超载<<插入运算符无法正常工作

Question

所以我不明白为什么我的插入运算符不适用于我的列表类。我已经研究了一段时间，我认为重载的语法是正确的。对此不太确定。关于为什么它不起作用的任何提示？这是代码：

编辑：将一些代码更改为当前的代码。

抱歉，现在的问题是我无法让它打印任何内容，它只是打印和空行。

这是驱动程序：

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

using namespace std;

int main(){
Polynomial* poly = new Polynomial();    

poly->set_coefficient(3,2);

poly->set_coefficient(0,2);

poly->set_coefficient(3,1);

cout << "trying to print data" << endl;
cout << *poly << endl;    
return 0;   
}

这是标题：

#ifndef _POLYNOMIAL_H_
#define _POLYNOMIAL_H_

#include <iostream>

class Polynomial {

public:

struct PolyNode {
    int coefficient, degree;
    struct PolyNode* next;      
    PolyNode(int c, int d, PolyNode* n): coefficient(c),degree(d),next(n){}
};

PolyNode* firstTerm;
Polynomial(): firstTerm(0) {} 

struct PolyNode* get_first(){
    return firstTerm;
}


//makes the term with degree d have a coefficient of c
void set_coefficient(int c, int d);     

~Polynomial();  

friend std::ostream& operator<<(std::ostream& o, const Polynomial& p);          
};

#endif

这是实现：

#include "polynomial.h"
#include <iostream>
#include <ostream>

using namespace std;

void Polynomial::set_coefficient(int c, int d){
PolyNode* start = firstTerm;
if(c != 0 && firstTerm == 0)    
    firstTerm = new PolyNode(c,d,NULL);
else{   
    cout << "Entered set_coefficient()" << endl;
    while(start->degree != d && start->next != NULL){
        cout << "Inside set_coefficient() while loop" << endl;          
        start = start->next;        
    }       
    if(c != 0 && start == 0)    
        start = new PolyNode(c,d,0);
    else if(c!= 0 && start != 0)
        start->coefficient = c;
    else if(c == 0){
        cout << "deleting a term" << endl;          
        delete start;
    }
}   
    cout << "Leaving set_coefficient()" << endl;
}

ostream& operator<<(ostream& o,const Polynomial& p){
Polynomial::PolyNode* start = p.firstTerm;  
for(unsigned int i = 0; start->next != 0; i++){
    o << "Term " << i << "'s coefficient is: " << start->coefficient << " degree is: " << start->degree << endl << flush;
    start = start->next;
}   
return o;
}

Answer 1

poly 是一个指针，要使用自定义运算符<<，您需要说“

cout << *poly; // output the object pointed-to, not the pointer itself

您还没有重载”插入多项式*意味着什么代码>.你也不应该尝试。

除此之外，您可能应该通过 const 引用接受对象，流输出运算符没有理由去更改对象。