segfault

Hello!
I have got a class SmsGui which contains 2 forms generated by qtdesigner: mainWindow and loginWindow. Firstly when program runs, mainWidnow is created and shown. When user presses Ok on mainWindow, loginWindow is created and shown. And here are 2 situations: in first situation I do:

Code:

connect(loginWindow->cancelButton, SIGNAL(clicked()), loginWindow, SLOT(close()));

And loginDialog closes normally. But in a secod situation I call loginDialog->close() manually.

Code:

connect(loginWindow->cancelButton, SIGNAL(clicked()), this, SLOT(kill()));
 
void SmsGui::kill()
{
	loginDialog->close();
}

And this gives me a segfault. Why? I just call the same function but in 2 different ways, so why it gives me a segfault?
Backtrace:

Code:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1223948608 (LWP 25558)]
0x0804d9a4 in SmsGui::kill (this=0x8061670) at sms_gui.cpp:125
125             loginDialog->close();
(gdb) backtrace
#0  0x0804d9a4 in SmsGui::kill (this=0x8061670)
    at sms_gui.cpp:125
 
#1  0x0804d995 in SmsGui::clickedLoginOk (this=0x8061670)
    at sms_gui.cpp:120
#2  0x08050d14 in SmsGui::qt_metacall (this=0x8061670, 
    _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0xbfa59790)
    at moc_sms_gui.cpp:83
#3  0xb746132c in QMetaObject::activate ()
   from /usr/lib/qt4/libQtCore_debug.so.4
#4  0xb746157e in QMetaObject::activate ()
   from /usr/lib/qt4/libQtCore_debug.so.4
#5  0xb7e011f6 in QAbstractButton::clicked ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#6  0xb7c66455 in QAbstractButtonPrivate::click ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#7  0xb7c67779 in QAbstractButton::mouseReleaseEvent ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#8  0xb7a3879d in QWidget::event ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#9  0xb7c6761b in QAbstractButton::event ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#10 0xb7ce0d52 in QPushButton::event ()
   from /usr/lib/qt4/libQtGui_debug.so.4
#11 0xb79ecea7 in QApplicationPrivate::notify_helper ()

Header file:

Code:

#ifndef SMS_GUI_H
#define SMS_GUI_H
 
#include <QDialog>
#include "ui_main_window.h"
#include "ui_login_dialog.h"
#include "types.h"
 
class SmsGui : public QObject
 
{
 
	Q_OBJECT
 
	public:
		QString username, password, number, message;
		bool limitCheck;
		unsigned short int port;
		void destroy();
		void showMainWindow();
 
		void connectSlots();
		void disconnectSlots();
		void setMiastoPlusaParameters();
		void showLoginDialog();
		Ui_mainWindow *mainWindow;
		QDialog *mainDialog;
 
		Ui_loginDialog *loginWindow;
		QDialog *loginDialog;
 
 
 
	public slots:
		void enableSendButtonText();
		void enableSendButtonLine(const QString &newText);
		void resetAll();
		void currentIndexChanged(int index);
		void clickedLoginOk();
		void clickedSend();
		void clickedLoginCancel();
 
		void closeMainWindow();
		void kill();
	public:
		SmsGui();
		~SmsGui();
 
	signals:
		void readyToSend(network);
 
 
};

source:

Code:

#include "sms_gui.h"
 
SmsGui::SmsGui()
{
	showMainWindow();
	connectSlots();
}
 
SmsGui::~SmsGui()
{
	closeMainWindow();
}
 
void SmsGui::showMainWindow()
{
	mainDialog = new QDialog;
	mainWindow = new Ui_mainWindow;
	mainWindow->setupUi(mainDialog);
	mainDialog->show();
}
 
void SmsGui::closeMainWindow()
{
	mainDialog->reject();
	delete mainDialog;
	mainDialog = NULL;
	delete mainWindow;
	mainWindow = NULL;
}
 
void SmsGui::connectSlots()
{
	connect(mainWindow->okButton, SIGNAL(clicked()), this, SLOT(clickedSend()));
}
 
 
void SmsGui::clickedSend()
{
	//mainDialog->close();
	switch(mainWindow->comboBox->currentIndex())
	{
		case 0: setMiastoPlusaParameters(); return;
		case 1: /*setPlusWWWParameters();*/ return;
		default: return;	
	}
}
 
void SmsGui::showLoginDialog()
{
	QDialog *loginDialog = new QDialog;
	loginWindow = new Ui_loginDialog;
	loginWindow->setupUi(loginDialog);
	connect(loginWindow->okButton, SIGNAL(clicked()), this, SLOT(clickedLoginOk()));
	connect(loginWindow->cancelButton, SIGNAL(clicked()), this, SLOT(clickedLoginCancel()));
	loginDialog->show();
}
 
void SmsGui::clickedLoginOk()
{
 
	kill();
}
 
void SmsGui::kill()
{
	loginDialog->close();
}
 
 
void SmsGui::clickedLoginCancel()
{
	loginDialog->close();
}
 
void SmsGui::setMiastoPlusaParameters()
{
	showLoginDialog();
}