From -1029196786835884244 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,176c9dc06a6729eb X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-03-24 20:45:01 PST Path: archiver1.google.com!news1.google.com!sn-xit-02!sn-xit-01!supernews.com!news.alt.net!comp-std-cpp-robomod!not-for-mail From: "James Kuyper Jr." Newsgroups: comp.std.c++ Subject: Re: why doesn't delete NULL the pointer? Date: Sun, 24 Mar 2002 22:41:26 CST Organization: Giganews.Com - Premium News Outsourcing Lines: 56 Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <3C9DD259.621506AB@wizard.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-Path: X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Accept-Language: en NNTP-Posting-Date: Sun, 24 Mar 2002 07:10:23 CST X-Trace: sv3-mZYbuqgivqWzASXSnYGviSjK8CUpPhHtGFgdFcOOYmGqbDjh1Ut6EvN13aO2xZQZj7AO4DUaDN4sc78!HALfY+v7e/4SyteF0/QxGjbcFfSCFyEcVTGp7bUTtu19Vph4aMXSbEzh0XYJ X-Complaints-To: abuse@GigaNews.Com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-Info: Please be sure to forward a copy of ALL headers X-Abuse-Info: Otherwise we will be unable to process your complaint properly Xref: archiver1.google.com comp.std.c++:10161 Pedro Sam wrote: > > Hi all, > > I'm curious about the delete operator and NULL pointers. Why doesn't > the standard require that the delete operator to set the pointer's value > to NULL? > > If the pointer is NULL, then if someone comes along and try to access > that pointer, it would crash with a segfault, instead of reading garbage > ( or even worse, write over some memory ). > > Crash early is a Good Thing(TM) right? > > I would appreciate any comments. > > p2sam There's an old principle that goes back to the design of C, and continues into C++: you don't pay for what you don't use. Most of the time, well-designed code doesn't need to null the pointer, not even as a safety precaution. I usually try to arrange it that a pointer goes out of scope immediately after freeing the memory it points at; it's not very difficult. Therefore, the (admittedly small) amount of time needed to null the pointer would be wasted. Code that needs the pointer to be nulled can do so explicitly. If you need that feature a lot, it's trivial to write a template wrapper for delete that will do it automatically. Now, this is a very minor matter, and it might have been changed when C++ supplemented free() with the 'delete' operator. However, C++ code generally makes far less explicit use of dynamic memory allocation than C. You should be using containers, and certain kinds of smart pointers, which handle the allocation in an exception-safe manner, rather that doing it yourself, and having to worry about making sure that exceptions don't prevent the 'delete' from occurring. The word NULL, when written entirely in capital letters, should be treated as a noun, not a verb or an adjective. It's the name of a particular stardard library macro. The word 'null', in lower case, it the appropriate one to use in all other cases. In particular, it's not possible for a pointer value to be NULL; NULL is required to be a null pointer constant (NPC), and NPCs are required to have an integer type, not a pointer type. A pointer value can be null, and such a pointer will always compare equal to NULL, but that's because of the special rules for equality comparisons involving NPCs, not because the pointer value is NULL. --- [ 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://www.research.att.com/~austern/csc/faq.html ]