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Adding a virtual function causes strange result...

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  • SPlattenS SPlatten

    @jsulm :

                                                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                      
    1  QListData::size() const                                                                                                                                qlist.h                                                                                                             115  0x10000799f    
    2  QList<std::pair<QString, QString>>::length() const                                                                                                     qlist.h                                                                                                             360  0x100043265    
    3  clsXMLnode::strGetAttribute(QString)                                                                                                                   clsMainWnd.cpp                                                                                                      4281 0x100028276    
    4  clsQtLayout::addButton(QAbstractButton *, QString const&)                                                                                              clsQtLayout.cpp                                                                                                     149  0x10008ad47    
    5  clsXMLnode::setWidget(QWidget *)                                                                                                                       clsMainWnd.cpp                                                                                                      3860 0x10002b026    
    6  clsQtRadioButton::clsQtRadioButton(clsXMLnode *, QString *, QWidget *)                                                                                 clsQtRadionButton.cpp                                                                                               40   0x1000a6a8f    
    7  clsQtRadioButton::clsQtRadioButton(clsXMLnode *, QString *, QWidget *)                                                                                 clsQtRadionButton.cpp                                                                                               38   0x1000a993d    
    8  clsCNT::pCreate(clsXMLnode *, QString const&, QString&, QStringList&, QWidget *)                                                                       clsCNT.cpp                                                                                                          141  0x100005f59    
    9  clsXMLnode::clsXMLnode(QStringList&, clsXMLnode *)                                                                                                     clsMainWnd.cpp                                                                                                      766  0x1000232c9    
    10 clsXMLnode::clsXMLnode(QStringList&, clsXMLnode *)                                                                                                     clsMainWnd.cpp                                                                                                      545  0x10002ed35    
    11 clsScriptHelper::addNodesToGUI(clsXMLnode *, QLayout *, QJsonArray&, int *, int *)                                                                     clsScriptHelper.cpp                                                                                                 317  0x1000bf08b    
    12 clsScriptHelper::addNodesToGUI(clsXMLnode *, QLayout *, QJsonArray&, int *, int *)                                                                     clsScriptHelper.cpp                                                                                                 419  0x1000bfed7    
    13 clsScriptHelper::addNodesToGUI(clsXMLnode *, QLayout *, QJsonArray&, int *, int *)                                                                     clsScriptHelper.cpp                                                                                                 419  0x1000bfed7    
    14 clsScriptHelper::addGUIelement(QJsonObject const&)                                                                                                     clsScriptHelper.cpp                                                                                                 232  0x1000bd8c2    
    15 clsScriptHelper::qt_static_metacall(QObject *, QMetaObject::Call, int, void * *)                                                                       moc_clsScriptHelper.cpp                                                                                             216  0x1000dae2a    
    16 clsScriptHelper::qt_metacall(QMetaObject::Call, int, void * *)                                                                                         moc_clsScriptHelper.cpp                                                                                             303  0x1000db8dc    
    17 CallMethod(QQmlObjectOrGadget const&, int, int, int, int *, QV4::ExecutionEngine *, QV4::CallData *, QMetaObject::Call)                                qv4qobjectwrapper.cpp                                                                                               1301 0x1012bf559    
    18 CallPrecise(QQmlObjectOrGadget const&, QQmlPropertyData const&, QV4::ExecutionEngine *, QV4::CallData *, QMetaObject::Call)                            qv4qobjectwrapper.cpp                                                                                               1569 0x1012bb753    
    19 QV4::QObjectMethod::callInternal(QV4::Value const *, QV4::Value const *, int) const                                                                    qv4qobjectwrapper.cpp                                                                                               2131 0x1012bafda    
    20 QV4::FunctionObject::call(QV4::Value const *, QV4::Value const *, int) const                                                                           qv4functionobject_p.h                                                                                               202  0x1012e97bc    
    21 QV4::Runtime::CallProperty::call(QV4::ExecutionEngine *, QV4::Value const&, int, QV4::Value *, int)                                                    qv4runtime.cpp                                                                                                      1448 0x1012e9799    
    22 QV4::Moth::VME::interpret(QV4::CppStackFrame *, QV4::ExecutionEngine *, const char *)                                                                  qv4vme_moth.cpp                                                                                                     727  0x1012d56b0    
    23 QV4::Moth::VME::exec(QV4::CppStackFrame *, QV4::ExecutionEngine *)                                                                                     qv4vme_moth.cpp                                                                                                     463  0x1012d4542    
    24 QV4::ArrowFunction::virtualCall(QV4::FunctionObject const *, QV4::Value const *, QV4::Value const *, int)                                              qv4functionobject.cpp                                                                                               528  0x10127d8cf    
    25 QV4::FunctionObject::call(QV4::Value const *, QV4::Value const *, int) const                                                                           qv4functionobject_p.h                                                                                               202  0x1012e9578    
    26 QV4::Runtime::CallName::call(QV4::ExecutionEngine *, int, QV4::Value *, int)                                                                           qv4runtime.cpp                                                                                                      1406 0x1012e9562    
    27 QV4::Moth::VME::interpret(QV4::CppStackFrame *, QV4::ExecutionEngine *, const char *)                                                                  qv4vme_moth.cpp                                                                                                     766  0x1012d5c13    
    28 QV4::Moth::VME::exec(QV4::CppStackFrame *, QV4::ExecutionEngine *)                                                                                     qv4vme_moth.cpp                                                                                                     463  0x1012d4542    
    29 QV4::Function::call(QV4::Value const *, QV4::Value const *, int, QV4::ExecutionContext const *)                                                        qv4function.cpp                                                                                                     69   0x10127a985    
    30 QV4::Script::run(QV4::Value const *)                                                                                                                   qv4script.cpp                                                                                                       162  0x1012af6ca    
