Mechanism of Vptr and Vtable in C++

Question

In C++, during dynamic binding, consider the following example...

class Base
{
  virtual void fun()
  {
     cout<<\"Base\";
  }      
};

class Derive         


        

Answer 1

The Standard doesn't specify the mechanism by which polymorphism is implemented. All the Standard says is how it should work -- not how compiler vendors should implement it.

That being said, you have it pretty much right as far as GCC under Linux and MSVC under Windows is concerned, and I would expect most other compilers to be similar.

Answer 2

And bptr->fun() will be getting resolved to bptr->vptr->fun();. This points to the base class function itself.

Wrong. The Derived instance's vptr (a hidden field in each instance) points to the Derived vtable.

Answer 3

Just went through this link virtual table and _vptr

It says that the workflow will be like ..

1. base_ptr->base_vptr----> to check the access of virtual function in base class.

2. base_ptr->derived_vptr->virtual_function()---> to call/invoke the virtual function.

Hence the derived class virtual function is called.. Hope you find it helpful.