//Observer.h
#include <Subject.h>
class Observer
{
  public:
    Observer() {}
    virtual ~Observer() {}
  private:
    virtual void notify() {}
    friend class Subject;
}

//Subject.h
#include <Observer.h>
#include <stdlib.h>
class Subject
{
  public:
    Subject();
    virtual ~Subject();

    void registerObserver(Observer& o);
    void unregisterObserver(Observer& o);
  private:
    virtual void notifyAll();
    std::vector<Observer*> m_list;
}

//Class A.h
class A : public Subject
{
  ...
}

//A.cpp
...
void A::notifyAll()
{
  if(m_list.size() <= 0)
    return;

  for(std::vector<Observer*>::iterator I = m_list.begin(); I != m_list.end(); I++)
  {
    ((Observer*) I)->notify();  // C2248
  }
}