在链表末尾插入字符串

我在链表的末尾插入一个字符串。当我编译文件时，我收到 2 个错误：

错误："setData"未在此范围内声明 设置数据(*string_p(;

错误："getNext"未在此范围内声明 newNode = getNext((;

但是，它们是在使用它们之前定义的(在上述方法中定义(，所以我不明白错误。

    #include <iostream>
    #include <string>
    using std::string;
    using std::cout;
    using std::endl;
    #define SUCCESS 0
    #define FAIL    1

    // Represents an entry object in the linked-list
    class ListEntry
    {
    public:
    explicit     ListEntry();
    explicit     ListEntry(const char *string_p);
             ~ListEntry();
    string       getData();
    void         setData(const char* string_p);
    void         setData(string string);
    ListEntry   *getNext();
    ListEntry   *getPrevious();
    ListEntry   *prev_p;   // pointer to previous entry in the linked-list
    ListEntry   *next_p;   // pointer to next entry in the linked-list
    private:
    string          data;      // entry's string
    };
    // Represents the linked-list object
    class List
    {
    public:
    List();
    ~List();
    bool printForward();
    bool printReverse();
    bool insert(const char *string_p);
    private:
    int        entryCount;  // number of entries present in the linked-list
    ListEntry *head_p;      // pointer to the first entry in the list
    ListEntry *tail_p;      // pointer to the last entry in the list
    };
    // ListEntry constructor
    ListEntry::ListEntry()
    {
    this->prev_p = NULL;
    this->next_p = NULL;
    return;
    }
    // ListEntry constructor
    ListEntry::ListEntry(const char *string_p)
    {
    this->data   = string_p;
    this->prev_p = NULL;
    this->next_p = NULL;
    return;
    }
    // List entry destructor 
    ListEntry::~ListEntry()
    {
    return;
    }
    // Return the stored string object
    string ListEntry::getData()
    {
    return this->data;
    }
    // Set the internal string data from a char*
    void ListEntry::setData(const char* string_p)
    {
    this->data = string_p;
    }
    // Set the internal string data from a string
    void ListEntry::setData(string string)
    {
    this->data = string;
    }
    // Returns reference to the next entry in the list
    ListEntry *ListEntry::getNext()
    {
    return this->next_p;
    }
    // Returns reference to the previous entry in the list
    ListEntry *ListEntry::getPrevious()
    {
    return this->prev_p;
    }

还有我的插入函数(在我的程序中低于上述方法(：

    bool List::insert(const char *string_p)
    {
      // Please write the list insert function
        //new node to be inserted
        ListEntry* newNode = new ListEntry();
        //List *newList = new List();
        if(newNode == NULL)
        {
          cout << "FAILED";
        }
        else
        {
          setData(*string_p); //////ERROR HERE
          if(this->head_p = NULL)
          {
            newNode = getNext(); //////ERROR HERE
            newNode = this->head_p;
            this->head_p = newNode; // newNode now points to the head node
            this->entryCount++;
            return SUCCESS;
          }
          else
          {
            ListEntry* temp = this->head_p;
            while(temp -> next_p != NULL)
            {
              temp = temp -> next_p;
            }
            temp -> next_p = newNode;
            this->entryCount++;
            return SUCCESS;
          }
        }
    }