Detailed explanation of C++ friend functions: What is the role of friend functions in multiple inheritance?

Friend functions allow non-member functions to access private members and play a role in multiple inheritance, allowing derived class functions to access private members of the base class.

C Detailed explanation of friend functions: The role of friend functions in multiple inheritance

Introduction to friend functions

A friend function is a special function that is given access to private members without requiring an object of the class. It is often used to allow non-member functions to access private data.

Syntax:

class ClassName {
    ... // 类成员
    friend FunctionName;
};

The role of friend functions in multiple inheritance

In multiple inheritance, a derived class Data members and methods can be inherited from multiple base classes. If a function in a derived class needs to access a private member of the base class, the function can be declared as a friend function.

Practical case

Suppose we have a Base class and a derived classDerived that inherits from Base :

class Base {
private:
    int data;
};

class Derived : public Base {
public:
    void printData() {
        std::cout << data << std::endl;
    }
    friend void printData2(Derived& obj);
};

Since data is a private member of Base, the printData() function in Derived There is no way to access it directly. Therefore, we declare the printData2() function as a friend function of Derived:

void printData2(Derived& obj) {
    std::cout << obj.data << std::endl;
}

Now, printData2() can access ## Private data member in #Derived.

Usage:

int main() {
    Derived obj;
    obj.printData();
    printData2(obj);
}

Output:

0
0

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