Objective-C ARC and passing C arrays of objects

Question

I'm sorry if this is a bit of a C-noob question: I know I need to swot up on my pointers. Unfortunately I'm on a deadline so don't have time to work through a whole book chapter, so I'm hoping for a bit more targeted advice.

I want to store some objective-C objects in a C array. I'm using ARC. If I were on the Mac I'd be able to use NSPointerArray instead, but I'm on iOS and that's not available.

I'll be storing a three-dimensional C array: conceptually my dimensions are day, height, and cacheNumber. Each element will either be a pointer to an objective-C object, or NULL.

The number of caches (i.e. the size of the cacheNumber dimension) is known at compile time, but the other two are not known. Also, the array could be very large, so I need to dynamically allocate memory for it.

Regarding ownership semantics, I need strong references to the objects.

I would like the whole three-dimensional array to be an instance variable on an objective-C object.

I plan to have a method that is - tableForCacheNumber:(int)num days:(int*)days height:(int*)height. That method should return a two-dimensional array, that is one specific cache number. (It also passes back by reference the size of the array it is returning.)

My questions:

• What order should I put my dimensions so that I can easily return a pointer to the subarray for one specific cache number? (I think it should be first, but I'm not 100%.)

• What should the return type of my method be, so that ARC doesn't complain? I don't mind if the returned array has an increased reference count or not, as long as I know which it's doing.

• What type should my instance variable that holds the three dimensional array be? I think it should just be a pointer, since that ivar just represents the pointer to the first item that's in my array. Correct? If so, how do I specify that?

• When I create the three-dimensional array (for my ivar), I guess I do something like calloc(X * Y * Z, sizeof(id)), and cast the result to the type for my ivar?

• When accessing items from the three-dimensional array in the ivar, I believe I have to dereference the pointer each time, with something like (*myArray)[4][7][2]. Correct?

• Will the two-dimensional array I return from the method be similarly accessed?

• Do I need to tag the returned two-dimensional array with objc_returns_inner_pointer?

I'm sorry once again that this is a bit of a bad Stack Overflow question (it's too long and with too many parts). I hope the SO citizens will forgive me. To improve my interweb karma, maybe I'll write it up as a blog post when this project has shipped.