如何防止Gradle / Android Studio覆盖CMake提供的C ++编译器设置？

Question

I'm trying to integrate my existing CMake scripts into Android Studio / Gradle. I've got it generating and building with CMake, but for whatever reason, the CPP flags I specify in my CMake scripts are not being used when run through Gradle. I want my CMake scripts to have complete control over settings like -std=c++14 , -fexceptions , etc. All I really need Gradle to do is provide a toolchain file to specify the toolset information (compiler, path to includes, etc). I guess Gradle is trying to take more control over CMake than is necessary (at least as far as I can tell).

Is there a way to make Gradle not overwrite these CMake settings? It's going to be a pain to maintain and duplicate these settings between Gradle and CMake scripts themselves. So far I'm really not a fan of the Gradle integration of CMake, they seem to use their own hand-built version with custom patches.

Answer 1

Gradle doesn't overwrite any CMake c++ flags. What you're seeing is probably the Android SDK CMake toolchain that sets up tools, c++ flags, and per-ABI configuration.

Here is how gradle calls CMake:

{root}/Sdk/cmake/3.6.3155560/bin/cmake
-H{project}/app
-B{project}/app/.externalNativeBuild/cmake/debug/arm64-v8a
-GAndroid Gradle - Ninja
-DANDROID_ABI=arm64-v8a
-DANDROID_NDK={root}/Sdk/ndk-bundle
-DCMAKE_LIBRARY_OUTPUT_DIRECTORY={project}/app/build/intermediates/cmake/debug/obj/arm64-v8a
-DCMAKE_BUILD_TYPE=Debug
-DCMAKE_MAKE_PROGRAM={root}/Sdk/cmake/3.6.3155560/bin/ninja
-DCMAKE_TOOLCHAIN_FILE={root}/Sdk/ndk-bundle/build/cmake/android.toolchain.cmake
-DANDROID_PLATFORM=android-21

You can see what it is for your particular case by looking at one of the cmake_build_output.txt files that gradle generated.

You can look at android.toolchain.cmake to see when and how the toolchain sets particular flags. (You can open bugs on that file and provide feedback by going to b.android.com. If you cc me--jomof@google.com--I will make sure it gets to the right person). We're definitely planning to beef up documentation as well and you can open bugs for suggestions for documentation improvement as well.

You should be able to append your own flags like -fexceptions to what the toolchain sets and your values will override any prior values. If that isn't what you're seeing can you give some more details on how your CMakeLists.txt is set up?