List Container and Iterators

1. Chapter 6 The List Container and Iterators

2. Outline • Sample list • The list ADT • CLASS list Constructors • CLASS list Operations • CLASS list::iterator Operations • Inserting an element into a list • Removing an element from a list • Ordered lists • Splicing two lists

3. §- list - A Sequence of elements stored by position. - Index access is not available… §- to access the value of an element, must pass through its preceding elements. 3

4. Shifting blocks of elements to insert or delete a vector item

5. Model of a list object with links to next and previous element

6. The List ADT • The list API documents the member function prototype as well as pre- and postconditions. • provides three constructors to declare a list object.

7. list(); Create an empty list. This is the default constructor. CLASS list <list> Constructors list(int n, const T&value = T()); Create a list with n elements, each having a specified value. If the value argument is omitted, the elements are filled with the default value for type T. Type T must have a default constructor, and the default value of type T is specified by the notation T(). list(T *first, T *last); Initialize the list, using the address range [first, last).

8. T& back(); Return the value of the item at the rear of the list. Precondition: The list must contain at least one element. CLASS list <list> Operations bool empty() const; Return true if the list is empty, false otherwise. T& front(); Return the value of the item at the front of the list. Precondition: The list must contain at least one element.

9. void push_back(const T& value); Add a value at the rear of the list. Postcondition: The list has a new element at the rear, and its size increases by 1. CLASS list <list> Operations void pop_back(); Remove the item at the rear of the list. Precondition: The list is not empty. Postcondition: The list has a new element at the rear or is empty.

10. void push_front(const T& value); Add a value at the front of the list. Postcondition: The list has a new element at the front, and its size increases by 1. CLASS list <list> Operations void pop_front(); Remove the item at the front of the list. Precondition: The list is not empty. Postcondition: The list has a new element at the front or is empty. int size() const; Return the number of elements in the list.

11. iterator begin(); Returns an iterator that references the first position (front) of the list. If the list is empty, the iterator value end() is returned. CLASS list <list> Operations const_iterator begin(); Returns a const_iterator that points to the first position (front) of a constant list. If the list is empty, the const_iterator value end() is returned. iterator end(); Returns an iterator that signifies a location immediately out of the range of actual elements. A program must not dereference the value of end() with the * operator.

12. iterator end(); Returns an iterator that signifies a location immediately out of the range of actual elements. A program must not dereference the value of end() with the * operator. CLASS list <list> Operations const_iterator end(); Returns a const_iterator that signifies a location immediately out of the range of actual elements in a constant list. A program must not dereference the value of end() with the * operator.

13. void erase(iterator pos); Erase the element pointed to by pos. Precondition: The list is not empty. Postcondition: The list has one fewer element. CLASS list <list> Operations void erase(iterator first, iterator last); Erase all list elements within the iterator range [first, last]. Precondition: The list is not empty. Postcondition: The size of the list decreases by the number of elements in the range.

14. CLASS list <list> Operations iterator insert(iterator pos, const T& value); Insert value before pos, and return an iterator pointing to the position of the new value in the list. The operation does not affect any existing iterators. Postcondition: The list has a new element.

15. §-iterator - A generalized pointer that moves through a container(eg. vector, list) element by element… forward or backward - At any point, the * operator accesses the value of a container item. Example: PP1010 15

16. *: Accesses the value of the item currently pointed to by the iterator. *iter; CLASS list::iterator <list> Operations ++: Moves the iterator to the next item in the list. iter++; --: Moves the iterator to the previous item in the list. iter--; ==: Takes two iterators as operands and returns true when they both point at the same item in the list. iter1 == iter2 !=: Returns true when the two iterators do not point at the same item in the list. iter1 != iter2

17. Inserting an element into a list Insertion function returns an iterator pointing at the new element The original iterator continues to point at the same element

18. Removing an element from a list Erase function make the iterator invalid and the iterator must be reinitialized.

19. §- The list class has two iterator types: 1) iterator: A generalized list traversal pointer. 2) const_iterator: must be used with a constant list object. Each type is a nested class of list and must be accessed by using the scope operator :: For example: list<int>::iterator iter; 19

20. §- the list member function begin() - Gives an iterator an initial value that points to the first element. §- the list member function end() - Returns an iterator pointing just past the last element of the list. 20

21. §- list class member functions insert() and erase() • - Both use an iterator argument to modify a list. • insert(): places value in the list before the data referenced by the iteratorpos. • erase(): removes the data item referenced by pos from the list. 21

22. §- The sequential search of a list object - implemented by using an iterator range [first, last). - It returns an iterator that points at the target value or has value last if the target is not in the list. Example: PP 1057: program 17-6 22