---
~~Title: Lists~~
~~NOCACHE~~
---

# Lists #

The ``Eina_List`` is a double-linked list that can store data of any type as void pointers. It provides a set of functions to create and manipulate the list to avoid the access to the struct's fields, similar to a self-made double-link list. 

In addition to the previous and next node and its data, the ``Eina_List`` nodes keep a reference to an accounting structure. The accounting structure is used to improve the performance of some functions. The structure is private and must not be modified.

In an ``Eina_List``, everything is a "list": the list itself is a list where each node is a list as well.

Eina provides 2 list types: the classic (``Eina_List``) and inline (``Eina_Inlist``).

## Creating and Destroying a List ##

To use an ``Eina_List``, first declare the list with ``NULL`` as the default value:

```c
[...]
int list()
{
   // Declaration of the Eina_List with NULL as default value;
   Eina_List *list = NULL;
[...]
```

> **NOTE:**
> ``[...]`` in a Code Block indicates there will usually be code above and below the shown snippet but that it has been excluded for the sake of brevity. There is no need to type ``[...]`` into your program.

Then call the ``eina_list_append()`` function with the list and the data you want to append as parameters.

The list must be a pointer to the first element of the list (or ``NULL``). The function returns a pointer to the list.

```c
[...]
   // Creating the first element of the list
   list = eina_list_append(list, "watch");

   // Adding more elements
   list = eina_list_append(list, "phone");
   list = eina_list_append(list, "ivi");
   list = eina_list_append(list, "notebook");
[...]
```

When you no longer need the list, free it:

```c
[...]
   // Free the Eina_List
   eina_list_free(list);

   return 0;
}
[...]
```

## Modifying List Content ##

### Adding Data to a List ###

To add data at the end of the list, use the ``eina_list_append()`` function. To add data at the top of the list, use ``eina_list_prepend()``. The functions work in the same way, only adding the data to different places:

```c
[...]
list = eina_list_prepend(list, "set-top box");
[...]
```

To insert data into the list after a specified data, use the ``eina_list_append_relative()`` function. As the last parameter, define the element after which the data is added. For example, to append data after the "phone" element:

```c
[...]
list = eina_list_append_relative(list, "single-board computer", "phone");
[...]
```

To add a new entry before a specified data, use ``eina_list_prepend_relative()``. This function is similar to ``eina_list_append_relative()``:

```c
[...]
list = eina_list_prepend_relative(list, "ultrabook", "ivi");
[...]
```

To append a list node to a linked list after a specified element use the ``eina_list_append_relative_list()`` function. To prepend a list node to a linked list before a specified member, use ``Eina_List * eina_list_prepend_relative_list()``.

### Setting Data in a List Element ###

To do this use the ``eina_list_data_set()`` function. Pass the *list* (node) as the first argument and the data to set as the second.

The following example also shows the usage of the ``eina_list_last()`` function, which returns the last element of an ``Eina_List``:

```c
[...]
// Setting new data for the last element
eina_list_data_set(eina_list_last(list), eina_stringshare_add("Boris"));
[...]
```

### Removing a Node from the List ###

Use the ``eina_list_remove()`` function. This function removes the first instance of the specified data from the given list.

```c
[...]
list = eina_list_remove(list, "ultrabook");
[...]
```

You can also remove a *list* (node) from a list using the ``eina_list_remove_list()`` function. Pass the list you want to delete an element from and a 'list' (node) you want to delete:

```c
[...]
Eina_List *app_list = NULL;
Eina_List *to_remove = NULL;

// Adding some elements to the list (using stringshares)
app_list = eina_list_append(app_list, eina_stringshare_add("enna"));
app_list = eina_list_append(app_list, eina_stringshare_add("ebird"));
app_list = eina_list_append(app_list, eina_stringshare_add("calaos"));
app_list = eina_list_append(app_list, eina_stringshare_add("rage"));
app_list = eina_list_append(app_list, eina_stringshare_add("terminology"));
app_list = eina_list_append(app_list, eina_stringshare_add("enlightenment"));
app_list = eina_list_append(app_list, eina_stringshare_add("eyelight"));
app_list = eina_list_append(app_list, eina_stringshare_add("ephoto"));

// Finding the "list" to remove
to_remove = eina_list_data_find_list(list, eina_string_share_add("enlightenment"));

list = eina_list_remove_list(list, to_remove);
[...]
```

### Moving Elements in a List ###

You can use various function such as ``eina_list_promote_list()`` to push an element to the top of a list or ``eina_list_demote_list()`` to move an element to the end. The second parameter represents the *list* (node) you want to move. Use the functions in the same way as ``eina_list_remove_list()``:

```c
[...]
list = eina_list_promote_list(list, eina_list_data_find_list(list, "ivi"));
[...]
```

