Date: Sun, 15 Feb 2004 11:19:28 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: current@freebsd.org Subject: Re: GCC bug ? Message-ID: <20040215105358.Y6635@gamplex.bde.org> In-Reply-To: <8832.1076796994@critter.freebsd.dk> References: <8832.1076796994@critter.freebsd.dk>
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On Sat, 14 Feb 2004, Poul-Henning Kamp wrote:
> This seems wrong to me, GCC should warn about the double initialization.
>
> critter phk> cat a.c
>
> struct foo {
> int bar;
> int barf;
> };
>
> struct foo myfoo = {
> .bar = 1,
> .bar = 2,
> };
> critter phk> cc -Wall -c a.c
> critter phk>
This seems to be a feature. From n869.txt:
%%%
[#19] The initialization shall occur in initializer list
order, each initializer provided for a particular subobject
overriding any previously listed initializer for the same
subobject; all subobjects that are not initialized
explicitly shall be initialized implicitly the same as
objects that have static storage duration.
%%%
Initialization of a previously inititialized subobject should be allowed
when the previous initialization was the default. Perhaps it was too
hard to specify a non-overriding behaviour for later initializations in
special cases. Yes, the following should work too:
%%%
struct foo {
int f_bar;
int f_barf;
};
struct foobar {
struct foo fb_bar;
int fb_barf;
};
struct foobar myfoobar = {
.fb_bar = { 1 },
.fb_bar.f_barf = 2,
};
%%%
".fb_bar.f_barf" is initialized twice, first with the default part of an
expilicit initialization. I could have avoided the first initialization
by initializing only .fb_bar.f_bar, but chose not to, to give an example.
More complicated examples might not have a choice in practice. Also, the
opposite order might be needed:
struct foobar myfoobar = {
.fb_bar.f_barf = 2,
.fb_bar = { 1 },
};
to suit complexities not shown in this example. The above just clobbers
the first initialization of ".fb_bar.f_barf". In a more complicated
example, clobbering some initializations might be hard to avoid. Then
further initializations would be needed to unclobber them.
Bruce
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