Michael Van Canneyt wrote:
While finding the bug #12897 I found that a memory stream position could
be set to before the start of the file without giving an error, and
subsequent reads would appear to work (unless the position was so far
off an invalid region of memory was read). I found the precise problem
by patching TCustomMemoryStream to raise an exception if the position is
set before the start of the file. Should an exception be raised in this
circumstance, which would make finding bugs easier? Or should the
position just be set to 0, which would be more consistent with the
behaviour when going beyond the end of the stream?
I think that an exception is better. If you set the position to a non-existing
position, there is an error in your logic anyway.
Just tested with delphi
procedure TForm1.Button1Click(Sender: TObject);
var
S: TMemoryStream;
begin
S := TMemoryStream.Create;
S.Position := 10;
ShowMessage(IntToStr(S.Position));
S.Position := -1;
ShowMessage(IntToStr(S.Position));
S.Free;
end;
It shows 10 and -1.
If you do an exception or silent change of position it can cause
incompatibilities. Maybe read operation must be fixed to ignore
positions out of the range 0..Size -1?
Best regards,
Paul Ishenin.
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