Re: Restricted unsigned integer range would have been better?

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Date	Wed, 01 Aug 2012 08:18:00 -0400
From	pete <pfiland@mindspring.com>
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Subject	Re: Restricted unsigned integer range would have been better?
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Ben Bacarisse wrote:
> 
> David Brown <david@westcontrol.removethisbit.com> writes:
> 
> > On 01/08/2012 06:18, pete wrote:
> >> Philip Lantz wrote:
> >>>
> >>> David Brown wrote:
> >>>> Les Cargill wrote:
> >>>>> Keith Thompson wrote:
> >>>>>> Les Cargill writes:
> >>>>>>> Type conversions must be made explicit.
> >>>>>>
> >>>>>> I presume that's meant as advice, not a language rule.
> >>>>>
> >>>>> Sorry - yes, it's advice.
> >>>>
> >>>> Good advice.
> >>>>
> >>>> For my work, it is more than advice - it is a style rule,
> >>>> and I enforce
> >>>> it with compiler warnings (-Wconversion -Wsign-conversion in gcc).
> >>>
> >>> Do you really? Would you use casts in situations like these?
> >>>    1. char c = 'x';
> >>>    2. int *p = malloc(N * sizeof *p);
> >>>    3. free(p);
> >>>    4. printf("%c\n", c);
> >>>    5. while (*s != '\0')
> >>>           n = n * 10 + (*s - '0');
> >>>
> >>> I would find them to be undesirable clutter.
> >>
> >> I was thinking the same thing.
> >>
> >> And I think you meant to imply
> >> that (*s) is an expression of type char.
> >>
> >> If n is of type int and also not negative,
> >> then you could write without having to use parentheses
> >>      n = n * 10 - '0' + *s;
> >> with no possibility of overflow.
> 
> I don't understand that.  Did you mean "and also unsigned" rather than
> "and also not negative"?

No. 
It reminded me of a line from a toy atoi 
that I once wrote as an exercise.



int 
a_toi(const char *nptr)
{
    int n;

    n = 0;
    while (isspace(*nptr)) {
        ++nptr;
    }
    if (*nptr != '-') {
        if (*nptr == '+') {
            ++nptr;
        }
        while (isdigit(*nptr)) {
            n = 10 * n - '0' + *nptr++;
        }
    } else {
        ++nptr;
        while (isdigit(*nptr)) {
            n = 10 * n + '0' - *nptr++;
        } 
    }
    return n;
}

-- 
pete

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