Declaring extern NSString causes linker error

Question

This is ridiculous, im trying to create a sound bool to turn of in app sounds. I keep getting

Undefined symbols for architecture i386:
\"_kPlaySoundPrefsKey\",         


        

Answer 1

First, ensure it is defined:

// AppDelegate.h
extern NSString* const kPlaySoundPrefsKey; // << declaration

// AppDelegate.m
NSString * const kPlaySoundPrefsKey = @"kPlaySoundPrefsKey";  // << definition

see also:

"extern const" vs "extern" only

3 questions about extern used in an Objective-C project

Linker error using extern "C" in Objective-C code

Answer 2

Thanks for your help guys

I added

NSString *kPlaySoundPrefsKey = @"playSoundKey";

[[NSUserDefaults standardUserDefaults] registerDefaults:defaultDict];

to app delegate. That fixed it

Answer 3

I am also got the same error even if I am properly declared and define the extern const string , The problem is, my constant file not in the compile source list .

Make sure that your .m file appears in the "Compile Sources" Build Phase for your build target. Sometimes, adding files to a project in Xcode doesn't add all implementation files to the appropriate targets.

Hope this will helpful for some people. Refe: linker-error-undefined-symbols-symbols-not-found

Answer 4

When you declaring something as extern you are telling the compiler the type AND that you will define it somewhere else. In your case you never define your variable.

So in your .h you would have:

extern NSString* kPlaySoundPrefsKey;

But in some .m you must also have

NSString* kPlaySoundPrefsKey = @"play_sounds"; // or some value

Since in your case these are constants you can also specify:

extern NSString* const kPlaySoundPrefsKey;

and

NSString* const kPlaySoundPrefsKey = @"play_sounds"; 

The addition of the const qualifier will cause a compiler error if someone ever writes something like

kPlaySoundPrefsKey = @"some_other_value";