From -4118640570568093947 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,9684813612e15361 X-Google-Attributes: gidf78e5,public From: jcoffin@taeus.com (Jerry Coffin) Subject: Re: pointers: sizeof(pointer) Date: 1998/06/23 Message-ID: #1/1 X-Deja-AN: 365198226 Approved: Fergus Henderson References: X-Original-Date: Mon, 22 Jun 1998 10:24:22 -0600 Organization: TAEUS X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANY8r9eEDnX0m9pzZAQFoGwF+K+qsi2xWEE3lHnWg+lCZP2umjCYeX2Bi QiHsGjc/qVyLoZjlMg6boaBLfF5krcyB =EtIN Newsgroups: comp.std.c++ In article , sbnaran@bardeen.ceg.uiuc.edu says... > (1) > > [X] Do all pointers have the same size? This > makes sense because a pointer of any type is > just a memory addresss. No -- pointers to different things may have different sizes. A pointer to void is guaranteed to be able to hold a pointer to any other object type, and you can convert it back to a pointer to the object type without loss of information though. (Here I'm using "object" in the sense it's used in the C standard, not particularly restricted to an instantiation of a class.) However, this does NOT apply to things like pointers to functions, especially pointers to member functions, which are typically considerably different from other pointers. > [X] But what about inheritance where one pointer > can really be two pointers? For example, if > class D derives from class B, the a pointer to > a B can also possibly be a pointer to a D. Unless you're dealing with multiple inheritance, this doesn't really affect the pointer itself -- it only affects how you interpret what the pointer points AT. You can always convert a pointer to a derived type to a pointer to its base type without problems. > [X] The business of casting is just a compile > time check on the correctness of our code. > Correct? Rather the opposite: as far as code correctness goes, a cast _prevents_ the compiler from doing testing that it might otherwise do. However, a cast can also involve the generation of code -- things like casting from a floating point type to an integer type, or doing a dynamic_cast are both likely to generate actual code. In addition, a cast may result in constructing an object of the specified type, via a call to a constructor, which may involve more or less arbitrary amounts of code. > (2) Can we assume that sizeof(pointer)=sizeof(int)? Not if you're at all interested in portability. There are quite a few environments in which this is not the case right now, and likely to be more in the future. -- Later, Jerry. The Universe is a figment of its own imagination. --- [ 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 ]