Qwt 6.0.1 / Qt 4.4.1 / VC++ 9.0 / Win XP

I have written a graphics module for the SigLib library (Digital Signal Library from Numerix-DSP) and have encountered a problem with the zooming function. I get a memory access violation in my routine handling the return to the zoom base:
Unhandled exception at 0x1007463a (qwtd.dll) in SigLibGraph.exe: 0xC0000005: Access violation reading location 0xcdcdcded.
Following the fragment of code where the access violation occured:
uint QwtPlotZoomer::zoomRectIndex() const
{
return d_data->zoomRectIndex;
}

d_data seems to have been not initialized, where should I do it?

Qt Code: 
  1. // main.cpp
  2. // AW - 14.03.2012
  3.  
  4. #include <QApplication>				// Qt library
  5. #include <qwt_plot.h>				// Qwt Plot library
  6. #include <qwt_plot_curve.h>
  7. #include <qwt_math.h>
  8. #include <siglib.h>					// SigLib DSP library 
  9. #include "SigLibGraph.h"			// Qt/Qwt SigLib Graphics library
  10.  
  11. int main( int argc, char * argv[] )
  12. {
  13. 	QApplication app( argc,argv );
  14.  
  15. 	const unsigned int FFT_LENGTH = 512;
  16. 	double *pXData = new double[FFT_LENGTH];
  17. 	double *pResult = new double[FFT_LENGTH];
  18. 	double *pResult2 = new double[FFT_LENGTH];
  19.  
  20.  
  21. 	// fill data arrays
  22. 	for ( unsigned int idx = 0; idx < FFT_LENGTH; idx++ ) {
  23. 		pXData[idx] = double( idx );
  24. 		pResult[idx] = sin( M_PI * 0.02 * double( idx ));
  25. 		pResult2[idx] = cos( M_PI * 0.02 * double( idx ));
  26. 	}
  27.  
  28. 	// plot object
  29. 	Plot2D *myPlot = new Plot2D( "function plot", "time", "amplitude" );
  30. 	myPlot->attachCurve( pXData, pResult, FFT_LENGTH, "sine" );
  31. 	myPlot->attachCurve( pXData, pResult2, FFT_LENGTH, "cosine", Qt::cyan );
  32. 	myPlot->show();
  33.  
  34. 	return app.exec();
  35. }
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Qt Code: 
  1. /***************************************************************	
  2. 	SigLibGraph.h
  3.  AW - 31.03.2012
  4. ***************************************************************/
  5.  
  6. #ifndef SIGLIBGRAPH_H
  7. #define SIGLIBGRAPH_H
  8.  
  9. #include <siglib.h>					// SigLib DSP library 
  10. #include <qwt_plot.h>				// Qwt library
  11. #include <qwt_plot_grid.h>
  12. #include <qwt_legend.h>
  13. #include <qwt_plot_zoomer.h>
  14.  
  15.  
  16. class Plot2D: public QwtPlot
  17. {
  18. 	Q_OBJECT
  19.  
  20. public:	
  21. 	Plot2D( QString plotTitle = "",
  22. 				QString xLabel = "x-axis",
  23. 				QString yLabel = "y-axis",
  24. 				QWidget *parent = NULL ); 
  25.  
  26. 	void attachCurve( double *xData,
  27. 							double *yData,
  28. 							uint dataCount, 
  29. 							QString curveLabel = "",
  30. 							QColor curveColor = Qt::yellow );
  31.  
  32. 	void setXAxisScale( double firstValue, double lastValue );
  33. 	void setYAxisScale( double firstValue, double lastValue );
  34. 	void setXLogAxis();
  35. 	void setYLogAxis();
  36. 	void setBackgroundColor( QColor backgroundColor );
  37.  
  38. public Q_SLOTS:
  39.     void autoRescale( QRectF );
  40.  
  41. protected:
  42.     virtual void resizeEvent( QResizeEvent * );
  43.  
  44. private:
  45. 	QwtPlotGrid *grid;
  46. 	QwtLegend *legend;
  47. 	QwtPlotZoomer *zoomer;
  48. };
  49.  
  50. #endif	// SIGLIBGRAPH_H
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Qt Code: 
  1. /************************************************************
  2. 	SigLibGraph.cpp
  3. 	AW - 31.03.2012
  4. ************************************************************/
  5.  
  6. #include <QApplication>
  7. #include <QtDebug>
  8. #include <qpainter.h>
  9. #include <qwt_plot.h>
  10. #include <qwt_scale_engine.h>
  11. #include <qwt_symbol.h>
  12. #include <qwt_plot_grid.h>
  13. #include <qwt_plot_curve.h>
  14. #include <qwt_legend.h>
  15. #include <qwt_text.h>
  16. #include <qwt_picker.h>
  17. #include <qwt_picker_machine.h>
