Double-linked list with just one link field. xor-trick.

gistfile1.c

#include <stdio.h>
#include <inttypes.h>

typedef struct node {
    void *link;
    int value;
} node_t;

#define LINK(prev, next) (void *)((uintptr_t)(prev) ^ (uintptr_t)(next))

void
iter(node_t *node) {
    node_t *prev = 0;

    while (node) {
        printf("%d\n", node->value);
        node_t *this_node = node;
        node = (node_t *)((uintptr_t)prev ^ (uintptr_t)node->link);
        prev = this_node;
    }
}

int
main() {
    node_t n1 = {0, 11};
    node_t n2 = {0, 22};
    node_t n3 = {0, 33};
    node_t n4 = {0, 44};

    n1.link = LINK(0, &n2);
    n2.link = LINK(&n1, &n3);
    n3.link = LINK(&n2, &n4);
    n4.link = LINK(&n3, 0);

    iter(&n1);
}