Qt LNK1120 Unresolved External - c++

Question

I'm trying to make the following code work, but no idea why im getting this error.
Im having a mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "user.h"
#include <QObject>
#include <QEvent>
#include "logindialog.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_actionTest_triggered();
void on_actionExit_triggered();
private:
Ui::MainWindow *ui;
User *_User;
void doLogin(void);
User getUser(QString);
};
#endif // MAINWINDOW_H
and a windwindow.cpp
#include "mainwindow.h"
#include "ui_RMS_MainWindow.h"
#include "logindialog.h"
#include <QtCore>
#include <QtGui>
#include <QDebug>
#include <QApplication>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
this->installEventFilter(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void doLogin()
{
//LoginDialog aLoginDialog;
//aLoginDialog.setModal(true);
//aLoginDialog.exec();
qDebug() << "user log in needed";
}
void MainWindow::on_actionTest_triggered()
{
if(_User == NULL)
{
qDebug() << "user log in needed";
MainWindow::doLogin();
}
else
{
qDebug() << "sepp";
}
}
void MainWindow::on_actionExit_triggered()
{
QCoreApplication::quit();
}
When i try to run the code to open the dialog in the button triggered action it runs, when i try to call MainWindow::doLogin i get the "unresolved externals" error.

Answer 1

Hm. You have doLogin() function defined but it's not a MainWindow class method.
You need to define it as
void MainWindow::doLogin()

Answer 2

In windwindow.cpp you have:
void doLogin()
{
//LoginDialog aLoginDialog;
//aLoginDialog.setModal(true);
//aLoginDialog.exec();
qDebug() << "user log in needed";
}
You should change to:
void MainWindow::doLogin()
{
//LoginDialog aLoginDialog;
//aLoginDialog.setModal(true);
//aLoginDialog.exec();
qDebug() << "user log in needed";
}
As it is now this function is not implemented in MainWindow class.