如何用链表重载运算符<<？

Question

对于类，我试图重载

WORD you; //this is a linked list that contains 'y' 'o' 'u'

我想这样做

cout << you; //error: no operator "<<" matches theses operands

我必须将插入运算符重载为友元函数，并通过链接打印一个单词。

我已经声明并定义了重载函数，但它仍然不起作用。这是类声明文件，后面是带有函数的.cpp文件

#include <iostream>

using namespace std;
#pragma once

class alpha_numeric //node
{
public:
char symbol; //data in node
alpha_numeric *next;//points to next node
};

class WORD
{
public:
WORD(); //front of list initially set to Null
//WORD(const WORD& other);
bool IsEmpty(); //done
int Length();
void Add(char); //done
void Print(); //dont
//void Insert(WORD bword, int position);
//WORD operator=(const string& other);

friend ostream & operator<<(ostream & out, alpha_numeric *front);//******************<-----------------

private:
alpha_numeric *front; //points to the front node of a list
int length;

}; 

在 .cpp 文件中，我将 *front 放在参数中，因为它说 front 在我尝试在函数内使用时未定义，即使我在类中声明了它。然后我尝试了这个。我不知道它是否正确。

ostream & operator<<(ostream & out, alpha_numeric *front)
{
alpha_numeric *p;
for(p = front; p != 0; p = p -> next)
{
    out << p -> symbol << endl;
}
}

Answer 1

如果要为WORD类重载

class WORD
{
friend ostream & operator<<(ostream & out, const WORD& w);
}

ostream & operator<<(ostream & out, const WORD& w)
{
alpha_numeric *p;
for(p = w.front; p != 0; p = p -> next)
    out << p -> symbol;
out<<endl;
return out;
}