### Reversing Elements in a List ###

Use the ``eina_list_reverse()`` function. To obtain a reversed copy of the list while keeping the initial list unchanged, use``eina_list_reverse_clone()``:


```c
[...]
Eina_List *rev_copy;

app_list = eina_list_reverse(app_list);
rev_copy = eina_list_reverse_clone(app_list);
[...]
```

### Sorting a List ###

Use the ``eina_list_sort()`` function. This function takes a list that needs sorting, the maximum number of elements to sort and a callback function that compares data. To sort all list elements set the maximum number of elements to 0:

```c
[...]
int sort_cb(const void *d1, const void *d2)
{
   const char *txt = d1;
   const char *txt2 = d2;
   if(!txt) return(1);
   if(!txt2) return(-1);

   return(strcmp(txt, txt2));
}

extern Eina_List *list;
list = eina_list_sort(list, 0, sort_cb);
[...]
```

### Merging Two Lists into One ###

Use the ``eina_list_merge()`` function. The ``eina_list_sorted_merge()`` function merges 2 sorted lists according to the ordering function that you pass as the last argument, for instance:

```c
[...]
int sort_cb(void *d1, void *d2)
{
   const char *txt = NULL;
   const char *txt2 = NULL;
   if(!d1) return(1);
   if(!d2) return(-1);

   return(strcmp((const char*)d1, (const char*)d2));
}

Eina_List *sorted1;
Eina_List *sorted2;
Eina_List *newlist;

// Insert some values and sort your lists

// Simply merge 2 lists without any process
newlist = eina_list_merge(sorted1, sorted2);

newlist = eina_list_sorted_merge(sorted1, sorted2, sort_cb);
[...]
```

### Splitting a List ###

Use the ``eina_list_split_list()`` function. The first parameter is the list to split and the second parameter is the *list* (element) after which the list is to be split. The last parameter is the head of the second list.


```c
[...]
// Original list (left list)
Eina_List *list = NULL;

// New list (right list)
Eina_List *other_list = NULL;

// Eina_List (element)
Eina_List *l;

list = eina_list_append(list, "super tux");
list = eina_list_append(list, "frozen bubble");
list = eina_list_append(list, "lincity-ng");

// Sorting the list (just for fun)
list = eina_list_sort(list, 0, cmp_func);

// Looking for the 'split' element
l = eina_list_search_sorted_list(list, cmp_func, "frozen bubble");

// Splitting the list
list = eina_list_split_list(list, l, &other_list);
[...]
```

### Copying a List ###

Use the ``eina_list_clone()`` function. The function copies all the elements in the list in the exact same order:

```c
[...]
Eina_List *app_list_copy;

app_list_copy = eina_list_clone(app_list);
[...]
```

## Accessing List Data ##

### Finding Data in your List ###

Use the ``eina_list_data_find()`` function. Pass the list containing your data as the first parameter and the data you are looking for as the last one. The function returns the found element's data pointer if found, ``NULL`` otherwise.

The ``eina_list_data_find()`` function searches the list from the beginning to the end for the first element's data pointer that coincides with the search term. If it is found, it returns the the data, otherwise it return ``NULL``. The function only compares pointers, which is why using ``Eina_Stringshare`` is very useful with lists, because it always returns the same pointer for the same string:


```c
[...]
Eina_List *app_list = NULL;
const char *res_str;

// Adding some elements to the list (using stringshares)
app_list = eina_list_append(app_list, eina_stringshare_add("enna"));
app_list = eina_list_append(app_list, eina_stringshare_add("ebird"));
app_list = eina_list_append(app_list, eina_stringshare_add("calaos"));
app_list = eina_list_append(app_list, eina_stringshare_add("rage"));
app_list = eina_list_append(app_list, eina_stringshare_add("terminology"));
app_list = eina_list_append(app_list, eina_stringshare_add("enlightenment"));
app_list = eina_list_append(app_list, eina_stringshare_add("eyelight"));
app_list = eina_list_append(app_list, eina_stringshare_add("ephoto"));

// Finding the data
res_str = eina_list_data_find(list, eina_string_share_add("enlightenment"));
if (res_str #### eina_stringshare_add("enlightenment"))
   printf("Data is present");
else
   printf("Data not present");
[...]
```

The above example returns *"Data is present"*.

The ``eina_list_data_find_list()`` function does the same thing as ``eina_list_data_find()`` but returns an ``Eina_List``. For an example, see the ``eina_list_remove_list()`` function. 