    31 QJSEngine::evaluate(QString const&, QString const&, int)                                                                                               qjsengine.cpp                                                                                                       545  0x101237d86    
    32 clsJSON::blnDecodeAccordingToType(QJsonObject const&, QTcpSocket *)                                                                                    clsJSON.cpp                                                                                                         377  0x10001859d    
    33 clsModule::manageReceivedData(QTcpSocket *)                                                                                                            clsModule.cpp                                                                                                       230  0x100069269    
    34 clsServer::onReadyRead()                                                                                                                               clsListener.cpp                                                                                                     84   0x10001b1e1    
    35 QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, void (clsServer:: *)()>::call(void (clsServer:: *)(), clsServer *, void * *) qobjectdefs_impl.h                                                                                                  152  0x10001d1ab    
    36 void QtPrivate::FunctionPointer<void (clsServer:: *)()>::call<QtPrivate::List<>, void>(void (clsServer:: *)(), clsServer *, void * *)                  qobjectdefs_impl.h                                                                                                  185  0x10001d11d    
    37 QtPrivate::QSlotObject<void (clsServer:: *)(), QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *)          qobjectdefs_impl.h                                                                                                  418  0x10001d072    
    38 QObject::event(QEvent *)                                                                                                                               qobject.cpp                                                                                                         1314 0x10278bb9f    
    39 QApplicationPrivate::notify_helper(QObject *, QEvent *)                                                                                                qapplication.cpp                                                                                                    3632 0x100b8c9ea    
    40 QApplication::notify(QObject *, QEvent *)                                                                                                              qapplication.cpp                                                                                                         0x100b8de11    
    41 QCoreApplication::notifyInternal2(QObject *, QEvent *)                                                                                                 qcoreapplication.cpp                                                                                                1063 0x102760a34    
    42 QCoreApplication::sendEvent(QObject *, QEvent *)                                                                                                       qcoreapplication.cpp                                                                                                1458 0x102761d79    
    43 QCoreApplicationPrivate::sendPostedEvents(QObject *, int, QThreadData *)                                                                               qcoreapplication.cpp                                                                                                1817 0x102761d64    
    44 QCocoaEventDispatcherPrivate::processPostedEvents()                                                                                                    qcocoaeventdispatcher.mm                                                                                            904  0x102232259    
    45 QCocoaEventDispatcherPrivate::postedEventsSourceCallback(void *)                                                                                       qcocoaeventdispatcher.mm                                                                                            927  0x1022329c8    
    46 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__                                                                                             (x86_64h) /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation                                  0x7ff8188138fd 
    47 __CFRunLoopDoSource0                                                                                                                                   (x86_64h) /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation                                  0x7ff818813865 
    48 __CFRunLoopDoSources0                                                                                                                                  (x86_64h) /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation                                  0x7ff8188135e4 
    49 __CFRunLoopRun                                                                                                                                         (x86_64h) /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation                                  0x7ff81881201b 
    50 CFRunLoopRunSpecific                                                                                                                                   (x86_64h) /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation                                  0x7ff8188115dd 
    51 RunCurrentEventLoopInMode                                                                                                                              (x86_64) /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox      0x7ff8214444f1 
    52 ReceiveNextEventCommon                                                                                                                                 (x86_64) /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox      0x7ff821444247 
    53 _BlockUntilNextEventMatchingListInModeWithFilter                                                                                                       (x86_64) /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox      0x7ff821443fe5 
    54 _DPSNextEvent                                                                                                                                          (x86_64) /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit                                                   0x7ff81b240b4c 
    55 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]                                                                        (x86_64) /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit                                                   0x7ff81b23f1b8 
    56 -[NSApplication run]                                                                                                                                   (x86_64) /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit                                                   0x7ff81b2315a9 
    57 QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)                                                                            qcocoaeventdispatcher.mm                                                                                            437  0x10223162f    
    58 QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)                                                                                       qeventloop.cpp                                                                                                      139  0x10275cacf    
    59 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)                                                                                                qeventloop.cpp                                                                                                      232  0x10275caab    
    60 QCoreApplication::exec()                                                                                                                               qcoreapplication.cpp                                                                                                1371 0x102761042    
    61 main                                                                                                                                                   XMLMPAM.cpp                                                                                                         120  0x1000d3cf4    
    62 start                                                                                                                                                  (x86_64) /usr/lib/dyld                                                                                                   0x1002e94fe    
    
