Qt strange debugger error QWidget and QApplication - c++

Question

This happens when i enter the code to the slots of my buttons
when i debug the app normally ,all functions etc everything is ok.
but when i try use my code in UI something brokes down.
I'm making the Parking System for my uni classes ,
i got one parent class vehicle and 4 child classes which inherits by public.
here's the code from the UI source file :
#include "datain.h"
#include "ui_datain.h"
#include <QMessageBox>
#include <car.h>
#include <bike.h>
#include <motorbike.h>
#include <tir.h>
#include <vehicle.h>
#include <iostream>
using namespace std;
dataIn::dataIn(QWidget *parent) :
QDialog(parent),
ui(new Ui::dataIn)
{
ui->setupUi(this);
}
dataIn::~dataIn()
{
delete ui;
}
dataIn siema;
void dataIn::on_lineEdit_textEdited(const QString &arg1)
{
siema.rejestracja=arg1;
}
void dataIn::on_lineEdit_2_textEdited(const QString &arg1)
{
siema.marka=arg1;
}
void dataIn::on_car_clicked()
{
Vehicle *wsk;
string reje,mareczka;
reje=siema.rejestracja.toStdString();
mareczka=siema.marka.toStdString();
Car obj(reje,mareczka);
wsk=&obj;
wsk->add();
}
void dataIn::on_motorcycle_clicked()
{
Vehicle *wsk;
string reje,mareczka;
reje=siema.rejestracja.toStdString();
mareczka=siema.marka.toStdString();
Motorbike obj(reje,mareczka);
wsk=&obj;
wsk->add();
}
void dataIn::on_bike_clicked()
{
Vehicle *wsk;
string reje,mareczka;
reje=siema.rejestracja.toStdString();
mareczka=siema.marka.toStdString();
Bike obj(reje,mareczka);
wsk=&obj;
wsk->add();
}
void dataIn::on_tir_clicked()
{
Vehicle *wsk;
string reje,mareczka;
reje=siema.rejestracja.toStdString();
mareczka=siema.marka.toStdString();
Tir obj(reje,mareczka);
wsk=&obj;
wsk->add();
}
Here's the main:
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
dataIn code:
#ifndef DATAIN_H
#define DATAIN_H
#include <QString>
#include <iostream>
#include <QDialog>
using namespace std;
namespace Ui {
class dataIn;
}
class dataIn : public QDialog
{
Q_OBJECT
QString rejestracja;
QString marka;
public:
explicit dataIn(QWidget *parent = 0);
~dataIn();
private slots:
void on_lineEdit_textEdited(const QString &arg1);
void on_lineEdit_2_textEdited(const QString &arg1);
void on_car_clicked();
void on_motorcycle_clicked();
void on_bike_clicked();
void on_tir_clicked();
private:
Ui::dataIn *ui;
};
#endif // DATAIN_H

Answer 1

You may not declare
dataIn siema;
and you should not refer to it - remove all siema.... references from your dataIn functions (replace siema. with nothing or with this->).
When you need your dialog for the first time, create it in (and as child of) MainWindow:
void MainWindow::whateverEvent() {
dataIn *siema = new dataIn(this);
siema->show();
}
If you need to reference it again or want do prevent it from being created twice, store the pointer in a member of your MainWindow.