How to link static library in jni?

Question

I have created a header file "abc.h" with declaration

int abc();

Then, I created a .cpp file "abc.cpp" with definition

int abc()
{ 
  return 0;
}

Now I created a static library libabc.a from above files.

I have then created a HelloWorld Android project. Then I created a jni folder in it with subfolders "header" and "src" in it. In header folder I have put abc.h and in src folder I have put "abc.cpp". Now I have created another file "xyz.cpp" in jni folder which wants to use abc() function. But when I run ndk-build command I get this error. jni/JNIMagicCleanManager.cpp:84: error: undefined reference to function abc (something like this)

How to get definition of abc() with the static library libabc.a I have put libabc.a in same folder parallel to Android.mk. Following is my Android.mk file

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
MAGIC_CLEAN_ROOT := ..
MAGIC_CLEAN_SRC_ROOT := ../$(LOCAL_PATH)/src
MAGIC_CLEAN_SRC_FILES := xyz.cpp
MAGIC_CLEAN_C_INCLUDES := $(LOCAL_PATH)/headers/

LOCAL_STATIC_LIBRARIES := magicClean
LOCAL_MODULE := myJniLib2


LOCAL_SRC_FILES := $(MAGIC_CLEAN_SRC_FILES)
LOCAL_C_INCLUDES := $(MAGIC_CLEAN_C_INCLUDES)
LOCAL_C_INCLUDES += .
include $(BUILD_SHARED_LIBRARY)

Edit 1 : Many are asking why I have abc.cpp when I have static library, this is just for keeping code only. Please tell how to call the function from static library.

`LOCAL_C_INCLUDES = .` <-- might not be related to your issue, but should that be `:=` rather than `=` ? — Michael, Nov 27 '14 at 10:15
It seems you need to set `LOCAL_LDLIBS` too, seee http://stackoverflow.com/questions/6475944/how-to-mention-path-of-libraries-in-android-mk-file-or-application-mk-file. -- And why is your `MAGIC_CLEAN_SRC_ROOT` set to the `headers` folder? - I'm confused about why you build a static library and then include its sources in your project's build. Either include the headers only and link to the library, or skip the library step and include header+source. — JimmyB, Nov 27 '14 at 10:16
@18446744073709551615 May you please explain more. I am not able to understand — Utkarsh Srivastav, Nov 27 '14 at 11:11
Not sure about .a, for .so I had `LOCAL_LDLIBS := -llog` (for liblog.so) — 18446744073709551615, Nov 27 '14 at 11:23

score 1 · Answer 1 · answered Nov 27 '14 at 18:34

Before use LOCAL_STATIC_LIBRARIES you need use PREBUILT_STATIC_LIBRARY like this example, this example uses gnu static lib, but is the same for yours.

include $(CLEAR_VARS)

LOCAL_MODULE            := gnustl_static
LOCAL_CPPFLAGS += -std=c++11
LOCAL_SRC_FILES         := ${NDK_ROOT}/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi/thumb/libgnustl_static.a
LOCAL_EXPORT_C_INCLUDES := ${NDK_ROOT}/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi/include
LOCAL_EXPORT_C_INCLUDES += ${NDK_ROOT}/sources/cxx-stl/gnu-libstdc++/4.9/include/

include $(PREBUILT_STATIC_LIBRARY)

You should put that in your Android.mk

How to link static library in jni?

1 Answers1