[DUG] Is it a bug in latest version of Delphi? - Solution

[Jolyon Smith]

There was no change in the “Windows standard”.  It’s a simple error in some poorly implemented error handling code added to the VCL at some point (subsequently fixed in combo boxes, but not listboxes – as of D2006).

 

You needn’t have waded through all the replies to find that the answer was provided.  The answer came very quickly… what then followed was a great deal of pointless and diverting/misleading speculation as to other possible explanations that disregarded the fact that the answer was very quickly apparent from an inspection of the VCL source.

 

 

FYI - Your “multiple by 2” solution worked because it transformed a stored value of “-1” into “-2”, which then avoided the collision between that value (-1) and the Windows “error” code and thus avoided the problem caused by the overly-helpful and incorrectly implemented error handling code in the VCL.

 

 

 

From: delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz] On Behalf Of Rohit Gupta
Sent: Wednesday, 24 February 2010 9:55 a.m.
To: NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Is it a bug in latest version of Delphi? - Solution

 

Sinu,

I dont know if its been answered satisfactorily.  There are too many replies to wade through.  I recall that along the way Windows standard changed from 0 being a null pointer to -1.  I had to change some of my code in stringlist to work.  I think my solution was to just multiply by 2 and then store it.  Found my note - it happened in 2003.  My conclusion now, is that its a combination of windows version/updates and version of Delphi that causes this issue.

Rohit

sinu sudhakaran wrote: 

Hi all,

I came across a strange bug(???) in latest versions of Delphi.

Have a look at the following code.

procedure TForm1.Button1Click(Sender: TObject);
var
i : integer;
begin
ComboBox1.Clear;
ComboBox1.Items.AddObject('All Locations', TObject(-1));
ComboBox1.Items.AddObject('Only this Location', TObject(0));
ComboBox1.Items.AddObject(Test Location', TObject(1));

i := Integer(ComboBox1.Items.Objects[0]);
showmessage(inttostr(i));
end;

When I tried to run this code in Delphi 6 and Delphi 2007 , I am getting List Index out of bounds[0] error in Showmessage. When I tried -2, -3, -4… instead of -1 object , I got the proper output without any 
List index out of bounds error. Also I am getting -1 without any error when I tried this code in Delphi 3. 

Is it a bug in latest version of Delphi ? Any help is appreciated.

Thank you

Regards,
Sinu


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