From -9027960268497537334 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,2aed2eaedf310bad X-Google-Attributes: gidf78e5,public From: Michiel Salters Subject: Re: stl list with VC++5 Date: 1999/12/01 Message-ID: <3844EF35.F02623CC@lucent.com>#1/1 X-Deja-AN: 555231841 Content-Transfer-Encoding: 7bit Approved: Fergus Henderson References: <3840B365.646F5247@insa-lyon.fr> X-Original-Date: Wed, 01 Dec 1999 10:49:41 +0100 X-Accept-Language: en Content-Type: text/plain; charset=us-ascii X-Complaints-To: news@news.unimelb.edu.au X-Trace: ariel.ucs.unimelb.edu.au 944042716 28238 128.250.37.153 (1 Dec 1999 10:05:16 GMT) Organization: Lucent Technologies, Hilversum X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUAOETy5OEDnX0m9pzZAQEqwAF/dlq30+NFUec0+OQQBw6iSMCC+1tCdAMx BtEKtFjZy0VWIjtyIwiXdHleKlqmdOmH =RDCG Mime-Version: 1.0 NNTP-Posting-Date: 1 Dec 1999 10:05:16 GMT Newsgroups: comp.std.c++ Gilles ROUX wrote: > > Hi, > The following code compiles perfectly with gcc, but not with VC++5 (see > error message). > Have I made a silly mistake, or is vc++ wrong (once more). Is it going > to work if I use vc++6 ? > If not, how can I solve this problem ? > Thanks. > Gilles. > -------------------------------------- > #include > class A > { > public: > A(); > std::list::iterator a; > }; > void main() > { > } > ---------------------------------------- > d:\Prog\DevStudio\VC\INCLUDE\list(24) : error C2079: '_Value' uses > undefined class 'A' > d:\Prog\DevStudio\VC\INCLUDE\functional(180) : error C2079: 'value' uses > undefined class 'A' > d:\Prog\DevStudio\VC\INCLUDE\list(173) : error C2440: 'default argument' > : cannot convert from 'class A' to 'class A' > Source or target > has incomplete type > --- You made a silly mistake - but that's void main(). The not so silly mistake that (probably :-) causes the compiler trip-up is the use of std::list inside class A. What if e.g. the size of std::list depends on the size of A? Not unreasonable, but in that case you can't put an std::list inside an A. The basic rule is that you can't use class A as a template parameter (to std::list, that is) until after the final '}' of its definition. It isn't complete yet; hence the last warning. Using A* is of course possible (its size does not depend on the sizeof(A) ). This might give you the intended behavior. I'm wondering why an A object has to hold an iterator to the list, though. In one way, that makes class A like a linked list node, which is quite confusing, since it is (presumably) on another (std::)list, too. On the compiler comparison. gcc is as right as vc++; this behavior is undefined behavior. Accepting it without diagnostic is fine; refusing it is fine too. The only thing not fine is using A as you did. Michiel Salters --- [ 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 ]