I am trying to print the address of a virtual member function. If I know which class implements the function I can write:
print("address: %p", &A::func);
But I want to do something like this:
A *b = new B();
printf("address: %p", &b->func);
printf("address: %p", &b->A::func);
However this does not compile. Is it possible to do something like this, perhaps looking up the address in the vtable at runtime?
Currently there is no standard way of doing this in C++ although the information must be available somewhere. Otherwise, how could the program call the function? However, GCC provides an extension that allows us to retrieve the address of a virtual function:
void (A::*mfp)() = &A::func;
printf("address: %p", (void*)(b->*mfp));
...assuming the member function has the prototype void func().
This can be pretty useful when you want to cache the address of a virtual function or use it in generated code. GCC will warn you about this construct unless you specify -Wno-pmf-conversions. It's unlikely that it works with any other compiler.