Re: Undefined reference to...

However, what you've just shown *is* the closest working
approximation of what he seems to be trying to do. Unless he
actually wants more than one instance---it's not really clear.
For more than one instance, he'd need a factory function, e.g.

     class Base
     {
     public:
         virtual void printOut() = 0;
         static std::auto_ptr<Base> getLower();
     };

     class Extended: public Base
     {
     public:
         void printOut() { cout<< "hello"; }
     };

     std::auto_ptr<Base> Base::getLower()
     {
         return std::auto_ptr<Base>( new Extended );
     }