Error compiling source file and header file together in C++

Question

This is not actual code i am working on but sample code i had written to understand what i am doing wrong. So i have three files main.cpp, favourite.cpp and favourite.h. I am trying to compile main.cpp but get some weird error.

// main.cpp File

#include <iostream>
#include "favourite.h"

using namespace std;

int main()
{
    favNum(12);

}

// favourite.cpp File

#include "favourite.h"
#include <iostream>

using namespace std;

void favNum(int num)
{
    cout << "My Favourate number is " << num << endl;
}

// favourite.h File

#ifndef FAVOURITE_H
#define FAVOURITE_H

void favNum(int num);

#endif

This all files are in same folder and i am compiling it normally like g++ main.cpp I am not sure if i need to compile it diffrently as i am using custom header files.

Answer 1

If you say g++ main.cpp and this is your whole command line, the error is a linker error that it can't find favNum, right? In that case, try:

g++ main.cpp favourite.cpp

or split compilation and linking:

g++ -c main.cpp -o main.o
g++ -c favourite.cpp -o favourite.o
g++ main.o favourite.o

Where -c means: Compile only, no linking and -ofilename is required because you want to write the output to two different object files to link them with the last command.

You might also add additional flag, the most important ones are:

-Wall -Wextra -O3