格式

第一操作数是标准类类型ostream的对象的引用，比如：“&out”，第二操作数是本类的对象

  1. ostream &operator<<(ostream &out, const 类类型 &obj );//重载<<

示例

  1. #pragma once
  2. #include<algorithm>
  3. #include<functional>
  4. #include<iostream>
  5. using namespace std;
  6. class Complex {
  7.     private:
  8.     double real;
  9.     double imag;
  10.     public:
  11.     Complex(double real, double imag) :real(real), imag(imag) {}
  12.     Complex() :real(0), imag(0) {}
  13.     Complex(const Complex& c) :real(c.real), imag(c.imag) {}
  14.     Complex& operator=(const Complex& c) {
  15.         real = c.real;
  16.         imag = c.imag;
  17.         return *this;
  18.     }
  19.     Complex operator+(const Complex& c)const {
  20.         return Complex(real + c.real, imag + c.imag);
  21.     }
  22.     Complex operator-(const Complex& c) {
  23.         return Complex(real - c.real, imag - c.imag);
  24.     }
  25.     Complex operator*(const Complex& c) {
  26.         return Complex(real * c.real - imag * c.imag, real * c.imag + imag * c.real);
  27.     }
  28.     Complex operator/(const Complex& c) {
  29.         return Complex((real * c.real + imag * c.imag) / (c.real * c.real + c.imag * c.imag), (imag * c.real - real * c.imag) / (c.real * c.real + c.imag * c.imag));
  30.     }
  31.     double getReal() {
  32.         return real;
  33.     }
  34.     double getImag() {
  35.         return imag;
  36.     }
  37.     friend ostream& operator<<(ostream& os, const Complex& c);
  39. };
  40. ostream& operator<<(ostream& os, const Complex& c) {
  41.     os << c.real << " + " << c.imag << "i";
  42.     return os;
  43. }

调用

因为plus()中的参数是常量对象，因此只能调用常量成员函数，因此重载加法运算符要用const修饰

  1. #include"Complex.h"
  2. Complex operator+(Complex& c1, Complex& c2) {
  3.     return Complex(c1.getReal() + c2.getReal(), c1.getImag() + c2.getImag());
  4. }
  5. void testComplex() {
  6.     Complex c1(1, 2);
  7.     Complex c2(3, 4);
  8.     Complex c3 = c1 + c2;
  9.     cout << c3 << endl;
  10.     plus<Complex> c4;
  11.     cout << c4(c1, c2)<< endl;
  12.     cout << c1 - c2 << endl;
  13. }
  14. int main() {
  15.     testComplex();
  16. }

运行结果

image.png