Understanding array pointer

Question

I'm new to Objective-C and need help with the concept of pointers. I've written this code:

//myArray is of type NSMutableArray
NSString *objectFromArray = [myArray objectAtIndex:2];
[objectFromArray uppercaseString];

I assumed that this would change the string at myArray[2] since I got the actual pointer to it. Shouldn't any changes to the dereferenced pointer mean that the object in that location changes? Or does this have something to do with 'string immutability'? Either way, when I use NSLog and iterate through myArray, all the strings are still lowercase.

Ole gives you the answer you need. But some additional guidance for someone new to ObjC, I've found it doesn't pay to think of pointers to ObjC objects as pointers, per se. Just think of them as "objects" that you can "message" with objc bracket notation, dot notation, etc. If you try to do anything pointerish with them (like explicitly dereference, pointer arithmetic, etc), it's almost always the Wrong Way and often Bad Things will happen. — jemmons
– jemmons, Commented Sep 17, 2011 at 19:01
Thanks for the tip. I had a very basic idea of pointers before, but after learning ObjC, I feel like I've forgotten everything :D — XSL
– XSL, Commented Sep 17, 2011 at 19:10

Ole Begemann · Accepted Answer · 2011-09-17 18:50:15Z

2

Shouldn't any changes to the dereferenced pointer mean that the object in that location changes?

Yes, they would. But if you read the documentation for uppercaseString, you see that it does not modify the string in place. Rather, it returns a new uppercase version of the original string. All methods on NSString work like that.

You would need an instance of NSMutableString to be able to modify its contents in place. But NSMutableString does not have a corresponding uppercase method, so you would have to write it yourself (as a category on NSMutableString).

answered Sep 17, 2011 at 18:50

Ole Begemann

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Saurabh Passolia · Accepted Answer · 2011-09-17 18:50:11Z

-1

of course!! no string in the array will be converted to uppercase as the statement [objectFromArray uppercaseString]; would have returned the uppercase string which was not collected in any object though. "uppercaseString" does not modify the string object itself with which is is called...!!

answered Sep 17, 2011 at 18:50

Saurabh Passolia

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