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Add to Qt GUI logger functionality

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  • G Gaetano03

    @JonB I actually can access the source code of the logger library

    So best way would be to act directly on that library and modify it to be a Qt library?

    JonBJ Offline
    JonBJ Offline
    JonB
    wrote on last edited by JonB
    #6

    @Gaetano03
    That --- or something similar --- would be the best/easiest if you need your Qt UI program to know when/what the external library does in the way of issuing some message which you would like the UI to know about, so that it can put it in its QPlainText. That is what @jsulm had in mind when he wrote:

    Does this lib use Qt? If so you could use signals/slots to send log messages as signal parameter to your QPlainText.

    You could probably also do it by having the lib not know about Qt but have an exported "function pointer". If the calling program (Qt) sets that to a non-nullptr static function in itself, the library could call that and then the Qt program act on it (e.g. emit a signal). That's if you don't want your library to know anything about Qt.

    G 1 Reply Last reply
    0
    • JonBJ JonB

      @Gaetano03
      That --- or something similar --- would be the best/easiest if you need your Qt UI program to know when/what the external library does in the way of issuing some message which you would like the UI to know about, so that it can put it in its QPlainText. That is what @jsulm had in mind when he wrote:

      Does this lib use Qt? If so you could use signals/slots to send log messages as signal parameter to your QPlainText.

      You could probably also do it by having the lib not know about Qt but have an exported "function pointer". If the calling program (Qt) sets that to a non-nullptr static function in itself, the library could call that and then the Qt program act on it (e.g. emit a signal). That's if you don't want your library to know anything about Qt.

      G Offline
      G Offline
      Gaetano03
      wrote on last edited by
      #7

      @JonB Thanks a lot!

      Yep that was the original idea: having the logger not knowing anything about Qt.

      But might go back to first option, second one scares me a bit XD

      Do you have any examples, links to share on second option btw?

      Thanks again, appreciate a lot your help

      jsulmJ JonBJ 2 Replies Last reply
      0
      • G Gaetano03

        @JonB Thanks a lot!

        Yep that was the original idea: having the logger not knowing anything about Qt.

        But might go back to first option, second one scares me a bit XD

        Do you have any examples, links to share on second option btw?

        Thanks again, appreciate a lot your help

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #8

        @Gaetano03 No need to be scared :-)

        // Define a function pointer type
        typedef void (*LoggerCallback)(std::string message);
        
        // A function to use as callback
        void log(std::string message)
        {
            std::cout << message << std::endl;
        }
        
        // Example how to use a function pointer (callBack) to call a function (log)
        LoggerCallback callBack = &log;
        callBack("Hello!");
        

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

        1 Reply Last reply
        2
        • G Gaetano03

          @JonB Thanks a lot!

          Yep that was the original idea: having the logger not knowing anything about Qt.

          But might go back to first option, second one scares me a bit XD

          Do you have any examples, links to share on second option btw?

          Thanks again, appreciate a lot your help

          JonBJ Offline
          JonBJ Offline
          JonB
          wrote on last edited by JonB
          #9

          @Gaetano03 said in Add to Qt GUI logger functionality:

          Do you have any examples, links to share on second option btw?

          Basically what @jsulm has shown above. Certainly for type declaring. To make it clear where i have in mind what goes, the principle is:

          • In some library logger.h file:
          typedef void (*LoggerCallback)(std::string message);
          extern LoggerCallback g_loggerCallback;
          
          • In some library logger.cpp file:
          #include "logger.h"
          LoggerCallback g_loggerCallback = nullptr;
          ...
          void libraryLoggingFunction(std::string message)
          {
              selfLoggingWhatever(message);
              if (g_loggerCallback != nullptr)
                  g_loggerCallback(message);
          }
          
          • In one of your Qt app .cpp files:
          #include "library/logger.h"
          ...
          g_loggerCallback = log;
          ...
          void log(std::string message)
          {
              emit libraryLogged(message);
          }
          

          Something along these lines. The point is that the library has a g_loggerCallback exported variable. It is set to nullptr initially, in which case it is never called/used. You can link it as-is with any outside-world which knows/cares nothing about the existence of the function pointer variable. The library still knows nothing about Qt.

          If and only if the outside-world program the library is linked with chooses to set g_loggerCallback to a suitable logging function of its own then that will be called by the library's if (g_loggerCallback != nullptr) ... logging code. Whereupon the host Qt or otherwise application can decide what to do with the message in its callback function.

