Subject:
|
Re: Help with pointers
|
Newsgroups:
|
lugnet.robotics.handyboard
|
Date:
|
Thu, 25 Mar 1999 21:10:51 GMT
|
Original-From:
|
Max Davies <MDAVIES@CAM.ORGnospam>
|
Viewed:
|
960 times
|
| |
|
|
Keith Hearn wrote:
>
> If you want to point to the low byte of x, you might be able to do
> something like this:
>
> int x;
> char * p; /*this assumes that a char is one byte*/
>
> p = &x;
> p++;
>
> Be warned that that is pretty non-portable code. What it actually does
> depends on how big int and char are with the specific
> compiler/machine combination, and details like byte ordering within
> words.
>
> The above all applies to "normal" C. I'm not exactl sure how IC would
> handle it.
Actually, in 'normal C', to be completely correct you would cast the
pointer
conversion to show that you really knew what you were doing, like this:
p = (char *) &x;
Unfortunately, neither the free ware IC nor IC 3.2 support this.
Here is another way to retrieve the individual bytes of an int:
lo_byte = x & 0xff;
hi_byte = (x >> 4) & 0xff;
Setting the individual bytes is a bit more complicated:
x = (x & 0xff00) | lo_byte;
x = (x & 0x00ff) | (hi_byte << 4);
If you wanted to set both bytes at the same time you could use:
x = (hi_byte << 4) | lo_byte;
These should work fine in IC and are fairly portable in that changes in
byte
ordering don't affect them. Just keep in mind that in other environments
an
int is often 4 bytes long rather than just 2.
|
|
1 Message in This Thread:
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
