c style 2d array not retaining value between functions - ios

Question

Ok so I'm creating a map using a c-style 2d array containing position structs:
typedef struct{
int x;
int y;
} posn;
I upload the values fine and print them out to make sure the values are correct. The 2d array is stored as an instance variable in my class.
In my next function I start by printing the array to make sure it's the same but it's not. The values are totally different and the array is even shortened. Can anyone tell me why I'm getting this issue. I'm using structs and c style arrays because I'm designing a game and I figured using them would be faster than NSMutableArray.
this is how I fill the array
mapa_camino = (posn *)malloc(w * h * sizeof(posn));
int i, j = 0;
for (i = 0; i < w; i++){
for (j = 0; j < h; j++){
SKNode *act;
act = [self.main_view nodeAtPoint:CGPointMake(i-algorimo_compensado.x, j-algorimo_compensado.y)];
if([act isKindOfClass:[BasicActor class]] && ![act isKindOfClass:[CMActor class]]){
//crea pt
posn pt = {.x = i,
.y = j,
.ocupado = YES,
.visitado = NO};
//fija posicion actual como pt
*(mapa_camino + i*h + j) = pt;
}else{
posn pt = {.x = i,
.y = j,
.ocupado = NO,
.visitado = NO};
*(mapa_camino + i*h + j) = pt;
}
}
}
this is how I print it:
- (NSMutableArray*) printtwodarray:(posn*)matriz{
int array_w = self.frame.size.width;
int array_h = self.frame.size.height;
NSMutableArray* regresa_matriz = [[NSMutableArray alloc] initWithCapacity:array_w];
for(int i=0;i<array_w;i++){
[regresa_matriz addObject:[[NSMutableArray alloc] initWithCapacity:array_h]];
for(int j=0;j<array_h;j++){
posn *pt = (matriz + i*array_h + j);
[[regresa_matriz objectAtIndex:i] insertObject:[[Posn alloc] initWithX:pt->x Y:pt->y H:pt->h G:pt->g Ocupado:pt->ocupado Goal:pt->is_goal] atIndex:j];
}
}
return regresa_matriz;
}

Answer 1

In order to store a 2D array in an instance variable from one function and use it in another function you need to declare the variable as an array, not as a pointer. Assignment would not work, so you would need to initialize the data with memcpy:
#interface Foo : NSObject {
posn p[20][30];
}
#end
...
-(void)bar {
posn d[20][30] = {{...}, {...},...,{...}};
memcpy(p, d, sizeof(p));
}