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"Undebuggable" segmentation fault

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  • M Mark81

    @mrjj said in "Undebuggable" segmentation fault:

    i assume
    this->_line->setText("test");
    with no dialog also crashes ?

    Instead this works!
    BUT:

    this also works:

    connect(_btn, &QToolButton::clicked, [this]()
            {
                QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
            });
    

    while this crashes:

    connect(_btn, &QToolButton::clicked, [this]()
            {
                QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
                this->_line->setText("test");
            });
    
    kshegunovK Offline
    kshegunovK Offline
    kshegunov
    Moderators
    wrote on last edited by kshegunov
    #13

    Does this:

    connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
        QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
        _line->setText("test");
    });
    

    crash?

    From the behaviour described it does seem you have a dangling pointer/reference. Also don't do that:

    SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
    

    without at least having a debug-time check on it:

    Q_ASSERT(qobject_cast<SignatureEditor *>(editor));
    SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
    

    Read and abide by the Qt Code of Conduct

    M 1 Reply Last reply
    1
    • kshegunovK kshegunov

      Does this:

      connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
          QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
          _line->setText("test");
      });
      

      crash?

      From the behaviour described it does seem you have a dangling pointer/reference. Also don't do that:

      SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
      

      without at least having a debug-time check on it:

      Q_ASSERT(qobject_cast<SignatureEditor *>(editor));
      SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
      
      M Offline
      M Offline
      Mark81
      wrote on last edited by
      #14

      @kshegunov said in "Undebuggable" segmentation fault:

      Does this:

      connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
          QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
          _line->setText("test");
      });
      

      crash?

      Yes, it crashes.

      From the behaviour described it does seem you have dangling pointer/reference. Also don't do that:
      without at least having a debug time check on it:

      We've already checked the pointers and are not null.

      kshegunovK 1 Reply Last reply
      0
      • M Mark81

        @kshegunov said in "Undebuggable" segmentation fault:

        Does this:

        connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
            QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
            _line->setText("test");
        });
        

        crash?

        Yes, it crashes.

        From the behaviour described it does seem you have dangling pointer/reference. Also don't do that:
        without at least having a debug time check on it:

        We've already checked the pointers and are not null.

        kshegunovK Offline
        kshegunovK Offline
        kshegunov
        Moderators
        wrote on last edited by kshegunov
        #15

        @Mark81 said in "Undebuggable" segmentation fault:

        Yes, it crashes.

        Please break before the QLineEdit::setText and extract the backtrace for the thread.

        We've already checked the pointers and are not null.

        static_cast does not check if the types involved behind the pointer are compatible or convertible, so whether the pointer's null or not is meaningless if the typing is wrong.

        Read and abide by the Qt Code of Conduct

        1 Reply Last reply
        2
        • mrjjM Offline
          mrjjM Offline
          mrjj
          Lifetime Qt Champion
          wrote on last edited by mrjj
          #16

          Hi
          Shit i read
          SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
          as qobject_cast
          so good catch, its most likely that.

          M 1 Reply Last reply
          0
          • mrjjM mrjj

            Hi
            Shit i read
            SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
            as qobject_cast
            so good catch, its most likely that.

            M Offline
            M Offline
            Mark81
            wrote on last edited by
            #17

            @mrjj said in "Undebuggable" segmentation fault:

            as qobject_cast
            so good catch, its most likely that.

            I changed all static_cast to qobject_cast with no differences.

            @kshegunov
            here we are:

            0_1548257528392_Clipboard 1.jpg

            kshegunovK 1 Reply Last reply
            0
            • M Mark81

              @mrjj said in "Undebuggable" segmentation fault:

              as qobject_cast
              so good catch, its most likely that.

              I changed all static_cast to qobject_cast with no differences.

              @kshegunov
              here we are:

              0_1548257528392_Clipboard 1.jpg

              kshegunovK Offline
              kshegunovK Offline
              kshegunov
              Moderators
              wrote on last edited by kshegunov
              #18

              @Mark81 said in "Undebuggable" segmentation fault:

              here we are:

              Two problems with the screenshot:

              1. I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
              2. You didn't specify a context object for the lambda, which I requested in my previous post.

              Read and abide by the Qt Code of Conduct

              M 1 Reply Last reply
              2
              • kshegunovK kshegunov

                @Mark81 said in "Undebuggable" segmentation fault:

                here we are:

                Two problems with the screenshot:

                1. I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
                2. You didn't specify a context object for the lambda, which I requested in my previous post.
                M Offline
                M Offline
                Mark81
                wrote on last edited by
                #19

                @kshegunov said in "Undebuggable" segmentation fault:

                Two problems with the screenshot:

                1. I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
                2. You didn't specify a context object for the lambda, which I requested in my previous post.

                Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why? Here the update screenshot and text:

                0_1548257990470_Clipboard 1.jpg

                Full backtrace attached as it's too big for the post. Here just the same info extracted as text:

                1  SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}::operator()() const                                                                                                              customdelegateoperators.h      37   0x492bb0   
                2  QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}>::call({lambda()#1}&, void * *)                        qobjectdefs_impl.h             128  0x48739a   
                3  QtPrivate::Functor<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0>::call<QtPrivate::List<>, void>({lambda()#1}&, void *, {lambda()#1}& *)                                    qobjectdefs_impl.h             238  0x48bf44   
                4  QtPrivate::QFunctorSlotObject<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *) qobjectdefs_impl.h             421  0x48ba8d   
                5  QtPrivate::QSlotObjectBase::call                                                                                                                                                           qobjectdefs_impl.h             376  0x281c173  
                6  QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3754 0x281c173  
                7  QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3633 0x281c575  
                8  QAbstractButton::clicked                                                                                                                                                                   moc_qabstractbutton.cpp        308  0x1b48b7ac 
                9  QAbstractButtonPrivate::emitClicked                                                                                                                                                        qabstractbutton.cpp            414  0x1b48b9d5 
                10 QAbstractButtonPrivate::click                                                                                                                                                              qabstractbutton.cpp            407  0x1b48d17a 
                11 QAbstractButton::mouseReleaseEvent                                                                                                                                                         qabstractbutton.cpp            1011 0x1b48d3aa 
                12 QToolButton::mouseReleaseEvent                                                                                                                                                             qtoolbutton.cpp                622  0x1b576fd1 
                13 QWidget::event                                                                                                                                                                             qwidget.cpp                    8901 0x1b3db0e0 
                14 QAbstractButton::event                                                                                                                                                                     qabstractbutton.cpp            968  0x1b48e7bc 
                15 QToolButton::event                                                                                                                                                                         qtoolbutton.cpp                985  0x1b57711e 
                16 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                17 QApplication::notify                                                                                                                                                                       qapplication.cpp               3203 0x1b3a0107 
                18 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                19 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x1b39f077 
                20 QApplicationPrivate::sendMouseEvent                                                                                                                                                        qapplication.cpp               2693 0x1b39f077 
                21 QWidgetWindow::handleMouseEvent                                                                                                                                                            qwidgetwindow.cpp              660  0x1b3f1af4 
                22 QWidgetWindow::event                                                                                                                                                                       qwidgetwindow.cpp              281  0x1b3f3bf9 
                23 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                24 QApplication::notify                                                                                                                                                                       qapplication.cpp               3099 0x1b39fb83 
                25 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                26 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x99cabfc  
                27 QGuiApplicationPrivate::processMouseEvent                                                                                                                                                  qguiapplication.cpp            2081 0x99cabfc  
                28 QGuiApplicationPrivate::processWindowSystemEvent                                                                                                                                           qguiapplication.cpp            1816 0x99cc4d7  
                29 QWindowSystemInterface::sendWindowSystemEvents                                                                                                                                             qwindowsysteminterface.cpp     1032 0x99adf99  
                30 QWindowsGuiEventDispatcher::sendPostedEvents                                                                                                                                               qwindowsguieventdispatcher.cpp 82   0x2883dae4 
                31 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16                                                                                                                           qeventdispatcher_win.cpp       237  0x284538d  
                32 gapfnScSendMessage                                                                                                                                                                                                             0x769f62fa 
                33 ??                                                                                                                                                                                                                             0x62047e   
                34 USER32!GetThreadDesktop                                                                                                                                                                                                        0x769f6d3a 
                35 QEventDispatcherWin32Private::sendTimerEvent                                                                                                                                               qeventdispatcher_win.cpp       456  0x2844dc9  
                36 ??                                                                                                                                                                                                                             0x62047e   
                37 USER32!CharPrevW                                                                                                                                                                                                               0x769f77c4 
                38 USER32!DispatchMessageW                                                                                                                                                                                                        0x769f788a 
                39 QEventDispatcherWin32::processEvents                                                                                                                                                       qeventdispatcher_win.cpp       629  0x2844ae8  
                40 QWindowsGuiEventDispatcher::processEvents                                                                                                                                                  qwindowsguieventdispatcher.cpp 74   0x2883dab7 
                41 QEventLoop::processEvents                                                                                                                                                                  qeventloop.cpp                 136  0x27f37c8  
                42 QEventLoop::exec                                                                                                                                                                           qeventloop.cpp                 214  0x27f3c20  
                43 QDialog::exec                                                                                                                                                                              qdialog.cpp                    546  0x1b5907de 
                44 MainWindow::on_actionImpostazioni_triggered                                                                                                                                                mainwindow.cpp                 1518 0x40e152   
                45 MainWindow::qt_static_metacall                                                                                                                                                             moc_mainwindow.cpp             298  0x43f973   
