[C] Double linked list

linked_list.c

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

/* Linked list entry */
typedef struct llEntry {
	struct llEntry* prev;
	struct llEntry* next;
	void* data;
} llEntry;

/* Double linked list */
typedef struct llList {
	llEntry* first;
	llEntry* last;
	int count;
} llList;

llList* newList(void);
void deleteList(llList* list);
llEntry* pushEntry(llList* list, void* data);
llEntry* getEntry(llList* list, int idx);
llEntry* popEntryIndex(llList* list, int idx);
llEntry* iterateUpwards(llList* list, int from, int to, void (*callback)(llList*, llEntry*, int));

///////////////////////////////////////////// IMPLEMENTATION //////////////////

// Allocate a new list with 0 elements.
llList* newList(void) {
	llList* newl = malloc(sizeof(llList));
	memset(newl, 0, sizeof(llList));
	return newl;
}
// Free every element and the list itself.
void deleteList(llList* list) {
	llEntry* curr = list->first;
	while(curr) {
		free(curr);
		curr = curr->next;
	}
	free(list);
}
// Push llEntry to the very end of the list.
llEntry* pushEntry(llList* list, void* data) {
	llEntry* newe = malloc(sizeof(llEntry));
	if(newe == NULL)
		return NULL;

	memset(newe, 0, sizeof(llEntry));
	newe->data = data;
	if(list->first == NULL) {
		list->first = newe;
		list->last = newe;
		list->count = 1;
		//printf("newe: %p - first: %p, last: %p - newe->prev: %p, newe->next: %p\n", newe, list->first, list->last, newe->prev, newe->next);
		return newe;
	}
	newe->prev = list->last;
	list->last->next = newe;
	list->last = newe;
	list->count++;
	//printf("newe: %p - first: %p, last: %p - newe->prev: %p, newe->next: %p\n", newe, list->first, list->last, newe->prev, newe->next);
	return newe;
}
// Returns one entry from the linked list according to its index in list
llEntry* getEntry(llList* list, int idx) {
	if(idx == 0)
		return list->first;
	if(idx + 1 == list->count)
		return list->last;
	if(idx >= list->count)
		return NULL;

	llEntry* curr = list->first;
	while(idx-- && curr) {
		//printf("%d: curr: %p, next: %p\n", idx, curr, curr->next);
		curr = curr->next;
	}
	return curr;
}
// Remove element from linked list and return the following one
llEntry* popEntryIndex(llList* list, int idx) {
	if(idx == 0) {
		if(list->count == 1) {
			free(list->first);
			memset(list, 0, sizeof(llList));
			return NULL;
		}
		list->first->next->prev = NULL;
		list->count--;
		list->first = list->first->next;
		return list->first;
	}

	if(idx + 1 == list->count) {
		list->last->prev->next = NULL;
		llEntry* temp = list->last;
		list->last = list->last->prev;
		list->count--;
		free(temp);
		return NULL;
	}

	llEntry* curr = list->first;
	while(idx-- && curr) {
		curr = curr->next;
	}
	curr->prev->next = curr->next;
	curr->next->prev = curr->prev;
	list->count--;
	llEntry* toReturn = curr->next;
	free(curr);
	return toReturn;
}
// Iterate the linked list upwards and return the final entry.
llEntry* iterateUpwards(llList* list, int from, int to, void (*callback)(llList*, llEntry*, int)) {
	if(list->count <= from)
		return NULL;
	if(from > to)
		return NULL;

	llEntry* curr = getEntry(list, from);
	if(curr == NULL)
		return NULL;

	for (int i = from; i <= to; ++i) {
		curr = curr->next;
		(*callback)(list, curr, i);
	}
	return curr;
}
void myCallback(llList* list, llEntry* entry, int idx) {
	printf("Called for %d\n", idx);
}
int main(int argc, char const *argv[]) {
	llList* ll = newList();
	int x = 5, y = 7, z = 9, za = 10;
	pushEntry(ll, &x);
	pushEntry(ll, &y);
	pushEntry(ll, &z);
	pushEntry(ll, &za);

	for (int i = 0; i < ll->count; ++i) {
		llEntry* e = getEntry(ll, i);
		printf("#%d: %d\n", i, *((int*)e->data));
	}

	popEntryIndex(ll, 2);
	printf("\n");
	for (int i = 0; i < ll->count; ++i) {
		llEntry* e = getEntry(ll, i);
		printf("#%d: %d\n", i, *((int*)e->data));
	}
	printf("\nITERATE UPWARDS: %d\n", ll->count);
	iterateUpwards(ll, 0, ll->count - 1, myCallback);
	return 0;
}