Lists +

1. Lists + • CS3240, L. Grewe

2. Goals • Use the C++ template mechanism fr defining generic data types • Implement a circular linked list • Implement a linked list with a header node or a trailer node or both • Implement a doubly linked list • Distinguish between shallow copying and deep copying

3. Goals • Overload C++ operators • Implement a linked list as an array of records • Implement dynamic binding with virtual functions

4. C++ Templates Generic Data Type A data type for which the operations are defined but the types of the items being manipulated are not Template A C++ construct that allows the computer to generate multiple versions of a class type or a function by allowing parameterized types Templates implement generic types

5. C++ Templates template <class ItemType> class StackType { ... } // client code StackType<int>; StackType<float>; StackType<NameType>; Formal parameter Actual parameters

6. C++ Templates • Summary • The formal parameters are in the class template definition • The actual parameters are in the client code • Both formal and actual parameters are enclosed in angle brackets <...> • The actual parameter can be any type, built-in or user-defined

7. C++ Templates What about function templates? Formal parameter precedes function definition and follows class name before scope resolution operator

8. C++ Templates template<class ItemType> void StackType<ItemType>::Push(ItemType newItem) { if (IsFull()) throw FullStack(); else { top++; items[top] = newItem; } } Formal parameters

9. Circular Linked Lists Circular linked list A list in which each node has a successor; the “last” element is succeeded by the “first” element

10. Circular Linked List Why is it better to have the external pointer point to the last element ?

11. Circular Linked List Initialization for search

12. Circular Linked List FindItem cases

13. Circular Linked List Insert an item

14. Circular Linked List Delete an Item

15. Doubly Linked List Doubly linked list A is in which each node is linked to both its successor and its predecessor

16. Doubly Linked List Insert an item

17. Doubly Linked List Does it matter in which order we change the pointers ?

18. Doubly Linked List Delete an item

19. Header and Trailer Nodes • Header Node • A placeholder node at the beginning of a list that contains a key value smaller than any possible key • Trailer Node • A placeholder node at the end of a list that contains a key larger than any possible key How do header/trailer nodes simplify processing ?

20. Copy Structures void CopyStack(StackType oldStack), StackType& copy) { StackType tempStack; ItemType item; while (!oldStack.IsEmpty()) { item = oldStack.Top(); oldStack.Pop(); temptStack.Push(item); } while (!tempStack.IsEmpty()) { item = tempStack.Top(); copy.Pop(); } } What is the status of oldStack? copy? Does the implementation structure matter?

21. Copy Structures oldStack is a value parameter; doesn’t that protect it from change? Yes, but only in the array-based implementation private: int top; ItemType items[MAX_ITEMS]; top and items are enclosed within the stack object

22. Copy Structures In a linked structure, the external pointer is enclosed within the stack object, but the linked structure to which it points is not What causes this problem ?

23. Copy Structures Shallow copy An operation that copies one class object to another without copying pointed-to data Deep copy An operation that not only copies one class object to another but also makes copies of any pointed-to data See the difference?

24. Copy Structures

25. Copy Structures • In summary • A shallow copyshares the pointed to data with the original class object • A deep copystores its own copy of the pointed to data at different locations than the data in the original class object How do we make a deep copy?

26. Copy Structures MyStack Private data: 7000 6000 topPtr 7000 20 30 SomeStack Private data: 5000 2000 topPtr 5000 20 30 Yes, but how? deep copy

27. Copy Structures Deep Copy if anotherStack.topPtr is NULL Set topPtr to NULL else Set topPtr to the address of a newly allocated node Set Info(topPtr) to Info(anotherStack.topPtr) Set ptr1 to Next(anotherStack.topPtr) Set ptr2 to topPtr while ptr1 is not NULL Set Next(ptr2) to the address of a newly allocated node Set ptr2 to next(ptr2) Set Info(ptr2) to Info(ptr1) Set ptr1 to Next(ptr1) Set Next(ptr2) to NULL

28. Copy Structures Relative position of pointers at the beginning of each iteration

29. Copy Structures Copy constructor A special member function of a class that is implicitly invoked when passing a parameter by value, initializing a variable in a declaration, and returning an object as the value of function StackType(const StackType& anotherStack); Of course, the code should implement a deep copy!

30. Copy Structures • That about the assignment operator? • The assignment operator does a shallow copy! • We can overload the assignment operator class StackType { public: ... void operator=(StackType); private: ... void StackType::operator=(StackType anotherStack) // code for a deep copy } Can we overload other operators ?

31. Copy Structrres Al relational operators can be overloaded bool operator<(ItemType other) const; // Returns true if self is less than other bool operator>(ItemType other) const; // Returns true if self is greater than other bool operator==(ItemType other) const; // Returns true if self is equal to other ... Of course, you must write the code as for any other function

32. Array-of-Records Implementation Array in static storage Array in dynamic storage

33. Array-of-Records Implementation Linked list in static storage Linked list in dynamic storage

34. Array-of-Records Implementation Sorted list

35. Array-of-Records Implementation A sorted list of values and a list of free space

36. Array-of-Records Implementation Two linked lists plus free list

37. Array-of-Records Implementation One structure for each list

38. Polymorphism • Polymorphism • The ability to determine which of several operations with the same name to apply to a particular object; a combination of static and dynamic binding • Binding • The time at which a name or symbol is bound to the appropriate • static binding: bound at compile time • dynamic binding: bound at run time

39. Polymorphism NewItemType is derived from ItemType void PrintResult(ItemType& first, ItemType& second); How can this be?

40. Polymorphism C++ relaxes scope rules to allow dynamic binding The type of the actual parameter may be an object of a derived class of the formal parameter virtual void PrintResult(ItemType& first, ItemType& second); Word virtual in base class (ItemType), definition forces dynamic binding Note: Parameters must be reference

41. Circular Doubly Linked List What are the advantages of this structure?

42. Circular Doubly Linked List

43. C++ Tips • Operators :: . sizeof, and ?: may not be overloaded • At least one operand must be a class instance • Precedence, operator symbols, or number of operands cannot be changed • Overloading ++ and -- requires prefix form use by client • To overload these operators = ( ) [ ], member functions must be used • An operator can be given multiple meanings if the data types of operands differ