C macro that creates an NSString variable with the variable name as the content of the string

Question

Despite the fact that this is not good coding practice, I want a macro that should work like the following:

CREATE_STRING(fooBar)

And it should create the following code:

NSString *fooBar = @"fooBar";

My macro looks like this:

#define CREATE_STRING(varName) NSString *varName = @"varName";

But now I get the following

NSString *fooBar = @"varName";

It seems to be such an easy problem to solve and I have already checked the documentation from IBM but I just can't seem to get the varName into the string.

score 15 · Accepted Answer · 2013-03-14 22:22:52Z

15

Use

#define CREATE_STRING(varName) NSString *varName = @#varName

instead. (also note that you don't need the trailing semicolon in order to be able to "call" your macro as a C-like function.)

edited Mar 14, 2013 at 22:22

answered May 4, 2012 at 13:30

user529758

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13 Comments

user23743 Over a year ago

[...]Untitled.m:7:34: error: use of undeclared identifier 'foo'; did you mean 'for'? NSString *mary = CREATE_STRING(foo); ^ Untitled.m:3:42: note: expanded from macro 'CREATE_STRING' #define CREATE_STRING(varName) NSString *varName = @#varName ^ 2 errors generated.

user529758 Over a year ago

Did you call it as CREATE_STRING(foo); (with a semicolon at the end when calling)? If not, try to do so. The error is NOT at the point the macro is used.

user23743 Over a year ago

I just swapped your macro definition for mine to get that error, yours can't work. You can only stringify macros in the preprocessor, so the approach I used in my answer is needed to convert the bare characters into a macro before it gets stringified.

user529758 Over a year ago

"You can only stringify macros in the preprocessor" <- nope. Arguments can be stringified as well.

JeremyP Over a year ago

+1 I just have tested this answer and it is perfectly fine. Until I tried it I thought @#varName would be a syntax error.

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JeremyP · Accepted Answer · 2012-05-04 13:53:45Z

10

This is how to do it

#define CREATE_STRING(varName) NSString *varName = @"" #varName

It takes advantage of the fact that two string constants one after the other get concatenated by the compiler.

answered May 4, 2012 at 13:53

JeremyP

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10 Comments

user529758 Over a year ago

Did ANYBODY actually try my solution before downvoting?

trojanfoe Over a year ago

How is this different to @H2CO3's answer?

user529758 Over a year ago

It's different in that it concatenates two strings, not just inserts the C-stringified name after the '@'.

trojanfoe Over a year ago

@H2CO3 He could have commented on your answer and you could have corrected it, couldn't you?

JeremyP Over a year ago

@trojanfoe @H2CO3 When I posted my answer, I adidn't believe the straight @#varName would work, because in olden days it didn't. However, I have just tried it with the current clang compiler and now it does. It was not me, by the way, that downvoted H2CO3's answer. I always post comments when I down vote.

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