          1 Reply Last reply
          2
          • G Offline
            G Offline
            Gaetano03
            wrote on last edited by
            #10

            Thanks a lot to both :))) . That is actually amazing!

            So if I understood well, the last add will be to catch that signal from QPlainText and that's it?!?!

            Really appreciated your help guys :)

            JonBJ 1 Reply Last reply
            0
            • G Gaetano03

              Thanks a lot to both :))) . That is actually amazing!

              So if I understood well, the last add will be to catch that signal from QPlainText and that's it?!?!

              Really appreciated your help guys :)

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by JonB
              #11

              @Gaetano03 said in Add to Qt GUI logger functionality:

              So if I understood well, the last add will be to catch that signal from QPlainText and that's it?!?!

              Yes. The "tricky" bit, I think, is that you need a QObject-derived object to emit any signal. And the function your Qt app will need to set, like g_loggerCallback = log;, will I believe not be able to be a member of any class, it will need to be global/static. I think you will need that log function to have access to a global QObject object, e.g. it may have to call on your QApplication global object, or perhaps some other singleton class, to emit a signal.

              1 Reply Last reply
              1
              • G Offline
                G Offline
                Gaetano03
                wrote on last edited by
                #12

                @JonB said in Add to Qt GUI logger functionality:

                QApplication a(argc, argv);
                MainWindow w;
                w.show();
                return a.exec();

                You mean on the "a" object in the application main? How would this be possible in such a case?

                my understanding of what you are pointing out is that even if g_loggerCallback has global visibility, not sure what happens when it points to a QObject function (the call in the external logger library does not know what to do)?

                What about making both the function pointer and the log function static? Maybe I am telling blasfemies, sorry for that

                JonBJ 1 Reply Last reply
                0
                • G Gaetano03

                  @JonB said in Add to Qt GUI logger functionality:

                  QApplication a(argc, argv);
                  MainWindow w;
                  w.show();
                  return a.exec();

                  You mean on the "a" object in the application main? How would this be possible in such a case?

                  my understanding of what you are pointing out is that even if g_loggerCallback has global visibility, not sure what happens when it points to a QObject function (the call in the external logger library does not know what to do)?

                  What about making both the function pointer and the log function static? Maybe I am telling blasfemies, sorry for that

                  JonBJ Offline
                  JonBJ Offline
                  JonB
                  wrote on last edited by JonB
                  #13

                  @Gaetano03
                  That a object in main() --- or rather, the QApplication object --- can be accessed from anywhere in a Qt program (because it's a singleton) via qApp macro or qGuiApp macro or QCoreApplication *QCoreApplication::instance(). That means you can use those anywhere in a Qt application, without worrying about the a variable in main().

                  You could use that to do something like create your own signal (must subclass QAppplication, but that's no problem), which you could connect() to a slot somewhere to update your QPlainText widget. Then even a static C function which is called from the function pointer we discussed can get at a Qt object to emit a signal. Or, you could skip signal/slot if you have, by whatever means, a global pointer to your desired QPlainText, which the static log function can use to set its text directly. Just be careful with coding, but it should be doable!

                  not sure what happens when it points to a QObject function (the call in the external logger library does not know what to do)?

                  All the external library knows is the outside world has set g_loggerCallback to the address of some function which takes a std:string (or whatever) as a parameter. That is all it needs to know to be able to call it. What happens at the other end in the function pointed to --- log(std::string message), which is in your Qt program, not the library --- is the other end's problem, so far as the library is concerned. [Which is why it would be nice if it worked and didn't crash :) ]

                  G 1 Reply Last reply
                  1
                  • JonBJ JonB

                    @Gaetano03
                    That a object in main() --- or rather, the QApplication object --- can be accessed from anywhere in a Qt program (because it's a singleton) via qApp macro or qGuiApp macro or QCoreApplication *QCoreApplication::instance(). That means you can use those anywhere in a Qt application, without worrying about the a variable in main().

                    You could use that to do something like create your own signal (must subclass QAppplication, but that's no problem), which you could connect() to a slot somewhere to update your QPlainText widget. Then even a static C function which is called from the function pointer we discussed can get at a Qt object to emit a signal. Or, you could skip signal/slot if you have, by whatever means, a global pointer to your desired QPlainText, which the static log function can use to set its text directly. Just be careful with coding, but it should be doable!

                    not sure what happens when it points to a QObject function (the call in the external logger library does not know what to do)?

