How can I map native HWND type from JNA?

[Shajid Johnny]

I am trying to access a dll through JNA.
the dll contains a method

int  startSampleSystem(HWND wid, int mid, int devices, int protocol, int message);

I am new to JNA. I tried to went through the tutorials and examples. so far I've understood is- I have done the following thing:

public class MyJNAForSampleSystem {

    public interface SampleSystem extends StdCallLibrary {
        SampleSystem INSTANCE = (SampleSystem) Native.loadLibrary("sampleSystem", SampleSystem.class);
        interface HWND extends StdCallCallback {
            boolean callback(Pointer hWnd, Pointer arg);
        }
        int  opensamplesystem(int port);
        int  startsamplesystem(HWND wid, int mid, int devices, int protocol, int message);
    }
    public static void main(String[] args) {
        final SampleSystem sampleSystem = SampleSystem.INSTANCE;
        try{
            int returned2 = SampleSystem.INSTANCE.opensamplesystem(0x10000);
            System.out.println("opensamplesystem returned: "+returned2);

            int returned3 = sampleSystem.startsamplesystem(new SampleSystem.HWND() {
                public boolean callback(Pointer hWnd, Pointer arg) {
                    System.out.println("inside callback");
                    byte[] windowText = new byte[512];
                    String wText = Native.toString(windowText);
                    wText = (wText.isEmpty()) ? "" : "; text: " + wText;
                    System.out.println("Found window " + hWnd + ", total " + ++count + wText);
                    return true;
                }
            }, 0x0400, 0x0000, 0x0000, 0);
            String strHexNumber = Integer.toHexString(returned3);
            System.out.println("startsamplesystem returned: 0x"+strHexNumber);
        }catch(Exception e){
            System.out.println("could not load library");
        }finally{
            System.out.println("finally block");
        }
    }
}

the opensamplesystem() method executes and returns 0 which, according to the dll documentation, is ok.
but the problem is with the startsamplesystem(HWND wid, int mid, int devices, int protocol, int message) where I am not sure how to map HWND data type from my code.

would anyone please show me some way?

thanks in advance

[Rob Spoor]

http://stackoverflow.com/questions/90493/long-to-hwnd-vs8-c

In short, HWND is another name for HANDLE which is another name for PVOID which is another name for void*, or a pointer of any type.

Well, that is one possible type definition. I've checked my MinGW's windef.h. It says that DECLARE_HANDLE(HWND);DECLARE_HANDLE is a macro from winnt.h with two possible definitions:
#ifdef STRICT typedef void *HANDLE; #define DECLARE_HANDLE(n) typedef struct n##__{int i;}*n #else typedef PVOID HANDLE; #define DECLARE_HANDLE(n) typedef HANDLE n #endifThe second is what's described above: HWND is HANDLE is PVOID is void*. The first still says that HANDLE is void* but without the intermediate PVOID. HWND though is a pointer to a struct with one int element (if my C knowledge doesn't desert me). Not exactly the same.

Still, in the end there is one common type: a generic pointer. I think you can use the Pointer class for that.