From 1928465415272671173 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 109fba,df06663c0326d841 X-Google-Attributes: gid109fba,public X-Google-Thread: f78e5,df06663c0326d841 X-Google-Attributes: gidf78e5,public From: "Larry Brasfield" Subject: Re: auto_ptr copy semantics Date: 1999/04/11 Message-ID: #1/1 X-Deja-AN: 465031366 Approved: Fergus Henderson References: <7el5br$kjj$1@nnrp1.dejanews.com> X-Original-Date: Sun, 11 Apr 1999 02:52:28 GMT X-Priority: 3 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2014.211 X-Complaints-To: news@news.unimelb.edu.au X-Trace: izvestia.its.unimelb.edu.au 923815142 3205 128.250.29.16 (11 Apr 1999 07:19:02 GMT) Organization: Serendipitous Endeavors X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANxBMz+EDnX0m9pzZAQErUwF+MIVxfJSIsEGTLbX48E6aWCkhvxFQFoPE YjantUMlJiPuf6C4M5yigXTHMxW0t+aO =SaHK X-MSMail-Priority: Normal NNTP-Posting-Date: 11 Apr 1999 07:19:02 GMT Newsgroups: comp.lang.c++,comp.std.c++ wrote in message news:7el5br$kjj$1@nnrp1.dejanews.com... > What is the rationale behind the copy semantics of auto_ptr > transfering ownership of its contained pointer? I don't think "copy semantics" is quite the right phrase for what auto_ptr does. The rationale is all in support of making it easy to write exception safe code that uses the freestore. For that limited purpose, and with certain caveats, auto_ptr works just fine. In general, the caveat is that copies are always for the purpose of getting the pointer to its ultimate point of use and destruction. > If the auto_ptr is passed to a function by *value*, then isn't > your referenced object extinct upon return (because of local > copies being made which claim ownership and then release the > contained object upon their own demise)? > > e.g. > > auto_ptr ptr( new Thing ); > doStuff( ptr ); // ...by value. > // here, ptr no longer refers to anything. Yes. That is one of many reasons to avoid passing auto_ptr's by value. When I have occasion to pass them, I always pass them by reference. > Wouldn't it be better for the *original* auto_ptr to *always* > retain ownership, and for copies to *never* do so? I very useful usage that would be made useless by that rule is where some function returns an auto_ptr. In that case, you would not want the object to die alongside some local variable in that function. auto_ptr is best used for pointers that are not copied except as a consequence of creation. -- --Larry Brasfield Above opinions may be mine alone. (Humans may reply at unundered larry_br@sea_net.com ) --- [ 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 ]