C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Compiler Generated Default Functions          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Guest Posted: Wed Jul 26, 2006 1:50 am    Post subject: Compiler Generated Default Functions Hi, In a recent discussion, some of us were in disagreement about the functions the C++ compiler generates. How many functions are generated by the compiler when you declare: class Foo { }; ? I thought 4. As in: class Foo { public: Foo(); // default constructor Foo(const Foo& f); // default copy constructor ~Foo(); // default destructor const Foo &operator(const Foo& f); // default assigment operator }; Is this list correct? Is that all? Someone said you must also add the new and delete operators, so that's 6. I have not read the standard, but I'd argue that if this is so, then you should also count operator* () and operator& () [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Thu Jul 27, 2006 12:36 am    Post subject: Re: Compiler Generated Default Functions kanze wrote: Quote: The operator& is the hard one. It's defined for all objects, of all types. The standard doesn't consider it an implicitly defined operator; it says that the built in operator is used if there is no user defined one. And in fact, there is no way to define the operator to give the semantics of the built-in operator. How about... class Foo { // ... public: Foo* operator&() { return this; } const Foo* operator&() const { return this; } // ... }; Quote: Technically, when the compiler implicitly generates a function, it behaves like a user defined function; the compiler generated operator=, for example, has an address, participates in overload resolution, and introduces sequence points. The global operator& which the compiler uses if their is not a user defined one requires an lvalue (which a user defined function cannot), doesn't have an address, and doesn't introduce sequence points. So a user-defined operator& can't be completely identical to the built-in operator&. But "no way... to give the [same] semantics" is still a bit overstated, isn't it? I have found exactly one legal way to tell if operator& is user-defined or not -- take the address. Foo* (Foo::*p)() = &(Foo::operator &); This fails if operator& is not user-defined. Is there any other difference, in legal code? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Matthias Hofmann Guest Posted: Thu Jul 27, 2006 7:58 pm    Post subject: Re: Compiler Generated Default Functions "kanze" <kanze@gabi-soft.fr> schrieb im Newsbeitrag news:1153919089.902645.33960 (AT) i42g2000cwa (DOT) googlegroups.com... Quote: extern void* operator new( size_t, int ) ; struct A {} ; A* p = new A ; // Not an error, although a compiler // generated default would hide the // global operator. If I understand this correctly, the allocation of a new A should invoke the above declared placement version of operator new(), shouldn't it? But doesn't this require the following? // Pass 42 as the second // argument of operator new(). A* p = new( 42 ) A; Otherwise, I do not understand why the example you provided should not be an error. -- Matthias Hofmann Anvil-Soft, CEO http://www.anvil-soft.com - The Creators of Toilet Tycoon http://www.anvil-soft.de - Die Macher des Klomanagers [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] 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 (Moderated) 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.