Observer Model example for C++

• Observer Model
• The Observer dose not actively to get the data from the Subject else the Subject will
  notify the Observer when there are something changed.
• 觀察者模式定義了物件之間一對多的關係
• 主題(Subject) 更新觀察者的方式 ，是透過一個共用介面。
• 觀察者與可觀察者之間採用鬆綁的方式結合(loose-coupling)，因為可觀察者不知道觀察者的細節，只知道觀察者有實踐特定的觀察者介面。

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <list>

using namespace std;

class CObserver
{
public:
        virtual void update(int data) = 0;
};

class CSubject
{
public:
        virtual void registerObserver(CObserver *obs) = 0;
        virtual void deleteObserver(CObserver *obs) = 0;
        virtual void notify(void) = 0;
};

class CInformationStation : public CSubject
{
private:
        list<CObserver *> m_observerList;
public:
        virtual void registerObserver(CObserver *obs);
        virtual void deleteObserver(CObserver *obs);
        virtual void notify(void);
};

void CInformationStation::registerObserver(CObserver *obs)

{

        list<CObserver *>::iterator it;

        bool found = false;

        for(it = m_observerList.begin(); it != m_observerList.end(); it++) {

                if(*it == obs){

                        found = true;

                        break;

                }

        }

        if(!found)

                m_observerList.push_back(obs);

}

void CInformationStation::deleteObserver(CObserver *obs)

{

        list<CObserver *>::iterator it;

        for(it = m_observerList.begin(); it != m_observerList.end(); it++) {

                if(*it == obs) {

                        m_observerList.erase(it);

                        break;

                }

        }

}

void CInformationStation::notify(void)

{

        list<CObserver *>::iterator it;

        for(it = m_observerList.begin(); it != m_observerList.end(); it++) {

                srand((int)time(0));

                sleep(1);

                (*it)->update( rand() % 1000);

        }

}

class CStatistic : public CObserver

{

private:

        int m_data;

public:

        CStatistic() : m_data(0) {}

        virtual void update(int data)

        {

                m_data = data;

        }

        void display(void)

        {

                printf("[%s] m_data:%d\n", __PRETTY_FUNCTION__, m_data);

        }

};

int main()

{

        CInformationStation station;

        CStatistic statistic1, statistic2, statistic3;

        station.registerObserver(&statistic1);

        station.registerObserver(&statistic2);

        station.registerObserver(&statistic3);

        station.notify();

        statistic1.display();

        statistic2.display();

        statistic3.display();

        return 0;

}