## Keyed Data Lists

Keyed Data Lists — lists of data elements which are accessible by a string or GQuark identifier.

## Synopsis

    #include <glib.h>

    struct      GData;
    void        g_datalist_init                 (GData **datalist);

    #define     g_datalist_id_set_data          (dl, q, d)
    void        g_datalist_id_set_data_full     (GData **datalist,
                                                 GQuark key_id,
                                                 gpointer data,
                                                 GDestroyNotify destroy_func);
    gpointer    g_datalist_id_get_data          (GData **datalist,
                                                 GQuark key_id);
    #define     g_datalist_id_remove_data       (dl, q)
    gpointer    g_datalist_id_remove_no_notify  (GData **datalist,
                                                 GQuark key_id);

    #define     g_datalist_set_data             (dl, k, d)
    #define     g_datalist_set_data_full        (dl, k, d, f)
    #define     g_datalist_get_data             (dl, k)
    #define     g_datalist_remove_data          (dl, k)
    #define     g_datalist_remove_no_notify     (dl, k)

    void        g_datalist_foreach              (GData **datalist,
                                                 GDataForeachFunc func,
                                                 gpointer user_data);
    void        g_datalist_clear                (GData **datalist);

## Description

Keyed data lists provide lists of arbitrary data elements which can be accessed either with a string or with a GQuark corresponding to the string.

The GQuark methods are quicker, since the strings have to be converted to GQuarks anyway.

Data lists are used for associating arbitrary data with GObjects, using g_object_set_data() and related functions.

To create a datalist, use g_datalist_init().

To add data elements to a datalist use g_datalist_id_set_data(), g_datalist_id_set_data_full(), g_datalist_set_data() and g_datalist_set_data_full().

To get data elements from a datalist use g_datalist_id_get_data() and g_datalist_get_data().

To iterate over all data elements in a datalist use g_datalist_foreach().

To remove data elements from a datalist use g_datalist_id_remove_data() and g_datalist_remove_data().

To remove all data elements from a datalist, use g_datalist_clear().

## Details

### struct GData

    struct GData;

The GData struct is an opaque data structure to represent a Keyed Data List. It should only be accessed via the following functions.

### g_datalist_init ()

    void        g_datalist_init                 (GData **datalist);

Resets the datalist to `NULL`. It does not free any memory or call any destroy functions.

`datalist` : | a pointer to a pointer to a datalist.

### g_datalist_id_set_data()

    #define     g_datalist_id_set_data(dl, q, d)

Sets the data corresponding to the given GQuark id. Any previous data with the same key is removed, and its destroy function is called.

`dl` : | a datalist.
`q` : | the GQuark to identify the data element.
`d` : | the data element, or `NULL` to remove any previous element corresponding to `q`.

### g_datalist_id_set_data_full ()

    void        g_datalist_id_set_data_full     (GData **datalist,
                                                 GQuark key_id,
                                                 gpointer data,
                                                 GDestroyNotify destroy_func);

Sets the data corresponding to the given GQuark id, and the function to be called when the element is removed from the datalist. Any previous data with the same key is removed, and its destroy function is called.

`datalist` : | a datalist.
`key_id` : | the GQuark to identify the data element.
`data` : | the data element or `NULL` to remove any previous element corresponding to `key_id`.
`destroy_func` : | the function to call when the data element is removed. This function will be called with the data element and can be used to free any memory allocated for it. If `data` is `NULL`, then `destroy_func` must also be `NULL`.

### g_datalist_id_get_data ()

    gpointer    g_datalist_id_get_data          (GData **datalist,
                                                 GQuark key_id);

Retrieves the data element corresponding to `key_id`.

`datalist` : | a datalist.
`key_id` : | the GQuark identifying a data element.
Returns : | the data element, or `NULL` if it is not found.

### g_datalist_id_remove_data()

    #define     g_datalist_id_remove_data(dl, q)

Removes an element, using its GQuark identifier.

`dl` : | a datalist.
`q` : | the GQuark identifying the data element.

### g_datalist_id_remove_no_notify ()

    gpointer    g_datalist_id_remove_no_notify  (GData **datalist,
                                                 GQuark key_id);

Removes an element, without calling its destroy notification function.

`datalist` : | a datalist.
`key_id` : | the GQuark identifying a data element.
Returns : | the data previously stored at `key_id`, or `NULL` if none.

### g_datalist_set_data()

    #define     g_datalist_set_data(dl, k, d)

Sets the data element corresponding to the given string identifier.

`dl` : | a datalist.
`k` : | the string to identify the data element.
`d` : | the data element, or `NULL` to remove any previous element corresponding to `k`.

### g_datalist_set_data_full()

    #define     g_datalist_set_data_full(dl, k, d, f)

Sets the data element corresponding to the given string identifier, and the function to be called when the data element is removed.

`dl` : | a datalist.
`k` : | the string to identify the data element.
`d` : | the data element, or `NULL` to remove any previous element corresponding to `k`.
`f` : | the function to call when the data element is removed. This function will be called with the data element and can be used to free any memory allocated for it. If `d` is `NULL`, then `f` must also be `NULL`.

### g_datalist_get_data()

    #define     g_datalist_get_data(dl, k)

Gets a data element, using its string identifer. This is slower than g_datalist_id_get_data() because the string is first converted to a GQuark.

`dl` : | a datalist.
`k` : | the string identifying a data element.
Returns : | the data element, or `NULL` if it is not found.

### g_datalist_remove_data()

    #define     g_datalist_remove_data(dl, k)

Removes an element using its string identifier. The data element's destroy function is called if it has been set.

`dl` : | a datalist.
`k` : | the string identifying the data element.

### g_datalist_remove_no_notify()

    #define     g_datalist_remove_no_notify(dl, k)

Removes an element, without calling its destroy notifier.

`dl` : | a datalist.
`k` : | the string identifying the data element.

### g_datalist_foreach ()

    void        g_datalist_foreach              (GData **datalist,
                                                 GDataForeachFunc func,
                                                 gpointer user_data);

Calls the given function for each data element of the datalist. The function is called with each data element's GQuark id and data, together with the given `user_data` parameter.

`datalist` : | a datalist.
`func` : | the function to call for each data element.
`user_data` : | user data to pass to the function.

### g_datalist_clear ()

    void        g_datalist_clear                (GData **datalist);

Frees all the data elements of the datalist. The data elements' destroy functions are called if they have been set.

`datalist` : | a datalist.