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Date: Wed, 01 Aug 2012 09:57:27 -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:
> 
> pete <pfiland@mindspring.com> writes:
> 
> > Ben Bacarisse wrote:
> <snip>
> >> > On 01/08/2012 06:18, pete wrote:
> >> >> Philip Lantz wrote:
> <snip>
> >> >>>    5. while (*s != '\0')
> >> >>>           n = n * 10 + (*s - '0');
> <snip>
> >> >> 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.
> 
> Ah!  You meant that the parentheses can be removed without causing an
> otherwise avoidable overflow, I think.

Yes. That's what I meant.
Thank you.

> Both versions can overflow, but
> the "bad" version (n = n * 10 + *s - '0')
> can cause a needless overflow.

I also think I should change the condition my loop from
        while (isdigit(*nptr)) {
to 
        while (*nptr != '\0') {
similar to what Philip Lantz had.
I think that the spirit of atoi
is that it is supposed to be a simple function,
which is only to be used 
when it is known that the input won't cause any problems.

-- 
pete