Note the possibly unexpected result of:
printf("typeid(&C::b) = %s\n",typeid(&C::b).name());
printf("typeid(&B::b) = %s\n",typeid(&B::b).name());
Which on VS2010 yields:
typeid(&C::b) = int B::*
typeid(&B::b) = int B::*
This indicates that the resulting type for &C::b is a member pointer on type B. Since C is derived from B the pointer is freely convertible to a member pointer on type C. This explains the difference between the two values you see. &C::b is a member function pointer on type B, int C::*p is a member function pointer on type C.
int B::*p_b = &B::b;
int C::*p_c = p_b;
printf("p_b = %p\n", p_b);
printf("p_c = %p\n", p_c);