more headachy c++ gubbish.

[zwol]

In C you can totally do this.

  typedef struct { ... } S;
  typedef struct { ...; S s; ... } T;

  /* ESS assumed to be contained in a T.  */
  T * TfromS(S * ess) {
    return (T *)(((char *)ess) - offsetof(T, s));
  }

But in C++, offsetof is not defined when its first argument is a “non-POD type” (approximately, “a type you couldn't have declared in C.”) The replacement for offsetof is the “pointer to member.”

But you can't do the above with a pointer to member.

So how the Belgium do you do it?