    jsulmJ Online
    jsulmJ Online
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #9

    @SPlatten said in Adding a virtual function causes strange result...:

    clsXMLnode::strGetAttribute(QString)

    You should check what is happening there

    https://forum.qt.io/topic/113070/qt-code-of-conduct

    SPlattenS 1 Reply Last reply
    0
    • jsulmJ jsulm

      @SPlatten said in Adding a virtual function causes strange result...:

      clsXMLnode::strGetAttribute(QString)

      You should check what is happening there

      SPlattenS Offline
      SPlattenS Offline
      SPlatten
      wrote on last edited by
      #10

      @jsulm , I didn't use the override keyword, should I?

      Kind Regards,
      Sy

      jsulmJ 1 Reply Last reply
      0
      • SPlattenS SPlatten

        @jsulm , this is where its called:

        QString clsScriptHelper::getValue(const QString& crstrID) {
            QString strValue;
            if ( crstrID.isEmpty() != true ) {
                clsXMLnode* pobjNode(clsXMLnode::spobjGetNodeById(crstrID));
                if ( pobjNode != nullptr ) {
                    clsXMLinterface* pobjXMLif(reinterpret_cast<clsXMLinterface*>(pobjNode));
                    if ( pobjXMLif != nullptr ) {
                        strValue = pobjXMLif->strGetData();
                    }
                }
        
            }
            return strValue;
        }
        

        The prototype for the above:

        Q_INVOKABLE QString getValue(const QString& crstrID);
        

        There is presently only one call to this, the only overridden instance is defined in the class clsQtLineEdit.

