If you derive your own class from the ios class, or from one of
  its derived classes, the ios sub-object must be properly initialized
  during instantiation.  Specifically, you must ensure that the
  streambuf pointer within the ios sub-object is valid. To do this, you
  can specify the ios(streambuf *) constructor as a member initializer
  for your class constructor.  Optionally, you can call the
  ios::init(streambuf *) member function.