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

[Chris Green]

Ack! Apparently even the hard way won't work, because apparently one 
cannot nest $<IF clauses, viz:

  set(CXX_STD_FLAG "$<IF:$<TARGET_PROPERTY:${dictname}_dict,CXX_EXTENSIONS>,\
$<IF:$<EQUAL:11,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX11_EXTENSION_COMPILE_OPTION},\
$<IF:$<EQUAL:14,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX14_EXTENSION_COMPILE_OPTION},\
$<IF:$<EQUAL:17,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX17_EXTENSION_COMPILE_OPTION},\
$<IF:$<EQUAL:20,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX20_EXTENSION_COMPILE_OPTION},\
${CMAKE_CXX98_EXTENSION_COMPILE_OPTION}>>>>,\
$<IF:$<EQUAL:11,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX11_STANDARD_COMPILE_OPTION},\
$<IF:$<EQUAL:14,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX14_STANDARD_COMPILE_OPTION},\
$<IF:$<EQUAL:17,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX17_STANDARD_COMPILE_OPTION},\
$<IF:$<EQUAL:20,$<TARGET_PROPERTY:${dictname}_dict,CXX_STANDARD>>,${CMAKE_CXX20_STANDARD_COMPILE_OPTION},\
${CMAKE_CXX98_STANDARD_COMPILE_OPTION}>>>>>")

begets:

   First parameter to $<IF> must resolve to exactly one '0' or '1' value.

I'm all out of ideas. Any new ones would be appreciated.

Thanks,

Chris.


On 6/1/18 3:00 PM, Chris Green wrote:
>
> 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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