Observer

#include <iostream>
#include <list>

using namespace std;

#define DESTROY_POINTER(ptr) if (ptr) { delete ptr; ptr = NULL; }



class Observer
{
public:
    virtual void Update(string sSubjectAttr)=0;
};


class ConcreteObserverA : public Observer
{
public:
    ConcreteObserverA() {}
    ~ConcreteObserverA() {}

    void Update(string sSubjectAttr) { cout<<"ConcreteObserverA::Udate accoring to ["<<sSubjectAttr<<"]"<<endl; }
};

class ConcreteObserverB : public Observer
{
public:
    ConcreteObserverB() {}
    ~ConcreteObserverB() {}

    void Update(string sSubjectAttr) { cout<<"ConcreteObserverB::Udate accoring to ["<<sSubjectAttr<<"]"<<endl; }
};

class ConcreteObserverC : public Observer
{
public:
    ConcreteObserverC() {}
    ~ConcreteObserverC() {}

    void Update(string sSubjectAttr) { cout<<"ConcreteObserverC::Udate accoring to ["<<sSubjectAttr<<"]"<<endl; }
};



class Subject
{
public:
    Subject() {}
    ~Subject();
    
    void AddObserver(Observer* pObserver) { m_observerList.push_back(pObserver); }
    void SetAttr(string sAttr);
    
private:
    list<Observer*> m_observerList;
};

Subject::~Subject()
{
    list<Observer*>::iterator iter;

    for (iter = m_observerList.begin(); iter != m_observerList.end(); iter++)
    {
        Observer* pTemp = *iter;
        DESTROY_POINTER(pTemp);
    }

    m_observerList.clear();
}

void Subject::SetAttr(string sAttr)
{
    list<Observer*>::iterator iter;

    for (iter = m_observerList.begin(); iter != m_observerList.end(); iter++)
    {
        (*iter)->Update(sAttr);
    }
}



int main(int argc, char *argv[])
{
    Subject subject;

    subject.AddObserver(new ConcreteObserverA);
    subject.AddObserver(new ConcreteObserverB);
    subject.AddObserver(new ConcreteObserverC);
    
    subject.SetAttr("Attr add");
    subject.SetAttr("Attr remove");

    return 0;
}