Re: I suppose the idea of classes and inheritance is

"J French" <erewhon@xxxxxxxxxx> wrote

Please, Maarten, Alan, DoDi, Dr J would you test Jamie's example
and convince him that S[ Length(S) + 1 ] throws a range check
error with $R+ on a normal Delphi setup.

Well, if Delphi 2 is *not* a "normal Delphi setup" then you are
correct.

But in Delphi 2 (and perhaps in Delphi 3) S[ Length(S) + 1 ] does
not throw a range check error.

Even S[Length(S)+256] does not trigger a range check error in
Delphi 2.

I tested the following code in Delphi 1, Delphi 2 and Delphi 4 with
results as in the comments.

<CODE>
{ In D2 and D4, compiled with global range checking on AND off}

procedure TForm1.Button1Click(Sender: TObject);
Var S :String;
C :Char;
begin
{$R+}
S := 'aaaaaaaaaa'; {no StringOfChar in Delphi 1}
C := S[ Length( S ) + 1 ]; { RangeCheck Error in D4}
ShowMessage( IntToStr( Ord(C) ) );
{ in D1 shows 69 i.e. C = 'E' (random value)
in D2 Shows 0 i.e. C = #0
Does not get to here in D4}
{ Note: RANGE-CHECK MESSAGE IN D4 BUT NOT IN D1 OR D2}
{$R-}
end;

procedure TForm1.Button2Click(Sender: TObject);
var S:String;
X:Integer;
C:char;
begin
{$R+}
C:= #$FF; {Hint:..."Value assigned to C is never used"}
X := 5;
C := TestStr[X];
Label1.Caption := C;
{ RangeCheck Error in D4}
if C = #0 then
{$IfDef VER80} {Delphi 1}
MessageBeep(0);
{No beep in D1}
{$Else}
beep; { does not compile in D1}
{Beeps in D2}
{$Endif}
ShowMessage ( IntToStr( Ord(C) ) );
{ in D2 Shows 0 i.e. C = #0 but Does not get to here in D4}
{ Note: RANGE-CHECK MESSAGE IN D4 BUT NOT IN D1 OR D2}
//{$R-}
end;
</CODE>

Thus there is no String-length Range checking in Delphi 2.

Jamie once said:

i am using D3 and D7.

So if he tested in Delphi 3 (and not Delphi 7) its quite possible that
he got the results he reported.

It appears from this that Borland introduced String-length Range
checking in Delphi 4. This is quite reasonable as it protects against
access violations and I would prefer to see a Range-check error than
an AV.

Note that I get similar results to those of J French, Rob and Maarten
when I use Delphi 4.

--
Henry Bartlett
Delphi Links Page:
( http://www.hotkey.net.au/~hambar/habit/delflink.htm )




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