The Linked List

The linked list implementation of a list

A linked list is a linear collection of self-referential structures, called nodes, connected by pointer links. A linked list is accessed by keeping a pointer to the first node of the list. This pointer to the first node of a list is typically named head. Subsequent nodes are accessed via a link pointer member that is stored in each node.

The operations on linked lists include :

creation of a node
putting information into the node
inserting a node into the list
deleting a node from the list
is the list empty
print the list
etc.

A node is a structure that has whatever members are needed to hold the data, and a member that is pointer to a structure of the same type, the link. Since this pointer typically is a pointer to the next item in the list, it is traditionally called next.

One possible interface for a linked list

/********************************************************\ * Filename: linkedlist.h * * Author: Sue Bogar * * Written: 11/17/98 * * Section: 201staff * * SSN: 123-45-6789 * * Email: bogar@cs.umbc.edu * * * * This file contains the structure definition of a node, * * and typedefs of the types NODE and NODEPTR. It also * * contains the function prototypes for the functions * * defined in linkedlist.c, which are the linked list * * implementation of a list abstract data type. * \********************************************************/ /* NODEPTR is defined as an alias for ** "struct node *" so it can be used within ** the structure before it is completely defined */ typedef struct node * NODEPTR; /* A NODE is a structure that allows us to build a linked ** list since it has both a data portion and a NODEPTR as ** its members. The NODEPTR called next is known as the ** link. */ typedef struct node { int data; NODEPTR next; /* OR struct node *next; */ }NODE; /************************************** ** Function: CreateNode ** Input: none ** Output: memory for a node is malloced ** and a pointer (nodePtr) to the memory ** is returned to the user ** Note: ** CreateNode initializes the members ** CreateNode exits if there is insufficient ** memory **************************************/ NODEPTR CreateNode (void); /************************************** ** Function: GetData ** Input: a pointer to a node (NODEPTR) ** Output: the node pointed to is populated ** with data input from the user ** **************************************/ void GetData (NODEPTR temp); /************************************** * Function: Insert * Input: a pointer to a pointer to the head of the * linked list (headPtr) * a pointer to the node (NODEPTR) to be * inserted * Output: the node is inserted at the end of the * linked list * there is no return value **************************************/ void Insert (NODEPTR* headPtr, NODEPTR temp); /************************************** * Function: Delete * Input: a pointer to a pointer to the head * (headPtr) of the linked list * an integer (target) containing the value * of the data in the node to be deleted * Output: if found, the first node with the corresponding * value (target) is deleted from the * linked list * if the node is deleted, the value found * in the deleted node (NOT target) is * returned * if no node is deleted, an error is * printed and -1 is returned **************************************/ int Delete (NODEPTR* headPtr, int data); /************************************** * Function: IsEmpty * Input: a pointer to the head of the linked list * Output: returns 1 (true) if the list is empty * returns 0 (false) if the list is not empty *********************************************/ int IsEmpty (NODEPTR head); /************************************** * Function: PrintList * Input: a pointer to the head of the list * Ouput: each node in the list is printed according * to the format specified in this code **************************************/ void PrintList (NODEPTR head);

Thursday, 17-Jan-2002 13:52:31 EST