Good luck with GetLastError(). There's nothing to indicate that
LB_GETITEMDATA processing will set a Windows "LastError".
And empirically I would have to say that it doesn't:
// On an empty Listbox1 ..
r := SendMessage(Listbox1.Handle, LB_GETITEMDATA, 100, 0);
if GetLastError <> 0 then
RaiseLastOSError;
if r = -1 then
ShowMessage('oops');
Will yield only the "oops" message, no OS error.
I am speculating (in this case I don't have the source for SendMessage() or
the LISTBOX wndproc) that SendMessage() isn't setting an error condition
(after all it is successfully sending a message and returning the result)
and that the LISTBOX wndproc doesn't SetLastError() when processing
LB_GETITEMDATA, at least not for an invalid item index.
> -----Original Message-----
> From: delphi-boun...@delphi.org.nz [mailto:delphi-
> boun...@delphi.org.nz] On Behalf Of Karl Reynolds
> Sent: Tuesday, 16 February 2010 3:29 p.m.
> To: NZ Borland Developers Group - Delphi List
> Subject: Re: [DUG] Is it a bug in latest version of Delphi?
>
> On Tue, Feb 16, 2010 at 3:06 PM, Jolyon Smith <jsm...@deltics.co.nz>
> wrote:
> > Win API returns -1 to indicate an error. Any error. Not a
> specific
> > error. Certainly not specifically a list index error.
>
> Pardon me for being pedantic, but while I agree with everything else
> you said, I feel the need to reiterate that -1 isn't actually returned
> to *indicate* an error (and you mentioned the conflict between an
> error result and a valid result yourself at one point). It's just the
> value returned when an error has occured. And yes, that means the VCL
> code is wrong.
>
> GetLastError... I won't say it again, promise. ;)
>
> Cheers,
> Karl
>
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