[CMake] CMake, VS, Nsight Tegra, NDK, mixed C/C++ - applies C++ options to C source

[Florent Castelli]

I'm pretty sure that the toolchain bundled with the NDK, made by Google, 
hasn't been tested with other generators than Ninja or possibly Make.
Also, there are some known bugs with it, including the one related to 
CMAKE_CXX_STANDARD (see 
https://code.google.com/p/android/issues/detail?id=227915 and 
https://github.com/android-ndk/ndk/issues/222 ).

I'd recommend using other generators if you want to use this toolchain 
or maybe try the Android support released with CMake 3.7.1 instead, 
though I have no idea if it's supposed to work with the Visual Studio 
generators either!

/Florent

On 15/12/2016 01:44, Scott Eberline wrote:
> We have a large project library of mostly C++, mixed with a handful of
> C. The C++ compilation commands look correct and work fine. But C
> files are passed to clang++.exe -x c, rather than clang.exe. Which
> should work, except that CMAKE_CXX_FLAGS is applied while
> CMAKE_C_FLAGS is ignored. CMAKE_CXX_FLAGS includes options not
> supported for C, so the build fails with messages like,
>
> TRACKEDTOOLTASKWRAPPER`1 : error : invalid argument '-std=c++11' not
> allowed with 'C/ObjC'
>
> I've tried overriding the C++ options with C-compatible options, for
> example set_source_files_properties(${C_SOURCES} PROPERTIES
> COMPILE_FLAGS "-std=c99"). But I've found that per-file COMPILE_FLAGS
> precede CMAKE_CXX_FLAGS on the resulting compiler command line, so the
> C++ flags still get priority.
>
> I've searched CMake list archives, Stack Overflow, Nvidia's
> development tool forums etc. but not found any solution.
>
> (Caveat - I'm trying to use NDK r13b which is not yet supported by
> Nsight Tegra. So far, this just involves falsifying the NDK's revision
> in its source.properties file, and creating a couple of directory
> symbolic links so LLVM libc++ headers can be found where they lived in
> NDK r12b. If falsifying the NDK version eventually causes problems,
> I'll reconsider it, but for now it seems promising.)
>
> CMake 3.7.1
> Visual Studio 2015 Update 3
> Nsight Tegra Visual Studio Edition 3.4
> NDK r13b
>
> cmake.exe ^
>      -DANDROID_PLATFORM=android-24 ^
>      -DANDROID_STL=c++_static ^
>      -DCMAKE_C_FLAGS="-std=c99" ^
>      -DCMAKE_C_STANDARD=99 ^
>      -DCMAKE_C_STANDARD_REQUIRED=ON ^
>      -DCMAKE_CXX_STANDARD=14 ^
>      -DCMAKE_CXX_STANDARD_REQUIRED=ON ^
>      -DCMAKE_TOOLCHAIN_FILE=C:\Android\NDK-r13b\build\cmake\android.toolchain.cmake
> ^
>      -G"Visual Studio 14 2015" ^
>      -T"DefaultClang" ^
>
> The generated CMakeCCompiler.cmake looks mostly correct, in particular
> CMAKE_C_COMPILER and CMAKE_C_SOURCE_FILE_EXTENSIONS, although
> CMAKE_<LANG>_IMPLICIT_LINK_LIBRARIES and
> CMAKE_<LANG>_IMPLICIT_LINK_DIRECTORIES are set for android-9 and GNU
> libstdc++ rather than the values specified in ANDROID_PLATFORM and
> ANDROID_STL. As an aside, it seems ANDROID_PLATFORM, ANDROID_STL,
> CMAKE_C_STANDARD and CMAKE_CXX_STANDARD are completely ignored in the
> generated VS project. I assume that's a topic for a different thread.
>
> Thanks for taking the time to read; any advice is appreciated.