The DLL won't carry any struct information. That's all generated by the compiler based on the header file.

Not sure when I'll get the chance. It's straightforward to add a new JNA test to verify the behavior (including a native method that returns an int-sized struct, if there isn't one already). That might've been easier than writing a vc++ dll :)

PointerByReference is "void **", which you use if you're expecting the native code to provide you with a value (the native code writes a "void *" into the pointer-sized memory you provide). byte[] is if you're providing the native code with a buffer in which to write. Use the wrong one and you'll get an access violation.