Department of Computer Science and Engineering, HKUST 1 HKUST Summer Programming Course 2008 Linked List and Namespace ~ include dynamic objects

2 Overview  Linked List Class Definition Add Node Delete Node Destructor  Namespace

3 Linked List  A linked list is a collection of data.  Each element of the linked list has Some data A link to the next element  The link is used to chain the data, usually they are pointers.  Example: A linked list of integers: Data Link

4 Linked List  A linked-list is a useful structure to hold a collection of data.  A linked-list is dynamic. It can grow and shrink to any size.  It can be implemented using dynamic class (dynamic objects). Dynamic objects are objects created and deleted by ‘ new ’ and ‘ delete ’.  The main task of a linked list class is to maintain the chain (pointer) between the items it holds.

5 Linked List  Original linked list of integers:  Insertion, add(60):  Deletion, delete(45): Old pointer Rearrange pointers

6 Linked List – class definition  This is the definition of class ListNode (holding data).  Pay attention to the techniques we have learned before. class ListNode { public: // no default constructor, user must call the // constructor explicitly ListNode(int i_data, ListNode* i_next=NULL): data(i_data), next(i_next) {} friend class List; // no destructor, let List class // handles memory deallocation (delete) private: int data; ListNode* next; };

7 Linked List – class definition  This is the definition of class List (organizing data). class List { public: List() : head(NULL), tail(NULL), num_node(0) {} ~List(); void print(); bool addNode(int new_data); bool deleteNode(int del_data); int getSize() { return num_node; } private: ListNode* head; ListNode* tail; int num_node; };

8 Linked List – add node  To insert a new node: Create a new node with ListNode* temp = new ListNode(new_data); Update the tail pointer, move its next pointer to the new node. Move the tail pointer to the new end.  In our example, new nodes are added to the end of list. Full code are showed in main.cpp, linked.h and linked.cpp  You can try to add nodes to the head or according to the number sequence. The procedure is similar.

9 Linked List – delete node  To delete a node: Locate the node to be deleted  temp points to the node.  prev points to its predecessor Disconnect node from list using: prev->next = temp->next; Delete unnecessary node, return memory to system: delete temp;  Be careful when deleting in data in special location, e.g. head. Depends on your implementation, sometime tail is another special case too.

10 Linked List - destructor  ListNode class don’t have a destructor, because it doesn’t have any dynamic data member.  But List class has dynamic members, therefore we have to write a destructor for it. List::~List() { ListNode* temp = head; while (head != NULL) { head = head->next; delete temp; temp = head; }  Pay attention to the terminating condition when you use this kind of loops. They will easily get wrong.

11 Comparison between Array and Linked List  Static Array: Size are fixed at compilation time. Elements can be random accessed.  Binary search is efficient when elements can be random accessed. Elements are continuously stored.  Dynamic Array: Size are not fixed at compilation time.  You may resize the array, but copying is needed. A slow process. Elements can be random accessed. Delete an element also needs copying. Elements are continuously stored.

12 Comparison between Array and Linked List  Linked List: Size are not fixed at compilation time. You may resize the linked list any time, no copying is needed.  Elements can only be sequentially accessed. Slow to use binary search. Easy to delete an element. Elements are not continuously stored.  Slow when caching is considered.

13 Namespace  Suppose you want to use two libraries, but some names collide, what can you do? // file: classA.h// file: classB.h class Service {…}; class ClassB {…}; class ClassA {…}; class Service {…}; int del_all();  Even if you don't use “Service” and “del_all”, you run into trouble: the compiler will complain about multiple definitions of “Service” the linker may complain about multiple definitions of “del_all()”

14 Namespace  Use namespace can solve multiple names problem. // file: classA.h namespace service_class_A { class Service {…}; class ClassA {…}; int del_all(); } // file: classB.h namespace service_class_B { class Service {…}; class ClassB {…}; int del_all(); }

15 Namespace  You can refer to names in a namespace with ::, it is called scope resoultion operator. service_class_A::del_all(); service_class_B::Service serB;  If the namespace is too long, you can define your own namespace alias, namespace cA = service_class_A; namespace cB = service_class_B; cA::del_all(); cB::Service serB;

16 Namespace  You can also import the whole namespace by a “using” declaration.  You can import a single name, using service_class_A::del_all;  Everytime you use del_all(), it will refer to the del_all() of “classA.h”

17 Namespace  Or you can import the whole namespace, using namespace service_class_B;  Everytime you use del_all() or Service class, they will refer to the one in “classB.h”.  One famous example is “ using namespace std; ”  Of course, after you imported the whole namespace, you can specify the whole name if you do want to use other functions, e.g. using namespace service_class_B; service_class_A::del_all();

18 Namespace  You can also bring all the names of a namespace into your program at once, but make sure it won't cause any ambiguities. namespace cA = service_class_A; namespace cB = service_class_B; using namespace cA; using namespace cB; Service ser_K;// error: ambiguous classB gun_dum;// ok, no problem.  If the above ambiguity is removed, the program above can be compiled.

19 Namespace  The following will cause error too, using service_class_A::Service; using service_class_B::Service;  Do you know why?