incompatible class types

[y2bismil@engmail.uwaterloo.ca]

Hi all,

This is a bit of a weird one.  Basically this is old code that I don't want to
change a lot of it.  Someone, someday made some assumptions about class layout
that aren't valid in GCC.

consider these two classes.

*********************************
class C1 {
public:
   C1() { initQC() ; }
   C1(unsigned q_type) { initQC(q_type) ; }

   inline void  initQC() ;
   inline void  initQC(unsigned q_type) ;

private:
   struct LINK {
      C1 *fwd ,
         *bkwd ;
   } ;
   LINK  links[MAX_LINKS] ;

   //member functions
};
***********************************

***********************************
class TEVENT {
public:
   TEVENT() ;
   TEVENT( void *dump_addr ) ;           // only used in dump debug build.
   virtual ~TEVENT() ;

   virtual void   event_activate( void ) = 0 ;
   //other functions

private:
   QC          *_fwd ;
   QC          *_bkwd ;
// other member variables
} 
****************************************

class QC is the main class used in function calls, but its done in a funny
manner.  All params into such functions are done through void*.

void ADD_TO_Q( void *element)
{
  //element is assumed in here to be of type QC
}

But throughout the code, both QC* and TEVENT* are passed into ADD_TO_Q type
functions.  (Other variants of TEVENT* also exist, but this is just an example).

This worked fine with the greenhills compiler and the watcom compiler for a long
time.  Of course, that doesn't make the code right by any means.  Basically the
two types differ by 4 bytes from their first instance of QC *_fwd (one in the
array, one in a direct variable).  I am assuming this is due to the virtual
functions in TEVENT leading to a prefix of a pointer to a v-table.

Other classes do derive from TEVENT and do make use of the virtual functions.

My solution to this so far is to write a cast routine from TEVENT to QC and
vice-versa.  Going from TEVENT to QC would not be too bad.  But going from QC to
TEVENT is going to have to be a hard-coded number (4) correct?

I'm open to any suggestions here.  

Thanks,

Yamin

----------------------------------------
This mail sent through www.mywaterloo.ca