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From: tell@oscar.cs.unc.edu (Stephen Tell)
Newsgroups: comp.lang.c++
Subject: Re: bug with making C++ functions have C linkage ?
Message-ID: <3407@borg.cs.unc.edu>
Date: 24 Apr 91 01:44:05 GMT
References: <1991Apr16.122905.23613@cs.nott.ac.uk> <675@taumet.com> <1991Apr22.081254@Unify.com>
Sender: news@cs.unc.edu
Organization: University of North Carolina, Chapel Hill
Lines: 63

In article <1991Apr22.081254@Unify.com> grp@Unify.com (Greg Pasquariello) writes:
>In article <675@taumet.com>, steve@taumet.com (Stephen Clamage) writes:
>> 
>> Almost all current C++ compilers require that main() be compiled by
>> the C++ compiler, even if other modules are compiled with a compatbile
>> C compiler.  Your compiler manual should tell you this.
>> 
>> In general, C++ programs will require initialization of static objects
>> via their constructors at runtime; cout is such an object.  The C++
>> compiler arranges for the constructors (and destructors) to be called
>> via special code emitted in the module in which main() appears.  This
>> ensures the special code is emitted and called exactly once.

>[Iostreams with 2.0 provide an initializer object...]
>[but not all class libraries do]

>> In your example, main() was not compiled by the C++ compiler, cout
>> was not initialized, and the program failed when it tried to use
>> member functions of cout.


Another C++ hacker and I figured out a way to do this for a simulator
that was written in C and allows user code to be linked in with the
program.

Patch the .o files from the system so that the C main is renamed to
somthing like "MaIn."

Write short C++ file consisting of:

extern "C" MaIn(int argc; char **argv);

main(int argc, char **argv)
{
	return MaIn(argc, argv);
}

This way, the real main is written in C++ and the constructors get
called.

The other code that you link in with the system can then be C++ and use
whatever classes it likes since static objects will have had their
constructors called.

This may not be ideal, but it works.  We did the C++ stuff with g++.
I don't know what C compiler the original program was written with.

It requires that the product be shipped with ordinary .o files that you
run "ld" on to make customized versions, instead of funky schemes to
attach user code to a running program.
	

>> Steve Clamage, TauMetric Corp, steve@taumet.com
>Greg Pasquariello	grp@unify.com
>Unify Corporation 	Be good and never poison people


Steve
-- 
Steve Tell       tell@cs.unc.edu    H: +1 919 968 1792   #5L Estes Park apts
CS Grad Student, UNC Chapel Hill.   W: +1 919 962 1845   Carrboro NC 27510
Duke Blue Devils:  1991 NCAA Basketball National Champions! We're Number 1 !!
UNLV 90-91 record:  "34 and DUKE."