What impact do friend functions have on class inheritance?
Apr 17, 2024 am 08:33 AMInheritance of friend functions When a subclass inherits a class with friend functions: The subclass cannot inherit the friend function. Friend functions of the parent class can access private members of the child class. Friend functions of a subclass cannot access private members of the parent class.
The influence of friend functions on class inheritance
Preface
Friends A metafunction is a special C function that can access private members of a class outside the scope of the class. When it comes to class inheritance, understanding the behavior of friend functions is crucial.
Friend Functions and Inheritance
When a subclass inherits a class that has friend functions, the following rules apply:
- Subclasses cannot inherit friend functions: Friend functions are associated with a specific class. Subclasses cannot inherit friend functions of parent classes.
- Friend functions of the parent class can access the private members of the subclass: If the parent class and the subclass know each other (i.e., the parent class is the base class of the subclass or the subclass is the parent derived class), the friend function of the parent class can access the private members of the subclass.
- The friend function of the subclass cannot access the private members of the parent class: On the contrary, the friend function of the subclass cannot access the private members of the parent class, even if the parent Classes and subclasses know each other.
Practical Case
Consider the following example code:#include <iostream> class Base { friend void print(Base& b); // 父類友元函數(shù) private: int x; }; class Derived : public Base { friend void access(Derived& d); // 子類友元函數(shù) private: int y; }; void print(Base& b) { std::cout << b.x << std::endl; } // 父類友元函數(shù)訪問私有成員 x void access(Derived& d) { std::cout << d.x << " " << d.y << std::endl; } // 子類友元函數(shù)訪問私有成員 x 和 y int main() { Base b; b.x = 10; print(b); // 輸出:10 Derived d; d.x = 20; d.y = 30; access(d); // 輸出:20 30 print(d); // 輸出:20 }In this example:
- Parent Class
- Base
has a friend function
print(), which has access to
xprivate members.
Subclass - Derived
has a friend function
access(), which can access the parent class private members
x.
The object - d
of the subclass
Derivedcan be accessed by the parent class
Basefriend function
print(), but cannot Access the private member
xof the parent class.
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