Pass C array to a objective C method

Question

I want to make an array of integers with as little code as possible and pass that array to an objective C method.

I tried the below. sequence starts out as an array and is passed to setLights: but when sequence is looked at in the method (via breakpoint) it is no longer an array.

*EDIT: I didnt want to use an NSArray because an NSArray of integers is so verbose:

Using NSArray:

NSArray *sequence = [[NSArray alloc] initWithObjects: [NSNumber numberWithInt:0], [NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], [NSNumber numberWithInt:4],[NSNumber numberWithInt:5],nil];

Using C array:

int sequence[6] = {0,1,2,3,4,5};

What am I doing wrong?

- (IBAction)testLights:(id)sender {
    int sequence[6] = {0,1,2,3,4,5};
    //int *sequence[0][1][2][3][4][5]; //also tried this
    [self setLights:sequence];
}


- (void)setLights:(int *)sequence {

    UIImageView *light=[lgtArray objectAtIndex: sequence[0]];
    light.alpha = 0;
    [UIView animateWithDuration:0.3f
                     animations:^{
                         light.alpha = 1;
                     }completion:nil
     ];


}

enter image description here

does it help to know that it doesn't change anything that it is an Objective C method... that all Objective C functions are really C functions? — Grady Player
– Grady Player, Commented May 2, 2014 at 4:42
Lookup "array decays to pointer" - This must have been answered somewhere ... — Martin R
– Martin R, Commented May 2, 2014 at 4:44
You can use short notation too just in case if you plan to use nsarray as NSArray *sequence = @[@(0),@(1),@(2),@(3),@(4),@(5)]; — Janak Nirmal
– Janak Nirmal, Commented May 2, 2014 at 4:58
No, just use NSNumbers, which is what the shorthand notation that Janak commented on is. — rdelmar
– rdelmar, Commented May 2, 2014 at 5:02

Enrico Susatyo · Accepted Answer · 2014-05-02 04:51:16Z

2

Use this syntax to pass the array:

- (void)setLights:(int[] )sequence

answered May 2, 2014 at 4:51

Enrico Susatyo

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4 Comments

Wesley Smith Over a year ago

Some of the other comments and answers show a better way to do what I need, but this answered my original question best

Enrico Susatyo Over a year ago

@DelightedD0D For what it's worth, I agree with the other guys that you should try to avoid C arrays. If the only reason is verbosity, then you should still use NSArray. If the reason is because a third party library uses this, then maybe you would have to use C arrays.

Wesley Smith Over a year ago

Agreed, I ended up going with `NSMutableArray *sequence = [@[@0, @1, @2, @3, @4, @5] mutableCopy]; for my actual project.

Enrico Susatyo Over a year ago

@Delighted0D Good decision.

Enrico Susatyo · Accepted Answer · 2014-05-02 04:51:58Z

1

You are running into a bizarre feature of C that has propagated through its variants: the [mostly] equivalence of pointers and arrays.

if you do

int *sequence ;

then you can do

sequence [4] ;

or

*(sequence + 4)

Arrays and points are mostly interchangeable. Arrays in C variants are merely data allocation. Your definition of

- (void)setLights:(int *)sequence

conveys no information array information. You can still access sequence as though it is an array. setLights simply has no intrinsic information as to how many elements sequence has allocated to it.

The problem here is that your usage of the array in setLights needs to match how you have allotted the data.

If you did

sequence [100] = 10 ;

it would be syntactically correct but likely to create an error.

edited May 2, 2014 at 4:51

Enrico Susatyo

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answered May 2, 2014 at 4:48

user3344003

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1 Comment

Brian Tracy Over a year ago

Change *(sequence + 4] to *(sequence + 4)

thxou · Accepted Answer · 2014-05-02 05:03:00Z

1

Is verbose only if you want. Use literals instead:

NSArray *sequence = @[@0, @1, @2, @3, @4, @5];

And access to the value like this:

UIImageView *light = lgtArray[[sequence[0] intValue]]];

answered May 2, 2014 at 5:03

thxou

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2 Comments

Wesley Smith Over a year ago

Can this be done with NSMutableArray? or should I then just do NSMutableArray *newSequence = [(NSArray*) sequence mutableCopy];

thxou Over a year ago

Yes, but make a mutable copy before: NSMutableArray *sequence = [@[@0, @1, @2, @3, @4, @5] mutableCopy];

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