C / C++ / MFC

void f ( Matrix& m )
{
  m(2,5) = 3.14;  // calls double& Matrix::operator()
}

void g ( const Matrix& m )
{
  m(4,1) = 42;  // calls double Matrix::operator() const
                     // error, can't assign to a plain double
}

1. Your Func method has to be static if you want to pass it on as a regular function pointer. Check Mike Dunn's C++ FAQ for details.
   
2. Once you hace declared your method static, you can set its calling convention like this:

   class CMy{
     ...
     static void __cdecl Func();
   };

   
   

static CMy* pMy = NULL;
 
static void StaticFunc()
{
  if (pMy != NULL) {
     pMy->Func();
  }
}

CMy my;
pMy = &my;
CallIt (&StaticFunc);

class MyGlutWindow{
private:
  static std::map<int,MyGlutWindow*> ID2MyGlutWindow;
public:
  MyGlutWindow(){
    ...
    ID2MyGlutWindow[glutGetWindow()]=this; // associates current GLUT window ID to myself
  }
  static void __cdecl glutMouseFuncCallback(int button,int state,int x, int y){
   ID2MyGlutWindow[glutGetWindow()]->doGlutMouseFuncCallback(button,state,x,y);
  }
  void doGlutMouseFuncCallback(int button,int state,int x, int y){
    ...
  }
};