is it a C++ error or Qt/Qwt related?

[jiveaxe]

Hi, I'm trying some Qwt programming. I have made a simple program to show my problem: in the following application there are two checkboxes controlling if the respective curves are displayed and a pushbutton to get new data for the curves (here I have simulated the data with rand(), but in my real application they are retrieved from a database). The checkboxes are connected to drawCurves() which attach/detach curves to plot. Now if I click on the button the curves are displayed properly but if i toggle the checkboxes to show/hide a curve all curves gone.

#include <QtGui>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <cstdlib>
#include <ctime>
 
class Dialog: public QDialog
{
	Q_OBJECT
 
	public:
		Dialog(QWidget *parent = 0);
 
	public slots:
		void getData();
		void drawCurves();
 
	private:
		QwtPlot *plot;
		QwtPlotCurve redCurve;
		QwtPlotCurve greenCurve;
		QCheckBox *redCurveCheckBox;
		QCheckBox *greenCurveCheckBox;
};
 
Dialog::Dialog(QWidget *parent)
	: QDialog(parent)
{
	srand(time(0));
 
	redCurveCheckBox = new QCheckBox("Red Curve");
	redCurveCheckBox->setChecked(true);
	greenCurveCheckBox = new QCheckBox("Green Curve");
	QPushButton *drawButton = new QPushButton("Draw");
 
	plot = new QwtPlot;
 
	redCurve.setPen(QPen(QColor(Qt::red),2));
	redCurve.setStyle(QwtPlotCurve::Lines);
	redCurve.setRenderHint(QwtPlotItem::RenderAntialiased);
 
	greenCurve.setPen(QPen(QColor(Qt::green),2));
	greenCurve.setStyle(QwtPlotCurve::Lines);
	greenCurve.setRenderHint(QwtPlotItem::RenderAntialiased);
 
	getData();
 
	QVBoxLayout *rightLayout = new QVBoxLayout;
	rightLayout->addWidget(redCurveCheckBox);
	rightLayout->addWidget(greenCurveCheckBox);
	rightLayout->addWidget(drawButton);
	rightLayout->addStretch();
 
	QHBoxLayout *mainLayout = new QHBoxLayout;
	mainLayout->addWidget(plot);
	mainLayout->addLayout(rightLayout);
 
	setLayout(mainLayout);
	resize(640,480);
 
	connect(redCurveCheckBox, SIGNAL(clicked()), this, SLOT(drawCurves()));
	connect(greenCurveCheckBox, SIGNAL(clicked()), this, SLOT(drawCurves()));
	connect(drawButton, SIGNAL(clicked()), this, SLOT(getData()));
}
 
void Dialog::getData()
{
	int size = 1+rand()%10 + 10;
 
	double redCurveData[size];
	double greenCurveData[size];
	double xval[size];
 
	for(int i = 0; i < size; i++)
	{
		redCurveData[i] = 0+rand()%10;
		greenCurveData[i] = 0+rand()%10;
		xval[i] = i + 1;
	}
 
	redCurve.setRawData(xval,redCurveData,size);
	greenCurve.setRawData(xval,greenCurveData,size);
 
	plot->setAxisScale(QwtPlot::xBottom, 1, size);
	plot->setAxisScale(QwtPlot::yLeft, 0, 10);
 
	drawCurves();
}
 
void Dialog::drawCurves()
{
	if(redCurveCheckBox->isChecked())
		redCurve.attach(plot);
	else
		redCurve.detach();
 
	if(greenCurveCheckBox->isChecked())
		greenCurve.attach(plot);
	else
		greenCurve.detach();
 
	plot->replot();
}
 
int main(int argc, char *argv[])
{
	QApplication app(argc, argv);
	Dialog *dialog = new Dialog;
	dialog->show();
	return app.exec();
}
 
#include "main.moc"

#include <QtGui>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <cstdlib>
#include <ctime>

class Dialog: public QDialog
{
	Q_OBJECT

	public:
		Dialog(QWidget *parent = 0);

	public slots:
		void getData();
		void drawCurves();

	private:
		QwtPlot *plot;
		QwtPlotCurve redCurve;
		QwtPlotCurve greenCurve;
		QCheckBox *redCurveCheckBox;
		QCheckBox *greenCurveCheckBox;
};

