left shift then right shift an unsigned int

[Wenjie]

Hello, for the following code:
unsigned int var = 0xFF2277F0UL;
unsigned char take2 = (var << 8) >> 24;
Is there any pitfall about the shift? (get '22' i.e. 34 or '"' as wanted)


Thanks and best regards,
Wenjie

[Bob Hairgrove]

Re: left shift then right shift an unsigned int

On 11 Jul 2003 04:07:43 -0700, gokkog@yahoo.co m (Wenjie) wrote:
[color=blue]
>Hello, for the following code:
> unsigned int var = 0xFF2277F0UL;
> unsigned char take2 = (var << 8) >> 24;
>Is there any pitfall about the shift? (get '22' i.e. 34 or '"' as wanted)[/color]

It looks OK to me...


--
Bob Hairgrove
rhairgroveNoSpa m@Pleasebigfoot .com

[Ron Natalie]

Re: left shift then right shift an unsigned int


"Greg Schmidt" <gregs@trawna.c om> wrote in message news:6k0ugvsn92 ecngaglqeqlfcs4 1s5iane4e@4ax.c om...[color=blue]
> On 11 Jul 2003 04:07:43 -0700, gokkog@yahoo.co m (Wenjie) wrote:
>[color=green]
> >Hello, for the following code:
> > unsigned int var = 0xFF2277F0UL;
> > unsigned char take2 = (var << 8) >> 24;
> >Is there any pitfall about the shift? (get '22' i.e. 34 or '"' as wanted)[/color]
>
> As others have said, it looks fine, but it seems to me that
> unsigned int var = 0xFF2277F0UL;
> unsigned char take2 = (var >> 16) & 0xFF;
> might be clearer as to the purpose, and easier to modify down the road.[/color]

I don't know what your assumptions are (since you hardcoded a lot of numbers
here), but if char is an 8 bit quantity, even the & 0xFF is superfluous.

[Ron Samuel Klatchko]

Re: left shift then right shift an unsigned int

gokkog@yahoo.co m (Wenjie) wrote in message news:<d2804eb3. 0307110307.1f7e 3d40@posting.go ogle.com>...[color=blue]
> Hello, for the following code:
> unsigned int var = 0xFF2277F0UL;
> unsigned char take2 = (var << 8) >> 24;
> Is there any pitfall about the shift? (get '22' i.e. 34 or '"' as wanted)[/color]

One pitfall is that it is dependent on the size of an unsigned int to
get the expected results. If unsigned int holds more then 32 bits,
the << 8 won't do the intended stripping.

Even worse, I think it isn't clear what this code is doing. I can
picture someone accidentally changing the code to:

var >> 16;

If I were writing the code, I'd making the stripping more explicit.

(var >> 16) & 0xFF

or possibly:

(var & 0xFF0000) >> 16

samuel