What's the difference between a derived object and a base object in c++?

Question

What\'s the difference between a derived object and a base object in c++,

especially, when there is a virtual function in the class.

Does the derived object

Answer 1

Derived is Base, but Base is not a Derived

Answer 2

A base object is one from which others are derived. Typically it'll have some virtual methods (or even pure virtual) that subclasses can override to specialize.

A subclass of a base object is known as a derived object.

Answer 3

let's have:

class Base {
   virtual void f();
};

class Derived : public Base {
   void f();
}

without f being virtual (as implemented in pseudo "c"):

struct {
   BaseAttributes;
} Base;

struct {
   BaseAttributes;
   DerivedAttributes;
} Derived;

with virtual functions:

struct {
   vfptr = Base_vfptr,
   BaseAttributes;
} Base;

struct {
   vfptr = Derived_vfptr,
   BaseAttributes;
   DerivedAttributes;
} Derived;

struct {
   &Base::f
} Base_vfptr

struct {
   &Derived::f
} Base_vfptr

For multiple inheritance, things get more complicated :o)

Answer 4

a public colon. ( I told you C++ was nasty )

class base { }
class derived : public base { }