LNK2001,作业题,绝望,求大佬解答

计算机大二生,初学c++,老师让做个图书馆的程序,要求用链表和继承,然后还要用文件。手动满脸绝望。花了三四天才写成这样,但是出现了个这样的错误 。

LNK2001 无法解析的外部符号 "class person * * p_per" (?p_per@@3PAPAVperson@@A) 图书馆 D:\C++\实验\图书馆\图书馆\源.obj 1

不知要怎么改,看网上的解释是因为编译环境,但我觉得错误里有这个class person ** ,应该不是环境的问题,想让各位大佬看看可是我什么地方没写对,概念模糊了。

以下代码是,一个基类item,底下种种派生,一个librery类以供操作,person储存用户信息,储存方式都是链表,在item后面建了两个指针,两个数组。


class person
{
public:
    person(string n = "jk", string add = "207", int m = 666666)
    {
        name = n; address = add; mima = m;
    }
    virtual ~person() { delete this; }
    person*next;
    string name, address; int mima;
private:
};

class item
{
public:
    item(string n=" ",int number=00000,string d=" ")
    {
        name = n; num = number; data = d;
    }
    virtual ~item() { delete this; }
    item*search(int);//链表头结点地址和作品编号
    void display(int);//链表头结点地址和类型,类型编号不写默认为全输出
    void borrow(int ,string);//作品编号和借阅人姓名
    item*next;
protected:
    string name, data;//名称与发行日期
    int num;//项目编号
    string writer;   //作者
    float room;//储存空间
    float time;//周期
    string actor;//演员
    float level;//清晰等级
    int zhuagntai = 1;//zhuangtai是用来查看是否被借用的,1为未被借用,0为被借用
    int chose = 0;
    string person ;//借阅人姓名
private:
};

item* it = NULL;
item* p[];
person*per = NULL;
person *p_per[];

void item::borrow(int ch ,string pername)
{
    int n;
loop:
    item*q = search(ch);
    q->person = pername;
    q->zhuagntai = 0;
    cout << "请问是否还需要借书,需要请输入1"<<endl;
    cin >> n;
    if(n==1)
    {
        cout << "请输入作品编号" << endl;
        cin >> ch;
        goto loop;
    }
    cout << "尊敬的" << pername << ",您已借阅成功,请按时归还";
}
void item::display(int ch=0)
{
    item *p = it->next;
    cout << "所有项目如下:" << endl;

    if (p == NULL)
    {
        cout << "======================================" << endl;
        cout << "          并没有任何项目!!          " << endl;
        cout << "======================================" << endl;
        return;
    }
    for (; p != NULL; p = p->next)
    {
        if (ch == p->chose||ch==0) 
        {
            cout << "======================================" << endl;
            cout << "作品名称为:" << p->name << endl;
            cout << "发行日期为:" << p->data << endl;
            cout << "作品编号为:" << p->num << endl;
            if (p->chose == 1)
                cout << "作者为:" << p->writer << endl;
            if (p->chose == 2)
                cout << "发行间隔为:" << p->time << endl;
            if (p->chose == 3)
                cout << "作品储存空间为:" << p->room << endl;
            if (p->chose == 4)
            {
                cout << "作品演员有:" << p->actor << endl;
                cout << "作品储存空间为:" << p->room << endl;
            }
            if (p->chose == 5)
            {
                cout << "作品演员有:" << p->actor << endl;
                cout << "作品清晰等级为:" << p->level << endl;
            }
            cout << "======================================" << endl;
        }
    }
}
item* item::search(int n)
{
    bool have = 0; item*p = it, *found = NULL;
    for (p; p != NULL; p->next)
    {
        if (p->num == n)
        {
            have = 1;
            found = p;
        }
    }
    if (have == 0)
    {
        cout << "======================================" << endl;
        cout << "查无此项目!!" << endl;
        cout << "======================================" << endl;
    }
    return found;
}

