Date: Wed, 28 Jan 2009 12:47:44 +0100 From: Christoph Mallon <christoph.mallon@gmx.de> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: current@freebsd.org Subject: Re: duplicate typedefs and system headers ? Message-ID: <498045E0.3050405@gmx.de> In-Reply-To: <20090127232103.GA40501@onelab2.iet.unipi.it> References: <20090127132102.GA21574@onelab2.iet.unipi.it> <497F91C3.7040502@gmx.de> <20090127232103.GA40501@onelab2.iet.unipi.it>
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Luigi Rizzo schrieb:
> On Tue, Jan 27, 2009 at 11:59:15PM +0100, Christoph Mallon wrote:
>> Luigi Rizzo schrieb:
>>> In a recent commit tp sbin/ipfw, in an attempt to avoid
>>> a large set of header deependencies, i put a 'forward typedef'
>>> declaration in a common header, duplicating something that is in a
>>> system header:
>>>
>>> ipfw2.h: typedef struct _ipfw_insn ipfw_insn;
>>>
>>> netiinet/ip_fw2.h
>>> typedef struct _ipfw_insn { /* template for instructions */
>>> ...
>>> } ipfw_insn;
>> This just begs to break, if somebody decides to change the name of the
>> underlying type of the typedef.
>
> Fortunately this is almost impossible -- the system header is
> basically frozend and if I could change it I would remove the
> typedef in the first place.
>
> I am more worried of compatibility with different compiler.
>
> A workaround that seems to work is putting forward declarations
> just for "struct _ipfw_insn" and use it (instead of the typedef
> name) in the place that does not include netiinet/ip_fw2.h
>
> Would this be better/more compliant with standards -- i.e.,
> is the following code correct ? gcc seems to have no objections.
>
> struct foo;
> int a(struct foo *);
> typedef struct foo bar;
> int a(bar *x) { ... }
What is the problem with just including the correct header? This would
be The Right Thing(tm). Everything else is just an ugly hack.
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