LNK 2019: Unresolved External Symbol in VS 2017 and Code Correction - lnk2019

Question

This is my code, I am facing problem while build and run.
LNK 2019 Unresolved external symbol error it is.
Please help me to solve this problem.
Person.h
#pragma once
#include<string>
class Person
{
private:
std::string firstname;
std::string lastname;
int age;
public:
Person();
Person(std::string fname, std::string lname);
Person(std::string fname, std::string lname, int age);
~Person();
void setfirstname(std::string fname);
std::string getfirstname();
void setlastname(std::string lname);
std::string getlastname();
void setage(int age);
int getage();
void sayhello();
};
Person.cpp
#include "Person.h"
#include"stdafx.h"
#include<iostream>
Person::Person()
{
firstname = "";
lastname = "";
age = 0;
}
Person::Person(std::string fname, std::string lname)
{
firstname = fname;
lastname = lname;
}
Person::Person(std::string fname, std::string lname, int age)
{
firstname = fname;
lastname = lname;
this->age = age;
}
Person::~Person()
{
}
void Person::setfirstname(std::string fname)
{
this->firstname = fname;
}
void Person::setlastname(std::string lname)
{
this->lastname = lname;
}
void Person::setage(int age)
{
if (age > 0)
{
this->age = age;
}
else
{
std::cout << "Plz Enter a valid age" << std::endl;
}
}
std::string Person::getfirstname()
{
return this->firstname;
}
std::string Person::getlastname()
{
return this->lastname;
}
int Person::getage()
{
return this->age;
}
void Person::sayhello()
{
std::cout << "Hello" << std::endl;
}
Main Function
#include "stdafx.h"
#include<iostream>
#include"Person.h"
int main()
{
Person *p = new Person("Barry", "Allen", 30);
std::cout << "The name of Person is" << p->getfirstname() << " " <<
p>getlastname() << " And the age is" << p->getage() << std::endl;
p->sayhello();
return 0;
}
The message I am getting is :
Severity Code Description Project File Line Suppression State
Error LNK2019 unresolved external symbol "public: __thiscall
Person::Person(class std::basic_string,class std::allocator >,class
std::basic_string,class
std::allocator >,int)"
(??0Person##QAE#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##0H#Z)
referenced in function
_main ConsoleApplication2 C:\Users\Subhajyoti-PC\source\repos\ConsoleApplication2\ConsoleApplication2\ConsoleApplication2.obj 1