[#7] A pointer to an object or incomplete type may be converted
       to a pointer to a different object or incomplete type.  If the
       resulting pointer is not correctly aligned for the pointed-to
       type, the behavior is undefined.  Otherwise, when converted
       back again, the result shall compare equal to the original
       pointer.  When a pointer to an object is converted to a pointer
       to a character type, the result points to the lowest addressed
       byte of the object.