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

struct node {
    struct node *next;
    char payload[0];
};

static struct node *node_from_payload(void *p)
{
    return (void *)((char *)p - offsetof(struct node, payload));
}

static void *list_push_(void **head, const void *data, size_t size)
{
    struct node *n = malloc(sizeof *n + size);
    if (!n)
        return NULL;

    memcpy(n->payload, data, size);
    n->next = *head ? node_from_payload(*head) : NULL;
    *head = n->payload;
    return n->payload;
}

#define list_push(head, value) \
    list_push_((void **)(head), &(value), sizeof(value))

static void *list_next_(void *p)
{
    struct node *n = node_from_payload(p);
    return n->next ? n->next->payload : NULL;
}

#define list_next(p) ((typeof(p))list_next_(p))

static void list_free(void *head)
{
    while (head) {
        struct node *n = node_from_payload(head);
        head = n->next ? n->next->payload : NULL;
        free(n);
    }
}

struct point {
    int x, y;
};

int main(void)
{
    int *numbers = NULL;
    int a = 1, b = 2, c = 3;

    list_push(&numbers, a);
    list_push(&numbers, b);
    list_push(&numbers, c);

    for (int *p = numbers; p; p = list_next(p))
        printf("%d\n", *p);

    struct point *points = NULL;
    struct point p1 = {1, 2};
    struct point p2 = {3, 4};

    list_push(&points, p1);
    list_push(&points, p2);

    for (struct point *p = points; p; p = list_next(p))
        printf("(%d, %d)\n", p->x, p->y);

    list_free(numbers);
    list_free(points);
}