使用JNAerator和ftd2xx库的JNA / Java

Question

I'm relatively new to using JNA, and found the JNAerator tool. I thought it would be an easy way to get going, however, how I have generated my interfaces and various files I'm finding it hard to debug or understand why it might not be working. Windows programming isn't my forte, hence the attempt with JNA to make life easy for myself...

The Header file is here: http://www.ftdichip.com/Support/Knowledgebase/index.html?ftd2xx_h.htm

And it generated the following Java JNA File here: http://pastebin.com/hpJgSRMk

Now my sample App is simply trying to list those connected devices, which i can then iterate around and manipulate etc..

import com.sun.jna.NativeLong;

import ft2xx.Ftd2xxLibrary;
import ft2xx.Ftd2xxLibrary.LPDWORD;

public class Test {
    public static void main(String[] args){
        LPDWORD lpd = new LPDWORD();
        NativeLong nl = Ftd2xxLibrary.INSTANCE.FT_CreateDeviceInfoList(lpd);
        System.out.println("Call State: " + nl);
    }
}

This following what i have read here: http://www.ftdichip.com/Support/Documents/ProgramGuides/D2XX_Programmer's_Guide(FT_000071).pdf which details how to list the connected devices, which can then be iterated around etc..

So, my method returns a 6, which is indicative of an invalid parameter, but given that I auto-generated the code, and it doesn't stack, I'm a little clueless as to how to proceed.

I used JNAerator given the sheer number of methods that I needed to implement and use, and was le to believe that JNA, and such generated code would be easy enough to make work for this particular purpose.

Any clues, or should I head back to the basics?

I'm on Windows 7, using Eclipse (Mars), and the webstarted version of JNAerator.

Answer 1

If you don't have a decent understanding of pointers, you're in for a world of confusion. Your call expects a pointer to a DWORD (Java int ). You're passing one in, but it has a default value of zero, which is the same as a NULL pointer. If you use IntByReference , you can at least use IntByReference.getValue() after the call to see what the native method "returned" to you in the memory buffer you passed it.