C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Variadic functions with no parameters          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message peter_ammon@rocketmail.co Guest Posted: Wed Apr 27, 2005 7:07 am    Post subject: Variadic functions with no parameters The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? And what was the motivation for allowing functions of this type where C forbids them? I also notice that C++ makes the comma optional, whereas it's mandatory in C. That is, this is a legal prototype: void function2(int ...); What is the motivation for this change? Followups set to comp.lang.c++ Thanks, -Peter --- [ 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.jamesd.demon.co.uk/csc/faq.html ] Back to top Victor Bazarov Guest Posted: Wed Apr 27, 2005 2:24 pm    Post subject: Re: Variadic functions with no parameters [email]peter_ammon (AT) rocketmail (DOT) com[/email] wrote: Quote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? [..] There is no way. Back to top Howard Guest Posted: Wed Apr 27, 2005 10:06 pm    Post subject: Re: Variadic functions with no parameters "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote Quote: peter_ammon (AT) rocketmail (DOT) com wrote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? [..] There is no way. Eh? Isn't that what the macros va_list, va_start, va_arg, and va_end are for? -Howard Back to top Ken Human Guest Posted: Wed Apr 27, 2005 10:25 pm    Post subject: Re: Variadic functions with no parameters Howard wrote: Quote: "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote in message news:ngNbe.66305$NC6.31154 (AT) newsread1 (DOT) mlpsca01.us.to.verio.net... [email]peter_ammon (AT) rocketmail (DOT) com[/email] wrote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? [..] There is no way. Eh? Isn't that what the macros va_list, va_start, va_arg, and va_end are for? -Howard Yes, but va_start requires a pointer to the first argument in the list. The function's format must be similiar to "void function(T pFirstElement, ...);" Back to top Victor Bazarov Guest Posted: Wed Apr 27, 2005 10:25 pm    Post subject: Re: Variadic functions with no parameters Howard wrote: Quote: "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote in message news:ngNbe.66305$NC6.31154 (AT) newsread1 (DOT) mlpsca01.us.to.verio.net... [email]peter_ammon (AT) rocketmail (DOT) com[/email] wrote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? [..] There is no way. Eh? Isn't that what the macros va_list, va_start, va_arg, and va_end are for? Yes they are. Please explain how you'd use them in the case where there are no _named_ arguments. Back to top Howard Guest Posted: Thu Apr 28, 2005 2:02 pm    Post subject: Re: Variadic functions with no parameters "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote Quote: Howard wrote: "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote in message news:ngNbe.66305$NC6.31154 (AT) newsread1 (DOT) mlpsca01.us.to.verio.net... [email]peter_ammon (AT) rocketmail (DOT) com[/email] wrote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? [..] There is no way. Eh? Isn't that what the macros va_list, va_start, va_arg, and va_end are for? Yes they are. Please explain how you'd use them in the case where there are no _named_ arguments. Oh, I get your point now. I forgot that you need one named parameter to get started. Thanks. -Howard Back to top James Dennett Guest Posted: Fri Apr 29, 2005 6:06 am    Post subject: Re: Variadic functions with no parameters [email]peter_ammon (AT) rocketmail (DOT) com[/email] wrote: Quote: The C++ grammar appears to admit (and g++ accepts) void function(...); Yes, it's allowed. Quote: In such a function, how do you access any of the parameters? You cannot portably do so. It may be possible in implementation-specific ways. Quote: And what was the motivation for allowing functions of this type where C forbids them? I don't know what the motivation was (apart from it being simpler than disallowing them), but this does have useful consequences in providing a worst-match for overload resolution, which can be useful in situations such as template metaprogramming. Quote: I also notice that C++ makes the comma optional, whereas it's mandatory in C. That is, this is a legal prototype: void function2(int ...); What is the motivation for this change? D&E might answer that, though I'm not sure if it does and don't have my copy handy right now to check. -- James Back to top Krzysztof Zelechowski Guest Posted: Wed May 04, 2005 9:39 pm    Post subject: Re: Variadic functions with no parameters Uzytkownik <peter_ammon (AT) rocketmail (DOT) com> napisal w wiadomosci news:1114551200.309625.229930 (AT) z14g2000cwz (DOT) googlegroups.com... Quote: The C++ grammar appears to admit (and g++ accepts) void function(...); In such a function, how do you access any of the parameters? And what was the motivation for allowing functions of this type where C forbids them? The reason is overloading. C language forbids overloaded functions, so there is no point of declaring formal parameters and not using them afterwards. You can just do without them. 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