C链表末尾插入节点

Question

我在使用 C 中的链表插入方法时遇到了一些问题。它似乎只在列表的开头添加。我做的任何其他插入都失败了。而且这个 CodeBlocks 调试器太难理解了，我还是不明白。它从不给我值(value)，只是内存中的地址。不管怎样，这是我的职责。你看到它失败的任何原因了吗？

/* function to add a new node at the end of the list */
int addNodeBottom(int val, node *head){

    //create new node
    node *newNode = (node*)malloc(sizeof(node));

    if(newNode == NULL){
        fprintf(stderr, "Unable to allocate memory for new node\n");
        exit(-1);
    }

    newNode->value = val;

    //check for first insertion
    if(head->next == NULL){
        head->next = newNode;
        printf("added at beginning\n");
    }

    else
    {
        //else loop through the list and find the last
        //node, insert next to it
        node *current = head;
        while(current->next != NULL)
        {
            if(current->next == NULL)
            {
                current->next = newNode;
                printf("added later\n");
            }
            current = current->next;
        }
    }
    return 0;
}

然后在main中，只加了929。

   //testing addNodeBottom function
    addNodeBottom(929, head);
    addNodeBottom(98, head);
    addNodeBottom(122, head);
    addNodeBottom(11, head);
    addNodeBottom(1034, head);

Answer 1

此代码将起作用。 samplebias 的答案几乎是正确的，但您需要第三次更改:

int addNodeBottom(int val, node *head){

    //create new node
    node *newNode = (node*)malloc(sizeof(node));

    if(newNode == NULL){
        fprintf(stderr, "Unable to allocate memory for new node\n");
        exit(-1);
    }

    newNode->value = val;
    newNode->next = NULL;  // Change 1

    //check for first insertion
    if(head->next == NULL){
        head->next = newNode;
        printf("added at beginning\n");
    }

    else
    {
        //else loop through the list and find the last
        //node, insert next to it
        node *current = head;
        while (true) { // Change 2
            if(current->next == NULL)
            {
                current->next = newNode;
                printf("added later\n");
                break; // Change 3
            }
            current = current->next;
        };
    }
    return 0;
}

更改 1:newNode->next 必须设置为 NULL，这样我们就不会在列表末尾插入无效指针。

变化2/3:循环改为无限循环，当我们找到最后一个元素时，用break;跳出。请注意 while(current->next != NULL) 与之前的 if(current->next == NULL) 是如何矛盾的。

编辑:关于 while 循环，这种方式要好得多:

  node *current = head;
  while (current->next != NULL) {
    current = current->next;
  }
  current->next = newNode;
  printf("added later\n");