Inheritance

1
Inheritance

• What is inheritance?
• An Is a relationship between two classes of
  objects in which a class
• (the derived class) inherits all members of
  another class (the base class)
• Can be used to develop a hierarchy of classes
  based on abstractions in a top down fashion, e.g.
  the Location-Point-Circle-Arch hierarchy
  introduced before
• It is also needed for code refinement,
  expandability, and reuse by
• a) Refining the implementation of a class by
  building a refined
• derived class, were some member functions are
  redefined,
• b) Expanding the functionality of the a class by
  adding new functions
• c) Reusing the code in a base class in several
  derived classes

2
Inheritance

• Types of inheritance
• Types of inheritance can be defined depending
  on the access attributes
• of class members as viewed in the derived class,
  each class may have
• private members (can only be accessed by class
  members or friends),
• protected members (as private but can also be
  accessed by derived classes)
• public members ( can be accessed by all)
• The types of inheritance are
• a) Public derivation, which is the default
  derivation type for structs
• class D public B // define class D,
  also struct D B// define D
• leaves the access level unchanged,
  i.e.,
• public members of B are public in D
• protected members of B are
  protected in D
• private members of B remain private to B (can
  not be accessed in
• D but they are still inherited in D)

3
Inheritance
Types of inheritance (cont.) b) private
derivation, which is the default derivation type
for classes, class D private B //
define class D , or class D B // define
D.. converts the public and protected members
of the base class into private members of
the derived class public members of B are
private in D protected members of B are private
in D private members of B remain private to B
c) protected derivation, class D protected
B // define class D converts the public
and protected members of the base class into
protected members of the derived class
public members of B are protected in
D protected members of B are protected in
D private members of B remain private to B In
all cases, note that private members of B remain
private to B
4
Inheritance

• Types of inheritance (cont.)
• suppose we have the following members of a
  base class
• class Parent private d1m1 protected
  d2m2
• public d3 m3
• An object of type Parent can access the public
  members d3 and m3
• class child_1 public Parentprivate d4m4
  
• protected d5 m5 public d6m6
• Members of child1 have also direct access to
  d2,m2, d3, and m3, the protected and public
  members of Parent
• An object of type child1can access d6, m6, d3,
  and m3

5
Inheritance

• class child2 private Parentprivated7m7
  protected d8m8
• public d9m9
• Members of child2 also have direct access to d2,
  d3, m2,
• and m3 of members of Parent same as members of
  Child_1
• An object of type child2 can only access d9,
  and m9
• class child3 protected Parentprivate d10
  protected d11
• public d12 m12
• Members of child3 and classes derived from
  child3 can have
• also direct access to d2,m2, d3, and m3 of
  Parent
• Objects of type child 3 can access only d12, and
  m12
• Note that d1, and m1 are private to Parent and
  remain
• private to Parent

6
Inheritance
Examples in inheritance class B int a
public int b,c int Bfun(void) class X
private B int d public Bc //c inherited as
private now is public int Xfun(void) int I
Bfun() b 100 // OK, b is declared as
public in B a 10 // Error a is declared
as private in B Friend Relations under
inheritance The access privilege of friend
functions of a class is similar to that of the
member functions of the class. Friend functions
of a derived class can access the inherited
protected and public members of the base class.
Class Base int x friend int fbase(void)
protected float g public fun()..
class X private Base int a,b friend int
xf(void) public X(int) fun() int
xf(void) X z(10) z.a 100 z.g 0.01 //
OK z.x 100 //error..
7
Inheritance

• Friend Relations under inheritance (cont.)
• A friend function to the base class can access
  the base class members inherited in the instance
  of an object of the derived class,
• int fbase(void) X z(100) z.x 10 z.g
  0.001 //OK
• z.a 100 // Error.
• Multiple Inheritance
• A class can have several base classes
• class B1int x,y public B1(int I)x(I)y 0
  
• class B2int x public B2(int I)x I
• class X public B1, private B2int a,b
• public X(int I, int j) B1(I), B2(j) ab0
  
• X z // the instance of z contains B1x, B1y,
  B2x, Xa, and Xb

8
Inheritance

• Multiple Inheritance (cont.)
• Suppose that both classes B1 AND B2 are
  derived from the same base class B, i.e.,
• class B int u,v public B(int i)uvi
• class B1 public B . public B1(int
  I)B(I),x(I)y0
• class B2 public B public B2(int I) B(I)
  x I
• X z // the instance of z contains B1x, B2x,
  Xa,b, and two different copies of the inherited
  data members of B, one is initialized thr B1 and
  the other is initialized thr B2.
• Virtual Base Class
• is used to prevent the above problem by having
  only one copy of the base inherited by any
  derived class in complex class hierarchy,
• class B1 virtual public B. class B2 virtual
  public B
• The virtual base class is initialized by its
  most derived class in the class hierarchy, the
  initialization of B from B1 and B2 are completely
  ignored