## Double-ended Queues

Double-ended Queues — double-ended queue data structure

## Synopsis

    #include <glib.h>

                        GQueue;
    GQueue*             g_queue_new                         (void);
    void                g_queue_free                        (GQueue *queue);
    #define             G_QUEUE_INIT
    void                g_queue_init                        (GQueue *queue);
    void                g_queue_clear                       (GQueue *queue);
    gboolean            g_queue_is_empty                    (GQueue *queue);
    guint               g_queue_get_length                  (GQueue *queue);
    void                g_queue_reverse                     (GQueue *queue);
    GQueue *            g_queue_copy                        (GQueue *queue);
    void                g_queue_foreach                     (GQueue *queue,
                                                             GFunc func,
                                                             gpointer user_data);
    GList *             g_queue_find                        (GQueue *queue,
                                                             gconstpointer data);
    GList *             g_queue_find_custom                 (GQueue *queue,
                                                             gconstpointer data,
                                                             GCompareFunc func);
    void                g_queue_sort                        (GQueue *queue,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);
    void                g_queue_push_head                   (GQueue *queue,
                                                             gpointer data);
    void                g_queue_push_tail                   (GQueue *queue,
                                                             gpointer data);
    void                g_queue_push_nth                    (GQueue *queue,
                                                             gpointer data,
                                                             gint n);
    gpointer            g_queue_pop_head                    (GQueue *queue);
    gpointer            g_queue_pop_tail                    (GQueue *queue);
    gpointer            g_queue_pop_nth                     (GQueue *queue,
                                                             guint n);
    gpointer            g_queue_peek_head                   (GQueue *queue);
    gpointer            g_queue_peek_tail                   (GQueue *queue);
    gpointer            g_queue_peek_nth                    (GQueue *queue,
                                                             guint n);
    gint                g_queue_index                       (GQueue *queue,
                                                             gconstpointer data);
    void                g_queue_remove                      (GQueue *queue,
                                                             gconstpointer data);
    void                g_queue_remove_all                  (GQueue *queue,
                                                             gconstpointer data);
    void                g_queue_insert_before               (GQueue *queue,
                                                             GList *sibling,
                                                             gpointer data);
    void                g_queue_insert_after                (GQueue *queue,
                                                             GList *sibling,
                                                             gpointer data);
    void                g_queue_insert_sorted               (GQueue *queue,
                                                             gpointer data,
                                                             GCompareDataFunc func,
                                                             gpointer user_data);
    void                g_queue_push_head_link              (GQueue *queue,
                                                             GList *link_);
    void                g_queue_push_tail_link              (GQueue *queue,
                                                             GList *link_);
    void                g_queue_push_nth_link               (GQueue *queue,
                                                             gint n,
                                                             GList *link_);
    GList*              g_queue_pop_head_link               (GQueue *queue);
    GList*              g_queue_pop_tail_link               (GQueue *queue);
    GList*              g_queue_pop_nth_link                (GQueue *queue,
                                                             guint n);
    GList*              g_queue_peek_head_link              (GQueue *queue);
    GList*              g_queue_peek_tail_link              (GQueue *queue);
    GList*              g_queue_peek_nth_link               (GQueue *queue,
                                                             guint n);
    gint                g_queue_link_index                  (GQueue *queue,
                                                             GList *link_);
    void                g_queue_unlink                      (GQueue *queue,
                                                             GList *link_);
    void                g_queue_delete_link                 (GQueue *queue,
                                                             GList *link_);

## Description

The GQueue structure and its associated functions provide a standard queue data structure. Internally, GQueue uses the same data structure as GList to store elements.

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.

To create a new GQueue, use `g_queue_new()`.

To initialize a statically-allocated GQueue, use G_QUEUE_INIT or `g_queue_init()`.

To add elements, use `g_queue_push_head()`, `g_queue_push_head_link()`, `g_queue_push_tail()` and `g_queue_push_tail_link()`.

To remove elements, use `g_queue_pop_head()` and `g_queue_pop_tail()`.

To free the entire queue, use `g_queue_free()`.

