Open QWidget or QWindow from the current one - c++

Question

I know this was asked here, but it doesn't work...
Here's my problem: my program actually has 2 forms: LoginWindow and MainWindow, the programme starts on LoginWindow and then I called a class Login where are all methods and attributes for checking users
Here's some code:
//in LoginWindow class
Login log;
log.checkID(ui->usrnmle->text().toStdString(), ui->passwdle->text().toStdString());
//in Login class
void Login::checkID(string usr, string passwd)
{
if(usr == "Test" && passwd == "root")
{
cout << "Ok!" << endl;
MainWindow mw = MainWindow();
mw.show();
LoginWindow lw = LoginWindow();
lw.hide();
}
else
{
cout << "Connection failed " << endl;
}
}
I type the good username and password, I got the 'Ok!' in the output console but MainWindow never appears.
Someone can help?

Answer 1

Your MainWindow mw is a local variable that is destroyed as soon as you are out of checkID function (or even out of if but that does not really matters)
You need to create it on heap
MainWindow *mw = new MainWindow();
mw->show();
Then to avoid memory leak you would need to destroy it when it is of no further use:
delete mw;

Answer 2

I'm not a QT developer, but
{
cout << "Ok!" << endl;
MainWindow mw = MainWindow();
mw.show();
LoginWindow lw = LoginWindow();
lw.hide();
}
You are creating two local windows here, which are destroyed on the spot when the scope ends.
you need to keep these instances alive throught their use. for example, make them member variables of some bigger object like "App" class os so.