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From: Linus Torvalds <torvalds@osdl.org>
To: Anton Altaparmakov <aia21@cam.ac.uk>
Cc: viro@parcelfarce.linux.theplanet.co.uk,
	Andrew Morton <akpm@osdl.org>,
	linux-kernel@vger.kernel.org,
	linux-ntfs-dev@lists.sourceforge.net
Subject: Re: [PATCH 8/10] Re: [2.6-BK-URL] NTFS: 2.1.19 sparse annotation, cleanups and a bugfix
Date: Fri, 24 Sep 2004 19:46:20 -0700 (PDT)
Message-ID: <Pine.LNX.4.58.0409241930510.2317@ppc970.osdl.org> (raw)
In-Reply-To: <Pine.LNX.4.60.0409242059420.5443@hermes-1.csi.cam.ac.uk>



On Fri, 24 Sep 2004, Anton Altaparmakov wrote:

> On Fri, 24 Sep 2004, Linus Torvalds wrote:
> > 
> > Btw, Al is fixing this. We'll make enum's properly typed, rather than just 
> > plain integers. It's not traditional C behaviour, but it gives you better 
> > type safety, and Al points out that other C compilers (the Plan 9 one, to 
> > be specific) have done the same thing for similar reasons.

Well, when I said "Al is fixing this", I lied.

I just fixed it myself. 

> This is good news.  Once that is done I will be very happy to go back to 
> using enums as I also agree that they can and in this case do look a 
> lot nicer...

Try the current sparse, I think it should work for you.

So if you make an enum where the initializer expression is a little-endian 
expression, the type of that (single) enumerator will be little-endian.

HOWEVER, the type of an enum _variable_ will still be just "int". So

	enum myenum {
		one = 1ULL,
		two = 2,
	};

has the strange behaviour that if you use "one" in an expression, it will
have the type "unsigned long long", but if you use a "enum myenum" entry
(even if it has the value "1"), it will be an "int":

	sizeof(one) == 8
	sizeof(enum myenum) == 4

So I would stronly suggest (and I may make sparse warn) against using
non-integertyped enum values with any enum that actually has any backing
store (ie if you ever use a variable of type "enum myenum", that would
result in a warning - you can really just use the values "one" and "two"
directly).

Note that gcc has some similarly strange behaviour wrt enum types that
depends on the _values_ of the enum entries themselves, and that can
result in serious problems if you declare the enum in a different place
from where you defined the values. Again, those problems only happen for
enums that actually get used with backing store (as opposed to just
readable compile-time constants).

		Linus

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-09-24 16:11 Anton Altaparmakov
2004-09-24 16:12 ` [PATCH 1/10] " Anton Altaparmakov
2004-09-24 16:12   ` [PATCH 2/10] " Anton Altaparmakov
2004-09-24 16:13     ` [PATCH 3/10] " Anton Altaparmakov
2004-09-24 16:13       ` [PATCH 4/10] " Anton Altaparmakov
2004-09-24 16:13         ` [PATCH 5/10] " Anton Altaparmakov
2004-09-24 16:13           ` [PATCH 6/10] " Anton Altaparmakov
2004-09-24 16:14             ` [PATCH 7/10] " Anton Altaparmakov
2004-09-24 16:14               ` [PATCH 8/10] " Anton Altaparmakov
2004-09-24 16:15                 ` [PATCH 9/10] " Anton Altaparmakov
2004-09-24 16:15                   ` [PATCH 10/10] " Anton Altaparmakov
2004-09-24 16:30                 ` [PATCH 8/10] " Linus Torvalds
2004-09-24 20:02                   ` Anton Altaparmakov
2004-09-25  2:46                     ` Linus Torvalds [this message]
2004-09-25  7:25                       ` viro
2004-09-25 15:43                         ` Linus Torvalds
2004-09-26  7:48                           ` Anton Altaparmakov
2004-09-26 16:39                             ` Linus Torvalds
2004-09-26  7:47                       ` Anton Altaparmakov
2004-09-26  7:51                         ` Anton Altaparmakov
2004-09-25  6:38               ` [PATCH 7/10] " viro
2004-09-25 23:31                 ` Anton Altaparmakov
2004-09-25  6:35             ` [PATCH 6/10] " viro
2004-09-25 23:09               ` Anton Altaparmakov
2004-09-26  0:10                 ` Anton Altaparmakov
2004-09-25  6:32         ` [PATCH 4/10] " viro
2004-09-26  0:06           ` Anton Altaparmakov

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