PRB: offsetof() Macro Fails with Virtual Base Class

MORE INFORMATION

Sample Code

   /* Compile options needed: none
   */ 

   #include <stdio.h>
   #include <iostream.h>
   #include <stddef.h>

   class A { public: int a; };
   class B : virtual public A { public: int v_a; };
   class C : virtual public A { public: int v_b; };
   class D : virtual public B, virtual public C { public: int b; };

   int main()
   {

      D xD;

      xD.b   = 16;
      xD.v_a = 8;
      xD.v_b = 4;
      xD.a   = 2;

      cout << "sizeof(D) == " << sizeof(D)   << endl;
      cout << "sizeof(C) == " << sizeof(C)   << endl;
      cout << "sizeof(B) == " << sizeof(B)   << endl;
      cout << "sizeof(A) == " << sizeof(A)   << endl << endl;

   // The following code section works around the offsetof() problem
      cout << "offsetof(D.b)   == " << (char *)&xD.b - (char *)&xD << endl;
      cout << "offsetof(D.v_a) == " << (char *)&xD.v_a - (char *)&xD <<
      endl;
      cout << "offsetof(D.v_b) == " << (char *)&xD.v_b - (char *)&xD <<
      endl;
      cout << "offsetof(D.a)   == " << (char *)&xD.a - (char *)&xD << endl;
      cout << endl;

   // The following statement is generated correctly
      cout << "offsetof(D.b)   == " << offsetof(D, b)   << endl;

   // The following three statements cause access violations when executed
      cout << "offsetof(D.v_a) == " << offsetof(D, v_a) << endl;
      cout << "offsetof(D.v_b) == " << offsetof(D, v_b) << endl;
      cout << "offsetof(D.a)   == " << offsetof(D, a)   << endl << endl;

      cout << "Press Enter...";
      cin.get();

      return 0;
   }