## Singly-Linked Lists

Singly-Linked Lists — linked lists that can be iterated in one direction

## Synopsis

    #include <glib.h>

    struct              GSList;

    GSList *            g_slist_alloc                       (void);
    GSList *            g_slist_append                      (GSList *list,
                                                             gpointer data);
    GSList *            g_slist_prepend                     (GSList *list,
                                                             gpointer data);
    GSList *            g_slist_insert                      (GSList *list,
                                                             gpointer data,
                                                             gint position);
    GSList *            g_slist_insert_before               (GSList *slist,
                                                             GSList *sibling,
                                                             gpointer data);
    GSList *            g_slist_insert_sorted               (GSList *list,
                                                             gpointer data,
                                                             GCompareFunc func);
    GSList *            g_slist_remove                      (GSList *list,
                                                             gconstpointer data);
    GSList *            g_slist_remove_link                 (GSList *list,
                                                             GSList *link_);
    GSList *            g_slist_delete_link                 (GSList *list,
                                                             GSList *link_);
    GSList *            g_slist_remove_all                  (GSList *list,
                                                             gconstpointer data);
    void                g_slist_free                        (GSList *list);
    void                g_slist_free_full                   (GSList *list,
                                                             GDestroyNotify free_func);
    void                g_slist_free_1                      (GSList *list);
    #define             g_slist_free1

    guint               g_slist_length                      (GSList *list);
    GSList *            g_slist_copy                        (GSList *list);
    GSList *            g_slist_copy_deep                   (GSList *list,
                                                             GCopyFunc func,
                                                             gpointer user_data);
    GSList *            g_slist_reverse                     (GSList *list);
    GSList *            g_slist_insert_sorted_with_data     (GSList *list,
                                                             gpointer data,
                                                             GCompareDataFunc func,
                                                             gpointer user_data);
    GSList *            g_slist_sort                        (GSList *list,
                                                             GCompareFunc compare_func);
    GSList *            g_slist_sort_with_data              (GSList *list,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);
    GSList *            g_slist_concat                      (GSList *list1,
                                                             GSList *list2);
    void                g_slist_foreach                     (GSList *list,
                                                             GFunc func,
                                                             gpointer user_data);

    GSList *            g_slist_last                        (GSList *list);
    #define             g_slist_next                        (slist)
    GSList *            g_slist_nth                         (GSList *list,
                                                             guint n);
    gpointer            g_slist_nth_data                    (GSList *list,
                                                             guint n);

    GSList *            g_slist_find                        (GSList *list,
                                                             gconstpointer data);
    GSList *            g_slist_find_custom                 (GSList *list,
                                                             gconstpointer data,
                                                             GCompareFunc func);
    gint                g_slist_position                    (GSList *list,
                                                             GSList *llink);
    gint                g_slist_index                       (GSList *list,
                                                             gconstpointer data);

## Description

The GSList structure and its associated functions provide a standard singly-linked list data structure.

Each element in the list contains a piece of data, together with a pointer which links to the next element in the list. Using this pointer it is possible to move through the list in one direction only (unlike the Doubly-Linked Lists which allow movement in both directions).

The data contained in each element can be either integer values, by using one of the Type Conversion Macros, or simply pointers to any type of data.

List elements are allocated from the slice allocator, which is more efficient than allocating elements individually.

Note that most of the GSList functions expect to be passed a pointer to the first element in the list. The functions which insert elements return the new start of the list, which may have changed.

There is no function to create a GSList. `NULL` is considered to be the empty list so you simply set a GSList* to `NULL`.

To add elements, use `g_slist_append()`, `g_slist_prepend()`, `g_slist_insert()` and `g_slist_insert_sorted()`.

To remove elements, use `g_slist_remove()`.

To find elements in the list use `g_slist_last()`, `g_slist_next()`, `g_slist_nth()`, `g_slist_nth_data()`, `g_slist_find()` and `g_slist_find_custom()`.

To find the index of an element use `g_slist_position()` and `g_slist_index()`.

To call a function for each element in the list use `g_slist_foreach()`.

