devenum: Fix order of operations bug (Coverity id 709)

Chris Robinson chris.kcat at
Wed Sep 10 16:32:42 CDT 2008

On Wednesday 10 September 2008 01:52:02 pm David Laight wrote:
> On Wed, Sep 10, 2008 at 01:38:03PM -0700, Juan Lang wrote:
> > Why use two parentheses when 6 will do, eh?  Sorry, I don't agree that
> > this is clearer.
> Agreed, if you add too many parenthesis it gets difficult to see
> where they line up (which some tool to show you).

Any good editor should be able to highlight parenthesis and bracket pairs.

> I get peeved that gcc always warns about && and || - where the order
> is obvious and correctly defined.

The order may be properly defined, but it's hardly obvious to everyone, all of 
the time. And just because you know it doesn't mean someone who'll look over 
the code later will, and make an incorrect assumption based off it.

> Blindly putting parenthesis around conditional expressions leads people
> to write:
>     dwMediaTypeSize + (dwMediaTypeSize < 2) ? 1 : dwMediaTypeSize / 2
> which is unlikely to have the desired effect!

That's exactly the point. It's better to be verbose than to confuse oneself. 
I've personally had several cases where I thought the order of operation was 
obvious (mostly with the ?: op), didn't use parenthesis, and ran into 
inexplicable bugs. It wasn't until I went back over the code and added 
explicit parenthesis that I found out the problem.

Of course, I never went to school to learn this stuff. All I know about 
programming has largely been self-taught. But, for me at least, it helps 
visualizing what happens when things are properly grouped (spacing helps, eg. 
foo<2 ? 1 : bar/2, but it still leaves a question since the spacing can be 
wrong given the order of operations, and give unexpected results; parenthesis 
gaurantees the evaluation is as specified).

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