Comp 2673, Spring 2002

May 8, lecture notes



Reading assignment:
    Read about iterators and lists in D&D Chapter 20

Here's a simple program that creates a vector and traverses through
the vector:  vectortest1.cpp.
The method of traversing:
    for (i=0; i < ivec.size(); i++)
is a primitive way to use the vector class.  A more sophisticated method
is to use iterators.

An iterator is a smart pointer that allows you to traverse through an stl
container without necessarily having knowledge of how that container works.
Examine this program, which shows how to define iterators, how to increment
them, and how to use them to traverse through a vector:
vectortest2.cpp

Like the stl vector class implements a smart array,  there is also an stl
container that implements a linked list.  This linked-list container
is called "list".  To gain access to it, #include <list>
A linked list holds a sequential list of objects just as a vector does, but
it is implemented in a completely different way.  The items in the list are
no longer necessarily stored contiguously in memory, but rather each element
has a pointer that indicates where to find the next element and the previous
element in the list.  Linked lists are efficient when insertions and/or
deletions are regularly made in the middle of the list.
By using an iterator to traverse the list, we can bypass having to access these
next and previous pointers - incrementing an iterator in a list automatically
makes the iterator follow the pointers to the next element.  Note that
the < operator  and > operator are not available for lists - use the
!= operator instead. 
Examine this program to see how to create a list, insert items into the list,
traverse the list, and access elements of the list.
listtest.cpp