Dialog::Dialog(QWidget *parent)
	: QDialog(parent)
{
	srand(time(0));

	redCurveCheckBox = new QCheckBox("Red Curve");
	redCurveCheckBox->setChecked(true);
	greenCurveCheckBox = new QCheckBox("Green Curve");
	QPushButton *drawButton = new QPushButton("Draw");

	plot = new QwtPlot;

	redCurve.setPen(QPen(QColor(Qt::red),2));
	redCurve.setStyle(QwtPlotCurve::Lines);
	redCurve.setRenderHint(QwtPlotItem::RenderAntialiased);

	greenCurve.setPen(QPen(QColor(Qt::green),2));
	greenCurve.setStyle(QwtPlotCurve::Lines);
	greenCurve.setRenderHint(QwtPlotItem::RenderAntialiased);

	getData();

	QVBoxLayout *rightLayout = new QVBoxLayout;
	rightLayout->addWidget(redCurveCheckBox);
	rightLayout->addWidget(greenCurveCheckBox);
	rightLayout->addWidget(drawButton);
	rightLayout->addStretch();

	QHBoxLayout *mainLayout = new QHBoxLayout;
	mainLayout->addWidget(plot);
	mainLayout->addLayout(rightLayout);

	setLayout(mainLayout);
	resize(640,480);

	connect(redCurveCheckBox, SIGNAL(clicked()), this, SLOT(drawCurves()));
	connect(greenCurveCheckBox, SIGNAL(clicked()), this, SLOT(drawCurves()));
	connect(drawButton, SIGNAL(clicked()), this, SLOT(getData()));
}

void Dialog::getData()
{
	int size = 1+rand()%10 + 10;

	double redCurveData[size];
	double greenCurveData[size];
	double xval[size];

	for(int i = 0; i < size; i++)
	{
		redCurveData[i] = 0+rand()%10;
		greenCurveData[i] = 0+rand()%10;
		xval[i] = i + 1;
	}

	redCurve.setRawData(xval,redCurveData,size);
	greenCurve.setRawData(xval,greenCurveData,size);

	plot->setAxisScale(QwtPlot::xBottom, 1, size);
	plot->setAxisScale(QwtPlot::yLeft, 0, 10);

	drawCurves();
}

void Dialog::drawCurves()
{
	if(redCurveCheckBox->isChecked())
		redCurve.attach(plot);
	else
		redCurve.detach();

	if(greenCurveCheckBox->isChecked())
		greenCurve.attach(plot);
	else
		greenCurve.detach();

	plot->replot();
}

int main(int argc, char *argv[])
{
	QApplication app(argc, argv);
	Dialog *dialog = new Dialog;
	dialog->show();
	return app.exec();
}

#include "main.moc"

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Seems that the data associated to each curve is lost when un/checking: if I output the curves data during drawCurves() with this piece of code:

for(int i = 0; i < 9; i++)
	std::cout << redCurve.y(i) << " ";
std::cout << std::endl;

for(int i = 0; i < 9; i++)
	std::cout << redCurve.y(i) << " ";
std::cout << std::endl;

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after pushing the button I have, for example, 7 5 3 0 7 2 6 6 1, while un/checking one of the checkbox i have, for example

[HTML]3.30667e-317 -8.91495e+303 3.90058e-314 2.36344e-310 4.94066e-324 4.94066e-324 4.94066e-324 4.94066e-324 0[/HTML]

Maybe is a c++ error but I don't know where.

Regards

[jacek]

Qwt docs say:

setRawData is provided for efficiency. It is important to keep the pointers during the lifetime of the underlying QwtCPointerData class.

but you pass pointers to local variables to every call to setRawData().

[jiveaxe]

Sorry if I ask, but how should I modify the code?

Thanks

[mcostalba]

Allocate data on the heap.

