When to use static string vs. #define

Question

I am a little confused as to when it's best to use:

static NSString *AppQuitGracefullyKey = @"AppQuitGracefully"; 

instead of

#define AppQuitGracefullyKey    @"AppQuitGracefully" 

I've seen questions like this for C or C++, and I think what's different here is that this is specifically for Objective C, utilizing an object, and on a device like the iPhone, there may be stack, code space or memory issues that I don't yet grasp.

One usage would be:

appQuitGracefully =  [[NSUserDefaults standardUserDefaults] integerForKey: AppQuitGracefullyKey]; 

Or it is just a matter of style?

Thanks.

Answer 1

If you use a static, the compiler will embed exactly one copy of the string in your binary and just pass pointers to that string around, resulting in more compact binaries. If you use a #define, there will be a separate copy of the string stored in the source on each use. Constant string coalescing will handle many of the dups but you're making the linker work harder for no reason.