Re: [KJ] what's the deal with using real "boolean" variables?

[walter harms <wharms@bfs.de>]

hi,
i took a dive into the 'c reference manual' and found that the header stdbool.h
defines (#define) bool/true/false. It is permited to undefine and redefine these
defines. It defines also the macro "__bool_true_false_are_defined".
The best ways seems to emulate this way and provide a kernelbased stdbool.h if
"__bool_true_false_are_defined" does not exist.

my 2 cents,
walter



Richard Knutsson wrote:
> Alexey Dobriyan wrote:
>> On 1/10/07, Robert P. J. Day <rpjday@mindspring.com> wrote:
>>> On Wed, 10 Jan 2007, Richard Knutsson wrote:
>>>
>>>> Robert P. J. Day wrote:
>>>>> is there a consensus on how to use actual C99 boolean variables in
>>>>> the kernel source? C99 defines the unsigned integer type "_Bool" 
>>> and,
>>>>> from that point on, it's all downhill:
>>>>>
>>>> <snip>
>>>>> ./include/linux/types.h:typedef _Bool bool;
>>>>>
>>>> This is the one that was added to replace the rest.
>>> so the approved way to define boolean variables is with "bool," then?
>>> ok, that makes sense. i was asking since that would be the obvious
>>> return type of something like "is_power_of_2()", of course.
>>>
>>>> There is also 'true' and 'false' defined (enum'ed) in
>>> include/linux/stddef.h.
>>>> A few file-systems, including ntfs, has been converted to this one.
>>> ah, yes, i see that now. it might be worth submitting a short patch
>>> to update "CodingStyle" to mention all of this, if this is in fact the
>>> consensus.
>> Before you'll decide whether consesus was reached, read thread
>> when TRUE and FALSE consolidation patch was first introduced.
> You mean the one started by akpm on March 16'th? There were much about 
> people who wanted FALSE/TRUE converted to 0/1. But since there is those 
> who wants booleans then a generic one is preferable, don't you think?
>> Bonus points for getting a warning on this code:
>>
>> void f(void)
>> {
>> bool foo = 42;
>> }
> Hint: false is 0, true is !false (so that statement is actually correct. 
> But if you check "foo", you will find the value 1 :) )
> But we have potential bugs because of some "self-made" booleans. For 
> example:
> 
> typedef boolean_t int;
> 
> #define FALSE 0
> 
> #define TRUE  1
> 
> ...
> 
> boolean_t foo = 42;
> 
> 	if (foo =TRUE) {
> 
> 	...
> 
> 
> /Richard Knutsson
> 
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