How to create 2-dimensional array with nil elements

Question

In a chess game I would like to use a 2-dimensional array to track positions of pieces at the chess board.

Initially I thought to create an NSMuteableArray and indicate unoccupied squares by nil. The occupied slots should hold a pointer to a Piece object...

However the following code:

NSMutableArray* _board;
...

_board = [[NSMutableArray alloc] init];
for (int i = 0; i < 8; i++) {
    NSMutableArray *row = [[NSMutableArray alloc] init];
    for (int j = 0; j < 8; j++) {
        [row addObject:nil];
    }
    [_board addObject:row];
}

fails with the runtime error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'

So nil can't be passed as argument to addObject... what to do here instead?

score 2 · Accepted Answer · edited May 23 '17 at 10:26

2

Try

NSMutableArray* _board;
...

_board = [[NSMutableArray alloc] init];
for (int i = 0; i < 8; i++) {
    NSMutableArray *row = [[NSMutableArray alloc] init];
    for (int j = 0; j < 8; j++) {
        [row addObject:[NSNull null]];
    }
    [_board addObject:row];
}

Reason for using [NSNull null] instead of nil can be seen here

edited May 23 '17 at 10:26

Community

1
1

answered Apr 06 '14 at 17:25

Faisal Ali

1,135
10
17

Thank you, but how to check for an unoccupied chess board square then? – Alexander Farber Apr 06 '14 at 17:54
1

if ([row objectAtIndex:i] == [NSNull null]) // Your statements – Faisal Ali Apr 06 '14 at 17:55
1

Actually [NSNull null] will return singleton of nil so that we can easily compare it without any pointer(Address) issues – Faisal Ali Apr 06 '14 at 18:01

How to create 2-dimensional array with nil elements

1 Answers1