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Integer expression to boolean Operator !!

 
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ejeuler



Joined: 18 May 2011
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Integer expression to boolean Operator !!
PostPosted: Wed May 18, 2011 4:27 pm     Reply with quote
Hi All,

I've found examples of CCS C code using a "!!" operator, and comments indicating this converts an integer expression to boolean representation. I can find no references to this operator in my PCM compiler manual, older and newer CCS compiler manuals, Nigel Gardner's PIC Micro MCU C book, or searches in this forum or Google. Can someone please point me to where this operator is documented?

Thanks much!

ejeuler
dyeatman



Joined: 06 Sep 2003
Posts: 1933
Location: Norman, OK

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PostPosted: Wed May 18, 2011 5:14 pm     Reply with quote
...

Last edited by dyeatman on Wed May 18, 2011 8:34 pm; edited 2 times in total
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Wed May 18, 2011 7:24 pm     Reply with quote
Here is another forum thread that discuss the double-not:
http://stackoverflow.com/questions/248693/double-negation-in-c-code
ejeuler



Joined: 18 May 2011
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PostPosted: Wed May 18, 2011 7:46 pm     Reply with quote
Thanks PCM programmer....


That link had some excellent discussion points/suggestions regarding integer/boolean conversions.


Thank you for taking the time to share this info!

ejeuler
FvM



Joined: 27 Aug 2008
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PostPosted: Wed May 18, 2011 11:06 pm     Reply with quote
Quote:
comments indicating this converts an integer expression to boolean representation

By C specification, integer operands can be used in a boolean expression. So the construct would be pretty useless. The discussion is referring to reasons as avoiding warnings with some compilers, or is speculating that if might serve a purpose somehow.

With CCS, I remember cases, at least with V3.xxx compilers, where the construct would help as bug workaround. A logical "&&" of int1 operands had been partly carried out as a & of the respective memory bytes and a bitmask, evaluating always false.
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