c++ - "lvalue required as left operand of assignment"写链表错误

Question

我目前正在为我在学校修读的类(class)学习一些 C++。我对左值和右值有基本的了解，但我无法确定为什么会收到编译器错误。

我正在创建一个单向链表并且需要能够反转它。根据我的任务，我有两个类(class)。第一个是节点，它只包含一个整数和一个指针。

 class Node {
  int data;
  Node *next;

  public:
    //Constructor
    Node(int d) {
      data = d;
      next = NULL;}

    //Set to next Node
    void SetNext(Node *nextOne) {
      next = nextOne;}

    //Returns data value
    int Data(){return data;}

    //Returns next Node
    Node *Next() {return next;}
};

然后我有一个链表类，它有一个标题指针，然后是一些用于添加、打印等列表的函数。

class LinkedList {
  Node *head;

  public:
    //Constructor
    LinkedList(){head = NULL;}

    void AddNode(int d) {
      //Create a new Node
      Node *newNode = new Node(d);

      //Create a temporary pointer
      Node *temp = head;

      //If there are already nodes in the list
      if(temp != NULL) {
        //Parse through to the end of the list
        while(temp->Next() != NULL) {
          temp = temp->Next();}
        //Point the last Node in the list to the new Node
        temp->SetNext(newNode);
      }

      //If adding as the first Node
      else{
        head = newNode;}
    }

    void PrintList() {
      //Temporary pointer
      Node *temp = head;

      //If there are no nodes in the list
      if(temp == NULL) {
        std::cout << "The list is empty" << std::endl;}

      //If there is only one node in the list
      if(temp->Next() == NULL) {
          std::cout << temp->Data() << std::endl;}

        //Parse through the list and print
      else {
        do {
          std::cout << temp->Data();
          temp = temp->Next();
        }
        while(temp != NULL);
      }
    }

    //Returns the number of nodes in the list
    int CountList() {
      //Temporary pointer
      Node *temp = head;
      //Counter variable
      int counter = 0;

      //If the list is empty
      if(temp == NULL) {
        return counter;}

      //Parse through Nodes counting them
      else {
        do {counter++;
          temp = temp->Next();
        }
        while(temp != NULL);
      }
      return counter;
    }

    //Reverses the list
    Node *ReverseList() {
      //Initially set to NULL then tracks the new head
      Node *marker = NULL;
      //Tracks the next one in the list
      Node *nextOne;

      //Sets the first Node to NULL and then sets the last Node to point to
      //the first one and rotates through the list pointing the last to the
      //first
      while(head != NULL) {
        nextOne = head->Next();
        head->Next() = marker;
        marker = head;
        head = nextOne;
      }
      //Setting the head back to the start again
      head = marker;
    }

};

其中一个函数应该反转列表。 “head->Next() = marker;”这一行在 ReverseList 函数中导致编译时出现“需要左值作为赋值的左操作数”错误。

关于为什么会发生这种情况以及如何解决问题的任何见解？

提前致谢!

Answer 1

调用 Next() 的返回值是一个右值。由于您在类函数中，因此无需调用 Next 函数来获取私有(private) next 指针，您可以直接使用它。

head->next = marker;