Class template inheritance C++

Question

I'd like to inherit from the template class and change the behavior when the operators "()" are called - I want to call another function. This code

template<typename T> class InsertItem {  protected:  int counter;  T   destination;    public:   virtual void operator()(std::string item) {      destination->Insert(item.c_str(), counter++);   }   public:   InsertItem(T argDestination) {           counter= 0;     destination = argDestination;   } };  template<typename T> class InsertItem2 : InsertItem { public:  virtual void operator()(std::string item) {   destination ->Insert2(item.c_str(), counter++, 0);  } }; 

gives me this error:

Error 1 error C2955: 'InsertItem' : use of class template requires template argument list... 

I'd like to ask you how to do this properly, or if there is another way to do this. Thanks.

Answer 1

When inheriting you must show how to instantiate the parent template, if same template class T can be used do this:

template<typename T> class InsertItem { protected:     int counter;     T   destination;   public:     virtual void operator()(std::string item) {         destination->Insert(item.c_str(), counter++);     }  public:     InsertItem(T argDestination) {         counter= 0;         destination = argDestination;     } };  template<typename T> class InsertItem2 : InsertItem<T> { public:     virtual void operator()(std::string item) {         destination ->Insert2(item.c_str(), counter++, 0);     } }; 

If something else is needed just change the line:

class InsertItem2 : InsertItem<needed template type here>