                46 MainWindow::qt_metacall                                                                                                                                                                    moc_mainwindow.cpp             368  0x43fcc2   
                47 QMetaObject::metacall                                                                                                                                                                      qmetaobject.cpp                301  0x27fe365  
                48 QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3786 0x281c37f  
                49 QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3633 0x281c575  
                50 QAction::triggered                                                                                                                                                                         moc_qaction.cpp                376  0x1b391618 
                51 QAction::activate                                                                                                                                                                          qaction.cpp                    1167 0x1b394579 
                52 QMenuPrivate::activateCausedStack                                                                                                                                                          qmenu.cpp                      1371 0x1b50d432 
                53 QMenuPrivate::activateAction                                                                                                                                                               qmenu.cpp                      1448 0x1b51507e 
                54 QMenu::mouseReleaseEvent                                                                                                                                                                   qmenu.cpp                      2942 0x1b515c07 
                55 QWidget::event                                                                                                                                                                             qwidget.cpp                    8901 0x1b3db0e0 
                56 QMenu::event                                                                                                                                                                               qmenu.cpp                      3064 0x1b5180de 
                57 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                58 QApplication::notify                                                                                                                                                                       qapplication.cpp               3203 0x1b3a0107 
                59 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                60 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x1b39f077 
                61 QApplicationPrivate::sendMouseEvent                                                                                                                                                        qapplication.cpp               2693 0x1b39f077 
                62 QWidgetWindow::handleMouseEvent                                                                                                                                                            qwidgetwindow.cpp              556  0x1b3f0ed3 
                63 QWidgetWindow::event                                                                                                                                                                       qwidgetwindow.cpp              281  0x1b3f3bf9 
                64 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                65 QApplication::notify                                                                                                                                                                       qapplication.cpp               3099 0x1b39fb83 
                66 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                67 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x99cabfc  
                68 QGuiApplicationPrivate::processMouseEvent                                                                                                                                                  qguiapplication.cpp            2081 0x99cabfc  
                69 QGuiApplicationPrivate::processWindowSystemEvent                                                                                                                                           qguiapplication.cpp            1816 0x99cc4d7  
                70 QWindowSystemInterface::sendWindowSystemEvents                                                                                                                                             qwindowsysteminterface.cpp     1032 0x99adf99  
                71 QWindowsGuiEventDispatcher::sendPostedEvents                                                                                                                                               qwindowsguieventdispatcher.cpp 82   0x2883dae4 
                72 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16                                                                                                                           qeventdispatcher_win.cpp       237  0x284538d  
                73 gapfnScSendMessage                                                                                                                                                                                                             0x769f62fa 
                74 ??                                                                                                                                                                                                                             0x62047e   
                75 USER32!GetThreadDesktop                                                                                                                                                                                                        0x769f6d3a 
                76 QEventDispatcherWin32Private::sendTimerEvent                                                                                                                                               qeventdispatcher_win.cpp       456  0x2844dc9  
                77 ??                                                                                                                                                                                                                             0x62047e   
                78 USER32!CharPrevW                                                                                                                                                                                                               0x769f77c4 
                79 USER32!DispatchMessageW                                                                                                                                                                                                        0x769f788a 
                80 QEventDispatcherWin32::processEvents                                                                                                                                                       qeventdispatcher_win.cpp       629  0x2844ae8  
                81 QWindowsGuiEventDispatcher::processEvents                                                                                                                                                  qwindowsguieventdispatcher.cpp 74   0x2883dab7 
                82 QEventLoop::processEvents                                                                                                                                                                  qeventloop.cpp                 136  0x27f37c8  
                83 QEventLoop::exec                                                                                                                                                                           qeventloop.cpp                 214  0x27f3c20  
                84 QCoreApplication::exec                                                                                                                                                                     qcoreapplication.cpp           1336 0x27fc30e  
                85 QGuiApplication::exec                                                                                                                                                                      qguiapplication.cpp            1761 0x99c1552  
                86 QApplication::exec                                                                                                                                                                         qapplication.cpp               2901 0x1b3984a9 
                87 qMain                                                                                                                                                                                      main.cpp                       37   0x401859   
                88 WinMain *16                                                                                                                                                                                qtmain_win.cpp                 104  0x447465   
                89 main                                                                                                                                                                                                                           0x49883d   [0_1548258146048_backtrace.txt](Uploading 100%) 
                
                kshegunovK 1 Reply Last reply
                0
                • mrjjM Offline
                  mrjjM Offline
                  mrjj
                  Lifetime Qt Champion
                  wrote on last edited by
                  #20

