From -1866635217741129790 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,ea96cc047f6a22cc X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2001-08-11 05:14:01 PST Path: archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!news.tele.dk!small.news.tele.dk!212.74.64.35!colt.net!dispose.news.demon.net!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: "James Russell Kuyper Jr." Newsgroups: comp.std.c++ Subject: Re: extern "C" -- what is the intent? Date: Sat, 11 Aug 2001 12:13:32 GMT Organization: Posted via Supernews, http://www.supernews.com Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <3B74739E.54485C0C@wizard.net> References: <090820010209154805%BobbySchmidt@mac.com> X-Trace: mail2news.demon.co.uk 997532017 mail2news:16009 mail2news mail2news.demon.co.uk X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Accept-Language: en MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 58 Xref: archiver1.google.com comp.std.c++:6938 Hans Aberg wrote: > > In article , Francis Glassborow > wrote: > >>Here, A and B must be C types > > > >What are those, and how do you come by that requirement? I am not aware > >that the Standard imposes any such restriction (though to use an extern > >"C" function defined in C++ you need compatible parameters, C++ does > >not, AFAIK, define such (well it does define PODs). > > Well, I don't see in > extern "C" A f(B x) { > // C++ definition > } > if A and B are not C types, how f could be viewed as a C function from the > linking point of view. If they are something else, one must still be able > to convert them to objects that the linker can view as binary C objects > before handing them over to the linker. > > Or so was my impression. If you know how it works, perhaps you should > describe it. A and B don't have to be C types. However, if they are not C types, then the way in which they can be used is implementation defined. An implementation is free to define it's C++ interfaces in such a way that the following header file, if included in both C and C++ code, would allow a definition of f() in one language to be called from within the other: connector.h: #ifdef __cplusplus typedef int &A; class MyClass{ int i; int j; }; typedef int MyClass::*B; extern "C" A f(B); #else typedef int *A; typedef long int B; extern A f(B); #endif Of course, an implementation is also free to make such a program blow up; it's implemenation-defined. --- [ 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 ]