C++ LNK2019 unresolved external symbol

Question

I have read many posts about LNK2019, but can't resolve this error.

Here is my code:

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;
}

The main.cpp simply creates Time objects and uses the overloaded operators, doesn't seem like there can be problems(these codes are provided so are themselves good).

I have tried to remove the "&" behind all the "Time" symbol, and I got the same error.

And here is the error message:

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); declares a function with the name tempTime, and return tempTime(lhsHours + rhsHours, lhsMinutes + rhsMinutes, lhsSeconds + rhsSeconds); calls that function. Since the function does not have an implementation anywhere, you get a linker error.

Since operator += is presumably supposed to return a reference to the object it is invoked on, you should modify the object's member variables through this rather than creating a new Time, and return *this. Edit: Any sane implementation of operator += would modify the left-hand-side operand, rather than creating a new object. I suggest you reconsider how your operator should work.