#include <stdlib.h> #include <assert.h> #define must_be(e) \ ( \ 0 * (int) sizeof( \ struct { \ static_assert(e, ""); \ int ISO_C_forbids_a_struct_with_no_members_; \ } \ ) \ ) #define is_same_type(a, b) \ ( \ __builtin_types_compatible_p(a, b) \ ) #define is_same_typeof(a, b) \ ( \ is_same_type(typeof(a), typeof(b)) \ ) #define is_array(a) \ ( \ !is_same_typeof(a, &(a)[0]) \ ) int main(void) { return must_be(is_array(((int []) {rand(), rand()}))); }

alx@devuan:~/tmp$ gcc -Wall -Wextra -S cnt.c alx@devuan:~/tmp$

alx@devuan:~/tmp$ clang -Wall -Wextra -S cnt.c cnt.c:34:37: error: initializer element is not a compile-time constant 34 | return must_be(is_array(((int []) {rand(), rand()}))); | ^~~~~~ cnt.c:27:25: note: expanded from macro 'is_array' 27 | !is_same_typeof(a, &(a)[0]) \ | ^ cnt.c:22:29: note: expanded from macro 'is_same_typeof' 22 | is_same_type(typeof(a), typeof(b)) \ | ^ cnt.c:17:38: note: expanded from macro 'is_same_type' 17 | __builtin_types_compatible_p(a, b) \ | ^ cnt.c:9:39: note: expanded from macro 'must_be' 9 | static_assert(e, ""); \ | ^ 1 error generated.