[CMake] c++2a

[Robert Maynard]

CMake hasn't been updated to be aware that XCode 10 added support for
C++20 (via -std=c++2a). I have opened a MR to correct this which you
can track at: https://gitlab.kitware.com/cmake/cmake/merge_requests/3294

On Tue, May 7, 2019 at 12:24 PM Angel Campoverde
<campoverdeangelf at gmail.com> wrote:
>
> Hi,
>
> No, It does not work, I told Cmake to use c++ 20, but it still goes back to c++17. You can see what I get here:
>
> https://pastebin.com/5ub18cMU
>
> my CMakeLists.txt is here:
>
> https://pastebin.com/3bwMKrWB
>
> do you know what could be the problem?
>
> Cheers.
>
> On Tue, May 7, 2019 at 2:33 AM Mateusz Loskot <mateusz at loskot.net> wrote:
>>
>> On Tue, 7 May 2019 at 01:15, Angel Campoverde
>> <campoverdeangelf at gmail.com> wrote:
>> >
>> > I am looking at:
>> >
>> > https://cmake.org/cmake/help/v3.14/prop_tgt/CXX_STANDARD.html
>> >
>> > and I see that I can pass 20, for c++20. However I do not have that in my compiler,
>> > I only have c++2a and gnu++2a, this means that CMake goes back to c++17
>>
>> No, it doesn't mean that.
>>
>> The valid values documented for CXX_STANDARD are CMake generalisation
>> and not what is directly passed via -std= or /std: or whatever option
>> your compiler uses.
>>
>> If you run this cmake command
>> cmake -DCMAKE_CXX_STANDARD=20 -DCMAKE_CXX_EXTENSIONS=OFF ..
>> and then
>> VERBOSE=1 make
>> you will clearly see that CMake generated the compiler
>> command lines with -std=c++2a
>>
>> IFF, you are using version of GCC or clang that supports c++2a, obviously
>> (i.e. GCC 8/clang 6 or later. I'm not entirely confident about clang)
>>
>> Best regards,
>> --
>> Mateusz Loskot, http://mateusz.loskot.net
>> --
>>
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>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ
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