Re: [Boost-users] [numeric_cast] Warning with MSVC

Subject: Re: [Boost-users] [numeric_cast] Warning with MSVC
From: Andrew Holden (aholden_at_[hidden])
Date: 2009-07-16 09:29:38

Alexander Lamaison wrote:
Sent: Thursday, July 16, 2009 6:09 AM
> 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

The issue is a compiler option called "detect 64-bit portability issues"
or "/Wp64".  As it is both non-standard and a rather brutal hack, there
is probably no way for Boost to support it.

I would recommend turning that option off.