Re: How are virtual function calls implemented?

Just over a week ago, I got burnt by an update to MFC for VS 2005 that
caused my previously working print preview code to stop working.

My original post is here:
http://groups.google.com/group/microsoft.public.vc.mfc/browse_thread/thread/148a24041d6713f8

Because the "fix" in the service pack was in a virtual function, I could
override the function, however, because of where the object was created,
it would be a lot of work. So, I decided the most expedient solution
would be to patch the vtable in my process to point to my implmentation
instead of the MFC version.

However, I found two different implementations of
CPreviewDC::ComputeDeltas in my program linked to an MFC as a shared DLL:

In a debug version, this:
tmp.TTO 0x004569d6 [thunk]:CPreviewDC::`vcall'{108,{flat}}' }' CSize (int,
int, const char *, int, int, int *, int)*
with the flat thunk doing this:
 // code bytes look like this:
  // 004569D6 E9 05 64 02 00 jmp CPreviewDC::`vcall'{108}'
(47CDE0h)

but in a release version, this:
But in the release build it points straight at this:
 tmp.TTO 0x0047cde0 CPreviewDC::`vcall'{108}' CSize (int, int, const char
*, int, int, int *, int)*

  // code bytes look like this:
  // 0047CDE0 8B 01 mov eax,dword ptr [ecx]
  // 0047CDE2 FF 60 6C jmp dword ptr [eax+6Ch]

Do these constitute the universe of ways VC2005 might implement a vtable,
or are there still more that I haven't run across.

Any pointers to how I might find out?

Does anybody have a better suggestion as to how to solve this problem?

Thanks.

Anthony Wieser
Wieser Software Ltd