Thread: Multiple definition error

Hi everyone!

I have a .h file in which I declare a global variable.
Many .cpp files include my .h, and this generates an error in my linker.

////// my.h /////
int variable;
////// 1.cpp //////
#include ¨my.h¨
////// 2.cpp //////
#include ¨my.h¨

How can I solve this problem? Thanks any help!

Only declarations should be in headers, but you can avoid multiple definition errors by enclosing the header in inclusion guards:

Code:

#ifndef MY_H
#define MY_H

int variable;

#endif

but even then the linker will complain if the include is used in more than one module.

You may however declare the global in a cpp file and use the extern keyword in the .h file. For instance:

// in the cpp module
int variable;


//in the .h file
extern int variable;

This will give every module that includes the .h file the ability to use it.

Prelude: sorry for not have told, but I already tryied to do this.
FillYourBrain: it worked, I tryied to do this too, but in every .cpp I put extern, now, with the definition in my main .cpp file and just extern in .h worked.

Thanks to both of you!!!!

This also works

Code:

// main.cpp
#define NEED_VARS
#include "local.h"

// local.h
#ifdef NEED_VARS
     int var;
     float other var;
#else
     extern int var;
     extern float var;
#endif

This is a bit strange dbgt goten, never saw nothing like this.

I don't suggest you do it that way.

>Prelude: sorry for not have told, but I already tryied to do this.
That's okay, it was a bogus answer written by a sleepy programmer.