                    All the external library knows is the outside world has set g_loggerCallback to the address of some function which takes a std:string (or whatever) as a parameter. That is all it needs to know to be able to call it. What happens at the other end in the function pointed to --- log(std::string message), which is in your Qt program, not the library --- is the other end's problem, so far as the library is concerned. [Which is why it would be nice if it worked and didn't crash :) ]

                    G Offline
                    G Offline
                    Gaetano03
                    wrote on last edited by Gaetano03
                    #14

                    @JonB Getting a little bit of shakes now XD

                    "You could use that to do something like create your own signal (must subclass QAppplication, but that's no problem), which you could connect() to a slot somewhere to update your QPlainText widget. "

                    The other problem would be that signal and slot should be static as well? can you use connect on static objects?

                    If I understand well, your first option would be to create a class that inherits Qapplication and get an instance of the Qapplication. Here I define my own signal (static?) which I then emits thorugh the log function defined above (still static). This should be catched by the QPlainText widget, but at this point how? Should I make the slot static as well? Actually it seems I am getting real troubles when I try to use connect with static methods.

                    Will investigate also second option

                    Thanks a lot

                    JonBJ 1 Reply Last reply
                    0
                    • G Gaetano03

                      @JonB Getting a little bit of shakes now XD

                      "You could use that to do something like create your own signal (must subclass QAppplication, but that's no problem), which you could connect() to a slot somewhere to update your QPlainText widget. "

                      The other problem would be that signal and slot should be static as well? can you use connect on static objects?

                      If I understand well, your first option would be to create a class that inherits Qapplication and get an instance of the Qapplication. Here I define my own signal (static?) which I then emits thorugh the log function defined above (still static). This should be catched by the QPlainText widget, but at this point how? Should I make the slot static as well? Actually it seems I am getting real troubles when I try to use connect with static methods.

                      Will investigate also second option

                      Thanks a lot

                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by
                      #15

                      @Gaetano03
                      The only thing which needs to be "static" is the global, non-member function void log(std::string message), to which you set g_loggerCallback = log;, so that the library can invoke it via g_loggerCallback(message).

                      That can go something like:

                      void log(std::string message)
                      {
                          emit qApp()->libraryLogged(message);
                          // or probably
                          MyApplication *myApp = qobject_cast<MyApplication *>(qApp());
                          emit myApp->libraryLogged(message);
                      }
                      

                      You would need to subclass and use QApplication something like:

                      class MyApplication : public QApplication
                      {
                      signals:
                          void libraryLogged(std::string message);
                      }
                      

                      Now it remains to have done the connect(). Somewhere in your code which can "see" wherever you create the QTextEdit *logmessageTextEdit = new QTextEdit, or afterwards, and can see the class MyApplication definition, needs e.g.

                      MyApplication *myApp = qobject_cast<MyApplication *>(qApp());
                      connect(myApp(), &MyApplication::libraryLogged, this, &ThisClass::onLibraryLogged);
                      
                      class ThisClass
                      {
                      slots:
                          void onLibraryLogged(std::string message) { this->logmessageTextEdit->append(message); }
                      }
                      

                      Alternatively, if you don't want to use signals/slots, keep some global reference to the logmessageTextEdit pointer to the QTextEdit and just go

                      void log(std::string message)
                      {
                          if (g_logmessageTextEdit != nullptr)
                              g_logmessageTextEdit->append(message);
                      }
                      
                      G 1 Reply Last reply
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                      • JonBJ JonB

                        @Gaetano03
                        The only thing which needs to be "static" is the global, non-member function void log(std::string message), to which you set g_loggerCallback = log;, so that the library can invoke it via g_loggerCallback(message).

                        That can go something like:

                        void log(std::string message)
                        {
                            emit qApp()->libraryLogged(message);
                            // or probably
                            MyApplication *myApp = qobject_cast<MyApplication *>(qApp());
                            emit myApp->libraryLogged(message);
                        }
                        

                        You would need to subclass and use QApplication something like:

                        class MyApplication : public QApplication
                        {
                        signals:
                            void libraryLogged(std::string message);
                        }
                        

                        Now it remains to have done the connect(). Somewhere in your code which can "see" wherever you create the QTextEdit *logmessageTextEdit = new QTextEdit, or afterwards, and can see the class MyApplication definition, needs e.g.

