Saving/loading a 2D C array with NSKeyedArchiver - iphone

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];