在由PInvoke返回给C函数的实例化C ++类上调用函数

Question

I have an unmanaged DLL that exports C style non-member functions for creating (say CreateObject) and destroying objects (DestroyObject). CreateObject returns a C++ class as a void*, which in the unmanaged code is cast to a known interface (defined only in a header file) and worked with. Is there a way to call methods on the IntPtr that is returned to me by CreateObject?

Dumpbin /EXPORT doesn't show me any methods of the C++ class, just the exported C functions (mentioned above).

I would like to avoid having to write C++ CLI code or a purely unmanaged DLL that simply exposes methods on this class as function wrappers if possible

This is Windows/MSVC only, so answers that restrict compatibility to Windows/MSVC are fine.

NOTE: I'm talking about invoking C++ methods on a void*/IntPtr returned by a C function - not P/Invoking the C functions.

Thanks!

Answer 1

If you are ruling out C++/CLI, and only have an IntPtr containing the address of the instance then you have few options remaining.

As I see it you are left with p/invoke. In order to call a method you'll need to export it from your unmanaged code. You'll also need to be careful about the calling convention. Commonly it will be __thiscall . When you write the p/invoke, you must explicitly add the this pointer as the first parameter.

This is fine so far as it goes. But you'll not be able to export virtual methods this way. You cannot call them using p/invoke.

Frankly though the cleanest and simplest way to do this interop is with our old friend, tried and tested COM. This very scenario is just what it was designed for. C++ classes are not designed for interop across compiler/language boundaries. That's what COM is for.