CODEWITHSUNDEEP
c++
stumpbeard
stumpbeard

Reputation: 61

How to use Child functions from Parent pointers?

Here is a sample parent and child I'm working with.

class Home{
    public:
        virtual void input();
        virtual void output();
    private:
};

class Ocelot : public Home{
    public:
        void input(istream& ins = cin);
        void output(ostream& outs = cout);
    private:
        int revolvers;
        double shadeCover;
        int waterSources;
};

And here is my main where I'm trying to make a pointer that can hold different kinds of children and call their functions.

int main(){
    list<Home> animals;
    Home * ptr;
    ptr = new Ocelot;
    ptr->input();
    ptr->output();
    return 0;
}

When I attempt to compile, I'm just getting undefined references to Home::input and Home::output. What exactly is it that I'm doing incorrectly here? Thank you for your time.

Edit: In case it wasn't clear, I am trying to call the Ocelot input and output functions. The Home ones don't exist.

Upvotes: 0

Views: 99

Answers (2)

E. Moffat
E. Moffat

Reputation: 3288

If Home::input and Home::output don't require implementations, make them pure virtual functions:

virtual void input() = 0;
virtual void output() = 0;

Otherwise, you need to define an implementation for them in Home so the linker doesn't complain about it:

virtual void input() { /* code */ }
virtual void output() { /* code */ }

You will also need to make the signatures of input and output the same for the base class Home and derived class Ocelot. Either add the stream parameters to the signatures of Home::input and Home::output or remove them from Ocelot::input and Ocelot::output.

Additionally: list<Home> will cause problems for you; you will need to use list<Home*> instead so the base class (which is now abstract because of the pure virtual functions) is not being instantiated.

Upvotes: 3

A.S.H
A.S.H

Reputation: 29332

list animals;

You cannot do this if Home is an abstract class. std containers cannot hold abstract classes (interfaces), simply because these cannot be constructed or instanciated. What you can do is:

list<Home*> animals;

Apart from this, make your input() and output() methods pure virtual (=0;) and do implement them in child classes that inherit the Home interface.

Upvotes: 0

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