From -2191292566927066004 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,ea96cc047f6a22cc X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2001-08-28 07:54:01 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: comeau@panix.com (Greg Comeau) Newsgroups: comp.std.c++ Subject: Re: extern "C" -- what is the intent? Date: Tue, 28 Aug 2001 14:53:36 GMT Organization: Comeau Computing; http://www.comeaucomputing.com Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <9mf2n0$7dq$1@panix3.panix.com> References: <090820010209154805%BobbySchmidt@mac.com> <1eys049.1mtaactofnng2N%joerg.barfurth@attglobal.net> Reply-To: comeau@comeaucomputing.com X-Trace: mail2news.demon.co.uk 999010425 mail2news:13124 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) Lines: 91 Xref: archiver1.google.com comp.std.c++:7208 In article <1eytm7g.12quiy6u3s1qwN%joerg.barfurth@attglobal.net>, Joerg Barfurth wrote: >Hans Aberg wrote: >> >> extern "C" short foo(int); >> >> is not legal unless one has specified conversion operators >> >> extern "C++" int -> extern "C" int >> >> extern "C" short -> extern "C++" short > >> The main point is that >> extern "C++" int >> and >> extern "C" int >> need not anymore have the same underlying binary structure. > >Even if a language linkage does allow linking to code written in a given >language, that does not mean that C++-declarations under that language >linkage are textually equivalent to declarations of the same entity in >the other language. > >Thus in > extern "C" int foo(); > >'int' is the C++-Type int and is not necessarily identical to type int >in all linkable C implementations. Agreed. >Thus the same function may need to be >declared as > long foo(void); > >in C. Agreed. Perhaps even in C++ :) >This may seem confusing for C, but it becomes clear when you consider >that > > extern "Pascal"= > procedure foo(i : Integer) forward; > >is not well-formed C++, while a C++ implementation might define that > > extern "Pascal" void foo(short); > >can be used to declare and call in C++ code a function that is defined >in some Pascal dialect as > > procedure foo( i : Integer ) BEGIN { ... } END Sure, the C++ side still needs to be C++. >Thus you also don't need any 'conversion operators' to define a >conversion between homonymous types having different binary >representations. A C++ declaration is only concerned with C++ types, >even under a language linkage that is not 'extern "C++"'. Thus we >needn't require builtin support for type 'Boolean' to link to Pascal >code. We may not need them in the core C++ language itself, but that doesn't mean they don't need to be somewhere. >All that is needed is a mapping from one type system to the other which >allows finding the corresponding declaration in the other language. This >means that there needn't be any code or operational definitions, but >only descriptions of correspondence. If there only are matches for a >subset of the type system(s), then that means that only for declarations >from that subset linkage can be achieved. This is left vague in the Standard, but purposely so, so I agree what you say seems possible. >Of course there isn't anything to prevent builtin conversions either. >Maybe a linker could automatically build stubs that do type conversions >and adjusts calling conventions. But I don't think that could be >considered a core part of what language linkage is intende for. It may not be core w.r.t intent, but it sure it core as to an expected implementation detail. -- Greg Comeau Countdown to "export": December 1, 2001 Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90. Comeau C/C++ with Dinkumware's Libraries... Have you tried it? --- [ 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 ]