I have a program where I want to be able to switch between a logarithmic and linear scale. It works fine for the first couple of times, but then fails with a segmentation fault. Any pointers on what I might be doing wrong before submitting a bug report.

Here is a sample code to reproduce the bug
Qt Code: 
  1. #include "TestQwtPlot.h"
  2. #include "TestQwtPlot.moc"
  3.  
  4. #include <QtGui/QMenu>
  5. #include <QtGui/QMenuBar>
  6. #include <QtGui/QAction>
  7. #include <qwt/qwt_plot.h>
  8. #include <qwt/qwt_scale_engine.h>
  9. #include <qwt/qwt_data.h>
  10. #include <qwt/qwt_plot_curve.h>
  11.  
  12. TestQwtPlot::TestQwtPlot()
  13. {
  14.   plot = new QwtPlot(this);
  15.   linScale = new QwtLinearScaleEngine();
  16.   logScale = new QwtLog10ScaleEngine();
  17.   double x[5] = {1,2,3,4,5};
  18.   QwtArrayData qwtArray ( x, x, 5 );
  19.   QwtPlotCurve *curve1 = new QwtPlotCurve ( "Curve 1" );
  20.   curve1->setData ( qwtArray );
  21.   curve1->attach( plot );
  22.   plot->replot();
  23.   QAction* log = new QAction(this);
  24.   QAction* lin = new QAction(this);
  25.   log->setText( "Logarithmic scale" );
  26.   lin->setText( "Linear scale" );
  27.   setCentralWidget(plot);
  28.     QAction* a = new QAction(this);
  29.     a->setText( "Quit" );
  30.     connect(a, SIGNAL(triggered()), SLOT(close()) );
  31.     connect(lin, SIGNAL(triggered()), SLOT(on_lin_triggered()));
  32.     connect(log, SIGNAL(triggered()), SLOT(on_log_triggered()));
  33.     QMenu * m = menuBar()->addMenu( "File" );
  34.     m->addAction( a );
  35.     m->addAction( log );
  36.     m->addAction( lin );
  37. }
  38.  
  39. TestQwtPlot::~TestQwtPlot()
  40. {}
  41.  
  42. void TestQwtPlot::on_lin_triggered(){
  43.   plot->setAxisScaleEngine(QwtPlot::yLeft, linScale);
  44.   plot->setAxisScaleEngine(QwtPlot::xBottom, linScale);
  45.   plot->replot();
  46. }
  47.  
  48. void TestQwtPlot::on_log_triggered(){
  49.   plot->setAxisScaleEngine(QwtPlot::yLeft, logScale);
  50.   plot->setAxisScaleEngine(QwtPlot::xBottom, logScale);
  51.   plot->replot();
  52. }
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and the header

Qt Code: 
  1. #ifndef TestQwtPlot_H
  2. #define TestQwtPlot_H
  3.  
  4. #include <QtGui/QMainWindow>
  5. #include <qwt/qwt_plot.h>
  6. #include <qwt/qwt_scale_engine.h>
  7.  
  8. class TestQwtPlot : public QMainWindow
  9. {
  10. Q_OBJECT
  11. public:
  12.     TestQwtPlot();
  13.     virtual ~TestQwtPlot();
  14.   private:
  15.     QwtPlot *plot;
  18.   private slots:
  19.     void on_log_triggered();
  20.     void on_lin_triggered();
  21. };
  22.  
  23. #endif // TestQwtPlot_H
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and finally the backtrace

