No, assuming the constructors of neither the derived or base classes were NOT called, meaning that no objects created in the constructors would be created, then an instance of TDerived would occupy 16 bytes (12 from TBase plus 4 from TDerives FAge). Assuming that TDerived's constructor called TBase's constructor through "Inherited", then TDerived would occupy 552 bytes (12 from TBase + 536 from the TButton created by TBase + 4 from TDerived's FAge). Remember that TDerived's fields are just an extension of TBase to TDerived only adds an additional 4 bytes, not another 12.
Again, TDerived's footprint is just a 4 byte extension of TBase's 12 bytes. So when the TDerived instance is freed, 16 bytes of memory are reclaimed. If TDerived's destructor does not call the TBase's destructor, then the 536 TButton instance will not be freed causing a 536 byte leak. Two books that really helped me when I started were: "Secrets of Delphi 2" by Ray Lischner ISBN 1-57169-026-3 It was published by Waite Group Press And "Delphi Component Design" by Danny Thorpe ISBN 0-201-46136-6 Published by Addison Wesley Both books have been out of print for a long time, but I just checked on www.half.com and both books are being sold by previous owners. -----Original Message----- From: Alan Colburn [mailto:[EMAIL PROTECTED] Sent: Saturday, April 15, 2006 2:10 PM To: [email protected] Cc: [EMAIL PROTECTED] Subject: RE: Re[2]: Class constructor and destructor Scott -- What a great explanation ... thanks for posting it! As a newbie, I learned a lot. Can I ask a couple quick follow-ups? First, from your explanation it seems like when one creates a derived class instance (TDerived), including the inherited constructor, then memory is allocated for the base class. In your example, a TDerived object would occupy 16 bites and TBase would occupy 548 bites, so an instance of TDerived would require 564 bites. Is that right? Likewise, it seems like freeing TDerived, without calling an inherited destructor, would leave the instance of TBase still in memory, leaking 548 bites. Is that right? Finally, I really liked your explanation--it worked well for my learning style. Do you have any particular books or internet resources that worked well for *you* for learning about OOP and/or Delphi? I figure that something you found clear might be clear to me, too. Thanks again -- Al C. >From: "Scott Kellish" <[EMAIL PROTECTED]> _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
