Re: !!, what is it?

Charlie Gordon wrote: 
"Kenneth Brody" <kenbrody@xxxxxxxxxxx> wrote in message
news:4324D57D.44516C35@xxxxxxxxxxxxxx

Flash Gordon wrote:

Cafer ÅzimÅYek wrote: 

[...]

I think, C standarts says something about logical operations resusts;
if the result is false, it's value is 0 (zero). if the result is true,
it's value is non-zero (like -2, -1, 2, 3, ...). So, it must NOT be
one. This difference has seen according to compiler or target
platform.


Incorrect. The result of any logical operator is *always* 0 or 1 and
this is defined by the standard. What probably has you confused is that
any non-zero value will act as true, so all the values you quote will
act as true. However, I repeat, the boolean operators will never return
any value other than 0 or 1 on *any* implementation.


[...]

Well, any C89 or later, I assume.  I've worked on platforms (prior to
1989) where boolean expressions were 0 or -1.


You must have been programming in Basic!

No C implementation ever used -1 as the value of 0==0 

As an aside:
I recall seeing some platform specific headers which went for the
all-bits-one representation of "true" -- but the C implementations
gave 1 for !!TRUE as well...


One other explanation for this misunderstanding is that you may have been using
1 bit bitfields: it is implementation defined whether these have values 0 and 1
or 0 and -1.  As far as I recall, C99 did not change that.


Naive question after having a look at C99, 6.7.2.1:
Does this ambiguity only hold for "int" bitfields or also for
"signed int" bitfields?

Cheers
 Michael
--
E-Mail: Mine is an   /at/ gmx /dot/ de   address.
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