C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Question about language compliance          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message DJ Franke Guest Posted: Thu Sep 29, 2005 11:49 pm    Post subject: Question about language compliance Hi ! The following code compiles on the Borland5 C++ compiler (simplified version): class SomeClass{ public: SomeClass() { Son = NULL; } SomeClass(const SomeClass& sc) { Son = sc.Son; } SomeClass& find() { return *Son; } SomeClass* Son; }; SomeClass Useless = Useless.find(); In the case where I encountered it, the find function did do quite some things and caused a very understandable runtime error, since Useless was not intialised at that stage. I looked at the code in the debugger and the standard constructor is never called; the find function is called first and then the copy constructor, which means that Useless is known and can be used before it is initialised. I am not very good an the language internals, so my question is wether this is a bug in the compiler, or wether there is a good reason that this is allowed to happen. Thanks Back to top Ali Çehreli Guest Posted: Fri Sep 30, 2005 12:13 am    Post subject: Re: Question about language compliance "DJ Franke" <longreef (AT) gmail (DOT) com> wrote Quote: The following code compiles on the Borland5 C++ compiler (simplified version): [...] SomeClass Useless = Useless.find(); In the case where I encountered it, the find function did do quite some things and caused a very understandable runtime error, since Useless was not intialised at that stage. Your problem can be expressed in a simpler way: SomeClass Useless = Useless; In order to construct Useless, first the right hand side must be evaluated. Right hand side uses the very object that you are in the process of constructing. That object is not yet an object; it is not constructed. The solution: don't do it. :) Ali Back to top DJ Franke Guest Posted: Fri Sep 30, 2005 1:14 am    Post subject: Re: Question about language compliance Hi ! Thanks for your reply. I know that I shouldn't do it and why it doesn't do any good, I just stumbled over it due to a typo and now wonder wether it complies with the standard (and if then why) or wether the compiler should not allow it. Back to top Ali Çehreli Guest Posted: Fri Sep 30, 2005 1:41 am    Post subject: Re: Question about language compliance Summary: Class object = use(object); "DJ Franke" <longreef (AT) gmail (DOT) com> wrote Quote: I just stumbled over it due to a typo and now wonder wether it complies with the standard (and if then why) or wether the compiler should not allow it. I stumbled on it a few weeks ago myself. I think the compiler can give warnings in most (all?) of such cases, because there is no good of using a non-constructed object to construct the same object. A quality of implementation issue I guess... :/ Ali Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.