2009-11-25 12:38:09 +00:00
< html >
< head >
2009-11-27 11:13:02 +00:00
< meta http-equiv = "Content-Type" content = "text/html; charset=US-ASCII" >
2009-11-25 12:38:09 +00:00
< title > Integer Traits</ title >
< link rel = "stylesheet" href = "../../../../../doc/html/boostbook.css" type = "text/css" >
2010-04-05 07:27:25 +00:00
< meta name = "generator" content = "DocBook XSL Stylesheets V1.75.2" >
2009-11-25 12:38:09 +00:00
< link rel = "home" href = "../index.html" title = "Boost.Integer" >
< link rel = "up" href = "../index.html" title = "Boost.Integer" >
< link rel = "prev" href = "cstdint.html" title = "Standard Integer Types" >
< link rel = "next" href = "integer.html" title = "Integer Type Selection" >
</ head >
< body bgcolor = "white" text = "black" link = "#0000FF" vlink = "#840084" alink = "#0000FF" >
< table cellpadding = "2" width = "100%" >< tr >
< td valign = "top" >< img alt = "Boost C++ Libraries" width = "277" height = "86" src = "../../../../../boost.png" ></ td >
< td align = "center" >< a href = "../../../../../index.html" > Home</ a ></ td >
< td align = "center" >< a href = "../../../../../libs/libraries.htm" > Libraries</ a ></ td >
< td align = "center" >< a href = "http://www.boost.org/users/people.html" > People</ a ></ td >
< td align = "center" >< a href = "http://www.boost.org/users/faq.html" > FAQ</ a ></ td >
< td align = "center" >< a href = "../../../../../more/index.htm" > More</ a ></ td >
</ tr ></ table >
< hr >
< div class = "spirit-nav" >
< a accesskey = "p" href = "cstdint.html" >< img src = "../../../../../doc/html/images/prev.png" alt = "Prev" ></ a >< a accesskey = "u" href = "../index.html" >< img src = "../../../../../doc/html/images/up.png" alt = "Up" ></ a >< a accesskey = "h" href = "../index.html" >< img src = "../../../../../doc/html/images/home.png" alt = "Home" ></ a >< a accesskey = "n" href = "integer.html" >< img src = "../../../../../doc/html/images/next.png" alt = "Next" ></ a >
</ div >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Integer Traits" >
2009-11-25 12:38:09 +00:00
< 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 >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Motivation" >
2009-11-25 12:38:09 +00:00
< 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 >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Synopsis" >
2009-11-25 12:38:09 +00:00
< 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 >
2009-11-28 17:08:31 +00:00
< span class = "keyword" > public</ span >< span class = "special" > :</ span >
2009-11-25 12:38:09 +00:00
< 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 >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Description" >
2009-11-25 12:38:09 +00:00
< 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 > .
2009-11-28 17:08:31 +00:00
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]),
2009-11-25 12:38:09 +00:00
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 >
2010-04-05 07:27:25 +00:00
< p >
member
</ p >
2009-11-25 12:38:09 +00:00
</ th >
< th >
2010-04-05 07:27:25 +00:00
< p >
type
</ p >
2009-11-25 12:38:09 +00:00
</ th >
< th >
2010-04-05 07:27:25 +00:00
< p >
value
</ p >
2009-11-25 12:38:09 +00:00
</ th >
</ tr ></ thead >
< tbody >
< tr >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > is_integral</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
bool
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > true</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
</ tr >
< tr >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > const_min</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > T</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
equivalent to < code class = "literal" > std::numeric_limits< T> ::min()</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
</ tr >
< tr >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > const_max</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
< code class = "literal" > T</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
< td >
2010-04-05 07:27:25 +00:00
< p >
equivalent to < code class = "literal" > std::numeric_limits< T> ::max()</ code >
</ p >
2009-11-25 12:38:09 +00:00
</ td >
</ tr >
</ tbody >
</ table ></ div >
< p >
2009-11-28 17:08:31 +00:00
Note: The < span class = "emphasis" >< em > is_integral</ em ></ span > flag is provided, because a user-defined
2009-11-25 12:38:09 +00:00
integer class should specialize < code class = "literal" > std::numeric_limits<> ::is_integer
2009-11-28 17:08:31 +00:00
= 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.
2009-11-25 12:38:09 +00:00
</ p >
</ div >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Test Program" >
2009-11-25 12:38:09 +00:00
< 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 >
2010-04-05 07:27:25 +00:00
< div class = "section" title = "Acknowledgements" >
2009-11-25 12:38:09 +00:00
< 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 >
2009-11-27 11:13:02 +00:00
< td align = "right" >< div class = "copyright-footer" > Copyright © 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota,
2009-11-25 12:38:09 +00:00
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 >
</ tr ></ table >
< hr >
< div class = "spirit-nav" >
< a accesskey = "p" href = "cstdint.html" >< img src = "../../../../../doc/html/images/prev.png" alt = "Prev" ></ a >< a accesskey = "u" href = "../index.html" >< img src = "../../../../../doc/html/images/up.png" alt = "Up" ></ a >< a accesskey = "h" href = "../index.html" >< img src = "../../../../../doc/html/images/home.png" alt = "Home" ></ a >< a accesskey = "n" href = "integer.html" >< img src = "../../../../../doc/html/images/next.png" alt = "Next" ></ a >
</ div >
</ body >
</ html >
