我无法在链表 class 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 ReservationList 的头部 class(ReservationList.h)

#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

这些是我到目前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

使用“std::cout”我跟踪了插入方法的 tmp->Code = resCode; 部分的错误问题出在 std::cout<<"inside insert 1"<<std::endl; 之后，但是当我评论 tmp->Code = resCode; 时，它在紧接着的那一行给出了错误。据我了解，访问结构中的变量或分配它们存在问题。

Answer 1

这段代码

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 未初始化且未指向 ReservationNode.

类型的有效对象

您似乎忘记调用运算符 new 来创建 ReservationNode.

类型的对象

同时调用函数find两次

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

效率低下。

函数定义更简单，无需重复代码。

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;
}

注意如果数据成员size是无符号整数类型size_t而不是有符号整数类型int会更好。同样对函数参数index.

有效

我无法在链表 class 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

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