This change produces invalid JSON in my setup:

"stdcpp-path":" "/opt/android-ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/arm64-v8a/libgnustl_shared.so" -nodefaultlibs -lgcc -lc -lm -ldl",

So it think there's some refinement required to make this more robust. The file stl contains "/opt/android-ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/arm64-v8a/libgnustl_shared.so" -nodefaultlibs -lgcc -lc -lm -ldl in my case. When escaping the quotes correctly so the JSON is no longer invalid the next error I get is:

STL library does not exist at  "/opt/android-ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/arm64-v8a/libgnustl_shared.so" -nodefaultlibs -lgcc -lc -lm -ldl

So I suppose only a single file should be specified here. When I change it to only /opt/android-ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/arm64-v8a/libgnustl_shared.so it finally works.

BTW, I'm using Arch Linux and the following packages/versions:

pacman -Q cmake android-sdk android-ndk android-qt5-arm64-v8a extra-cmake-modules 
cmake 3.12.1-1
android-sdk 26.1.1-1
android-ndk r17.b-1
android-qt5-arm64-v8a 5.11.1-1
extra-cmake-modules 5.49.0-1

@Martchus sounds like your CMAKE_CXX_STANDARD_LIBRARIES gets initialized wrong somehow, no?

@apol I'm not that familiar with Android, but I guess the variable CMAKE_CXX_STANDARD_LIBRARIES is not limited to contain only a single library (note the plural in the variable name). So I think we should handle that.

BTW, I'm just testing with the accelbubble example from Qt. I created a fairly simple CMakeLists.txt for it which definitely doesn't mess with the variables:

cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)

set(CMAKE_AUTORCC ON)

find_package(Qt5Core)
find_package(Qt5Quick)
find_package(Qt5Sensors)
find_package(Qt5Svg)
find_package(Qt5Xml)

add_executable(accelbubble main.cpp accelbubble.qrc)
target_link_libraries(accelbubble Qt5::Quick Qt5::Sensors Qt5::Svg Qt5::Xml)

I also didn't touch that variable via CLI options when invoking CMake. However, to workaround the issue I tried it. But using -DCMAKE_CXX_STANDARD_LIBRARIES=/opt/android-ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/arm64-v8a/libgnustl_shared.so only leads to the specified value being pretended to the auto-detected values (so I end up having .../libgnustl_shared.so twice).

It's the same issue I have here, but after our discussion at Akademy I assumed this to be local setup issue. Similar versions here, on Tumbleweed.

@vkrause Thanks for confirming. So it is not a local issue. Could you find a workaround (beside reverting these changes)?

As I already mentioned, I'm not so familiar with Android. However, for me the way CMake populates CMAKE_CXX_STANDARD_LIBRARIES doesn't look completely unconceivable and in fact compilation/linking seems to work fine that way. To improve we could just iterate over the list of libraries CMake detects and pick the first one which is a full path. That's also not very reliable, but it would at least fix the problem I have right now.

In D11776#318339, @Martchus wrote:

@vkrause Thanks for confirming. So it is not a local issue. Could you find a workaround (beside reverting these changes)?

I edit the file stl in the build dir to strip out the additional -lxxx entries, but that has to be redone after every cmake run. Haven't found the time to properly investigate this yet unfortunately.