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<div class="section" lang="en">
<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" lang="en">
<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" lang="en">
<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" lang="en">
<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" lang="en">
<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" lang="en">
<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>)
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