Question

I have 2 files, A.cpp and B.cpp, in a Win32 console application.

Both 2 files contain only the following 2 lines of code:

#include "stdafx.h"
int k;

When compiling it produces the error

Error   1   error LNK2005: "int k" (?a@@3HA) already defined in A.obj

I don’t understand what is happening.

Can someone please explain this to me?

Answer 1

Why this error?

You broke the one definition rule and hence the linking error.

Suggested Solutions:

---

If you need the same named variable in the two cpp files then You need to use Nameless namespace(Anonymous Namespace) to avoid the error.

namespace 
{
    int k;
}

---

If you need to share the same variable across multiple files then you need to use extern.

A.h

extern int k;

A.cpp

#include "A.h"
int k = 0;

B.cpp

#include "A.h"

//Use `k` anywhere in the file