Thread: .h files: "constant already defined"

Hi, I'm newbie in c++.
I have 2 cpp files, and their 2 .h files. I have another .h file with constant too.
The first cpp file use the second cpp file. And First ands second file are using constants .h file. In two cpp files I have #include "constants.h" line. When I compile I get this error:

Generating Code...
Linking...
Recristalazation_CEIT.obj : error LNK2005: "double QGB" (?QGB@@3NA) already defined in Functions.obj

One line for constant en constants.h

I have searched in google and I have probe this solution. In constants file I have written:

Code:

#ifndef _CONSTANTS_H_
#define _CONSTANTS_H_
// las definiciones
#endif

But I get the same error. How can I solve it?
Thanksss

PD: sorry my engish is very bad, I'm spanish

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