In constructo error: ‘data’ was not declared in this scope

Question

I don't know that why the son class can't use the variable from the parent class. I used to use java but it does not occur in Java. I am a c++ beginner;

the parent class

#include <iostream>

template<class T>
class List{
protected:
    int length;
    T *data;
public:
    List() {
        length = 0;
        data = nullptr;
        std::cout << "父类构造函数..." << std::endl;
    }

    virtual ~List() {
        length = 0;
        data = nullptr;
        std::cout << "父类析构函数..." << std::endl;
    }
}

the son class

#include "List.h"

template<class T>
class ArrayList : public List<T> {
private:
    const int INIT_SIZE = 10;
    const int INCREMENT_SIZE = 10;

    int maxSize;


public:
    ArrayList() {
        std::cout << "子类构造函数..." << std::endl;
        data = new T[INIT_SIZE];
        maxSize = INIT_SIZE;
    }

    virtual ~ArrayList() {
        std::cout << "子类析构函数..." << std::endl;
        maxSize = 0;
    }
}

error:

In constructor ‘ArrayList<T>::ArrayList()’:

error: ‘data’ was not declared in this scope
         data = new T[INIT_SIZE];
         ^~~~

It also occurred on the variable 'length' which in the son's functions.

See [Derived template-class access to base-class member-data](https://stackoverflow.com/a/24368629/3309790) for more. — songyuanyao, Aug 05 '18 at 03:55
thanks! Because I must write data struct in C/C++ but I used to use Java and I am a c++ beginner. I'll go to have a see. — 何佳成, Aug 05 '18 at 04:05

score 1 · Answer 1 · edited Jun 20 '20 at 09:12

Copied from C++ Super FAQ

Change the call from f() to this->f(). Since this is always implicitly dependent in a template, this->f is dependent and the lookup is therefore deferred until the template is actually instantiated, at which point all base classes are considered.

Insert using B<T>::f; just prior to calling f().

Change the call from f() to B<T>::f(). Note however that this might not give you what you want if f() is virtual, since it inhibits the virtual dispatch mechanism.

score 0 · Accepted Answer · answered Aug 05 '18 at 03:53

0

Use this->data . This should fix your problems.

answered Aug 05 '18 at 03:53

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In constructo error: ‘data’ was not declared in this scope

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