C++ LNK2019 未解析的外部符号

Question

我看了很多关于LNK2019的帖子，但是无法解决这个错误。

这是我的代码：

Time.h:

#ifndef PROJECT2_TIME_H
#define PROJECT2_TIME_H

#include<iostream>
using std::ostream;

namespace Project2  
{
class Time
{
    friend Time& operator+=(const Time& lhs, const Time& rhs);
    friend ostream& operator<<(ostream& os, const Time& rhs);
public:
    static const unsigned secondsInOneHour = 3600;
    static const unsigned secondsInOneMinute = 60;
    Time(unsigned hours, unsigned minutes, unsigned seconds);
    unsigned getTotalTimeAsSeconds() const;
private:
    unsigned seconds;
};

Time& operator+=(const Time& lhs, const Time& rhs);
ostream& operator<<(ostream& os, const Time& rhs);

}

#endif

Time.cpp:

#include "Time.h"


Project2::Time::Time(unsigned hours, unsigned minutes, unsigned seconds)   
{
    this->seconds = hours*secondsInOneHour + minutes*secondsInOneMinute + seconds;
}

unsigned
Project2::Time::getTotalTimeAsSeconds() const
{
return this->seconds;
}


Project2::Time&
Project2::operator+=(const Time& lhs, const Time& rhs)
{
Time& tempTime(unsigned hours, unsigned minutes, unsigned seconds);
unsigned lhsHours = lhs.seconds / Time::secondsInOneHour;
unsigned lhsMinutes = (lhs.seconds / 60) % 60;
unsigned lhsSeconds = (lhs.seconds / 60 / 60) % 60;
unsigned rhsHours = rhs.seconds / Time::secondsInOneHour;
unsigned rhsMinutes = (rhs.seconds / 60) % 60;
unsigned rhsSeconds = (rhs.seconds / 60 / 60) % 60;
return tempTime(lhsHours + rhsHours, lhsMinutes + rhsMinutes, lhsSeconds + rhsSeconds);
}

ostream&
Project2::operator<<(ostream& os, const Time& rhs)
{
unsigned rhsHours = rhs.seconds / Time::secondsInOneHour;
unsigned rhsMinutes = (rhs.seconds / 60) % 60;
unsigned rhsSeconds = (rhs.seconds / 60 / 60) % 60;
os << rhsHours << "h:" << rhsMinutes << "m:" << rhsSeconds << "s";
return os;
}

main.cpp只是简单的创建了Time对象，并使用了重载的运算符，好像没有什么问题（提供了这些代码，本身就不错）。

我试图删除所有 "Time" 符号后面的“&”，但我得到了同样的错误。

这是错误消息：

Error 1 error LNK2019: unresolved external symbol "class Project2::Time & __cdecl tempTime(unsigned int,unsigned int,unsigned int)" (?tempTime@@YAAAVTime@Project2@@III@Z) referenced in function "class Project2::Time & __cdecl Project2::operator+=(class Project2::Time const &,class Project2::Time const &)" (??YProject2@@YAAAVTime@0@ABV10@0@Z) c:\Users\Eon-Gwei\documents\visual studio 2013\Projects\c++III_Project2_GW\c++III_Project2_GW\Time.obj c++III_Project2_GW

Answer 1

Time& tempTime(unsigned hours, unsigned minutes, unsigned seconds); 声明一个名为 tempTime 的函数，return tempTime(lhsHours + rhsHours, lhsMinutes + rhsMinutes, lhsSeconds + rhsSeconds); 调用该函数。由于该函数在任何地方都没有实现，因此您会收到链接器错误。

~~因为 operator += 大概是 return 对调用它的对象的引用，你应该通过 this 修改对象的成员变量而不是创建新的 Time 和 return *this.~~ 编辑： operator += 的任何合理实现都会修改左侧操作数，而不是创建新对象。我建议你重新考虑你的运营商应该如何工作。

C++ LNK2019 未解析的外部符号

C++ LNK2019 unresolved external symbol

c++

linker-errors

lnk2019