Question

I know that this will not work, but hopefully you can see what I’m trying to do

#if ASSIGN_ALLOWED
    #define MAYBE_SKIP_REST_OF_LINE 
#else
    #define MAYBE_SKIP_REST_OF_LINE ; //
#endif

char str[80]  MAYBE_SKIP_REST_OF_LINE = "Hello\n";
long array[3] MAYBE_SKIP_REST_OF_LINE = { 7,8,9 };
int x         MAYBE_SKIP_REST_OF_LINE = 3;
//...many many more similar lines...

Is there a way to do this such that it works?

Answer 1

Sure:

#ifdef ASSIGN_ALLOWED
    #define OPTIONAL_INITIALISER(x) = x 
#else
    #define OPTIONAL_INITIALISER(x) 
#endif

char str[80] OPTIONAL_INTIALISER("Hello\n");
#define ARRAY_INIT { 7,8,9 }
long array[3] OPTIONAL_INITIALISER(ARRAY_INIT);
#undef ARRAY_INIT
int x OPTIONAL_INITIALISER(3);

Any initialisers containing commas, like for array in the example, will need to be expanded from their own macro, like ARRAY_INIT in the above. If your compiler supports C99 varargs macros, then you can instead do it in a cleaner way:

#ifdef ASSIGN_ALLOWED
    #define OPTIONAL_INITIALISER(...) = __VA_ARGS__ 
#else
    #define OPTIONAL_INITIALISER(...) 
#endif

char str[80] OPTIONAL_INTIALISER("Hello\n");
long array[3] OPTIONAL_INITIALISER({ 7,8,9 });
int x OPTIONAL_INITIALISER(3);