header file

list.c

#include "list.h"
#include "dbg.h"

List *List_create()
{
	return calloc(1, sizeof(List));
}

void List_destroy(List *list)
{
	LIST_FOREACH(list, first, next, cur) {
		if(cur->prev) {
			free(cur->prev);
		}
	}

	free(list->last);
	free(list);
}

void List_clear(List *list)
{
	LIST_FOREACH(list, first, next, cur) {
		free(cur->value);
	}
}

void List_clear_destroy(List *list)
{
	List_clear(list);
	List_destroy(list);
}

void List_push(List *list, void *value)
{
	ListNode *node = calloc(1, sizeof(ListNode));
	check_mem(node);

	node->value = value;

	if(list->last == NULL) {
		list->first = node;
		list->last = node;
	} else {
		list->last->next = node;
		node->prev = list->last;
		list->last = node;
	}

	list->count++;

error:
	return;
}

void *List_pop(List *list)
{
	ListNode *node = list->last;
	return node != NULL ? List_remove(list, node) : NULL;
}

void List_unshift(List *list, void *value)
{
	ListNode *node = calloc(1, sizeof(ListNode));
	check_mem(node);

	node->value = value;

	if(list->first == NULL) {
		list->first = node;
		list->last = node;
	} else {
		node->next = list->first;
		list->first->prev = node;
		list->first = node;
	}

	list->count++;

error:
	return;
}

void *List_shift(List *list)
{
	ListNode *node = list->first;
	return node != NULL ? List_remove(list, node) : NULL;
}

void *List_remove(List *list, ListNode *node)
{
	void *result = NULL;

	check(list->first && list->last, "List is empty.");
	check(node, "node can't be NULL");

	if(node == list->first && node == list->last) {
		list->first = NULL;
		list->last = NULL;
	} else if(node == list->first) {
		list->first = node->next;
		check(list->first != NULL, "Invalid list, somehow got a first that is NULL");
		list->first->prev = NULL;	
	} else if(node == list->last) {
		list->last = node->prev;
		check(list->last != NULL, "Invalid list, somehow got a next that is NULL.");
		list->last->next = NULL;
	} else {
		// here we set the pointers to the surrounding nodes to point to the
		// correct nodes
		ListNode *after = node->next;
		ListNode *before = node->prev;
		after->prev = before;
		before->next = after;
	}

	list->count--;
	result = node->value;
	free(node);

error:
	return result;
}

int main(int argc, char const *argv[])
{
	/* code */
	return 0;
}

list.h

#ifndef lcthw_List_h
#define lcthw_List_h

#include <stdlib.h>

struct ListNode;

typedef struct ListNode {
	struct ListNode *next;
	struct ListNode *prev;
	void *value;
} ListNode;

typedef struct List {
	int count;
	ListNode *first;
	ListNode *last;
} List;

List *List_create();
void List_destroy(List *list);
void List_clear(List *list);
void List_clear_destroy(List *list);

#define List_count(A) ((A)->count)
#define List_first(A) ((A)->first != NULL ? (A)->first->value : NULL)
#define List_last(A) ((A)->last != NULL ? (A)->last->value : NULL)

void List_push(List *list, void *value);
void *List_pop(List *list);

void List_unshift(List *list, void *value);
void *List_shift(List *list);

void *List_remove(List *list, ListNode *node);

#define LIST_FOREACH(L, S, M, V) ListNode *_node = NULL;\
	ListNode *V = NULL;\
	for(V = _node = L->S; _node != NULL; V = _node = _node->M)

#endif