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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_numericconversion.improved_numeric_cast__"></a><a class="link" href="improved_numeric_cast__.html" title="Improved numeric_cast<>">Improved
numeric_cast<></a>
</h2></div></div></div>
-
- <div class="section">
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.introduction">Introduction</a></span></dt>
+<dt><span class="section"><a href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.numeric_cast">numeric_cast</a></span></dt>
+<dt><span class="section"><a href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.numeric_cast_traits">numeric_cast_traits</a></span></dt>
+<dt><span class="section"><a href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.examples">Examples</a></span></dt>
+</dl></div>
+<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_numericconversion.improved_numeric_cast__.introduction"></a><a class="link" href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.introduction" title="Introduction">Introduction</a>
</h3></div></div></div>
-
- <p>
+<p>
The lack of preservation of range makes conversions between numeric types
error prone. This is true for both implicit conversions and explicit conversions
(through <code class="computeroutput"><span class="keyword">static_cast</span></code>). <a class="link" href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.numeric_cast" title="numeric_cast"><code class="computeroutput"><span class="identifier">numeric_cast</span></code></a> detects loss of range
when a numeric type is converted, and throws an exception if the range cannot
be preserved.
</p>
+<p>
There are several situations where conversions are unsafe:
</p>
- <div class="itemizedlist"><ul class="itemizedlist" type="disc">
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
-
Conversions from an integral type with a wider range than the target
integral type.
-
- </li>
+ </li>
<li class="listitem">
-
Conversions from unsigned to signed (and vice versa) integral types.
-
- </li>
+ </li>
<li class="listitem">
-
Conversions from floating point types to integral types.
-
- </li>
+ </li>
</ul></div>
+<p>
The C++ Standard does not specify the behavior when a numeric type is assigned
a value that cannot be represented by the type, except for unsigned integral
types [3.9.1.4], which must obey the laws of arithmetic modulo 2n (this implies
to unsigned) makes any code that may produce positive or negative overflows
exposed to portability issues.
</p>
+<p>
By default <code class="computeroutput"><span class="identifier">numeric_cast</span></code> adheres
to the rules for implicit conversions mandated by the C++ Standard, such
as truncating floating point types when converting to integral types. The
implementation must guarantee that for a conversion to a type that can hold
all possible values of the source type, there will be no runtime overhead.
</p>
- </div>
+</div>
+<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_numericconversion.improved_numeric_cast__.numeric_cast"></a><a class="link" href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.numeric_cast" title="numeric_cast">numeric_cast</a>
</h3></div></div></div>
-
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">></span> <span class="keyword">inline</span>
<span class="identifier">Target</span> <span class="identifier">numeric_cast</span><span class="special">(</span> <span class="identifier">Source</span> <span class="identifier">arg</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">converter</span><span class="special">::</span><span class="identifier">convert</span><span class="special">(</span><span class="identifier">arg</span><span class="special">);</span>
<span class="special">}</span>
</pre>
+<p>
<code class="computeroutput"><span class="identifier">numeric_cast</span></code> returns the
result of converting a value of type Source to a value of type Target. If
out-of-range is detected, an overflow policy is executed whose default behavior
and <a class="link" href="numeric_converter_policy_classes.html#numeric_conversion_possitive_overflow">positive_overflow</a>
).
</p>
- </div>
+</div>
+<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_numericconversion.improved_numeric_cast__.numeric_cast_traits"></a><a class="link" href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.numeric_cast_traits" title="numeric_cast_traits">numeric_cast_traits</a>
</h3></div></div></div>
-
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">EnableIf</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">numeric_cast_traits</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="identifier">Trunc</span><span class="special"><</span><span class="identifier">Source</span><span class="special">></span> <span class="identifier">rounding_policy</span><span class="special">;</span>
<span class="special">};</span>
</pre>
+<p>
The behavior of <code class="computeroutput"><span class="identifier">numeric_cast</span></code>
may be tailored for custom numeric types through the specialization of <code class="computeroutput"><span class="identifier">numeric_cast_traits</span></code>. (see <a class="link" href="type_requirements_and_user_defined_types_support.html" title="Type Requirements and User-defined-types support">User
Defined Types</a> for details. )
</p>
- </div>
+</div>
+<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_numericconversion.improved_numeric_cast__.examples"></a><a class="link" href="improved_numeric_cast__.html#boost_numericconversion.improved_numeric_cast__.examples" title="Examples">Examples</a>
</h3></div></div></div>
-
- <p>
+<p>
The following example performs some typical conversions between numeric types:
</p>
-
<div class="orderedlist"><ol class="orderedlist" type="1">
+<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
-
include <boost/numeric/conversion/cast.hpp>
-
- </li>
+ </li>
<li class="listitem">
-
include <iostream>
-
- </li>
+ </li>
</ol></div>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
- </div>
- </div>
+</div>
+</div>
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+<td align="right"><div class="copyright-footer">Copyright © 2004-2007 Fernando
+ Luis Cacciola Carballal<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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