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< a name = "boost_integer.traits" > < / a > < a class = "link" href = "traits.html" title = "Integer Traits" > Integer Traits< / a >
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< 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 >
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< div class = "section" >
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< 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 >
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< div class = "section" >
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< 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 >
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< span class = "keyword" > public< / span > < span class = "special" > :< / span >
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< 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 >
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< 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 > .
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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]),
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there are specializations provided with the following compile-time constants
defined:
< / p >
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member
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type
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value
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< code class = "literal" > is_integral< / code >
< / p >
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< / td >
< td >
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< p >
bool
< / p >
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< td >
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< code class = "literal" > true< / code >
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< / tr >
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< td >
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< p >
< code class = "literal" > const_min< / code >
< / p >
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< / td >
< td >
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< p >
< code class = "literal" > T< / code >
< / p >
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< / td >
< td >
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< p >
equivalent to < code class = "literal" > std::numeric_limits< T> ::min()< / code >
< / p >
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< / td >
< / tr >
< tr >
< td >
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< p >
< code class = "literal" > const_max< / code >
< / p >
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< / td >
< td >
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< p >
< code class = "literal" > T< / code >
< / p >
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< / td >
< td >
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< p >
equivalent to < code class = "literal" > std::numeric_limits< T> ::max()< / code >
< / p >
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< / td >
< / tr >
< / tbody >
< / table > < / div >
< p >
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Note: The < span class = "emphasis" > < em > is_integral< / em > < / span > flag is provided, because a user-defined
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integer class should specialize < code class = "literal" > std::numeric_limits< > ::is_integer
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= 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.
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< / p >
< / div >
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< div class = "section" >
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< 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 >
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< div class = "section" >
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< 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 >
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< td align = "right" > < div class = "copyright-footer" > Copyright © 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota,
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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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