Creating a private 2D float array - Objective C

I am tring to create a private 2D float array and initialize it in constructor. I am getting "Expected Expression" error. I searched for a long while and couldn't find anything.

Here is my code:

@interface SampleClass : NSObject{
@private
float stops[2][2];
}

@end

@implementation SampleClass

- (id) init{
self = [super init]; // Edited
stops = { {1.0, 1.0}, {1.0, 2.0} }; // It gives "Expected Expression" at this line
return self;
}

@end


I tried different versions like:

stops = { {1.0, 1.0}, {1.0, 2.0} };
stops = { 1.0, 1.0, 1.0, 2.0 };
stops = { {1.0, 1.0}, {1.0, 2.0} };


Non of them seems to work.

I am new to Objective C so any recommendation is appreciated.

super

init

1 Answer
1

(Objective-)C does not support assignment of one array to another, there are workarounds involving struct as they are assignable but you don't need to go there.

struct

If you are after a constant array to be used by instances you can just declare it as static:

static

static const float stops[2][2] = { {27.3, 51.7}, {93.2, 42.24}};


The static makes stops accessible only to code within the same file. You can place the declaration between the @implementation and @end to at least visually associate it as belonging to a class.

static

stops

@implementation

@end

The above is not suitable if you need a variable array, but does form part of a solution. Keep your instance variable:

@private
float stops[2][2];


This must be an array, not some pointer, as it must allocate the space for your floats. Next use the above declaration but give it a different name:

static const float _stops_init[2][2] = { {27.3, 51.7}, {93.2, 42.24}};


and then in your init use the standard C function memcpy() to copy the values in the memory occupied by _stops_init into the memory occupied by stops:

init

memcpy()

_stops_init

stops

memcpy(stops, _stops_init, sizeof(_stops_init));


Here sizeof() will return the total size in bytes of the memory used by your float array _stops_init and memcpy() copies those bytes over those associated with stops – that is it implements array assignment which C doesn't directly support.

sizeof()

_stops_init

memcpy()

stops

Using the static const array rather than a local variable define in init() as the source of your values saves re-creating the source on every call to init().

static const

init()

init()

The above code doesn't do all the checks it should - at minimum an assert() checking that the sizes of stops and _stops_init are the same is advisable.

assert()

stops

_stops_init

HTH

@implementation

@private

stops

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