[Boost-users] [numeric_cast] Warning with MSVC

Subject: [Boost-users] [numeric_cast] Warning with MSVC
From: Alexander Lamaison (awl03_at_[hidden])
Date: 2009-07-16 06:09:20

I'm using boost::numeric_cast to convert the size of a wstring (presumably 
a size_t) to an int. 

  const int size = boost::numeric_cast<int>(my_string.size());

MSVC still gives me a warning about possible loss of data:

  c:\program files\boost\boost_1_38\boost\numeric\conversion\
  cast.hpp(41) : warning C4267: 'argument' : conversion from 'size_t' 
  to 'unsigned int', possible loss of data
  c:\users\awl03\documents\visual studio 2005\projects\swish_trunk 
  (padd)\swish\utils.hpp(91) : see reference to function template 
  instantiation 'Target boost::numeric_cast<int,__w64 unsigned 
  int>(Source)' being compiled
        with
        [
            Target=int,
           Source=__w64 unsigned int
        ]
  c:\users\awl03\documents\visual studio 2005\projects\swish_trunk 
  (padd)\swish\utils.hpp(121) : see reference to function template 
  instantiation 'std::basic_string<_Elem,_Traits,_Ax> 
  swish::utils::ConvertString<`anonymous-namespace'::Narrow>(const 
  std::basic_string<wchar_t,std::char_traits<wchar_t>,std::
  allocator<_Ty>> &)' being compiled
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>,
            _Ax=std::allocator<char>,
            _Ty=wchar_t
        ]

Unless I misunderstand, isn't the idea of numeric_cast that warnings aren't 
needed because the casts are checked for loss of data?  Any advice is 
greatly appreaciated.

I am using the MSVC 8.0 compiler with Boost 1.38.0 on 32-bit Windows Vista.

Thanks.

Alex Lamaison