CSI 400/500 Operating SystemsSpring 2009

LAB - Dynamic Allocation in C Using Linked Lists

Week of February 24-26

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Creating structures in C

• Use struct keyword

• Create new variable class using typedef

• Can nest structures

• Simple way to gather data that defines a particular data item

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Dynamic structures

• Can combine malloc and sizeof to allocate dynamic storage of structures

• Conducive to creating lists of structure elements

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Dynamic Linked List

• Linear chain of structures created during execution

• Definitions:– NODE : individual item on chain– FIELD : individual data item in node– HEAD : start of chain– TAIL : end of chain– NEXT : pointer to next node– NULL : no node at end of pointer

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Linked List implementation in C

• Most linked lists require two structures:– One for data contained in node– One for node

• Nodes created by obtaining storage, setting data value, and initializing *next and *prev to 0

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Linked List functions

• So now we have one -- what do we do with it?– Insert new node– Remove existing node– Find a given node– List all nodes

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Inserting a node

• Receive key value of new node

• Obtain storage

• Check if list exists

• Find location in list– Do not add if already exists

• Add to list

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Record look-ahead

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Deleting a node

• Find it

• Reset pointers to remove it from list

• Free storage

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Finding a node

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List values in list

• Appears in sorted order automatically

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Why discuss lists in an Operating Systems course?

• Many operating systems use lists as their queues

• Others use more complex structures like trees and hash tables, which will be discussed later in this course