Size of NSArray

When I tried to check the size of NSArray which is declared without any capacity, I found it 4. Now the question开发者_如何学JAVA is why it is always 4? please help me out to find it.... Thanks

If you're talking about sizeof, it is not the right way to find out how much data an NSArray is holding. Objective-C objects are always accessed through pointers, and the size of a pointer on the iPhone is 4 bytes. That's what sizeof is telling you. To find out how many objects are in an array, ask the array for its count.

Given this:

NSArray *foo;
NSLog(@"%d", sizeof(foo));

You'll either get 4 or 8, depending on if you are on a 32 or 64 bit system. Note that I quite purposefully didn't initialize foo; there is no need to do so as sizeof(foo) is giving the bytesize of foo and foo is just a random pointer to an object. Wouldn't matter if that were id foo; void*foo; NSString*foo; all would be 4 or 8.

If you want the allocated size of an instance of a particular class, the Objective-C runtime provides introspection API that can do exactly that. However, I can't really think of any reason why that would be more than passingly interesting in a program.

Note that the allocation size of an instance does not account for any sub-allocations. I.e. an NSArray likely has a backing store which is a separate allocation.

To reiterate:

sizeof(foo) in the above code has nothing to do with the size of the allocated instance.