From -7937167317887714674 X-Google-Thread: f78e5,13848293b54382c8 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.speakeasy.net!news.speakeasy.net.POSTED!not-for-mail NNTP-Posting-Date: Wed, 19 Apr 2006 12:20:02 -0500 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.1.1 (2006-03-10) on ak74.algebra.com X-Spam-Level: *** X-Spam-Status: No, score=3.4 required=5.0 tests=HEADER_SPAM,MISSING_HEADERS, TO_CC_NONE autolearn=disabled version=3.1.1 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-Original-To: std-c++@mailman.ucar.edu Delivered-To: std-c++@mailman.ucar.edu Delivered-To: std-c++@ucar.edu From: "SuperKoko" Newsgroups: comp.std.c++ Subject: Re: Encapsulation of variables Organization: http://groups.google.com Message-ID: <1145464591.411704.314680@j33g2000cwa.googlegroups.com> References: <1145365947.835536.81010@u72g2000cwu.googlegroups.com> <4Te1g.87563$PR2.1399736@twister2.libero.it> <1145433404.436690.81060@e56g2000cwe.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Complaints-To: groups-abuse@google.com User-Agent: G2/0.2 X-HTTP-UserAgent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1),gzip(gfe),gzip(gfe) X-HTTP-Via: 1.1 styx.pedago1.unicaen.fr:3128 (squid/2.5.STABLE6), 1.0 proxy2.unicaen.fr:3128 (squid/2.5.STABLE9), 1.0 groups.google.com Complaints-To: groups-abuse@google.com Injection-Info: j33g2000cwa.googlegroups.com; posting-host=193.55.130.208; posting-account=vOfC2w0AAABzHsIWnglmMRchI1pVxsvC X-Greylisting: NO DELAY (Relay+Sender autoqualified); processed by UCSD_GL-v2.1 on mailbox4.ucsd.edu; Wed, 19 April 2006 09:36:40 -0700 (PDT) X-Spamscanner: mailbox4.ucsd.edu (v1.6 Aug 4 2005 15:27:38, -2.8/5.0 3.0.4) X-MailScanner: PASSED (v1.2.8 4702 k3JGacoA020117 mailbox4.ucsd.edu) X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU Approved: Fergus Henderson , moderator of comp.std.c++ X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU Date: Wed, 19 Apr 2006 12:18:10 CST Lines: 56 NNTP-Posting-Host: 65.182.171.162 X-Trace: sv3-C1IXYsKvtkwkl2cxjxvodxStywiaJV2gi2jwYLArcT+gUsukDK8h0Cl0mmZR6fj04aA/+EZL1OHnHBn!9qc2x+uSTzNUdXNsFJIHOWs4FRUKwJPSc14uLv+/SquhbdoYeRXnPHcXkwZKYMTMQHfQhwG6PjzP!NrDwQG5st7pcTSny26h8hQoEEKlv9kCaZMoZ5EUPeyY= X-Complaints-To: abuse@speakeasy.net X-DMCA-Complaints-To: abuse@speakeasy.net X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.32 Xref: g2news1.google.com comp.std.c++:1615 philparsonage@hotmail.com wrote: > OK, so maybe my example wasn't the best, I typed a private instead of a > protected. The actual code (which compiles using 4.0.2, or 3.3.6) is: > > #include > > class A { > protected: int _fred; > /// no-one can see fred directly > }; > > class B : public A { > public : using A::_fred; > /// but this magically turns A::_fred to be public! > }; > > int main(int argc, char** argv) > { > B b; > b._fred = 10; // you can do this > return 0; > } > This code is fine. class B derives from class A, and so, is perfectly aware of all protected members of A. Thus, it can expose them to everybody. That's not much different from: class B : public A { public : int& fred() {return _fred;} }; Similarly, using directives can be used to expose privately inherited members. class B : private A public: using A::_fred; } Of course, having a public data member in a non-aggregate class, is usually a sign of bad design... But the point here was the correctness of data hiding. The morale here, is that "protected" is nearly equivalent, in terms of contract, to "public". A "protected" member is NOT private! If you write a class with protected members, you make the contract that you'll not change these members in future... That is also why, protected data members are a bad idea. --- [ 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.comeaucomputing.com/csc/faq.html ]