[CMake] Is there a way to obtain the current compiler standard flag?

[Chris Green]

Hi,

I was hoping this would work:

$<IF:$<TARGET_PROPERTY:CXX_EXTENSIONS>,${CMAKE_CXX$<TARGET_PROPERTY:CXX_STANDARD>_EXTENSION_COMPILE_OPTION},${CMAKE_CXX$<TARGET_PROPERTY:CXX_STANDARD>_STANDARD_COMPILE_OPTION}>

But apparently it's not legal to calculate a variable name based on a 
generator expression. Is there some elegant way to get want I want here 
or do I have to check specifically for 98, 11, 14, 17, 20, etc?

Thanks,

Chris.


On 6/1/18 8:27 AM, Chris Green wrote:
>
> Hi,
>
> I'll give this a shot, thank you. Ideally we'd have a generator 
> expression pick up ${std} from the relevant target property, but I'll 
> have to play with that since I'm not familiar enough with generator 
> expressions to know /a priori/ how this will turn out.
>
> Thanks for your help,
>
> Chris.
>
>
> On 5/30/18 3:12 PM, Chuck Atkins wrote:
>> Hi Chris.
>>
>> Try using the the CMAKE_CXX${std}_STANDARD_COMPILE_OPTION variable.  
>> For example, the folowing piece of CMake code:
>> cmake_minimum_required(VERSION 3.9)
>>
>> project(foo CXX)
>>
>> foreach(std IN ITEMS 98 11 14 17)
>>   message("C++${std} std flags: 
>> ${CMAKE_CXX${std}_STANDARD_COMPILE_OPTION}")
>>   message("C++${std} ext flags: 
>> ${CMAKE_CXX${std}_EXTENSION_COMPILE_OPTION}")
>> endforeach()
>>
>> Wll generate for GCC on Linux:
>> -- The CXX compiler identification is GNU 8.1.1
>> -- Check for working CXX compiler: /usr/bin/c++
>> -- Check for working CXX compiler: /usr/bin/c++ -- works
>> -- Detecting CXX compiler ABI info
>> -- Detecting CXX compiler ABI info - done
>> -- Detecting CXX compile features
>> -- Detecting CXX compile features - done
>> C++98 std flags: -std=c++98
>> C++98 ext flags: -std=gnu++98
>> C++11 std flags: -std=c++11
>> C++11 ext flags: -std=gnu++11
>> C++14 std flags: -std=c++14
>> C++14 ext flags: -std=gnu++14
>> C++17 std flags: -std=c++1z
>> C++17 ext flags: -std=gnu++1z
>> -- Configuring done
>>
>> PGI on Linux:
>> -- The CXX compiler identification is PGI 18.4.0
>> -- Check for working CXX compiler: /opt/pgi/linux86-64/18.4/bin/pgc++
>> -- Check for working CXX compiler: /opt/pgi/linux86-64/18.4/bin/pgc++ 
>> -- works
>> -- Detecting CXX compiler ABI info
>> -- Detecting CXX compiler ABI info - done
>> -- Detecting CXX compile features
>> -- Detecting CXX compile features - done
>> C++98 std flags: -A
>> C++98 ext flags: --gnu_extensions
>> C++11 std flags: --c++11;-A
>> C++11 ext flags: --c++11;--gnu_extensions
>> C++14 std flags: --c++14;-A
>> C++14 ext flags: --c++14;--gnu_extensions
>> C++17 std flags: --c++17;-A
>> C++17 ext flags: --c++17;--gnu_extensions
>> -- Configuring done
>>
>>
>> And for IBM XL on AIX:
>> -- The CXX compiler identification is XL 13.1.3
>> -- Check for working CXX compiler: /usr/bin/xlC
>> -- Check for working CXX compiler: /usr/bin/xlC -- works
>> -- Detecting CXX compiler ABI info
>> -- Detecting CXX compiler ABI info - done
>> -- Detecting CXX compile features
>> -- Detecting CXX compile features - done
>> C++98 std flags: -qlanglvl=strict98
>> C++98 ext flags: -qlanglvl=extended
>> C++11 std flags: -qlanglvl=extended0x
>> C++11 ext flags: -qlanglvl=extended0x
>> C++14 std flags:
>> C++14 ext flags:
>> C++17 std flags:
>> C++17 ext flags:
>> -- Configuring done
>> -- Generating done
>>
>> - Chuck
>

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