Add example for classic singleton

cpp/patterns/singleton/main.cpp

@@ -1,8 +1,13 @@
 
-#include "singleton.h"
+#include "singleton.hpp"
+#include "singleton-pointer.hpp"
 
 int main(const int argc, const char *argv[])
 {
+
+  /****************************************************************************/
+  // Meyers Singleton - static getInstance
+
   // Creates a singleton, initializes message in ctor
   Singleton &s = Singleton::getInstance();
   s.showMessage();
@@ -12,4 +17,20 @@ int main(const int argc, const char *argv[])
   // Update already existing Singleton message, show it
   Singleton::getInstance().updateMessage("Second update\n");
   s.showMessage();
+
+  /****************************************************************************/
+  // Classic Singleton - pointer getInstance
+
+
+  std::cout << "\n##### ClassicSingleton #####\n\n";
+
+  // Creates a classic singleton, initializes message in ctor
+  ClassicSingleton *classicSingleton = ClassicSingleton::getInstance();
+  classicSingleton->showMessage();
+  // Update already existing ClassicSingleton message, show it
+  classicSingleton->updateMessage("First update\n");
+  ClassicSingleton::getInstance()->showMessage();
+  // Update already existing ClassicSingleton message, show it
+  ClassicSingleton::getInstance()->updateMessage("Second update\n");
+  classicSingleton->showMessage();
 }