////   This file contains the C++ code from Program 4.19 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm04_19.cpp//template <class T>void LinkedList<T>::InsertAfter (    ListElement<T> const* arg, T const& item){    ListElement<T>* ptr = const_cast<ListElement<T>*> (arg);    if (ptr == 0)	throw invalid_argument ("invalid position");    ListElement<T>* const tmp =	new ListElement<T> (item, ptr->next);    ptr->next = tmp;    if (tail == ptr)	tail = tmp;}template <class T>void LinkedList<T>::InsertBefore (    ListElement<T> const* arg, T const& item){    ListElement<T>* ptr = const_cast<ListElement<T>*> (arg);    if (ptr == 0)	throw invalid_argument ("invalid position");    ListElement<T>* const tmp = new ListElement<T> (item, ptr);    if (head == ptr)	head = tmp;    else    {	ListElement<T>* prevPtr = head;	while (prevPtr != 0 && prevPtr->next != ptr)	    prevPtr = prevPtr->next;	if (prevPtr == 0)	    throw invalid_argument ("invalid position");	prevPtr->next = tmp;    }}