Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

Leon Romanovsky
2021-08-14T15:53:02Z

On Sat, Aug 14, 2021 at 02:57:06PM +0000, Al Viro wrote:
> On Sat, Aug 14, 2021 at 05:38:27PM +0300, Leon Romanovsky wrote:
>
> > There are number of reasons why you didn't notice any difference.
> > 1. {} is GCC extension
> > 2. {} was adopted in latest C standards, so need to check which one GCC 10
> > is using by default.
> > 3. Main difference will be in padding - {0} will set to zero fields but
> > won't touch padding, while {} will zero everything.
>
> References on (3), please?

I reread gcc/c/c-typeck.c and at lest for GCC 10, I'm wrong about padding.
Sorry about that.

8630 struct c_expr
8631 pop_init_level (location_t loc, int implicit,
8632 struct obstack *braced_init_obstack,
8633 location_t insert_before)
....
8692 switch (vec_safe_length (constructor_elements))
8693 {
8694 case 0:
8695 /* Initialization with { } counts as zeroinit. */
8696 constructor_zeroinit = 1;
8697 break;
8698 case 1:
8699 /* This might be zeroinit as well. */
8700 if (integer_zerop ((*constructor_elements)[0].value))
8701 constructor_zeroinit = 1;
8702 break;
8703 default:
8704 /* If the constructor has more than one element, it can't be { 0 }. */
8705 constructor_zeroinit = 0;
8706 break;
8707 }
8708