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

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Message-ID: <20110612230901.GB11580@hexapodia.org>
Date:	Sun, 12 Jun 2011 16:09:01 -0700
From:	Andy Isaacson <adi@...apodia.org>
To:	Jean Sacren <sakiwit@...il.com>
Cc:	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, 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
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"
 };

HTH, HAND,
-andy
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