Dynamic graph, access read violation

Hello,

I'm trying to make a plot which updates dynamically like in cpuplot example of QWT.
Everything goes fine excepted that when I'm trying to set new datas with setRawSamples in Qt's timer I experiment read violation access. Here is my sample class :

Code:

#include "StdAfx.h"
 
QTimeStepView::QTimeStepView(QWidget *parent)
	: QwtPlot(parent)
	, count(0.0)
{
	{
		m_x.push_back(count);
		m_y.push_back(count);
 
		count +=1;
 
		m_x.push_back(count);
		m_y.push_back(count);
 
		count +=1;
 
		m_x.push_back(count);
		m_y.push_back(count);
 
		count +=1;
	}
	this->setAutoReplot(false);
 
	// Show a title
	setTitle( "This is an Example" );
 
	// Show the axes
	setAxisTitle( xBottom, "Time" );
	setAxisTitle( yLeft, "Timestep" );
 
	QwtPlotCurve *m_timestep = new QwtPlotCurve("timestep");
	m_timestep->attach(this);
	replot();
 
	m_timestep->setRawSamples(&m_x[0], &m_y[0], m_x.size());
	replot();
 
	{
		m_x.push_back(count);
		m_y.push_back(count);
 
		count +=1;
	}
	m_timestep->setRawSamples(&m_x[0], &m_y[0], m_x.size());
	replot();
 
	(void)startTimer(1000);
}
 
QTimeStepView::~QTimeStepView()
{
 
}
 
void QTimeStepView::timerEvent(QTimerEvent* event)
{
	m_x.push_back(count);
	m_y.push_back(count);
 
	count +=1;
 
	m_timestep->setRawSamples(&m_x[0], &m_y[0], m_x.size()); //Here happens the error
	replot();
}

Severals setRawSamples goes fine in constructor but if I try to make it in the timer it doesn't work.