1. 1 Nell Dale Chapter 6 Lists Plus Slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus C++ Plus Data Structures

2. ADT Sorted List Operations Transformers n MakeEmpty n InsertItem n DeleteItem Observers n IsFull n LengthIs n RetrieveItem Iterators n ResetList n GetNextItem change state observe state process all

3. 3 class SortedType MakeEmpty ~SortedType DeleteItem. InsertItem SortedType RetrieveItem GetNextItem ‘C’ ‘L’ ‘X’ Private data: length 3 listData currentPos

4. 4 What is a Circular Linked List? l A circular linked list is a list in which every node has a successor; the “last” element is succeeded by the “first” element. ‘B’ ‘C’ ‘L’‘T’ ‘V’ ‘Y’ listData

5. 5 ‘A’ ‘C’ ‘F’ ‘T’ ‘Z’ What is a Doubly Linked List? l A doubly linked list is a list in which each node is linked to both its successor and its predecessor. listData

6. 6 Each node contains two pointers template struct NodeType { ItemType info; // Data member NodeType * back; // Pointer to predecessor NodeType * next; // Pointer to successor };. back. info. next 3000 ‘A’ NULL

7. 7 What are Header and Trailer Nodes? l A Header Node is a node at the beginning of a list that contains a key value smaller than any possible key. l A Trailer Node is a node at the end of a list that contains a key larger than any possible key. l Both header and trailer are placeholding nodes used to simplify list processing. listData INT_MIN 5 8 13 INT_MAX

8. 8 Recall Definition of Stack l Logical (or ADT) level: A stack is an ordered group of homogeneous items (elements), in which the removal and addition of stack items can take place only at the top of the stack. l A stack is a LIFO “last in, first out” structure.

9. Stack ADT Operations l MakeEmpty -- Sets stack to an empty state. l IsEmpty -- Determines whether the stack is currently empty. l IsFull -- Determines whether the stack is currently full. l Push (ItemType newItem) -- Adds newItem to the top of the stack. l Pop (ItemType& item) -- Removes the item at the top of the stack and returns it in item. 9

10. 10 class StackType StackType MakeEmpty Pop Push IsFull IsEmpty Private data: topPtr ~StackType 20 30

11. 11 What happens... l When a function is called that uses pass by value for a class object like our dynamically linked stack? StackType MakeEmpty Pop Push IsFull IsEmpty Private data: topPtr ~StackType 20 30

12. 12 // FUNCTION CODE template void MyFunction( StackType SomeStack ) // Uses pass by value {. } 12 Passing a class object by value

13. 13 Pass by value makes a shallow copy 20 30 StackType MyStack; // CLIENT CODE. MyFunction( MyStack ); // function call Private data: 7000 6000 topPtr 7000 Private data: topPtr 7000 MyStack SomeStack shallow copy

14. 14 Shallow Copy vs. Deep Copy l A shallow copy copies only the class data members, and does not copy any pointed-to data. l A deep copy copies not only the class data members, but also makes separately stored copies of any pointed-to data.

15. 15 What’s the difference? l A shallow copy shares the pointed to data with the original class object. l A deep copy stores its own copy of the pointed to data at different locations than the data in the original class object.

16. 16 Making a deep copy 20 30 Private data: 7000 6000 topPtr 7000 SomeStack 20 30 Private data: 5000 2000 topPtr 5000 MyStack deep copy

17. 17 // FUNCTION CODE template void MyFunction( StackType SomeStack ) // Uses pass by value { ItemType item; SomeStack.Pop(item);. } WHAT HAPPENS IN THE SHALLOW COPY SCENARIO? 17 Suppose MyFunction Uses Pop

18. 18 MyStack.topPtr is left dangling ? 30 StackType MyStack; // CLIENT CODE. MyFunction( MyStack ); Private data: topPtr 6000 MyStack SomeStack shallow copy Private data: 7000 6000 topPtr 7000

19. 19 MyStack.topPtr is left dangling ? 30 Private data: topPtr 6000 MyStack SomeStack shallow copy Private data: 7000 6000 topPtr 7000 NOTICE THAT NOT JUST FOR THE SHALLOW COPY, BUT ALSO FOR ACTUAL PARAMETER MyStack, THE DYNAMIC DATA HAS CHANGED!

20. 20 As a result... l This default method used for pass by value is not the best way when a data member pointer points to dynamic data. l Instead, you should write what is called a copy constructor, which makes a deep copy of the dynamic data in a different memory location.

21. 21 More about copy constructors l When there is a copy constructor provided for a class, the copy constructor is used to make copies for pass by value. l You do not call the copy constructor. l Like other constructors, it has no return type. l Because the copy constructor properly defines pass by value for your class, it must use pass by reference in its definition.

22. 22 Copy Constructor l Copy constructor is a special member function of a class that is implicitly called in these three situations: n passing object parameters by value, n initializing an object variable in a declaration, n returning an object as the return value of a function.

