objective-c setter 2d-array

Question

Hi,

i want to initialize a 2d array.. but my code doesn`t work,

can somebody tell me what is wrong?

Thanks Chris

@interface Map : NSObject {
    int mapData[8][8]; 
}
@property(readwrite) int** mapData;
@end


@implementation Map
@synthesize **mapData; (Error: Syntax before *)

- (id)initWithMap:(int[8][8])map {

    for (int i=0; i<8; i++) {
     for (int j=0; j<8; j++) {
      self.mapData[i][j] = map[i][j];
     }
    }
    return self;
}

@end

(Warning mapData requires method... use @synthesize or.......)

Edit: if i remove the type at synthesize as suggested, the compiler tells me another error:error type of property mapData does not match type of ivar mapData

Edit#2: can somebody please post the corrected code? i´m working at this really silly problem for over an hour.. (no c/c++ background, but java)

Answer 1

The synthesize statement of a property does not need to specify the type, just the name.

So;

@synthesize mapData;

Also because mapData is an instance variable you do not need to use the "self.mapData" syntax. You could just do;

mapData[i][j] = map[i][j];

Finally, realise that these are just blocks of data so you can copy everything in one go. E.g

// could also be sizeof(mapData) but this is more instructive
memcpy(mapData, map, sizeof(int) * 8 * 8);

Answer 2

also

int mapData[8][8];

and

int **mapData;

is interpreted differently. The first will be an array with 64 consecutive ints and the other a pointer to a pointer to an int.

Maybe this can work for you, wrapping the 2d array in a struct...

struct map_s {
  int map[8][8];
};
typedef struct map_s map_t;

@interface Map : NSObject {
  map_t mapData;
}
@property (nonatomic, readwrite) map_t mapData;
@end


@implementation Map
@synthesize mapData;

- (id)initWithMap:(map_t)map {
  int i, j;
  for (i=0; i<8; i++) {
    for (j=0; j<8; j++) {
      self.mapData.map[i][j] = map.map[i][j];
    }
  }
  return self;
}

@end

Rewritten a little to show a map initializer

struct map_s {
  int map[8][8];
};
typedef struct map_s map_t;

@interface Map : NSObject {
  map_t mapData;
}
@property (nonatomic, readwrite) map_t mapData;
- (void)init;
- (id)initWithMap:(map_t)map;
@end


@implementation Map
@synthesize mapData;

- (void)init
{
  map_t first = {
    {
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 },
      { 0,0,0,0,0,0,0,0 }
    }
  };
  [self initWithMap:first];
}

- (id)initWithMap:(map_t)map {
  mapData = map;
  return self;
}

@end

Answer 3

I don't think you can have properties of array types. Can you just use a getter/setter instead? For example:

@interface Map : NSObject {
    int mapData[8][8];  
}
- (int)getI:(int)i j:(int)j;
- (int)setI:(int)i j:(int)j to:(int)v;
@end


@implementation Map

- (id)initWithMap:(int[8][8])map {

    for (int i=0; i<8; i++) {
        for (int j=0; j<8; j++) {
            mapData[i][j] = map[i][j];
        }
    }
    return self;
}

- (int)getI:(int)i j:(int)j {
    return mapData[i][j];
}

- (void)setI:(int)j j:(int)j toValue:(int)v {
    mapData[i][j] = v;
}

@end