C++ linked list file operation

Structure

typedef struct student
{
    
    
    string name;             //学生姓名
    string num;              //准考证号
    string ID;               //身份证号
    int exam_room=-1;        //考生考场
    int exam_seat=-1;        //考生座号
    int _num;
    double CET4_grades=-1;   //四级成绩
    double CET6_grades=-1;   //六级成绩
    double CET4_condition=-1;//四级报名状态
    double CET6_condition=-1;//六级报名状态
}ElemType;

/*读取存档*/
void ReadLinkList(LinkList &L)
{
    
    
    LNode *p = L;
    ifstream in("a.txt",ios::in);
    if(!in.is_open())
    {
    
    cout << "Error opening file"; exit (1); }

    while (!in.eof()){
    
    
        LNode *s = new LNode;
        in>>s->data.name>>s->data.num>>s->data.ID
        >>s->data.exam_room>>s->data.exam_seat
        >>s->data.CET4_grades>>s->data.CET6_grades
        >>s->data.CET4_condition>>s->data.CET6_condition;
        if(s->data.CET4_condition==-1&&s->data.CET6_condition==-1){
    
    
            delete s;       //若读取的数据为空，则删除s结点
        }
        else{
    
    
            s->next = NULL;
            p->next = s;
            p = s;
        }
    }
}

/*存档链表*/
void SaveLinkList(LinkList & L)
{
    
    
    ofstream  out("a.txt",ios::out);
    LNode* p;
    p=L->next;

    while(p){
    
    
        out<<p->data.name<<" "<<p->data.num<<" "<<p->data.ID<<" "
        <<p->data.exam_room<<" "<<p->data.exam_seat<<" "
        <<p->data.CET4_grades<<" "<<p->data.CET6_grades<<" "
        <<p->data.CET4_condition<<" "<<p->data.CET6_condition<<"\n";
        p=p->next;
    }
    out.close();
}