Develop Reference

Android Studio ndk example build errors

I am new to using an ndk and was trying to use some of the sample projects that came in the android ndk10d folder. For example the hello-jni sample project. I keep getting this error:
Error:Execution failed for task ':app:compileDebugNdk'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
C:\Users\Jonathon\android-ndk-r10d\ndk-build.cmd NDK_PROJECT_PATH=null APP_BUILD_SCRIPT=C:\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\build\intermediates\ndk\debug\Android.mk APP_PLATFORM=android-21 NDK_OUT=C:\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\build\intermediates\ndk\debug\obj NDK_LIBS_OUT=C:\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\build\intermediates\ndk\debug\lib APP_ABI=all
Error Code: 2 Output:
make.exe: *** No rule to make target `C:\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/objs/hello-jni/C_\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\src\main\jni', needed by `C:\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/objs/hello-jni/C_\Users\Jonathon\AndroidStudioProjects\hello-jni2\app\src\main\jni\hello-jni.o'. Stop.
I have checked and the file: ndk-build.cmd is indeed in the location specified. When I try to open it command prompt says that it cannot find the application project directory. Please define the NDK_PROJECT_PATH variable to it
I re-installed and updated my whole environment from 0.8.9 to android studio 0.9.9 and now 1.01 and I get the same error. It seems it can't find the file or file directory and that must mean my configuration isn't right but I can't determine what to do to fix it.
local.properties
sdk.dir=C\:\\Users\\Jonathon\\AppData\\Local\\Android\\sdk
ndk.dir=C\:\\Users\\Jonathon\\android-ndk-r10d
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := hello-jni
LOCAL_SRC_FILES := hello-jni.c
include $(BUILD_SHARED_LIBRARY)

Check out this video for building simple NDK projects with Android studio
https://www.youtube.com/watch?v=kFtxo7rr2HQ&list=UUkbLy9aj5IBXfS6WqLy5Qmw
Alternatively you can also download Intel Native Developer Experience tool that comes with the NDK plugin for Android Studio

You can remove the Android.mk file: it will be ignored as a new one is generated on the fly from your gradle configuration (build.gradle file). You can get more information on this from my article on NDK support in Android Studio.
The bug you're experiencing is this one: https://code.google.com/p/android/issues/detail?id=66937&
A simple workaround is to create a empty .c file next to hello-jni.c.

If you have only one .c (or .cpp) file add a dummy .c (or .cpp) file and it works.

i can't get opencv to work in android

I'm using eclipse to write android programs and i can successfully run them on adt but recently i had to write a program that uses opencv but i can't get opencv to work with android i got ndk and add it to system variables and also downloaded opencv4android sdk from this link: http://docs.opencv.org/doc/tutorials/introduction/android_binary_package/O4A_SDK.html and i imported all the examples now i get numerous error for any of the examples and when i click project->clean->clean all it comes up with following error :
C:\Documentation_Android\android-ndk-r9d-windows-x86_64\android-ndk-r9d\ndk-build.cmd
Android NDK: WARNING:jni/Android.mk:mixed_sample: non-system libraries
in linker flags: -lopencv_java Android NDK: This is likely to
result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES
Android NDK: or LOCAL_SHARED_LIBRARIES instead to list the library
dependencies of the Android NDK: current module
[armeabi-v7a] Install : libmixed_sample.so =>
libs/armeabi-v7a/libmixed_sample.so
I also tried Fix Project Properties but nothing happened and i tried to change jni/Application.mk and change armeabi-v7a to armeabi and that didn't helped too what should i do now ? is there anything I missing here ?

have you added LOCAL_LDLIBS in android.mk file?
LOCAL_LDLIBS := $(LOCAL_PATH)/jniLibs/libmixed_sample.so //path of .so file

OK i found the answer ! How stupid I am ! i just have to go to opencv library project properties in android tab select project build target as android 4.2.2 and everything worked well

OpenCV Android NDK: non-system libraries in linker error

This is the error I get, I followed different guides to install and run NDK but just couldn't manage it. Always a problem
20:58:58 **** Auto Build of configuration Default for project OpenCV Sample - face-detection ****
"C:\\Users\\Gok2\\workspace\\android-ndk-r9b\\ndk-build.cmd"
Android NDK: WARNING:jni/Android.mk:detection_based_tracker: non-system libraries in linker flags: -lopencv_java
Android NDK: This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES
Android NDK: or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the
Android NDK: current module
[armeabi-v7a] Install : libdetection_based_tracker.so => libs/armeabi-v7a/libdetection_based_tracker.so

It's a warning, not an error. This warning has been introduced recently, in the latest release of NDK. The OpenCV build scripts have not yet accomodated the necessary workarounds, but I have no doubt the fix will be ready quite soon.
In the mean time, you can ignore the warning. I would advise to keep your eye on it, so that except for opencv libraries, no unexpected names appear in the build log.

Android NDK Include Path In Eclipse

I have an Android NDK project that builds fine in cygwin using ndk-build.
However, I wanted to have it build in eclipse, so I installed C/C++ Development tools into my ADT version of eclipse and added native support to the project in eclipse. However, after building, I get the following error:
fatal error: timer.h: No such file or directory
In my original Android.mk file, I have the following include that lets it work in cygwin:
LOCAL_C_INCLUDES := /cygdrive/c/ADT/includes/
I tried adding a similar include path (C:\ADT\includes) to Project->Properties->C/C++ General->Paths and Symbols, but still no luck. Any suggestions?

The fix was to use windows paths
LOCAL_C_INCLUDES := C:/ADT/includes/
Note that using the following works as well (per cpu2's answer)
LOCAL_CFLAGS := -IC:/ADT/includes/

Add -I/path/to/includes to your cflags.

Android.mk not linking system library libandroid.so

In my android 2.3 project , i am using the native asset manager. In the docs it says add the
LOCAL_LDLIBS += -landroid to the android.mk file which I have
but the linker is giving the following error saying it can't find it
/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/ld: cannot find -landroid
I've compiled a sample in the NDK with the same library and that works so I can't understand why a different project is giving this problem

turned out I needed to target a later platform 2.3