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    SubjectRe: double exclamation (!!) suckage in the kernel

    On May 25 2007 14:14, David Miller wrote:
    >
    >WHat is with multiple people asking about "!!" all of a
    >sudden today?
    >
    >> 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?
    >
    >"!!" is used in contexts where pointers might be being
    >tested as well as plain integers, the "!!" turns a pointer
    >into the equivalent integer boolean for testing.
    >
    >NULL pointers become 0
    >non-NULL pointers become 1

    Though,
    if(!!ptr)
    is effectively the same as
    if(ptr)

    !! is mostly used where non-zero values need to be mapped to 1.
    Not so much in logic expressions (if,while,etc.) but in arithmetic
    (who'd do that?).

    Jan
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