Why am I getting the \'Error LNK2005: Multiple Definitions\' error in my Win32 console application?

Error LNK2005: Multiple Definitions

In a Win32 console application, you have two source files, A.cpp and B.cpp, each containing the following code:

<code class="cpp">#include "stdafx.h"
int k;</code>

Upon compilation, an error is encountered:

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

Explanation:

This error stems from violating the one definition rule. In C , every global variable or function can only have a single definition across all translation units (source files). In your case, both A.cpp and B.cpp define the variable k, leading to multiple definitions and the linking error.

Solutions:

To resolve this issue, consider the following options:

1. Using Anonymous Namespace:

If you require the variable k to be used within both A.cpp and B.cpp but want to avoid external linkage, you can utilize an anonymous namespace:

<code class="cpp">namespace 
{
    int k;
}</code>

2. Using extern:

If you need to share the variable k across multiple files, you should declare it as extern in a header file (A.h) and define it in one source file (e.g., A.cpp):

A.h

<code class="cpp">extern int k;   </code>

A.cpp

<code class="cpp">#include "A.h"
int k = 0;</code>

B.cpp

<code class="cpp">#include "A.h"

// Use `k` within B.cpp</code>

By following these solutions, you can avoid multiple definitions of k and successfully compile your application.

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