You can access the data or a *list* (node) of an ``Eina_List`` using ``eina_list_nth()`` and ``eina_list_nth_list()``. The first function returns a pointer to the data of the *n*th element and the second a pointer to the *list*. To access the data of the 3rd element of an ``Eina_List`` try:

```c
[...]
const char *res;
Eina_List *res_lst;

res = eina_list_nth(app_list, 2);
res_lst = eina_list_nth_list(app_list, 2);
[...]
```

The ``res`` variable contains the pointer to the string *"calaos"*. The ``res_lst`` variable is the list containing *"calaos"*.

### Searching for Data in a List ###

Select your function based on whether the list is sorted or unsorted. 

To search in an unsorted list, use the ``eina_list_search_unsorted()`` function: The first parameter is the list. The second parameter is a callback function for comparison. The last parameter is the data you are looking for.

The ``eina_list_search_unsorted_list()`` function does the same but returns an "Eina_List".

The following example shows 2 searches using both the ``eina_list_search_unsorted()`` and ``eina_list_search_unsorted_list()`` functions:

```c
[...]
int search_list()
{
   // Declaring the list
   Eina_List *list = NULL;
   Eina_List *l;
   // Little trick to use strcmp as Eina_Compare_Cb
   Eina_Compare_Cb cmp_func = (Eina_Compare_Cb)strcmp;

   void *data;
   int cmp_result;

   list = eina_list_append(list, "debian");
   list = eina_list_append(list, "archlinux");
   list = eina_list_append(list, "centos");

   data = eina_list_search_unsorted(list, cmp_func, "archlinux");
   l = eina_list_search_unsorted_list(list, cmp_func, "archlinux");
   if (l->data != data)
     {
        eina_list_free(list);

        return 1;
     }

   eina_list_free(list);

   return 0;
}
[...]
```

To search in sorted lists use the functions ``eina_list_search_sorted_list()`` and ``eina_list_search_sorted()``. These work in a similar way to ``eina_list_search_unsorted()``.

### Retrieving Data from a List Element ###

Use the ``eina_list_data_get()`` function, which returns the data contained in the given list.

The following example uses the ``eina_list_next()`` function to move through the list in a statement:

```c
[...]
int list_data_set()
{
   // Declaring the list
   Eina_List *list = NULL;
   // Eina_List in which to place the elements or lists
   Eina_List *l;

   void *list_data;

   list = eina_list_append(list, eina_stringshare_add("Bertrand"));
   list = eina_list_append(list, eina_stringshare_add("Cedric"));
   list = eina_list_append(list, eina_stringshare_add("Nicolas"));
   list = eina_list_append(list, eina_stringshare_add("Vincent"));
   list = eina_list_append(list, eina_stringshare_add("Raoul"));
   list = eina_list_append(list, eina_stringshare_add("Fabien"));
   list = eina_list_append(list, eina_stringshare_add("Philippe"));
   list = eina_list_append(list, eina_stringshare_add("billiob"));

   for(l = list; l; l = eina_list_next(l))
      // Printing the data returned by eina_list_data_get
      printf("%s\n", (char*)eina_list_data_get(l));

   EINA_LIST_FREE(list, list_data)
      eina_stringshare_del(list_data);

   return 0;
}
[...]
```

### Moving within a List ###

Use the ``eina_list_last()``, ``eina_list_next()`` or ``eina_list_prev()`` functions to move to the last, next, or previous element in a list.

The following example moves backwards starting from the end of the list:

```c
[...]
for(l = eina_list_last(list); l; l = eina_list_prev(l))
   printf("%s\n", (char*)eina_list_data_get(l));
[...]
```

### Counting the Number of List Elements ###

Use the ``eina_list_count()`` function. This returns the number of elements in a list:

```c
[...]
printf("List size: %d\n", eina_list_count(list));
[...]
```

### Iterating through a List ###

There are several iterators you can use. To iterate over a list from the beginning to the end use the ``EINA_LIST_FOREACH`` macro. In this macro the first parameter is the list over which you want to iterate, the second parameter is an ``Eina_List *`` to hold the current *list* (node). The last parameter receives the current data during the run.

The following example prints the data of each *list* (node) of the list:

```c
[...]
Eina_List *list = NULL;
Eina_List *l;
void *list_data;

list = eina_list_append(list, "ls");
list = eina_list_append(list, "top");
list = eina_list_append(list, "rmdir");
list = eina_list_append(list, "uname");

EINA_LIST_FOREACH(list, l, list_data)
   printf("%s\n", (char*)list_data);

eina_list_free(list);
[...]
```
To iterate from the last element to the first, use the ``EINA_LIST_REVERSE_FOREACH`` macro. It works similarly to ``EINA_LIST_FOREACH()``.