                  Hi
                  Just to be 100% sure.
                  You still have the checks at your casts, right ?

                  SignatureEditor *widget = qobject_cast<SignatureEditor *>(editor); // Note qobject_cast !
                  if (widget) {
                    widget->setText(value);
                    widget->activate();
                  } else
                    qDebug() << "invalid cast for editor";
                  
                  1 Reply Last reply
                  1
                  • M Mark81

                    @kshegunov said in "Undebuggable" segmentation fault:

                    Two problems with the screenshot:

                    1. I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
                    2. You didn't specify a context object for the lambda, which I requested in my previous post.

                    Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why? Here the update screenshot and text:

                    0_1548257990470_Clipboard 1.jpg

                    Full backtrace attached as it's too big for the post. Here just the same info extracted as text:

                    1  SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}::operator()() const                                                                                                              customdelegateoperators.h      37   0x492bb0   
                    2  QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}>::call({lambda()#1}&, void * *)                        qobjectdefs_impl.h             128  0x48739a   
                    3  QtPrivate::Functor<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0>::call<QtPrivate::List<>, void>({lambda()#1}&, void *, {lambda()#1}& *)                                    qobjectdefs_impl.h             238  0x48bf44   
                    4  QtPrivate::QFunctorSlotObject<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *) qobjectdefs_impl.h             421  0x48ba8d   
                    5  QtPrivate::QSlotObjectBase::call                                                                                                                                                           qobjectdefs_impl.h             376  0x281c173  
                    6  QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3754 0x281c173  
                    7  QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3633 0x281c575  
                    8  QAbstractButton::clicked                                                                                                                                                                   moc_qabstractbutton.cpp        308  0x1b48b7ac 
                    9  QAbstractButtonPrivate::emitClicked                                                                                                                                                        qabstractbutton.cpp            414  0x1b48b9d5 
                    10 QAbstractButtonPrivate::click                                                                                                                                                              qabstractbutton.cpp            407  0x1b48d17a 
                    11 QAbstractButton::mouseReleaseEvent                                                                                                                                                         qabstractbutton.cpp            1011 0x1b48d3aa 
                    12 QToolButton::mouseReleaseEvent                                                                                                                                                             qtoolbutton.cpp                622  0x1b576fd1 
                    13 QWidget::event                                                                                                                                                                             qwidget.cpp                    8901 0x1b3db0e0 
                    14 QAbstractButton::event                                                                                                                                                                     qabstractbutton.cpp            968  0x1b48e7bc 
                    15 QToolButton::event                                                                                                                                                                         qtoolbutton.cpp                985  0x1b57711e 
                    16 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                    17 QApplication::notify                                                                                                                                                                       qapplication.cpp               3203 0x1b3a0107 
                    18 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                    19 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x1b39f077 
                    20 QApplicationPrivate::sendMouseEvent                                                                                                                                                        qapplication.cpp               2693 0x1b39f077 
                    21 QWidgetWindow::handleMouseEvent                                                                                                                                                            qwidgetwindow.cpp              660  0x1b3f1af4 
                    22 QWidgetWindow::event                                                                                                                                                                       qwidgetwindow.cpp              281  0x1b3f3bf9 
                    23 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                    24 QApplication::notify                                                                                                                                                                       qapplication.cpp               3099 0x1b39fb83 
                    25 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                    26 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x99cabfc  
                    27 QGuiApplicationPrivate::processMouseEvent                                                                                                                                                  qguiapplication.cpp            2081 0x99cabfc  
                    28 QGuiApplicationPrivate::processWindowSystemEvent                                                                                                                                           qguiapplication.cpp            1816 0x99cc4d7  
                    29 QWindowSystemInterface::sendWindowSystemEvents                                                                                                                                             qwindowsysteminterface.cpp     1032 0x99adf99  
                    30 QWindowsGuiEventDispatcher::sendPostedEvents                                                                                                                                               qwindowsguieventdispatcher.cpp 82   0x2883dae4 
                    31 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16                                                                                                                           qeventdispatcher_win.cpp       237  0x284538d  
                    32 gapfnScSendMessage                                                                                                                                                                                                             0x769f62fa 
                    33 ??                                                                                                                                                                                                                             0x62047e   
                    34 USER32!GetThreadDesktop                                                                                                                                                                                                        0x769f6d3a 
                    35 QEventDispatcherWin32Private::sendTimerEvent                                                                                                                                               qeventdispatcher_win.cpp       456  0x2844dc9  
                    36 ??                                                                                                                                                                                                                             0x62047e   
                    37 USER32!CharPrevW                                                                                                                                                                                                               0x769f77c4 
                    38 USER32!DispatchMessageW                                                                                                                                                                                                        0x769f788a 
                    39 QEventDispatcherWin32::processEvents                                                                                                                                                       qeventdispatcher_win.cpp       629  0x2844ae8  
                    40 QWindowsGuiEventDispatcher::processEvents                                                                                                                                                  qwindowsguieventdispatcher.cpp 74   0x2883dab7 
                    41 QEventLoop::processEvents                                                                                                                                                                  qeventloop.cpp                 136  0x27f37c8  
                    42 QEventLoop::exec                                                                                                                                                                           qeventloop.cpp                 214  0x27f3c20  
                    43 QDialog::exec                                                                                                                                                                              qdialog.cpp                    546  0x1b5907de 
                    44 MainWindow::on_actionImpostazioni_triggered                                                                                                                                                mainwindow.cpp                 1518 0x40e152   
