C++: Undef Ref Error For Class Construction

Question

I have been following a C++ course on Udemy. However, they do not seem to separate classes (ie: they keep all classes in the main.cpp file). I wanted to try to separate classes for a personal project.

I have a class "Prefecture". I split it into "Prefecture.h" and "Prefecture.cpp" as I have seen online.

Prefecture.h:

#include <string>
#include <vector>
#include <utility>

// user defined classes
using namespace std;

#pragma once 

class Prefecture{
    private:
        string _name;
        string _capital;
        string _region;
        double _area;
        string _island;
        // data for yearly pop change
        vector<pair<double,double>> _pairVec;
    public:
        Prefecture(string aName);
        void pushToPairVec(double aYear, double aPop);
        // setters
        void setName(string aName);
        // getters
        string getName();
        vector<pair<double,double>> getPairVec();
};

Prefecture.cpp:

#include <utility>
#include <string>

#include "Prefecture.h"
using namespace std;

Prefecture::Prefecture(string aName){
    _name = aName;
}

void Prefecture::setName(string aName){
    _name = aName;
}
string Prefecture::getName(){
    return _name;
}
vector<pair<double,double>> Prefecture:: getPairVec(){
    return _pairVec;
}

void Prefecture::pushToPairVec(double aYear, double aPop){
    _pairVec.push_back(pair(aYear,aPop));
}

Note that my outside classes are in a folder "classes". Thus to get to the header file I do ./classes/Prefecture.h , and for the cpp I do ./classes/Prefecture.cpp

Here is my main.cpp:

#include <iostream>
#include <string>
#include <vector>
#include "./classes/Prefecture.h"


using namespace std;

int main(int argc, char const *argv[])
{
    Prefecture g("hello");
    cout << g.getName() << endl;
    return 0;
}

When I run this in VSCode, the following error occurs:

C:\Users\whale\AppData\Local\Temp\ccMIrBlR.o:main.cpp:(.text+0x55): undefined reference to `Prefecture::Prefecture(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
C:\Users\whale\AppData\Local\Temp\ccMIrBlR.o:main.cpp:(.text+0x7d): undefined reference to `Prefecture::getName[abi:cxx11]()'
collect2.exe: error: ld returned 1 exit status
PS D:\Desktop\cppData> 

I am not sure how to fix this.