Question

I am trying to generate a dll which I can access from java via JNA.

I just try a simple one:

CPP:

void Initialize()
{
  std::cout<< "Hello World!";
}

iostream is also included and after compiling I get: CreateDll.dll

Via Visual Studio I can generate now a *.dll.

which I try loading into Java like:

public class mainRoutine {
  public static void main(String[] args) {
    NativeWrapper INSTANCE = (NativeWrapper) Native.loadLibrary("CreateDll" , NativeWrapper.class);             
    INSTANCE.Initialize();
  }

  static {
    System.setProperty("jna.library.path", "C:\\workspace\\JNA");
  }
}

There is also another Interface:

import com.sun.jna.Library;

public interface NativeWrapper extends Library {
  void Initialize();
}

So but now running the Java function I get the error,

 java.lang.UnsatisfiedLinkError: 
  Error looking up function 'Initialize': 
   The specified procedure could not be found.

What am I missing?

PS: I know there are many topics, but trying for a day already I have not found the solution. Please help me.

Answer 1

You need to both export and (if using C++) un-decorate the function name.

On windows, functions are typically made available for export with __declspec(dllexport).

On any platform, to ensure a function is exported in unmanagled form, you must use extern "C".

Specifically:

extern "C" void __declspec(dllexport) Initialize() { ... }

There are other ways to designate exported functions, but this is probably the most common and straightforward to use. If you don’t use extern "C", your function will look something like InitializeZ@ASDF@, where the additional garbage characters are used by the compiler and linker to make a given function uniquely recognizable based on its calling signature.