Error: Class computer comp is already defined in computer.obj

Question

I am currently playing with C++, and attempting to rebuild a Tic Tac Toe batch console game I made in C++, but have hit a wall, where I cannot figure out how to get rid of the error TicTacToe.obj : error LNK2005: "class computer comp" (?comp@@3Vcomputer@@A) already defined in computer.obj. I have tried removing the declaration of the function computer from the header, and the definition of the function in the C++, but that didn't fix the error. The only way I figured out how to remove this error was to remove the object name, which I kind of don't want to do. I used the example given on the website http://www.cplusplus.com/doc/tutorial/classes/ to set up the class computer. Any information you can provide on any errors that I currently have, or any functions I may not need are most definately welcome, as I am wanting to know much much more about C++.

CODE:

TicTacToe.cpp

// TicTacToe.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <Windows.h>
#include "computer.h"
#include <iostream>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
    comp.Select();
    Sleep(1000);
}

computer.cpp

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

computer::computer()
{
}

computer::~computer()
{
}

void computer::Select()
{
}

computer.h

#pragma once
class computer
{
public:
    computer();
    ~computer();
    void Select(void);
} comp;

EXTRA INFO:

I am using Microsoft Visual Studio Professional 2013 on a laptop running Windows 7.

Answer 1

As you included header "computer.h" in both modules computer.cpp and TicTacToe.cpp then the both modules contain the same definition of object comp

pragma once
class computer
{
public:
    computer();
    ~computer();
    void Select(void);
} comp;

So the linker issues the error.

Define the object only in one cpp module. The header should contain only the class definition.

For example

computer.h

#pragma once
class computer
{
public:
    computer();
    ~computer();
    void Select(void);
};

TicTacToe.cpp

// TicTacToe.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <Windows.h>
#include "computer.h"
#include <iostream>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
    computer comp;

    comp.Select();
    Sleep(1000);
}