In C++, can I prevent derived class being instantiated by classes other than friends

Question

In C++, if I have a abstract base class, is it possible to prevent its derived classes being instantiated by classes other than friends that the base class knows?

Answer 1

You can define constructors as private, just like any other function. For example:

class foo
{

friend foo *FooConstructor(void);

public:
  void Method();
  void Method2();

private:
  foo();
  foo(const &foo);
};

foo *FooConstructor(void) 
{ 
  return new foo(); 
}

This prevents a foo being created in any way, save with the FooContructor function.