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Generic Linked List in C

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#include <stdio.h>
#include <stdlib.h>
typedef struct node {
    void* data;
    struct node* next;
} Node;
typedef struct list {
    int size;
    Node* head;
} List;
List* create_list() {
    List* new_list = (List*)malloc(sizeof(List));
    new_list->size = 0;
    new_list->head = NULL;
    return new_list;
void add_to_list(List* list, void* data) {
    Node* new_node = (Node*)malloc(sizeof(Node));
    new_node->data = data;
    new_node->next = list->head;
    list->head = new_node;
void* remove_from_list(List* list) {
    if (list->size == 0) {
        return NULL;
    Node* node_to_remove = list->head;
    void* data = node_to_remove->data;
    list->head = node_to_remove->next;
    return data;
void free_list(List* list) {
    Node* current_node = list->head;
    while (current_node != NULL) {
        Node* next_node = current_node->next;
        current_node = next_node;
int main() {
    // create a new list
    List* int_list = create_list();
    // add some integers to the list
    int x = 42;
    add_to_list(int_list, (void*)&x);
    int y = 13;
    add_to_list(int_list, (void*)&y);
    int z = 99;
    add_to_list(int_list, (void*)&z);
    // remove the integers from the list and print them
    int* int_ptr = NULL;
    while ((int_ptr = (int*)remove_from_list(int_list)) != NULL) {
        printf("%d\n", *int_ptr);
    // free the memory used by the list
    return 0;



Time complexity-The time complexity of adding an element to the beginning of the linked list using add_to_list function is O(1), as it only requires creating a new node and updating the head pointer.

The time complexity of removing an element from the beginning of the linked list using remove_from_list function is also O(1), as it only requires updating the head pointer and freeing the memory of the removed node.

Space complexity-The space complexity of the linked list implementation is proportional to the number of elements in the list. For each element added to the list, a new node is created using dynamic memory allocation, and this node contains a pointer to the data. Therefore, the space complexity is O(n), where n is the number of elements in the list.

Unlike C++ and Java, C doesn’t support generics. How to create a linked list in C that can be used for any data type? In C, we can use a void pointer and a function pointer to implement the same functionality. The great thing about void pointer is it can be used to point to any data type. Also, the size of all types of pointers is always is same, so we can always allocate a linked list node. Function pointer is needed to process actual content stored at the address pointed by the void pointer. 

Following is a sample C code to demonstrate the working of a generic linked list.


// C program for generic linked list
/* A linked list node */
struct Node
    // Any data type can be stored in this node
    void  *data;
    struct Node *next;
/* Function to add a node at the beginning of Linked List.
   This function expects a pointer to the data to be added
   and size of the data type */
void push(struct Node** head_ref, void *new_data, size_t data_size)
    // Allocate memory for node
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
    new_node->data  = malloc(data_size);
    new_node->next = (*head_ref);
    // Copy contents of new_data to newly allocated memory.
    // Assumption: char takes 1 byte.
    int i;
    for (i=0; i<data_size; i++)
        *(char *)(new_node->data + i) = *(char *)(new_data + i);
    // Change head pointer as new node is added at the beginning
    (*head_ref)    = new_node;
/* Function to print nodes in a given linked list. fpitr is used
   to access the function to be used for printing current node data.
   Note that different data types need different specifier in printf() */
void printList(struct Node *node, void (*fptr)(void *))
    while (node != NULL)
        node = node->next;
// Function to print an integer
void printInt(void *n)
   printf(" %d", *(int *)n);
// Function to print a float
void printFloat(void *f)
   printf(" %f", *(float *)f);
/* Driver program to test above function */
int main()
    struct Node *start = NULL;
    // Create and print an int linked list
    unsigned int_size = sizeof(int);
    int arr[] = {10, 20, 30, 40, 50}, i;
    for (i=4; i>=0; i--)
       push(&start, &arr[i], int_size);
    printf("Created integer linked list is \n");
    printList(start, printInt);
    // Create and print a float linked list
    unsigned float_size = sizeof(float);
    start = NULL;
    float arr2[] = {10.1, 20.2, 30.3, 40.4, 50.5};
    for (i=4; i>=0; i--)
       push(&start, &arr2[i], float_size);
    printf("\n\nCreated float linked list is \n");
    printList(start, printFloat);
    return 0;


Created integer linked list is 
 10 20 30 40 50

Created float linked list is 
 10.100000 20.200001 30.299999 40.400002 50.500000

Time Complexity : O(n), here n is number of nodes in linked list. 

Auxiliary Space :O(1)

Last Updated : 28 Apr, 2023
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