Re: [Qemu-devel] [PATCH 2/5] CODING_STYLE: add C type rules

[Avi Kivity]

 On 08/17/2010 11:09 AM, Jes Sorensen wrote:
> On 08/12/10 19:50, Blue Swirl wrote:
> > +While using "bool" is good for readability, it comes with minor caveats:
> > + - Don't use "bool" in places where the type size must be constant across
> > +   all systems, like public interfaces and on-the-wire protocols.
> > + - Don't compare a bool variable against the literal, "true",
> > +   since a value with a logical non-false value need not be "1".
> > +   I.e., don't write "if (seen == true) ...".  Rather, write "if (seen)...".
> I'd strongly discourage the use of bool in any code. It doesn't provide
> anything guarantees

It's actually better than int:

     int flag = word & BIT;

can lose the BIT if it is outside the range of an int, whereas

    bool flag = word & BIT;

will be true if BIT is set.  Not to mention the improved readability 
(which appears to be a downside to C fans).

> and you are not sure about the size of it. Using int
> is safer. IMHO bool is one of the worse examples of changes to the C
> standard :(
>
> bool foo = false;
> foo++;

What's incrementing a bool supposed to mean?  Even more true?

> if (foo == true)....

As it happens, this will succeed.

> The other thing that might be worth mentioning in the int/long section
> is that long is complicated in broken development environments such as
> Windows where it is only 32 bit :(

It's only complicated if you assume sizeof(long) == sizeof(void *).  
While we're used to it from Linux, all you need is s/long/intptr_t/ and 
you're all set.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.