C++ - Pointer to a class method

Question

I have to set up a pointer to a library function (IHTMLDocument2::write) which is a method of the class IHTMLDocument2. (for the curious: i have to hook that function with Detours)

I can't do this directly, because of type mismatch, neither can I use a cast (reinterpret_cast<> which is the "right one" afaik doesn't work)

Here's what I am doing:

HRESULT (WINAPI *Real_IHTMLDocument2_write)(SAFEARRAY *) = &IHTMLDocument2::write

Thanks for your help!

Answer 1

You need to use a member function pointer. A normal function pointer won't work, because when you call a (non-static) class member function there is an implicit this pointer referring to an instance of the class.

Answer 2

The pointer to function has the following type:

HRESULT (WINAPI IHTMLDocument2::*)(SAFEARRAY*)

As you can see, it's qualified with it's class name. It requires an instance of a class to call on (because it is not a static function):

typedef HRESULT (WINAPI IHTMLDocument2::*DocumentWriter)(SAFEARRAY*);

DocumentWriter writeFunction = &IHTMLDocument2::write;

IHTMLDocument2 someDocument = /* Get an instance */;
IHTMLDocument2 *someDocumentPointer = /* Get an instance */;

(someDocument.*writefunction)(/* blah */);
(someDocumentPointer->*writefunction)(/* blah */);