On Friday, March 15, 2013 9:43 AM, Ian Abbott wrote:
> On 2013-03-15 16:16, Greg Kroah-Hartman wrote:
>> On Fri, Mar 15, 2013 at 01:15:33PM +0000, Ian Abbott wrote:
>>> --- a/drivers/staging/comedi/comedidev.h
>>> +++ b/drivers/staging/comedi/comedidev.h
>>> @@ -207,7 +207,7 @@ struct comedi_device {
>>>
>>> const char *board_name;
>>> const void *board_ptr;
>>> - int attached;
>>> + bool attached:1;
>>
>> I'm not objecting to this, but for some reason I thought that bit fields
>> could only be a 'unsigned int'. Or am I just used to C88 or some such
>> really old spec of the C standard?
>
> It's used elsewhere in the kernel in quite a few places, e.g. in
> "kernel/printk.c" for the `flushed` member of `static struct cont`.
>
> C99 certainly allows `_Bool` bit-fields (and a `bool` is a `_Bool` in
> the kernel).
In case anyone is interested...
I created a test case with 4 structs.
struct test1 {
unsigned int var0;
...
unsigned int var8;
};
struct test2 {
unsigned int var0:1;
...
unsigned int var8:1;
};
struct test3 {
_Bool var0;
...
_Bool var8;
};
struct test4 {
_Bool var0:1;
...
_Bool var8:1;
};
A quick test with gcc 4.4.5 shows this:
sizeof(test1): 36
sizeof(test2): 4
sizeof(test3): 9
sizeof(test4): 2
It appears the underlying type is an unsigned char and using
bit fields is not a problem.
Regards,
Hartley
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