        Execution stops as I stated on the line I specified in the original post, how can I see if an error or exception has occurred because it isn't obvious.

        J.HilkJ Online
        J.HilkJ Online
        J.Hilk
        Moderators
        wrote on last edited by J.Hilk
        #11

        @SPlatten said in Adding a virtual function causes strange result...:

        reinterpret_cast

        when using virtual inheritance !?!?!?

        use dynamic_cast or if QObject classes object_cast

        reinterpret_cast takes the raw pointer and considers it as being of the derived type. However, because of the virtual inheritance, a slight adjustment must be done to the pointer to point to the correct method dispatch table, and that's precisely what dynamic_cast will do.

        just as wrong, but probably wouldn't have resulted in a crash would be the use of static_cast.


        Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


        Q: What's that?
        A: It's blue light.
        Q: What does it do?
        A: It turns blue.

        SPlattenS 1 Reply Last reply
        3
        • SPlattenS SPlatten

          @jsulm , this is where its called:

          QString clsScriptHelper::getValue(const QString& crstrID) {
              QString strValue;
              if ( crstrID.isEmpty() != true ) {
                  clsXMLnode* pobjNode(clsXMLnode::spobjGetNodeById(crstrID));
                  if ( pobjNode != nullptr ) {
                      clsXMLinterface* pobjXMLif(reinterpret_cast<clsXMLinterface*>(pobjNode));
                      if ( pobjXMLif != nullptr ) {
                          strValue = pobjXMLif->strGetData();
                      }
                  }
          
              }
              return strValue;
          }
          

          The prototype for the above:

          Q_INVOKABLE QString getValue(const QString& crstrID);
          

          There is presently only one call to this, the only overridden instance is defined in the class clsQtLineEdit.

          Execution stops as I stated on the line I specified in the original post, how can I see if an error or exception has occurred because it isn't obvious.

          Christian EhrlicherC Offline
          Christian EhrlicherC Offline
          Christian Ehrlicher
          Lifetime Qt Champion
          wrote on last edited by
          #12
          This post is deleted!
          1 Reply Last reply
          0
          • J.HilkJ J.Hilk

            @SPlatten said in Adding a virtual function causes strange result...:

            reinterpret_cast

            when using virtual inheritance !?!?!?

            use dynamic_cast or if QObject classes object_cast

            reinterpret_cast takes the raw pointer and considers it as being of the derived type. However, because of the virtual inheritance, a slight adjustment must be done to the pointer to point to the correct method dispatch table, and that's precisely what dynamic_cast will do.

            just as wrong, but probably wouldn't have resulted in a crash would be the use of static_cast.

            SPlattenS Offline
            SPlattenS Offline
            SPlatten
            wrote on last edited by
            #13

            @J-Hilk said in Adding a virtual function causes strange result...:

            dynamic_cast

            I've replaced reinterpret_cast with dynamic_cast, same result.

            Kind Regards,
            Sy

            Christian EhrlicherC 1 Reply Last reply
            0
            • SPlattenS SPlatten

              @jsulm , I didn't use the override keyword, should I?

              jsulmJ Online
              jsulmJ Online
              jsulm
              Lifetime Qt Champion
              wrote on last edited by jsulm
              #14

              @SPlatten said in Adding a virtual function causes strange result...:

              I didn't use the override keyword, should I?

              Yes you should. To ask the compiler to check whether you're really overriding virtual method. Can help to detect bugs at compile time.

              As I suggested: check what is happening in clsXMLnode::strGetAttribute(QString).
              My guess is that the strGetData() method from base class is called which returns an empty string, so the code then fails later.

              https://forum.qt.io/topic/113070/qt-code-of-conduct

              SPlattenS 1 Reply Last reply
              0
              • SPlattenS SPlatten

                @J-Hilk said in Adding a virtual function causes strange result...:

                dynamic_cast

                I've replaced reinterpret_cast with dynamic_cast, same result.

