NSArray out of bounds check

Question

noobie question.. What is the best way to check if the index of an NSArray or NSMutableArray exists. I search everywhere to no avail!!

This is what I have tried:

if (sections = [arr objectAtIndex:4])
{
    /*.....*/
}

or

sections = [arr objectAtIndex:4]
if (sections == nil)
{
    /*.....*/
}

but both throws an "out of bounds" error not allowing me to continue

(do not reply with a try catch because thats not a solution for me)

Thanks in advance

score 18 · Accepted Answer · answered Mar 15 '12 at 07:08

18

if (array.count > 4) {
    sections = [array objectAtIndex:4];
}

answered Mar 15 '12 at 07:08

sch

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1

Damn.. im so stupid.. of course!! an array gets filled sequentially. i made my head a mess. Thanks mate +1 – spacebiker Mar 15 '12 at 07:19
4

I think objective-c language is a little bit stupid here. I would be more comfortable with if `[array objectAtIndex:outOfBounds]` returned `nil` instead of crashing. – turingtested May 24 '16 at 10:20

score 2 · Answer 2 · answered Jan 24 '13 at 20:58

If you have an integer index (e.g. i), you can generally prevent this error by checking the arrays bounds like this

int indexForObjectInArray = 4;
NSArray yourArray = ...

if (indexForObjectInArray < [yourArray count])
{
    id objectOfArray = [yourArray objectAtIndex:indexForObjectInArray];
}

Paresh Navadiya · Answer 3 · 2015-03-25T07:11:33.497

0

Keep in mind NSArray is in sequential order from 0 to N-1 items

Your are trying to access item which has exceeded limit and a array is nil then compiler would throw out of bound error.

EDIT : @sch's answer above shows how can we check if NSArray has required ordered item present in it or not.

edited Mar 25 '15 at 07:11

answered May 17 '12 at 11:48

Paresh Navadiya

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11
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An array of N items is in sequential order from 0 to N-1 – tothemario Mar 24 '15 at 21:27

turingtested · Answer 4 · 2016-05-24T10:29:35.143

You can use the MIN operator to fail silently like this [array objectAtIndex:MIN(i, array.count-1)], to either get next object in the array or the last. Can be useful when you for example want to concatenate strings:

NSArray *array = @[@"Some", @"random", @"array", @"of", @"strings", @"."];
NSString *concatenatedString = @"";
for (NSUInteger i=0; i<10; i++) {  //this would normally lead to crash
    NSString *nextString = [[array objectAtIndex:MIN(i, array.count-1)]stringByAppendingString:@" "];
    concatenatedString = [concatenatedString stringByAppendingString:nextString];
    }
NSLog(@"%@", concatenatedString);

Result: "Some random array of strings . . . . . "

NSArray out of bounds check

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