Thread: list function / test linked lists

Perhaps you could start by fixing the errors such as

> return (head);
But the function is declared void.

> /* deletes entry from list and reinitialize it, returns pointer to entry */
> struct list_head*
> list_del(struct list_head *entry)
But it has no return statement.

> I have difficulties coding the test_list_function to test each function to manipulate the list.
Well not showing us you've at least made an attempt (ie, not left the function completely empty) would be a start.

How about creating a new empty list and checking that list_empty() does indeed return true?

Thank you for your help! So I corrected the return statements.
I actually didn't want to confuse you with my attempt cause it makes no sense at all, but I sure can post it now.
The print_all function is obviously wrong, but I have no Idea how to print the list. Also I'm not sure how to fill the actual list with values so I got confused and this is what happend:

Code:

void test_list_functions() 
{ 
  /* write test code for list functions */ 
    /* Init new list */ 
    struct list_head *head = list_init(head); 
    struct list_head *pid = head; 
    int i; 
 
    /* fill with pit 1-4 */ 
    for(i = 0; i <= 4; i++){ 
        pid = list_init(i); 
    } 
    /* print list */ 
    print_all(head); 
    print_all(pid); 
 
    pid = list_add(pid, head);  
    print_all(pid); 
 
    pid = list_add_tail(pid, head); 
    print_all(pid); 
 
    pid = list_del(pid);  
    print_all(pid); 
 
    pid = list_move(pid, head); 
    print_all(pid); 
 
    pid = list_move_tail(pid, head); 
    print_all(pid); 
 
    pid = list_empty(head); 
    print_all(head); 
 
    return 0; 
}

and here is the part I corrected:

Code:

/* initialize "shortcut links" for empty list */ 
void 
list_init(struct list_head *head) 
{ 
    head->next = head; 
    head->prev = head; 
}

/* deletes entry from list and reinitialize it, returns pointer to entry */ 
struct list_head*  
list_del(struct list_head *entry) 
{ 
    entry->prev->next = entry->next; 
    entry->next->prev = entry->prev; 
    entry->next = entry; 
    entry->prev = entry;
    return(entry); 
}

as far as I can see you are not allocating memory for your items. here is function to create an empty item

Code:

struct list_head* new_item(){
  return (list_head *) malloc(sizeof(list_head));
}
struct list_head*
list_init(struct list_head *head) 

{ 

    head->next = head; 

    head->prev = head; 
    return head;

}



void test_list_functions() 

{ 

    struct list_head *head = list_init(new_item());     struct list_head *pid = head; 

    int i; 

  

    /* fill with pit 1-4 */

//    for(i = 0; i <= 4; i++){ 

//        pid = list_init(i); 

//    } //this is wrong list_init 

    /* print list */

    print_all(head); 
    print_all(pid); 
  
    pid = list_add(pid, head);  
    print_all(pid); 

  

    pid = list_add_tail(pid, head); 
    print_all(pid); 
  

    pid = list_del(pid);  

    print_all(pid); 

  

    pid = list_move(pid, head); 
    print_all(pid); 
  
    pid = list_move_tail(pid, head); 

    print_all(pid); 
  
    pid = list_empty(head); 
    print_all(head); 
  
    return 0; 
}

The logic on the rest of the functions look ok if you ignore the fact that there is nowhere code to handle the data of the list only the item's links or any sanity checks but I only looked at your code for a few seconds. It would be useful on describing what you expect to happen and what actually happens for example you are using the list_init function in two different ways in one you pass a list item to be initialized in the other you pass an integer value to be used how exactly?

You should get rid of the pid variable.

Everything should be
head = function(head); // this function modifies the list
or
function(head); // this function doesn't modify the list