Why is inherited member not allowed?

Question

I'm beginner to C++ and I'm doing one of the exercises about abstract class and inheritance.

This is my abstract class:

#ifndef   SHAPE_H  #define  SHAPE_H class Shape {     public:         virtual void area();         virtual void perimeter();         virtual void volume(); }; #endif 

This is my concrete class that implements the abstract class:

#include <iostream> #include <cmath> #include "Shape.h" using namespace std;  class Circle : public Shape {     public:         Circle(int);     private:         int r; };  Circle::Circle(int rad) {     r = rad; }  void Circle::area() {     cout << "Area of this cirle = " << 3.14 * pow(r, 2) << endl; }  void Circle::perimeter() {     cout << "Perimeter of this cirle = " << 2 * 3.14 * r << endl; }  void Circle::volume() {     cout << "Volume is not defined for circle." << endl; } 

I got red lines under area(), perimeter(), and volume() in my Circle class, which showed "Error: inherited member is not allowed". I went through my class ppt and googled for answer but no luck. Any help is appreciated.

Answer 1

You have to declare the over-ridden functions as part of your class definition

class Circle : public Shape     {     public:         Circle(int);         virtual void area(); // overrides Shape::area         void perimeter();    // overrides Shape::perimeter         virtual void volume();     private:         int r;     }; 

Note that the use of virtual here is optional.

As n.m. noted, you should also include a virtual destructor in Shape. You may also want to make its virtual functions pure virtual (based on your comment about Shape being abstract)

class Shape { public:     virtual ~Shape() {}     virtual void area() = 0;     virtual void perimeter() = 0;     virtual void volume() = 0; }; 

Answer 2

you have to declare the override methods too in the Circle class

class Circle : public Shape     {     public:         Circle(int);         virtual void area();         virtual void perimeter();         virtual void volume();     private:         int r;     };