Accessing the value of a Preprocessor Macro definition
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16-09-2020 - |
Question
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?
Solution
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
OTHER TIPS
NSLog(@"%s", #FOO);
See Stringification. It's the technique you're already using. What was wrong with it?
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