                        MyApplication *myApp = qobject_cast<MyApplication *>(qApp());
                        connect(myApp(), &MyApplication::libraryLogged, this, &ThisClass::onLibraryLogged);
                        
                        class ThisClass
                        {
                        slots:
                            void onLibraryLogged(std::string message) { this->logmessageTextEdit->append(message); }
                        }
                        

                        Alternatively, if you don't want to use signals/slots, keep some global reference to the logmessageTextEdit pointer to the QTextEdit and just go

                        void log(std::string message)
                        {
                            if (g_logmessageTextEdit != nullptr)
                                g_logmessageTextEdit->append(message);
                        }
                        
                        G Offline
                        G Offline
                        Gaetano03
                        wrote on last edited by
                        #16

                        @JonB said in Add to Qt GUI logger functionality:

                        Not sure where to declare the log function though

                        At this point what I did is

                        I created a QApplication subclass in a .h file (integer_interface.h) which looks like this

                        class integer_interface : public QApplication
                        {
                            Q_OBJECT
                        public:
                            integer_interface(int &argc, char *argv[]) {}; // empty constructor
                        
                        signals:
                            void libraryLogged(std::string message);
                        
                        };
                        

                        then in my logger_widget class, logger_widget.h (the one that contains the QPlainTextWidget) I have the following class definition:

                        namespace Ui {
                        class logger_widget; 
                        }
                        
                        class logger_widget : public QWidget
                        {
                            Q_OBJECT
                        
                        public:
                            explicit logger_widget(QWidget *parent = nullptr);
                            ~logger_widget();
                        
                        signals:
                        
                        
                        public slots:
                            void onLibraryLogged(std::string message);
                        
                        
                        private:
                            Ui::logger_widget *ui;
                        
                            integer::logger::errors err_init;
                            integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance();
                            integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                        
                        };
                        

                        and a declaration of the log static function outside the class

                        static void log(std::string message); 
                        

                        In the logger_widget constructor I have the following two lines to define the connection

                        integer::logger::g_loggerCallback = log;
                        connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);
                        

                        while log and onLibraryLogged implementations look like this

                        void logger_widget::onLibraryLogged(std::string message)
                        {
                            ui->plainTextEdit_logger->appendPlainText(QString::fromStdString(message));
                        }
                        
                        void log(std::string message)
                        {
                            integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                            emit myApp->libraryLogged(message);
                        }
                        

                        constructor and function implementations are obviously in the corresponding logger_widget.cpp file

                        It compiles fine, but I get a runtime error "abort()" and the following message

                        qt.core.qobject.connect: QObject::connect(integer_interface, logger_widget): invalid nullptr parameter
                        
                        JonBJ 1 Reply Last reply
                        0
                        • G Gaetano03

                          @JonB said in Add to Qt GUI logger functionality:

                          Not sure where to declare the log function though

                          At this point what I did is

                          I created a QApplication subclass in a .h file (integer_interface.h) which looks like this

                          class integer_interface : public QApplication
                          {
                              Q_OBJECT
                          public:
                              integer_interface(int &argc, char *argv[]) {}; // empty constructor
                          
                          signals:
                              void libraryLogged(std::string message);
                          
                          };
                          

                          then in my logger_widget class, logger_widget.h (the one that contains the QPlainTextWidget) I have the following class definition:

                          namespace Ui {
                          class logger_widget; 
                          }
                          
                          class logger_widget : public QWidget
                          {
                              Q_OBJECT
                          
                          public:
                              explicit logger_widget(QWidget *parent = nullptr);
                              ~logger_widget();
                          
                          signals:
                          
                          
                          public slots:
                              void onLibraryLogged(std::string message);
                          
                          
                          private:
                              Ui::logger_widget *ui;
                          
                              integer::logger::errors err_init;
                              integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance();
                              integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                          
                          };
                          

                          and a declaration of the log static function outside the class

                          static void log(std::string message); 
                          

                          In the logger_widget constructor I have the following two lines to define the connection

                          integer::logger::g_loggerCallback = log;
                          connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);
                          

                          while log and onLibraryLogged implementations look like this

                          void logger_widget::onLibraryLogged(std::string message)
                          {
                              ui->plainTextEdit_logger->appendPlainText(QString::fromStdString(message));
                          }
                          
                          void log(std::string message)
                          {
                              integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                              emit myApp->libraryLogged(message);
                          }
                          

                          constructor and function implementations are obviously in the corresponding logger_widget.cpp file

                          It compiles fine, but I get a runtime error "abort()" and the following message

                          qt.core.qobject.connect: QObject::connect(integer_interface, logger_widget): invalid nullptr parameter
                          
                          JonBJ Offline
                          JonBJ Offline
                          JonB
                          wrote on last edited by JonB
                          #17

                          @Gaetano03
                          So I assume that occurs at runtime when it hits

                          connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);
                          

                          and indicates one of the two objects are nullptr. Check on line above with e.g.

