Calling C++ functions from native code

So far, we have called a C function implemented in the c_functions.c source, so, in the next section, we will show you how to call a C++ member class.

First, we will add the isPrimeCPlusPlus native method to MyNativeActivty that returns String as a result. Let's see how the native function declaration will look:

public class MyNativeActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
      ...
      TextView cPlusTv = (TextView)  
          findViewById(R.id.helloFromCPlusPlus);
      cPlusTv.setText(isPrimeCPlusPlus(4));
    }

    public native String isPrimeCPlusPlus(int number);
}

Running the javah tool against the new MyNativeActivity class definition will generate a new function declaration with the following signature:

JNIEXPORT jstring JNICALL Java_com_packpublishing_asynchronousandroid_chapter9_MyNativeActivity_isPrimeCPlusPlus(JNIEnv *, jobject, jint);

Next, we are going to implement the prime function...