How to link a prebuilt shared Library to an Android NDK project?

Question

Here I used this Android.mk file in jni/ folder.

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

# Here we give our module name and source file(s)
LOCAL_MODULE    := offlineDownload
LOCAL_SRC_FILES := offline_download.c

LOCAL_SHARED_LIBRARIES :=../lib/libpackext.so.1.0
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog

include $(BUILD_SHARED_LIBRARY)

And make one lib folder in project directory and put my prebuilt .so library and make one Android.mk file which contains following

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := packext
LOCAL_SRC_FILES := libpackext.so.1.0
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../include

include $(PREBUILT_SHARED_LIBRARY)

And when i use ndk-build -B command than i got undefined reference to packageExtraction. Here I use my prebuilt library functions means I can't link my prebuilt shared library to my offlinedownload library.

So any body please help me to solved out this issue.

Can you please explain your question in detail? – Nimit Mar 26 '12 at 12:44 — Nimit, Mar 26 '12 at 12:44

Dan Brough · Answer 1 · 2013-05-20T20:40:22.080

37

Here is a complete Android.mk file for using a 3rd party shared library. The library (libffmpeg.so) is placed in the jni folder. Its "LOCAL_EXPORT_C_INCLUDES" specifies where the header files are kept for the library.

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg
LOCAL_SRC_FILES := libffmpeg.so
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/../../ffmpeg/libs/arm-linux-androideabi4.7_1/include
include $(PREBUILT_SHARED_LIBRARY)


include $(CLEAR_VARS)
LOCAL_MODULE    := ffmpegandroid
LOCAL_SRC_FILES := ffmpegandroid.c
LOCAL_SHARED_LIBRARIES := ffmpeg
include $(BUILD_SHARED_LIBRARY)

If you wanted to support multiple architectures then you could specify:

APP_ABI := armeabi armeabi-v7a x86 mips

in your jni/Application.mk and change the LOCAL_SRC_FILES to something like:

LOCAL_SRC_FILES := $(TARGET_ARCH_ABI)/libffmpeg.so

and place a libffmpeg.so at jni/armeabi/libffmpeg.so, jni/armeabi-v7a/libffmpeg.so etc ..

edited May 20 '13 at 20:40

answered Mar 01 '13 at 19:53

Dan Brough

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Why the libffmpeg.so need to be in jni folder? With all the architectures, how to make it easier? – xgdgsc May 20 '13 at 13:16
1

I modified the example to show how to support multiple architectures. – Dan Brough May 20 '13 at 20:40
it's also possible to put the external libs in `jniLibs/...` and use: `LOCAL_SRC_FILES := ..\jniLibs\$(TARGET_ARCH_ABI)\libffmpeg.so` – Francois Aug 18 '15 at 21:10
Have a look at https://github.com/danbrough/andrudio for an example of compiling ffmpeg (or libav) for android. – Dan Brough Aug 18 '15 at 22:57
Where should add shared library finally?! PREBUILT_SHARED_LIBRARY ? LOCAL_JNI_SHARED_LIBRARIES ? LOCAL_SHARED_LIBRARIES ? – Dr.jacky Oct 14 '15 at 12:00
Thank you! Hard to find examples for this that actually have a complete Android.mk with multiple entries. – Dave Dec 22 '15 at 20:18

Ciro Santilli OurBigBook.com · Answer 2 · 2017-11-30T10:50:41.930

Android NDK official hello-libs CMake example

https://github.com/googlesamples/android-ndk/tree/840858984e1bb8a7fab37c1b7c571efbe7d6eb75/hello-libs

Just worked for me on Ubuntu 17.10 host, Android Studio 3, Android SDK 26, NDK 15.2. so I strongly recommend that you base your project on it.

The shared library is called libgperf, the key code parts are:

hello-libs/app/src/main/cpp/CMakeLists.txt:

// -L
add_library(lib_gperf SHARED IMPORTED)
set_target_properties(lib_gperf PROPERTIES IMPORTED_LOCATION
          ${distribution_DIR}/gperf/lib/${ANDROID_ABI}/libgperf.so)

// -I
target_include_directories(hello-libs PRIVATE
                           ${distribution_DIR}/gperf/include)
// -lgperf
target_link_libraries(hello-libs
                      lib_gperf)

on C++ code, use: #include <gperf.h>
header location: hello-libs/distribution/gperf/include/gperf.h
lib location: distribution/gperf/lib/arm64-v8a/libgperf.so

app/build.gradle:

android {
    sourceSets {
        main {
            // let gradle pack the shared library into apk
            jniLibs.srcDirs = ['../distribution/gperf/lib']

Then, if you look under /data/app on the device, libgperf.so will be there as well.

If you only support some architectures, see: Gradle Build NDK target only ARM

The example git tracks the prebuilt shared libraries, but it also contains the build system to actually build them as well: https://github.com/googlesamples/android-ndk/tree/840858984e1bb8a7fab37c1b7c571efbe7d6eb75/hello-libs/gen-libs

score 2 · Answer 3 · answered Mar 29 '12 at 09:42

You have to do either one of the following:

Cut and paste everything except LOCAL_PATH := $(call my-dir) from your second Android.mk into your first.
Put the following in the end of your first Android.mk:

$(call import-module,packext)

Also make sure that you set your NDK_MODULE_PATH environment variable to a path where the Android.mk-file defining the module packext can be found.

You also have to change the LOCAL_SHARED_LIBRARIES in the same way mgiza said in the first answer. I suppose the packageExtraction that you got undefined reference to is in your prebuilt library so unless you have other linking problems this should solve the issue.

score 0 · Answer 4 · answered Mar 27 '12 at 21:38

0

Have a look at the ndk documentation for prebuilts:

android-ndk/docs/PREBUILTS.html

You have to change

LOCAL_SHARED_LIBRARIES :=../lib/libpackext.so.1.0

to

LOCAL_SHARED_LIBRARIES := packext

Be sure that your folder containing the Android.mk for the packext module is named packext and can be found in in your NDK_MODULE_PATH.

answered Mar 27 '12 at 21:38

mgiza

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Here i put my Android.mk and libpackext.so.1.0 in lib folder .this lib folder is in project directory path.where i make jni folder – user1089679 Mar 28 '12 at 01:42

How to link a prebuilt shared Library to an Android NDK project?

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