CODEWITHSUNDEEP
c++
DirichletIsaPartyPooper
DirichletIsaPartyPooper

Reputation: 273

Problem with inheritance from abstract class which is also template (c++)

I defined the following abstract List class:

#ifndef LIST_H
#define LIST_H

template <class T>
class List
{
    public:
        List();

        virtual bool isEmpty() const=0;
        virtual void Set(int index, T value)=0;
        virtual int getSize() const=0;
        virtual void add(T value)=0;
        virtual T Remove(int index)=0;
        virtual ~List();
        
    protected:

        int m_size;

    private:
};
#endif // LIST_H

And then I defined a succesor DynamicArray:

#ifndef DYNAMICARRAY_H
#define DYNAMICARRAY_H
#include <iostream>
#include "List.h"
#define CAPACITY 15


template<class T>
class DynamicArray : public List<T>
{
    public:
    //|========================Constructors============================

        DynamicArray(): m_size(0), m_capacity(CAPACITY) {                   //|Default constructor
            m_data = new T[CAPACITY];
        }
 protected:


    private:

        //|========================Private Fields=========================
        int m_capacity;
        T* m_data;
        
};

(This is not the full class definition, of course I implemented a destructor and more methods but it does not concern my problem).

For some reason I get the following error:

 'm_size' was not declared in this scope|

But m_size is defined in the base abstract class "List" and DyanamicArray inherits from List. So what went wrong here?

Thanks in advance.

Upvotes: 0

Views: 114

Answers (1)

Christoph
Christoph

Reputation: 461

Add a constructor List(int) to the base class which initializes the m_size field.

template <class T>
class List
{
    public:
        List();
        List(int _size): m_size(_size) {};
    // .... 
    protected:
        int m_size;
};

Add this constructor to the initializers of DynamicArray:

template<class T>
class DynamicArray : public List<T>
{
public:
    DynamicArray(): List<T>(CAPACITY), m_capacity(CAPACITY) {                   
        m_data = new T[CAPACITY];
    }
private:
    int m_capacity;
    T* m_data;
};

Base initializers can set const fields. What DynamicArray(): m_size(0) is trying to do is:

  1. initialize DynamicArray
  2. initiatlize List with default constructor
  3. set m_size

Step 3 is not allowed (what if m_size is const?).

In terms of Software Architecture, classes should be responsible for initializing their own fields. Otherwise making changes to the internals of a base class will break child classes.

Upvotes: 2

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