  18. #include <qwt_plot_zoomer.h>
  19. #include <qwt_plot_renderer.h>
  20. #include <qwt_event_pattern.h>
  21. #include <qwt_text.h>
  22. #include "SigLibGraph.h"
  23.  
  24.  
  25. Plot2D::Plot2D( QString plotTitle,
  26. 					QString xLabel,
  27. 					QString yLabel,
  28. 					QWidget *parent ): 
  29. 					QwtPlot( parent )
  30. {
  31. 	// plot object
  32. 	setTitle( plotTitle );
  33. 	setCanvasBackground( QColor( Qt::darkBlue ));
  34.  
  35. 	// axis
  36. 	setAxisTitle( QwtPlot::xBottom, xLabel );
  37. 	setAxisTitle( QwtPlot::yLeft, yLabel );
  38.  
  39. 	// grid 
  40. 	QwtPlotGrid* grid = new QwtPlotGrid;
  41. 	grid->enableXMin( true );
  42. 	grid->setMajPen( QPen( Qt::white, 0, Qt::DotLine ));
  43. 	grid->setMinPen( QPen( Qt::gray, 0 , Qt::DotLine ));
  44. 	grid->attach( this );
  45.  
  46. 	// legend
  47. 	QwtLegend* legend = new QwtLegend;
  48. 	insertLegend( legend, QwtPlot::RightLegend );
  49.  
  50. 	//zoomer
  51. 	QwtPlotZoomer* zoomer = new QwtPlotZoomer( QwtPlot::xBottom, 
  52. 															QwtPlot::yLeft, 
  53. 															this->canvas() );
  54. 	zoomer->setRubberBand( QwtPicker::RectRubberBand );
  55. 	zoomer->setRubberBandPen( QColor( Qt::green ));
  56. 	zoomer->setTrackerMode( QwtPicker::ActiveOnly );
  57. 	zoomer->setTrackerPen( QColor( Qt::white ));
  58. 	// RightButton: zoom out by one step
  59. 	zoomer->setMousePattern( QwtEventPattern::MouseSelect3,
  60. 										Qt::RightButton );
  61. 	// Ctrl+RightButton: zoom out to full size
  62. 	zoomer->setMousePattern( QwtEventPattern::MouseSelect2,
  63. 										Qt::RightButton, 
  64. 										Qt::ControlModifier );
  65. 	// handle zoom base
  66. 	connect( zoomer, 
  67. 				SIGNAL( zoomed( QRectF )), 
  68. 				SLOT( autoRescale( QRectF )));
  69.  
  70. 	// resize Widget
  71. 	resize( 600, 400 );
  72.  
  73. 	show();
  74. }
  75.  
  76. void Plot2D::autoRescale( QRectF )
  77. {
  78. 	qDebug("Plot2D::autoRescale called!");
  79. 	if( zoomer->zoomRectIndex() == 0 )				// autorescale only if you are at base... 
  80. 	{	
  81. 		this->setAxisAutoScale( QwtPlot::xBottom );
  82. 		this->setAxisAutoScale( QwtPlot::yLeft );
  83. 		this->updateAxes();
  84. 		zoomer->setZoomBase( false );
  85. 	}
  86. }
  87.  
  88. void Plot2D::attachCurve( 	double *xData,
  89. 									double *yData,
  90. 									uint dataCount, 
  91. 									QString curveLabel,
  92. 									QColor curveColor )
  93. {
  94. 	// define the curve object
  95. 	QwtPlotCurve* curve = new QwtPlotCurve;
  96. 	curve->setSamples( xData, yData, dataCount );
  97. 	curve->setPen( QPen( curveColor ));
  98. 	curve->setRenderHint( QwtPlotItem::RenderAntialiased );
  99. 	curve->setTitle( curveLabel );
  100. 	// qDebug() << "curveLabel.isEmpty = " << curveLabel.isEmpty();
  101. 	if ( curveLabel.isEmpty() )
  102. 		curve->setItemAttribute( QwtPlotItem::Legend, false );
  103. 	else 
  104. 		curve->setLegendAttribute( QwtPlotCurve::LegendShowLine );	
  105. 	curve->attach( this );
  106. }
  107.  
  108. void Plot2D::setXAxisScale( double firstValue, double lastValue )
  109. {
  110. 	setAxisScale( xBottom, firstValue, lastValue );
  111. }
  112.  
  113. void Plot2D::setYAxisScale( double firstValue, double lastValue )
  114. {
  115. 	setAxisScale( yLeft, firstValue, lastValue );
  116. }
  117.  
  118. void Plot2D::setXLogAxis()
  119. {
  120. 	setAxisScaleEngine( QwtPlot::xBottom, new QwtLog10ScaleEngine );
  121. }
  122.  
  123. void Plot2D::setYLogAxis()
  124. {
  125. 	setAxisScaleEngine( QwtPlot::yLeft, new QwtLog10ScaleEngine );
  126. }
  127.  
  128. void Plot2D::setBackgroundColor( QColor backgroundColor )
  129. {
  130. 	setCanvasBackground( backgroundColor );
  131. }
  132.  
  133. void Plot2D::resizeEvent( QResizeEvent *event )
  134. {
  135.     QwtPlot::resizeEvent( event );
  136. }
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