How do I return a 2-dimensional C style array from an Objective C method?

A C (or Objective-C) function cannot return an array. However, it can return a struct containing an array:

struct array {
    int v[5][5];
};

struct array f() {
    struct array a;
    // fill 'a' here
    a.v[0][0] = 1;
    ...
    return a;
}

If you really need to be able to index like [x][y] and you care about memory management, perhaps you could create a wrapper class that, upon initialization, mallocs an id** (or the appropriate class, if you know ahead of time) of length x_max, and fills each x with a malloc of length y_max. Then, obviously, it all needs to be released in the dealloc method. You could call that with wrapper.array[x][y]. You could even store the lengths so you can ask the wrapper how big its array is.

One thing: I'm not sure how well malloc plays with apple's [Class alloc]. Might want to check that first.

There is no problem declaring a C-style multi-dimensional array of Obj-C objects and access

n = myArray[x][y].myProperty;

or do

[myArray[x][y] someMethod: someArgument];

It is just like using one variable, instead of an element of an array. But that is a simple C style array of object references, and not an object.

You want something different. Your array is an array inside a class and you want to access the elements. To access the elements, do as with single-dimensional arrays, but e.g.

a = [my2DimArray objectAtIndexX: x indexY: y];

and

[my2DimArray replaceObjectAtIndexX: x indexY: y withObject: myObject];

or

[my2DimArray addRow: myNSArray];

and

RV2DimArray *my2DimArray = [RV2DimArray arrayWithX: 17 Y: 39];

Or, if you are going for more:

RVMultiDimArray *a = [[RVMultiDimArray alloc] initWithDimensions: 4, 4, 8, 0];

etc...

You can set your obj-c function to return an NSArray. And inside that NSArray is an NSArray. So it's like returning an array of NSArray.
yourNSArray = [self getArray]; //returns an array of array

After you have your NSArray, you can then transfer it to a two-dimensional C-style array:
c[0][0] = [[[yourNSArray objectAtIndex:0] objectAtIndex:0] intValue];
c[0][1] = [[[yourNSArray objectAtIndex:0] objectAtIndex:1] intValue];