Inheritance: constructors

1
Inheritance constructors

• Constructors, copy constructors and destructors
  are NOT inherited.
• Each subclass has its own constructors and
  destructor to handle the creation and destruction
  of its own data members.
• The superclass constructor initializes the data
  members defined in the superclass
• The subclass constructor calls the superclass
  constructor (which initializes the inherited
  members) and then goes on to initialize its own
  data members.
• The destructor works in a similar way, but in
  reverse order.

2
Inheritance constructors

• Example 1

class Base public Base() cout ltlt
BaseBase()\n class Derived public
Base public Derived() cout ltlt
DerivedDerived()\n int main ()
Derived obj return 0
Output BaseBase() DerivedDerived()
3
Inheritance constructors

• Example 2

class Derived public Base public
Derived() cout ltlt DerivedDerived()\n
Derived(int x) Base(x)
cout ltlt DerivedDerived(x)\n
class Base public Base() cout
ltlt BaseBase()\n Base(int x)
cout ltlt BaseBase(x)\n int main
() Derived obj(10) return 0
Output BaseBase(x) DerivedDerived(x)
4
Inheritance destructors

• Example 3

class Base public Base() Base()
cout ltlt BaseBase()\n class Derived
public Base public Derived()
Derived() cout ltlt DerivedDerived()\
n int main () Derived obj return
0
Output DerivedDerived() BaseBase()
5
Inheritance hiding methods

• A derived class may use the base classs member
  functions.
• A derived class may also redefine the base
  classs member functions.
• In that case, the derived classs definition
  hides the one in the base class.

6
Inheritance hiding methods

• Example 1

class Base private public Base()
void print() cout ltlt "Baseprint()\n"
class Derived public Base
private public Derived() int main ()
Derived obj obj.print()
return 0
Output Baseprint()
7
Inheritance hiding methods

• Example 2

class Base private public Base()
void print() cout ltlt "Baseprint()\n"
class Derived public Base
private public Derived() void print()
cout ltlt Derivedprint()\n" int main ()
Derived obj obj.print()
return 0
Output Derivedprint()
8
Inheritance hiding methods

• Example 3

class Base private public Base()
void print() cout ltlt "Baseprint()\n"
void print(int x) cout ltlt Baseprint(x)\n
class Derived public Base
private public Derived() void print()
cout ltlt Derivedprint()\n" int main ()
Derived obj obj.print(10)
return 0
print() is overloaded
this definition hides BOTH Baseprints.
COMPILER ERROR! Baseprint(x) is hidden by
Derivedprint()
9
Inheritance hiding methods

• Example 4

class Base private public Base()
void print() cout ltlt "Baseprint()\n"
void print(int x) cout ltlt Baseprint(x)\n
class Derived public Base
private public Derived() void print()
cout ltlt Derivedprint()\n" void print(int
x) cout ltlt Derivedprint(x)\n" int main
() Derived obj obj.print(10)
return 0
Output Derivedprint(x)
10
Virtual functions

• Recall the class hierarchy
• We wish to create an array of pointers to various
  subtypes of Vehicles. In addition, each member of
  the array should behave according to each
  subclass.
• This can be achieved if every Vehicle member
  function that is overriden in the subclasses is
  declared as virtual.

Vehicle
Truck
Train
Bicycle
11
Virtual functions

• Example

int main () Vehicle fleet2 fleet0
new Train fleet1 new Truck
fleet0-gtprint() fleet1-gtprint()
delete fleet0 delete fleet1 return
0
class Vehicle public Vehicle()
virtual void print() cout ltlt Vehicle\n cl
ass Train public Vehicle public Train()
virtual void print() cout ltlt
Train\n class Truck public Vehicle
public Truck() virtual void
print() cout ltlt Truck\n
Output Train Truck
12
Multiple inheritance

• A class may inherit from more than one base
  class.
• BoatCar inherits the members of Car and those of
  Boat.
• BoatCar's constructor calls the constructors of
  Car and Boat in the order specified in BoatCar's
  definition (i.e. as they appear after the colon)

class Car ... class Boat ... class
BoatCar public Car, public Boat ...