How to implement a linked list in C?

Question

I am creating a linked list as in the previous question I asked. I have found that the best way to develop the linked list is to have the head and tail in another structure.

Answer 1

A demo for Singly Linked List. If you prefer, try to check Circular Linked List and Doubly Linked List.

#include 
#include 


typedef struct node {
    int val;
    struct node * next;
} node_t;


// Iterating over a list
void
print_list(node_t *head)
{
    node_t *current = head;

    while(current != NULL)
    {
        printf("%d\n", current->val);
        current = current->next;
    }
}


// Adding an item to the end of the list
void
push_end(node_t *head, int val)
{
    node_t *current = head;
    while (current->next != NULL)
    {
        current = current->next;
    }

    current->next = malloc(sizeof(node_t));
    current->next->val = val;
    current->next->next = NULL;
}

// Adding an item to the head of the list
void
push_head(node_t **head, int val)
{
    node_t *new_node = NULL;

    new_node = malloc(sizeof(node_t));
    new_node->val = val;
    new_node->next = *head;

    *head = new_node;
}

// Removing the head item of the list
int
pop_head(node_t **head)
{
    int retval = -1;
    node_t *next_node = NULL;

    if (*head == NULL) {
        return -1;
    }

    next_node = (*head)->next;
    retval = (*head)->val;
    free(*head);
    *head = next_node;

    return retval;
}

// Removing the last item of the list
int
pop_last(node_t *head)
{
    int retval = 0;
    node_t *current = NULL;

    if (head->next == NULL) {
        retval = head->val;
        free(head);
        return retval;
    }

    /* get to the second to last node in the list */
    current = head;
    while (current->next->next != NULL) {
        current = current->next;
    }

    /* now current points to the second to last item of the list.
       so let's remove current->next */
    retval = current->next->val;
    free(current->next);
    current->next = NULL;

    return retval;
}

// Removing a specific item
int
remove_by_index(node_t **head, int n)
{
    int i = 0;
    int retval = -1;
    node_t *current = *head;
    node_t *temp_node = NULL;

    if (n == 0) {
        return pop_head(head);
    }

    for (i = 0; i < n - 1; i++) {
        if (current->next == NULL) {
            return -1;
        }
        current = current->next;
    }

    temp_node = current->next;
    retval = temp_node->val;
    current->next = temp_node->next;
    free(temp_node);

    return retval;
}


int
main(int argc, const char *argv[])
{
    int i;
    node_t * testnode;

    for (i = 0; i < argc; i++)
    {
        push_head(&testnode, atoi(argv[i]));
    }

    print_list(testnode);

    return 0;
}

// http://www.learn-c.org/en/Linked_lists
// https://www.geeksforgeeks.org/data-structures/linked-list/