Hello.

I have a base class that has a variable that needs to be set when the class object is made.

But when i inherit the class, i have no idea how to invoke the constructor, what are workarounds?

How can constructor of MainMenu class also invoke Collision constructor?

//I have class like this, its used as a base class
//NOTE its constructor is taking a argument
class Collision

{

public:

    Collision(sf::RenderWindow *RenWin);

    bool Col_RectMouse(sf::RectangleShape &rec);

private:

    sf::RenderWindow *renWin;

};
 
//The functions the above class uses
Collision::Collision(sf::RenderWindow *RenWin)

{

    this->renWin = RenWin;

}



bool Collision::Col_RectMouse(sf::RectangleShape &rec)

{

    int x = sf::Mouse::getPosition(*renWin).x;

    int y = sf::Mouse::getPosition(*renWin).y;

    if(x > rec.getPosition().x &&

       x < rec.getPosition().x + rec.getSize().x &&

       y > rec.getPosition().y &&

       y < rec.getPosition().y + rec.getSize().y)

    {

        return true;//Collision

    }

    return false;//No collision

}
 
//Then a class that inherits the base class
class MainMenu : public Collision

{

public:

    MainMenu();

    void Draw(sf::RenderWindow &renWin);

private:

    sf::RectangleShape Continue, NewGame, Options, Exit;

};
 
//Code of functions for above class
MainMenu::MainMenu()

{ //Error, no default constructor exists for class "Collision"

    Continue.setFillColor(sf::Color(100,100,100));

    Continue.setPosition(0, 0);

//...

}

You need a MainMenu constructor that gets the required RenderWindow* as parameters and use it to construct its base class.

Transate into code:

your declaration becomes:

MainMenu(sf::RenderWindow* rw);

your implementation becomes:

MainMenu::MainMenu(sf::RenderWindow* rw) : Collision(rw)

{

// bla bla
}

I suggest you to study constructor initializer lists.

MainMenu::MainMenu(sf::RenderWindow* rw) : Collision(rw)

I suggest you to study constructor initializer lists.

These two things, thanks!

The only way to call a constructor of a base class in C++ is through an intialiser list as shown before, this is the same principle as base or super in java. However they work completely opposite from each other. As C# constructs the derived class first and then the base, in C++ however the base gets constructed before the derived class. This is also the reason why you can't call overloaded or virtual methods in the constructor of a C++ class but can in C# and have them being redirected to the derived implementation of that method.