## Details

### GQueue

    typedef struct {
      GList *head;
      GList *tail;
      guint  length;
    } GQueue;

Contains the public fields of a Queue.

GList *`head`; | a pointer to the first element of the queue.
GList *`tail`; | a pointer to the last element of the queue.
guint `length`; | the number of elements in the queue.

### g_queue_new ()

    GQueue*             g_queue_new                         (void);

Creates a new GQueue.

Returns : | a new GQueue.

### g_queue_free ()

    void                g_queue_free                        (GQueue *queue);

Frees the memory allocated for the GQueue. Only call this function if `queue` was created with `g_queue_new()`. If queue elements contain dynamically-allocated memory, they should be freed first.

`queue` : | a GQueue.

### G_QUEUE_INIT

    #define G_QUEUE_INIT { NULL, NULL, 0 }

A statically-allocated GQueue must be initialized with this macro before it can be used. This macro can be used to initialize a variable, but it cannot be assigned to a variable. In that case you have to use `g_queue_init()`.

    GQueue my_queue = G_QUEUE_INIT;

Since 2.14

### g_queue_init ()

    void                g_queue_init                        (GQueue *queue);

A statically-allocated GQueue must be initialized with this function before it can be used. Alternatively you can initialize it with G_QUEUE_INIT. It is not necessary to initialize queues created with `g_queue_new()`.

`queue` : | an uninitialized GQueue

Since 2.14

### g_queue_clear ()

    void                g_queue_clear                       (GQueue *queue);

Removes all the elements in `queue`. If queue elements contain dynamically-allocated memory, they should be freed first.

`queue` : | a GQueue

Since 2.14

### g_queue_is_empty ()

    gboolean            g_queue_is_empty                    (GQueue *queue);

Returns `TRUE` if the queue is empty.

`queue` : | a GQueue.
Returns : | `TRUE` if the queue is empty.

### g_queue_get_length ()

    guint               g_queue_get_length                  (GQueue *queue);

Returns the number of items in `queue`.

`queue` : | a GQueue
Returns : | The number of items in `queue`.

Since 2.4

### g_queue_reverse ()

    void                g_queue_reverse                     (GQueue *queue);

Reverses the order of the items in `queue`.

`queue` : | a GQueue

Since 2.4

### g_queue_copy ()

    GQueue *            g_queue_copy                        (GQueue *queue);

Copies a `queue`. Note that is a shallow copy. If the elements in the queue consist of pointers to data, the pointers are copied, but the actual data is not.

`queue` : | a GQueue
Returns : | A copy of `queue`

Since 2.4

### g_queue_foreach ()

    void                g_queue_foreach                     (GQueue *queue,
                                                             GFunc func,
                                                             gpointer user_data);

Calls `func` for each element in the queue passing `user_data` to the function.

`queue` : | a GQueue
`func` : | the function to call for each element's data
`user_data` : | user data to pass to `func`

Since 2.4

### g_queue_find ()

    GList *             g_queue_find                        (GQueue *queue,
                                                             gconstpointer data);

Finds the first link in `queue` which contains `data`.

`queue` : | a GQueue
`data` : | data to find
Returns : | The first link in `queue` which contains `data`.

Since 2.4

### g_queue_find_custom ()

    GList *             g_queue_find_custom                 (GQueue *queue,
                                                             gconstpointer data,
                                                             GCompareFunc func);

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

`queue` : | a GQueue
`data` : | user data passed to `func`
`func` : | a GCompareFunc to call for each element. It should return 0 when the desired element is found
Returns : | The found link, or `NULL` if it wasn't found

Since 2.4

### g_queue_sort ()

    void                g_queue_sort                        (GQueue *queue,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);

Sorts `queue` using `compare_func`.

`queue` : | a GQueue
`compare_func` : | the GCompareDataFunc used to sort `queue`. This function is passed two elements of the queue and should return 0 if they are equal, a negative value if the first comes before the second, and a positive value if the second comes before the first.
`user_data` : | user data passed to `compare_func`

Since 2.4

### g_queue_push_head ()

    void                g_queue_push_head                   (GQueue *queue,
                                                             gpointer data);

Adds a new element at the head of the queue.