                Christian EhrlicherC Offline
                Christian EhrlicherC Offline
                Christian Ehrlicher
                Lifetime Qt Champion
                wrote on last edited by
                #15

                @SPlatten said in Adding a virtual function causes strange result...:

                I've replaced reinterpret_cast with dynamic_cast, same result.

                For sure not.

                btw: dynamic_cast was proposed to your exact same problem some weeks ago already: https://forum.qt.io/topic/132420/how-to-access/4

                SPlattenS 1 Reply Last reply
                0
                • jsulmJ jsulm

                  @SPlatten said in Adding a virtual function causes strange result...:

                  I didn't use the override keyword, should I?

                  Yes you should. To ask the compiler to check whether you're really overriding virtual method. Can help to detect bugs at compile time.

                  As I suggested: check what is happening in clsXMLnode::strGetAttribute(QString).
                  My guess is that the strGetData() method from base class is called which returns an empty string, so the code then fails later.

                  SPlattenS Offline
                  SPlattenS Offline
                  SPlatten
                  wrote on last edited by
                  #16

                  @jsulm, I have a breakpoint on the first line of the function getValue, execution doesn't get as far as the breakpoint before the issue occurs.

                  Kind Regards,
                  Sy

                  J.HilkJ jsulmJ 2 Replies Last reply
                  0
                  • Christian EhrlicherC Christian Ehrlicher

                    @SPlatten said in Adding a virtual function causes strange result...:

                    I've replaced reinterpret_cast with dynamic_cast, same result.

                    For sure not.

                    btw: dynamic_cast was proposed to your exact same problem some weeks ago already: https://forum.qt.io/topic/132420/how-to-access/4

                    SPlattenS Offline
                    SPlattenS Offline
                    SPlatten
                    wrote on last edited by SPlatten
                    #17

                    @Christian-Ehrlicher That issue was resolved, this is new and dynamic_cast wasn't used to resolve the last issue, it was resolved with the suggested qobject_cast.

                    Kind Regards,
                    Sy

                    Christian EhrlicherC 1 Reply Last reply
                    0
                    • SPlattenS SPlatten

                      @jsulm, I have a breakpoint on the first line of the function getValue, execution doesn't get as far as the breakpoint before the issue occurs.

                      J.HilkJ Online
                      J.HilkJ Online
                      J.Hilk
                      Moderators
                      wrote on last edited by
                      #18

                      @SPlatten your stack trace actually points to your clsXMLnode class.
                      clsXMLnode::strGetAttribute


                      Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                      Q: What's that?
                      A: It's blue light.
                      Q: What does it do?
                      A: It turns blue.

                      kshegunovK 1 Reply Last reply
                      1
                      • SPlattenS SPlatten

                        @jsulm, I have a breakpoint on the first line of the function getValue, execution doesn't get as far as the breakpoint before the issue occurs.

                        jsulmJ Online
                        jsulmJ Online
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by jsulm
                        #19

                        @SPlatten I'm talking about clsXMLnode::strGetAttribute(QString).
                        If you check the stack trace you posted you will see that it is called shortly before the application stopps...

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                        1 Reply Last reply
                        2
                        • SPlattenS SPlatten

                          @Christian-Ehrlicher That issue was resolved, this is new and dynamic_cast wasn't used to resolve the last issue, it was resolved with the suggested qobject_cast.

                          Christian EhrlicherC Offline
                          Christian EhrlicherC Offline
                          Christian Ehrlicher
                          Lifetime Qt Champion
                          wrote on last edited by
                          #20

                          @SPlatten said in Adding a virtual function causes strange result...:

                          it was resolved with the suggested qobject_cast.

