Dynamic Allocation and Linked Lists

Dynamic memory allocation in C C uses the functions malloc() and free() to implement dynamic allocation. malloc is defined in stdlib.h and malloc.h header files. malloc returns a void pointer. the pointer returned from malloc requires a type cast to make it usable.

Type Casting To make one data type appear like another you can use a type cast. int I; int a = (int)sqrt((float) I ); To make the void pointer returned by malloc look like your struct you must typecast it to a pointer to a struct.

Example struct rec { char LastName[41]; charFirstName[41]; }; struct rec *r; r = (struct rec) malloc( sizeof(struct rec));

Freeing Memory Memory allocated with malloc must be released after you are done with them. this memory is released by calling the function free(). Since free expects as an argument the pointer returned by malloc it expects a void pointer. free( r );

Linked List A linked list is a basic data structure. For easier understanding divide the linked list into two parts. Nodes make up linked lists. Nodes are structures made up of data and a pointer to another node. Usually the pointer is called next.

Nodes struct node { struct rec r; struct node *next; };

LIST The list will contain a pointer to the start of the list. For our purposes all data will be added to the start of the list. Initialize the start pointer to NULL.

Creating a New Node Allocate space for a new node. Set the next pointer to the value of NULL Set the data value for the node.

Adding Nodes to the List If the start node is null then the start node becomes the new node. If start is not null then start becomes the new node’s next and the start becomes the new node.