Interface /Abstract Classes in C++

An interface describes the behavior or capabilities of a C++ class without committing to a particular implementation of that class.

The C++ interfaces are implemented using abstract classes and these abstract classes should not be confused with data abstraction which is a concept of keeping implementation details separate from associated data.

A class is made abstract by declaring at least one of its functions as pure virtual function. A pure virtual function is specified by placing "= 0" in its declaration as follows:

#include <iostream.h>

class Shape

{

public:

// pure virtual function providing interface framework.

virtual int getArea() = 0;

void setWidth(int w)

{

width = w;

}

void setHeight(int h)

{

height = h;

}

protected:

int width;

int height;

};



class Rectangle: public Shape

{

public:

int getArea()

{

return (width * height);

}

};

class Triangle: public Shape

{

public:

int getArea()

{

return (width * height)/2;

}

};



int main(void){

Rectangle Rect;

Triangle Tri;

Rect.setWidth(5);

Rect.setHeight(7);

cout << "Total Rectangle area: " << Rect.getArea() << endl;

Tri.setWidth(5);

Tri.setHeight(7);

cout << "Total Triangle area: " << Tri.getArea() << endl;

return 0;

}