class book :public item
{
public:
    book(string n = " ", int  number = 00000, string d = " ",string w=" ")
    {
        name = n; num = number; data = d; writer = w;
    }
private:
    const int chose = 1; string writer;
};

class music :public item
{
public:
    music(string n = " ", int  number = 00000, string d = " ",float r=0)
    {
        name = n; num = number; data = d; room = r;
    }

private:
    const int chose = 3; float room;
};

class magizne :public item
{
public:
    magizne(string n = " ", int number = 00000, string d = " ",string t=" ")
{
    name = n; num = number; data = d; time = t;
}

private:
    const int chose = 2; string time;
};

class movie :public item
{
public:
    movie(string n = " ", int number = 00000, string d = " ", string act=" ")
    {
        name = n; num = number; data = d; actor = act;
    }
     string actor;
private:
    const int chose = 0;
};

class dvd :public movie
{
public:
    dvd(string n = " ", int number = 00000, string d = " ", string act = " ",float r=0)
    {
        name = n; num = number; data = d; actor = act; room = r;
    }
private:
    const int chose = 4; float room;
};

class languang :public movie
{
public:
    languang(string n = " ", int number = 00000, string d = " ", string act = " ",int lev=1)
    {
        name = n; num = number; data = d; actor = act; level = lev;
    }
private:
    const int chose = 5; int level;
};


class library
{
public:
    library();
    void welcome();
    person* denglu();
    void gongneng();
private:

};
library::library()
{}
void library::welcome()
{
    denglu();
    gongneng();
}
person* library::denglu()
{

    string name_1; int mima_1; person*p = per; int x = 0;
loop:
    cout << "请输入您的用户名和密码" << endl;
    cin >> name_1;
    cin >> mima_1;
    for (p; p != NULL; p = p->next)
    {
        if (p->name == name_1&&p->mima == mima_1)
            ;
        else
        {
            cout << "用户名或密码错误,请重新输入" << endl;
            cout << "如果需要退出,请回复1";
        loop1:
            cin >> x;
            if (x == 0)
                goto loop;
            if (x == 1)
                return NULL;
            else
            {
                cout << "错误指示,请重新输入";
                goto loop1;
            }
        }
    }
    return p;
}
void library::gongneng()
{
    int y = 0;
    while (1) 
    {
        cout << "请选择您所需要的服务"<<endl
            << "1.查询所有项目" << endl
            << "2.借阅" << endl
            << "请输入:" << endl;
        cin >> y;
        if (y == 1)
        {
            int leixin = 0;
            cout << "请输入你要查询的项目类型" << endl
                << "1为书籍类,2为杂志类,3为音乐类,4为电影DVD类,5为电影蓝光类" << endl;
            cin >> leixin;
            it->display(leixin);
        }
        if (y == 2)
        {
            int n;
            cout << "请输入您要借阅的项目编号" << endl;
            cin >> n;
            person*p = denglu();
            if (p == NULL) { continue; }
            it->borrow(n, p->name);
        }
    }
}

void Add(item*h, item*t)
{
     t->next=h; h = t;
}
void add(person*h,person*t)
{
    t->next = h; h = t;
}



int main()
{
     library lib;
     p[1] = new item();
     p[2] = new book("c++真得难", 1, "2018/12/10", "jk");
     p[3] = new music("程序员之歌", 2, "2018/12/8", 2.0);
     p[4] = new magizne("程序员的自我修养", 3, "2018/12/9", "7day");
     p[5] = new dvd("python从入门到放弃", 4, "2018/12/11","jk", 600.5);
     p[6] = new languang("学习c++吧,少年", 5, "2018/12/7","j_k", 5);
     for (int i = 1;i<=6; i++)
     {
         Add(it,p[i]);
     }

     p_per[1] = new person();
     p_per[2] = new person("j_K", "208-1", 666666);
     add(per, p_per[1]);
     add(per, p_per[2]);
     lib.welcome();
}

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