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>