Question

I have this Parent Class call

Shape (ShapeTwoD.cpp)

He got 2 Child Class

1 is Rectangle (Rectangle.cpp)
1 is Square (Square.cpp)

There this variable call area declare at Rectangle & Square , but not at Shape(the parent)

So i was trying to sort by area ascending, however area can be access by

class->getArea();


vector<ShapeTwoD*> myVector;

//during the period of recording data like width ,height to the shape.

myVector[arrayCount] = new Rectangle();
myVector[arrayCount].setWidth(inWidth);
myVector[arrayCount].setHeight(inHeight);
myVector[arrayCount].computeArea();

arrayCount ++;

//done record width , height and then compute area of the shape

Assuming myVector now Contains about 2 Rectangle and 1 Square

Now I want to sort them by area ascending.

But my getArea() function is only available at child class.

If i try do this

sort(myVector.begin(),myVector.end(),funcAreaSort);

I not sure where to create funcAreaSort , next is how do i send in child area , assuming if they are same shape class(rectangle against rectangle) or different shape class (rectangle against shape)

how i create a boolean operator overload that can compare by getArea() then see which is better return a.getArea() > b.getArea() and sort myVector

Question is Where do i create those function I was thinking of making it a free method at main.cpp but i fail getting the thing sort and compile with error like qualifier error

error: passing 'const shapeTwoD' as 'this' argument of 'virtual double shapeTwoD::getArea()' discards qualifers.
error: passing 'const shapeTwoD' as 'this' argument of 'virtual double shapeTwoD::getArea()' discards qualifers.

Answer 1

1) Make the compare function take ShapeTwoD* as parameters, and have a virtual getArea method in the base class, which you override in the children.

2) Make the method getArea const:

int getArea() const;

because it logically makes sense & so that you can call it on const objects.