1. Linked Lists CSE 2451 Matt Boggus

2. Dynamic memory reminder Allocate memory during run-time malloc() and calloc() – return a void pointer to memory or a NULL pointer if allocation failed – The programmer must check for the NULL value before dereferencing the pointer free() – relinquishes memory allocated during run-time – Every malloc and calloc call should have a corresponding free call later – Pointer value is not changed after free, but it is not safe to dereference it (dangling pointer) Memory leak – Memory that has been Dynamically allocated, Not freed, and Is no longer in use/there is no pointer to it

3. Dynamic memory example/practice int x; int *pi; pi = (int*)malloc(5 * sizeof(int)); if (pi == NULL) { printf(Out of memory!\n); exit(1); } for (x = 0; x < 5; x +=1) *pi++ = 1; // Print array // free memory What are the values in the new memory before initializing to zero? Where is pi pointing to after the for loop? How to free?

4. Dynamic arrays – realloc See remember.c example

5. Linked list Data structure consisting of a group of nodes which together represent a sequence A node consists of – Data – A reference/link/pointer to the next node in the sequence Advantages – Efficient insertion or removal of elements from any position – Data items do not have to be stored contiguously in memory Disadvantage – No random access or efficient indexing

6. Singly linked list node /* Node Structure */ struct node { int data; struct node *next; }

7. Doubly linked list node /* Node Structure */ struct node { int data; struct node *next; struct node *prev; }

8. NULL terminated lists Singly linked Doubly linked Boxes with x represent NULL values

9. Circularly linked lists Last pointer is set to the first node

10. Accessing lists Still need a pointer to that refers to the first node in the list: head pointer struct node * head

11. Adding nodes Step through the list until the correct location is found (for a sorted list) newNodes pointer = nodes pointer nodes pointer = newNode

12. List search found = false; ptr = head; while(ptr != NULL) { if(ptr->data = = val) { found = true; break; } else { ptr = ptr->next; } // found = true then ptr points to that node // found = false then value is not in the list, ptr is NULL

13. Removing nodes Step through the list until the node is found nodes pointer = node.nexts pointer Need a pointer to node.next for free

14. Lab3

15. Additional examples http://rosettacode.org/wiki/Linked_list http://www.macs.hw.ac.uk/~rjp/Coursewww/ Cwww/linklist.html http://www.macs.hw.ac.uk/~rjp/Coursewww/ Cwww/linklist.html – Building a linked list, but not freeing it