Add example of observer pattern in C++

cpp/patterns/observer/observer.hpp

@@ -0,0 +1,47 @@
+
+#ifndef OBSERVER_HPP
+#define OBSERVER_HPP
+
+#include <string>
+#include <list>
+#include <iostream>
+
+#include "observer.hpp"
+
+class Observer;
+
+class Subject {
+public:
+  Subject(std::string name_) : name(name_) {}
+  virtual ~Subject() { std::cout << name << " subject destroyed\n";}
+
+  void Attach(Observer * o) { observerList.push_back(o);}
+  void Detach(Observer * o) { observerList.remove(o);}
+  void Notify();
+
+  void SendMessage(std::string message_);
+  inline std::string getName() const { return name;}
+
+private:
+  std::list<Observer *> observerList;
+  std::string message, name;
+};
+
+
+/******************************************************************************/
+// Observer
+
+class Observer {
+public:
+  Observer(Subject &s);
+
+  void Update(std::string &message);
+  void Detach();
+
+private:
+  Subject &subject;
+  int number;
+  static int totalObservers;
+};
+
+#endif // OBSERVER_HPP