Add example for classic singleton

cpp/patterns/singleton/singleton-pointer.hpp

@@ -0,0 +1,29 @@
+
+#ifndef SINGLETON_POINTER_HPP
+#define SINGLETON_POINTER_HPP
+
+#include <iostream>
+#include <string>
+
+class ClassicSingleton{
+public:
+  // returns pointer to single getInstance
+  static ClassicSingleton* getInstance();
+
+  // example functions manipulating singleton object
+  inline void showMessage() const { std::cout << message;}
+  void updateMessage(const std::string &m) { message=m;}
+
+private:
+  // Do not allow construction of this object; Use getInstance() instead
+  ClassicSingleton(){ message = "New ClassicSingleton\n";}
+  // Do not allow copying of this object
+  ClassicSingleton(const ClassicSingleton&){}
+  ClassicSingleton& operator=(const ClassicSingleton&){}
+
+  // Static pointer to instance of this singleton
+  static ClassicSingleton* instance;
+  std::string message;
+};
+
+#endif // SINGLETON_POINTER_HPP