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From: Edward Diener (eldiener_at_[hidden])
Date: 2021-02-25 22:48:48

On 2/25/2021 5:22 PM, Edward Diener via Boost wrote:
> On 2/25/2021 5:04 PM, Andrey Semashev via Boost wrote:
>> On 2/26/21 12:15 AM, Robert Ramey via Boost wrote:
>>> On 2/25/21 12:48 PM, Gavin Lambert via Boost wrote:
>>>> Conditioning a boost test on boost version < N is equivalent to just
>>>> unconditionally suppressing it, no?
>>> No - because boost version <= 1.75 math library supports C++03 while
>>> other versions don't/wont.
>> I think the point was that with the Boost version check you won't be
>> running these tests *at all* in the current and future Boost.
>>>> Isn't the goal to only suppress it when not compiling >= C++11?
>>> yep
>>>> Shouldn't you just check __cplusplus >= 201103 for that?
>>> Hmmm - is this portable on all compilers?  Is this part of config.hpp?
>> __cplusplus is a standard C++ macro, but not all compilers
>> consistently define it to >= 201103 in C++11 mode. Most notably, MSVC
>> doesn't.
> The compilers that emulate the msvc non-standard preprocessor, such as
> the VC++ based versions of Intel C++ and also NVCC I believe, report
> incorrect  __cplusplus values. I also recall that some past versions of
> gcc reported an incorrect _cplusplus value, although I do not recall in
> which gcc version this was corrected.

gcc-4.6 and below had an incorrect value of '1' and it was fixed to be
correct for gcc-4.7 on up. Not that I would bother worrying about such
old compiler versions of gcc myself.

> So unfortunately it is not
> completely reliable, even with major compilers. BTW the new C++ standard
> non-default preprocessor ( /Zc:preprocessor ) in VS2019 gets it right
> and is a very good C++ standard preprocessor.
>> If you want to check macros (which is what I'm doing in Boost.Integer
>> to solve a similar problem with Boost.Multiprecision) then I'd suggest
>> to check Boost.Config macros for the particular C++11 features that
>> are required by Boost.Math. You may even peek in Boost.Math sources to
>> see what these macros are, if they are checked there.
> Yes, that is the only reliable solution right now.

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