Messages in this thread | | | Date | Fri, 25 May 2007 21:41:27 +0100 | From | Al Viro <> | Subject | Re: double exclamation (!!) suckage in the kernel |
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On Sat, May 26, 2007 at 01:53:59AM +0530, Satyam Sharma wrote: > Hello, > > Grepping through the sources I found 500+ occurrences of double > exclamation marks before identifier names (such as !!x -- I took care > to ignore occurrences of !! inside comment blocks, because there > are plenty of that sort too). > > !! are to be found even in the definitions of common macros such as > likely() and unlikely(), which hundreds of eyes must have seen over > the last year or so ... > > Are all these occurrences merely the debris of > s/something/!notsomething/g kind of patches or is there some > dark, unknown C / gcc wizardry I have absolutely no clue of?
That's a question for a quiz in introductory course on C: what type should x have for !!x to be a valid expression? what will be the type of result? what are the possible values of the result? describe which values of x correspond to each possible value of !!x
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