是否继承了朋友功能?为什么基类FRIEND函数在派生类对象上起作用? [英] Are friend functions inherited? and why would a base class FRIEND function work on a derived class object?

问题描述

class baseClass {
public:
  friend int friendFuncReturn(baseClass &obj) { return obj.baseInt; }
  baseClass(int x) : baseInt(x) {}
private:
  int baseInt;
};

class derivedClass : public baseClass {
public:
  derivedClass(int x, int y) : baseClass(x), derivedInt(y) {}
private:
  int derivedInt;
};

在功能friend int friendFuncReturn(baseClass &obj) { return obj.baseInt; }中的

我不明白为什么基类的友函数对派生类起作用? 不应传递派生类obj.而不是基类obj.被视为错误? 我的问题是，当我将派生类对象传递给它时，为什么它起作用?

in the function friend int friendFuncReturn(baseClass &obj) { return obj.baseInt; } I don't understand why would the friend function of the base class work for the derived class? should not passing derived class obj. instead of a base class obj. tconsidered as error? my question is why it works when i pass a derived class object to it?

推荐答案

朋友功能是否继承?

Are friend functions inherited?

不，不继承好友功能.

基类函数为什么要在派生类对象上工作?

Why would a base class function work on a derived class object?

因为朋友功能仅使用base class中可用的数据成员.不是derived class的数据成员.由于derived class是base class的一种类型，因此，朋友功能可以正常工作.但是请注意，这里的derived class实例是sliced，并且仅可用于base class的信息. 如果您尝试访问derived class的受限成员，则friend function将报告错误.例如

Because friend function is using the data members available in base class only. Not the data members of derived class. Since derived class is a type of base class So, friend function is working fine. But note that here derived class instance is sliced and having information available only for base class. friend function will report an error if you will try to access restricted members of derived class. e.g.

 int friendFuncReturn(baseClass &obj) { return ((derivedClass)obj).derivedInt; }

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