c plus plus

When we are required to find offset of an element within a structure? Or, how do we call the function of an outer class from a function in the inner class? (The inner class is nested in the outer class).

#include  <iostream.h>  
class outer   
{  
      int i ;   
      float f ;  
   public :  
      class inner   
      {  
         public :  
            infunc( )   
            {  
               outer *pout ;   
               pout = (outer*) this - ( size_t ) &( ( ( outer* ) 0 ) -> in ) ;   
               pout -> outfunc( ) ;  
            }  
      } ;   
      inner in ;   
      outfunc( )   
      {  
         cout << "in outer class's function" ;  
      }  
} ;   
void main( )   
{  
   outer out ;   
   out.in.infunc( )   
} 

In the above example we are calling outer::outfunc( ) from inner::infunc( ). To call outfunc( ) we need a pointer to the outer class. To get the pointer we have subtracted offset of the inner class's object (base address of outer class's object - address of inner class's object) from the address of the inner class's object.