create constant 2d array in objective-c

Question

Does anyone know how I might create a constant 2d-array in iOS/Ojective-c? In java it would be

public static final String MY_2D_ARRAY = {{"dog","cat","sheep"},{"bread","end","van"}};

The following is not working for me

extern NSString * const MY_2D_ARRAY[][]; //etc

@p4sh4 if it's a duplicate, do you mind writing the answer here? The link you provide does not address 2D arrays. — learner, Aug 06 '14 at 04:41
You can see my answer below. If you can't create a single-dimensional array as a constant, you obviously cannot create a two-dimensional one. Some answers to the other question describe how you can try to use a C array to do it. — p4sh4, Aug 06 '14 at 04:43

score 0 · Answer 1 · answered Aug 06 '14 at 04:18

0

In Objective-C to create Array you need to use NSArray(Immutable). Alternatively NSMutableArray(mutable).

NSArray *arr = @[@[@"a", @"b"], @[@"c", @"d"]];

answered Aug 06 '14 at 04:18

Yogesh Suthar

30,424
18
72
100

@{} is not for array. It's for dictionary. – Ryan Aug 06 '14 at 04:20
Where in the code would I put that line? Because Xcode gives the error: `Initializer element is not a compile-time constant` – learner Aug 06 '14 at 04:26
@learner Put it in Implementation section. – Yogesh Suthar Aug 06 '14 at 04:27
Yes. That's what I did. – learner Aug 06 '14 at 04:29

score 0 · Answer 2 · answered Aug 06 '14 at 04:18

0

Here's how

NSArray *arr = @[
                 @[@"dog", @"cat", @"sheep"], 
                 @[@"bread", @"end", @"van"],
                  ...
                ];

answered Aug 06 '14 at 04:18

Ryan

4,799
1
29
56

Where in the code would I put that line? Because Xcode gives the error: `Initializer element is not a compile-time constant` – learner Aug 06 '14 at 04:26
1

it would need to go inside a function that would run at the start of your app, you cant define it as an const/extern because when using the `@[]` notation, its not actually a constant, its shorthand for writing `[NSArray arrayWithObjects:x,y,z,nil];` – Fonix Aug 06 '14 at 04:32

score 0 · Answer 3 · answered Aug 06 '14 at 04:36

0

You cannot create a constant NSArray, because as any Objective-C object (besides NSString), it is created at runtime and you cannot use an expression to initialise it. You should consider using some other approach, perhaps use a singleton.

answered Aug 06 '14 at 04:36

p4sh4

3,292
1
20
33

score -1 · Accepted Answer · edited Aug 06 '14 at 05:19

-1

Since in ios you can't create constant array as you shown but you can use it as alternate

//  constants.h

+ (NSArray*) MY_2D_ARRAY;

//  constants.m

+ (NSArray*) MY_2D_ARRAY{ 

    static NSArray* arr = nil;

    if (arr == nil) {
        arr = @[@"a",@"b"]];
    }
    return arr;
}

// you can Use it where you required 

[constants MY_2D_ARRAY];

If this help you then you can accept it as solution.

edited Aug 06 '14 at 05:19

Bryan Chen

45,816
18
112
143

answered Aug 06 '14 at 05:16

vnaren001

244
2
11

you need to use dispatch_once to make it thread-safe – Bryan Chen Aug 06 '14 at 05:20
Why this answer is down voted ? If someone have any better suggestion then write their answer, so that will help us to understand the things. – vnaren001 Feb 23 '16 at 07:34

create constant 2d array in objective-c

4 Answers4