錯誤C2512，但我有默認的構造函數可用

Question

我的代碼有錯誤（錯誤C2512：'節點'：沒有適當的默認構造函數可用） 但我有默認的構造函數爲什麼？ 代碼評論我的錯誤位置，請幫我

Node.h

#pragma once 
#include "stat.h" 
#include "Automata.h" 
#include <cstdlib> 

class Node 
{ 
    friend class Automata; 
    friend class stat_a; 
    friend stat_a* makeauto(char *str); 
    friend int main(); 
private: 
    stat_a* mess; 
    char data;//harfi ke ba in masir estefadeh mishe :) 
    Node *next;//node badi dar araye node ha class stat_a :) 
public: 
    Node() 
    { 
     mess = NULL; 
     next = NULL; 
    }; 
}; 

stat.h

#pragma once 
#include "Node.h" 
#include <iostream> 

using namespace std; 
class stat_a 
{ 
    friend class Automata; 
    friend class Node; 
    friend int main(); 
private: 
    bool is_final_stat_a;  //aya final stat_a hast ??? 
    int stat_a_num;    //shomareh halat 0,1,2,... 
    Node *last;     //akharin node dar araye node haye neshan dahande masir 
    Node *first;    //Avalin node dar araye node haye neshan dahande masir 
public: 
    void add(char d,stat_a * a)//ezafeh kardan masiri ke ba estefadeh 
    {      //az harf (char d) be halat (stat_a a) miravad 
     if(first == NULL) 
     { 
      first = new Node;//error is here 
      first->data = d; 
      first->mess = a; 
      last=first; 
     } 
     else 
     { 
      last->next = new Node ;//erorr is here 
      last=last->next; 
      last->data=d; 
      last->next=NULL; 
      last->mess=a; 
     } 
    }; 

    /***********************************************************************/ 

    void print() 
    { 
     cout<<stat_a_num<<"========> is final_stat_a : "<<is_final_stat_a<<endl; 
     Node *a; 

     a=first; 
     while(a != NULL) 
     { 
      cout<<"========> By '"<<a->data<<"' go to stat "<<a->mess->stat_a_num<<endl; 
      a=a->next; 
     } 
    }; 

    stat_a() 
    { 
     last=NULL; 
     first=NULL; 
     is_final_stat_a=false; 
    }; 

    ~stat_a(void); 
}; 

我有默認的構造函數可用，爲什麼出錯

Answer 1

這是一個經典的例子循環依賴。頭文件Node.h取決於頭文件stat.h，這取決於Node.h等。

因爲只在Node聲明stat_h類型的指針變量，你並不需要包括的頭文件，它足以聲明類stat_a：

#pragma once 
#include "Automata.h" 
#include <cstdlib> 

class stat_a; // Declare the class, so the compiler know there's a class by this name 

class Node 
{ 
    // ... 

private: 
    stat_a* mess; // Works because you're only declaring a pointer 

    // ... 

public: 
    // ... 
}; 

然後在stat.h頭當你包含Node.h時，不再有循環依賴。

Answer 2

更換

Node(); 
{ 
    mess = NULL; 
    next = NULL; 
} 

與

Node() 
{ 
    mess = NULL; 
    next = NULL; 
};