boost/cast.hpp

   1 //  boost cast.hpp header file  ----------------------------------------------//
   2
   3 //  (C) Copyright Kevlin Henney and Dave Abrahams 1999.
   4 //  Distributed under the Boost
   5 //  Software License, Version 1.0. (See accompanying file
   6 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7
   8 //  See http://www.boost.org/libs/conversion for Documentation.
   9
  10 //  Revision History
  11 //  23 JUn 05  numeric_cast removed and redirected to the new verion (Fernando Cacciola)
  12 //  02 Apr 01  Removed BOOST_NO_LIMITS workarounds and included
  13 //             <boost/limits.hpp> instead (the workaround did not
  14 //             actually compile when BOOST_NO_LIMITS was defined in
  15 //             any case, so we loose nothing). (John Maddock)
  16 //  21 Jan 01  Undid a bug I introduced yesterday. numeric_cast<> never
  17 //             worked with stock GCC; trying to get it to do that broke
  18 //             vc-stlport.
  19 //  20 Jan 01  Moved BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS to config.hpp.
  20 //             Removed unused BOOST_EXPLICIT_TARGET macro. Moved
  21 //             boost::detail::type to boost/type.hpp. Made it compile with
  22 //             stock gcc again (Dave Abrahams)
  23 //  29 Nov 00  Remove nested namespace cast, cleanup spacing before Formal
  24 //             Review (Beman Dawes)
  25 //  19 Oct 00  Fix numeric_cast for floating-point types (Dave Abrahams)
  26 //  15 Jul 00  Suppress numeric_cast warnings for GCC, Borland and MSVC
  27 //             (Dave Abrahams)
  28 //  30 Jun 00  More MSVC6 wordarounds.  See comments below.  (Dave Abrahams)
  29 //  28 Jun 00  Removed implicit_cast<>.  See comment below. (Beman Dawes)
  30 //  27 Jun 00  More MSVC6 workarounds
  31 //  15 Jun 00  Add workarounds for MSVC6
  32 //   2 Feb 00  Remove bad_numeric_cast ";" syntax error (Doncho Angelov)
  33 //  26 Jan 00  Add missing throw() to bad_numeric_cast::what(0 (Adam Levar)
  34 //  29 Dec 99  Change using declarations so usages in other namespaces work
  35 //             correctly (Dave Abrahams)
  36 //  23 Sep 99  Change polymorphic_downcast assert to also detect M.I. errors
  37 //             as suggested Darin Adler and improved by Valentin Bonnard.
  38 //   2 Sep 99  Remove controversial asserts, simplify, rename.
  39 //  30 Aug 99  Move to cast.hpp, replace value_cast with numeric_cast,
  40 //             place in nested namespace.
  41 //   3 Aug 99  Initial version
  42
  43 #ifndef BOOST_CAST_HPP
  44 #define BOOST_CAST_HPP
  45
  46 # include <boost/config.hpp>
  47 # include <boost/assert.hpp>
  48 # include <typeinfo>
  49 # include <boost/type.hpp>
  50 # include <boost/limits.hpp>
  51 # include <boost/detail/select_type.hpp>
  52
  53 //  It has been demonstrated numerous times that MSVC 6.0 fails silently at link
  54 //  time if you use a template function which has template parameters that don't
  55 //  appear in the function's argument list.
  56 //
  57 //  TODO: Add this to config.hpp?
  58 # if defined(BOOST_MSVC) && BOOST_MSVC < 1300
  59 #  define BOOST_EXPLICIT_DEFAULT_TARGET , ::boost::type<Target>* = 0
  60 # else
  61 #  define BOOST_EXPLICIT_DEFAULT_TARGET
  62 # endif
  63
  64 namespace boost
  65 {
  66 //  See the documentation for descriptions of how to choose between
  67 //  static_cast<>, dynamic_cast<>, polymorphic_cast<> and polymorphic_downcast<>
  68
  69 //  polymorphic_cast  --------------------------------------------------------//
  70
  71     //  Runtime checked polymorphic downcasts and crosscasts.
  72     //  Suggested in The C++ Programming Language, 3rd Ed, Bjarne Stroustrup,
  73     //  section 15.8 exercise 1, page 425.
  74
  75     template <class Target, class Source>
  76     inline Target polymorphic_cast(Source* x BOOST_EXPLICIT_DEFAULT_TARGET)
  77     {
  78         Target tmp = dynamic_cast<Target>(x);
  79         if ( tmp == 0 ) throw std::bad_cast();
  80         return tmp;
  81     }
  82
  83 //  polymorphic_downcast  ----------------------------------------------------//
  84
  85     //  BOOST_ASSERT() checked polymorphic downcast.  Crosscasts prohibited.
  86
  87     //  WARNING: Because this cast uses BOOST_ASSERT(), it violates
  88     //  the One Definition Rule if used in multiple translation units
  89     //  where BOOST_DISABLE_ASSERTS, BOOST_ENABLE_ASSERT_HANDLER
  90     //  NDEBUG are defined inconsistently.
  91
  92     //  Contributed by Dave Abrahams
  93
  94     template <class Target, class Source>
  95     inline Target polymorphic_downcast(Source* x BOOST_EXPLICIT_DEFAULT_TARGET)
  96     {
  97         BOOST_ASSERT( dynamic_cast<Target>(x) == x );  // detect logic error
  98         return static_cast<Target>(x);
  99     }
 100
 101 #  undef BOOST_EXPLICIT_DEFAULT_TARGET
 102
 103 } // namespace boost
 104
 105 # include <boost/numeric/conversion/cast.hpp>
 106
 107 #endif  // BOOST_CAST_HPP