Re: feature for C++ standards compliance

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-02-25 22:22:18

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. 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.