error LNK2005, already defined?

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; } 

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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  

Answer 2

In the Project’s Settings, add /FORCE:MULTIPLE to the Linker’s Command Line options.

From MSDN: "Use /FORCE:MULTIPLE to create an output file whether or not LINK finds more than one definition for a symbol."