"Marked as override but does not override" Problem in OOP Code

Question

I am trying to practice OOP in C++ but I am running into an issue regarding overriding of functions. In my Shape2D and Shape3D classes, I have virtual functions which I redefine in the Square and Sphere classes (ShowArea() and ShowVolume() respectively). However, when I redefine the function and try to run the main, it outputs the errors:

Shapes.cpp:88:14: error: 'void Square::ShowArea() const' marked 'override', but does not override
         
void ShowArea() const override{

Shapes.cpp:353:14: error: 'void Sphere::ShowVolume() const' marked 'override', but does not override
         
void ShowVolume() const override {

Below is a snippet of relevant code from both the Shape2D, Square, Shape3D, and Sphere classes.

class Shape2D : virtual public Shape {

public:

    virtual float Area() const = 0;

    void ShowArea() const;

    virtual string GetName2D() const = 0;
}



class Square: public Shape2D {

private:
    float squareLen;

public:

    // Constructors
    Square() {
        squareLen = 0;
    }

    Square(float len) {
        squareLen = len;
    }

    string GetName2D() const override {
        string res;

        return res;
    }

    // Returns the area of the shape
    float Area() const override {
        return (squareLen * squareLen);
    }

    void ShowArea() const override{
        cout << "Square Area: " << endl;
    }
}


class Shape3D : virtual public Shape {
    public:
        virtual float Volume() const = 0;
        void ShowVolume() const;
        virtual string GetName3D() const = 0;
}



class Sphere: public Shape3D {

private:
    Circle* SphereBase;

public:
    Sphere() {
        SphereBase = new Circle();
    }

    Sphere(float radius) {
        SphereBase = new Circle(radius);
    }

    float Volume() const {
        return (1.3333 * pi * pow(SphereBase->GetRadius(), 3));
    }

    void ShowVolume() const override {

    }

Why is this the case when I am redefining the function in the subclasses and the function is virtual in its original definition? It does not work for any of my shapes (I have 6 shapes but only included 2 in this post) so I dont think its a typo and its crashes across both 2D and 3D shapes so its not an issue with those specific classes.

Answer 1

The function ShowArea declared in the class Shape2D

void ShowArea() const;

is not a virtual function. So this declaration in the derived class Square

void ShowArea() const override{
    cout << "Square Area: " << endl;
}

is incorrect.

Also the function ShowVolume declared in the class Shape3D is not a virtual function

void ShowVolume() const;

It may not be overridden in a derived class.

You need to declare the functions to be virtual in base classes that they could be overridden.

Answer 2

The problem is that currently the member functions showArea and showVolume are not virtual member functions and we can use override keyword only when overriding a virtual member function.

To solve this you need to make showArea and showVolume virtual member functions by adding the keyword virtual as shown below:

class Shape2D : virtual public Shape {

public:

//--vvvvvvv------------------------->virtual added here
    virtual void ShowArea() const;
    //other code here 
};
class Shape3D : virtual public Shape {
    public:
//------vvvvvvv------------------------------>virtual  added here        
        virtual void ShowVolume() const;
        //other code here
};
//other code here