Undefined reference constructor while compiling C++ code

Question

I receive the following error when I try to compile three c++ files with g++ main.cpp. If I combine them in one file, it works.

main.cpp:(.text+0x10): undefined reference to `Time::Time()'

Time.cpp

#include <iostream>
#include "Time.h"
using namespace std;

Time::Time()
{
    a=5;
}

Time.h

#ifndef TIME_H
#define TIME_H

class Time {

public:
Time();
private:
int a;
};
#endif

main.cpp

#include <iostream>
#include "Time.h" 
using namespace std;


int main()
{
    Time t;
}

You will need to tell the compiler to compile Time.cpp as well. For example: g++ main.cpp Time.cpp -o main — aschepler
– aschepler, Commented Mar 17, 2017 at 2:24
Possible duplicate of What is an undefined reference/unresolved external symbol error and how do I fix it? — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Mar 17, 2017 at 2:45

phuclv · Accepted Answer · 2019-10-11 04:54:50Z

3

You need to compile all the CPP files because each one is a separate compilation unit

g++ main.cpp Time.cpp -o main

For more information about that read

edited Oct 11, 2019 at 4:54

answered Mar 17, 2017 at 2:24

phuclv

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3 Comments

Dave Over a year ago

is there a shortcut? what about if I have more than 100 files?

phuclv Over a year ago

if you have that many files then you must create a makefile, otherwise you'll end up compiling a file again and again. In MSVC or some other IDEs just create a new solution/project and the IDE will handle the compilation for you

M.M Over a year ago

You could use shell expansion, e.g. g++ *.cpp -o main

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