CODEWITHSUNDEEP
c++oopc++11inheritance
pistacchio
pistacchio

Reputation: 58863

C++ override inherited methods

I have the following two classes. Since Child inherits from Father, I think that Child::init() overrides Father::init(). Why, when I run the program, I get "I'm the Father" and not "I'm the Child"? How to execute Child::init()?

You can test it here: https://ideone.com/6jFCRm

#include <iostream>

using namespace std;

class Father {
    public:
        void start () {
            this->init();
        };

        void init () {
            cout << "I'm the father" << endl;
        };
};

class Child: public Father {
    void init () {
        cout << "I'm the child" << endl;
    };
};

int main (int argc, char** argv) {
    Child child;
    child.start();
}

Upvotes: 28

Views: 67643

Answers (3)

Dimitri
Dimitri

Reputation: 1966

If you want the child to override the init method, you must make the init method in the base class virtual.

class Father {
    public:
        void start () {
            this->init();
        };

        virtual void init () {
            cout << "I'm the father" << endl;
        };
};

A class that re-declares and re-implements a virtual method of one of its bases, is said to override that method. In order for late binding to occur for a method, you need to declare that method virtual.

Upvotes: 3

Vlad from Moscow
Vlad from Moscow

Reputation: 310950

You should define the function with function specifier virtual

For example

#include <iostream>

using namespace std;

class Father {
    public:
        virtual ~Father() {}

        void start () {
            this->init();
        };

        virtual void init () const {
            cout << "I'm the father" << endl;
        };
};

class Child: public Father {
    void init () const override {
        cout << "I'm the child" << endl;
    };
};

int main()
{
    Child child;
    child.start();

    return 0;
}

Otherwise function start searches name init in the scope of its own class. And because function init is not virtual that is it is not overriden in the derived class the base class function init is called.

Upvotes: 5

TartanLlama
TartanLlama

Reputation: 65610

Currently Child::init is hiding Father::init, not overriding it. Your init member function needs to be virtual in order to get dynamic dispatch:

virtual void init () {
    cout << "I'm the father" << endl;
};

Optionally, you could mark Child::init as override to be explicit that you want to override a virtual function (requires C++11):

void init () override {
    cout << "I'm the child" << endl;
};

Upvotes: 40

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