Re: Issue: compare-strings

[Eli Zaretskii <eliz@gnu.org>]

> From: "Stephen J. Turnbull" <stephen@xemacs.org>
> Date: Wed, 23 Dec 2009 12:32:55 +0900
> 
> We have the following report on xemacs-beta.  I would like a
> clarification as to the intended behavior of `compare-strings' for
> arguments out of range.  The behavior of Emacs makes more sense to me.
> It seems silly to force users to check length of variable strings to
> avoid errors in cases like
> 
>     (compare-strings "the other string is too short" "the" 0 9 0 9)
> 
> Marcus Harnisch writes:
> 
>  > `compare-strings', a primitive added in 21.5.9 mainly for GNU
>  > compatibility as far as the ChangeLog says, is *not* compatible to the
>  > same function in Emacs 22.2.1 (Ubuntu 9.10 version). Not sure if they
>  > changed `compare-strings's behavior since we added it.
>  > 
>  > We create an args out of range error when the positions don't seem to
>  > make sense (e.g. END is beyond length of the string) -- GNU doesn't.
>  > 
>  > In any case, the behavior in such cases is not specified.

It's quite clear from the Emacs implementation that the behavior is
intentional:

  end1_char = SCHARS (str1);
  if (! NILP (end1) && end1_char > XINT (end1))
    end1_char = XINT (end1);

  end2_char = SCHARS (str2);
  if (! NILP (end2) && end2_char > XINT (end2))
    end2_char = XINT (end2);

According to "cvs annotate", this code did not change since April
1998, when this function was introduced.