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Date: Thu, 23 Apr 2009 15:28:44 -0400
Subject: Re: [Qemu-devel] [7234] Use a more natural order
Message-ID: <20090423192844.GJ3795@csclub.uwaterloo.ca>
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From: lsorense@csclub.uwaterloo.ca (Lennart Sorensen)
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To: "M. Warner Losh" <imp@bsdimp.com>
Cc: blauwirbel@gmail.com, qemu-devel@nongnu.org

On Thu, Apr 23, 2009 at 01:12:50PM -0600, M. Warner Losh wrote:
> In message: <20090423185308.GH3795@csclub.uwaterloo.ca>
>             lsorense@csclub.uwaterloo.ca (Lennart Sorensen) writes:
> : On Thu, Apr 23, 2009 at 06:29:47PM +0000, Blue Swirl wrote:
> : > Revision: 7234
> : >           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=7234
> : > Author:   blueswir1
> : > Date:     2009-04-23 18:29:47 +0000 (Thu, 23 Apr 2009)
> : > Log Message:
> : > -----------
> : > Use a more natural order
> : 
> : It may be more natural, but it is also less safe.
> : 
> : After all
> : 
> : if (0 = x) {
> : 
> : fails compile, while
> : 
> : if (x = 0) {
> : 
> : compiles silently even when you didn't mean that.
> 
> This style is evil and must die.  I don't know any nice way to put
> it.  It encourages sloppiness.  Also, it breaks down when you add
> inequality:
> 
> if (x < 1)
> 
> becomes
> 
> if (1 >= x)

No it doesn't.  It becomes:

if (1 > x)

Why would it be anything else?

> which is also error prone.
> 
> The compiler will warn about your example, but won't warn if I
> transcribe things wrongly as
> 
> if (1 < x)

Nothing wrong with that.  That's perfectly valid, if you want to check
that x is greater than 1.

Putting constants first means that you can't accidentally use assignment
when you meant equality.  You can't fix all the stupidies possible in C,
but you can at least try to avoid some of them when possible.

-- 
Len Sorensen