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| <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> |
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