Interfaces in C++ (Abstract Classes)

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Abstract classes are the way to achieve abstraction in C++. Abstraction in C++ is the process to hide the internal details and showing functionality only. Abstraction can be achieved by two ways:

• Abstract class
• Interface Abstract class and interface both can have abstract methods which are necessary for abstraction.

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C++ Abstract class

In C++ class is made abstract by declaring at least one of its functions as <>strong>pure virtual function. A pure virtual function is specified by placing “= 0” in its declaration. Its implementation must be provided by derived classes.

Let’s see an example of abstract class in C++ which has one abstract method draw(). Its implementation is provided by derived classes: Rectangle and Circle. Both classes have different implementation.

#include <iostream>  
using namespace std;  
 class Shape    
{    
    public:   
    virtual void draw()=0;    
};    
 class Rectangle : Shape    
{    
    public:  
     void draw()    
    {    
        cout < <"drawing rectangle..." < <endl;    
    }    
};    
class Circle : Shape    
{    
    public:  
     void draw()    
    {    
        cout <<"drawing circle..." < <endl;    
    }    
};    
int main( ) {  
    Rectangle rec;  
    Circle cir;  
    rec.draw();    
    cir.draw();   
   return 0;  
}  

Output

drawing rectangle...
drawing circle...

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