Runtime Polymorphism in various types of Inheritance in C++
C++ allows users to use the concept of Run-Time Polymorphism using Virtual Functions for any type of Inheritance .
Below is how to implement Run-Time Polymorphism in all types of inheritance:
- Single Inheritance:
// C++ program to demonstrate Run Time
// Polymorphism in Single Inheritance
#include <iostream>
using
namespace
std;
// Base Class
class
Base {
public
:
// Virtual function
virtual
void
funct1()
{
cout <<
"Base::funct1() is called\n"
;
}
// Virtual function
virtual
void
funct2(
int
x)
{
cout <<
"Base's Val of x:"
<< x << endl;
}
// Non-Virtual Function
void
funct3()
{
cout <<
"Base is the Parent class!"
<< endl;
}
};
// Derived Class or Sub Class
class
Derived :
public
Base {
private
:
// Virtual Functions
// can also be Private!
void
funct1()
{
cout <<
"Derived::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Derived Class's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"It's the Derived class's"
<<
" funct3() called!"
<< endl;
}
};
int
main()
{
// Run-Time Polymorphism
// in Single Inheritance
Base* bptr =
new
Derived();
// virtual function
bptr->funct1();
// virtual function
bptr->funct2(12);
// Non-virtual function
bptr->funct3();
return
0;
}
Output:Derived::funct1() is called Derived Class's Val of x:12 Base is the Parent class!
- Multiple Inheritance:
#include <iostream>
using
namespace
std;
// Parent to Derived class
class
Base1 {
public
:
// Non-Virtual function
void
funct1()
{
cout <<
"Base1::funct1() is called\n"
;
}
// Virtual function
virtual
void
funct2(
int
x)
{
cout <<
"Base1's Val of x:"
<< x << endl;
}
// Non-Virtual Function
void
funct3()
{
cout <<
"Base1 is the Parent class!"
<< endl;
}
};
// Second Parent to Derived class
class
Base2 {
public
:
void
funct1()
{
cout <<
"Base2::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Base2's Val of x:"
<< x << endl;
}
// Only Virtual Function
// in Base2 Parent class
virtual
void
funct3()
{
cout <<
"Base2 is Also a Parent class!"
<< endl;
}
};
// Derived Class of Base1 and Base2
class
Derived :
public
Base1,
public
Base2 {
private
:
void
funct1()
{
cout <<
"Derived::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Derived Class's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Derived::funct3() is called "
<<
"and not Base2::funct3() due"
<<
" to RTP"
<< endl;
}
};
int
main()
{
Derived d;
// Run-Time Polymorphism
// in Multiple Inheritance
Base1* b1ptr = &d;
// Compile-Time Binding,
// Hence Base1::funct1() will be called!
b1ptr->funct1();
// virtual function of Base1
// RunTime PolyMorphism
b1ptr->funct2(10);
// Now Parent Class Base2
// is also pointed to object 'd'
// of Derived (to demonstrate RTP)
Base2* b2ptr = &d;
// virtual function of Base2
// RunTime PolyMorphism
b2ptr->funct3();
return
0;
}
Output:Base1::funct1() is called Derived Class's Val of x:10 Derived::funct3() is called and not Base2::funct3() due to RTP
Note: Here Both Base1 pointer and Base2 pointer may be pointing to the same Derived Class object ‘d’ but actually the Compiler selects difference Virtual Functions during Run-Time due to the use of different Base Class pointers.
- Multi-level inheritance:
// C++ Program to illustrate Run-Time
// Polymorphism in multi-level inheritance
#include <iostream>
using
namespace
std;
// Parent Class
class
Base1 {
public
:
// Virtual function
virtual
void
funct1()
{
cout <<
"Base1::funct1() is called\n"
;
}
// Virtual function
virtual
void
funct2(
int
x)
{
cout <<
"Base1's Val of x:"
<< x << endl;
}
// Non-Virtual Function
void
funct3()
{
cout <<
"Base1 is the Parent class!"
