Initializing Global Variables in Obj C

Question

I'm trying to initialize global variables, however I'm not sure what I'm doing wrong, as I get an error.

Right now, I have a Globals.h file that I import into my AppDelegate. Here, I declare:

#ifndef Globals_h #define Globals_h #endif /* Globals_h */ extern NSArray *CompetencyOne; extern NSArray *CompetencyTwo; extern NSArray *CompetencyThree; extern NSArray *CompetencyFour; extern NSArray *CompetencyFive; extern NSArray *CompetencySix; extern NSArray *CompetencySeven; extern NSArray *CompetencyEight; extern NSArray *CompetencyNine; extern NSArray *CompetencyTen; extern NSArray *CompetencyEleven; extern NSArray *CompetencyTwelve; extern NSArray *Competencies;

Then, I'm not sure where to define these arrays. I tried in AppDelegate.m in the didFinishWithLaunchingOptions method, and the ViewController's viewDidLoad method, and I created a separate method,

-(void) initializeCompetencies{ <arrays with values>}

in the ViewController, but I keep getting the same error:

Undefined symbols for architecture x86_64: "_Competencies", referenced from: -[QuestionViewController viewDidLoad] in QuestionViewController.o -[QuestionViewController changed:] in QuestionViewController.o -[QuestionViewController nextMilestone:] in QuestionViewController.o -[QuestionViewController pressBack:] in QuestionViewController.o -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyEight", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyEleven", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyFive", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyFour", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyNine", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyOne", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencySeven", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencySix", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyTen", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyThree", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyTwelve", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o "_CompetencyTwo", referenced from: -[QuestionViewController initializeCompetencies] in QuestionViewController.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

Any ideas how to properly declare and initialize global arrays? Or, how to fix this error? Thank you!

Community · Accepted Answer · 2017-05-23 11:51:54Z

Objective-C objects are, with the exception of NSString constants, only ever created at runtime, thus you can't use an expression to initialize them otherwise you'll get error: initializer element is not a compile-time constant

If you declare:

//Globals.h extern NSArray *CompetencyOne; //Globals.m NSArray *CompetencyOne = nil; //this works coz nil is compile time constant

Please check out the link

The = nil is actually not necessary because all "objects of static storage duration" are initialized to zero. That's from the C standard.

Logan · Accepted Answer · 2015-11-06 21:07:46Z

Sooo, arrays are tricky because they're not compile time constants. You'll have to do this:

Constants.h

extern NSArray *myArray;

Constants.m

NSArray *myArray = nil;

Then, somewhere on app initialize, probably app delegate did finish launching call your function:

myArray = @[@1, @2, @3];

Thanks for the heads up Logan. To clarify, where in the .h and .m do I declare and initialize the arrays?
Declare the arrays anywhere directly in the file, then initialize maybe in a global function called from app delegate did finish launching

davbryn · Accepted Answer · 2015-11-06 21:21:23Z

This sounds more like you want an object to create immutable arrays for consumption within the app.

How about a class called CompentencyFactory that has a bunch of static methods:

+ (NSArray *) competencyOne; + (NSArray *) competencyTwo;

etc that look like this:

+ (NSArray *) competencyOne { return @[ @"foo", @"bar", @"fubnut" ]; }

That you can reference throughout the app like:

NSArray *comp = [CompetencyFactory competencyOne];

Nikolai Ruhe · Accepted Answer · 2015-11-08 09:15:26Z

0

Declaring and initializing is not enough. You also have to define the variables.

Add a Globals.m file and copy the declarations, removing extern:

// Globals.m: NSArray *CompetencyOne; NSArray *CompetencyTwo; NSArray *CompetencyThree; ...

edited Nov 8, 2015 at 9:15

answered Nov 6, 2015 at 20:41

Nikolai Ruhe

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2 Comments

Nadir Bilici Over a year ago

Thanks. Ok, I have a Globals.m file with a method -(void) initializeCompetencies { <array definitions> }. Now, how do I get that info to my viewController?

davbryn Over a year ago

Your Globals.m should simply have the arrays declared at the top of the class, i.e NSArray *CompetencyOne = @{....};

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