C++中将运算符重载为全局函数

怼烎@ 2022-04-24 00:36 278阅读 0赞

**注意：**  
1.将运算符重载为全局函数时，形参中至少要有一个为自定义的数据类型，即不能全为基本数据类型；  
2.注意运用friend关键字可将非成员函数定义为某个类的友元，此时，该函数便可访问该类的私有成员变量了。

/*---------------------------------------
    功能：将运算符重载为全局函数(非成员函数)
    运行结果：
    c1 = (2, 3)
    c2 = (4, 5)
    c3 = (6, 8)
    c3 = (-2, -2)
    ----------------------------------------
    Author: Zhang Kaizhou
    Date: 2019-4-10 08:43:30
    ---------------------------------------*/
    #include <iostream>
    
    using namespace std;
    
    class Complex{ // 定义一个复数类
    private:
        double real, imag;
    public:
        Complex(double r = 0.0, double i = 0.0):real(r), imag(i){} // 构造函数
        /*将以下三个运算符重载函数定义为Complex类的友元函数，此时他们就可以访问Complex类的私有成员变量*/
        friend Complex operator +(const Complex & c1, const Complex & c2);
        friend Complex operator -(const Complex & c1, const Complex & c2);
        friend ostream & operator <<(ostream & out, const Complex & c);
    };
    
    /*将三个运算符函数以全局函数的方式实现*/
    Complex operator +(const Complex & c1, const Complex & c2){
        return Complex(c1.real + c2.real, c1.imag + c2.imag);
    }
    
    Complex operator -(const Complex & c1, const Complex & c2){
        return Complex(c1.real - c2.real, c1.imag - c2.imag);
    }
    
    ostream & operator <<(ostream & out, const Complex & c){
        out << "(" << c.real << ", " << c.imag << ")";
        return out;
    }
    
    int main(){
        Complex c1(2, 3), c2(4, 5), c3;
        cout << "c1 = " << c1 << endl;
        cout << "c2 = " << c2 << endl;
        c3 = c1 + c2;
        cout << "c3 = " << c3 << endl;
        c3 = c1 - c2;
        cout << "c3 = " << c3 << endl;
    
        return 0;
    }