C++ Template interface (list implementation) - c++

Question

I am trying to implement a list data structure in C++.
I want to define a list interface which would be later inherited by implementation such as ArrayList or LinkedList.
I'd like to be able to use it like
List<int>* testList = new LinkedList<int>;
So i've tried to implement full virtual templated class but then realized i cannot mix virtual and templated methods. I tried much different ways and im encountering problems all the way.
Whats the best way to do it ?
Edit (problematic code). I'm trying to make interface to look like this:
template<typename T>
class List {
public:
virtual void add(T*) {};
virtual void remove(unsigned int) = 0;
virtual unsigned int size() = 0;
virtual void get(unsigned int) = 0;
virtual ~List();
};
and then im trying to implement it here:
template<typename T>
class LinkedList : public List<T> {
/* some stuff */
public:
LinkedList();
virtual unsigned int size();
virtual void add(T*); // the problem i guess
virtual void remove(unsigned int);
virtual void get(unsigned int);
virtual ~LinkedList();
};

Answer 1

So i've tried to implement full virtual templated class but then
realized i cannot mix virtual and templated methods.
Your example code indicates, that you don't want virtual, templated methods, but a template class that has virtual methods. The former is not allowed, the latter IS (this is a common point of confusion).
So this is perfectly valid code:
#include <iostream>
#include <memory>
template<class T>
class List{
public:
virtual void push()=0;
virtual void pop()=0;
virtual ~List()=default;
};
template<class T>
class LinkedList: public List<T>{
public:
virtual void push() {
std::cout << "Pushed element to Linked List"<< std::endl;
}
virtual void pop() {
std::cout << "Poped element from Linked List"<< std::endl;
}
};
template<class T>
class ArrayList: public List<T>{
public:
virtual void push() {
std::cout << "Pushed element to ArrayList"<< std::endl;
}
virtual void pop() {
std::cout << "Poped element from ArrayList"<< std::endl;
}
};
int main()
{
List<int>* list1=new LinkedList<int>();
List<int>* list2=new ArrayList<int>();
// And this is how you would actually create objects on the heap nower days:
std::unique_ptr<List<int>> list3=std::make_unique<LinkedList<int>>();
list1->push();
list2->push();
list3->push();
list1->pop();
list2->pop();
list3->pop();
delete(list1);
delete(list2);
//no delete(list3) needed
return 0;
}
Besides that, I don't know, why you want to do that. C++ has a perfectly fine implementation of a linked list and an implementation of and array/vector and thanks to iterator based semantic, you can run (almost) any algorithm on them without the need for a common base class.
I apologize, if this sounds harsh, but it looks like you are comming from Java and trying to learn C++. But instead of learning C++, you try to write wrappers, that make C++ look like java. While this is certainly possible most of the time (as long as you don't forget, that standard c++ doesn't have a garbage collector) its often not a sensible approach. whether that holds true in your case of course depends on your application. But my recommendation ist to learn about iterators and the standard library algorithms.