Duplicate interface definition for class 'NSValue'

Question

I'm getting a very strange error trying to compile my project, I get an error in NSValue.h saying 'Duplicate interface definition for class 'NSValue' (and NSNumber).

I've tried cleaning and rebuilding, I've tried clearing the module cache using:

rm -rf /Users/me/Library/Developer/Xcode/DerivedData/ModuleCache/*

I've tried removing and re-adding the Foundation framework in combination with the above, but I still get the error.

What's going on?

Probably you imported something twice or you have headers cycle. Use #import instead of #include to avoid such problems and in header files do forward declaraction with @class instead of importing other headers. — Grzegorz Krukowski, Jan 20 '14 at 10:54
Have you read this [answer](http://stackoverflow.com/a/5180324/1673400)? — Dmitry Zhukov, Jan 20 '14 at 10:54
@GrzegorzKrukowski The `#import` statement (unlike the `#include` statement) guards against such errors. — trojanfoe, Jan 20 '14 at 10:55
@trojanfoe for multiple imports yes, but for header cycles the solution is to do "@class" forward declaration instead of #import. — Grzegorz Krukowski, Jan 20 '14 at 10:56
@GrzegorzKrukowski You edited your comment multiple times and I didn't keep-up. — trojanfoe, Jan 20 '14 at 10:57

score 2 · Answer 1 · answered Jan 20 '14 at 10:56

2

Okay I spotted what was causing the error: in one of my files I had

#import <foundation/Foundation.h>

instead of

#import <Foundation/Foundation.h>

(with a capital F). Fixing this solved the problem.

answered Jan 20 '14 at 10:56

fredley

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Duplicate interface definition for class 'NSValue'

1 Answers1