Observer Pattern implemented in C++.

.gitignore

observer

observer.cpp

#include <iostream>
#include <string>
#include <list>

using namespace std;

class Subject;

class Observer {
public:
  virtual void update(Subject&) = 0;
};

class Subject {
  typedef std::list<Observer*>::iterator iterator;
private:
  list<Observer*> observers;
  string name;
public:
  void add_observer(Observer&);
  void notify();
  void set_name(string);
  string get_name();
};

void Subject::add_observer(Observer& _observer) {
  observers.push_back(&_observer);
}

void Subject::notify() {
  for (iterator it = observers.begin(); it != observers.end(); it++) {
    (*it)->update(*this);
  }
}

void Subject::set_name(string s) {
  name = s;
  notify();
}

string Subject::get_name() {
  return name;
}

class NameObserver : public Observer {
public:
  void update(Subject &s) {
    cout << "Subject's name is changed as '" << s.get_name() << "'." << endl;
  }
};

class CountObserver : public Observer {
private:
  int count;
public:
  CountObserver() {
    count = 0;
  }
  void update(Subject &s) {
    count++;
    cout << count << " times updated." << endl;
  }
};

int main()
{
  Subject subject;
  subject.add_observer(*new NameObserver);
  subject.add_observer(*new CountObserver);
  subject.set_name("Yuya");
  subject.set_name("John");
}

Very good example. Thanks!