Re: printf \xNNN

Paul Eggert <eggert@xxxxxxxxxxx> wrote:
>> From: Jim Meyering
>> Date: Wed Nov 6 05:12:26 2002
>
>> That looks like a bug.  It is at least 10 years old, since that code
>> was there for my initial cvs import on Nov 1, 1992.
>
> I don't think it's a bug, since it's how printf behaves in the C language.
> For example, if I write this program:
>
>       #include <stdio.h>
>       int main (void)
>       {
>         return printf ("(\x00000040)\n");
>       }
>
> the output is "(@)".  The GNU coreutils manual says that GNU printf is
> supposed to behave like the C printf function, so I'd say that the
> 1992 behavior was correct.

Hi Paul,

Thank you for the patch.  However,
I was surprised to see that according to POSIX,

  http://www.opengroup.org/onlinepubs/007904975/utilities/printf.html

printf does not recognize hexadecimal constants:

  Hexadecimal character constants as defined in the ISO C standard are not
  recognized in the format operand because there is no consistent way to
  detect the end of the constant. Octal character constants are limited
  to, at most, three octal digits, but hexadecimal character constants
  are only terminated by a non-hex-digit character. In the ISO C standard,
  the "##" concatenation operator can be used to terminate a constant and
  follow it with a hexadecimal character to be written. In the shell,
  concatenation occurs before the printf utility has a chance to parse
  the end of the hexadecimal constant.

The current implementation is consistent (at least in this respect)
with the one in bash's built-in printf command, so I think it's best
to leave it the way it is, at least for the upcoming coreutils-5.0.
What do you think?

Also, if coreutils' printf does eventually accept arbitrarily
long hexadecimal character constants, it should warn when the value
would be out of range, and should probably align with the C behavior
of ignoring all but the last two hex digits.

> Here is a proposed patch to revert the behavior, and fix some texinfo
> formatting bugs.  You also need to remove tests/misc/printf-hex, but I

Thanks!
I've fixed those formatting bugs.

> didn't do this (sorry, I've gotta run....).
>
> 2003-03-24  Paul Eggert  <eggert@xxxxxxxxxxx>
>
>       * doc/coreutils.texi (printf invocation): \x can take any
>       number of digits.
>       * src/printf.c (print_esc): Implement this.
>       This undoes the 2002-11-06 patch.