Byte size of an NSDictionary

Question

This may sound like a completely stupid question, but how can I get the size in bytes of an NSDictionary? Can I convert it to NSData, and then get the length of that?

Help!

Answer 1

You should say more about why you care about the size of the dictionary in bytes, because the answer might be different depending.

In general, the "size" of an NSDictionary's footprint in memory is not something you can see or care about. It abstracts its storage mechanism from the programmer, and uses some form of overhead beyond the actual data it's storing.

You can, however, serialize the dictionary to NSData. If the contents of the dictionary are only "primitive" types like NSNumber, NSString, NSArray, NSData, NSDictionary, you can use the NSPropertyListSerialization class to turn it into a binary property list, which will be about the most compact byte representation of its contents that you can get:

NSDictionary * myDictionary = /* ... */;
NSData * data = [NSPropertyListSerialization dataFromPropertyList:myDictionary
    format:NSPropertyListBinaryFormat_v1_0 errorDescription:NULL];    
NSLog(@"size: %d", [data length]);

If it contains other custom objects, you could use NSKeyedArchiver to archive it to an NSData, but this will be significantly larger and requires the cooperation of your custom classes.

Answer 2

You can get the size of any class by calling this:

#import "objc/runtime.h"
int size = class_getInstanceSize([NSDictionary class]);

This will return you the size of the class, but not the actual size occupied by an instantiated object. If you want the size of an instantiated object:

#import "malloc/malloc.h"
int size = malloc_size(myObject);