Android calling C++ function getting UnsatisfiedLinkError

Question

I have following function in my native-lib.cpp file:

JNIEXPORT jlong JNICALL
Java_com_example_z_myapplication_MainActivity_convert32to64(JNIEnv *env, jobject instance,
                                                             jlong l) {

// TODO
l = l + 76561197960265728L;
return l;
}

In my MainActivity.java:

public class MainActivity extends AppCompatActivity {
    static {
        System.loadLibrary("native-lib");
    }
    public static native long convert32to64(long l);

    ...
}

I have a CMakeList.txt:

cmake_minimum_required(VERSION 3.4.1)

# Specifies a library name, specifies whether the library is STATIC or
# SHARED, and provides relative paths to the source code. You can
# define multiple libraries by adding multiple add.library() commands,
# and CMake builds them for you. When you build your app, Gradle
# automatically packages shared libraries with your APK.

add_library( # Specifies the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/cpp/native-lib.cpp )        

However I am getting this error:

java.lang.UnsatisfiedLinkError: No implementation found for long com.example.z.myapplication.MainActivity.convert32to64(long) (tried Java_com_example_z_myapplication_MainActivity_convert32to64 and Java_com_example_z_myapplication_MainActivity_convert32to64__J)

can anyone tell me whats wrong here?

Answer 1

You need extern "C" for C++ JNI.

extern "C" JNIEXPORT jlong JNICALL
Java_com_example_z_myapplication_MainActivity_convert32to64(
        JNIEnv *env, jobject instance, jlong l) {
    // ...
}

Answer 2

It seems like jni library is builded wrongly. Please check jni library file to confirm there is exact symbol link in library file.