bEgInSlIdE OOP-1 Simple Containers in C++ uList: simple container class uIterators uMemory Allocation Responsibility uMixed type collections uAbstract Container Classes uNon-Intrusive lists

bEgInSlIdE OOP-2 Iterators i i const N = 100; double a[N]; for (int i = 0; i < N; i++) {... // Process a[i]... } const N = 100; double a[N]; for (int i = 0; i < N; i++) {... // Process a[i]... } uAn iterator is used for iterating (traversing/scanning) over all members of a container. Required operations are: lDeclare lInitialize lGet element lIncrement (Decrement?) lCheck if last uArray iterators are just integers...

bEgInSlIdE OOP-3 List Container Class void driver(void) { List mid_east; mid_east.insert(new Leader("Assad", "Syria")); mid_east.insert(new Leader("Peres", "Israel")); mid_east.insert(new Leader("Hussein", "Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak", "Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } void driver(void) { List mid_east; mid_east.insert(new Leader("Assad", "Syria")); mid_east.insert(new Leader("Peres", "Israel")); mid_east.insert(new Leader("Hussein", "Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak", "Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } uGeneralization: array with integer iterators - into a generalized list container with typical list operations, which could be used to store objects of any type. uWe would like our container class used as follows:

bEgInSlIdE OOP-4 Memory Allocation Responsibilities uWhat’s stored in the container? lobjects Container must make a copy of all stored objects and be responsible for allocating and deallocating them. lpointers Who allocates memory for the stored objects? User - Automatic objects cannot be stored. Container - Stored objects are created using copy constructor. Who deallocates the objects? User - The user code must keep record of all objects stored in the container, so that it could erase them. Container - Usually the preferred way. Node::Node(const String& s) : str(s){} Node::Node(const String* s) : sptr(s){} Node::Node(const String& s) : sptr(new String(s)){}

bEgInSlIdE OOP-5 Memory Allocation and Deallocation Responsibilities with Our Interface void driver(void) { List mid_east; mid_east.insert(new Leader("Assad", "Syria")); mid_east.insert(new Leader("Peres", "Israel")); mid_east.insert(new Leader("Hussein", "Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak", "Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } void driver(void) { List mid_east; mid_east.insert(new Leader("Assad", "Syria")); mid_east.insert(new Leader("Peres", "Israel")); mid_east.insert(new Leader("Hussein", "Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak", "Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } Allocation in user code The container stores pointers to objects allocated in user code. Allocation in user code The container stores pointers to objects allocated in user code. Deallocation in container code The List destructor mid_east.~List executed when driver() returns must delete all the inserted items Deallocation in container code The List destructor mid_east.~List executed when driver() returns must delete all the inserted items

bEgInSlIdE OOP-6 The List Interface class List { public: class Node {... }; class Iterator {... }; void insert(Node *object) { object->next = first.next; first.next = object; }.... private: Node first; // Dummy record }; class List { public: class Node {... }; class Iterator {... }; void insert(Node *object) { object->next = first.next; first.next = object; }.... private: Node first; // Dummy record }; Nested type definition are used mainly for scope definition and for minimizing the pollution of the global name space. Indeed, the Ansi-C++ committee decided to add a namespace keyword to C++.

bEgInSlIdE OOP-7 uDeclare and initialize - List::iterator i(mid_east) uInitialize - i.reset() uGet element - Value of i.next() uIncrement - i.next() uCheck if last - Cast to int. If 0 then list exhausted. List Iterators... List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ;... for (i.reset(); i; ((Leader *)i.next())->print()) ;... List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ;... for (i.reset(); i; ((Leader *)i.next())->print()) ; Is next a mutator or an observer?

bEgInSlIdE OOP-8 Inheritance and Heterogeneous Containers class List {... class Node { Node *next; Node(Node *n): next(n) {} friend class List; protected: Node(void): next(NULL) {} virtual ~Node(void) { delete next; } };... }; class List {... class Node { Node *next; Node(Node *n): next(n) {} friend class List; protected: Node(void): next(NULL) {} virtual ~Node(void) { delete next; } };... }; Recursive deletion is not terribly efficient... Note that delete NULL is perfectly legal in C++! uThe List::Node data type is nothing but its identity and linkage information. uThe List data type may contain any type derived from List::Node.

bEgInSlIdE OOP-9 Inheriting From List::Node #include class Leader: public List::Node { String name; String country; public: Leader(const char *n, const char *c): name(n), country(c) {} void print(void) { cout << name << ';' << country << '\n'; } }; #include class Leader: public List::Node { String name; String country; public: Leader(const char *n, const char *c): name(n), country(c) {} void print(void) { cout << name << ';' << country << '\n'; } }; u Leader ’s constructor will invoke List::Node ’s default constructor u Leader ’s destructor will invoke List::Node ’s destructor

bEgInSlIdE OOP-10 The Type Hierarchy so Far List List::Node List::Iterator Leader uThe nested class definitions are done only for minimizing pollution of the global name space

bEgInSlIdE OOP-11 New & Delete class List {... class Node {... protected: virtual ~Node(void) {... } public: void *operator new(size_t size) { return ::operator new(size); void operator delete(void *p, size_t size) { ::operator delete(p); };... }; class List {... class Node {... protected: virtual ~Node(void) {... } public: void *operator new(size_t size) { return ::operator new(size); void operator delete(void *p, size_t size) { ::operator delete(p); };... }; Employee::new for all classes derived from Employee Always static, even if not declared as such! The size parameter is that of the actual object allocated/deallocated.