                          qDebug() << myApp << this;
                          

                          ?

                          If myApp == nullptr, you did remember to create an integer_interface, not just a QApplication now, didn't you...??

                          Everywhere you go integer_interface *myApp = qobject_cast<integer_interface *>(qApp); you might follow that with Q_ASSERT(myApp); to verify all is well at that instant.

                          P.S.

                          integer_interface(int &argc, char *argv[]) {}; // empty constructor

                          Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?

                          G JonBJ 2 Replies Last reply
                          0
                          • JonBJ JonB

                            @Gaetano03
                            So I assume that occurs at runtime when it hits

                            connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);
                            

                            and indicates one of the two objects are nullptr. Check on line above with e.g.

                            qDebug() << myApp << this;
                            

                            ?

                            If myApp == nullptr, you did remember to create an integer_interface, not just a QApplication now, didn't you...??

                            Everywhere you go integer_interface *myApp = qobject_cast<integer_interface *>(qApp); you might follow that with Q_ASSERT(myApp); to verify all is well at that instant.

                            P.S.

                            integer_interface(int &argc, char *argv[]) {}; // empty constructor

                            Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?

                            G Offline
                            G Offline
                            Gaetano03
                            wrote on last edited by
                            #18

                            @JonB
                            I think the problem might be where I define myApp is not correct? Which is at the moment into the logger_widget class

                            when I qDebug as you said I get indeed the following value for myApp

                            QObject(0x0) logger_widget(0x1e04f63bcd0, name="logger_widget")
                            

                            and the app crashes few seconds after it starts

                            Should I declare the myApp out of any member class as I did for the log function?

                            1 Reply Last reply
                            0
                            • JonBJ JonB

                              @Gaetano03
                              So I assume that occurs at runtime when it hits

                              connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);
                              

                              and indicates one of the two objects are nullptr. Check on line above with e.g.

                              qDebug() << myApp << this;
                              

                              ?

                              If myApp == nullptr, you did remember to create an integer_interface, not just a QApplication now, didn't you...??

                              Everywhere you go integer_interface *myApp = qobject_cast<integer_interface *>(qApp); you might follow that with Q_ASSERT(myApp); to verify all is well at that instant.

                              P.S.

                              integer_interface(int &argc, char *argv[]) {}; // empty constructor

                              Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?

                              JonBJ Offline
                              JonBJ Offline
                              JonB
                              wrote on last edited by
                              #19

                              @Gaetano03

                              @JonB said in Add to Qt GUI logger functionality:

                              If myApp == nullptr, you did remember to create an integer_interface, not just a QApplication now, didn't you...??

                              ??

                              G 1 Reply Last reply
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                              • JonBJ JonB

                                @Gaetano03

                                @JonB said in Add to Qt GUI logger functionality:

                                If myApp == nullptr, you did remember to create an integer_interface, not just a QApplication now, didn't you...??

                                ??

                                G Offline
                                G Offline
                                Gaetano03
                                wrote on last edited by
                                #20

                                @JonB

                                Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?

                                ye I have it in an integer_interface.cpp, looks like this

                                #include "integer_interface.h"
                                
                                integer_interface::integer_interface(int &argc, char *argv[])
                                    : QApplication(argc, argv)
                                {
                                
                                }
                                

                                ??

                                I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?

                                Or maybe you meant something else from this

                                Christian EhrlicherC 1 Reply Last reply
                                0
                                • G Gaetano03

                                  @JonB

                                  Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?

                                  ye I have it in an integer_interface.cpp, looks like this

                                  #include "integer_interface.h"
                                  
                                  integer_interface::integer_interface(int &argc, char *argv[])
                                      : QApplication(argc, argv)
                                  {
                                  
                                  }
                                  

                                  ??

                                  I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?

                                  Or maybe you meant something else from this

                                  Christian EhrlicherC Offline
                                  Christian EhrlicherC Offline
                                  Christian Ehrlicher
                                  Lifetime Qt Champion
                                  wrote on last edited by
                                  #21

                                  @Gaetano03 said in Add to Qt GUI logger functionality:

                                  I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?

                                  You should also instantiate it somewhere.

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                                  • Christian EhrlicherC Christian Ehrlicher

                                    @Gaetano03 said in Add to Qt GUI logger functionality:

                                    I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?

                                    You should also instantiate it somewhere.

