c++ - 构造错误 : ‘data’ was not declared in this scope

Question

我不知道为什么子类不能使用父类的变量。我曾经使用 java 但它不会出现在 Java 中。我是一个c++初学者；

---

父类

#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;
    }
}

---

子类

#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;
    }
}

---

错误:

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

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

它也发生在儿子函数中的变量'length'上。

Answer 1

复制自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.