Review of Inheritance

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Review of Inheritance
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Several Levels of Inheritance
Base Class B
Derived class D
Derived class D1
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Type Conversions
Base Class B
B b //is not of type D or D1
Derived class D
D d //is also of type B
Derived class D1
D1 d1 //is also of type D, B
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Assignment b d
Base Class B
Derived class D
D d //is also of type B
Derived class D1
D1 d1 //is also of type D, B
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Assignment d b
Base Class B
B b //is not of type D
Derived class D
D d //is also of type B
Derived class D1
D1 d1 //is also of type D, B
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Function calls
Base Class B
void print() cout ltlt B

Derived class D
D d //is also of type B
void print() Baseprint()

Derived class D1
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Function calls
Base Class B
B b //is not of type D
void print() Dprint()

Derived class D
D d //is also of type B
void print() Baseprint()

Derived class D1
D1 d1 //is also of type D, B
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Use of Virtual (Dynamic Binding)

• To enable programming with pointers to different
  object
• types
• The compiler generates code to
• inspect the type of the object the pointer
  points to at run- time and then call the
  appropriate function

D
D1
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Use of Virtual (Dynamic Binding)

• D ptr new D1()
• ptr?f() //dynamic binding calls f from D1
• For dynamic binding to occur for function f
• - must use pointers or references
• - f must exist in D
• - f must be declared virtual in D

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Use of Virtual (Dynamic Binding)

• D d
• d.f() //static binding calls f from D
• For dynamic binding to occur for function f
• - must use pointers or references
• - f must exist in D
• - f must be declared virtual in D

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Use of Virtual (Dynamic Binding)

• D ptr new D1()
• ptr?print() //dynamic binding calls print from
  D1
• For dynamic binding to occur for function print
• - must use pointers or references
• - print must exist in D (could be implemented or
  pure
• virtual)
• - print must be declared virtual in D

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Use of Virtual (Dynamic Binding)

• D ptr new D1()
• ptr?print() //dynamic binding calls print from
  D1
• Make sure you go through the steps
• Find type of ptr (D here)
• Look in that class (D here) for the function
  (print)
• If print - is not there (neither declared in D
  nor inherited
• from B) ? compiler error !
• - is there and is virtual (either declared
  virtual explicitly
• or inherited from B) ? dynamic binding (print
  from D1)
• - is there and not virtual ? static binding
  (print from D)

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Inheritance with Virtual Functions
Base Class B
virtual void print()cout ltltB
Derived class D

not overriden
Derived class D1
void print()cout ltltD1 which print() is
called?
D ptr new D1 ptr-gtprint() D1 Dynamic
binding
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Inheritance with Virtual Functions
Base Class B
virtual void print()cout ltltB
Derived class D

not overriden
Derived class D1

not overriden
which one is
it then ?
Dynamic binding occurs but print is not overriden
in D1, it is inherited as is from B
D ptr new D1 ptr-gtprint() B the one
closest in the hierarchy
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Inheritance with Virtual Functions
Base Class B
void print()cout ltltB
Derived class D
void print() cout ltlt D overridden
Derived class D1
which one is it?
Dynamic binding occurs but print is not
overridden in D1
D ptr new D1 ptr-gtprint() -- D the one
closest in the hierarchy
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Virtual Destructors !
Base Class B
B()
Derived class D
D()
Derived class D1
which destructor
is called ?
D1()
D ptr new D1 Delete ptr
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Virtual Destructors !
Base Class B
B()
Derived class D
D()
Derived class D1
which destructor
is called ?
D1()
Static binding occurs, because D is not virtual
D ptr new D1 Delete ptr //D and B called
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Virtual Destructors !
Base Class B
B()
Derived class D
virtual D()
Derived class D1
which destructor
is called ?
D1()
Dynamic binding occurs, because D is virtual
D ptr new D1 Delete ptr //D1, D and B
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Virtual Destructors !
Base Class B
virtual B()
Derived class D
D()
Derived class D1
which destructor
is called ?
D1()
D ptr new D1 Delete ptr //D1, D and B