Using a field of an abstract class as a default argument of a method (c++)

I wrote an abstract class called "List", which I basically use as an interface for other implementation methods of lists (such as dynamic array and linked list).

Now, I have a method called "add", with 2 arguments, the first one is the data to add and the second is the position where to add. I want to set the default value of this position to be the end of the list (i.e, its size).

Here’s what I wrote:

#ifndef LIST_H
#define LIST_H

template <class T>
class List
{
    public:
        List(): m_size(0) {}
        virtual bool isEmpty() const=0;
        virtual void set(int index, T value)=0;
        virtual int getSize() const=0;
        virtual void add(T data, int index = m_size )=0;        //The problem is here    
        virtual T remove(int index)=0;
        virtual ~List(){}
        virtual T operator[](int index) const =0;
        virtual bool operator==(const List<T>& other) const =0;

    protected:

        int m_size;

};
#endif // LIST_H

But I get the following error:

error: invalid use of non-static data member 'List<T>::m_size'|

Is there a way to fix this problem?

Also, is it correct to implement the constructor as I did? do I need to call this constructor in the init line of the derived classes constructors or does the compiler does it implicitly?

Thanks in advance.

>Solution :

You cannot use members as default arguments of methods. Instead write an overload (it doesnt need to be virtual when it calls the virtual add(T,int):

void add(T data) {
     add(data,m_size );
}