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

On Thu, Jul 16, 2009 at 8:29 AM, Andrew Holden wrote:

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(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,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.

For what it's worth, this compiler option is deprecated in recent versions of MSVC, so that adds one more to the list of reasons to disable the option.