Observer Pattern in C++

   #include <iostream>

   // The Observer class, which the subject calls out to with updates:
   class Observer
   {
       public:
           // Constructor:
           Observer()
           : pNext(nullptr)
           {};
           // Helper pointer for a linked-list structure:
           // however feel free to use another structure as you see fit.
           Observer* pNext;

           // The update method for the observer. This is usually called from the Subject class.
           void Update(const char* message)
           {
               std::cout << message << std::endl;
           }

   };

   // The Subject class, responsible for sending out updates to all observing objects:
   class Subject
   {
       public:
           // Constructor:
           Subject()
           : pRoot(nullptr)
           {};

           // We can either delete things here, or let the owners deal with them.
           // Since we do not create observers in this class, 
           // we might not want this class to be responsible for deleting them.
           ~Subject() { };

           // The notify message in this example passes a string along to all of the subscribers.
           // In other use cases, this could be objects, states, controller inputs, and more!
           void Notify(const char* message)
           {
               Observer* pTmp = this->pRoot;
               while (pTmp != nullptr)
               {
                   pTmp->Update(message);

                   pTmp = pTmp->pNext;
               }
               
           }

           // Insert an observer into the list.
           // For example sake, we won't worry about unsubscribing, 
           // which is just a simple linked-list removal for us.
           void AddObserver(Observer& observer)
           {
               // Insert at the front of the list:
               observer.pNext = this->pRoot;
               this->pRoot = &observer;
           }
       
       private:
           // Our Subject data: the root Observer in our list:
           Observer* pRoot;
   };