native function naming convention in Qt for Android

Question

In a project, I cannot find the names of native functions in the .so libraries. That is, a native function must be called something like Java_com_package_ClassName_functionName(). I do find functionName in the .so libraries, but either without the Java_com_package_ClassName_ prefix, or wrapped into a mangled C++ name.

So:

1. Does Qt (Necessitas) use a special naming convention?

2. If yes, how it is done?

3. If no, what is going on?

Answer 1

The naming conventions for JNI functions are given by the Dalvik VM, a library couldn't change them and expect them to work, i.e. be callable from the Java part of the application. But, the Java_package_function convention is only needed for functions that Java wants to call, it it not neccesary for a C/C++ function calling another one.

If you compile

jint Java_com_example_foo(JNIEnv*  env, jobject  this) { return bar(); }
int bar() { return 3; }

into a library, you can call Java_com_example_foo from java, and you won't be able to call bar from java, but nothing prevents Java_com_example_foo from calling bar.

So, there are 2 possibilities that come to mind:

1. the Java part is nothing but a stub that calls a main function in one library, and all the rest is done in C or C++. This main function probably will be called Java_package_function, not main, but it's the only function that uses this naming convention.
2. There's another wrapper library which provides the Java_package_function JNI API calls to the Java part, and calls the C/C++ functions which it imports from a different library. This library would probably be very small, so you might not have considered it interesting, and missed it in your previous analysis.