Lecture Preview: Pointers and Linked Nodes

(Suggested book reading: Programming Abstractions in C++, 12.2 - 12.3; 14.3)

Today we will learn about a C++ feature called pointers. A pointer stores the memory address of another value. Get the address of an existing value by preceding it with & . Declare a pointer by following a data type with * . You can also follow a pointer to the memory address at which it points by preceding its name with * . Here is a brief example: 

int x = 42;
int* p = &x;
cout <<  p << endl;   // 0x7f8e20
cout << *p << endl;   // 42
*p = 99;
cout << x << endl;    // 99

We can use pointers to create a collection called a linked list. A linked list is like a Vector or ArrayList, but instead of storing its elements in one large array block of data, it stores each element in a small object called a node. Nodes are linked together by having each node store a pointer that remembers the memory address of the next node that follows it. Here is an example structure for representing a node: 

struct ListNode {
    int data;
    ListNode* next;
};

You could use this structure in the following way to create a simple list of elements of data: 

ListNode* list = new ListNode();
list->data = 10;

list->next = new ListNode();
list->next->data = 20;

list->next->next = new ListNode();
list->next->next->data = 30;
list->next->next->next = NULL;

This would produce the following list:

linked nodes

We use the special value NULL to indicate the end of the list. NULL is a special value in C++ representing a pointer to nothing; it indicates the lack of any further data.

This document and its content are copyright © Marty Stepp and Julie Zelenski, 2019. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the authors' expressed written permission.