Question

class Vec
{
    double dim[];
public:
    Vec(void);
    ~Vec(void);
    virtual void Add(Vec vector) = 0;

};

I want to replace the Vec in Vec::Add() with “any class that inherits from Vec“.
Is there a way to do that?

Answer 1

Change the parameter to a reference to const Vec:

virtual void Add(Vec const &vector) = 0;

A class (publicly) derived from Vec can be passed by reference to the base class.

Also, since you apparently plan to use Vec as a base class, you probably want to make its dtor virtual too. Otherwise, if you attempt to destroy an object of the derived type via a pointer or reference to the base, you’ll get undefined behavior.