Linked list

Learn to create a linked list with struct.

Linked list

A linked list is a data structure where each node points to the next. Unlike arrays, its size isn't fixed; it grows as you add nodes.

Each node has two parts: data (the value carried) and next (the address of the next node). In C you define it with a struct: typedef struct Node { int data; struct Node *next; } Node;. With typedef you can write the short Node instead of struct Node. At the end of the list the next field is NULL; this signals the list is over.

Creating a node

A new node is allocated from the heap with malloc. The call Node *n = malloc(sizeof(Node)); reserves memory the size of one Node and gives its address to n.

The node's fields are filled like n->data = 42; and n->next = NULL;. The -> operator accesses a field of the struct a pointer addresses. When the node is alone in the list, next is still NULL. When done, release the memory with free(n); or a leak occurs. malloc and free require the <stdlib.h> header.

Exercise Single-node list

Write typedef struct Node { int data; struct Node *next; } Node;. In main allocate one node with Node *n = malloc(sizeof(Node));. Set n->data = 42; and n->next = NULL;. Print with printf("%d\n", n->data);. Finally call free(n);.

Show example solution

#include <stdio.h>
#include <stdlib.h>

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

int main(void) {
    Node *n = malloc(sizeof(Node));
    n->data = 42;
    n->next = NULL;
    printf("%d\n", n->data);
    free(n);
    return 0;
}

Test yourself

Which field in a Node struct holds the next node?
- data
- prev
- next
- size
Show answer

next — The next field carries the address of the following Node.

Allocate memory for a Node

Node *n = malloc(sizeof(____));

Show answer

Node *n = malloc(sizeof(Node));

Node parts

data

carried value
next

next node address
malloc

allocate memory
free

release memory

Next lesson: Adding to list

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