                    45 MainWindow::qt_static_metacall                                                                                                                                                             moc_mainwindow.cpp             298  0x43f973   
                    46 MainWindow::qt_metacall                                                                                                                                                                    moc_mainwindow.cpp             368  0x43fcc2   
                    47 QMetaObject::metacall                                                                                                                                                                      qmetaobject.cpp                301  0x27fe365  
                    48 QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3786 0x281c37f  
                    49 QMetaObject::activate                                                                                                                                                                      qobject.cpp                    3633 0x281c575  
                    50 QAction::triggered                                                                                                                                                                         moc_qaction.cpp                376  0x1b391618 
                    51 QAction::activate                                                                                                                                                                          qaction.cpp                    1167 0x1b394579 
                    52 QMenuPrivate::activateCausedStack                                                                                                                                                          qmenu.cpp                      1371 0x1b50d432 
                    53 QMenuPrivate::activateAction                                                                                                                                                               qmenu.cpp                      1448 0x1b51507e 
                    54 QMenu::mouseReleaseEvent                                                                                                                                                                   qmenu.cpp                      2942 0x1b515c07 
                    55 QWidget::event                                                                                                                                                                             qwidget.cpp                    8901 0x1b3db0e0 
                    56 QMenu::event                                                                                                                                                                               qmenu.cpp                      3064 0x1b5180de 
                    57 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                    58 QApplication::notify                                                                                                                                                                       qapplication.cpp               3203 0x1b3a0107 
                    59 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                    60 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x1b39f077 
                    61 QApplicationPrivate::sendMouseEvent                                                                                                                                                        qapplication.cpp               2693 0x1b39f077 
                    62 QWidgetWindow::handleMouseEvent                                                                                                                                                            qwidgetwindow.cpp              556  0x1b3f0ed3 
                    63 QWidgetWindow::event                                                                                                                                                                       qwidgetwindow.cpp              281  0x1b3f3bf9 
                    64 QApplicationPrivate::notify_helper                                                                                                                                                         qapplication.cpp               3727 0x1b3985ca 
                    65 QApplication::notify                                                                                                                                                                       qapplication.cpp               3099 0x1b39fb83 
                    66 QCoreApplication::notifyInternal2                                                                                                                                                          qcoreapplication.cpp           1048 0x27f5119  
                    67 QCoreApplication::sendSpontaneousEvent                                                                                                                                                     qcoreapplication.h             237  0x99cabfc  
                    68 QGuiApplicationPrivate::processMouseEvent                                                                                                                                                  qguiapplication.cpp            2081 0x99cabfc  
                    69 QGuiApplicationPrivate::processWindowSystemEvent                                                                                                                                           qguiapplication.cpp            1816 0x99cc4d7  
                    70 QWindowSystemInterface::sendWindowSystemEvents                                                                                                                                             qwindowsysteminterface.cpp     1032 0x99adf99  
                    71 QWindowsGuiEventDispatcher::sendPostedEvents                                                                                                                                               qwindowsguieventdispatcher.cpp 82   0x2883dae4 
                    72 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16                                                                                                                           qeventdispatcher_win.cpp       237  0x284538d  
                    73 gapfnScSendMessage                                                                                                                                                                                                             0x769f62fa 
                    74 ??                                                                                                                                                                                                                             0x62047e   
                    75 USER32!GetThreadDesktop                                                                                                                                                                                                        0x769f6d3a 
                    76 QEventDispatcherWin32Private::sendTimerEvent                                                                                                                                               qeventdispatcher_win.cpp       456  0x2844dc9  
                    77 ??                                                                                                                                                                                                                             0x62047e   
                    78 USER32!CharPrevW                                                                                                                                                                                                               0x769f77c4 
                    79 USER32!DispatchMessageW                                                                                                                                                                                                        0x769f788a 
                    80 QEventDispatcherWin32::processEvents                                                                                                                                                       qeventdispatcher_win.cpp       629  0x2844ae8  
                    81 QWindowsGuiEventDispatcher::processEvents                                                                                                                                                  qwindowsguieventdispatcher.cpp 74   0x2883dab7 
                    82 QEventLoop::processEvents                                                                                                                                                                  qeventloop.cpp                 136  0x27f37c8  
                    83 QEventLoop::exec                                                                                                                                                                           qeventloop.cpp                 214  0x27f3c20  
                    84 QCoreApplication::exec                                                                                                                                                                     qcoreapplication.cpp           1336 0x27fc30e  
                    85 QGuiApplication::exec                                                                                                                                                                      qguiapplication.cpp            1761 0x99c1552  
                    86 QApplication::exec                                                                                                                                                                         qapplication.cpp               2901 0x1b3984a9 
                    87 qMain                                                                                                                                                                                      main.cpp                       37   0x401859   
                    88 WinMain *16                                                                                                                                                                                qtmain_win.cpp                 104  0x447465   
                    89 main                                                                                                                                                                                                                           0x49883d   [0_1548258146048_backtrace.txt](Uploading 100%) 
                    
