CODEWITHSUNDEEP
objective-cxcodemacrosc-preprocessorstringification
Adriaan Tijsseling
Adriaan Tijsseling

Reputation: 2015

Accessing the value of a Preprocessor Macro definition

If I add a macro "FOO=bar" under GCC_PREPROCESSOR_DEFINITIONS (or Preprocessor Macros if you use XCode"), what would be the best way to access the value of "FOO"?

Currently, I use the clumsy:

    #define MACRO_NAME(f) #f
    #define MACRO_VALUE(f)  MACRO_NAME(f)

    #ifdef FOO
        NSLog(@"%s", MACRO_VALUE(FOO));
    #else
        NSLog(@"undefined");
    #endif

This will output "bar"

Surely, there must be a better/cleaner way?

Upvotes: 14

Views: 6753

Answers (2)

Georg Fritzsche
Georg Fritzsche

Reputation: 98984

What you are doing is the way to stringize (or stringify) macro values. The indirection is unavoidable.

This is mentioned in the GCC preprocessor manual section (archived link) that Rob linked to:

 #define xstr(s) str(s)
 #define str(s) #s
 #define foo 4
 str (foo)
      ==> "foo"
 xstr (foo)
      ==> xstr (4)
      ==> str (4)
      ==> "4

Upvotes: 10

Rob Napier
Rob Napier

Reputation: 299325

NSLog(@"%s", #FOO);

See Stringification. It's the technique you're already using. What was wrong with it?

Upvotes: 2

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