Duplicate symbol error in objective-c

Question

I need some globals in my Objective-C application. For that purpose, I've created class Globals (that inherits NSObject) and put readonly properties in it. I've also declared some constants, like this:

imports, etc.
.
.
.
#ifndef GLOBALS_H
#define GLOBALS_H

const int DIFFICULTY_CUSTOM = -1;
const int other_constants ...
#endif
.
.
.
interface, etc.

But when I try to compile it, I get linker error: "Duplicate symbol DIFFICULTY_CUSTOM". Why is that happening, should ifndef prefent it?

possible duplicate of [Where do you declare constant in objective c?](http://stackoverflow.com/questions/6188672/where-do-you-declare-constant-in-objective-c) — mmmmmm, Jul 12 '12 at 14:04

score 3 · Accepted Answer · answered Jul 12 '12 at 14:02

The issue is that const int DIFFICULTY_CUSTOM = -1; allocates a int of that name is in every object file you include the header for.
You should only have the declaration extern const int DIFFICULTY_CUSTOM; in each header. The actual value should then be defined const int DIFFICULTY_CUSTOM = -1; in one object file ( ie .m or .c ).

In this case I would just use #define to set the value.

score 1 · Answer 2 · answered Jul 12 '12 at 14:05

1

Here's how I'd do it:

In constants.m:

const int DIFFICULTY_CUSTOM = -1;

In constants.h:

extern const int DIFFICULTY_CUSTOM;

and in the .pch file:

#import "constants.h"

answered Jul 12 '12 at 14:05

Ashley Mills

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Duplicate symbol error in objective-c

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