A query about typeof

[Dave Hylands]

Hi ctmzb,

On Sat, Dec 24, 2011 at 10:34 AM, contemplating zombie
<contemplatingzombie at gmail.com> wrote:
> Hi,
>
> I see following code in kfifo.h
>
> typeof((fifo) + 1) __tmp = (fifo);
> [http://lxr.linux.no/linux+v3.1.6/include/linux/kfifo.h#L334]
>
> I do not understand this specific code construct. Why is it necessary
> to add 1 to fifo before getting its type?
> Is it related to some 'C' magic?

This has to do with the difference between arrays and pointers.

int *x;
int y[5];

have different types. y by itself has an array type. y + 1 is the same
as &y[1] which has an int * type.

If we assume that an int is 32 bits and an int * is 32 bits then

sizeof( typeof( x )) = 4
sizeof( typeof( y )) = 20
sizeof( typeof( (x) + 1 ) = 4
sizeof( typeof( (y) + 1 ) = 4

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com