error LNK2005: "int __cdecl number(void)" (?number@@YAHXZ) already defined in functions.obj

Question

I think I am having a similar problem to LNK2005, LNK1169 errors, "int __cdecl g(void)" (?g@@YAHXZ) already defined but I cannot find the issue.

I am working with Visual Basic and I am having the following files

main.cpp

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

int main(){
    number();
    return 0;
}

I had a functions.cpp but after reading the question I linked before I renamed it for functions.h

int number(){
    int i = 1;
    return i;
}

Now it is displaying error LNK2005: "int __cdecl number(void)" (?number@@YAHXZ) already defined in functions.obj

Is there anything wrong with the function number() in functions.h?

Are you, by any chance, including `functions.h` somewhere else as well, in your project? — Mats Petersson, Aug 02 '13 at 16:08

score 5 · Accepted Answer · edited Jun 20 '20 at 09:12

You are having linking issues.

Your immediate issue is that the functions.obj contains code that is being linked in. Then you redefine number() in main.cpp so they collide. Go ahead and clean the project (which should delete functions.obj, and you should be able to compile. I, however, recommend doing it this way.

functions.hpp (or functions.h)

int number();

functions.cpp

int number(){
    int i = 1;
    return i;
}

main.cpp

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

int main(){
    number();
    return 0;
}

When you compile, your program will create 2 objects with compiled code functions.obj, and main.obj. Since you use number in the main file, the compiler looks for the implementation of that function. Since the implementation of that function is in the functions.obj object, then you need to link that in.

If you are going to use number() across several C++ files, then you should always separate the code out into its own file and implementation.

If I try to fix / add the .cpp file in my old project is doesn't work, but if I do a new one it does. Why is that? Is there anything related with what you meant by cleaning? http://stackoverflow.com/a/1475038/2565304 — zurfyx, Aug 02 '13 at 16:20
Well, lots of IDE's provide a "Clean" function of sorts, which deletes any unnecessary files. Go and look for the `functions.obj` file and delete it! — Kirk Backus, Aug 02 '13 at 16:21

score 2 · Answer 2 · answered Aug 02 '13 at 16:09

functions.h should only declare the functio, as in

int number();

then functions.cpp should contain the function definition

int number(){
    int i = 1;
    return i;
}

Of course functions.cpp needs to be compiled (add it to the project).

The problem here is that you are including functions.h in multiple files. The issue could be avoided also by simply declaring the function static as in

static int number(){
    int i = 1;
    return i;
}

However, since it seems you are just learning, I would suggest you to study the basics of compiling c++ code.

score 0 · Answer 3 · answered Aug 02 '13 at 16:11

0

In one of the modules you link in there is a function with the name number(). You define you own implementation so the linker does not know which one to use.

Either rename your function or use namespaces.

answered Aug 02 '13 at 16:11

doron

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error LNK2005: "int __cdecl number(void)" (?number@@YAHXZ) already defined in functions.obj

3 Answers3

You are having linking issues.