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From: alanb@sdl.mdcbbs.com
Newsgroups: comp.lang.c++
Subject: Re: call C++ from C
Message-ID: <1991Jun28.143521.1@sdl.mdcbbs.com>
Date: 28 Jun 91 13:35:21 GMT
References: <359@soleil.jupiter.UUCP> <20463@alice.att.com>
Organization: Shape Data Ltd. (McDonnell Douglas M&E, Cambridge UK)
Lines: 40
Nntp-Posting-Host: shapeg
Nntp-Posting-User: alanb

In article <20463@alice.att.com>, ark@alice.att.com (Andrew Koenig) writes:
> In article <359@soleil.jupiter.UUCP> rh@jupiter.UUCP (#Rachid Himmi) writes:
> 
>> I'm looking for the way to call a C++ module from a C program through
>> the declaration of a class and the call of its function members.
> 
> Turn your C program into a C++ program and it's easy.
> Otherwise, it's a matter between you and your implementer(s)
> and it's not guaranteed to work no matter what you do.
> -- 
> 				--Andrew Koenig
> 				  ark@europa.att.com

In version 1, functions not declared as overloaded generally got the same name
as C functions would. In version 2, the linkage specification extern "C" can be
used to ensure this (Annotated C++ Reference Manual, Ellis and Stroustrup,
section 7.4)

e.g.

class class1
{
  public:
    void foo();
};

// C++ definition
extern "C" void CLASS1_foo( struct class1_t *me ) { me->foo(); }

/* C header file */
extern void CLASS1_foo( struct class1_t *me );

Season with friend declarations if you need a C interface to private functions,
and cast/constructor operators to turn your classes into C types.

(If you use structs in C++, they will be the same in C, but normally I would
expect the module to be passing out an opaque type. "(void *)this" will often
do, but having a type that reflects the C++ type is cleaner.)

alanb@sdl.mdcbbs.com    Alan Braggins    #include <disclaimer.hxx>