Question

我有一个基类如下：

// base class- arrayListType.h

class arrayListType
{
public:
//some function members;

protected:
elemType *list;
int length;
int maxSize;
};

然后是派生类：

// derived class-polynomialType.h

#include "arrayListType.h"

class polynomialType: public arrayListType<double>
{
friend ostream& operator<<(ostream& ,const polynomialType&);
friend istream& operator>>(istream& ,polynomialType&);

public:
polynomialType operator+(const polynomialType&);
polynomialType operator-(const polynomialType&);
//polynomialType operator*(const polynomialType&);
double operator() (double x);
polynomialType(int size = 100);
int min(int x,int y) const;
int max(int x,int y) const;
};

但是在编译代码之后，我得到了错误;

error C2248: 'arrayListType<elemType>::length' : cannot access protected member declared in class 'arrayListType<elemType>'

我搜索了解决方案，但找不到，请帮忙。运营商的定义＆gt;＆gt;给予参考;

istream& operator>>(istream is,polynomialType& p)
{
cout << "the degree of this polynomial is" << p.length-1 << endl;

for (int i = 0; i < p.length; i++)
{
    cout << "enter coefficient of x^" << i <<": ";
    is >> p.list[i];
}
return is;
}

错误仅显示朋友功能，为什么会这样？

Answer 1

friend istream& operator>>(istream& ,polynomialType&);

节

istream& operator>>(istream is,polynomialType& p)

您的流功能忘记了引用运算符&，因此具有不同的函数签名。不仅如此，它还可能导致细微的错误，例如复制流对象（可能有也可能没有其他副作用），而不是重复使用它。

无法从派生类中的友元函数访问类中声明的受保护成员

1 个答案: