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

struct s {
	int i;
};

static void fv(struct s *s)
{
	/* Do something with s */

	free(s);
	s = NULL;
}

static void fr(struct s **s)
{
	/* Do something with s */

	free(*s);
	*s = NULL;
}

int main(void)
{
	struct s *s;

	s = malloc(sizeof(*s));
	printf("s: %p\n", s);
	fv(s);
	printf("s: %p\n", s);

	printf("\n");

	s = malloc(sizeof(*s));
	printf("s: %p\n", s);
	fr(&s);
	printf("s: %p\n", s);

	return 0;
}