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Subject: Re: [PATCH] Re: sscanf("-1", "%d", &i) fails, returns 0
From: Henning Schmiedehausen <hps@intermeta.de>
To: "Randy.Dunlap" <rddunlap@osdl.org>
Cc: linux-kernel@vger.kernel.org
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Date: 11 Nov 2002 10:27:53 +0100
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Hi,

On Mon, 2002-11-11 at 04:05, Randy.Dunlap wrote:
> On Sun, 10 Nov 2002, Henning P. Schmiedehausen wrote:
> 
> | "Randy.Dunlap" <rddunlap@osdl.org> writes:
> |
> | >+		digit = *str;
> | >+		if (is_sign && digit == '-')
> | >+			digit = *(str + 1);
> |
> | If signed is not allowed and you get a "-", you're in an error case
> | again...
> 
> Yes, and a 0 value is returned.
> IOW, asking for an unsigned number (in the format string)
> and getting "-123" does return 0.
> 
> What should it do?

I would model this after user space. (Which does strange things:

--- cut ---
#include <stdio.h>

main()
{
  char *scan = "-100";
  unsigned int foo;
  int bar;

  int res = sscanf(scan, "%ud", &foo);

  printf("%s = %ud = %d\n", scan, foo, res);

  res = sscanf(scan, "%ud", &bar);

  printf("%s = %d = %d\n", scan, bar, res);

}
--- cut ---

% gcc -o xxx xxx.c
./xxx 
-100 = 4294967196d = 1
-100 = -100 = 1

Hm, so I guess, yes, a warning message would be nice IMHO. Returning an
error code would IMHO moot, because noone is checking these codes
anyway.

	Regards
		Henning



> This function can't return -EINPUTERROR or -EILSEQ.
> (since it's after feature-freeze :)
> And the original problem was that a leading '-' sign on a
> signed number (!) caused a return of 0.  At least that is fixed.
> 
> So now the problem (?) is that a '-' sign on an unsigned number
> returns 0.  We can always add a big printk() there that
> something is foul.  Other ideas?


-- 
Dipl.-Inf. (Univ.) Henning P. Schmiedehausen       -- Geschaeftsfuehrer
INTERMETA - Gesellschaft fuer Mehrwertdienste mbH     hps@intermeta.de

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