`queue` : | a GQueue.
`data` : | the data for the new element.

### g_queue_push_tail ()

    void                g_queue_push_tail                   (GQueue *queue,
                                                             gpointer data);

Adds a new element at the tail of the queue.

`queue` : | a GQueue.
`data` : | the data for the new element.

### g_queue_push_nth ()

    void                g_queue_push_nth                    (GQueue *queue,
                                                             gpointer data,
                                                             gint n);

Inserts a new element into `queue` at the given position

`queue` : | a GQueue
`data` : | the data for the new element
`n` : | the position to insert the new element. If `n` is negative or larger than the number of elements in the `queue`, the element is added to the end of the queue.

Since 2.4

### g_queue_pop_head ()

    gpointer            g_queue_pop_head                    (GQueue *queue);

Removes the first element of the queue.

`queue` : | a GQueue.
Returns : | the data of the first element in the queue, or `NULL` if the queue is empty.

### g_queue_pop_tail ()

    gpointer            g_queue_pop_tail                    (GQueue *queue);

Removes the last element of the queue.

`queue` : | a GQueue.
Returns : | the data of the last element in the queue, or `NULL` if the queue is empty.

### g_queue_pop_nth ()

    gpointer            g_queue_pop_nth                     (GQueue *queue,
                                                             guint n);

Removes the `n`'th element of `queue`.

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

Since 2.4

### g_queue_peek_head ()

    gpointer            g_queue_peek_head                   (GQueue *queue);

Returns the first element of the queue.

`queue` : | a GQueue.
Returns : | the data of the first element in the queue, or `NULL` if the queue is empty.

### g_queue_peek_tail ()

    gpointer            g_queue_peek_tail                   (GQueue *queue);

Returns the last element of the queue.

`queue` : | a GQueue.
Returns : | the data of the last element in the queue, or `NULL` if the queue is empty.

### g_queue_peek_nth ()

    gpointer            g_queue_peek_nth                    (GQueue *queue,
                                                             guint n);

Returns the `n`'th element of `queue`.

`queue` : | a GQueue
`n` : | the position of the element.
Returns : | The data for the `n`'th element of `queue`, or `NULL` if `n` is off the end of `queue`.

Since 2.4

### g_queue_index ()

    gint                g_queue_index                       (GQueue *queue,
                                                             gconstpointer data);

Returns the position of the first element in `queue` which contains `data`.

`queue` : | a GQueue
`data` : | the data to find.
Returns : | The position of the first element in `queue` which contains `data`, or -1 if no element in `queue` contains `data`.

Since 2.4

### g_queue_remove ()

    void                g_queue_remove                      (GQueue *queue,
                                                             gconstpointer data);

Removes the first element in `queue` that contains `data`.

`queue` : | a GQueue
`data` : | data to remove.

Since 2.4

### g_queue_remove_all ()

    void                g_queue_remove_all                  (GQueue *queue,
                                                             gconstpointer data);

Remove all elemeents in `queue` which contains `data`.

`queue` : | a GQueue
`data` : | data to remove

Since 2.4

### g_queue_insert_before ()

    void                g_queue_insert_before               (GQueue *queue,
                                                             GList *sibling,
                                                             gpointer data);

Inserts `data` into `queue` before `sibling`.

`sibling` must be part of `queue`.

`queue` : | a GQueue
`sibling` : | a GList link that must be part of `queue`
`data` : | the data to insert

Since 2.4

### g_queue_insert_after ()

    void                g_queue_insert_after                (GQueue *queue,
                                                             GList *sibling,
                                                             gpointer data);

Inserts `data` into `queue` after `sibling`

`sibling` must be part of `queue`

`queue` : | a GQueue
`sibling` : | a GList link that must be part of `queue`
`data` : | the data to insert

Since 2.4

### g_queue_insert_sorted ()

    void                g_queue_insert_sorted               (GQueue *queue,
                                                             gpointer data,
                                                             GCompareDataFunc func,
                                                             gpointer user_data);

Inserts `data` into `queue` using `func` to determine the new position.

