From 1814224832816438637 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,bb04047befc790b4 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2001-02-24 16:55:11 PST Path: supernews.google.com!sn-xit-02!supernews.com!news.gv.tsc.tdk.com!news.iac.net!news-out.cwix.com!newsfeed.cwix.com!news.maxwell.syr.edu!dispose.news.demon.net!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: "James Kuyper Jr." Newsgroups: comp.std.c++ Subject: Re: empty parameter list and extern "C" Date: Sun, 25 Feb 2001 00:48:52 GMT Organization: Not Enough Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <3A970F80.57D6AD5E@wizard.net> References: <3a91a017.213629713@news.nikoma.de> <3a968230.533654664@news.nikoma.de> X-Trace: mail2news.demon.co.uk 983062145 mail2news:10790 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,es,de,ru MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 72 Xref: supernews.google.com comp.std.c++:3771 Martin Aupperle wrote: > > On Thu, 22 Feb 2001 19:32:10 GMT, Jack Klein > wrote: > > > > >Understand that C++ does not guarantee interoperability with code > >compiled by a C compiler, or even by the same compiler in its C mode, > >if it has one. The intent is to provide this capability if possible, > >but all that extern "C" is guaranteed to do is provide C linkage. > > > I understand. So, please look at the following scenario: > > 1.) I have a very old and mean C-Library (i.e. one that is compiled > with a C-compiler). It exposes a header file foo.h that declares a > function f like this: > > void f(); > > 2.) Since it is a C-Library, I conclude that f can (syntactically) be > called with arbitrary arguments. Any C-Program that includes foo.h > should be able to do so. Syntactically, yes. Semantically, no. According to the current C standard, it's undefined behavior to call f() with arguments whose number and promoted types are incompatible with those of the parameters in the definition of f(). > 3.) But I have a C++ program and want to use the library. Therefore I > say > > extern "C" > { > #include "foo.h" > } > > Now I have a function f declared and can use it. BUT NOT with > arbitrary parameters! > > 4.) It is also not possible to declare f myself, as for example like > this If foo() does in fact take no arguments, you should change "foo.h" to declare it as void f(void); This is legal in C++, and means the same thing as in C. If foo() does in fact take a fixed number of arguments, declare it with that number of arguments. If the code using foo() takes advantage of the fact that C used to allow discrepances between the arguments in a function call and the parameters of the corresponding function definition, you may be out of luck, since that's equally illegal in modern C++ as in modern C. Offhand I see no easy way to trick a modern compiler into cooperating with such a discrepancy. You'd have to find a compiler with a "k&r" option that produces modules linkable to code compiled without that option. If "foo.h" is inaccessible, you will either have to write your own replacement for it with a different name, or write suitably defined wrapper functions, as you've already figured out. One thing you don't have to worry about is the impossibility of wrapping a function defined with an '...'. Such a function cannot be legally called using a declaration as "void f();", neither in C nor in C++. --- [ 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 ] [ Note that the FAQ URL has changed! Please update your bookmarks. ]