linux-kernel - Re: [PATCH 5/9] bfs: move function prototype to the proper header file

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Message-Id: <57F1F710-9135-413B-A811-88C1091389AC@moffetthome.net>
Date:	Thu, 24 Jan 2008 20:55:47 -0500
From:	Kyle Moffett <kyle@...fetthome.net>
To:	Dmitri Vorobiev <dmitri.vorobiev@...il.com>
Cc:	Heikki Orsila <shdl@...alwe.fi>, trivial@...nel.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	tigran@...azian.fsnet.co.uk
Subject: Re: [PATCH 5/9] bfs: move function prototype to the proper header file

On Jan 24, 2008, at 18:13, Dmitri Vorobiev wrote:
> Heikki Orsila пишет:
>> On Fri, Jan 25, 2008 at 01:32:04AM +0300, Dmitri Vorobiev wrote:
>>> +/* inode.c */
>>> +extern void dump_imap(const char *, struct super_block *);
>>> +
>>
>> Functions should not be externed, remove extern keyword.
>
> Care to explain why?
>
> Following is an explanation why the contrary is probably true:
>
> 1) We have lots of precedents in existing code:
>
> dmvo@...her:~/Projects/misc/linux$ git-grep 'extern void' include |  
> wc -l
> 5523
> dmvo@...her:~/Projects/misc/linux$


The "extern" keyword on functions is *completely* redundant.

For C variables:
   Declaration:  extern int foo;
   Definition:   int foo;
   File-scoped:  static int foo;

For C functions:
   Declaration:  void foo(int x);
   Definition:   void foo(int x) { /*...body...*/ }
   File-scoped:  static void foo(int x) { /*...body...*/ }

The compiler will *allow* you to use "extern" on the function  
prototype, but the presence or absence of a function body is  
sufficiently obvious for it to determine whether the prototype is a  
declaration or a definition that the "extern" keyword is not required  
and therefore redundant.

For maximum readability and cleanliness I recommend that you leave off  
the "extern" on the function declarations; it makes the lines much  
longer without obvious gain.

Cheers,
Kyle Moffett


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