                          Since your class is derived from QObject you can also use qobject_cast. Please learn the basics.

                          SPlattenS 1 Reply Last reply
                          1
                          • Christian EhrlicherC Christian Ehrlicher

                            @SPlatten said in Adding a virtual function causes strange result...:

                            it was resolved with the suggested qobject_cast.

                            Since your class is derived from QObject you can also use qobject_cast. Please learn the basics.

                            SPlattenS Offline
                            SPlattenS Offline
                            SPlatten
                            wrote on last edited by
                            #21

                            @Christian-Ehrlicher , I find your additions very insulting, I’ve been coding professionally since 1986.

                            Kind Regards,
                            Sy

                            JonBJ Christian EhrlicherC 2 Replies Last reply
                            0
                            • SPlattenS SPlatten

                              @Christian-Ehrlicher , I find your additions very insulting, I’ve been coding professionally since 1986.

                              JonBJ Online
                              JonBJ Online
                              JonB
                              wrote on last edited by JonB
                              #22

                              @SPlatten
                              I'm not sure what part of your code you think is implicated. I see:

                              1  QListData::size() const
                              2  QList<std::pair<QString, QString>>::length() const 
                              

                              and that is failing (according to your "the execution stops in qlist.h on line 115") on trying to get the length of the QList. Invalid QList at that point? That is what I see?

                              1 Reply Last reply
                              0
                              • SPlattenS SPlatten

                                @Christian-Ehrlicher , I find your additions very insulting, I’ve been coding professionally since 1986.

                                Christian EhrlicherC Offline
                                Christian EhrlicherC Offline
                                Christian Ehrlicher
                                Lifetime Qt Champion
                                wrote on last edited by
                                #23

                                @SPlatten said in Adding a virtual function causes strange result...:

                                I’ve been coding professionally since 1986.

                                But not with c++ (at least I hope so) - when I want to learn a new language I normally start to learn the basics. But you ignore those basics in nearly every 'problem' you have and then wonder why people complain about the lack of the basics.

                                SPlattenS 1 Reply Last reply
                                1
                                • Christian EhrlicherC Christian Ehrlicher

                                  @SPlatten said in Adding a virtual function causes strange result...:

                                  I’ve been coding professionally since 1986.

                                  But not with c++ (at least I hope so) - when I want to learn a new language I normally start to learn the basics. But you ignore those basics in nearly every 'problem' you have and then wonder why people complain about the lack of the basics.

                                  SPlattenS Offline
                                  SPlattenS Offline
                                  SPlatten
                                  wrote on last edited by
                                  #24

                                  @Christian-Ehrlicher that’s a huge assumption on your part.

                                  Kind Regards,
                                  Sy

                                  1 Reply Last reply
                                  0
                                  • J.HilkJ J.Hilk

                                    @SPlatten your stack trace actually points to your clsXMLnode class.
                                    clsXMLnode::strGetAttribute

                                    kshegunovK Offline
                                    kshegunovK Offline
                                    kshegunov
                                    Moderators
                                    wrote on last edited by kshegunov
                                    #25

                                    @J-Hilk said in Adding a virtual function causes strange result...:

                                    @SPlatten your stack trace actually points to your clsXMLnode class.
                                    clsXMLnode::strGetAttribute

                                    If he reinterpret_casts it's going to point to that class and method since that's what to "reinterpret" means.

                                    @SPlatten said in Adding a virtual function causes strange result...:

                                    I've replaced reinterpret_cast with dynamic_cast, same result.

                                    You shouldn't use reinterpret_cast to begin with, as it's rather apparent you don't understand the implications of it; specifically to polymorphic calls and multiple inheritance. So while @Christian-Ehrlicher may seem brusque, you should do yourself a favor and listen to the advice.