                                    G Offline
                                    G Offline
                                    Gaetano03
                                    wrote on last edited by
                                    #22

                                    @Christian-Ehrlicher

                                    I have it declared and instantiated both in the logger_widget.h class among the private members

                                    private:
                                        Ui::logger_widget *ui;
                                    
                                        integer::logger::errors err_init;
                                        integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance();
                                        integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                    

                                    and in the static log function

                                    void log(std::string message)
                                    {
                                        integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                        emit myApp->libraryLogged(message);
                                    }
                                    

                                    as suggested by @JonB

                                    PS
                                    @JonB doing as you suggested as sanity check with the following lines

                                        integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                        Q_ASSERT(myApp);
                                    

                                    gives a bunch of errors not sure I understand:
                                    logger_widget.h:42:14: C++ requires a type specifier for all declarations

                                    logger_widget.h:42:5: Expected ')'
                                    0:0: :42:5: note: to match this '('
                                    
                                    logger_widget.h:42:14: Duplicate member 'myApp'
                                    logger_widget.h:41:24: previous declaration is here
                                    
                                    JonBJ 2 Replies Last reply
                                    0
                                    • G Gaetano03

                                      @Christian-Ehrlicher

                                      I have it declared and instantiated both in the logger_widget.h class among the private members

                                      private:
                                          Ui::logger_widget *ui;
                                      
                                          integer::logger::errors err_init;
                                          integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance();
                                          integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                      

                                      and in the static log function

                                      void log(std::string message)
                                      {
                                          integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                          emit myApp->libraryLogged(message);
                                      }
                                      

                                      as suggested by @JonB

                                      PS
                                      @JonB doing as you suggested as sanity check with the following lines

                                          integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                          Q_ASSERT(myApp);
                                      

                                      gives a bunch of errors not sure I understand:
                                      logger_widget.h:42:14: C++ requires a type specifier for all declarations

                                      logger_widget.h:42:5: Expected ')'
                                      0:0: :42:5: note: to match this '('
                                      
                                      logger_widget.h:42:14: Duplicate member 'myApp'
                                      logger_widget.h:41:24: previous declaration is here
                                      
                                      JonBJ Offline
                                      JonBJ Offline
                                      JonB
                                      wrote on last edited by
                                      #23

                                      @Gaetano03
                                      Look, can you please show your main() function now. I have a funny feeling your still have QApplication a(argc, argv); there, and what do you think you actually need instead of that?

                                      G 1 Reply Last reply
                                      1
                                      • G Gaetano03

                                        @Christian-Ehrlicher

                                        I have it declared and instantiated both in the logger_widget.h class among the private members

                                        private:
                                            Ui::logger_widget *ui;
                                        
                                            integer::logger::errors err_init;
                                            integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance();
                                            integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                        

                                        and in the static log function

                                        void log(std::string message)
                                        {
                                            integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                            emit myApp->libraryLogged(message);
                                        }
                                        

                                        as suggested by @JonB

                                        PS
                                        @JonB doing as you suggested as sanity check with the following lines

                                            integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                            Q_ASSERT(myApp);
                                        

                                        gives a bunch of errors not sure I understand:
                                        logger_widget.h:42:14: C++ requires a type specifier for all declarations

                                        logger_widget.h:42:5: Expected ')'
                                        0:0: :42:5: note: to match this '('
                                        
                                        logger_widget.h:42:14: Duplicate member 'myApp'
                                        logger_widget.h:41:24: previous declaration is here
                                        
                                        JonBJ Offline
                                        JonBJ Offline
                                        JonB
                                        wrote on last edited by JonB
                                        #24

                                        @Gaetano03 said in Add to Qt GUI logger functionality:

                                        integer_interface *myApp = qobject_cast<integer_interface *>(qApp);
                                        Q_ASSERT(myApp);
                                        

                                        If that is in a .h where you are declaring member variables in a class definition you cannot add arbitrary C++ statements to execute..... Put the qobject_cast<> in the constructor, where you can verify it.

                                        1 Reply Last reply
                                        0
                                        • JonBJ JonB

                                          @Gaetano03
                                          Look, can you please show your main() function now. I have a funny feeling your still have QApplication a(argc, argv); there, and what do you think you actually need instead of that?

                                          G Offline
                                          G Offline
                                          Gaetano03
                                          wrote on last edited by
                                          #25

                                          @JonB
                                          you have the right funny feeling, just realized how silly I was.

                                          Everything works fine now and I get stuff printed on my QPlainText, at least for now XD.

                                          Thanks a lot, really!

                                          I really appreciate

                                          JonBJ 1 Reply Last reply
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