`queue` : | a GQueue
`data` : | the data to insert
`func` : | the GCompareDataFunc used to compare elements in the queue. It is called with two elements of the `queue` and `user_data`. It should return 0 if the elements are equal, a negative value if the first element comes before the second, and a positive value if the second element comes before the first.
`user_data` : | user data passed to `func`.

Since 2.4

### g_queue_push_head_link ()

    void                g_queue_push_head_link              (GQueue *queue,
                                                             GList *link_);

Adds a new element at the head of the queue.

`queue` : | a GQueue.
`link_` : | a single GList element, not a list with more than one element.

### g_queue_push_tail_link ()

    void                g_queue_push_tail_link              (GQueue *queue,
                                                             GList *link_);

Adds a new element at the tail of the queue.

`queue` : | a GQueue.
`link_` : | a single GList element, not a list with more than one element.

### g_queue_push_nth_link ()

    void                g_queue_push_nth_link               (GQueue *queue,
                                                             gint n,
                                                             GList *link_);

Inserts `link` into `queue` at the given position.

`queue` : | a GQueue
`n` : | the position to insert the link. If this is negative or larger than the number of elements in `queue`, the link is added to the end of `queue`.
`link_` : | the link to add to `queue`

Since 2.4

### g_queue_pop_head_link ()

    GList*              g_queue_pop_head_link               (GQueue *queue);

Removes the first element of the queue.

`queue` : | a GQueue.
Returns : | the GList element at the head of the queue, or `NULL` if the queue is empty.

### g_queue_pop_tail_link ()

    GList*              g_queue_pop_tail_link               (GQueue *queue);

Removes the last element of the queue.

`queue` : | a GQueue.
Returns : | the GList element at the tail of the queue, or `NULL` if the queue is empty.

### g_queue_pop_nth_link ()

    GList*              g_queue_pop_nth_link                (GQueue *queue,
                                                             guint n);

Removes and returns the link at the given position.

`queue` : | a GQueue
`n` : | the link's position
Returns : | The `n`'th link, or `NULL` if `n` is off the end of `queue`.

Since 2.4

### g_queue_peek_head_link ()

    GList*              g_queue_peek_head_link              (GQueue *queue);

Returns the first link in `queue`

`queue` : | a GQueue
Returns : | the first link in `queue`, or `NULL` if `queue` is empty

Since 2.4

### g_queue_peek_tail_link ()

    GList*              g_queue_peek_tail_link              (GQueue *queue);

Returns the last link `queue`.

`queue` : | a GQueue
Returns : | the last link in `queue`, or `NULL` if `queue` is empty

Since 2.4

### g_queue_peek_nth_link ()

    GList*              g_queue_peek_nth_link               (GQueue *queue,
                                                             guint n);

Returns the link at the given position

`queue` : | a GQueue
`n` : | the position of the link
Returns : | The link at the `n`'th position, or `NULL` if `n` is off the end of the list

Since 2.4

### g_queue_link_index ()

    gint                g_queue_link_index                  (GQueue *queue,
                                                             GList *link_);

Returns the position of `link_` in `queue`.

`queue` : | a Gqueue
`link_` : | A GList link
Returns : | The position of `link_`, or -1 if the link is not part of `queue`

Since 2.4

### g_queue_unlink ()

    void                g_queue_unlink                      (GQueue *queue,
                                                             GList *link_);

Unlinks `link_` so that it will no longer be part of `queue`. The link is not freed.

`link_` must be part of `queue`,

`queue` : | a GQueue
`link_` : | a GList link that must be part of `queue`

Since 2.4

### g_queue_delete_link ()

    void                g_queue_delete_link                 (GQueue *queue,
                                                             GList *link_);

Removes `link_` from `queue` and frees it.

`link_` must be part of `queue`.

`queue` : | a GQueue
`link_` : | a GList link that must be part of `queue`

Since 2.4