Newsgroups: comp.lang.c++
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!rice!cooker
From: cooker@newsrice.edu (Donald George Baker)
Subject: Re: Mixing C with C++
Message-ID: <1991Apr24.161641.5083@rice.edu>
Originator: cooker@vancouver.rice.edu
Sender: news@rice.edu (News)
Reply-To: cooker@newsrice.edu (Donald George Baker)
Organization: Rice University
References: <1991Apr22.064847.16929@cs.nott.ac.uk> <1991Apr23.133931.6716@ssd.kodak.com>
Date: Wed, 24 Apr 91 16:16:41 GMT


In article <1991Apr23.133931.6716@ssd.kodak.com>, strollo@ssd.kodak.com (larry strollo ) writes:
|> 
|> I'm confused.  Since the linker is just linking object files (generated
|> from C I might add), what is special about the C++ "linker" ?  Do you
|> really mean that some special C++ libraries are linked in (in which case I
|> should be able to do the same thing by just explicitly calling out the
|> libraries in the link command, shouldn't I) ?

I can see that there is still a lot of confusion about what is happening with
the C++ linker and how it relates to mixing in pure C code.  Besides linking
against the C++ library, the linker does the interesting part of getting the
constructors and destructors for global objects called at the right time. 
Note:  these comments refer to AT&T's CFront, so your milage may vary.

The C++ linker actually links a program twice.  The first time to make an
executable on which 'nm' can be run.  The second pass looks for routines that
follow a particular naming convention.  These routines are the constructors
and destructors for global objects.  The routines are gathered up and put into
two tables.  The order in which these appear is totally dependent on the
linking order--a serious problem with global objects.  A routine called _main
will call all of the constructors and _exit (I think) calls all of the
destructors.  It is hard not to have the destructors called, because you must
link against the special _exit, but when your main program is not C++, _main
does not get called automatically.  All you need to do is call _main() with
no arguments yourself.

I hope this helps.

-----------------------------------------------------------------------------
 Donald G. Baker  (cooker@Rice.edu)    \	Computer Science Department,
    Computer-human interaction,		\	Rice University
    Programming environments,		/\	P. O. Box 1892
    Software engineering	       /  \	Houston, TX  77251-1892, USA
-----------------------------------------------------------------------------
-- 
-----------------------------------------------------------------------------
 Donald G. Baker  (cooker@Rice.edu)    \	Computer Science Department,
    Computer-human interaction,		\	Rice University
    Programming environments,		/\	P. O. Box 1892