C++/CLI creating additional function to a form.h but not working

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C++

CLI

Made a GUI with Visual Studio. Trying to pass a string to another cpp file but it's difficult. I have tried extern std::string but it's always empty for the measure.cpp file. Extern int is working fine. Then I tried to make function inside to MyForm.h which could return a string but seems that my knowledge is not enough. Maybe I'm placing the function to wrong place in MyForm.h? Could someone assist me what I might be doing wrong?

This doesn't compile, because in measure.cpp: 'path' identifier not found.

measure.cpp:

using namespace std;
string path3;
string globalPath;
string path1;

int measure() {
path3 = path();
path1 = globalPath; //is empty

}

What I have tried:

MyForm.h:

#pragma once
#include <fstream>
#include <iostream>
#include "measure.h"
#include <string>
#include <msclr\marshal_cppstd.h>

extern int stop; //working
std::string path();
extern std::string globalPath; //not working

namespace Project1 {

	using namespace System;
	using namespace System::ComponentModel;
	using namespace System::Collections;
	using namespace System::Windows::Forms;
	using namespace System::Data;
	using namespace System::Drawing;
	using namespace System::IO::Ports;

	

	/// <summary>
	/// Summary for MyForm
	/// </summary>
	public ref class MyForm : public System::Windows::Forms::Form
	{
	public:
		MyForm(void)
		{
			InitializeComponent();
			findPorts();			
		}

		std::string path() {
			return globalPath;
		}

	protected:		
		~MyForm()
.
.
.