                    kshegunovK Offline
                    kshegunovK Offline
                    kshegunov
                    Moderators
                    wrote on last edited by kshegunov
                    #21

                    @Mark81 said in "Undebuggable" segmentation fault:

                    Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why?

                    No need for the formality. This overload of the connect makes sure that this exists at the point of the lambda call, the other doesn't that's why I wanted it specifically. The connection will be broken if this gets destroyed between the connect call and the actual lambda call, which isn't true for the overload without the context object.

                    Full backtrace attached as it's too big for the post. Here just the same info extracted as text:

                    This is perfectly fine, I was interested exactly in this one, the other threads are not interesting at this point. The trace looks okay.

                    Humor me once again, and substitute the:

                    QDialog myDialog;
                    // ...
                    myDialog.exec()
                    

                    you have in your MainWindow::on_actionImpostazioni_triggered slot with:

                    QDialog * myDialog = new QDialog();
                    // ...
                    myDialog->show();
                    

                    See if that makes a difference.

                    Also, could you print out the addresses of the variables involved in the lambda (you can see them in the "Application output pane" when you run the app), something like this:

                    connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
                        QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
                        qDebug() << this << _btn << _line;
                        _line->setText("test");
                    });
                    

                    (You'd need to include <QDebug> for this)

                    One more thing you could try is to add one guarded pointer to the _line pointer so you're 100% it's not destroyed in the mean time. It'd look like this:

                    QPointer<QLineEdit> testPointer(_line);
                    connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void  {
                        QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
                        qDebug() << this << _btn << _line << testPointer;
                        _line->setText("test");
                    });
                    

                    Read and abide by the Qt Code of Conduct

                    M 1 Reply Last reply
                    1
                    • kshegunovK kshegunov

                      @Mark81 said in "Undebuggable" segmentation fault:

                      Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why?

                      No need for the formality. This overload of the connect makes sure that this exists at the point of the lambda call, the other doesn't that's why I wanted it specifically. The connection will be broken if this gets destroyed between the connect call and the actual lambda call, which isn't true for the overload without the context object.

                      Full backtrace attached as it's too big for the post. Here just the same info extracted as text:

                      This is perfectly fine, I was interested exactly in this one, the other threads are not interesting at this point. The trace looks okay.

                      Humor me once again, and substitute the:

                      QDialog myDialog;
                      // ...
                      myDialog.exec()
                      

                      you have in your MainWindow::on_actionImpostazioni_triggered slot with:

                      QDialog * myDialog = new QDialog();
                      // ...
                      myDialog->show();
                      

                      See if that makes a difference.

