single_list.c

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

/* WARNING!
 *
 * Horrible linked list :p
 */

/* macros */
struct List {
	void *value;
	struct List *next;
};

#define FOREACH(out, in) \
	for (struct List *out = in; out->next != NULL; out = out->next)

/* function prototypes */
static struct List *init_list   (void);
static int          insert_list (struct List **list, void *data);
static void         clear_list  (struct List **list);


/* function implementations */
static struct List *
init_list(void)
{
	struct List *l = malloc(sizeof(struct List));
	if (l == NULL) {
		perror("init_list()");
		return NULL;
	}

	l->value = NULL;
	l->next  = NULL;

	return l;
}

static int
insert_list(struct List **list, void *data)
{
	if ((*list) == NULL) {
		errno = EINVAL;
		perror("insert_list()");
		return -1;
	}

	struct List *new_l = malloc(sizeof(struct List));
	if (new_l == NULL) {
		perror("insert_list(): new");
		return -1;
	}

	new_l->value = data;
	new_l->next  = (*list);
	(*list)    = new_l;

	return 0;
}

static void
clear_list(struct List **list)
{
	struct List *tmp = (*list);
	struct List *next;

	while (tmp != NULL) {
		next = tmp->next;
		free(tmp);
		tmp = next;
	}
	(*list) = NULL;
}


int
main(void)
{
	int arr[] = {10,2,4,5,6,21};

	struct List *l = init_list();

	/* array to linked list */
	for (int i = 5; i >= 0; i--) {
		if (insert_list(&l, (int*)&arr[i]) < 0)
			goto clean;
	}

	FOREACH(out, l)
		printf("%d\n", *(int*)out->value);


clean:
	clear_list(&l);
	return errno;
}