RE: [Dev-C++] C++ and C function pointers

[Ioannis V. <no...@ho...>]

 
 <http://run.to/noicys> 
-----Original Message-----
From: dev...@li...
[mailto:dev...@li...] On Behalf Of Patrick,
Michael
Sent: Tuesday, August 13, 2002 11:11 PM
To: 'dev...@li...'
Subject: [Dev-C++] C++ and C function pointers



Hello all,

I'm in no way a master of C++ and all its rules and regulations and I
don't think what I need to do can actually be done, but it never hurts
to ask anyway.

I have to create a simple API using a C++ library (required by
management) that interfaces with an old C library beneath it.  My
problem is that the old C library has 3 or 4 function calls, each of
which takes a function pointer, to allow you to handle the results as
you wish.  This is fine, but I need to take the returned values (from
the function pointer call) and use them with a bunch of my own variables
currently held in a class.

From my understanding, there is no way to mask a C++ class method as a C
function (something to do with the this pointer).  Do you know of any
way to overcome this? 

 
I hope i have understood what you are asking for. Below i am displaying
some of what you can do in a crazy example.
 
 
namespace outerspace
{
  int nspvalue;
 
  
  extern "C"
  {
   // You can use these inside C code
    void  setnspvalue(int nval) { nspvalue=nval; }
    int getnspvalue() { return nspvalue; }
  }    
  
}
 
// Your C function delcared here
extern "C" int your_c_function_declaration( int (*)(void) );
 
 
 
class A
{
 int x;
 public:
 // ...
 A(int n):x(n) {}
 void setvalue(int new_value) { x=new_value; }
 int getvalue() const { return x; }
};
 

int main()
{
  using outerspace::setnspvalue;
  using outerspace::getnspvalue;
   
  A a(7);
  
  setnspvalue(a.getvalue());  
 

  // You can use the function outerspace::setvalue() inside a C function

   int y=your_c_function_declaration (&getnspvalue);
 
  a.setvalue(y);
} 
 
 
Ioannis

* Ioannis Vranos
* Programming pages: http://www.noicys.cjb.net
<http://www.noicys.cjb.net/> 
* Alternative URL: http://run.to/noicys