[SOLVED]C++ Inherit help

[Zer0XoL]

Hi everyone, I am making a Gui system and ive come across something i cant seem to solve.
This is what the problem looks like:

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class g_element
{
protected:
int x, y;
public:
g_element(int _x, int _y){x = _x; y = _y;}
};

This is the base class for all elements like g_button should be based on

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class g_button : public g_element
{
private:
int w, h;
public:
g_button(int _x, int _y, int _w, int _h){x = _x; y = _y; w = _w; h = _h;}
void Handle();
void Draw();
};

And then when i handle all elements i use something similar to this:

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for(int i=0;i<element.size();i++)
{
element[i].Handle();
}

(element is a vector of g_element)
And well i know that g_element has no function named Handle(), but if i add one it gives me an error.
Also all objects in element are != g_element and all other classes should have the function Handle().
Im having a problem, i think its related to virtual functions but i dont know, i wish you guys could help me, thanks.

[Bakkon]

You may want to make g_element an abstract class by adding something like

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void virtual Handle() = 0;
void virtual Update() = 0;
void virtual Draw() = 0;

and you might want your vector to be of g_element pointers.

[Zer0XoL]

You may want to make g_element an abstract class by adding something like

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void virtual Handle() = 0;
void virtual Update() = 0;
void virtual Draw() = 0;

and you might want your vector to be of g_element pointers.

I tried but it gives me this:

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cannot instantiate abstract class
1>        due to following members:
1>        'void Gui::g_element::Handle(void)' : is abstract

[andrew]

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class g_element
{
protected:
	int x, y;
public:
	g_element(int _x, int _y){x = _x; y = _y;}
	void virtual Handle() = 0;
	void virtual Update() = 0;
	void virtual Draw() = 0;
};

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class g_button : public g_element
{
private:
	int w, h;
public:
	g_button(int _x, int _y, int _w, int _h){x = _x; y = _y; w = _w; h = _h;}
	void Handle();
	void Update();
	void Draw();
};

You have to implement those virtual functions.

[Bakkon]

I tried but it gives me this:

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cannot instantiate abstract class
1>        due to following members:
1>        'void Gui::g_element::Handle(void)' : is abstract

Did you switch your vector to hold pointers? You can't instantiate abstract objects but you can define pointers to one. What's it look like when you create and add a button object?

[GroundUpEngine]

my polymorphism is a bit rough, but I read ya post and threw this together real quick dunno if it helps

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class g_element {
    protected:
       int x, y;
    public:
       void set_values(int _x, int _y)
         { x = _x; y = _y; }
       virtual void Handle() = 0;
       virtual void Update() = 0;
       virtual void Draw() = 0;
};

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class g_button : public g_element {
    private:
       int width, height;
    public:
       void set_values(int _x, int _y, int _w, int _h)
         { x = _x; y = _y; width = _w; height = _h; }
       void Handle()
         { cout << "x: " << this->x << ", y: " << this->y
         << " w: " << this->width << ", h: " << this->height << endl; }
       void Update(){}
       void Draw(){}
};

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int main(){
    //5 Buttons
    vector<g_button>button(5);
    
    for(int i = 0; i < button.size(); i++){
        //Set random values
        button[i].set_values(rand(), rand(), rand(), rand());
        //Print values for each button
        button[i].Handle();
    }

    cin.get(); return 0;
}

[andrew]

Here's the simplest example of polymorphism I could come up with:

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#include <iostream>

class Animal {
    public:
        virtual void Speak() = 0;
};

class Duck : public Animal {
    public:
        void Speak() { std::cout << "Quack!\n"; }
};

class Dog : public Animal {
    public:
        void Speak() { std::cout << "Bark!\n"; }
};

int main() {
    Animal *Donald = new Duck;
    Animal *Spike = new Dog;
    Donald->Speak();
    Spike->Speak();
    delete Donald;
    delete Spike;
    return 0;
}

You could put them in a list like this:

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    std::list <Animal*> Animals;
    Animals.push_back(new Dog);
    Animals.push_back(new Duck);
    Animals.push_back(new Duck);
    Animals.push_back(new Dog);
    Animals.push_back(new Dog);

    std::list <Animal*>::iterator node = Animals.begin();
    while (node != Animals.end()) {
        (*node)->Speak();
        ++node;
    }

    node = Animals.begin();
    while (node != Animals.end()) {
        if ((*node) != NULL) {
            delete *node;
            *node = NULL;
        }
        ++node;
    }

You can't instantiate abstract objects but you can define pointers to one.

@Zer0Xol: This is true, if you don't do it you'll get that error that you posted.

[qpHalcy0n]

For interfaces and abstract types you'll want to consider using a virtual destructor in the above case as well.

[Falco Girgis]

For interfaces and abstract types you'll want to consider using a virtual destructor in the above case as well.

VERY important that you listen to this man.

[Zer0XoL]

For interfaces and abstract types you'll want to consider using a virtual destructor in the above case as well.

VERY important that you listen to this man.

And how do i make a virtual destructor?
Thanks all for the help btw :D

[GroundUpEngine]

For interfaces and abstract types you'll want to consider using a virtual destructor in the above case as well.

VERY important that you listen to this man.

And how do i make a virtual destructor?
Thanks all for the help btw :D

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class g_element
{
    public:    
      g_element() { // Constructor: Base // }
      virtual ~g_element() { //  Destructor : Base // }
};

class g_button : public g_element
{
    public:    
      g_button(){ // Constructor: Derived // }
      ~g_button { // Destructor : Derived // }
};