Robert Nordier <[EMAIL PROTECTED]> wrote:
>
> Thomas David Rivers wrote:
>
> > > > So why is using a "char" as an array subscript wrong? I had always
> > > > avoided it because the compiler complained and that was good enough
> > > > for me.
> > >
> > > Because your char value could be negative and end up referencing memory
> > > before your array start. Mainly a problem with the ctype macros and
> > > high-ascii characters.
> > >
> >
> > That's an interesting reason... any variable can be negative (well,
> > except for the unsigned types...) - what's so interesting about
> > `char'? Is it simply ctype macros that are the concern, or something
> > "bigger"?
>
> What's interesting about char is that it's implementation defined
> whether "plain" char is the equivalent of "signed char" or "unsigned
> char" (or even something else).
>
> So, given an 8-bit, two's complement implementation of char, the
> statement
>
> char i = 128;
>
> may cause 'i' to end up as -128 or 128, for example.
>
> An implementation-defined value to your subscript is almost never
> useful, so this kind of behavior does warrant a warning. You'll
> notice gcc doesn't warn if explicitly signed or unsigned chars are
> used as subscripts, as then there is no uncertainty.
>
> --
> Robert Nordier
Ah - yes! That makes perfect sense... when you consider
that `char' all alone can be signed or unsigned...
Thanks for the explanation!
- Dave Rivers -
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