To free the entire list, use `g_slist_free()`.

## Details

### struct GSList

    struct GSList {
      gpointer data;
      GSList *next;
    };

The GSList struct is used for each element in the singly-linked list.

gpointer `data`; | holds the element's data, which can be a pointer to any kind of data, or any integer value using the Type Conversion Macros.
GSList *`next`; | contains the link to the next element in the list.

### g_slist_alloc ()

    GSList *            g_slist_alloc                       (void);

Allocates space for one GSList element. It is called by the `g_slist_append()`, `g_slist_prepend()`, `g_slist_insert()` and `g_slist_insert_sorted()` functions and so is rarely used on its own.

Returns : | a pointer to the newly-allocated GSList element.

### g_slist_append ()

    GSList *            g_slist_append                      (GSList *list,
                                                             gpointer data);

Adds a new element on to the end of the list.

### Note

The return value is the new start of the list, which may have changed, so make sure you store the new value.

### Note

Note that `g_slist_append()` has to traverse the entire list to find the end, which is inefficient when adding multiple elements. A common idiom to avoid the inefficiency is to prepend the elements and reverse the list when all elements have been added.

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    /* Notice that these are initialized to the empty list. */
    GSList *list = NULL, *number_list = NULL;

    /* This is a list of strings. */
    list = g_slist_append (list, "first");
    list = g_slist_append (list, "second");

    /* This is a list of integers. */
    number_list = g_slist_append (number_list, GINT_TO_POINTER (27));
    number_list = g_slist_append (number_list, GINT_TO_POINTER (14));

`list` : | a GSList
`data` : | the data for the new element
Returns : | the new start of the GSList

### g_slist_prepend ()

    GSList *            g_slist_prepend                     (GSList *list,
                                                             gpointer data);

Adds a new element on to the start of the list.

### Note

The return value is the new start of the list, which may have changed, so make sure you store the new value.

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    /* Notice that it is initialized to the empty list. */
    GSList *list = NULL;
    list = g_slist_prepend (list, "last");
    list = g_slist_prepend (list, "first");

`list` : | a GSList
`data` : | the data for the new element
Returns : | the new start of the GSList

### g_slist_insert ()

    GSList *            g_slist_insert                      (GSList *list,
                                                             gpointer data,
                                                             gint position);

Inserts a new element into the list at the given position.

`list` : | a GSList
`data` : | the data for the new element
`position` : | the position to insert the element. If this is negative, or is larger than the number of elements in the list, the new element is added on to the end of the list.
Returns : | the new start of the GSList

### g_slist_insert_before ()

    GSList *            g_slist_insert_before               (GSList *slist,
                                                             GSList *sibling,
                                                             gpointer data);

Inserts a node before `sibling` containing `data`.

`slist` : | a GSList
`sibling` : | node to insert `data` before
`data` : | data to put in the newly-inserted node
Returns : | the new head of the list.

### g_slist_insert_sorted ()

    GSList *            g_slist_insert_sorted               (GSList *list,
                                                             gpointer data,
                                                             GCompareFunc func);

Inserts a new element into the list, using the given comparison function to determine its position.

`list` : | a GSList
`data` : | the data for the new element
`func` : | the function to compare elements in the list. It should return a number > 0 if the first parameter comes after the second parameter in the sort order.
Returns : | the new start of the GSList

### g_slist_remove ()

    GSList *            g_slist_remove                      (GSList *list,
                                                             gconstpointer data);

Removes an element from a GSList. If two elements contain the same data, only the first is removed. If none of the elements contain the data, the GSList is unchanged.

`list` : | a GSList
`data` : | the data of the element to remove
Returns : | the new start of the GSList

### g_slist_remove_link ()

    GSList *            g_slist_remove_link                 (GSList *list,
                                                             GSList *link_);

Removes an element from a GSList, without freeing the element. The removed element's next link is set to `NULL`, so that it becomes a self-contained list with one element.

### Note

Removing arbitrary nodes from a singly-linked list requires time that is proportional to the length of the list (ie. O(n)). If you find yourself using `g_slist_remove_link()` frequently, you should consider a different data structure, such as the doubly-linked GList.

