Esoteric C++ operators

Question

What is the purpose of the following esoteric C++ operators?

Pointer to member

::*

Bind pointer to member by pointer

Answer 1

There's no such operator as ::* and there's never been. I don't know where you got it.

As for ->* and .* - these are dereference operators for pointers of pointer-to-member type.

struct S {
  int i;
};

int main() {
  int S::*pi = &S::i; // pointer of pointer-to-member type

  S s;
  S* ps = &s;

  s.*pi = 0; // operator `.*` used
  assert(s.i == 0);

  ps->*pi = 1; // operator `->*` used
  assert(s.i == 1);
}

As for what pointers-to-members are... what does your favorite C++ book say on the subject?