linux-kernel - Re: [PATCH] staging: vboxvideo: vbox_main: Remove unnecessary local variable

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Date:   Fri, 11 Jan 2019 03:36:07 +0000
From:   Sidong Yang <realwakka@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: vboxvideo: vbox_main: Remove unnecessary local
 variable

On Thu, Jan 10, 2019 at 10:44:08PM +0300, Dan Carpenter wrote:
> On Thu, Jan 10, 2019 at 05:00:24PM +0000, Sidong Yang wrote:
> > I think you just point out that my code isn't obvious because the
> > function returns negative error codes. I agree with you. But what if
> > change my code like if(hgsmi_query_conf() != 0). 
> > 
> 
> That's even worse!  :P
> 
> You should do comparisons with zero when you are talking about zero
> meaning the number zero.  In this case, hgsmi_query_conf() returns "zezro
> meaning success" not "zero meaning the number zero".  How many bytes?
> Zero.  That is the number zero.
> 
> != zero is a double negative, because NOT and ZERO are negatives.  If
> double negatives simplified the code we would add four of them instead
> of just the one:
> 
> 	if ((((hgsmi_query_conf() != 0) != 0) != 0) != 0) {
> 
> See?  Adding != 0 doesn't make it simpler...
> 
> The other place where != 0 is appropriate besides talking about the
> number is when you're using a strcmp() function because it works like
> this:
> 
> 	if (strcmp(a, b) < 0) {  <-- means a < b
> 	if (strcmp(a, b) == 0) { <-- means a == b
> 	if (strcmp(a, b) != 0) { <-- means a != b
> 
> regards,
> dan carpenter
> 

You're right. that is even worse. I understand and thank you for pointing out.

regards,
Sidong Yang