23. // DYNAMICALLY LINKED IMPLEMENTATION OF STACK template class StackType { public: StackType( ); // Default constructor. // POST: Stack is created and empty. StackType( const StackType & anotherStack ); // Copy constructor. // Implicitly called for pass by value.. ~StackType( ); // Destructor. // POST: Memory for nodes has been deallocated. private: NodeType * topPtr ; }; 23

24. 24 CLASS CONSTRUCTOR CLASS COPY CONSTRUCTOR CLASS DESTRUCTOR Classes with Data Member Pointers Need

25. template // COPY CONSTRUCTOR StackType :: StackType( const StackType & anotherStack ) { NodeType * ptr1 ; NodeType * ptr2 ; if ( anotherStack.topPtr == NULL ) topPtr = NULL ; else // allocate memory for first node { topPtr = new NodeType ; topPtr->info = anotherStack.topPtr->info ; ptr1 = anotherStack.topPtr->next ; ptr2 = topPtr ; while ( ptr1 != NULL )// deep copy other nodes { ptr2->next = new NodeType ; ptr2 = ptr2->next ; ptr2->info = ptr1->info ; ptr1 = ptr1->next ; } ptr2->next = NULL ; } 25

26. 26 What about the assignment operator? l The default method used for assignment of class objects makes a shallow copy. l If your class has a data member pointer to dynamic data, you should write a member function to overload the assignment operator to make a deep copy of the dynamic data.

27. // DYNAMICALLY LINKED IMPLEMENTATION OF STACK template class StackType { public: StackType( ); // Default constructor. StackType( const StackType & anotherStack ); // Copy constructor. void operator= ( StackType ); // Overloads assignment operator.. ~StackType( ); // Destructor. private: NodeType * topPtr ; }; 27

28. 28 C++ Operator Overloading Guides 1All operators except these ::. sizeof ?: may be overloaded. 2At least one operand must be a class instance. 3You cannot change precedence, operator symbols, or number of operands. 4Overloading ++ and -- requires prefix form use by default, unless special mechanism is used. 5To overload these operators = ( ) [ ] member functions (not friend functions) must be used. 6An operator can be given multiple meanings if the data types of operands differ.

29. Using Overloaded Binary operator+ When a Member Function was defined myStack + yourStack myStack.operator+(yourStack) When a Friend Function was defined myStack + yourStack operator+(myStack, yourStack) 29

30. 30 Composition (containment) l Composition (or containment) means that an internal data member of one class is defined to be an object of another class type. A FAMILIAR EXAMPLE...

31. 31 Private data value ComparedTo Print Initialize class ItemType ItemType Class Interface Diagram

32. 32 Sorted list contains an array of ItemType SortedType class IsFull LengthIs ResetList DeleteItem InsertItem MakeEmpty RetrieveItem Private data: length info [ 0 ] [ 1 ] [ 2 ] [MAX_ITEMS-1] currentPos GetNextItem

33. 33 Inheritance l Inheritance is a means by which one class acquires the properties--both data and operations--of another class. l When this occurs, the class being inherited from is called the Base Class. l The class that inherits is called the Derived Class. AN EXAMPLE...

34. 34 Recall Definition of Queue l Logical (or ADT) level: A queue is an ordered group of homogeneous items (elements), in which new elements are added at one end (the rear), and elements are removed from the other end (the front). l A queue is a FIFO “first in, first out” structure.

35. Queue ADT Operations l MakeEmpty -- Sets queue to an empty state. l IsEmpty -- Determines whether the queue is currently empty. l IsFull -- Determines whether the queue is currently full. l Enqueue (ItemType newItem) -- Adds newItem to the rear of the queue. l Dequeue (ItemType& item) -- Removes the item at the front of the queue and returns it in item. 35

36. 36 class QueType QueType ~QueType Enqueue Dequeue. Private Data: qFront qRear ‘C’‘Z’ ‘T’

37. // DYNAMICALLY LINKED IMPLEMENTATION OF QUEUE #include "ItemType.h" // for ItemType template class QueType { public: QueType( ); // CONSTRUCTOR ~QueType( ) ;// DESTRUCTOR bool IsEmpty( ) const; bool IsFull( ) const; void Enqueue( ItemType item ); void Dequeue( ItemType& item ); void MakeEmpty( ); private: NodeType * qFront; NodeType * qRear; }; 37

38. 38 // DERIVED CLASS CountedQue FROM BASE CLASS QueType template class CountedQue : public QueType { public: CountedQue( ); void Enqueue( ItemType newItem ); void Dequeue( ItemType& item ); int LengthIs( ) const; // Returns number of items on the counted queue. private: int length; }; SAYS ALL PUBLIC MEMBERS OF QueType CAN BE INVOKED FOR OBJECTS OF TYPE CountedQue

39. 39 class CountedQue QueType ~QueType Enqueue Dequeue. Private Data: qFront qRear ‘C’‘Z’ ‘T’ CountedQue LengthIs Enqueue Dequeue. Private Data: length 3

40. 40 // Member function definitions for class CountedQue template CountedQue ::CountedQue( ) : QueType ( ) { length = 0 ; } template int CountedQue ::LengthIs( ) const { return length ; }

41. template void CountedQue ::Enqueue( ItemType newItem ) // Adds newItem to the rear of the queue. // Increments length. { length++; QueType ::Enqueue( newItem ); } template void CountedQue ::Dequeue(ItemType& item ) // Removes item from the rear of the queue. // Decrements length. { length--; QueType ::Dequeue( item ); } 41