PRODUCT  :  Borland C++                            NUMBER  :  655
  VERSION  :  All
       OS  :  PC DOS
     DATE  :  October 19, 1993                         PAGE  :  1/1

    TITLE  :  Getting the Offset of a Member of a Structure





  How to get the offset of a member of a structure:

  #include <stddef.h>

  struct mys {
     int member1;
     int member2;
  };

  int where_b = offsetof( struct mys , member2 );

  What this looks like is this:

  int where_b = (size_t)&(((struct mys _FAR *)0)->member2);

  What this does is typecast absolute address 0 to be a far pointer
  to the struct.   Then  it references member2 off of this address.
  Then we take the address of this location. Because 0 is cast to a
  far  pointer,  we  are  starting  at 0000:0000 so the address  of
  member2  will  be  the  relative  offset of a member2 within  any
  structure. All this can be evaluated at compile time.

  DISCLAIMER: You  have the right to use this technical information
  subject to the terms  of  the  No-Nonsense License Statement that
  you received with  the  Borland product to which this information
  pertains.