Objective-C. Property for C array

Question

I need something like this:

@property (nonatomic, retain) int field[10][10];

but this code doesn't work. How to replace it? I need both setter and getter methods

Refer this post: http://stackoverflow.com/questions/476843/create-an-array-of-integers-property-in-objective-c — NightFury, Jul 09 '13 at 12:52
1)You advice convert to NSArray and convert from. You also need to convert simple variables of int type to something like NSValue objects. Or I need to rewrite all the previous code to use an NSArray instead of c arrays. 2)I use a multiple c arrays of int instead of one NSArray of objects with parameters because the variables are enough simple and these arrays represent something like logic layers — Gargo, Jul 09 '13 at 14:03

joerick · Accepted Answer · 2013-07-09T14:21:47.290

You can do it if you wrap the array in a struct. Structs are supported in @property notation (see CGRect bounds on CALayer, for example).

First define your struct:

typedef struct {
    int contents[10][10];
} TenByTenMatrix;

Then, in your class interface, you can do:

@property (assign) TenByTenMatrix field;

Note that in this case, you can only get or set the whole array using the property. So you can't do

self.field.contents[0][0] = 1;

You'd have to do

TenByTenMatrix temp = self.field;
temp.contents[0][0] = 1;
self.field = temp;

score 4 · Answer 2 · answered Jul 09 '13 at 13:56

If I understood you correctly, you need something like this:

@property(nonatomic, assign) int** field;

Note that you can't use retain here because it is only available for objects (and int is a primitive type).

Then you can use this in a following way:

    //some initialization - just an example, can be done in other way
self.field = malloc(10 *  sizeof(int));

for(int i = 0; i < 10; i++) {
    self.field[i] = malloc(10 * sizeof(int));
}

//actual usage
self.field[2][7] = 42;
int someNumber = self.field[2][7];

Because property's type is assign, you have to take care of memory management. You can create custom setter for field property and call free() in it.

Parag Bafna · Answer 3 · 2013-07-09T13:22:00.223

0

Write setter and getter

- (int) field:(int)i j:(int)j {
    return field[i][j];
}

- (void)setField:(int)i j:(int)j toValue:(int)value {
    field[i][j] = value;
}

edited Jul 09 '13 at 13:22

answered Jul 09 '13 at 12:49

Parag Bafna

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I meaned to store the whole array, not separate values – Gargo Jul 09 '13 at 13:10
This won't work. Setters for Objective-C properties take exactly one parameter, and getters don't take any. – Michał Ciuba Jul 09 '13 at 13:13
I meaned a 2 methods to set and to get a whole array as it could be with using of @property. So this answer look likes as 30-50% of the correct answer. – Gargo Jul 09 '13 at 13:20
@MichałCiuba if you want only array you can use -(int **)getField { return field; } – Parag Bafna Jul 09 '13 at 13:20

score 0 · Answer 4 · answered Jul 09 '13 at 14:04

It s pretty simple.

    @interface MyClass
    {
        int _fields[10][10]; 
    }

    @property(readonly,nonatomic) int **fields;

    @end

    @implementation MyClass

    - (int *)fields
    {
        return _fields;
    }

    @end

Use readonly in property as it is a fixed pointer, which you wont be changing, which doesn't mean that you can't modify the values in the array.

Objective-C. Property for C array

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