Re: Need to create a C lib - using C++ classes - is it possible

From:

"Chris Thomasson" <cristom@comcast.net>

Newsgroups:

comp.lang.c++

Date:

Sat, 24 May 2008 14:13:00 -0700

Message-ID:

<TtqdnYR2YqdcGaXVnZ2dnUVZ_hninZ2d@comcast.com>

"Angus" <anguscomber@gmail.com> wrote in message
news:3cc390d2-129d-4fe7-a24f-99c02373a660@p25g2000hsf.googlegroups.com...

Hello

We have a lot of C++ code. And we need to now create a library which
can be used from C and C++. Given that we have a lot of C++ code
using classes how can we 'hide' the fact that it is C++ from C
compilers?

Can we have a C header file which uses the functionality of the C++
files and compile this into a lib file?

Can anyone give me some pointers as to how to get started?

You can try something like this:

<pseudo-code sketch>
________________________________________________________________

/* my_class.h
-------------------------------------------------------------*/
#ifndef MY_CLASS_H
#define MY_CLASS_H
#ifdef __cplusplus
# define EXTERN extern "C"
#else
# define EXTERN extern
#endif

typedef void* my_class_type;

EXTERN int my_class_create(my_class_type*)
EXTERN int my_class_destroy(my_class_type);
EXTERN int my_class_do_something(my_class_type);

#endif

/* my_class.hpp
-------------------------------------------------------------*/
#ifndef MY_CLASS_HPP
#define MY_CLASS_HPP

class my_class {
public:
  my_class();
  ~my_class() throw();
  void do_something();
};

#endif

/* my_class.cpp
-------------------------------------------------------------*/
#include "my_class.h"
#include "my_class.hpp"
#include <cstdio>

my_class::my_class() {
  std::printf("(%p)->my_class::my_class()\n", (void*)this);
}

my_class::~my_class() throw() {
  std::printf("(%p)->my_class::~my_class()\n", (void*)this);
}

void my_class::do_something() {
  std::printf("(%p)->my_class::do_something()\n", (void*)this);
}

int my_class_create(my_class_type* _pcthis) {
  try {
    *_pcthis = new my_class;
  } catch(...) {
    return -1;
  }
  return 0;
}

int my_class_destroy(my_class_type _cthis) {
  my_class* const _this = (my_class*)_cthis;
  try {
    delete _this;
  } catch(...) {
    return -1;
  }
  return 0;
}

int my_class_do_something(my_class_type _cthis) {
  my_class* const _this = (my_class*)_cthis;
  try {
    _this->do_something();
  } catch(...) {
    return -1;
  }
  return 0;
}
________________________________________________________________

Now you can use it from C like:
________________________________________________________________
#include "my_class.h"

int main(void) {
  my_class_type _this;
  my_class_create(&_this);
  my_class_do_something(_this);
  my_class_destroy(_this);
  return 0;
}

________________________________________________________________

Any thoughts?