`list` : | a GSList
`link_` : | an element in the GSList
Returns : | the new start of the GSList, without the element

### g_slist_delete_link ()

    GSList *            g_slist_delete_link                 (GSList *list,
                                                             GSList *link_);

Removes the node link_ from the list and frees it. Compare this to `g_slist_remove_link()` which removes the node without freeing it.

### Note

Removing arbitrary nodes from a singly-linked list requires time that is proportional to the length of the list (ie. O(n)). If you find yourself using `g_slist_delete_link()` frequently, you should consider a different data structure, such as the doubly-linked GList.

`list` : | a GSList
`link_` : | node to delete
Returns : | the new head of `list`

### g_slist_remove_all ()

    GSList *            g_slist_remove_all                  (GSList *list,
                                                             gconstpointer data);

Removes all list nodes with data equal to `data`. Returns the new head of the list. Contrast with `g_slist_remove()` which removes only the first node matching the given data.

`list` : | a GSList
`data` : | data to remove
Returns : | new head of `list`

### g_slist_free ()

    void                g_slist_free                        (GSList *list);

Frees all of the memory used by a GSList. The freed elements are returned to the slice allocator.

### Note

If list elements contain dynamically-allocated memory, you should either use `g_slist_free_full()` or free them manually first.

`list` : | a GSList

### g_slist_free_full ()

    void                g_slist_free_full                   (GSList *list,
                                                             GDestroyNotify free_func);

Convenience method, which frees all the memory used by a GSList, and calls the specified destroy function on every element's data.

`list` : | a pointer to a GSList
`free_func` : | the function to be called to free each element's data

Since 2.28

### g_slist_free_1 ()

    void                g_slist_free_1                      (GSList *list);

Frees one GSList element. It is usually used after `g_slist_remove_link()`.

`list` : | a GSList element

### g_slist_free1

    #define             g_slist_free1

A macro which does the same as `g_slist_free_1()`.

Since 2.10

### g_slist_length ()

    guint               g_slist_length                      (GSList *list);

Gets the number of elements in a GSList.

### Note

This function iterates over the whole list to count its elements.

`list` : | a GSList
Returns : | the number of elements in the GSList

### g_slist_copy ()

    GSList *            g_slist_copy                        (GSList *list);

Copies a GSList.

### Note

Note that this is a "shallow" copy. If the list elements consist of pointers to data, the pointers are copied but the actual data isn't. See `g_slist_copy_deep()` if you need to copy the data as well.

`list` : | a GSList
Returns : | a copy of `list`

### g_slist_copy_deep ()

    GSList *            g_slist_copy_deep                   (GSList *list,
                                                             GCopyFunc func,
                                                             gpointer user_data);

Makes a full (deep) copy of a GSList.

In contrast with `g_slist_copy()`, this function uses `func` to make a copy of each list element, in addition to copying the list container itself.

`func`, as a GCopyFunc, takes two arguments, the data to be copied and a user pointer. It's safe to pass NULL as user_data, if the copy function takes only one argument.

For instance, if `list` holds a list of GObjects, you can do:

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    another_list = g_slist_copy_deep (list, (GCopyFunc) g_object_ref, NULL);

And, to entirely free the new list, you could do:

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    g_slist_free_full (another_list, g_object_unref);

`list` : | a GSList
`func` : | a copy function used to copy every element in the list
`user_data` : | user data passed to the copy function `func`, or NULL
Returns : | a full copy of `list`, use g_slist_free_full to free it

Since 2.34

### g_slist_reverse ()

    GSList *            g_slist_reverse                     (GSList *list);

Reverses a GSList.

`list` : | a GSList
Returns : | the start of the reversed GSList

### g_slist_insert_sorted_with_data ()

    GSList *            g_slist_insert_sorted_with_data     (GSList *list,
                                                             gpointer data,
                                                             GCompareDataFunc func,
                                                             gpointer user_data);

Inserts a new element into the list, using the given comparison function to determine its position.