bEgInSlIdE OOP-12 Protected Data Members uDerived classes cannot access private parts (Or else it would have been a breach of privacy) uProtected data and methods can be accessed only by: lderived classes lmembers lfriends

bEgInSlIdE OOP-13 Protected Constructors class List { public: class Iterator; class Node { friend class List; friend class Iterator; Node *next; Node(Node *n): next(n) {} protected: Node(void): next(0) {} virtual ~Node(void) { delete next; } };... }; class List { public: class Iterator; class Node { friend class List; friend class Iterator; Node *next; Node(Node *n): next(n) {} protected: Node(void): next(0) {} virtual ~Node(void) { delete next; } };... }; uThe next field and the non-default constructor can be used by List and List::Iterator only. u Leader can only use the default constructor of List::Node.

bEgInSlIdE OOP-14 List Destruction and Virtual Destructors List class List {... class Node {... protected: virtual ~Node(void) { delete next; } }; Node first; }; class List {... class Node {... protected: virtual ~Node(void) { delete next; } }; Node first; }; uDestruction sequence l List goes out of scope lט List destructed lט First node destructed lט Other nodes destructed recursively u ~List::Node must be virtual to guarantee that ~Leader is called when the list is destructed Leader Node Leader Node Leader Node

bEgInSlIdE OOP-15 Iterator Implementation class List {... class public: class Iterator { Node *first, *curr; public: Iterator(List& l) { first = &l.first; reset(); } void reset(void) { curr = first->next; } operator int(void) { return curr != NULL; } Node *next(void) { Node* tmp = curr; if (curr != NULL) curr = curr->next; return tmp; } };... Node first; // Dummy node used as first list element }; class List {... class public: class Iterator { Node *first, *curr; public: Iterator(List& l) { first = &l.first; reset(); } void reset(void) { curr = first->next; } operator int(void) { return curr != NULL; } Node *next(void) { Node* tmp = curr; if (curr != NULL) curr = curr->next; return tmp; } };... Node first; // Dummy node used as first list element };

bEgInSlIdE OOP-16 Summary: List Interface class List { public: class Node {... }; class Iterator {... }; void insert(Node *object) { object->next = first.next; first.next = object; } }; class List { public: class Node {... }; class Iterator {... }; void insert(Node *object) { object->next = first.next; first.next = object; } }; u List stores any class derived from List::Node. uExported operations are insert and iteration Only. uConstructor and destructor are generated automatically.

bEgInSlIdE OOP-17 Quiz void driver(void) { List mid_east; mid_east.insert(new Leader("Assad","Syria")); mid_east.insert(new Leader("Peres","Israel")); mid_east.insert(new Leader("Hussein","Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak","Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } void driver(void) { List mid_east; mid_east.insert(new Leader("Assad","Syria")); mid_east.insert(new Leader("Peres","Israel")); mid_east.insert(new Leader("Hussein","Jordan")); List::Iterator i(mid_east); for (; i; ((Leader *)i.next())->print()) ; mid_east.insert(new Leader("Mubarak","Egypt")); for (i.reset(); i; ((Leader *)i.next())->print()) ; } uWhat will be printed? uDescribe the allocation and deallocation activities. uHow is the following an indication of a design problem? l ((Leader *)i.next())->print()

bEgInSlIdE OOP-18 class List {... class Iterator { Node *first, *curr; Node *next(void) { Node* tmp = curr; if (curr != NULL) curr = curr->next; return tmp; } public: Iterator(List& l) { first = curr = l.first.next; } void reset(void) { curr = first; } operator int(void) { return curr != NULL; } Node * operator()(void){ return curr; } Iterator& operator++(void){ next(); return *this; } };... };... for (List::Iterator i(mid_east); i; ++i) cout << *(Leader *)i(); class List {... class Iterator { Node *first, *curr; Node *next(void) { Node* tmp = curr; if (curr != NULL) curr = curr->next; return tmp; } public: Iterator(List& l) { first = curr = l.first.next; } void reset(void) { curr = first; } operator int(void) { return curr != NULL; } Node * operator()(void){ return curr; } Iterator& operator++(void){ next(); return *this; } };... };... for (List::Iterator i(mid_east); i; ++i) cout << *(Leader *)i(); Operator Overloading & Iterators Why prefix operator++ ? Assumption: operator<< is overloaded for class Leader

bEgInSlIdE OOP-19 Iteration Functions void ForEach(List& list, void (*func)(List::Node *current)) { for (List::Iterator i(l); i; ++i) func(i()); } List::Node *FirstThat(List& list, int (*func)(List::Node *current)) { List::Node *current; for (List::Iterator i(l); i; ++i) if (func(current = i())) return current; return (List::Node *)0; } void ForEach(List& list, void (*func)(List::Node *current)) { for (List::Iterator i(l); i; ++i) func(i()); } List::Node *FirstThat(List& list, int (*func)(List::Node *current)) { List::Node *current; for (List::Iterator i(l); i; ++i) if (func(current = i())) return current; return (List::Node *)0; } uCan be used for implementing general purpose iteration and search

bEgInSlIdE OOP-20 Using Iteration Functions void Print(List::Node *n) { cout << (Leader *)n; }... ForEach(mid_east,Print);... Leader Who, *found;... int Search(List::Node *n) { return (Leader *)n == Who; }... if ((found = FirstThat(mid_east,Search)) != NULL)... void Print(List::Node *n) { cout << (Leader *)n; }... ForEach(mid_east,Print);... Leader Who, *found;... int Search(List::Node *n) { return (Leader *)n == Who; }... if ((found = FirstThat(mid_east,Search)) != NULL)...

bEgInSlIdE OOP-21 Memory Allocation Responsibilities: Summary and Typical Errors uBetter to store pointers in a container uBetter let the container own the elements: l Elements destroyed when container destroyed. uTypical errors are: lStore an automatic object lStore a global/static object lStore the same object in more than one container. lDestroying explicitly an element in the container.