<< endl;
}
};
// Derived Class of Base1
// but Parent to Base3
class
Base2 :
public
Base1 {
// Virtual Functions can be Private!
private
:
void
funct1()
{
cout <<
"Base2::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Base2's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Base2 is the first "
<<
"Derived class!"
<< endl;
}
};
// Derived Class of Base2
// but Parent to Derived
class
Base3 :
public
Base2 {
private
:
void
funct1()
{
cout <<
"Base3::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Base3's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Class Base3 is second "
<<
"Derived class!"
<< endl;
}
};
// 3 Levels of Multi-Level Inheritance
// and final Child Class
class
Derived :
public
Base3 {
private
:
void
funct1()
{
cout <<
"Derived::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Derived Class's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Class Derived is Final"
<<
" Child class!"
<< endl;
}
};
int
main()
{
// Run-Time Polymorphism
// in multi-level Inheritance
Base1* b1ptr =
new
Derived;
b1ptr->funct1();
b1ptr->funct2(30);
// Compile-Time Binding
b1ptr->funct3();
return
0;
}
Output:Derived::funct1() is called Derived Class's Val of x:30 Base1 is the Parent class!
Explanation : In the above Example, the Derived class is the final Child class which inherits from Base3 which inherits from Base2 which again finally inherits from the Base1 (Parent Class to Base2). But if you see the Run-Time Polymorphism works even when you are trying to use Virtual Functions in Base1 Class and point its pointer to Derived Class (Which is the great grand-Child of Base1). Hence, even here Run-Time Polymorphism works according to the standard Rules.
- Hierarchical inheritance:
// C++ Program to illustrate Run-Time
// Polymorphism in Hierarchical inheritance
#include <iostream>
using
namespace
std;
class
Base1 {
public
:
// Virtual function of Parent Class
virtual
void
funct1()
{
cout <<
"Base1::funct1() is called\n"
;
}
virtual
void
funct2(
int
x)
{
cout <<
"Base1's Val of x:"
<< x << endl;
}
// Non-Virtual Function
void
funct3()
{
cout <<
"Base1 is the Parent class!"
<< endl;
}
};
class
Base2 :
public
Base1 {
private
:
void
funct1()
{
cout <<
"Base2::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Base2's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Base2 is the first"
<<
" Derived class!"
<< endl;
}
};
class
Base3 :
public
Base1 {
private
:
void
funct1()
{
cout <<
"Base3::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Base3's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Class Base3 is second"
<<
" Derived class!"
<< endl;
}
};
// Grand-Child_1 of Base1 class
class
Derived1 :
public
Base3 {
private
:
void
funct1()
{
cout <<
"Derived1::funct1() is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Derived1 Class's Val of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Class Derived1 is Good!!"
<< endl;
}
};
// Grand-Child_2 of Base1 class
class
Derived2 :
public
Base3 {
private
:
void
funct1()
{
cout <<
"Derived2::funct1()"
<<
" is called\n"
;
}
void
funct2(
int
x)
{
cout <<
"Derived2 Class's Val "
<<
"of x:"
<< x << endl;
}
void
funct3()
{
cout <<
"Class Derived2 is Good!!"
<< endl;
}
};
// Run-Time Polymorphism
// in Hierarchical Inheritance
int
main()
{
// Base1 class's(Parent class's)
// pointer points to Derived1 class
Base1* b1ptr =
new
Derived1();
// Run-Time Polymorphism
b1ptr->funct1();
Derived2 d2;
// Now the Base1 class pointer
// points to d2 object(Derived2 class)
b1ptr = &d2;
// Run-Time Polymorphism
b1ptr->funct2(30);
// Compile-Time Binding
b1ptr->funct3();
return
0;
}
Output:Derived1::funct1() is called Derived2 Class's Val of x:30 Base1 is the Parent class!
Explanation: Here, the Parent is Base1 and its Grand-children are Derived1 Class and Derived2 class. Even in this case, When the Base1 Class pointer is pointed to Derived1 object or Derived2 object, due to the Virtual Functions (‘VPTR’ and ‘VTABLE’), we can apply Run-Time Polymorphism here.