<<运算符仅打印空行
<<operator is only printing an empty line
在main中,列表使用插入运算符打印出来,但我得到的只是一行空行。不知道为什么。是不是即使使用set_coefficient,列表中也没有存储任何内容?欢迎任何其他批评。感谢
这是司机:
#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
以下是实现:
#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;
}
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;
}
if (c != 0 && start == 0) // this situation may occur ? you have already judged surrounding if
else if (c == 0) {
cout << "deleting a term" << endl;
delete start; // that may be cause linkedList detach.
}
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; }
看起来你想要一个链表,但你既没有创建也没有删除链接(start->next
),只是分配内存。如果不设置链接,就没有列表。
这里可能有多个错误:>
ostream& operator<<(ostream& o,const Polynomial& p){
Polynomial::PolyNode* start = p.firstTerm;
for(unsigned int i = 0; start->next != 0; i++){
这不会打印最后一个PolyNode。。。
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