CODEWITHSUNDEEP
c++cc-preprocessor
Hamza Yerlikaya
Hamza Yerlikaya

Reputation: 49329

Array Initialization Macro

I am trying to come up with a macro to do something like the following,

MY_MACRO(type,name,args...)
MY_MACRO(int,_array,1,2,3)

and expand to,

int _array[] = {1,2,3};
coll* __array = my_call(&array[0],&array[1],&array[2]);

is this possible with/without compiler specific magic?

my_call expects variable number of arguments and I do not want to pass the array directly.

EDIT: I am already using the accepted answer from the following SO question for var args,

Macro returning the number of arguments it is given in C?

So I can find how many elements are in the array.

Upvotes: 3

Views: 5472

Answers (1)

Jeremiah Willcock
Jeremiah Willcock

Reputation: 30969

You can start with (C99, not GCC-specific):

#define MY_MACRO(type, name, ...) \
  type name[] = {__VA_ARGS__};

The my_call part will be more difficult; there are macros online that can count the number of arguments, but you will need something like Boost.Preprocessor (which should work in C) to apply my_call to the consecutive elements of the array. How many elements do you have as a maximum? You might want something like:

#define COUNT(...) COUNT2(__VA_ARGS__, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
#define COUNT2(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, count, ...) count
#define PP_CAT(a, b) PP_CAT2(a, b)
#define PP_CAT2(a, b) a ## b
#define CALL_MY_FUNC(arr, ...) my_call(PP_CAT(ITER_, COUNT(__VA_ARGS__))(arr));
#define ITER_0(arr) /**/
#define ITER_1(arr) (arr)
#define ITER_2(arr) (arr), ITER_1((arr) + 1)
#define ITER_3(arr) (arr), ITER_2((arr) + 1)
#define ITER_4(arr) (arr), ITER_3((arr) + 1)

and so on.

Upvotes: 4

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