https://twitter.com/yugui/status/1250204306151620610

example.c

#include <stdio.h>

#define IS_ARRAY(ary) ((void*)(ary) == (void*)&(ary))
#define TEST(ary, expected) \
  printf( \
      "%s:%u: expected %s, actually %s\n", \
      __FILE__, \
      __LINE__, \
      expected, \
      (IS_ARRAY(ary) ? "array" : "ptr"))

struct S {
  int ary[3];
  int *ptr;
  int c99flexible[];
};

void func(int a[3], int b[], int* c, struct S* s) {
  TEST(a, "ptr");
  TEST(b, "ptr");
  TEST(c, "ptr");

  TEST(s->ary, "array");
  TEST(s->ptr, "ptr");
  TEST(s->c99flexible, "array");
}

int main() {
  int ary[3];
  int *ptr;
  struct S s = {{1,2,3}, ptr};

  TEST(ary, "array");
  TEST(ptr, "ptr");

  func(ary, ary, ptr, &s);
  return 0;
}