我无法在链表类中分配结构节点的变量。 当我将它们分配给任何东西时，它会产生未定义的行为

Question

//method for printing list
void printList(const ReservationList& ls){ 
for(int i = 0; i < ls.getLength(); i++){ std::cout<<"ls["<<i<<"]== "<<i+1<<ls.retrieve(i,i+1)<<std::endl; }
}
//main method
int main(){
ReservationList r;
std::cout<<"program starts!"<<std::endl;
std::cout<<"before printing empty list"<<std::endl;
printList(r);
std::cout<<"after printing empty list"<<std::endl;
std::cout<<"inserting starts!"<<std::endl;
r.insert(0,1);
std::cout<<"after inserting 1"<<std::endl;
r.insert(0,2);
std::cout<<"after inserting 2"<<std::endl;
r.insert(0,3);
std::cout<<"after inserting 3"<<std::endl;
r.insert(0,4);
std::cout<<"after inserting 4"<<std::endl;
r.insert(0,5);
std::cout<<"after inserting 5"<<std::endl;
printList(r);

return 0;
}

这是ReserveList类(ReserveList.h(的头部

#ifndef RESERVATION_H
#define RESERVATION_H
#include <iostream>
class ReservationList {
public:
ReservationList();/*
ReservationList( const ReservationList& aList );
~ReservationList();*/
bool isEmpty() const;
int getLength() const ;
bool retrieve(int index, int resCode) const;
bool insert(int index, int resCode);
bool remove(int index);
private:
struct ReservationNode {
int Code;
ReservationNode* next;
};
int size;

ReservationNode *head;
ReservationNode *find(int index) const;
}; 
#endif

这些是我迄今为止调用的构造函数和插入方法

//empty constructor
ReservationList::ReservationList() {
head = NULL;
size = 0;
}
//insert method
bool ReservationList::insert(int index, int resCode) {
if(index < 0 || index > size) { return 0; }
//making node to be added
ReservationNode* tmp;
std::cout<<"inside insert 1"<<std::endl;
tmp->Code = resCode;/*mistake is hear */
std::cout<<"inside insert 2"<<std::endl;
tmp->next = NULL;
std::cout<<"inside insert 3"<<std::endl;

if ( (index == 0) && (size == 0) ) { 
std::cout<<"inside insert 4"<<std::endl;
head = tmp;
size++; 
return 1; 
}
else if ( (index == 0) && (size == 1) ){
tmp->next = head;
head = tmp;
size++;
return 1;
}
ReservationNode  *curr , *prev; 
curr = find( index );
prev = find( index - 1 );
tmp->next = curr;
prev->next = tmp;
size++;
return 1; 
}

这是输出

program starts!
before printing empty list
after printing empty list
inserting starts!
inside insert 1
[Done] exited with code=3221225477 in 0.622 seconds

用"；std:：cout"；我跟踪了插入方法的tmp->Code = resCode;部分的错误问题出现在CCD_ 2之后，但是当我注释CCD_。据我所知，访问结构内部的变量或分配变量存在问题。

Answer 1

此代码片段

ReservationNode* tmp;
std::cout<<"inside insert 1"<<std::endl;
tmp->Code = resCode;/*mistake is hear */
std::cout<<"inside insert 2"<<std::endl;
tmp->next = NULL;

调用未定义的行为，因为指针tmp未初始化并且未指向类型为ReservationNode的有效对象。

您似乎忘记了调用运算符new来创建类型为ReservationNode的对象。

同时调用函数find两次

ReservationNode  *curr , *prev; 
curr = find( index );
prev = find( index - 1 );

效率低下。

在没有重复代码的情况下，可以更简单地定义函数。

bool ReservationList::insert( int index, int resCode )
{
bool success = not ( index < 0 || index > size );
if ( success )
{
ReservationNode **current = &head;
while ( index-- )
{
current = &( *current )->next;
}
ReservationNode *new_node = new ReservationNode { resCode, *current };
*current = new_node;
++size;
}
return success;
}

请注意，如果数据成员size将具有无符号整数类型size_t而不是有符号整数类型int，则会更好。这同样适用于函数参数index。