UnsatisfiedLinkError-如何创建c ++-DLL？

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

Are you exporting the symbol:

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

Answer 2

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.

Answer 3

What if there is a class to be implemented ? where the .h file looks like this:

namespace simpleDLLNS
{
    class simpleDLL
    {
    public:

       char giveVoidPtrGetChar(void* param);
       int giveIntGetInt(int a);
       void simpleCall(void);
       int giveVoidPtrGetInt(void* param);
    };
}

Where should extern "C" void __declspec(dllexport) be used ? I used it when implementing the functions. but when i opened the dll, it looked like this:

?simpleCall@simpleDLL@simpleDLLNS@@QAEXXZ