c++ - 运算符重载 Unresolved external 错误 LNK1120、LNK2019

Question

我一直在尝试让一类复数工作并且最近才成功地让我的 2 个 friend 函数定义编译没有错误现在我试图通过在(这是我的 main.cpp 文件)ExtraCredit.cpp 文件中创建 3 个复杂的类对象来测试重载的运算符

    complex x(3.2);
    complex y(3.4, 4.1);
    complex z;

    z = x + y;

    cout << z;

程序正确运行到 z = x + y 但当我添加时

cout << z;

输出应该是6.2 + 4.1bi

但是我得到了这两个错误

LNK1120 1 unresolved externals 

LNK2019 unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> >&_cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char>>&,class complex)"(??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@Vcomplex@@@Z)referenced n function_main

在我的 ExtraCredit.cpp 文件中有

#include "stdafx.h" // This is VSO
#include <iostream>
#include "complex.h"

using namespace std;

在 complex.h 的顶部

#ifndef COMPLEX_H
#define COMPLEX_H

#include <iostream>

在complex.h的末尾

#endif // COMPLEX_H

在我的 complex.cpp 文件的顶部

#include "stdafx.h"
#include "complex.h"
#include <iostream>

using namespace std;

这是complex.h中<<运算符的重载原型(prototype)

friend std::ostream &operator<<(std::ostream &out, complex c);

这是complex.cpp中的实现/定义

 std::ostream& operator<< (std::ostream& out, complex const& c) {
    return out << c.getReal() << "+" << c.getImag() << "i";
}

Answer 1

你的声明和你的定义不一样:

friend std::ostream &operator<<(std::ostream &out, complex c);
std::ostream& operator<< (std::ostream& out, complex const& c) {
    return out << c.getReal() << "+" << c.getImag() << "i";
}

您需要将您的声明更改为

friend std::ostream &operator<<(std::ostream &out, const complex &c);