NSString equivalent of CFSTR macro?

Discussion:

Rick Mann

2017-12-04 22:47:24 UTC

I have to use some C header file that #defines some string constants. Is there an equivalent to CFSTR() that constructs NSString literals? E.g.,

#define NSSTR(s) (@ ## s) <-- magic; this doesn't work
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

TIA,
--
Rick Mann
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Ben Kennedy

2017-12-04 22:51:30 UTC

Permalink

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.

#define NSSTR(s) (@ s)

-b

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Rick Mann

2017-12-04 22:53:46 UTC

Permalink

I tried that. It doesn't work.

Post by Ben Kennedy

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.
-b

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Ben Kennedy

2017-12-04 22:56:35 UTC

Permalink

Post by Rick Mann
I tried that. It doesn't work.

Weird. I just tried it here, using your exact example, and it worked fine under Xcode 9.2. (I slapped it into my iOS app's application:didFinishLaunchingWithOptions: as a quick and dirty test.)

#define NSSTR(s) (@ s)
#define kSomeCStringConstant "foo"
NSLog(@"foo is %@", NSSTR(kSomeCStringConstant));

Do you have some unusual circumstances in your build environment?

b

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Rick Mann

2017-12-04 22:58:29 UTC

Permalink

Ah, nvm, user error. I'm an idiot. It's not a #defined string. It's:

static const char* const kSomeCStringConstant = "foo";

Post by Ben Kennedy

Post by Rick Mann
I tried that. It doesn't work.

Greg Parker

2017-12-04 22:55:45 UTC

Permalink

Post by Ben Kennedy

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.

You can also skip the middleman and use `@kSomeCStringConstant`. After the preprocessor runs it will be `@"foo"` which the ObjC compiler is perfectly happy with.
--
Greg Parker ***@apple.com Runtime Wrangler

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Rick Mann

2017-12-04 22:56:55 UTC

Permalink

Post by Ben Kennedy

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.

Greg Parker

2017-12-04 23:00:02 UTC

Permalink

Post by Ben Kennedy

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.

What compiler version are you using?
Is this file compiled as Objective-C?
Is the #define spelled differently than you wrote?
Does anything look wrong with that line in the output of Product > Perform Action > Preprocess ?
--
Greg Parker ***@apple.com Runtime Wrangler

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Rick Mann

2017-12-04 23:22:53 UTC

Permalink

Ugh...been doing too much Swift (j/k). The right answer to this question is:

@(kSomeCStringConstant)

This works whether it's a #define or a static const char* const.

Post by Greg Parker

Post by Ben Kennedy

Post by Rick Mann
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

You're close. The preprocessor is removing the quotation marks, breaking the syntax. You don't need to token paste; simply remove the '##' from the NSSTR() def.

Greg Parker

2017-12-05 00:14:49 UTC

Permalink

Post by Rick Mann
@(kSomeCStringConstant)
This works whether it's a #define or a static const char* const.

The downsides are:
1. If the library requires that you use the actual address stored in string variable kSomeCStringConstant then it may fail because @(kSomeCStringConstant) may create a second object at a different address.
2. The compiler is not currently smart enough to optimize @(kSomeCStringConstant) into a constant string object, so it may allocate a new autoreleased string object every time it runs that line.
--
Greg Parker ***@apple.com Runtime Wrangler

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Rick Mann

2017-12-05 00:23:46 UTC

Permalink

Post by Rick Mann
@(kSomeCStringConstant)
This works whether it's a #define or a static const char* const.

Yeah, I figured as much. In this case, that's okay. I was just trying to declutter the call site. Thanks!
--
Rick Mann
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Alastair Houghton

2017-12-05 11:15:36 UTC

Permalink

Post by Rick Mann
I have to use some C header file that #defines some string constants. Is there an equivalent to CFSTR() that constructs NSString literals? E.g.,
#define kSomeCStringConstant "foo"
...
NSSTR(kSomeCStringConstant)

Why not just do

#define NSSTR(s) ((NSString *)CFSTR(s))

After all, constant NSStrings are the same as constant CFStrings, right?

Kind regards,

Alastair.

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