Overriding toString()

When another class (like Student) wants to provide a different implementation for a virtual member function, like toString(), it must:

  1. Use exactly the same signature (number and type of parameters) as the original virtual function in the base class. There are no conversions between int and double for instance as with overloading.
  2. Return exactly the same type as the original member functions.

Let's override toString() in the Student class. Here's the header: 

class Student : public Person
{
public:
    Student(const std::string name, long sid);
    long getID() const;
    std::string toString() const override;
private:
    long studentID;
};

Note that the prototype is copied exactly from Person::toString(), except for the keyword virtual. You do not need to repeat the word virtual in the derived class definition, (although you may for documentation purposes). A virtual function is always virtual, and a non-virtual function cannot be made virtual in one of its subclasses.