C - 链表的 addLast 函数的奇怪行为

Question

我正在用 C 语言创建链表数据结构。但是，我在执行 addLast 函数时收到一些奇怪的行为。直到我下次调用 addLast 时，添加的元素似乎才出现。我的代码(我将通过内联注释解释我认为我的代码是如何工作的):

辅助代码:

typedef struct LinkedList linkedlist;
typedef int ListElement;

struct LinkedList{
  ListElement data;
  linkedlist *next;
};

//Initializes a list;
void CreateList(linkedlist *list, ListElement contents){
  list->data = contents;
  list->next = NULL;
}

//Prints the items of the list, head first.
void displayList(linkedlist *list){
  printf("(%d", list->data);
  linkedlist *node = list->next;

  if(node == NULL){
  }
  else{
    while(node->next != NULL){
      printf(" %d", node->data);
      node = node->next;
    }
  }

  printf(")");
}

有问题的代码:

//Adds an element at the tail of the list
void addLast(linkedlist *list, ListElement forAdding){
  linkedlist *node = list;
  linkedlist *NewNode = (linkedlist *) malloc(sizeof(linkedlist));

  //Go to the last element in the list
  while(node->next != NULL){
    node = node->next;
  }

  //Prepare the node we will add
  NewNode->data = forAdding;
  NewNode->next = NULL;

  //Since node is pointing to the tail element, set its
  //next to the NewNode---the new tail
  node->next = NewNode;
}

//Special attention to this function!
void List(ListElement items[], linkedlist *list, int numItems){
  int i = 0;

  while(i < numItems){
    addLast(list, items[i]);
    printf("Before ");
    displayList(list);
    printf("\n");
    printf("Added %d", items[i]);
    displayList(list);
    printf("\n");
    i++;
  }
}

主要功能:

int main(){
  linkedlist *l= (linkedlist *) malloc(sizeof(linkedlist));
  CreateList(l, 0);
  int a_list[5] = {1, 2, 3, 5, 6};
  List(a_list, l, sizeof(a_list)/sizeof(a_list[0]));
  printf("A list of five elements: %d", sizeof(a_list)/sizeof(a_list[0]));
  displayList(l);
  removeLast(l);
  addLast(l, 7);
  printf("\nAdded something at last position: ");
  displayList(l);
  printf("\n");
}

为此我得到了输出:

Before (0)
Added 1(0)
Before (0)
Added 2(0 1)
Before (0 1)
Added 3(0 1 2)
Before (0 1 2)
Added 5(0 1 2 3)
Before (0 1 2 3)
Added 6(0 1 2 3 5)
A list of five elements: 5(0 1 2 3 5)
Added something at last position: (0 1 2 3 5 6)

如您所见，添加的项目似乎只会出现在我下次调用 addLast 时。

到目前为止，我已经知道它实际上在那里，尽管出于某种原因它不会被打印出来。例如，如果我在关闭函数 List 之前执行另一个 addLast(list, 6); 调用(当然是在循环之外!)，输出行 Added something at last position... (在调用 addLast(l, 7); 后实际会显示 Added something at last position: (0 1 2 3 5 6 6) 。

那么，我做错了什么？

谢谢!

Answer 1

问题不在 AddLast() 中，它只是您的 displayList() 函数:)。您在最后一个元素之前停止打印 1 个元素。

像这样更改 displayList() 函数:

void displayList(linkedlist *list){
  printf("(");
  linkedlist *node = list;

  while(node != NULL){
    printf(" %d", node->data);
    node = node->next;
  }   

  printf(")");
}

这个函数也可以打印空列表。