Re: [Boost-users] Bug in lexical_cast<> with doubles

From: Terje Slettebų (tslettebo_at_[hidden])
Date: 2005-01-29 16:50:07

Well, this is a long time ago, but I came across this posting when doing a
search for lexical_cast related issues.

I compiled and ran the code snipped below on Intel C++ 7.1 and STLPort, and
it printed "Successfuly", while it fails on MSVC 7.1 and g++ 3.2, so it
seems to depend on the platform/library used.

If anyone has a patch for it, it would be welcome, but otherwise, this seems
to be quite a boundary condition (converting numeric_limit<double>::max() to
string and back again), that I'd think it's rarely, if ever, a problem in
practice.

Regards,

Terje

>From: "Leon Raj" <Leon.Raj_at_[hidden]>
>To: <boost-users_at_[hidden]>
>Cc: "Leon Raj" <Leon.Raj_at_[hidden]>
>Sent: Wednesday, July 28, 2004 5:21 AM
>Subject: [Boost-users] Bug in lexical_cast<> with doubles

> I think I've found a bug in the boost::lexical_cast<>
> library (v1.31.0) on WinXP SP1, MSVC 6.0 (sp5) and
> MSVC.NET 2003.
>
> --- Start code snippet ---
>
> #include <boost/lexical_cast.hpp>
> #include <iostream>
>
> int main( int argc, char* argv[] )
> {
>     double dMax = = std::numeric_limits< double >::max();
>     // On a Win32 x86 system, dMax is now 1.7976931348623157e+308
>
>     // This is successful and strMax is "1.797693134862316e+308"
>     std::string strMax = boost::lexical_cast< std::string >( dMax );
>
>     try
>     {
>         double newDMax = boost::lexical_cast< double >( strMax );
>         std::cout << "Successfuly" << std::endl;
>     }
>     catch ( boost::bad_lexical_cast& )
>     {
>         std::cout << "Failed to cast" << std::endl;
>     }
>
>     // On a Win32 x86 system, this always fails,
>     // because (I think) strMax overflows a double,
>     // because 1.7976931348623157e+308 is *rounded UP*
>     // to      1.797693134862316e+308, which cannot be
>     // represented by a double
> }
>
> --- End code snippet ---