Put somewhere in your private section:

QVector<double*> samplesPtr;
	int samplesSize;

QVector<double*> samplesPtr;
	int samplesSize;

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Then modify as follows

void Dialog::getData()
{
 
    samplesSize = 1+rand()%10 + 10;
 
    double* redCurveDataPtr = new double[samplesSize];
    double* greenCurveData = new double[samplesSize];
    double* xval = new double[samplesSize];
 
    samplesPtr << redCurveDataPtr << greenCurveData << xval;
 
   .......
 
}

void Dialog::getData()
{

    samplesSize = 1+rand()%10 + 10;

    double* redCurveDataPtr = new double[samplesSize];
    double* greenCurveData = new double[samplesSize];
    double* xval = new double[samplesSize];

    samplesPtr << redCurveDataPtr << greenCurveData << xval;

   .......

}

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Of course you need to add a Dialog::freeData() to release the memory when no more needed. That's the reason you may want to set samplesPtr and samplesSize as class memeber data.

[mcostalba]

Interestin enough delete[] works also from copied pointers, it means that you don't need

int samplesSize;

as member data but a local variable will suffice and freeData() became:

void Dialog::freeData()
{
     for(int i = 0; i < samplesPtr.size(); i++)
            delete[] samplesPtr.at(i);
}

void Dialog::freeData()
{
     for(int i = 0; i < samplesPtr.size(); i++)
            delete[] samplesPtr.at(i);
}

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[jiveaxe]

Thank you, mcostalba, your code works good.

Regards

[jiveaxe]

One more question: the freeData() function must be called in the destructor only or before each getData()?

Thanks

[mcostalba]

After

redCurve.setRawData(xval,redCurveData,size);
greenCurve.setRawData(xval,greenCurveData,size);

redCurve.setRawData(xval,redCurveData,size);
greenCurve.setRawData(xval,greenCurveData,size);

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you don't need the previous samples anymore (it seems) so you can call freeData() after that, of course delaying assign of new pointers until after the free of old data:

void Dialog::getData()
{
    int size = 1+rand()%10 + 10;
 
    double* redCurveDataPtr = new double[size];
    double* greenCurveData = new double[size];
    double* xval = new double[size];
 
    for(int i = 0; i < size; i++)
    {
        redCurveData[i] = 0+rand()%10;
        greenCurveData[i] = 0+rand()%10;
        xval[i] = i + 1;
    }
 
    redCurve.setRawData(xval,redCurveData,size);
    greenCurve.setRawData(xval,greenCurveData,size);
 
    // old data is no more needed now
    freeData();
 
    // now we can add newly created samples pointers
    samplesPtr << redCurveDataPtr << greenCurveData << xval;
 
    plot->setAxisScale(QwtPlot::xBottom, 1, size);
    plot->setAxisScale(QwtPlot::yLeft, 0, 10);
 
    drawCurves();
}

void Dialog::getData()
{
    int size = 1+rand()%10 + 10;

    double* redCurveDataPtr = new double[size];
    double* greenCurveData = new double[size];
    double* xval = new double[size];

    for(int i = 0; i < size; i++)
    {
        redCurveData[i] = 0+rand()%10;
        greenCurveData[i] = 0+rand()%10;
        xval[i] = i + 1;
    }

    redCurve.setRawData(xval,redCurveData,size);
    greenCurve.setRawData(xval,greenCurveData,size);

    // old data is no more needed now
    freeData();

    // now we can add newly created samples pointers
    samplesPtr << redCurveDataPtr << greenCurveData << xval;

    plot->setAxisScale(QwtPlot::xBottom, 1, size);
    plot->setAxisScale(QwtPlot::yLeft, 0, 10);

    drawCurves();
}

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[mcostalba]

A couple of bugs

Because pointer vector is reused freeData() should be:

void Dialog::freeData()
{
   for(int i = 0; i < samplesPtr.size(); i++)
        delete[] samplesPtr.at(i);
 
   samplesPtr.clear(); 
}

void Dialog::freeData()
{
   for(int i = 0; i < samplesPtr.size(); i++)
        delete[] samplesPtr.at(i);

   samplesPtr.clear(); 
}

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And also remember to add a freeData() call in the d'tor to be sure the last samples data set is properly released when closing the dialog.

[jiveaxe]

Inserting freeData() where you say gives me strange graphs. Removing it works again right.

Regards