Extra warning

Extra warning

[Jeremy Sanders]

Hi,

gcc-3.1 doesn't seem to warn for the following code (even with
-Wconversion -W -Wall).

  unsigned a;
  double c;
  a = 10;
  c = -10 - a;

Which makes c 4294967276.00 rather than -20. It also doesn't warn for:

  unsigned a;
  int b;
  double c;
  a = 10;
  b = -10;
  c = b - a;

(which of course would be harder to warn for).

Am I missing the appropriate warning option? Would it be sensible/possible
to warn for the promotion of obvious negative integers to unsigned?

Perhaps int-unsigned should have a warning. (int+unsigned usually works if
int is -ve, but probably not according to the standard!).

Thanks

Jeremy

-- 
Jeremy Sanders <jss@ast.cam.ac.uk>   http://www-xray.ast.cam.ac.uk/~jss/
X-Ray Group, Institute of Astronomy, University of Cambridge, UK.
Public Key Server PGP Key ID: E1AAE053

Re: Extra warning

[Neil Booth]

Jeremy Sanders wrote:-

> Hi,
> 
> gcc-3.1 doesn't seem to warn for the following code (even with
> -Wconversion -W -Wall).
> 
>   unsigned a;
>   double c;
>   a = 10;
>   c = -10 - a;
> 
> Which makes c 4294967276.00 rather than -20. It also doesn't warn for:
> 
>   unsigned a;
>   int b;
>   double c;
>   a = 10;
>   b = -10;
>   c = b - a;
> 
> (which of course would be harder to warn for).

If you'd really like this addressed at some time in the future,
please file a PR (gcc.gnu.org/bugs.html).  Otherwise it will be
forgotten.

Neil.