1. The List Container and Iterators
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. Create an empty list. This is the default constructor.
CLASS list
Constructors
<list>
list();
Create an empty list. This is the default constructor.
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. Return the value of the item at the rear of the list.
CLASS list
Operations
<list>
T& back();
Return the value of the item at the rear of the list.
Precondition: The list must contain at least one element.
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.

9. void push_back(const T& value); Add a value at the rear of the list.
CLASS list
Operations
<list>
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.
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.
CLASS list
Operations
<list>
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.
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. const_iterator begin();
CLASS list
Operations
<list>
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.
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. const_iterator end();
CLASS list
Operations
<list>
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.
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.
CLASS list
Operations
<list>
void erase(iterator pos);
Erase the element pointed to by pos.
Precondition: The list is not empty.
Postcondition: The list has one fewer element.
void erase(iterator first, iterator last);
Erase all list elements within the iterator range [first, last].
Postcondition: The size of the list decreases by the number of elements in the range.

14. iterator insert(iterator pos, const T& value);
CLASS list
Operations
<list>
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. --: Moves the iterator to the previous item in the list.
CLASS list::iterator
Operations
<list>
*: Accesses the value of the item currently pointed to by the iterator.
*iter;
++: 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:
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() §- the list member function end()
- 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 iterator pos.
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