                                    As for the issue at hand, you have called strGetAttribute on an invalid object, I'm reasonably certain. The reasons may vary, and reinterpret_casting incompatible types is one. Dangling pointers and uninitialized memory are other candidates. You need to sift through the debugger to find it. Out of curiosity where does clsQtLayout::addButton call clsXMLnode::strGetAttribute and where does clsXMLnode::setWidget call clsQtLayout::addButton - provide the relevant code around the calls.

                                    Read and abide by the Qt Code of Conduct

                                    SPlattenS 1 Reply Last reply
                                    3
                                    • kshegunovK kshegunov

                                      @J-Hilk said in Adding a virtual function causes strange result...:

                                      @SPlatten your stack trace actually points to your clsXMLnode class.
                                      clsXMLnode::strGetAttribute

                                      If he reinterpret_casts it's going to point to that class and method since that's what to "reinterpret" means.

                                      @SPlatten said in Adding a virtual function causes strange result...:

                                      I've replaced reinterpret_cast with dynamic_cast, same result.

                                      You shouldn't use reinterpret_cast to begin with, as it's rather apparent you don't understand the implications of it; specifically to polymorphic calls and multiple inheritance. So while @Christian-Ehrlicher may seem brusque, you should do yourself a favor and listen to the advice.

                                      As for the issue at hand, you have called strGetAttribute on an invalid object, I'm reasonably certain. The reasons may vary, and reinterpret_casting incompatible types is one. Dangling pointers and uninitialized memory are other candidates. You need to sift through the debugger to find it. Out of curiosity where does clsQtLayout::addButton call clsXMLnode::strGetAttribute and where does clsXMLnode::setWidget call clsQtLayout::addButton - provide the relevant code around the calls.

                                      SPlattenS Offline
                                      SPlattenS Offline
                                      SPlatten
                                      wrote on last edited by SPlatten
                                      #26

                                      @kshegunov , using the debugger I have a break point on the last if condition below:

                                      clsXMLinterface* pobjInterface(reinterpret_cast<clsXMLinterface*>(pobjButton));
                                      clsXMLnode* pobjNode(nullptr);
                                      if ( pobjInterface != nullptr ) {
                                          pobjNode = pobjInterface->pobjGetNode();
                                      }
                                      if ( pobjNode == nullptr ) {
                                          return;
                                      }
                                      

                                      pobjButton is a pointer to an instance of my derived class clsQtRadioButton:

                                          class clsQtRadioButton : public QRadioButton, public clsXMLinterface {
                                          Q_OBJECT
                                      

                                      pobjNode is returned as not null, pobjGetNode:

                                      clsXMLnode* pobjGetNode() { return mpobjNode; }
                                      

                                      I can see in the debugger the pobjInterface looks ok and mpobjNode is correct as I have assigned a human readable description to it:
                                      Screenshot 2021-12-22 at 07.41.17.png
                                      However pobjNode doesn't appear to be correct:
                                      Screenshot 2021-12-22 at 07.42.40.png
                                      And then trying to call strGetAttribute fails and causes the problem, but its because pobjNode isn't correct, why ?
                                      If I change the code to:

                                      clsQtRadioButton* pobjRadioBtn(qobject_cast<clsQtRadioButton*>(pobjButton));
                                      clsXMLnode* pobjNode(pobjRadioBtn->pobjGetNode());
                                      

                                      This way pobjNode is valid and there is no problem, however I need a polymorphic way to access pobjGetNode because there can be lots of different types of object derived from the same base class and I need the functionality to work for all of them.

