Qt and serial communication - unidentified crash

I've written an application which sends a value (later this will be the value from QTextEdit) to an Arduino by clicking a button. I'm able to build it, but when I run the application, it crashes...

I can't seem to find the problem...

Thanks in advance!

main.cpp

#include "serialcommunication.h"
#include <QtGui>
#include <qextserialport.h>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	SerialCommunication w;
	w.show();
	return a.exec();
}

serialcommunication.h

#ifndef SERIALCOMMUNICATION_H
#define SERIALCOMMUNICATION_H

#include <QtGui>
#include "ui_serialcommunication.h"
#include <qextserialport.h>

class SerialCommunication : public QWidget
{
	Q_OBJECT

public:
	SerialCommunication();
	~SerialCommunication();
	QextSerialPort *port;
	void init_port();
	void transmitCmd(int value);

private slots:
	void clickclick();

private:
	Ui::SerialCommunicationClass ui;

	QTextEdit *textedit;
	QPushButton *pushbutton;
};

#endif // SERIALCOMMUNICATION_H

serialcommunication.cpp

<pre lang="c++">#include "serialcommunication.h"

SerialCommunication::SerialCommunication():QWidget()
{
	ui.setupUi(this);

	textedit = new QTextEdit;
	pushbutton = new QPushButton("PUSHBUTTON");

	init_port();

	connect(pushbutton, SIGNAL(clicked()), this, SLOT(clickclick()));

	QVBoxLayout *layout = new QVBoxLayout;
	layout->addWidget(textedit);
	layout->addWidget(pushbutton);

	setLayout(layout);
}

SerialCommunication::~SerialCommunication()
{
	
}

void SerialCommunication::clickclick()
{
	transmitCmd(123);	
}

void SerialCommunication::init_port()
{
    port = new QextSerialPort("COM4"); //we create the port

	port->open(QIODevice::ReadWrite | QIODevice::Unbuffered); //we open the port

    if(!port->isOpen())
    {
        QMessageBox::warning(this, "port error", "Impossible to open the port!");
    }
	else if(port->isOpen());

    //we set the port properties
    port->setBaudRate(BAUD9600);
    port->setFlowControl(FLOW_OFF);
    port->setParity(PAR_NONE);
    port->setDataBits(DATA_8);
    port->setStopBits(STOP_1);
}

void SerialCommunication::transmitCmd(int value)
{
  if(value < 0 || value >255)return; //if the value is not between 0 and 255
                                     //no transmission

  char *buf; //creation of a buffer
  *buf = value;

  //for messages longer than 1 character :
  /*
  char *buf[255]; //buffer size = 255char;
  sprintf(buf,"%c",value);
  */

  port->write(buf); //send the buffer
}

screenshot error
http://dl.dropbox.com/u/12844842/error.JPG[^]

Tags: C++, Arduino, QT, Serial port