Qt Code: 
  1. #0  0x0000000000000021 in ?? ()
  2. #1  0x00007ffff6b943b2 in QwtPlot::setAxisScaleEngine(int, QwtScaleEngine*) () from /usr/lib64/libqwt.so.5
  3. #2  0x0000000000403838 in TestQwtPlot::on_lin_triggered (this=0x7fffffffd200) at /home/gudlaugu/projects/TestQwtPlot/TestQwtPlot.cpp:44
  4. #3  0x00000000004049d8 in TestQwtPlot::qt_metacall (this=0x7fffffffd200, _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0x7fffffffa9f0) at /home/gudlaugu/projects/TestQwtPlot/build/TestQwtPlot.moc:69
  5. #4  0x00007ffff7affee2 in QMetaObject::activate (sender=0x887370, from_signal_index=<value optimized out>, to_signal_index=6, argv=0x0) at kernel/qobject.cpp:3113
  6. #5  0x00007ffff6f86a37 in QAction::triggered (this=0x749d10, _t1=false) at .moc/release-shared/moc_qaction.cpp:236
  7. #6  0x00007ffff6f87eb0 in QAction::activate (this=0x887370, event=<value optimized out>) at kernel/qaction.cpp:1167
  8. #7  0x00007ffff7370ddd in QMenuPrivate::activateCausedStack (this=0x82ba90, causedStack=@0x7fffffffab10, action=0x887370, action_e=QAction::Trigger, self=true) at widgets/qmenu.cpp:967
  9. #8  0x00007ffff7376dde in QMenuPrivate::activateAction (this=0x82ba90, action=0x887370, action_e=QAction::Trigger, self=true) at widgets/qmenu.cpp:1060
  10. #9  0x00007ffff6fdda3d in QWidget::event (this=0x72f5a0, event=0x7fffffffb2d0) at kernel/qwidget.cpp:7554
  11. #10 0x00007ffff737962b in QMenu::event (this=0x72f5a0, e=0x7fffffffb2d0) at widgets/qmenu.cpp:2358
  12. #11 0x00007ffff6f8ca4d in QApplicationPrivate::notify_helper (this=0x6072e0, receiver=0x72f5a0, e=0x7fffffffb2d0) at kernel/qapplication.cpp:4065
  13. #12 0x00007ffff6f9543a in QApplication::notify (this=<value optimized out>, receiver=0x72f5a0, e=0x7fffffffb2d0) at kernel/qapplication.cpp:3767
  14. #13 0x00007ffff7aeb15c in QCoreApplication::notifyInternal (this=0x7fffffffd240, receiver=0x72f5a0, event=0x7fffffffb2d0) at kernel/qcoreapplication.cpp:610
  15. #14 0x00007ffff6f94688 in QApplicationPrivate::sendMouseEvent (receiver=0x72f5a0, event=0x7fffffffb2d0, alienWidget=0x0, nativeWidget=0x72f5a0, buttonDown=<value optimized out>, lastMouseReceiver=@0x7ffff799ff30)
  16.     at ../../src/corelib/kernel/qcoreapplication.h:216
  17. #15 0x00007ffff6ffe644 in QETWidget::translateMouseEvent (this=0x72f5a0, event=<value optimized out>) at kernel/qapplication_x11.cpp:4343
  18. #16 0x00007ffff6ffd4f5 in QApplication::x11ProcessEvent (this=0x7fffffffd240, event=0x7fffffffce50) at kernel/qapplication_x11.cpp:3550
  19. #17 0x00007ffff7024854 in x11EventSourceDispatch (s=0x610340, callback=0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
  20. #18 0x00007ffff57970fb in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
  21. #19 0x00007ffff579a8cd in ?? () from /usr/lib64/libglib-2.0.so.0
  22. #20 0x00007ffff579aa8b in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
  23. #21 0x00007ffff7b1456c in QEventDispatcherGlib::processEvents (this=0x60c430, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:407
  24. #22 0x00007ffff7023fdf in QGuiEventDispatcherGlib::processEvents (this=0x749d10, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
  25. #23 0x00007ffff7ae99e2 in QEventLoop::processEvents (this=<value optimized out>, flags={i = -11968}) at kernel/qeventloop.cpp:149
  26. #24 0x00007ffff7ae9db4 in QEventLoop::exec (this=0x7fffffffd180, flags={i = -11888}) at kernel/qeventloop.cpp:201
  27. #25 0x00007ffff7aec0a4 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
  28. #26 0x0000000000404cb7 in main (argc=1, argv=0x7fffffffd338) at /home/gudlaugu/projects/TestQwtPlot/main.cpp:10
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