Virtual Base Class & Constructor :: C++

Hi.

I would like to know the best way to initialize a constructor in a virtual base base. For example,

Code:

// Base class
class Base()
{
public:
A(int i = 0);
virtual void printA() const = 0;
};

// Derived classes
class X() : public virtual Base
{
public:
X(char a, int j);
virtual void printA();
};

X::X(char a, int j)
{
char temp = a;
A::A(j);
}

class Y() : public virtual Base
{
public:
Y(long x, int k);
virtual void printA();
};

Y::Y(long x, int k)
{
long temp = x;
A::A(k);
}

// Next level down in hierarchy

class Z(); public X, public Y
{
public:
Z(...?...); // What data do I need here to construct X, Y, and Base?
void printA() const;
...
};

Z::Z(...?...)
{
// Do you contruct class X, Y, or Base first?
}

// Implementation

Z example(...?...); // You need to construct Base first.

I know the question is very basic to polymorphic C++ programming. Nonetheless, it is something that want really want to understand.

Thanks,
Kuphryn

Of course it depends on the actual classes you would use, but basically, each class should pass the required parameters to its parent constructor. If you do that, you don't have to worry about your child class's parent's parents.
And when you call it, it should be in your initializer list and not inside the body of the constructor.

Code:

///////////////////////
class Base {
  int _base;
public:
  Base(int base);
  virtual Base() = 0 { }
};

Base::Base(int base) 
: _base(base) {

}
///////////////////////
class X : public Base {
  int _x;
public:
  X(int x);
};

X::X(int x)
: _x(x), Base(x)//initialize here...
{
  //...not in here
}
///////////////////////
class Y : public Base {
  int _y;
public:
  Y(int y);
};

Y::Y(int y)
: _y(y), Base(y) {

}
///////////////////////
class Z : public X, public Y {
  int _z;
public:
  Z(int z);
};

Z::Z(int z)
: _z(z), X(z), Y(z) {//doesn't matter which you call first

}

Hope it helps

Nice! Thanks.

Kuphryn