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?