Segmentation fault

Hej, jeg ville lige prøve at implementere observer pattern i C++, men noget funker ikke helt. Jeg får en segmentation fault når programmet terminere..

#include <iostream>
#include <list>

using namespace std;

//Forward declaration
class Subject;

class Observer
{
public:
  virtual ~Observer();
  virtual void Update(Subject* aSubject) = 0;
};

Observer::~Observer()
{
  cout << "destructor i observer" << endl;
}

class Subject
{
public:
  virtual ~Subject();
  void Attach(Observer*);
  void Detach(Observer*);
  void Notify();
protected:
  Subject();
private:
  list<Observer*> *iObservers; //Creates a list of observer pointers
};

Subject::~Subject()
{
  cout << "destructor i subject" << endl;
  delete iObservers;
  iObservers = NULL;
}
Subject::Subject()
{
  iObservers = new list<Observer*>;
}
void Subject::Attach(Observer* aObserver)
{
  iObservers->push_back(aObserver);
}
void Subject::Detach(Observer* aObserver)
{
  iObservers->remove(aObserver);
}
void Subject::Notify()
{
  for(list<Observer*>::iterator it = iObservers->begin(); it != iObservers->end(); ++it)
    {
      Observer* obs = *it;
      obs->Update(this);
    }
}
 

class ClockTimer : public Subject
{
public:
  void HelloMoto(){ Notify(); }
};

class TheClock : public Observer
{
public:
  TheClock(ClockTimer* aTimer);
  ~TheClock();
  void Update(Subject* aSubject);

private:
  ClockTimer* iTimer;

};

TheClock::TheClock(ClockTimer* aTimer)
{
  aTimer->Attach(this);
}

TheClock::~TheClock()
{
  iTimer->Detach(this);
}

void TheClock::Update(Subject* aSubject)
{
  cout << "Der fik jeg en update" << endl;
}


int main()
{
  ClockTimer subject;
  TheClock observer(&subject);

  subject.HelloMoto();

  cout << "program terminated" << endl;

  return 0;

}

Giver følgende:

$ Der fik jeg en update
$ program terminated
$ Segmentation fault (core dumped)

Kan I se problemet?