How to create a dynamic array that can hold different objects all derived from the same base class in C++

Just wanted to elaborate on Nicky C's comment.

#include <memory> using namespace std; class Shape {}; class Rectangle : public Shape {}; class Circle : public Shape {}; template <class Type> class MyVector {}; // implement (with push method, etc.) int main() { MyVector<unique_ptr<Shape>> v; v.push(unique_ptr<Shape>(new Rectangle())); v.push(unique_ptr<Shape>(new Circle())); return 0; } 

The vector contains elements of type unique_ptr<Shape> which is the base class. Each element of the vector can be unique_ptr<Rectangle> or unique_ptr<Circle> as well. However, if the vector were of type unique_ptr<Rectangle>, each element would have to be of type unique_ptr<Rectangle> (i.e. it could not be of type unique_ptr<Circle>).

Since you are allocating memory on the heap, using unique_ptr just makes sure that you don't need to call delete yourself.

One of the strengths of inheritance/polymorphism is that you can use a derived class wherever a base class is needed. It is an important key concept. For instance, as in your code above, you can do:

Shape *s = new Shape(); s = new Rectangle(); s = new Circle(); 

This also applies to function parameters:

class DynamicArray { private: Shape **_shapes[]; ... public: void add_shape(Shape *s) { // Add the shape to _shapes; } ... }; void main() { DynamicArray array; array.add_shape(new Shape()): array.add_shape(new Rectangle()): array.add_shape(new Circle()): }