Total Size of NSMutableArray object

Question

Hi Folks,

I've got an NSMutableArray that holds a bunch of objects, what I'm trying to figure out is how much memory is the array using. After looking at a couple of places I know about the sizeof call, and when I make it I get 32 bits (which is the size of the NSMutableArray object it self).

Example code:

NSMutableArray *temp = [[NSMutableArray alloc]init];
[temp addObject:objectxyz];
[temp addObject:objectabc];
[temp addObject:object123];

now I want to know the size :)

Thanks,

Sj

Answer 1

There is no direct way to do this since all objects are just stored by reference. There is no concrete notion of "size" in cocoa, especially since objects can have multiple owners which might lead to double counting or other problems.

Answer 2

To get the number of objects in the array, use

[temp count]

If you want the total memory usage of the array, you'll have to loop through and add up how much memory each object uses, but I don't think that a generic object will give you its size. In general, you shouldn't really have to worry about memory usage, though.

Answer 3

Well, you could do something like:

size_t total;
id obj;
for (obj in temp)
  {
  total += class_getInstanceSize([obj class]);
  }

but that doesn't tell you exactly how much storage the array is actually using, since it can grow dynamically and might have more memory at any given time than it needs for just the objects it's pointing to, and of course you'd have to deal with any collections recursively.

If you're trying to get an idea of how much memory you're using, I suggest digging into the tutorials for Instruments, and getting your head around the memory usage probes it provids.

Answer 4

size_t size = class_getInstanceSize([temp Class]);
for (id obj in temp) {
    size += class_getInstanceSize([obj Class]);
}

Note that class_getInstanceSize is declared in /usr/include/objc/runtime.h

Also note that this will only count the memory size of the ivars declared in each class.