                      Also, could you print out the addresses of the variables involved in the lambda (you can see them in the "Application output pane" when you run the app), something like this:

                      connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
                          QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
                          qDebug() << this << _btn << _line;
                          _line->setText("test");
                      });
                      

                      (You'd need to include <QDebug> for this)

                      One more thing you could try is to add one guarded pointer to the _line pointer so you're 100% it's not destroyed in the mean time. It'd look like this:

                      QPointer<QLineEdit> testPointer(_line);
                      connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void  {
                          QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)"));
                          qDebug() << this << _btn << _line << testPointer;
                          _line->setText("test");
                      });
                      
                      M Offline
                      M Offline
                      Mark81
                      wrote on last edited by
                      #22

                      @kshegunov thanks for the detailed answer and for your effort.
                      The debugger says "no valid expression" for everything inside the lambda function, is it normal?

                      Let's summarize:

                      qDebug() << this << _btn << _line; leads to a SIGSEGV

                      qDebug() << this << _btn << _line << testPointer; leads to SIGILL

                      qDebug() << _btn << _line; leads also to a SIGSEGV

                      but removing the file dialog call:

                             QPointer<QLineEdit> testPointer(_line);
                             connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void  {
                                 qDebug() << this << _btn << _line << testPointer;
                                 _line->setText("test");
                             });
                      

                      prints out:

                      SignatureEditor(0x2f09b430) QToolButton(0x2e1910b0) QLineEdit(0x2e2e13e0) QLineEdit(0x2e2e13e0)

                      kshegunovK 1 Reply Last reply
                      0
                      • M Mark81

                        @kshegunov thanks for the detailed answer and for your effort.
                        The debugger says "no valid expression" for everything inside the lambda function, is it normal?

                        Let's summarize:

                        qDebug() << this << _btn << _line; leads to a SIGSEGV

                        qDebug() << this << _btn << _line << testPointer; leads to SIGILL

                        qDebug() << _btn << _line; leads also to a SIGSEGV

                        but removing the file dialog call:

                               QPointer<QLineEdit> testPointer(_line);
                               connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void  {
                                   qDebug() << this << _btn << _line << testPointer;
                                   _line->setText("test");
                               });
                        

                        prints out:

                        SignatureEditor(0x2f09b430) QToolButton(0x2e1910b0) QLineEdit(0x2e2e13e0) QLineEdit(0x2e2e13e0)

                        kshegunovK Offline
                        kshegunovK Offline
                        kshegunov
                        Moderators
                        wrote on last edited by kshegunov
                        #23

                        @Mark81 said in "Undebuggable" segmentation fault:

                        The debugger says "no valid expression" for everything inside the lambda function, is it normal?

                        Not really. What compiler, debugger are you using and what are their versions? Just the other day I had stumbled on a bug in one specific version of MSVC's code generation where it didn't properly copy objects that are passed by value in the lambda capture.

                        but removing the file dialog call:
                        [snip]
                        prints out:

                        The addresses are good. So for some reason the file dialog invalidates the object(s). This can happen in principle, depending on event order, because the static function spins the event loop. Can you try something else then (same idea):

                        connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
                            // Here use the non-static way of opening the dialog
                            QFileDialog * myDialog = new QFileDialog();
                            QObject::connect(myDialog, &QDialog::accepted, this, [this] () -> void  {
                                qDebug() << "If we see this message it's all good, otherwise `this` is deleted through `QDialog::exec`";
                            });
                            myDialog->show();
                            //_line->setText("test");
                        });
                        

                        Edit: Updated code, because I forgot to add the context parameter for connect

                        Read and abide by the Qt Code of Conduct

                        M 1 Reply Last reply
                        1
                        • kshegunovK kshegunov

                          @Mark81 said in "Undebuggable" segmentation fault:

                          The debugger says "no valid expression" for everything inside the lambda function, is it normal?

                          Not really. What compiler, debugger are you using and what are their versions? Just the other day I had stumbled on a bug in one specific version of MSVC's code generation where it didn't properly copy objects that are passed by value in the lambda capture.

