Saving/loading a 2D C array with NSKeyedArchiver

Question

Malloc like this

int **terrain;
terrain = malloc(sizeof(int*) * mapSize.x);
for (int i = 0; i < mapSize.x; i++) {
    terrain[i] = malloc(mapSize.y * sizeof(int));
}

Use it. Convert to NSdata like this before saving

NSData *data=[NSData dataWithBytes:terrain length:(30*sizeof(int*) +30*30*sizeof(int) )];   
[rootObject setValue:data forKey:@"terrain"];
[NSKeyedArchiver archiveRootObject: rootObject toFile: path];

loading into NSdata then converting back to int**

rootObject = [NSKeyedUnarchiver unarchiveObjectWithFile:path]; 
NSData *data = [rootObject valueForKey:@"terrain"];
terrain =(int**) [data bytes];

With this code, is it saving the *int addresses then when I load the data it does not point to the correct data any more? Or do I have a problem with the "endianness" as described in Documentation

If it is the address issue, should i put a for loop when saving to convert *int to NSData then save all those and recreate the **int with another for loop/malloc?

Answer 1

I haven't tested this but I suspect that with the mallocs above there is no guarantee that you will have a continuous area of memory allocated.

what you could do is save the data separately for all mapSize.x array of bytes:

int **terrain;
terrain = malloc(sizeof(int*) * mapSize.x);
for (int i = 0; i < mapSize.x; i++) {
    terrain[i] = malloc(mapSize.y * sizeof(int));
}

...

for (int j = 0; j < mapSize.x; j++)
{
    NSData *data=[NSData dataWithBytes:terrain[j] length:(mapSize.y * sizeof(int))];   
    [rootObject setValue:data forKey:[NSString stringWithFormat:@"terrain%i", j]];
}

[rootObject setValue:mapSize.x forKey:@"terrain"];
[NSKeyedArchiver archiveRootObject:rootObject toFile:path];

Answer 2

I would convert the 2D array into NSArrays before archiving, because it will save you a lot of hassle.

NSMutableArray* terrainForArchiving = [NSMutableArray arrayWithCapacity:mapSize.x];
for(int col = 0; col < mapSize.x; ++col){
    NSMutableArray* terrainCol = [NSMutableArray arrayWithCapacity:mapSize.y];
    for(int row = 0; row < mapSize.y; ++row){
        [terrainCol addObject:[NSNumber numberWithInt:terrain[col][row]]];
    }
    [terrainForArchiving addObject:terrainCol];
}

[NSKeyedArchiver archiveRootObject:terrainForArchiving];