                                      Kind Regards,
                                      Sy

                                      jsulmJ 1 Reply Last reply
                                      0
                                      • SPlattenS SPlatten

                                        @kshegunov , using the debugger I have a break point on the last if condition below:

                                        clsXMLinterface* pobjInterface(reinterpret_cast<clsXMLinterface*>(pobjButton));
                                        clsXMLnode* pobjNode(nullptr);
                                        if ( pobjInterface != nullptr ) {
                                            pobjNode = pobjInterface->pobjGetNode();
                                        }
                                        if ( pobjNode == nullptr ) {
                                            return;
                                        }
                                        

                                        pobjButton is a pointer to an instance of my derived class clsQtRadioButton:

                                            class clsQtRadioButton : public QRadioButton, public clsXMLinterface {
                                            Q_OBJECT
                                        

                                        pobjNode is returned as not null, pobjGetNode:

                                        clsXMLnode* pobjGetNode() { return mpobjNode; }
                                        

                                        I can see in the debugger the pobjInterface looks ok and mpobjNode is correct as I have assigned a human readable description to it:
                                        Screenshot 2021-12-22 at 07.41.17.png
                                        However pobjNode doesn't appear to be correct:
                                        Screenshot 2021-12-22 at 07.42.40.png
                                        And then trying to call strGetAttribute fails and causes the problem, but its because pobjNode isn't correct, why ?
                                        If I change the code to:

                                        clsQtRadioButton* pobjRadioBtn(qobject_cast<clsQtRadioButton*>(pobjButton));
                                        clsXMLnode* pobjNode(pobjRadioBtn->pobjGetNode());
                                        

                                        This way pobjNode is valid and there is no problem, however I need a polymorphic way to access pobjGetNode because there can be lots of different types of object derived from the same base class and I need the functionality to work for all of them.

                                        jsulmJ Online
                                        jsulmJ Online
                                        jsulm
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #27

                                        @SPlatten said in Adding a virtual function causes strange result...:

                                        why ?

                                        We do not know whether and how you're initialising it...

                                        "pobjNode is returned as not null" - doesn't mean it was initialised. You should initialise your pointers with nullptr before they are assigned proper pointers, else they can contain garbage.

                                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                                        SPlattenS 1 Reply Last reply
                                        0
                                        • jsulmJ jsulm

                                          @SPlatten said in Adding a virtual function causes strange result...:

                                          why ?

                                          We do not know whether and how you're initialising it...

                                          "pobjNode is returned as not null" - doesn't mean it was initialised. You should initialise your pointers with nullptr before they are assigned proper pointers, else they can contain garbage.

                                          SPlattenS Offline
                                          SPlattenS Offline
                                          SPlatten
                                          wrote on last edited by SPlatten
                                          #28

                                          @jsulm , here is the constructor for the class clsXMLinterface:

                                          clsXMLinterface::clsXMLinterface(clsXMLnode* pobjNode) : mpobjNode(pobjNode) {
                                          

                                          And clsQtRadioButton:

                                          clsQtRadioButton::clsQtRadioButton(clsXMLnode* pobjNode, QString* pstrCSS
                                                                                                 , QWidget* pParent)
                                                                      : QRadioButton(pParent), clsXMLinterface(pobjNode) {
                                          

                                          The formatting of this constructor is common to all instances. Widgets like instances of clsQtRadioButton are created by another call:

                                                      pobjWidget = qobject_cast<QWidget*>(clsCNT::pCreate(this,
                                                                                                          mstrName,
                                                                                                          strCSS,
                                                                                                          slstProperties,
                                                                                                          pobjParWidget));
                                          

                                          clsCNT::pCreate:

                                          QWidget* clsCNT::pCreate(clsXMLnode* pobjNode, const QString& crstrType
                                                                  ,QString& rstrCSS, QStringList& rslstProperties
                                                                  ,QWidget* pobjParent) {
                                              QWidget* pobjWidget(nullptr);    
                                              if ( pobjNode != nullptr ) {
                                                  if ( crstrType.compare(clsCNT::mscszButton) == 0 ) {
                                                      pobjWidget = new clsQtPushBtn(pobjNode, &rstrCSS, pobjParent);
                                          

                                          The above is just a sample, pobjNode is passed by pCreate as this.

                                          Kind Regards,
                                          Sy

                                          jsulmJ 1 Reply Last reply
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