Multidimensional arrays - what's the most convenient way to work with them in Objective-C?

Question

I'm a beginner in Objective-C and I'm trying to find the most convenient way to work with multidimensional arrays in Objective-C. Either I am missing something or they are very ugly to work with.

Let's say we have a classic problem:

• read input from file; on the first line, separated by space(" ") are the width and height of the matrix (eg: 3 4)
• on the following lines there is the content described by the values above

Eg:

3 4
a b c d
e f g h
i j k l

The first solution I thought of was:

NSMutableArray *matrix = [[NSMutableArray alloc] initWithCapacity: x]; //x = 3 in this specific case
NSMutableArray *cell;
for(cell in matrix)
{
    cell = [NSMutableArray initWithCapacity: y];
    for(int i = 0; i < y; i++) // y = 4
    {
        //object is a NSString containing the char[i][j] read from the file
        [cell insertObject:object atIndex: i];
    }
}

This was the first thing I had in mind when thinking about how I should get my values read from file in a multidimensional array. I know you can use C arrays, but since I will store NSObjects in it, I don't think is such a great idea. Nonetheless, from my point of view is easy to work with C arrays rather the solution I got with Objective-C.

Is there another way you could build a multidimensional array in obj-c and easier than the one above?

How about looping them? I know I can do something like

NSArray *myArray;
for(int i=0; i < [array count]; i++)
{
    [myArray arrayWithArray: [array objectAtIndex: i]];
    for(int j=0; j < [myArray count]; j++)
    {
        NSLog(@"array cell [%d,%d]: %s", i, i, [myArray objectAtIndex: j]);
    }
}

But that is still more complicated than your average C multidimensional array loop.

Any thoughts on this?

Answer 1

Objective-C is a superset of C, if you want to work with multidimensional arrays like you would in C, do it that way. If you want to work with objects doing it the Cocoa way, then that's fine too, but you will write more code to do it.

Answer 2

Can you not simply make an array of id?

#import <Foundation/Foundation.h>

int main(int argc, char **argv) {

        id ptr[3][4];
        NSObject *p;

        ptr[0][0] = p;

}

Answer 3

You can do nothing more with NSArray or NSMutableArray in this regard. That is there is nothing like

objectAtIndex:i :j

Answer 4

You can always create one-dimensional arrays of the size width * height instead:

const int size = width*height;
NSMutableArray *array = [NSMutableArray arrayWithCapacity:size];

for (int i=0; i<size; ++i) {
    NSString *string = [NSString stringWithFormat:@"col=%d, row=%d", i%width, i/width];
    [array insertObject:string atIndex:i];
}

Answer 5

Nobody uses direct multi-dimensional arrays of any size in any computer language (except for homework). They simply use too much memory and are therefore too slow. Objective-C is an object-oriented language. Build a class that does what you need.