NSString retain count -1

Question

I want to print retain count of NSString in AppDelegate class in didFinishLaunchingWithOptions method

NSString *str = [[N         


        

Answer 1

Generally you should no longer use the -retainCount method, as pointed out by others' answers. The reason is, a lot of retain/release work is done inside the NSString class depending on how you create it. When you create an NSString you could actually be creating one of many NSString subclasses (the id return type of the initialisers is not specific).

All NSConstantStrings (those created by @"") are not releasable - they exist for the duration of the program (as specified by both gcc and clang). Thus, Apple have arbitrarily set its retainCount to be the highest possible unsigned integer (or -1 if it is read as signed, as it is here) because it makes no sense for a constant object, alive for the duration of the program, to have a retain count.

When you create an empty string in the way you have, it is likely Apple just automatically point you to the constant @"" in memory as it takes up less space at runtime. As your object is now an NSConstantString, it is implemented to return a retain count of -1.

EDIT: Incidentally, as NSConstantString is a subclass of NSString it must implement the methods that NSString implements, including -retainCount. This is why you can actually call the -retainCount method on a constant string object (and why Apple make it return a special value). This inheritance relationship can be found near the bottom of the NSString.h header.