`list` : | a GSList
`data` : | the data for the new element
`func` : | the function to compare elements in the list. It should return a number > 0 if the first parameter comes after the second parameter in the sort order.
`user_data` : | data to pass to comparison function
Returns : | the new start of the GSList

Since 2.10

### g_slist_sort ()

    GSList *            g_slist_sort                        (GSList *list,
                                                             GCompareFunc compare_func);

Sorts a GSList using the given comparison function.

`list` : | a GSList
`compare_func` : | the comparison function used to sort the GSList. This function is passed the data from 2 elements of the GSList and should return 0 if they are equal, a negative value if the first element comes before the second, or a positive value if the first element comes after the second.
Returns : | the start of the sorted GSList

### g_slist_sort_with_data ()

    GSList *            g_slist_sort_with_data              (GSList *list,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);

Like `g_slist_sort()`, but the sort function accepts a user data argument.

`list` : | a GSList
`compare_func` : | comparison function
`user_data` : | data to pass to comparison function
Returns : | new head of the list

### g_slist_concat ()

    GSList *            g_slist_concat                      (GSList *list1,
                                                             GSList *list2);

Adds the second GSList onto the end of the first GSList. Note that the elements of the second GSList are not copied. They are used directly.

`list1` : | a GSList
`list2` : | the GSList to add to the end of the first GSList
Returns : | the start of the new GSList

### g_slist_foreach ()

    void                g_slist_foreach                     (GSList *list,
                                                             GFunc func,
                                                             gpointer user_data);

Calls a function for each element of a GSList.

`list` : | a GSList
`func` : | the function to call with each element's data
`user_data` : | user data to pass to the function

### g_slist_last ()

    GSList *            g_slist_last                        (GSList *list);

Gets the last element in a GSList.

### Note

This function iterates over the whole list.

`list` : | a GSList
Returns : | the last element in the GSList, or `NULL` if the GSList has no elements

### g_slist_next()

    #define             g_slist_next(slist)

A convenience macro to get the next element in a GSList.

`slist` : | an element in a GSList.
Returns : | the next element, or `NULL` if there are no more elements.

### g_slist_nth ()

    GSList *            g_slist_nth                         (GSList *list,
                                                             guint n);

Gets the element at the given position in a GSList.

`list` : | a GSList
`n` : | the position of the element, counting from 0
Returns : | the element, or `NULL` if the position is off the end of the GSList

### g_slist_nth_data ()

    gpointer            g_slist_nth_data                    (GSList *list,
                                                             guint n);

Gets the data of the element at the given position.

`list` : | a GSList
`n` : | the position of the element
Returns : | the element's data, or `NULL` if the position is off the end of the GSList

### g_slist_find ()

    GSList *            g_slist_find                        (GSList *list,
                                                             gconstpointer data);

Finds the element in a GSList which contains the given data.

`list` : | a GSList
`data` : | the element data to find
Returns : | the found GSList element, or `NULL` if it is not found

### g_slist_find_custom ()

    GSList *            g_slist_find_custom                 (GSList *list,
                                                             gconstpointer data,
                                                             GCompareFunc func);

Finds an element in a GSList, using a supplied function to find the desired element. It iterates over the list, calling the given function which should return 0 when the desired element is found. The function takes two gconstpointer arguments, the GSList element's data as the first argument and the given user data.

`list` : | a GSList
`data` : | user data passed to the function
`func` : | the function to call for each element. It should return 0 when the desired element is found
Returns : | the found GSList element, or `NULL` if it is not found

### g_slist_position ()

    gint                g_slist_position                    (GSList *list,
                                                             GSList *llink);

Gets the position of the given element in the GSList (starting from 0).

`list` : | a GSList
`llink` : | an element in the GSList
Returns : | the position of the element in the GSList, or -1 if the element is not found

### g_slist_index ()

    gint                g_slist_index                       (GSList *list,
                                                             gconstpointer data);

Gets the position of the element containing the given data (starting from 0).

`list` : | a GSList
`data` : | the data to find
Returns : | the index of the element containing the data, or -1 if the data is not found