Re: A pettiness question.

[Randy.Dunlap]

On Wed, 21 Sep 2005, Ustyugov Roman wrote:

> > Hi, All.
> >
> >     I found there are use double operator ! continuously sometimes in
> > kernel.
> > e.g:
> >
> >     static inline int is_page_cache_freeable(struct page *page)
> >     {
> >         return page_count(page) - !!PagePrivate(page) == 2;
> >     }
> >
> >     Who would like tell me why write like above?
> >
> >
> >     Thanks in advanced.
> >
> >
> > Liyu
>
> For example,
>
> 	int test = 5;
> 	!test will be  0,  !!test will be 1.
>
> This give a enum of {0,1}. If test is not 0, !!test will give 1, otherwise 0.
>
> Am I right?

Yes.  I think of it as a "truth value" predicate (or operator).

-- 
~Randy
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