To iterate over a list from the beginning to the end you can also use the ``EINA_LIST_FOREACH_SAFE`` macro. It is so-named as it stores the next *list* (node), so you can safely remove the current *list* (node) and continue the iteration:

```c
[...]
Eina_List *list;
Eina_List *l;
Eina_List *l_next;
char *data;

list = eina_list_append(list, "enlightenment");
list = eina_list_append(list, "enlightenment");
list = eina_list_append(list, "enlightenment");
list = eina_list_append(list, "enlightenment");

// Using EINA_LIST_FOREACH_SAFE to free the elements that match "enlightenment"

EINA_LIST_FOREACH_SAFE(list, l, l_next, data)
   if (strcmp(data, "enlightenment") #### 0)
     {
        free(data);
        list = eina_list_remove_list(list, l);
     }
[...]
```

To remove each list element while still having access to the node's data use the ``EINA_LIST_FREE`` macro. Pass the list and a pointer to hold the current data:

```c
[...]
Eina_List *list;
char *data;

// List is filled

EINA_LIST_FREE(list, data)
   free(data);
[...]
```

## Using an Inline List ##

The ``Eina_Inlist`` is a special data type designed to store nodes pointers in the same memory as data. This way the memory is less fragmented but operations such as sort and count are slower. The ``Eina_Inlist`` is designed for specific usage cases. If you're uncertain, use the regular ``Eina_List`` instead.

The ``Eina_Inlist`` nodes can be part of a regular ``Eina_List``, simply added with the ``eina_list_append()`` or ``eina_list_prepend()`` functions.

To use the inline list, first define the structure of the data before creating the inline list:

```c
[...]
struct my_struct
{
   EINA_INLIST;
   int a, b;
};
[...]
```

The structure is composed of 2 integers, the real data, and the ``EINA_INLIST`` type which is composed of 3 pointers defining the inline list structure:

* ``Eina_Inlist * next``: next node
* ``Eina_Inlist * prev``: previous node
* ``Eina_Inlist * last``: last node

To create the inlist nodes, allocate the memory and use the ``eina_inlist_append()`` function. The first parameter is the existing list head or NULL to create a new list. The following example passes ``NULL`` to create a new list.

The second parameter is the new list node, and it must not be NULL. You must use the ``EINA_INLIST_GET()`` macro to get the inlist object of the datastruct:

```c
[...]
struct my_struct *d, *cur;
Eina_Inlist *list, *itr, *tmp;

d = malloc(sizeof(*d));
d->a = 1;
d->b = 10;

list = eina_inlist_append(NULL, EINA_INLIST_GET(d));
[...]
```

Repeat this operation for every new node:

```c
[...]
d = malloc(sizeof(*d));
d->a = 2;
d->b = 20;
list = eina_inlist_append(list, EINA_INLIST_GET(d));
[...]
```

To add data to the inline list, place data at the end of the inline list with the ``eina_inlist_prepend()`` function:

```c
[...]
d = malloc(sizeof(*d));
d->a = 3;
d->b = 30;
list = eina_inlist_prepend(list, EINA_INLIST_GET(d));
[...]
```

Add a node before or after a given node with the ``eina_inlist_prepend_relative()`` and ``eina_inlist_append_relative()`` functions. In both functions, the first parameter is the target list, the second is the element you want to add and the last is the reference element to place data after (in this case). As for a regular ``Eina_List``, everything is a list, so the last parameter is an ``Eina_Inlist`` typed variable.

```c
[...]
d = malloc(sizeof(*d));
d->a = 4;
d->b = 40;
list = eina_inlist_append_relative(list, EINA_INLIST_GET(d), list);
[...]
```

To sort and iterate an inline list, find and move list elements and to perform other inline list operations, see the [Inline List API](PAGE DOES NOT EXIST).

When the inline list is no longer needed destroy it by looping over the list to free each ``EINA_INLIST`` structure and the data using the allocated memory. Use ``eina_inlist_remove()`` on each node.

In the following example, the ``EINA_INLIST_CONTAINER_GET()`` macro returns the container object of an inlist (the ``EINA_INLIST`` of ``my_struct``), the list element is removed and the allocated memory of the container "object" is freed:

```c
[...]
while (list)
  {
     struct my_struct *aux = EINA_INLIST_CONTAINER_GET(list, struct my_struct);

     // Remove the current list element
     list = eina_inlist_remove(list, list);
     free(aux);
  }
[...]
```
### Further Reading ###

[List API](https://www.enlightenment.org/develop/legacy/api/c/start#group__Eina__List__Group.html)
:     A reference for the List API.

[List Example](https://git.enlightenment.org/enlightenment/examples/src/branch/master/reference/c/eina/src/eina_list.c)
:    An example of List API usage.