Re: [DUG] TStringList.FList

Thu, 16 Sep 2004 21:28:19 -0700 

Hi Dennis

Thanks for the hack. It seems to be working in some respect but I can't access the data in the FList array for some reason. I'm getting either garbage or an access violation.

MasterDetails := TStringList.Create;
Index := MasterDetails.Add('ABC');
showmessage(THackStringList(MasterDetails).FList^[Index].FString);

THackStringList is defined as you specified.

I can't work out what is wrong with this.  Anyone?

Thanks,
Ross.

----- Original Message ----- From: "Dennis Chuah" <[EMAIL PROTECTED]>
To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]>
Sent: Friday, September 17, 2004 3:18 PM
Subject: Re: [DUG] TStringList.FList


Then I'm afraid RM is incorrect! This technique works on the principle that
the new class declares a memory footprint that is identical to TStringList.
What we are doing is casting the reference to the TStringList as the new
class and in the process, fooling the compiler into thinking that we are
accessing a genuine public member.

DC>THackedStringList = class(TStrings)
public
    FList: PStringItemList;
end;

According to RM, this is not possible. I had already coded it this way 
assuming it would work, but apparently only Protected members can be made
visible, not Private.

----- Original Message ----- From: "Ross Levis" <[EMAIL PROTECTED]>
To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]>
Sent: Friday, September 17, 2004 2:44 PM
Subject: Re: [DUG] TStringList.FList


RM> No its not possible to access private members without being in the same
pas. umm couldn't you just store an array of stringlist positions instead
or pointers to a string

I can't store the Index positions because it's a sorted list and they will
change as more items are added.

DC> Why can't you use at the Objects property?

The Objects property is already being used, and anyway, this is referencing
in the wrong direction. I need a pointer to the string list not the other
way around. It's a plan I came up with to reduce memory requirements and
provide fast retrieval for upwards of 50,000 strings.

DC>THackedStringList = class(TStrings)
public
   FList: PStringItemList;
end;

According to RM, this is not possible.  I had already coded it this way
assuming it would work, but apparently only Protected members can be made
visible, not Private.

Cheers,
Ross.
----- Original Message ----- From: Robert martin
To: NZ Borland Developers Group - Delphi List
Sent: Friday, September 17, 2004 2:20 PM
Subject: Re: [DUG] TStringList.FList


 No its not possible to access private members without being in the same
pas.  umm couldn't you just store an array of stringlist positions instead
or pointers to a string (not knowing what you are trying to do).

 I would look for other ways to implement your functionality or build your
own TStringList by copying the source out.  Don't change classes.



 Rob Martin
 Software Engineer

phone 03 377 0495
fax 03 377 0496
web www.chreos.com
Wild Software Ltd
----- Original Message ----- From: Ross Levis
To: NZ Borland Developers Group - Delphi List
Sent: Friday, September 17, 2004 2:02 PM
Subject: [DUG] TStringList.FList


Is it possible to make visible a private variable in an ancestor class?
I need to obtain the pointer to the FList record array in a TStringList so I
can store the pointer to each string in the array.

   If not then I may be faced with modifying the Classes unit or taking a
copy of the TStringList code from the unit and making my own TStringList.
Any ideas?

   Cheers,
   Ross.


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