From -4797183973042478464 X-Google-Language: ENGLISH,ASCII X-Google-Thread: f78e5,924f354765fe932a X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-05-23 01:51:01 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!skynet.be!skynet.be!kibo.news.demon.net!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: James Kanze Newsgroups: comp.std.c++ Subject: Re: constructor calls in vectors Date: Thu, 23 May 2002 08:50:13 GMT Organization: James Kanze Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <864rgy9fgh.fsf@alex.gabi-soft.de> References: <3CE562E8.8050403@acm.org> <86r8k4e1ec.fsf@alex.gabi-soft.de> <3CEAF4CA.20200@animats.com> X-Trace: mail2news.demon.co.uk 1022143818 mail2news:15554 mail2news mail2news.demon.co.uk X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au 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) User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/20.7 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 X-MIME-Autoconverted: from 8bit to quoted-printable by mr0.ash.ops.us.uu.net id QQmqbd26811 X-MIME-Autoconverted: from quoted-printable to 8bit by mulga.cs.mu.OZ.AU id RAA06098 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by mulga.cs.mu.OZ.AU id SAA02628 Lines: 49 Xref: archiver1.google.com comp.std.c++:11447 John Nagle writes: |> James Kanze wrote: |> > I would argue that this is the correct interpretation. I'm not |> > 100% sure, however, since I don't think that there is any |> > requirement concerning the default constructor, and there is a |> > guarantee that it is NOT called in constructing the vector. (It |> > may be called to construct the argument to the constructor, of |> > course.) |> I once reported that as a bug in some STL implementation. New |> objects were created by invoking the default constructor, then |> assigning, rather than by invoking the copy constructor. It was a |> bug; only by accident did it work that way. That is definitly non-conforming. |> This typically comes up when an class contains a data member |> which is a reference. That reference has to be initialized during |> construction, and so the default constructor is usually not |> meaningful. Thus, there's a reason to get this right. I was thinking more of the case where instead of using a default argument, the implementor provides two constructors: vector::vector( size_t ) vector::vector( size_t, T const& ) The second *MUST* use only the copy constructor; no call to the default constructor is allowed, as it must work with classes without default constructors. The formal semantics of the first are to default construct a T, then copy it. My question is rather whether using only the default constructor is a legal optimization. --=20 James Kanze mailto:kanze@gabi-soft.de Conseils en informatique orient=E9e objet/ Beratung in objektorientierter Datenverarbeitung Ziegelh=FCttenweg 17a, 60598 Frankfurt, Germany Tel. +49(0)179 2607481 --- [ 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.jamesd.demon.co.uk/csc/faq.html ]