Thanks, Jim...
Yeah - my example as a typo - I meant "<< 8", not "<< 256"... I used
the wierd shift example because the shift operator was documented as
using "ints", but when I use it in a direct assignment, it seems to
correctly use 32-bits.
SO my big question - if "int" is 16-bits, does that mean all constant
math is 16-bits?
For example:
#define LONG1 262144L // people say this works... (no overflow)
#define LONG2 (262143L + 1L) // will this work? Or will the "+" convert
to 16-bits?
Thanks!
- Jeff
Jim Schram wrote:
>
> At 7:43 PM -0400 2000/08/17, DIAMOND JEFF wrote:
> >It makes sense that on the Palm, ints are 16-bit, not 32-bit.
>
> Integers are whatever size you tell the compiler they are. This isn't unique to the
>Palm OS...
>
> >But what I didn't catch is that in macros, such as:
> >
> >#define MY_FLAG (32768 << 256)
> >
> >UInt32 flags |= MY_FLAG;
> >
> >Everything will act like it's working OK -> in fact, all the normally
> >"integer math" functions such as (a << b) still work in 32-bits.
> >
> >But the #defines don't. The #define above will only contain the low
> >word of the value, and since you can't see the value of a define in the
> >debugger, all you notice is that values and branches aren't working
> >right.
>
> Newcomers to C must ALWAYS remember that #defines are character-by-character
>replacements of the original C code, not compile-time macros like inline functions.
>You'll have the same problem above whether you use #defines or enter the constants
>directly into the source -- integer overflow is (almost) always silent.
>
> >The best way I found around this was just to check the USE 4 BYTE INTS
> >option.
>
> The example above is rather odd, in that one can't left shift *any* supported
>integer size 256 times and get a non-zero result. But regardless, a better solution
>all-around is to quantify the size of the naked constant by adding L after the
>constant to make it a long integer (e.g. 32768L) or by explicitly casting it to the
>desired size (e.g. (UInt32)32768).
>
> Regards,
>
> Jim Schram
> Palm Incorporated
> Partner Engineering
>
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