[PATCH 1/4] staging: comedi: make 'dev->attached' a bool bit-field

[Ian Abbott]

On 2013-03-15 16:43, H Hartley Sweeten wrote:

> I guess the real question is, what's the underlying type of a bool?
> It must be an unsigned "something" or the compiler would complain.
> And does assigning a bit field to the bool actually save any space?
>
> <linux/types.h>	typedef _Bool bool;
>
> _Bool is a standard type in C99
>
> I found this:
>
> http://gcc.gnu.org/ml/gcc-patches/2000-10/msg01127.html
>
> But honestly still don't know what a _Bool is... :-)

It's a special unsigned integer type.  Converting any scalar value to 
_Bool should produce 0 or 1 (false or true).  Assigning a scalar value 
to a _Bool involves such a conversion so the value 0 or 1 should be 
stored no matter what try and store in there.  _Bool bit-fields aren't 
the same as the _Bool type though, and the standard only says what shall 
happen if you store the value 0 or 1 in there and doesn't say what 
happens if you store a different value in there.

Search for n869.pdf if interested.  That's only a draft of the C99 
standard, but is the closest you'll find to the actual standard without 
shelling out the dosh for the actual standard.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk>        )=-
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