From -6536656620649605495 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,8466591b9cd11017 X-Google-Attributes: gidf78e5,public From: Christopher Smith Subject: Re: C++ 'philosophy' question, Constructors/Destructors Date: 2000/07/18 Message-ID: #1/1 X-Deja-AN: 647349890 Approved: Fergus Henderson , moderator of comp.std.c++ References: <394a5536.29331042@news.columbia.edu> X-Priority: 3 X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Trace: mail2news.demon.co.uk 963845697 mail2news:11687 mail2news mail2news.demon.co.uk Organization: SBC Internet Services X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-MSMail-Priority: Normal NNTP-Posting-Date: Sat, 15 Jul 2000 01:27:58 PDT Newsgroups: comp.std.c++ Ken Hagan wrote in message news:newscache$omc9wf$h71$1@firewall.thermoteknix.co.uk... > "Leonid Portnoy" wrote in message > news:394a5536.29331042@news.columbia.edu... > > > >> If there could be many destructors, I would specify, in my base Bitmap >> class, a second destructor which would not attempt to free memory. >> Let's say it would be called if constructor #2 of the base class was >> used to create the object. This constructor would not allocate any >> memory but just initialize other members. > >> Then in the derived class's constructor, I would specify how to create >> the base class (by calling constr. #2), and then when destroying my >> derived class it would automatically call the appropriate destructor >> (the one that doesn't free memory) of the base class... >The second constructor and destructor are only needed if someone >goes on to write the derived class. I have no objection to writing >a class with a view to deriving certain related classes from it, but >if I do this too much, I lose encapsulation. (The needs of the >derived classes are now driving the design of the base class.) And this second constructor does not fully construct the object -- it is broken as the memory doesnt point to anything! Another problem is that absent a "assign destructor" statement of some kind the only logical counterpart to 1 destructor is to have 1 per constructor. And this makes the normal case of many constructors all going to the same internal state require tons of identical code be maintained. Ick. And if you really want to make code that changes the behavoir of the base class variables, while not nice you can just change the base class to allow you to do this with some kind of flag variable. Of course, the best solution if the needs of the class have changed such that memory mgmt of the buffer should not be in the base is to create a manager class family derived from a common base. Then you can use virtual functions and inheritance to have different types of buffers be handled 'the same way' from our class' point of view but correctly, too. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]