QDialog derived class - c++

Question

I have derived class from QDialog that I use for showing the charts. The constructor looks like this:
myplot::myplot(QDialog *parent) : QDialog(parent)
{
chartView = new QChartView();
chart = new QChart();
Qt::WindowFlags flags = 0;
flags |= Qt::WindowMaximizeButtonHint;
flags |= Qt::WindowCloseButtonHint;
setWindowFlags(flags);
this->setLayout(new QVBoxLayout);
this->layout()->addWidget(chartView);
this->setModal(1);
chartView->setChart(chart);
}
I call my class from Mainwindow.cpp but dialog does not close after App exit:
myplot* plot = new myplot(); //does not close after app exit
plot->do_something();
plot->show();
I thought I will correct the problem by this but it does not work:
myplot* plot = new myplot(this); //does not work
When I use this the dialog is closed immediatelly
myplot plot; //immediatelly close
plot.do_something();
plot.show();
When I use exec instead of .show() I get the error "Debug Assertion Failed, _CtrlIsValidHeapPointer(block)" after dialog is closed
plot.exec();
//work but after exiting dialog error
Please, how to handle correctly my derived class to be closed after App exit? I also want to have myplot class to be not modal (now I have it modal in order the user would close it manually before app exit).
Added header file:
#ifndef MYPLOT_H
#define MYPLOT_H
class myplot : public QDialog
{
Q_OBJECT
private:
public:
explicit myplot(QDialog *parent = nullptr);
signals:
};
#endif // MYPLOT_H

Answer 1

This is probably a duplicate of this question.
The answer is you have to write that functionality yourself. If you have your myplot object as a member variable of your MainWindow class then you can properly close it in the MainWindow::closeEvent. See the linked answer above for a hint on how you might implement this.
BTW: Then you don't have to make your dialog modal to enforce closing it before the MainWindow.

Answer 2

you need to look what the QDialog looks like...
do: pass a QWidget instead of a QDialog to the constructor, add a destructor to the dialog and delete there all the things created by the myplot instance if any, call exec() instead of show()...
class myplot : public QDialog
{
Q_OBJECT
public:
explicit myplot(QWidget *parent = nullptr);
~myplot();
....