extern const declarations. How to get them to work?

[JRevor]

My code has several files.
This is a part of Peli.hpp .

/*==============================================================================
                                         CLASS PELI 
================================================================================*/

# ifndef _PELI_H
# define _PELI_H

# include <iostream>
# include <string>
//# include<sstream>

using namespace std ;

// ~~~~~~~~~~~~~~~~
// - Constants
// ~~~~~~~~~~~~~~~~

extern const unsigned TAM_TITULO = 53;
extern const unsigned TAM_DIRECTOR = 26;
extern const unsigned TAM_FECHA = 5;
extern const unsigned TAM_GENERO = 16;
extern const unsigned TAM_TOTAL = 100;
//etc.. etc.. 

Peli.hpp is included on Main.cpp. I don't declare TAM_TITULO, TAM_... anywhere else in the program... so , why do i receive error multiple definition of TAM_TITULO, TAM_DIRECTOR, etc.. ?

[JRevor]

Somehow, removing extern made the code work, but i don't know why.
Theoretically, const definitions are not linked globally, but locally. However, in my code, const worked at a global scope!!. That makes no sense!

[guestgulkan]

You will receive multiple definition errors because:
From the C++ specification:

[Example: all but one of the following are definitions:

int a; // defines a
extern const int c = 1; // defines c 
int f(int x) { return x+a; } // defines f and defines x
struct S { int a; int b; }; // defines S, S::a, and S::b
struct X { // defines X
int x; // defines nonstatic data member x
static int y; // declares static data member y
X(): x(0) { } // defines a constructor of X
};
int X::y = 1; // defines X::y
enum { up, down }; // defines up and down
namespace N { int d; } // definesN and N::d
namespace N1 = N; // defines N1
X anX; // defines anX 

whereas these are just declarations:

extern int a; // declares a
extern const int c; // declares c
int f(int); // declares f
struct S; // declares S
typedef int Int; // declares Int
extern X anotherX; // declares anotherX
using N::d; // declares N::d 

—end example]

[JRevor]

Oh.. i think i got it.
I should have written

extern const unsigned TAM_TITULO;

instead of

extern const unsigned TAM_TITULO = 53;

Thanks