C++ Inheritance: Virtual methods of base is invoked first and then derived method is invoked

0
votes

When a virtual method is called through a base pointer or a base reference pointing to a derived class object, base method is invoked first and then the derived method is invoked. Could someone explain why this behavior is implemented instead of directly calling the derived class method?

class Parent

class Parent{
    private:
        int money;
    public:
        void set_money(const int& m){
            money = m;
        }

        virtual const int& get_money() const{
            std::cout << "Parent version\n";
            return money;
        }
};

class Child

class Child : public  Parent{
    private:
    int my_money;
    mutable int family_money;
    public:
        void set_money(const int& m){
            my_money = m;
        }

        const int& get_money() const{
            family_money = my_money + Parent::get_money();
            std::cout << "Child version\n";
            return family_money;
        }

        void set_parent_money(const int& m){
            Parent::set_money(m);
        }
};

main

int main(){
    Child c;
    c.set_parent_money(20);
    c.set_money(50);
    Parent *p = &c;
    cout << "Pointer " << p->get_money() << endl;
    Parent& pr = c;
    cout << "Reference " << pr.get_money() << endl;
    Parent po = c;
    cout << "Object " << po.get_money() << endl;
    return 0;
}

Output

Parent version
Child version
Pointer 70
Parent version
Child version
Reference 70
Parent version
Object 20
1
pointersc++11inheritancereferencevirtual-functions
You call parent get_money inside child get_money. – hank

1 Answers

1
votes

No, it's invoked in correct order. The only problem is that you first call Parent method from Child method and after that you print Child message. If you swap the two lines the messages will appear as you expect:

        ...
        std::cout << "Child version\n";
        family_money = my_money + Parent::get_money();
         ....