Re: demo for using of qsort from lib and a little problem with it - Gpc

11 Sep 1997


      Hallo, Sven!  Hello, everybody!
According to Sven Hilscher:
...
[...]
type
  TestType = Integer; { works with Real, ShortInt, Integer, LongInt }
                      { crashs with Byte }
[...]
function CompNum(var e1, e2: TestType):Integer;
Var
  r : Real;
begin
  r       := e1 - e2;
  CompNum := Round(r);
end;
Consider this with "TestType = Byte", then in `CompNum' we are subtracting
two `Byte' variables from each other.  GPC chooses the result type to be
`Byte' again, so the result is never negative.
When I convert them to `Integer' by writing
r:= Integer ( e1 ) - Integer ( e2 );
it works.  (First it did not work because of a bug in conversions among
integer types, but I could fix this.;-)
However, is this the correct behaviour?  Or should the result type of a
subtraction be the "nearest" signed integer type - `ShortInt' in this
example?  Then, what to do when subtracting two `LongestCard's, especially
in cases like "$FFFFFFFFFFFFFFFF - 2" where the result does not fit in
`LongestInt'?
BTW, Sven, this type casting problem does of course *not* explain the
crash you have observed when calling `qsort' on an array of bytes.  :-(
Confused,
Peter
Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer
peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201]
 maintainer GNU Pascal [970714] - http://home.pages.de/~gnu-pascal/ [970125]