Declare and Initialize dynamic array of head nodes of linked lists

Question

I would like to know how to declare, allocate and initialize array of Node to null.

typedef struct Nodes_Of_List { 
        int data; 
        struct Nodes_Of_List *next;
} Node;

//declare array of head nodes
Node *table;

//ALOCATE memory for "x" x is provided at runtime, number of head nodes
table = malloc(sizeof(Node) * x); 

//Initialize elements to Null value
?? //How to do it

Explanation regarding initializing dynamic array of head nodes of linked list to Null requested. Purpose is to make array of linked lists, to make a hashtable.

It's unclear what you're trying to do. Do you have a single list, or a list of lists? — Fiddling Bits
– Fiddling Bits, Commented Jul 10, 2020 at 13:30
Is a Node what you mean by a head node? Or do you need another structure such as typedef struct Head_Node { Node *head; Node *tail; } Head_Node;? (Note that the 'tags' namespace is separate from the ordinary identifiers namespace, so struct Head_Node does not conflict with Head_Node.) You define an array of whatever type it is the same way as you define an array of int — except you use a different type name. If x is a variable rather than a constant, you use malloc() to allocate the memory. Using calloc() will (de facto if not de jure) initialize the allocated memory to null. — Jonathan Leffler
– Jonathan Leffler, Commented Jul 10, 2020 at 13:43
This link can help you a lot: stackoverflow.com/questions/46320526/… If you need more details, please elaborate on the comments(or edit question) so we can help. — Confidenc3
– Confidenc3, Commented Jul 10, 2020 at 14:46
You can initialize with table->data = NULL; table->next = NULL; — Shubham
– Shubham, Commented Jul 10, 2020 at 17:29
@Lucas: since the data element is an int, it would be best not to use NULL but just 0 to initialize it. — Jonathan Leffler
– Jonathan Leffler, Commented Jul 10, 2020 at 20:43

ThunderPhoenix · Accepted Answer · 2020-07-10 21:43:34Z

1

Based on what I understood, you want to declare an array of head nodes. After that, you want to initialize them to NULL:

//declare array of head nodes statically
Node * table[x];      // x value provided at runtime
// Or dynamically
Node ** table = (Node **) malloc(sizeof(Node *) * x);
// Or use calloc directly wich will initialize your pointers to 0
Node ** table = (Node **) calloc(x, sizeof(Node *));

// table is an array of pointers. Each pointer references a linked list.
// Now you have just to put NULL value in each element of table
int i;
for(i = 0; i < x; i++) 
    table[i] = 0;

answered Jul 10, 2020 at 21:43

ThunderPhoenix

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