access variable by pressing address

[nchithangvic]

Hello , I wanna use Instance w to access _x by pressing address (OlMain->vref->_x=10;) through ui_MainWidow::setupUI function, but when i compile this program then issues only 1 error: use of undefined type 'OlMainWindow'
help me for this error, thank so much.

My code File:
FILE ui_MainWidow.h
#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H
#include <iostream>
#include "olvalue.h"

class OlValue;
class OlMainWindow;
class ui_MainWidow;

class ui_MainWidow {
public:
	
	void setupUI(OlMainWindow* OlMain) {
		OlMain->vref->_x=10; // _x = 10;
		OlMain->vref->_x = 10;
		std::cout << " ok";
	}
};
#endif //UI_MAINWINDOW_H

FILE olvalue.h
#include <iostream>
#ifndef VALUE_H
#define VALUE_H

#include "ui_mainwindow.h"
class OlValue;
class OlMainWindow;
class ui_MainWidow;

class OlValue
{
public:
	int _x;
	int _y;
public:
	OlValue() {
		_x = 10;
		_y = 20;
	}
};
#endif //VALUE_H

FILE olmainwindow.h
#ifndef OLMAINWINDOW_H
#define OLMAINWINDOW_H
#include <iostream>
#include <string>
#include "olvalue.h"

class OlValue;
class OlMainWindow;
class ui_MainWidow;

class OlMainWindow
{
public:

	
	OlValue* vref = new OlValue;

	OlMainWindow();
	~OlMainWindow();

	void enterUsername();
private:	
	int val;
	std::string _Username;
};
#endif //OLMAINWINDOW_H

FILE olmainwidow.cpp
#include "olmainwindow.h"
#include <iostream>
#include <string>


class OlValue;
class OlMainWindow;
class ui_MainWidow;

OlMainWindow::OlMainWindow() {
	ui_MainWidow* ui = new ui_MainWidow();
	ui->setupUI(this);

}
OlMainWindow::~OlMainWindow() {
	//delete ui;
}

void OlMainWindow::enterUsername() {
	std::cout << "Please, enter Username: ";
	std::getline(std::cin, _Username);
	std::cout << "You'v accessed Username: " << _Username << std::endl;
}

FILE main.cpp
#include "olmainwindow.h"
#include <iostream>

int main(int argc, char* argv[])
{
	OlMainWindow* w = new OlMainWindow();
	return 0;
}

[coder777]

You need to move the definition of setupUI(...) to the appropriate .cpp. You cannot use any member of a class that is just a forward reference.

[nchithangvic]

@coder777 thank you so much,