Monday, February 14, 2011

Displaying vtable when debugging

Due to some limitations the virtual table of an object is not shown by default in the debugger. In some cases only the entries from the base class is shown.

class Base
{
   virtual void a();
};
class Derived : public Base
{
   virtual void b();
};

Base* ptr = new Derived();

which in a watch window gives

ptr->__vfptr 0x004420f8 const Derived::`vftable'
[0x0] 0x00415ed3 Base::a(void)

You can look at the entire vtable if you add this helper variable:

void (**vt)() = *(void (***)())ptr;

and then inspect vt,X in a watch window, where X is the number of expected virtual function entries.

Read more: Codeproject