Comments on: Java Developer’s Guide to String Constants in Objective-C

By: John Muchow

John Muchow — Thu, 16 Dec 2010 15:48:14 +0000

It’s hard to say why you are receiving the error without seeing the rest of your code. Have you previously defined the variable? Where are you declaring the variable, in a method, as an instance variable? You may cut/paste the definition elsewhere to see if you can narrow down where the error is occurring.

By: follower

follower — Thu, 16 Dec 2010 08:05:57 +0000

static NSString *const HTTP_METHOD_POST = @”POST”;

that throws
static declaration of HTTP_METHOD_POST follows non-static declaration…

Can any of you suggest why i am getting that error.

By: dnd

dnd — Fri, 12 Feb 2010 11:10:20 +0000

@Rodney

>> My experience is with J2ME/Java and CF/C#; in both of those platforms, String literals “add up” and should always be avoided.

I know this is an old post, but I came across it while googling for ‘constants in objective c’. I can’t speak for the other environments, but this is not true of Java.

String x = “xxx”;
String y = “xxx;

will result in only one String object being created. Both x and y will reference the same String object.

By: Hasnat

Hasnat — Mon, 23 Nov 2009 15:51:42 +0000

@david
yes you are correct
you can define in separate header file

By: stevebert

stevebert — Thu, 05 Feb 2009 19:38:34 +0000

You’re not incurring any more expense importing 999 unused #defines just to get that one string constant. The compiler does not incur any storage allocation just because a #define exists, it has to be used in the code being compiled and then it’s only a pointer reference to a global DATA item where the string constant is stored.

Of course if you’re using the same .h file across multiple executables, of course each binary will contain a copy of the string constant, but you knew that already. ;-)

By: stevebert

stevebert — Thu, 05 Feb 2009 19:34:37 +0000

There’s nothing magic about #defines so including them all in a massive .h is fine. The pre-processor will substitute the string constants and the compiler will correlate multiple instances of the same string constant.

By: david

david — Thu, 05 Feb 2009 12:54:19 +0000

so whats the conclusion..whats the better way to declare NSString constants across the application ?

———————————————————————–
I created a .h file and it contents look like

//myconstants.h
#define stringglobal1 @”ssss”
#define string2 @”zzzz”

#define kMywidth 123

//more than 50 constats are there
and in other files I am using #import myconstants.h
I am also importing this header file only for using a single constant
———————————————————————–

is it okay ?

By: david

david — Thu, 05 Feb 2009 12:48:25 +0000

so whats the conclusion..whats the better way to declare NSString constants across the application ?

———————————————————————–
I created a .h file and it contents look like

//myconstants.h
#define stringglobal1 @”ssss”
#define string2 @”zzzz”

#define kMywidth 123

and in other files I am using #import myconstants.h
———————————————————————–

is it okay ?

By: stevebert

stevebert — Wed, 29 Oct 2008 18:16:54 +0000

I have no special insight into the workings of the compiler, but I think the compiler detects the use of @”" string constants and makes instances of an “NSString-like” object in the DATA section of the executable (note the low-address reference for the string). I say NSString-like because this type of object can never be sent retain or release messages, so is probably not a 1st class NSString instance. Repeated uses of the string are probably matched by hashing the string literal and matching to an existing instance of the constant.

By: Rodney

Rodney — Wed, 29 Oct 2008 17:25:02 +0000

@Stevebert,

Thanks for the response. I stand corrected. It is interesting to see how different ObjC is compared to other languages. My experience is with J2ME/Java and CF/C#; in both of those platforms, String literals “add up” and should always be avoided. This is, yet again, an example of how Objective-C excels as a language for mobile application development.

I’ll update the article to include your feedback. Thanks again!
- Rodney