From 8055230441152417982 X-Google-Language: ENGLISH,ASCII X-Google-Thread: f78e5,ea96cc047f6a22cc X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2001-08-27 15:29:01 PST Path: archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!dispose.news.demon.net!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: joerg.barfurth@attglobal.net (Joerg Barfurth) Newsgroups: comp.std.c++ Subject: Re: extern "C" -- what is the intent? Date: Mon, 27 Aug 2001 22:28:25 GMT Organization: My beloved Family Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <1eytm7g.12quiy6u3s1qwN%joerg.barfurth@attglobal.net> References: <090820010209154805%BobbySchmidt@mac.com> <9l62tf$c2g$1@panix3.panix.com> <1eys049.1mtaactofnng2N%joerg.barfurth@attglobal.net> X-Trace: mail2news.demon.co.uk 998951310 mail2news:5896 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) MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 User-Agent: MacSOUP/D-2.4.6 (unregistered for 412 days) Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by mulga.cs.mu.OZ.AU id IAA00496 Lines: 76 Xref: archiver1.google.com comp.std.c++:7203 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=20 > 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=20 extern "C" int foo(); 'int' is the C++-Type int and is not necessarily identical to type int in all linkable C implementations. Thus the same function may need to be declared as=20 long foo(void); in C. This may seem confusing for C, but it becomes clear when you consider that extern "Pascal"=20 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 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. 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. 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. Regards, J=F6rg --=20 J=F6rg Barfurth joerg.barfurth@attglobal.net <<<<<<<<<<<<< using std::disclaimer; <<<<<<<<<<<<<<<<<<<<<<<<<<<< Software Developer http://www.OpenOffice.org StarOffice Configuration http://www.sun.com/staroffice --- [ 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 ]