reverse.c

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

struct list {
	int v;
	struct list *next;
};

void reverse (struct list **head) {
	struct list *p, *n;

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

	p = (*head)->next;
	(*head)->next = NULL;

	while (p != NULL) {
		n = p->next;
		
		p->next = *head;
		*head = p;

		p = n;
	}
}

void dump (struct list *l) {
	for (; l != NULL; l = l->next) {
		printf(" %p -> %d, %p\n", l, l->v, l->next);
	}
	fputc('\n', stdout);
}

void push (struct list **l, struct list *new) {
	new->next = *l;
	*l = new;
}

void unshift (struct list **l, struct list *new) {
	reverse(l);
	push(l, new);
	reverse(l);
}

void destroy (struct list *l) {
	struct list *p;
	while (l != NULL) {
		p = l->next;
		free(l);
		l = p;
	}
}

int main () {
	struct list *l, *p;
	int i;

	l = NULL;
	
	for (i = 0; i < 10; i++) {
		p = malloc(sizeof(*p));
	
		if (p == NULL) {
			exit(EXIT_FAILURE);
		}

		p->v = i;
		p->next = NULL;

		push(&l, p);
	}

	dump(l);
	reverse(&l);
	dump(l);

	destroy(l);

	l = NULL;

	for (i = 0; i < 10; i++) {
		p = malloc(sizeof(*p));

		if (p == NULL) {
			exit(EXIT_FAILURE);
		}

		p->v = i;
		p->next = NULL;

		unshift(&l, p);
	}

	dump(l);
	destroy(l);

	exit(EXIT_SUCCESS);
}