Date: Wed, 2 Nov 2011 17:42:46 -0700 From: mdf@FreeBSD.org To: Alexander Best <arundel@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: question regarding style(9) and field initialisers in structs Message-ID: <CAMBSHm8THuoCL3Eh7OfD-pNfj_rPihJzkXWD7QncZw7F8BwVXA@mail.gmail.com> In-Reply-To: <20111102235607.GA61095@freebsd.org> References: <20111102235607.GA61095@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Nov 2, 2011 at 4:56 PM, Alexander Best <arundel@freebsd.org> wrote:
> i sent the following message to freebsd-quaestions@ and got no answer. my=
be it
> is better suited for freebsd-hackers@.
>
> hi there,
>
> i found hundreds of the following cases in the FreeBSD src:
>
> [...]
> struct periph_driver {
> =A0 =A0 =A0 =A0periph_init_func_t =A0 =A0 =A0init;
> =A0 =A0 =A0 =A0char =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0*driver_name;
> =A0 =A0 =A0 =A0TAILQ_HEAD(,cam_periph) units;
> =A0 =A0 =A0 =A0u_int =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 generation;
> =A0 =A0 =A0 =A0u_int =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 flags;
> =A0 =A0 =A0 =A0#define CAM_PERIPH_DRV_EARLY =A0 =A00x01
> };
> [...]
> static struct periph_driver dadriver =3D
> {
> =A0 =A0 =A0 =A0dainit, "da",
> =A0 =A0 =A0 =A0TAILQ_HEAD_INITIALIZER(dadriver.units), /* generation */ 0
> };
>
> ...is it proper programming practice to forget about the last field, if i=
t
> would have been initialised to 0?
It's more likely that, in this instance, the field was added after the
initializer. Without named initializers, all fields until the last
non-zero one need to be explicitly present.
style(9) doesn't address it, having been written too long ago, but IMO
initializations in a C translation unit [1] should use C99's named
initializer feature, to protect against future member re-ordering.
And it would be style(9) compliant to leave out any field whose
initial value is zero (though sometimes it's good to list it anyways
to make it clear that 0 was the desired value).
[1] Note that C++ doesn't support C99's named initializer syntax (even
in C++0x, which is a bit silly), so any struct initializers in a
header file like <sys/malloc.h> must use old-style, since FreeBSD
should continue to support writing kernel modules in C++.
Cheers,
matthew
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAMBSHm8THuoCL3Eh7OfD-pNfj_rPihJzkXWD7QncZw7F8BwVXA>