C++.Operator Overloading

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1.友元函数

• friend修饰符

friend修饰符下的全局函数访问类的私有成员变量的权限。旨在增强与相关类的协作，减少代码的重写。

例如声明一个整型的复数类：

class Complex {
    private:
        int real, imag;
    public:
        Complex(int reals, int imags) : real(reals), imag(imags) {}
        ~Complex() {}
        friend Complex addOther(const Complex& obj_1, const Complex& obj_2);
};

Complex addOther(const Complex& obj_1, const Complex& obj_2) {
    return Complex(obj_1.real + obj_2.real, obj_1.imag + obj_2.imag);
}

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2.链式调用

在类的成员函数中利用this指针返回对自身的引用以完成链式调用。

For example:

class Complex {
    private:
        int real, imag;
    public:
        Complex(int reals, int imags) : real(reals), imag(imags) {}
        ~Complex() {}
        Complex& addSelf(const Complex& obj);
        void showCase() {
            cout << real << '+' << imag << 'i' << endl;
        }
};

Complex& Complex::addSelf(const Complex& obj) {
    real += obj.real;
    imag += obj.real;
    return *this;
}

auto main() {
    Complex c_1(1, 1), c_2(2, 2), c_3(3, 3);
    c_1.addSelf(c_2).addSelf(c_3).showCase();
    return 0;
}

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3.运算符重载

C++的运算符重载允许自定义类对象的运算，但是运算符的优先级和结合性不能更改，只能定义它们如何作用于类的对象。且以下运算符不能重载：

• :: (作用域解析运算符)
• . (成员访问运算符)
• * (成员指针访问运算符)
• ? (条件运算符)
• sizeof (大小运算符)
• typeid (类型信息运算符)

考虑设计一个复数类Complex，使用运算符重载实现复数类对象的加法运算：

class Complex {
    private:
        int real, imag;
    public:
        Complex(int reals, int imags) : real(reals), imag(imags) {}
        ~Complex() {}
        friend Complex operator + (const Complex& obj_1, const Complex& obj_2);
        void showCase() {
            cout << real << '+' << imag << 'i' << endl;
        }
        Complex& operator = (const Complex& obj) {
            if(this != &obj){   // 防止自复制
                real = obj.real;
                imag = obj.imag;
            }
            return *this;
        }
        Complex& operator += (const Complex& obj) {
            real += obj.real;
            imag += obj.imag;
            return *this;
        }
};

Complex operator + (const Complex& obj_1, const Complex& obj_2) {
    return Complex(obj_1.real + obj_2.real, obj_1.imag + obj_2.imag);
}

auto main() {
    Complex c_1(1, 1), c_2(2, 2), c_3(3, 3);
    (c_1 += c_2 + c_3).showCase();
}

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