From -1477357142261960826 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fc772,cda54862ecb4a41f X-Google-Attributes: gidfc772,public X-Google-Thread: f78e5,cda54862ecb4a41f X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2001-08-28 08:52:11 PST Path: archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!cpk-news-hub1.bbnplanet.com!denver-snf1.gtei.net!news.gtei.net!namche.sun.com!news2me.EBay.Sun.COM!engnews1.eng.sun.com!taumet!clamage From: Jack Klein Newsgroups: comp.std.c++,comp.lang.c++.moderated Subject: Re: storage order of inherited classes Date: 28 Aug 2001 15:36:57 GMT Organization: AT&T Worldnet Lines: 96 Approved: stephen.clamage@sun.com (comp.std.c++) Message-ID: <5pqjot40to3q1rcrhokquq3e6k9s1sv2k3@4ax.com> References: NNTP-Posting-Host: taumet.eng.sun.com X-NNTP-Posting-Host: netlab.cs.rpi.edu X-Original-Date: Mon, 27 Aug 2001 06:42:26 GMT X-Submission-Address: c++-submit@netlab.cs.rpi.edu X-Auth: PGPMoose V1.1 PGP comp.lang.c++.moderated iQBVAwUAO4pj2EHMCo9UcraBAQEdvgH+IxPFM6IAwfV3d6B6KoigwD6AR2auPLfL 8iu+8xzvqv0tAntWNI+5evkpLL3XTS5wMlULPR2tkM6HYwf9DBFw+w== =I3H2 X-Approved-For-Group: kuehl@fmi.uni-konstanz.de comp.lang.c++.moderated Content-Length: 2394 X-Status: $$$$ X-UID: 0000000001 Originator: clamage@taumet Xref: archiver1.google.com comp.std.c++:7211 comp.lang.c++.moderated:25536 On 25 Aug 2001 23:50:42 GMT, "Fray Bentos" wrote in comp.lang.c++.moderated: > > Hey peeps. > > Im involved in optimising a few C++ classes that interface with OpenGL > I was wondering if the memory storage order of class members is > standardised ? > > Will the array j from the derived class B always be stored before i from the > base class A ? Your own code, undefined as it is, shows the array of ints in class A being stored _before_ that from class B, not after. > ------------------------8<--------------------- > #include > > class A > { > public: > int i[4]; > > A(int a, int b, int c, int d) > { > i[0] = a*10 ; i[1] = b*10; > i[2] = c*10 ; i[3] = d*10; > } > }; > > class B : public A > { > public: > int j[4]; > > B(int a, int b, int c, int d) : A(a, b, c, d) > { > j[0] = a; j[1] = b; > j[2] = c; j[3] = d; > } > }; > > main() I had to change this to a legal "int main()" to get this to compile with my "better" compiler in strictly conforming mode. > { > B b(1, 2, 3, 4); > int *ptr_b = reinterpret_cast(&b); > > for(int i=0; i std::cout << ptr_b[i] << std::endl; > } > ------------------------8<--------------------- > output: > 10 > 20 > 30 > 40 > 1 > 2 > 3 > 4 > > Thanks A base class appears before any of the additional data items added in a derived class in a case like this. Otherwise it would not be possible for a pointer to a base class to point to a derived class object. The first sizeof(base class) bytes of the derived class must be the instance of the base class in the derived class. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq [ Send an empty e-mail to c++-help@netlab.cs.rpi.edu for info ] [ about comp.lang.c++.moderated. First time posters: do this! ] [ 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.research.att.com/~austern/csc/faq.html ] [ Note that the FAQ URL has changed! Please update your bookmarks. ]