"Ошибка 2 error LNK2019: ссылка на неразрешенный внешний символ

#pragma once
#include <iostream>
#include <iomanip>
#include <string>
#include <stdio.h>
#include <array>
#pragma warning(disable:4996)
using namespace std;
class Date
{
protected:
    int month;
    int year;
    int day;
public:
    Date(){ day = 1; month = 1; year = 1900; };
    Date(int d, int m, int y)
    {
        day = d;
        month = m;
        year = y;
    }
    virtual void Show(){}
};

class Person : public Date
{
protected:
    string name;
    string surname;
public:
    Person() :Date()
    {
        name = "Noname";
        surname = "Nosurname";
        //Date::day = 1;
        //Date::month = 1;
        //Date::year = 1999;
    }
    Person(string n, string s, int d, int m, int y) : Date(d, m, y)  {
        name = n;
        surname = s;
    }
    virtual void Show()
    {
        cout << "Name: " << name << endl;
        cout << "Surname: " << surname << endl;
        cout << "Day of birthday: " << day << endl;
        cout << "Month  of birthday: " << month << endl;
        cout << "Year of birthday: " << year << endl;
    }

};
class Type_of_file
{
protected:
    string type;
public:
    Type_of_file()
    {
        type = "*.txt";
    }
    Type_of_file(string type);
    /*virtual void Show(){
    cout << "Type of file: " << type << endl;
    }
    */
};
class File : public Type_of_file, public Date
{
protected:
    string title;
    long int size;
public:

    File() : Type_of_file(), Date(){ title = "TITLE"; size = 111111; }
    File(string type, int d, int m, int y, string t, long int s) :Type_of_file(t), Date(d, m, y)
    {
        title = t;
        size = s;
    }
    virtual void Show()
    {
        cout << "Title of the file: " << title << endl;
        cout << "Size of title: " << size << endl;
        cout << "Type of file: " << type << endl;
        cout << "Day of creating:" << day << endl;
        cout << "Month of creating: " << month << endl;
        cout << "Year of creating: " << year << endl;

    }
};
class Document : public File, public Person, public Date
{
protected:
    string file_spesification;
public:
    Document() :File(), Date(), Person(){ file_spesification = "SPESIFICATION"; }
    Document(File fl, Person per, string fs, int d, int m, int y) :File(fl), Person(per), Date(d, m, y)
    {
        file_spesification = fs;
    }
    virtual void Show()
    {
        File::Show();
        Person::Show();
        cout << "File spesification: " << file_spesification << endl;
    }
};
class List_of_documents : public File
{
protected:
    Document *Documents;
    int n;
public:
    List_of_documents() :File()
    {
        n = 5;
        Documents = new Document[n];
        for (int i = 0; i < n; i++)
        {
            Documents[i] = Document();
        }
    }
    List_of_documents(File fl, Document *doc, int n) :File(fl)
    {
        this->n = n;
        Documents = new Document[n];
        for (int i = 0; i < n; i++)
        {
            Documents[i] = Document(doc[i]);
        }
    }
    List_of_documents(const List_of_documents &copy) {
        this->n = copy.n;
        this->Documents = new Document[this->n];
        for (int i = 0; i < this->n; i++) {
            this->Documents[i] = copy.Documents[i];
        }
    }

};
#include <iostream>
#include <string>
#include <iomanip>
#include <stdio.h>
#include "lab6.h"
#pragma warning(disable:4996)
using namespace std;

int main()
{
    Person per1("Alexandr", "Laskavyi", 2, 9, 1999);
    Person per2("Alina", "Zagrebelnaia", 4, 6, 2000);
    File fl1("*.doc", 5, 12, 2016, "Document_1", 23432);
    File fl2("*.txt", 14, 9, 2015, "Document_2", 43252);
    Document dc1(fl1, per1, "First document", 2, 6, 2018);
    Document dc2(fl2, per2, "Second document", 9, 3, 2018);
    Document *doc = new Document[2];
    doc[0] = dc1;
    doc[1] = dc2;
    List_of_documents list1(fl1, doc,2);
    list1.Show();


    system("pause");
    return 0;

}

Ошибка:

Ошибка 2 error LNK2019: ссылка на неразрешенный внешний символ "public: __thiscall Type_of_file::Type_of_file(class std::basic_string,class std::allocator >)" (??0Type_of_file@@QAE@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) в функции "public: __thiscall File::File(class std::basic_string,class std::allocator >,int,int,int,class std::basic_string,class std::allocator >,long)" (??0File@@QAE@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@HHH0J@Z) C:\Users\laska_000\Desktop\new_6_laba\new_6_laba\Исходный код.obj new_6_laba