Please Help-->Not able to draw curves in QwtPlot Widget !

[Krish]

Hello! Friends,
I am using Qwt plugin with Qt4.3.4 in WinXP to design a GUI. Now i have created a Widget in Qt, added QwtPlot Widget to it named sampleqwtPlot and coded the following files: -

########sampleplot.h##########

#ifndef SAMPLEPLOT_H
#define SAMPLEPLOT_H
 
#include<QtGui>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
 
#include "ui_sampleplot.h"
 
const int PLOT_SIZE = 101;     
 
class samplePlot : public QWidget, private Ui::sampleForm
{
    Q_OBJECT
 
public:
	samplePlot(QWidget* parent = 0);
 
private:
	// Arrays holding the values.
	double xval[PLOT_SIZE];
	double yval[PLOT_SIZE];
	// Insert new curve
	QwtPlotCurve *curve;
};
 
#endif

#ifndef SAMPLEPLOT_H
#define SAMPLEPLOT_H

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

#include "ui_sampleplot.h"

const int PLOT_SIZE = 101;     

class samplePlot : public QWidget, private Ui::sampleForm
{
    Q_OBJECT

public:
	samplePlot(QWidget* parent = 0);

private:
	// Arrays holding the values.
	double xval[PLOT_SIZE];
	double yval[PLOT_SIZE];
	// Insert new curve
	QwtPlotCurve *curve;
};

#endif

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########sampleplot.cpp########

#include <QtGui> 
#include "sampleplot.h"
 
samplePlot::samplePlot( QWidget *parent )
: QWidget( parent )
{
	setupUi(this); // this sets up GUI
	connect( startPushButton, SIGNAL( clicked() ), this, SLOT( draw_curve() ) ); 
 
	// Axis 
	sampleqwtPlot->setAxisTitle(QwtPlot::xBottom, "Time/seconds");
	sampleqwtPlot->setAxisScale(QwtPlot::xBottom, 0, 100);
 
	sampleqwtPlot->setAxisTitle(QwtPlot::yLeft, "Values");
	sampleqwtPlot->setAxisScale(QwtPlot::yLeft, 0, 50);
 
        // Set curve styles
	curve->setPen(QPen(Qt::red));
 
	//
	// Calculate values
	//
	for(int i=0;i<PLOT_SIZE;i++)
	{
		xval[i] = i;
		yval[i] = 0.5*i;
	}
	//
	//Assign values to the curve.
	//            
	curve->setData( xval, yval,  PLOT_SIZE );
	//        
	//Attach the curve.
	//
	curve->attach( sampleqwtPlot );
	//
	// finally, refresh the plot
	//
	sampleqwtPlot->replot();
}

#include <QtGui> 
#include "sampleplot.h"

samplePlot::samplePlot( QWidget *parent )
: QWidget( parent )
{
	setupUi(this); // this sets up GUI
	connect( startPushButton, SIGNAL( clicked() ), this, SLOT( draw_curve() ) ); 

	// Axis 
	sampleqwtPlot->setAxisTitle(QwtPlot::xBottom, "Time/seconds");
	sampleqwtPlot->setAxisScale(QwtPlot::xBottom, 0, 100);

	sampleqwtPlot->setAxisTitle(QwtPlot::yLeft, "Values");
	sampleqwtPlot->setAxisScale(QwtPlot::yLeft, 0, 50);

        // Set curve styles
	curve->setPen(QPen(Qt::red));

	//
	// Calculate values
	//
	for(int i=0;i<PLOT_SIZE;i++)
	{
		xval[i] = i;
		yval[i] = 0.5*i;
	}
	//
	//Assign values to the curve.
	//            
	curve->setData( xval, yval,  PLOT_SIZE );
	//        
	//Attach the curve.
	//
	curve->attach( sampleqwtPlot );
	//
	// finally, refresh the plot
	//
	sampleqwtPlot->replot();
}

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I am able to get the sampleplot.exe file but its not working, like whenever i try to run it, displays error "encountered a problem".

I think i am making a small silly mistake somewhere.

Can anyone please help me out.--> I will be obliged

[jacek]

Could you post the exact error message? Maybe your OS can't find Qwt DLLs?

[jpn]

You have

QwtPlotCurve *curve;

QwtPlotCurve *curve;

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and I see it being used but never allocated. In other words, it's a dangling pointer.

[Krish]

Hello! Jacek & Jpn,
Thanks for taking out time and helping me out. I had made a same mistake as said by Jpn. But now i did few things and its working!!

But now i added a pushbutton to clear the drawn plot but its not clearing the curves n all, i dont know why? Even though i have properly connected it to sampleqwtPlot->clear() slot, its not working. I mean replot() slot is working but clear() slot is not!!!!

Also i tried to connect the same button to Form->close() slot, and its working but samplePlot->clear() slot isn't????

Thanks again.

Best Regards.

[jacek]

Also i tried to connect the same button to Form->close() slot, and its working but samplePlot->clear() slot isn't????

How did you declare samplePlot::clear() and how do you establish the connection?

[Krish]

Hello! Jacek Sir,
Thanks for taking out time and replying but i have somehow solved the problem.

Thanks again

Best Regards