c++实现双向链表，插入函数莫名错误

[qq_37466114]

添加和删除都没有问题，但是只要调用插入函数就会出错。

出错代码： StudentList::print() 的 "p = p->next;" 语句。

add()和insert()都重用了addBefore(),但是add()没有问题;remove()和insert()都重用了getNode(),但是remove()没有问题。

如果主函数只调用add(),remove()那么print()没有问题,但是一旦调用insert(),print()便会报错。

经过调试发现，在在insert()返回之后，链表就会被打断。



已经折磨了我好几天，跪求大神解答，无比感激！

#include "stdafx.h"
#include "Student.h"


Student::Student() { 
	this->prior = NULL;
	this->next = NULL;

	this->name = "";
	this->grade = ' ';
	this->score = 0;
}

Student::Student(Student& stu) {
	this->grade = stu.grade;
	this->name = stu.name;
	this->score = stu.score;
	this->next = stu.next;
	this->prior = stu.prior;
}

Student::Student(string name, char grade, int score,Student* p,Student* n){
	
	this->name = name;
	this->grade = grade;
	this->score = score;
	this->prior = p;
	this->next = n;
}

Student::~Student(){}

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

//下面是StudentList类

#include "stdafx.h"
#include "StudentList.h"

//StudentList缺省构造函数初始化时，初始化头结点和尾节点;
//并声明beginMarker和endMarker为静态全局变量;
//再在StudentList中连接头尾节点;

int StudentList::theSize(0);
Student StudentList::beginMarker;
Student StudentList::endMarker("",' ',0,&beginMarker,NULL);

StudentList::StudentList() {

	beginMarker.next = &endMarker;
}

StudentList::~StudentList(){

}

//将新建的student添加到s前;
void StudentList::addBefore(Student& s, string name, char grade, int score) {
	//student是指向Student对象的指针;
	//初始化student时已经让prior和next指向正确位置;
	Student *student = new Student(name, grade, score, s.prior, &s);
	//将引用s的prior和next指向正确位置
	student->prior->next = student;
	s.prior = student;
	//链表长度改变;
	theSize++;
	//student对象应该在析构函数释放;
}

bool StudentList::add(string name, char grade, int score)
{	//新建Student对象并添加到尾节点之前;
	addBefore(endMarker, name, grade, score);
	return true;
}

void StudentList::insert(int index, string name, char grade, int score) {
	//用参数新建一个Student对象,插入到index前；
	Student& p = this->getNode(index);
	addBefore(p, name, grade, score);
	//经调试发现,函数返回之后这里的参数name会变为空;
	//但是将print()输出从name改为grade也是会出错;
	//错误应该是addBefore之后，被传入的那个对象"失效？"了;
	return;
}

void StudentList::remove(int index) {

	Student* p = &(getNode(index));
	p->prior->next = p->next;
	p->next->prior = p->prior;
	p->prior = NULL;
	p->next = NULL;
	//链表长度减一;
	theSize--;
	
}

Student StudentList::getNode(int index) {
	
	Student *p = 0;
	if (index <= theSize / 2) {
		p = &beginMarker;
		for (int i = 0; i < index; i++) {	
			p = p->next;
		}
	}
	
	if (index > theSize / 2) {
		p = &endMarker;
		for (int i = theSize + 1; i > index; i--) {
			p = p->prior;
		}
	}

	return *p;
}

void StudentList::print() {

	Student *p = &beginMarker;
	
	for (int i = 0; i < theSize; i++) {
		cout << p->next->grade<< endl;
		p = p->next;

	}
}