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.
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