Use of virtual

Hallo,

Is it possible for a virtual function to take different arguments? Like this:

Code:

---

class Vehicle
{
        public:
                Object(void);
                ~Object(void);

                virtual void update() = 0;
                virtual void draw() = 0;
};

class Truck : public Vehicle
{
        public:
                Player();

                void update(int a, int b);
                void draw();               
};

---

Thanks

No. A function taking different arguments is a different function.

Wouldn't that be a little confusing if you did that though? The base class is essentially a contract between the code and the developer saying all derived classes will look at least like this.

I though it would be useful to do something like that. But after thinking about it for a while I guess it would be stupid if that worked in some way. It would break the whole concept behind virtual (i think)

The idea of virtual is that you can manipulate objects through a base pointer without caring what the concrete type is. If virtual functions would take different arguments in different classes, you'd have to first find out what type the pointer is actually pointing to in order to be able to call the function with correct parameters. If I'm not mistaken, you can already do that with non-virtual functions just fine.

It is of course possible to have TWO DIFFERENT virtual functions that are different only in the arguments they take, e.g.

Code:

---

struct coord
{
    int x;
    int y;
}
class base
{
  public:
      virtual void vfunc(int x, int y);
};

class derived: public base
{
  public:
      virtual void vfunc(int x, int y);
      virtual void vfunc(coord &c);
}

void base::vfunc(int x, int y)
{
... code here
}

void base::vfunc(coord &c)
{
  vfunc(c.x, c.y);
}

void derived::vfunc(int x, int y)
{
... code here
}

---

Note that since the base::vfunc(coord &) calls the virtual vfunc(int, int) form, it will automatically call the derived::vfunv(int, int).

--
Mats

matsp, your a clever man.

Thanks

Is it bad to have a derived class holding and instance of an other derived class from the same base? I had an argument with a friend about it.

Here is what I am doing

Code:

---

class Base
{
    public:
        Base();
        virtual void foo();
}

class DerivedA : public Base
{
    public:
        DerivedA();
        void foo();
}

class DerivedB : public Base
{
    public:
        DerivedB();
        void foo();

    private:
        DerivedA *a;
}

---

Is that OK?

Quote:

---

Is it bad to have a derived class holding and instance of an other derived class from the same base?

---

No.

Quote:

---

I had an argument with a friend about it.

---

What was the argument about?

I see no problem with that in itself.

--
Mats

Quote:

---

Originally Posted by laserlight

No.


What was the argument about?

---

He said it was bad design while I said it was ok. Going to force him to buy me a beer now.

Thanks