Doubly Linked List

• Basic Concepts
• Available APIs
• How to Develop
• Development Example
  • Example Description
  • Sample Code
  • Verification

Basic Concepts

A doubly linked list is a linked data structure that consists of a set of sequentially linked records called nodes. Each node contains a pointer to the previous node and a pointer to the next node in the sequence of nodes. The pointer head is unique.

A doubly linked list allows access from a list node to its next node and also the previous node on the list. This data structure facilitates data search, especially traversal of a large amount of data. The symmetry of the doubly linked list also makes operations, such as insertion and deletion, easy. However, pay attention to the pointer direction when performing operations.

Available APIs

The doubly linked list module provides the following APIs. For more details about the APIs, see the API reference.

How to Develop

The typical development process of the doubly linked list is as follows:

1. Call LOS_ListInit/LOS_DL_LIST_HEAD to initialize a doubly linked list.
2. Call LOS_ListAdd to insert a node to the list.
3. Call LOS_ListTailInsert to insert a node to the end of the list.
4. Call LOS_ListDelete to delete the specified node.
5. Call LOS_ListEmpty to check whether a linked list is empty.
6. Call LOS_ListDelInit to delete a specified node, and initialize the linked list based on this node.

NOTE:

• Pay attention to the operations of the front and back pointer of the node.
• The linked list operation APIs are underlying APIs and do not check whether the input parameters are empty. You must ensure that the input parameters are valid.
• If the memory of a linked list node is dynamically requested, release the memory after deleting the node.

Development Example

Example Description

This example implements the following:

1. Initialize a doubly linked list.
2. Add nodes.
3. Delete a node.
4. Check whether the operation is performed successfully.

Sample Code

The sample code is as follows:

#include "stdio.h"
#include "los_list.h"

static UINT32 ListSample(VOID)
{
    LOS_DL_LIST listHead = {NULL,NULL};
    LOS_DL_LIST listNode1 = {NULL,NULL};
    LOS_DL_LIST listNode2 = {NULL,NULL};

    // Initialize the linked list.
    printf("Initial head\n");
    LOS_ListInit(&listHead);

    // Add node 1 and node 2 and verify their relationship.
    LOS_ListAdd(&listHead, &listNode1);
    if (listNode1.pstNext == &listHead && listNode1.pstPrev == &listHead) {
        printf("Add listNode1 success\n");
    }

    LOS_ListTailInsert(&listHead, &listNode2);
    if (listNode2.pstNext == &listHead && listNode2.pstPrev == &listNode1) {
        printf("Tail insert listNode2 success\n");
    }

    // Delete the two nodes.
    LOS_ListDelete(&listNode1);
    LOS_ListDelete(&listNode2);

    // Check that the linked list is empty.
    if (LOS_ListEmpty(&listHead)) {
        printf("Delete success\n");
    }

    return LOS_OK;
}

Verification

The development is successful if the return result is as follows:

Initial head 
Add listNode1 success 
Tail insert listNode2 success
Delete success