my programm crach with this code

[yazan]

hi all,
can anybody tell me what is worng with this code:
i have taken the code from this thread http://www.qtcentre.org/threads/4042...IntervalSymbol

i'm trying to draw a curve where every point will be with errorbars. but wen i run the code the programm crash. 
messgraphFrame::messgraphFrame(QWidget *parent) :
    QFrame(parent),
    ui(new Ui::messgraphFrame)
{
    ui->setupUi(this);
    QVector<QwtIntervalSample> samples(3);
    samples.append( QwtIntervalSample( 10 ,QwtInterval( 8, 12 )) );
    samples.append( QwtIntervalSample( 2,QwtInterval( 3, 7 )) );
    samples.append( QwtIntervalSample( 18,QwtInterval( 17, 20 )) );
 
    QwtIntervalSymbol symbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );
 
    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( &symbol );
    curve1->setSamples( samples );
    curve1->attach(this->ui->qwtPlot);
//    curve1->setStyle( QwtPlotIntervalCurve::Tube );
    this->ui->qwtPlot->replot ();
 
}

i'm trying to draw a curve where every point will be with errorbars. but wen i run the code the programm crash. 
messgraphFrame::messgraphFrame(QWidget *parent) :
    QFrame(parent),
    ui(new Ui::messgraphFrame)
{
    ui->setupUi(this);
    QVector<QwtIntervalSample> samples(3);
    samples.append( QwtIntervalSample( 10 ,QwtInterval( 8, 12 )) );
    samples.append( QwtIntervalSample( 2,QwtInterval( 3, 7 )) );
    samples.append( QwtIntervalSample( 18,QwtInterval( 17, 20 )) );

    QwtIntervalSymbol symbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );

    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( &symbol );
    curve1->setSamples( samples );
    curve1->attach(this->ui->qwtPlot);
//    curve1->setStyle( QwtPlotIntervalCurve::Tube );
    this->ui->qwtPlot->replot ();

}

To copy to clipboard, switch view to plain text mode 

[Kangs]

QwtIntervalSymbol symbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );
 
    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( &symbol );

QwtIntervalSymbol symbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );

    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( &symbol );

To copy to clipboard, switch view to plain text mode 

Try to use a pointer for symbol

QwtIntervalSymbol* symbol = new QwtIntervalSymbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );
 
    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( symbol );

QwtIntervalSymbol* symbol = new QwtIntervalSymbol( QwtIntervalSymbol::Bar );
//    QwtPlot *myPlot = new QwtPlot( NULL );

    QwtPlotIntervalCurve *curve1 = new QwtPlotIntervalCurve("Curve 1");
    curve1->setSymbol( symbol );

To copy to clipboard, switch view to plain text mode 

[yazan]

thank you for your reply but it did not work.
i have found that the crash happens when i attach the curve to the plot.
but tel now i did not understand why.

[stampede]

Build debug version and run it with debugger, after the crash post the backtrace.

[Uwe]

Kangs hint is absolutely necessary - the symbol needs to be allocated by new. The rest of the code looks o.k.

When you have fixed your code and your application still crashes, use your debugger and show the call stack.

Uwe

[yazan]

thank you all it work