linux-kernel - Re: [Q] compiler no longer warning about undeclared struct?

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Message-ID: <m3ipqmek6y.fsf@hase.home>
Date:	Thu, 28 Jul 2011 13:08:53 +0200
From:	Andreas Schwab <schwab@...hat.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	linux-kernel@...r.kernel.org
Subject: Re: [Q] compiler no longer warning about undeclared struct?

Guennadi Liakhovetski <g.liakhovetski@....de> writes:

> I always thought you need forward declarations for those, as in
>
> struct yy;
>
> before declaring struct xx above.

You only need that if you would otherwise introduce the struct tag in a
different scope, like prototype scope (which ends at the end of the
prototype).

>> Otherwise you could not define recursive structures as in
>> ----  snip  ----
>> struct a {
>> 	struct *b;
>> };
>> struct b {
>> 	struct *a;
>> };
>> ----  snip  ----
>
> I would add a "struct b;" forward declaration before "struct a".

You can do that, but since a struct definition doesn't introduce a new
scope it is not necessary.

Andreas.

-- 
Andreas Schwab, schwab@...hat.com
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