Re: [PATCH] video/saa7164: Fix sparse warning: Using plain integer

Mauro Carvalho Chehab
2011-01-26T09:29:42Z

Em 25-01-2011 20:54, Peter Hüwe escreveu:
> Am Dienstag 25 Januar 2011, 23:20:44 schrieb Julia Lawall:
>> On Tue, 25 Jan 2011, Peter Huewe wrote:
>>> This patch fixes the warning "Using plain integer as NULL pointer",
>>> generated by sparse, by replacing the offending 0s with NULL.
>>
>> I recall (a number of years ago) being told that for things like kmalloc,
>> the proper test was !x, not x = NULL.
>>
>> julia
>>
>
>
> Hi Julia,
>
> thanks for your input.
> So do I understand you correctly if I say
> if(!x) is better than if(x=NULL) in any case?
>
> Or only for the kmalloc family?
>
> Do you remember the reason why !x should be preferred?
>
> In Documentation/CodingStyle , Chapter 7: Centralized exiting of functions
> there is a function fun with looks like this:
> int fun(int a)
> {
> int result = 0;
> char *buffer = kmalloc(SIZE);
>
> if (buffer = NULL)
> return -ENOMEM;
>
> if (condition1) {
> while (loop1) {
> ...
> }
> result = 1;
> goto out;
> }
> ...
> out:
> kfree(buffer);
> return result;
> }
>
>
> --> So if (buffer = NULL) is in the official CodingStyle - maybe we should
> add a paragraph there as well ;)
>
>
> Don't get me wrong, I just want to learn ;)

Both ways are acceptable. But because C is a Spartan language, and because
I need to review lots of code, I prefer the more synthetic way:
if (!buf)

That means less things to read, and saves me a few microsseconds of reading
and processing it on my mind. In general, such tests occur just after a malloc
or a malloc-like function, so it is really obvious that you're testing for
a pointer.

Cheers,
Mauro
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