Can't free linked list - c

Question

This is the struct:
typedef struct listeEle {
int pos;
struct listeEle *next;
} ListEle;
this is where I create the list:
ListEle *mokli(int n){
if(n<=0)
{
fprintf(stderr, "Falscher Parameter für mokli... Programm beendet.");
exit(0);
}
else
{
ListEle *lst;
lst = malloc(sizeof(ListEle));
lst->next = NULL;
lst->pos = 1;
int i;
ListEle *new;
ListEle *ptr;
ptr = lst;
for(i=1; i<n; i++)
{
new = NULL;
new = malloc(sizeof(ListEle));
new->next = NULL;
new->pos = i+1;
ptr->next = new;
ptr = ptr->next;
}
return lst;
}
}
and this is where I try to free it
void unmokli(ListEle *lst)
{
if(lst->next == NULL)
{
free(lst);
lst = NULL;
printList(lst);
printf("1 > Liste vollständig gelöscht.\n");
}
else
{
ListEle *head;
head = lst;
int del = 0;
while(head)
{
ListEle *temp = head;
head = head->next;
free(temp);
del+=1;
}
free(lst);
lst = NULL;
printf("2 > Liste deleted (%d).\n", del);
}
}
This is how I print it
void printList(ListEle *anfang){
if(anfang == NULL)
{
printf("List not av...\n");
}
else
{
ListEle *ptr;
ptr = anfang;
int i = 1;
while(ptr)
{
printf("Element %i -> ListeEle pos=%i\n", i++, ptr->pos);
ptr = ptr->next;
}
}
}
The problem is in the main method. The list I create here won't be freed, although I pass it correctly to the freeing function.
int main(void){
ListEle *liste;
liste = mokli(6);
printList(liste);
unmokli(liste);
printList(liste);
return 0;
}
After unmokli it should be freed completely, but the list inside the main function is still allocated. How can I completely free the list?

Answer 1

When you do
lst = NULL;
in the function unmokli you are only making the local copy lst NULL. Remember that arguments are passed by value, i.e. they are copied. You need to pass lst by reference, which can be done by passing a pointer (to the pointer):
void unmokli(ListEle **lst)
{
...
*lst = NULL;
...
}
You then call this by using the address-of operator:
unmokli(&liste);

Answer 2

Either pass reference of liste to unmokli() or take return parameter from it as you have done in mokli().
In your case, its getting freed, but variable liste in main() is not set to NULL and still references old memory. This is may cause you crash.
Update your code as
void unmokli(ListEle **lst_ref)
{
ListEle *lst = *lst_ref;
...
//your code freeing list
//set to null after freeing
*lst_ref = NULL;
}
From main() call it as
unmokli(&liste);

Answer 3

It's freed, but data still remains after calling free, so you just accessing deleted data by printing list after delete. (which you mustn't do actually)
Also, if you want to set 'liste' pointer to NULL inside free-function, you should pass pointer to a pointer. The following code in unmokli is useless:
free(lst); // Already freed in a loop before
lst = NULL; // Takes effect only inside this function

Answer 4

Typically, I would free (& NULL assign) the linked list as below:
void unmokli(ListEle **lst)
{
ListEle* nxt;
if(lst==NULL) return;
// printList(*lst); // not required by the free-list logic as such...
while(*lst)
{
nxt=(*lst)->next;
// printList(*lst); // not required by the free-list logic as such... You can test free code with this.
free(*lst);
*lst=nxt;
}
}
//usage
unmokli(&list_head);