c++ - PostActive visibility of class methods -

i have here abstract base class called base_class defined follows:

class base_class {   public:     virtual ~base_class() = 0 {}     virtual size_t area() const = 0;    protected:     base_class() {} }; 

one derived class it:

template <typename t> class : public base_class {   public:     a();     ~a();      size_t area() const;     void display();      (...) etc code }; 

and class still derived it:

template <typename t> class b : public base_class    {      public:        b();        ~b();         size_t area() const;        void set();         (...) etc code    }; 

than have instantiation , function call:

base_class *p = new a<int>; p->display();  delete p; p = new b<float>; p->set();  (...) code 

as might have observed, pointer p won't "see" display , set methods.

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the question is: when using pointers of type base_class, there chance of letting derived object call derived methods defined in class points to? being able access display , set methods without having make them virtual in base class.

otherwise have make 2 virtual functions in base_class, display , set, , that's inconvenient, because a doesn't have inherit set method, , b display method.

you can use dynamic_cast downcast base class derived class, if not determine runtime type of object.

base_class *p = new a<int>; if (a<int> *pa = dynamic_cast<a<int> *>(p))     pa->display();  delete p; p = new b<float>; if (b<float> *pb = dynamic_cast<b<float> *>(p))     pb->set(); 

if type of object confirmed @ compile time, static_cast can cast too, beware: telling compiler know fact being pointed of type. if wrong, cast cannot inform of problem (as dynamic_cast, return null pointer if cast failed, or throw std::bad_cast reference cast failure) and, @ best, spurious run-time errors and/or program crashes.

anyway, best practice should rearrange inheritance relationship, try use virtual function, avoid downcasts.