The pointer-to-array solution is okay, with the caveat that pointer-to-array typedefs should be avoided.

The problem is that they are attractive for reducing repeated declarations:

  typedef unsigned char thing_t[THING_SIZE];

  struct red_box_with_a_hook {
     thing_t thing1, thing2;
  }

  void shake_hands_with(thing_t *thing);

That is all well. But thing_t is an array type which still decays to pointer.

It looks as if thing_t can be passed by value, but since it is an array, it sneakily isn't passed by value:

  void catch_with_net(thing_t thing);  // thing's type is actually "usnsigned char *"

  // ...
    unsigned char x[42]];
    catch_with_net(x);        // pointer to first element passed; type checks