.traits.description">Description</a></span></dt> <dt><span class="section"><a href="traits.html#boost_integer.traits.test_program">Test Program</a></span></dt> <dt><span class="section"><a href="traits.html#boost_integer.traits.acknowledgements">Acknowledgements</a></span></dt> </dl></div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="boost_integer.traits.motivation"></a><a class="link" href="traits.html#boost_integer.traits.motivation" title="Motivation">Motivation</a> </h3></div></div></div> <p> The C++ Standard Library <limits> header supplies a class template <code class="computeroutput"><span class="identifier">numeric_limits</span><span class="special"><></span></code> with specializations for each fundamental type. </p> <p> 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: </p> <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><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><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><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><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><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><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></pre> <p> For many uses, these are sufficient. But min() and max() are problematical because they are not constant expressions (std::5.19), yet some usages require constant expressions. </p> <p> The template class <code class="literal">integer_traits</code> addresses this problem. </p> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="boost_integer.traits.synopsis"></a><a class="link" href="traits.html#boost_integer.traits.synopsis" title="Synopsis">Synopsis</a> </h3></div></div></div> <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <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> <span class="special">{</span> <span class="keyword">public</span><span class="special">:</span> <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> <span class="comment">// </span> <span class="comment">// These members are defined only if T is a built-in </span> <span class="comment">// integal type: </span> <span class="comment">// </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> <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> <span class="special">};</span> <span class="special">}</span> </pre> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="boost_integer.traits.description"></a><a class="link" href="traits.html#boost_integer.traits.description" title="Description">Description</a> </h3></div></div></div> <p> Template class <code class="literal">integer_traits</code> is derived from <code class="literal">std::numeric_limits</code>. The primary specialization adds the single <code class="literal">bool</code> member <code class="literal">is_integral</code> with the compile-time constant value <code class="literal">false</code>. However, for all integral types <code class="literal">T</code> (std::3.9.1/7 [basic.fundamental]), there are specializations provided with the following compile-time constants defined: </p> <div class="informaltable"><table class="table"> <colgroup> <col> <col> <col> </colgroup> <thead><tr> <th> <p> member </p> </th> <th> <p> type </p> </th> <th> <p> value </p> </th> </tr></thead> <tbody> <tr> <td> <p> <code class="literal">is_integral</code> </p> </td> <td> <p> bool </p> </td> <td> <p> <code class="literal">true</code> </p> </td> </tr> <tr> <td> <p> <code class="literal">const_min</code> </p> </td> <td> <p> <code class="literal">T</code> </p> </td> <td> <p> equivalent to <code class="literal">std::numeric_limits<T>::min()</code> </p> </td> </tr> <tr> <td> <p> <code class="literal">const_max</code> </p> </td> <td> <p> <code class="literal">T</code> </p> </td> <td> <p> equivalent to <code class="literal">std::numeric_limits<T>::max()</code> </p> </td> </tr> </tbody> </table></div> <p> Note: The <span class="emphasis"><em>is_integral</em></span> flag is provided, because a user-defined integer class should specialize <code class="literal">std::numeric_limits<>::is_integer = true</code>, while compile-time constants <code class="literal">const_min</code> and <code class="literal">const_max</code> are not provided for that user-defined class, unless boost::integer_traits is also specialized. </p> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <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> </h3></div></div></div> <p> The program <code class="literal"><a href="../../../test/integer_traits_test.cpp" target="_top">integer_traits_test.cpp</a></code> exercises the <code class="literal">integer_traits</code> class. </p> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="boost_integer.traits.acknowledgements"></a><a class="link" href="traits.html#boost_integer.traits.acknowledgements" title="Acknowledgements">Acknowledgements</a> </h3></div></div></div> <p> Beman Dawes, Ed Brey, Steve Cleary, and Nathan Myers discussed the integer traits idea on the boost mailing list in August 1999. </p> </div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota, John Maddock<p> Distributed under the Boost Software License, Version 1.0. (See accompanying 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <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> </div> </body> </html>