C/Java/etc. style arrays in Objective-C

Question

I know Apple is big on having you use NS objects instead of true primitive types, but I need the capabilities of an array (namely direct access of items at indices). However, it seems that they are so very keen on using NS objects that I can't find a single tutorial online or in a textbook about how to use basic primitive arrays. I want something that does things like this does in Java:

String inventory[] = new String[45];

inventory[5] = "Pickaxe";
inventory[12] = "Dirt";
inventory[8] = "Cobblestone";

inventory[12] = null;

System.out.println("There are " + inventory.length + " slots in inventory: " + java.util.Arrays.toString(inventory));

The following is the closest I've gotten in Objective-C, but it won't run properly:

NSString *inventory[45];

inventory[5] = @"Pickaxe";
inventory[12] = @"Dirt";
inventory[8] = @"Cobblestone";

inventory[12] = nil;

NSArray *temp = [NSArray arrayWithObjects:inventory count:45];
NSLog(@"There are %i slots in inventory: %@", [temp count], [temp description]);

Also, if at all possible, is there something in O-C that will give me the count of non-null/non-nil objects in the array? (This way, I can tell how much space is left in the inventory so that the player can't pack away anything if it's full)

It's natural that it doesn't work. [NSArray arrayWithObjects:inventory]; would have required that inventory be a list of variadic arguments. User [NSArray arrayWithObjects:count:] instead. — user529758
– user529758, Commented Apr 4, 2012 at 5:01
Don't forget that objective-c is built on top of C so any standard C code will work. Just search for an example of a C array if you aren't sure how to use one. — lnafziger
– lnafziger, Commented Apr 4, 2012 at 5:08
@H2CO3 thanks for that! However, it still throws an exception for putting a nil value in there — Ky -
– Ky -, Commented Apr 4, 2012 at 5:08
That's your fault anyway! Collection objects do throw exceptions upon being given nil, and this behaviour is documented. You should check for nil before passing it to the initializer methods. — user529758
– user529758, Commented Apr 4, 2012 at 13:48

justin · Accepted Answer · 2012-04-04 05:22:12Z

2

typically, you would use NSArray/NSMutableArray, although you could also use C arrays.

NSArray (and most Foundation collections) cannot contain nil entries - you can use NSPointerArray (OS X) if you need nil values, or simply use [NSNull null] in an NSArray to designate nil.

Here's your program using an NSArray:

NSMutableArray * inventory = [NSMutableArray array];
for (NSUInteger idx = 0; idx < 45; ++idx) {
  [inventory addObject:[NSNull null]];
}

[inventory replaceObjectAtIndex:5 withObject:@"Pickaxe"];
[inventory replaceObjectAtIndex:12 withObject:@"Dirt"];
[inventory replaceObjectAtIndex:8 withObject:@"Cobblestone"];

[inventory replaceObjectAtIndex:12 withObject:[NSNull null]];

NSArray *temp = [NSArray arrayWithObject:inventory];
NSLog(@"There are %i slots in inventory: %@", [temp count], [temp description]);

Also, if at all possible, is there something in O-C that will give me the count of non-null/non-nil objects in the array?

An NSArray is a CFArray - they are "toll free bridged". Use CFArrayGetCountOfValue with [NSNull null] as the value to seek. Most of the CF-APIs are available in the NS-APIs, but not this one. You could easily wrap it in a category, if needed often.

edited Apr 4, 2012 at 5:22

answered Apr 4, 2012 at 4:57

justin

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3 Comments

Ky - Over a year ago

when it tries to make the NSArray, it says Program received signal: EXC_BAD_ACCESS. and exits.

justin Over a year ago

@Supuhstar ah - i missed that. updated. that was taken from the original. you want arrayWithObject:, not arrayWithObjects: there. you need to nil-terminate arrayWithObjects:, like so: NSArray *temp = [NSArray arrayWithObjects:inventory, nil];

Ky - Over a year ago

awesome! I'm going to use this system, now :3

Adam Shiemke · Accepted Answer · 2012-04-04 04:54:31Z

2

Use c-style arrays. Any c code will work in objective c. Try not to mix objective c style objects with c style code unless you are very careful. The memory management stuff gets weird, and it is easy to get confused on object types vs. primitives.

answered Apr 4, 2012 at 4:54

Adam Shiemke

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2 Comments

Kurt Revis Over a year ago

... so go read a book, or google "C array tutorial"? SO isn't the place to get people to personally teach you material that you can easily research yourself.

Ky - Over a year ago

I just wanted a snippet, jeeze >.> If someone asked me for a sample of Java, HTML, CSS, VB, etc. code, I'd gladly write it out.

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