Polymorphism in C++
C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function.
Runtime Polymorphism Example
#include <iostream>
using namespace std;
class Animal {
public:
void eat(){
cout<<"Eating...";
}
};
class Dog: public Animal
{
public:
void eat()
{ cout<<"Eating bread...";
}
};
int main(void) {
Dog d = Dog();
d.eat();
return 0;
}
Eating bread...
#include <iostream>
using namespace std;
class Shape { // base class
public:
virtual void draw(){ // virtual function
cout<<"drawing..."<<endl;
}
};
class Rectangle: public Shape // inheriting Shape class.
{
public:
void draw()
{
cout<<"drawing rectangle..."<<endl;
}
};
class Circle: public Shape // inheriting Shape class.
{
public:
void draw()
{
cout<<"drawing circle..."<<endl;
}
};
int main(void) {
Shape *s; // base class pointer.
Shape sh; // base class object.
Rectangle rec;
Circle cir;
s=&sh;
s->draw();
s=&rec;
s->draw();
s=?
s->draw();
}
drawing...
drawing rectangle...
drawing circle...
Runtime Polymorphism with Data Members
#include <iostream>
using namespace std;
class Animal { // base class declaration.
public:
string color = "Black";
};
class Dog: public Animal // inheriting Animal class.
{
public:
string color = "Grey";
};
int main(void) {
Animal d= Dog();
cout<<d.color;
}
This code generates a pseudorandom number at run time. If it generates an even number, it directs p to point to a plain Text object; Which method will this code call, Text::get or FancyText::get?
#include <iostream>
// A class with no virtual methods
class NoVTable {
int data;
public:
void set(int d) {
data = d;
}
int get() {
return data;
}
};
// A class with virtual methods
class HasVTable {
int data;
public:
virtual void set(int d) {
data = d;
}
virtual int get() {
return data;
}
};
int main() {
NoVTable no_vtable;
HasVTable has_vtable;
no_vtable.set(10);
has_vtable.set(10);
std::cout << "no_vtable size = " << sizeof no_vtable << '\n';
std::cout << "has_vtable size = " << sizeof has_vtable << '\n';
}
no_vtable size = 4
has_vtable size = 8
Dynamic binding enables a powerful technique in object-oriented programming called polymorphism
#include <string>
#include <vector>
#include <iostream>
// Base class for all Text derived classes
class Text {
std::string text;
public:
Text(const std::string & t): text(t) {}
virtual std::string get() const {
return text;
}
};
// Provides minimal decoration for the text
class FancyText: public Text {
std::string left_bracket;
std::string right_bracket;
std::string connector;
public:
FancyText(const std::string & t,
const std::string & left,
const std::string & right,
const std::string & conn):
Text(t), left_bracket(left), right_bracket(right),
connector(conn) {}
std::string get() const override {
return left_bracket + Text::get() + right_bracket;
}
};
// The text is always the word FIXED
class FixedText: public Text {
public: FixedText(): Text("FIXED") {}
};
int main() {
std::vector < Text * > texts {
new Text("Wow"),
new FancyText("Wee", "[", "]", "-"),
new FixedText,
new FancyText("Whoa", ":", ":", ":")
};
for (auto t: texts)
std::cout << t - > get() << '\n';
}
We know from Section 11.1 that a vector is a collection of homogeneous elements. Homogeneous means the elements in a vector must all be of the same type. In the declared type of the texts vector is std::vector.
Wow
[Wee]
FIXED
:Whoa:
What is polymorphism and example?
The word polymorphism means having many forms. … Real life example of polymorphism: A person at the same time can have different characteristic. Like a man at the same time is a father, a husband, an employee. So the same person posses different behaviour in different situations. This is called polymorphism.
