Re: [boost] [lexical_cast][STLport 4.5.3][trunk] static assertion failed in boost/detail/lcast_precision.hpp

From: Paul A Bristow (pbristow_at_[hidden])
Date: 2007-10-08 14:34:56

>-----Original Message-----
>From: boost-bounces_at_[hidden] 
>[mailto:boost-bounces_at_[hidden]] On Behalf Of Joaquín Mª 
>López Muñoz
>Sent: 08 October 2007 18:37
>To: boost_at_[hidden]
>Subject: [boost] [lexical_cast][STLport 4.5.3][trunk] static 
>assertion failed in boost/detail/lcast_precision.hpp
>
>Compiling the following snippet in MSVC++ 6.5 + STLport 4.5.3
>with the trunk
>
>  #include <boost/lexical_cast.hpp>
>
>  int main()
>  {
>    return 0;
>  }
>
>results in
>
>...\boost\detail\lcast_precision.hpp(79) : error C2027:
>  use of undefined type 'STATIC_ASSERTION_FAILURE<0>'
>  ...\boost\detail\lcast_precision.hpp(89) : see reference to 
>class template instantiation
>  'boost::detail::lcast_precision<T>' being compiled
>[...]
>
>The offending asserion in boost/detail/lcast_precision.hpp is
>
>    BOOST_STATIC_ASSERT(!is_specialized_bin ||
>            limits::digits + 0UL < ULONG_MAX / 30103UL &&
>            precision_bin > limits::digits10 + 0UL &&
>            precision_bin <= streamsize_max + 0UL
>        );
>
>This problem did not arise with Boost 1.34 because 
>boost/lexical_cast.hpp
>did not use the newly created  lcast_precision.hpp. Other assertions in
>lcast_precision<> seem to work OK, so looks like is this particular one
>that should be fixed only. I lack the skills to propose a 
>patch myself, but I can locally try patches others may provide.

Although I made some input on this, I'm not the maintainer for lexical_cast (and don't have thiese platforms to test).

Maintainer is Alexander Nasonov [alexander.nasonov_at_[hidden]])
but in case he isn't listening:

I can't see an obvious cause (presume it works OK on other platforms), so I can only suggest breaking this down into separate
assertions to see which one is causing the trouble,
and perhaps getting the values of std::limits<T>::digits and boost::is_abstract<T>.

It seems that the suitable precision (decimal digits to use to get the full accuracy for type T) can't be calculated.

It would also be useful to see what T is?  Is this some funny type for which std::numeric_limits isn't properly specialised?

HTH

Paul

---
Paul A Bristow
Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB
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pbristow_at_[hidden]