Hi,
On Fri, 2018-12-07 at 08:03 -0500, Mauro Carvalho Chehab wrote:
> A common mistake is to assume that initializing a var with:
> struct foo f = { 0 };
>
> Would initialize a zeroed struct. Actually, what this does is
> to initialize the first element of the struct to zero.
>
> According to C99 Standard 6.7.8.21:
>
> "If there are fewer initializers in a brace-enclosed
> list than there are elements or members of an aggregate,
> or fewer characters in a string literal used to initialize
> an array of known size than there are elements in the array,
> the remainder of the aggregate shall be initialized implicitly
> the same as objects that have static storage duration."
>
> So, in practice, it could zero the entire struct, but, if the
> first element is not an integer, it will produce warnings:
>
>
> drivers/staging/media/sunxi/cedrus/cedrus.c:drivers/staging/media/sunxi/cedrus/cedrus.c:78:49:
> warning: Using plain integer as NULL pointer
>
> drivers/staging/media/sunxi/cedrus/cedrus_dec.c:drivers/staging/media/sunxi/cedrus/cedrus_dec.c:29:35:
> warning: Using plain integer as NULL pointer
>
> As the right initialization would be, instead:
>
> struct foo f = { NULL };
Thanks for sharing these details, it's definitely interesting and good
to know :)
> Another way to initialize it with gcc is to use:
>
> struct foo f = {};
>
> That seems to be a gcc extension, but clang also does the right thing,
> and that's a clean way for doing it.
>
> Anyway, I decided to check upstream what's the most commonly pattern.
> The "= {}" pattern has about 2000 entries:
>
> $ git grep -E "=\s*\{\s*\}"|wc -l
> 1951
>
> The standard-C compliant pattern has about 2500 entries:
>
> $ git grep -E "=\s*\{\s*NULL\s*\}"|wc -l
> 137
> $ git grep -E "=\s*\{\s*0\s*\}"|wc -l
> 2323
>
> Meaning that developers have split options on that.
>
> So, let's opt to the simpler form.
Acked-by: Paul Kocialkowski <paul.kocialkow...@bootlin.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+sams...@kernel.org>
> ---
> drivers/staging/media/sunxi/cedrus/cedrus.c | 2 +-
> drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c
> b/drivers/staging/media/sunxi/cedrus/cedrus.c
> index b538eb0321d8..b7c918fa5fd1 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
> @@ -75,7 +75,7 @@ static int cedrus_init_ctrls(struct cedrus_dev *dev, struct
> cedrus_ctx *ctx)
> memset(ctx->ctrls, 0, ctrl_size);
>
> for (i = 0; i < CEDRUS_CONTROLS_COUNT; i++) {
> - struct v4l2_ctrl_config cfg = { 0 };
> + struct v4l2_ctrl_config cfg = {};
>
> cfg.elem_size = cedrus_controls[i].elem_size;
> cfg.id = cedrus_controls[i].id;
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> index e40180a33951..f10c25f5460e 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> @@ -26,7 +26,7 @@ void cedrus_device_run(void *priv)
> {
> struct cedrus_ctx *ctx = priv;
> struct cedrus_dev *dev = ctx->dev;
> - struct cedrus_run run = { 0 };
> + struct cedrus_run run = {};
> struct media_request *src_req;
> unsigned long flags;
>
--
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com
