问：

我最近问了一个问题：ostream& operator<<在课堂上比使用 std：：cout 更好吗？并得到了一个很好的答案。

当我尝试实施该解决方案时，我遇到了错误：

no operator "<<" matches these operands

和

binary '<<': no operator found which takes a right-hand operand of type 'LinkedList' (or there is no acceptable conversion)

在这种情况下，最简单的解决方案是将参数添加到您的方法中，例如：std::ostreamdisplay()

链接列表.h

#include <iostream>

#pragma once

class LinkedList
{
   struct Node {
      int data = 0;
      Node* prev = nullptr;
      Node* next = nullptr;
   };

private:
   Node* m_head;

public:
   // CONSTRUCTOR
   LinkedList();

   // DESTRUCTOR
   ~LinkedList();

   void display(std::ostream& out) const;
};

链接列表：.cpp

#include <iostream>
#include "LinkedList.h"

LinkedList::LinkedList() {
   m_head = nullptr;
}

void LinkedList::display(std::ostream &out) const {
   Node* curr = m_head;

   while (curr) {
      out << curr->data << " -> ";
      curr = curr->next;
   }
   out << std::endl;
}

std::ostream& operator<<(std::ostream &out, const LinkedList &list) {
    list.display(out);
    return out;
}

Main，.cpp（生成错误）

#include <iostream>
#include "LinkedList.h"

int main() {

   LinkedList list;
   std::cout << list;
}