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  • From: "Lowden, James K" <LowdenJK AT bernstein.com>
  • To: "FreeTDS Development Group" <freetds AT lists.ibiblio.org>
  • Subject: Re: [freetds] FW: dblib patch
  • Date: Fri, 1 Jul 2005 13:58:56 -0400

> From: Ian Ashley
> Sent: Friday, July 01, 2005 12:13 PM
>
> > for (t = istr + ilen; --t > istr && *t == ' '; )
> > *t = '\0';
> > return t - str + 1;
> >
> > About char/varchar is the same, server fill needed spaces if
> > necessary.
> >
> > freddy77
>
> Shouldn¹t it be
>
> for (t = istr + ilen; --t >= istr && *t == ' '; )
> *t = '\0';
> return t - str + 1;
>
> to cope the string being all spaces. I assume the return value is
> meant to be the number of characters excluding the '\0'

No, Frediano is right. The loop exits when --t > str is false or when *t ==
' ' is false.

Whether or not t points to a blank, if t == str we don't want to return a
length of zero. We want to return a length of 1, else the server will
interpret ' ' as NULL.

If the input is 'abc ', the loop exits when *t == 'c'. At that point, t -
str == 2, telling the caller to trim the string to 'ab'. Hence t - str + 1,
or (as I think is slightly clearer) ++t - str.

Your loop would exit when t < str, in which case t - str would be a really
big number, to which adding 1 would (on most architectures, I think) yield
zero. Not that it matters in this case, but I don't know what ANSI has to
say about pointer arithmetic overflow.

--jkl


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