Why double not? (!!)

[Era Scarecrow via Digitalmars-d-learn]

On Saturday, 19 November 2016 at 04:54:22 UTC, Xinok wrote:
> On Saturday, 19 November 2016 at 03:52:02 UTC, Ryan wrote:
>> Why do I see double `not` operators sometimes in D code? An 
>> example it the last post of this thread.
>>
>> http://forum.dlang.org/thread/ktlpnikvdwgbvfaamrsk@forum.dlang.org
>>
>>> import core.sys.windows.windows : GetConsoleCP;
>>> bool hasConsole = !!GetConsoleCP();
>>
>> Thanks.
>
> It's a more concise way of writing:
>     GetConsoleCP() != 0
>
> You can do this in C/C++ as well (and presumably some other 
> languages).

  Hmmm... thinking about it, it does make perfect sense. The first 
! converts it to bool, the other inverts it back to it's 
positive/negative state.

  Although it's a combination of logic I wouldn't have through of 
unless I saw it. But testing the result on any number (float, 
double or real) won't be precise and would take far longer (and 
more complicated) using another method.