> ## Documentation Index > Fetch the complete documentation index at: https://dragonwingdocs-staging.qualcomm.com/llms.txt > Use this file to discover all available pages before exploring further. # AR Utility List > Defines public AudioReach UTIL APIs for double linked list. **Header:** `ar_util/api/ar_util_list.h` ## Structures ### `ar_list_node_t` **Members** Indicates the last known list for which this node belonged. The next node. ### `ar_list_t` **Members** A special dummy node to implement the NULL object pattern. Optional, the user supplied lock implementation function. optional, the user supplied unlock implementation function. Enable secure linked list flag. ## Functions ### `ar_list_init` ar\_list\_init: initialize a list to itself. ```cpp theme={null} int32_t ar_list_init(ar_list_t *list, ar_list_lock_enter_fn_t lock_fn, ar_list_lock_leave_fn_t unlock_fn) ``` **Parameters** pointer to ar\_list\_t. lock\_fn: lock function pointer. unlock\_fn: unlock function pointer. **Returns** 0 Success Nonzero Failure ### `ar_list_init_node` ar\_list\_init\_node ```cpp theme={null} int32_t ar_list_init_node(ar_list_node_t *node) ``` **Parameters** pointer to ar\_list\_node\_t. **Returns** 0 Success Nonzero Failure ### `ar_list_add_tail` ar\_list\_add\_tail ```cpp theme={null} int32_t ar_list_add_tail(ar_list_t *list, ar_list_node_t *node) ``` **Parameters** pointer to ar\_list\_t. node to be added to the list. **Returns** 0 Success Nonzero Failure ### `ar_list_remove_head` ar\_list\_remove\_head ```cpp theme={null} int32_t ar_list_remove_head(ar_list_t *list, ar_list_node_t **ret_node) ``` **Parameters** pointer to ar\_list\_t. **Returns** 0 Success Nonzero Failure ### `ar_list_delete` ar\_list\_delete ```cpp theme={null} int32_t ar_list_delete(ar_list_t *list, ar_list_node_t *node) ``` **Parameters** pointer to ar\_list\_t. pointer to node to be deleted. **Returns** 0 Success Nonzero Failure ### `ar_list_clear` ar\_list\_clear ```cpp theme={null} int32_t ar_list_clear(ar_list_t *list) ``` **Parameters** pointer to ar\_list\_t. **Returns** 0 Success Nonzero Failure ### `ar_list_is_empty` ar\_list\_is\_empty: check if the list is empty. ```cpp theme={null} int32_t ar_list_is_empty(ar_list_t *list) ``` **Parameters** pointer to ar\_list\_t. **Returns** 1 if the list is empty 0 otherwise ### `ar_list_get_head` ar\_list\_get\_head: return the head node from list. ```cpp theme={null} ar_list_node_t * ar_list_get_head(ar_list_t *list) ``` **Parameters** pointer to ar\_list\_t. **Returns** address of head node ### `ar_list_get_tail` ar\_list\_get\_tail: return the tail node from list. ```cpp theme={null} ar_list_node_t * ar_list_get_tail(ar_list_t *list) ``` **Parameters** pointer to ar\_list\_t. **Returns** address of tail node ## Type Definitions ### `ar_list_node_t` ```cpp theme={null} typedef struct ar_list_node_t ar_list_node_t ``` ### `ar_list_t` ```cpp theme={null} typedef struct ar_list_t ar_list_t ``` ### `ar_list_lock_enter_fn_t` ```cpp theme={null} typedef void(* ar_list_lock_enter_fn_t ``` ### `ar_list_lock_leave_fn_t` ```cpp theme={null} typedef void(* ar_list_lock_leave_fn_t ``` ## Macros ### `ar_list_for_each_entry` ar\_list\_for\_each\_entry: iterate over list ```c theme={null} #define ar_list_for_each_entry for (iter = (list)->dummy.next; \ iter != &((list)->dummy); iter = iter->next) ```