I am trying to replicate behaviour in a small PyQt application, but instead using C++.

The reason for this is purely education and I am not interested in answering stating to change the behaviour. I have a bug in a much larger codebase that when using PyQt and I delete the parent of a modal dialog, the window position changes.

I am trying to create the following scenario using Qt.

I have a Main application dialog, which is a parent of a dialog I called ABParent. ABParent is a dialog which is a parent of Dialogs A and B. A, B and ABParent are all modal. When dialog B appears, I want to do the following,

1. Call deleteLater on DialogB
2. Call deleteLater on the modal parent ABParent
3. Call deleteLater on Dialog C.

This replicates the code behaviour to which I observe the main window positioning change. However, unlike when doing this in Python, the application crashes with (process 34820) exited with code -1073740940.

MY C++ code is,

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QVBoxLayout>
#include <iostream>
#include "main.h"

#include "moc_main.cpp"  // Ensure the moc file is included

DialogB::DialogB(QWidget *parent) : QDialog(parent)
{
    setWindowTitle("Dialog B");
    setLayout(new QVBoxLayout());

    QPushButton *closeButton = new QPushButton("Close", this);
    layout()->addWidget(closeButton);

    setWindowModality(Qt::ApplicationModal);

    connect(closeButton, &QPushButton::clicked, this, &DialogB::close_dialog);
}

void DialogB::close_dialog()
{
    std::cout << "Deleting B" << std::endl;
    deleteLater();                             // Delete B

    ABParent *parentDialog = qobject_cast<ABParent *>(parent());
    if (parentDialog) {
        std::cout << "Deleting parent " << parentDialog->objectName().toStdString() << std::endl;
        parentDialog->deleteLater();           // Delete the Modal parent

        std::cout << "Deleting A" << std::endl;
        parentDialog->dialogA->deleteLater();  // Delete dialog A
    }
}


ABParent::ABParent(QWidget *parent) : QDialog(parent)
{
    setWindowTitle("AB Parent");
    setObjectName("AB Parent");
    setWindowModality(Qt::ApplicationModal);

    dialogA = new QDialog(this);
    dialogB = new DialogB(this);

    dialogA->setWindowTitle("Dialog A");
    dialogA->setWindowModality(Qt::ApplicationModal);

    dialogA->show();
    dialogB->show();
}


int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QDialog mainwindow;
    mainwindow.setWindowTitle("Main Window");
    mainwindow.show();

    ABParent abparent = ABParent(&mainwindow);
    abparent.show();

    return app.exec();
}

and the header file,

#pragma once

#include <QDialog>

class DialogB;

class ABParent : public QDialog {
    Q_OBJECT

   public:
    QDialog *dialogA;
    DialogB *dialogB;

    ABParent(QWidget *parent = nullptr);
};

class DialogB : public QDialog {
    Q_OBJECT

   public:
       DialogB(QWidget *parent = nullptr);
   public slots:
       void close_dialog();
};

Would anybody be able to help me understand why the application is crashing? When I have the equivalent in PyQt6 code, it does not.