[boost] Re: [ublas-dev] Re: abs doesn't work with VC .NET

From: Joerg Walter (jhr.walter_at_[hidden])
Date: 2003-02-03 14:38:40

Hi Michael (hi Kresimir, hi Julius, hi all ;-),

you wrote:

> I have come across this problem before. The same problem occured when I 
> was working on .NET patches for boost::quaternion.

So there's at least another boost library affected.

> The following is from memory of VC7, so actual names may be slightly 
> different. I no longer have access to the MSVC compilers. Luck me!!

:-)

> If turn on compiler warning level 3 you should see warnings for line 
> such as "abs(1.5)" that a double is being converted to and integer.
> If look in the <math.h> header you will see why  All the C++ definitions 
> are in there. The problem is that many (includeing abs(float/double) are 
> NOT defined when the macro _MSC_EXTENSIONS is defined.  This is for some 
> stupid backwards compatibilty with their previous broken headers!!
> 
> To make things work,  you must either
>      Use the compiler switch /Za to disable microsoft extensions.
>      OR use
> #ifdef  _MSC_EXTENSIONS
> #undef  _MSC_EXTENSIONS
> #include <cmath>
> #define  _MSC_EXTENSIONS
> #else
> #include <cmath>
> #endif
> 
> I do not recommend /Za.  The compiler has even more problems then normal 
> when it is set. VC7 cannot compile uBLAS and many other boost libraries 
> with /Za.

This agrees with Julius' statements.

> My long term solution was simply to edit <math.h> to remove the 
> offending conditional compilation!

:-)

> The is no specific solution in boost/config for this problem. I don't 
> see there is an easy fix either as _MSC_EXTENSIONS needs to be define 
> for some of MS own header files.

OK. I've prepared the following patch for ublas: 

- Add the following to the MSVC section of ublas/config.hpp

#ifdef _MSC_EXTENSIONS
#define BOOST_UBLAS_NO_CMATH
#endif

- Change the problematic parts of ublas/traits.hpp to

#if defined (BOOST_NO_STDC_NAMESPACE) || defined (BOOST_UBLAS_NO_CMATH)
            return ::fabsf (t);
#else
            return std::abs (t);
#endif

I'll commit this later, if noone objects.

Thanks,

Joerg