                          but removing the file dialog call:
                          [snip]
                          prints out:

                          The addresses are good. So for some reason the file dialog invalidates the object(s). This can happen in principle, depending on event order, because the static function spins the event loop. Can you try something else then (same idea):

                          connect(_btn, &QToolButton::clicked, this, [this] () -> void  {
                              // Here use the non-static way of opening the dialog
                              QFileDialog * myDialog = new QFileDialog();
                              QObject::connect(myDialog, &QDialog::accepted, this, [this] () -> void  {
                                  qDebug() << "If we see this message it's all good, otherwise `this` is deleted through `QDialog::exec`";
                              });
                              myDialog->show();
                              //_line->setText("test");
                          });
                          

                          Edit: Updated code, because I forgot to add the context parameter for connect

                          M Offline
                          M Offline
                          Mark81
                          wrote on last edited by
                          #24

                          @kshegunov said in "Undebuggable" segmentation fault:

                          Not really. What compiler, debugger are you using and what are their versions?

                          MinGW 5.3.0 32bit
                          GNU gdb 7.10.1 for MinGW 5.3.0 32bit
                          Qt5.11.1
                          Windows 7 PRO 64bit

                          The addresses are good. So for some reason the file dialog invalidates the object(s). This can happen in principle, depending on event order, because the static function spins the event loop. Can you try something else then (same idea):

                          No message, sadly...

                          kshegunovK 1 Reply Last reply
                          0
                          • M Offline
                            M Offline
                            Mark81
                            wrote on last edited by
                            #25
                            This post is deleted!
                            1 Reply Last reply
                            0
                            • M Mark81

                              @kshegunov said in "Undebuggable" segmentation fault:

                              Not really. What compiler, debugger are you using and what are their versions?

                              MinGW 5.3.0 32bit
                              GNU gdb 7.10.1 for MinGW 5.3.0 32bit
                              Qt5.11.1
                              Windows 7 PRO 64bit

                              The addresses are good. So for some reason the file dialog invalidates the object(s). This can happen in principle, depending on event order, because the static function spins the event loop. Can you try something else then (same idea):

                              No message, sadly...

                              kshegunovK Offline
                              kshegunovK Offline
                              kshegunov
                              Moderators
                              wrote on last edited by
                              #26

                              @Mark81 said in "Undebuggable" segmentation fault:

                              No message, sadly...

                              Well, you need to find out where and why your widget is destroyed before the dialog is closed. Probably the loosing of the focus causes your delegate to delete the editor, and since the dialog takes the focus ...

                              Read and abide by the Qt Code of Conduct

                              M 1 Reply Last reply
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                              • kshegunovK kshegunov

                                @Mark81 said in "Undebuggable" segmentation fault:

                                No message, sadly...

                                Well, you need to find out where and why your widget is destroyed before the dialog is closed. Probably the loosing of the focus causes your delegate to delete the editor, and since the dialog takes the focus ...

                                M Offline
                                M Offline
                                Mark81
                                wrote on last edited by
                                #27

                                @kshegunov ok, but nobody has ever used a QFileDialog in a delegate?
                                I just need to let the user to select a file when enters a cell... is there a simpler way?

                                kshegunovK 1 Reply Last reply
                                0
                                • M Mark81

                                  @kshegunov ok, but nobody has ever used a QFileDialog in a delegate?
                                  I just need to let the user to select a file when enters a cell... is there a simpler way?

                                  kshegunovK Offline
                                  kshegunovK Offline
                                  kshegunov
                                  Moderators
                                  wrote on last edited by kshegunov
                                  #28

                                  UIs are fiddly, as you can tell. My advice, override: QAbstractItemDelegate::destroyEditor and add breakpoints there and in the lambda. If you get to the destroyEditor first, then for sure that's the problem. Then you can add a flag to your editor whether you are showing additional UI (i.e. the dialog), when you click the button you can raise it, and then ignore the destroyEditor call if the dialog is shown. This would also require you to connect the closing of the dialog to lower the flag, but I think it should work.

                                  Read and abide by the Qt Code of Conduct

                                  M 1 Reply Last reply
                                  3
                                  • kshegunovK kshegunov

                                    UIs are fiddly, as you can tell. My advice, override: QAbstractItemDelegate::destroyEditor and add breakpoints there and in the lambda. If you get to the destroyEditor first, then for sure that's the problem. Then you can add a flag to your editor whether you are showing additional UI (i.e. the dialog), when you click the button you can raise it, and then ignore the destroyEditor call if the dialog is shown. This would also require you to connect the closing of the dialog to lower the flag, but I think it should work.

                                    M Offline
                                    M Offline
                                    Mark81
                                    wrote on last edited by
                                    #29

                                    @kshegunov Thanks for the advice, but it's too much effort for such a simple thing. I'm going to put a QPushButton "Browse" outside the table, so the user select a row and then press the button. It's not so nice but it would have saved me a whole day... and your time too :-)

                                    1 Reply Last reply
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