How to solve a build error for Android example project?

[a.burks]

I followed the instruction to setup Qt Creator for Android apps. To check my setup I try to build and deploy the calculator example. I can successfully start the emulator and trigger a build for the app, but I get the following error:

/Users/andrew/Library/Android/android-ndk-r20/toolchains/x86-4.9/prebuilt/darwin-x86_64/lib/gcc/i686-linux-android/4.9.x/../../../../i686-linux-android/bin/ld: error: cannot find -lc++
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [libcalculator.so] Error 1

I'm using Qt Creator on macOS Mojave. In the user's library directory I have installed the sdk and ndk, that are linked in the setup of Qt Creator. In the directory /Users/joerg/Library/Android/android-ndk-r20/toolchains/x86-4.9/prebuilt/darwin-x86_64/lib/gcc/i686-linux-android/4.9.x I can just just two files:

• crtbegin.o
• libgcc.a

Any ideas?

[a.burks]

I found a solution in another thread. Thanks @Albertino

The error: cannot find -lc++ using ndk r20 can be solved like this:
https://codereview.qt-project.org/c/qt/qtbase/+/264903/9/mkspecs/android-clang/qmake.conf#34
 
For example to compile for android armv7 ndk r20, locate the file:
C:\Qt\5.13.0\android_armv7\mkspecs\android-clang\qmake.conf
and add the missing -nostdlib++
for android x86 (i use this for emulator), locate the file:
C:\Qt\5.13.0\android_x86\mkspecs\android-clang\qmake.conf
 
For error: Execution failed for task ':compileDebugAidl'
locate the file on your build directory, mine is: C:\dev_qt\experiments\build-test_qt_5_13_0_ARMv7-Release\android-build\gradle.properties and change androidBuildToolsVersion
from: androidBuildToolsVersion=29.0.0
to: androidBuildToolsVersion=28.0.3

[mvuori]

Yes. Before posting you should check previous discussions. There is a topic a couple of days ago that has your exact error message as its title

[Refi]

@mvuori Please post the link

[a.burks]

@mvuori In fact, forum research is always the first step. They certainly refer to this thread. I'm afraid I can't come up with a solution.

I have installed everything from the scratch: First Android Studio for macOS with a setup of the SDK and NDK amd then Qt Creator. I have installed the following packages:

Here is are the Android settings in Qt Creator

And here are my kits. I'm not sure wich kits I need. I think, the forst one for the deployment to hardware devices, the third one for virtual devices.

I think you refer to this solution in the mentioned thread:

1st: correct some invalid variables in QT's build settings/build environment (i.e. wrong slash was / instead of )... AND add some. Specifically:
 
ANDROID_HOME = D:\Android-SDK
ANDROID_SDK_ROOT = D:\Android-SDK
GRADLE_USER_HOME = C:\Users\pc.gradle
JAVA_HOME = D:\Program Files\Java\jdk1.8.0_201
 
2nd: remove the 29.0.0RC1 from Android SDK build-tools via Android Studio SDK manager. Apply.
Select 'show package details' to then be able to select the 28.0.3 version. Apply.
 
3rd: go into theQT project/app's folder and edit the gradle.properties file... change the line to:
 
androidBuildToolsVersion=28.0.3
 
Finally: you should probably should close and reopen QT and the project.
Build/deploy should now (hopefully/finally) work!

I can't find the qt build settings as they are mentioned in the quote, just these:

Unfortunately the Qt guide is not clear. I would appreciate any help.

[a.burks]

I have found additional project specific settings. I think, they are derrived from a global settings template:

It looks korrect for me

[a.burks]

It seems to be this problem, that should be fixed in the new Qt version 5.12.4:

https://codereview.qt-project.org/c/qt/qtbase/+/264903

I have updated the Qt version in my Qt Creator installation. Unfortunately it doesn't solve the problem. At least, it is a known issue.

[a.burks]

I found a solution in another thread. Thanks @Albertino

The error: cannot find -lc++ using ndk r20 can be solved like this:
https://codereview.qt-project.org/c/qt/qtbase/+/264903/9/mkspecs/android-clang/qmake.conf#34
 
For example to compile for android armv7 ndk r20, locate the file:
C:\Qt\5.13.0\android_armv7\mkspecs\android-clang\qmake.conf
and add the missing -nostdlib++
for android x86 (i use this for emulator), locate the file:
C:\Qt\5.13.0\android_x86\mkspecs\android-clang\qmake.conf
 
For error: Execution failed for task ':compileDebugAidl'
locate the file on your build directory, mine is: C:\dev_qt\experiments\build-test_qt_5_13_0_ARMv7-Release\android-build\gradle.properties and change androidBuildToolsVersion
from: androidBuildToolsVersion=29.0.0
to: androidBuildToolsVersion=28.0.3