From 6126205325129175759 X-Google-Language: ENGLISH,ASCII X-Google-Thread: f78e5,f35f303f52b43897 X-Google-Attributes: gidf78e5,public From: kanze@lts.sel.alcatel.de (James Kanze US/ESC 60/3/141 #40763) Subject: Re: copy vs assignment Date: 1996/06/18 Message-ID: #1/1 X-Deja-AN: 160887950 references: <31C6B570.388A@scruznet.com> x-original-date: 18 Jun 1996 17:43:08 GMT apparently-to: std-c++@ncar.UCAR.EDU organization: GABI Software, Sarl. x-auth: PGPMoose V1.1 PGP comp.std.c++ newsgroups: comp.std.c++ originator: austern@isolde.mti.sgi.com In article <31C6B570.388A@scruznet.com> Peter Lawrence writes: |> What is the difference between a (compiler generated default) copy |> constructor and an assignment operator. Is it just that the interface |> is different, one operates on "this" and the other operates on an |> explicit reference. When does the compiler implicitly use copy verses |> assignement, and why. Do people ever make the semantics of copy and |> assignment different, and why. This is, or should be, in the C++ FAQ. (It also doesn't have much to do with the C++ standardization effort.) Basically, the compiler uses a constructor (including the copy constructor) to construct raw memory into an object. A constructor works on uninitialized memory. The assignment operator is used to assign one value to another already initialized object. An assignment operator expects to find a fully initialized object to work on. Think about an object which has a dynamically allocated pointer. The assignment operator might delete the pointer, then allocate new memory (of a different size). A constructor (copy or other) dare not delete the pointer, since when the constructor is called, the memory has not been initialized, and contains random bit patterns. See Scott Meyers, "Effective C++" for more details. -- James Kanze Tel.: (+33) 88 14 49 00 email: kanze@gabi-soft.fr GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France Conseils, �tudes et r�alisations en logiciel orient� objet -- -- A la recherche d'une activit� dans une region francophone --- [ comp.std.c++ is moderated. To submit articles: Try just posting with your newsreader. If that fails, use mailto:std-c++@ncar.ucar.edu comp.std.c++ FAQ: http://reality.sgi.com/austern/std-c++/faq.html Moderation policy: http://reality.sgi.com/austern/std-c++/policy.html Comments? mailto:std-c++-request@ncar.ucar.edu ]