linux-kernel - Re: [PATCH 1/1] kernel/sched.c: Fix array initialization typo

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Message-Id: <20110612165939.04ca68fa.rdunlap@xenotime.net>
Date:	Sun, 12 Jun 2011 16:59:39 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Andy Isaacson <adi@...apodia.org>
Cc:	Jean Sacren <sakiwit@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] kernel/sched.c: Fix array initialization typo

On Sun, 12 Jun 2011 16:09:01 -0700 Andy Isaacson wrote:

> On Sun, Jun 12, 2011 at 04:01:16PM -0600, Jean Sacren wrote:
> > From: Alexey Dobriyan <adobriyan@...il.com>
> > Date: Mon, 13 Jun 2011 00:35:49 +0300
> > >
> > > On Sun, Jun 12, 2011 at 03:31:07PM -0600, Jean Sacren wrote:
> > > > The fix makes certain so that the size of the initialized arrays doesn't
> > > > go beyond the boundary set by the array size of 40.
> > > 
> > > Why would it possibly do that?
> > 
> > With that ',' comma, doesn't it imply there might be the 41st element in
> > the array?
> 
> No, that's not how C works.
> 
> > Despite the fact that that element is bogus.
> 
> It's not bogus, it's utterly cromulent.  Trailing comma on array
> initializer was mentioned in the original K&R and is explicitly endorsed
> by ISO/IEC 9899:1999 6.7.8 paragraph 1.
> 
> > Further, if the comma is there, what's the benefit? I know you're cool,
> > but is it cool in code that way as well?
> > > 
> > > And it's not a typo.
> > 
> > What is it then?
> 
> It is a standard C idiom for defining array contents.  If you write

ack.  I once worked on on OS where the common idiom for array inits was:

int x[] = {
	1
,	2
,	3
};

so that additions only required one line of change.

> int x[] = {
>     1,
>     2,
>     3
> };
> 
> then when I add a fourth element to your array, I have to modify two
> lines, and the diff will say
> -    3
> +    3,
> +    4
>  };
> 
> whereas if you wrote "3," as the last line of the initializer, the diff
> would be one line long.
> 
> Furthermore, spot the error in this diff:
> 
> @@ -3,4 +3,5 @@ char *x[] = {
>      "quick",
>      "brown",
>      "fox"
> +    "jumped"
>  };



---
~Randy
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