hello every one,
i want to write a program that when i click button ,it will plot graph from a txt file
i have write a code as belows but can plot and have error ,plz help me

this is a code:
Qt Code: 
  1. void Form::on_pushButton_clicked()
  2. {
  3.     QFile plot;
  4.     plot.setFileName(":/history.txt");
  5.     plot.open(QFile::ReadOnly|QFile::Text);
  6.  
  7.     //set plot propetis
  8.     ui->qwtPlot->setCanvasBackground(Qt::white);
  9.     ui->qwtPlot->setAxisScale(QwtPlot::xBottom,0,150);
  10.     ui->qwtPlot->setAxisScale(QwtPlot::yLeft,0,150); //max is 150
  11.  
  12.     if(!curve)
  13.         curve=new QwtPlotCurve();
  14.     curve->attach(ui->qwtPlot);
  15.     QColor colour=Qt::blue;
  16.     colour.setAlpha(150);
  17.     curve->setPen(colour);
  18.  
  19.     QTextStream file(&plot);
  20.  
  21.     while (!file.atEnd())
  22.     {
  23.         QString line=plot.readLine();
  24.         QStringList fields=line.split('  ');
  25.         if(fields.size()>1)
  26.         {
  27.             QString xdata = fields.takeFirst();
  28.             QString ydata = fields.takeFirst();
  29.             xData.append((double)xdata.toDouble());
  30.             yData.append((double)ydata.toDouble());
  31.         }
  32.     }
  33.  
  34.     //plot
  35.     curve->setSamples(&xData[0],&yData[0],xData.size()); 
  36.     ui->qwtPlot->replot();
  37. }
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