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24</div>
25<div class="section">
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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 &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.</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">&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">//</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&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
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>
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