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113 lines
3.7 KiB
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<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
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<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<title>Integer Type Selection Templates</title>
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<body bgcolor="#FFFFFF" text="#000000">
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<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="center" width="277" height="86">Integer
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Type Selection Templates</h1>
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<p>The <code><a href="../../boost/integer.hpp"><boost/integer.hpp></a></code>
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type selection templates allow integer types to be selected based on desired
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characteristics such as number of bits or maximum value. This facility is
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particularly useful for solving generic programming problems.</p>
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<p>The templates <b>int_t<></b> and <b>uint_t<></b> supply typedefs <b>least</b>
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and <b>fast</b>. The <b>least</b> type be the smallest type which holds at
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least the number of bits (including sign) specified. The <b>fast</b> type will
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be at least as large as the <b>least</b> type, but may possible be larger.
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There is no guarantee that the <b>fast</b> type will actually be faster than
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other possible types.</p>
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<h2>Alternative</h2>
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<p>If the number of bits required is known beforehand, it may be more
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appropriate to use the types supplied in <code><a href="../../boost/cstdint.hpp"><boost/cstdint.hpp></a></code>.</p>
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<h2>Synopsis</h2>
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<blockquote>
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<pre>namespace boost
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{
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// fast integers from least integers
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// int_fast_t<> works correctly for unsigned too, in spite of the name.
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template< typename LeastInt > // Required: LeastInt is integral type, not bool
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struct int_fast_t { typedef LeastInt fast; }; // implementations may specialize
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// signed
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template< int Bits > // bits (including sign) required, 0-32 valid
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struct int_t
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{
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typedef <i>implementation-supplied</i> least;
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typedef int_fast_t<least>::fast fast;
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};
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// unsigned
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template< int Bits > // bits required, 0-32 valid
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struct uint_t
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{
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typedef <i>implementation-supplied</i> least;
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typedef int_fast_t<least>::fast fast;
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// int_fast_t<> works correctly for unsigned too, in spite of the name.
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};
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} // namespace boost
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</pre>
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</blockquote>
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<p>[Templates to select type based on maximum value are under development.]
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</p>
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<h2>Example</h2>
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<blockquote>
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<pre>#include <boost/integer.hpp>
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using boost::int_t;
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...
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int_t<24>::least my_var; </pre>
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</blockquote>
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<h2>Demonstration Program</h2>
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<p>The program <a href="integer_test.cpp">integer_test.cpp</a> is a not very
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smart demonstration of the results from instantiating various <b>int_t<></b>
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and <b>uint_t<></b> examples.</p>
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<h2>Rationale</h2>
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<p>The rationale for the design of the templates in this header includes:</p>
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<ul>
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<li>Avoid recursion because of concern about C++'s limited guaranteed
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recursion depth (17).</li>
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<li>Avoid macros on general principles.</li>
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<li>Try to keep the design as simple as possible.</li>
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</ul>
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<h2>Credits</h2>
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<p>The author of the Boost integer type choosing templates is <a href="../../people/beman_dawes.html">Beman
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Dawes</a>. He thanks to <a href="../../people/valentin_bonnard.htm"> Valentin Bonnard</a> and
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<a href="../../people/kevlin_henney.htm"> Kevlin Henney</a> for sharing their designs for similar templates.</p>
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<hr>
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<p>Revised August 31, 1999</p>
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<p><EFBFBD> Copyright Beman Dawes 1999. Permission to copy, use, modify, sell
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and distribute this document is granted provided this copyright notice appears in all
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copies. This document is provided "as is" without express or implied warranty,
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and with no claim as to its suitability for any purpose.</p>
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<p></p>
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<p> </p>
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</body>
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</html>
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