Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. General and Desktop
  4. QApplication a(argc, argv); hangs on this line
Forum Updated to NodeBB v4.3 + New Features

QApplication a(argc, argv); hangs on this line

Scheduled Pinned Locked Moved General and Desktop
qtapplication
16 Posts 4 Posters 6.0k Views 1 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #4

    And you can interact with it ?

    Interested in AI ? www.idiap.ch
    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

    banditoB 1 Reply Last reply
    0
    • SGaistS SGaist

      And you can interact with it ?

      banditoB Offline
      banditoB Offline
      bandito
      wrote on last edited by
      #5

      @SGaist no

      1 Reply Last reply
      0
      • SGaistS Offline
        SGaistS Offline
        SGaist
        Lifetime Qt Champion
        wrote on last edited by
        #6

        Then it might be nice to explain what exactly you are expecting to get and what you actually get.

        With the code you provided, there's nothing wrong that is visible.

        So are you doing anything else with your code ?

        What platform are you on ?
        What version of Qt are you using ?

        Interested in AI ? www.idiap.ch
        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

        banditoB 1 Reply Last reply
        1
        • SGaistS SGaist

          Then it might be nice to explain what exactly you are expecting to get and what you actually get.

          With the code you provided, there's nothing wrong that is visible.

          So are you doing anything else with your code ?

          What platform are you on ?
          What version of Qt are you using ?

          banditoB Offline
          banditoB Offline
          bandito
          wrote on last edited by
          #7

          @SGaist I understand that it displaying is correct but in main.cpp it should also output "2" after QApplication a(argc, argv); has finished and it should also output "1.1" from mainwindow.cpp. My original project displays that window with all of it's widgets but doesn't do anything and hangs. I used the same qDebug() lines in the same spots as the code in these posts and get the same results. So I decided to create a new project hence the code that you see and try the qDebug() lines to see if it was perhaps just my project which is not the case. So something else is happening. As for the platform I am using Ubuntu 17.10 and Qt version 5.9.2. Hope this helps.

          JonBJ 1 Reply Last reply
          0
          • banditoB bandito

            @SGaist I understand that it displaying is correct but in main.cpp it should also output "2" after QApplication a(argc, argv); has finished and it should also output "1.1" from mainwindow.cpp. My original project displays that window with all of it's widgets but doesn't do anything and hangs. I used the same qDebug() lines in the same spots as the code in these posts and get the same results. So I decided to create a new project hence the code that you see and try the qDebug() lines to see if it was perhaps just my project which is not the case. So something else is happening. As for the platform I am using Ubuntu 17.10 and Qt version 5.9.2. Hope this helps.

            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by JonB
            #8

            @bandito
            So you're saying the minimal example to exemplify your problem is just:

            int main(int argc, char *argv[])
            {
                qDebug()<<1;
                QApplication a(argc, argv);
                qDebug()<<2;
            }
            

            Right? No need for main window. And it would hang/not print 2 as:
            QApplication a(1, { "Hello", NULL });
            (or whatever for C++)?

            And this is strange: in your code:

                qDebug()<<2;
                MainWindow w;
            

            it shows a main window yet does not debug out 2, right? Since it's so weird, have you stepped through your code in debugger?

            1 Reply Last reply
            0
            • goldenhawkingG Offline
              goldenhawkingG Offline
              goldenhawking
              wrote on last edited by
              #9

              comment Main window and run it again?
              I met a similar problem when I run a Qt app in a VNC-Connected PC, and the video card is very old. I copy same app to another PC, everything is OK.

              Qt is the best C++ framework I've ever met.

              1 Reply Last reply
              0
              • banditoB Offline
                banditoB Offline
                bandito
                wrote on last edited by
                #10

                So I used the degugger which output nil. As for commenting out MainWindow, that didn't help. I also tried QMainWindow instead with the same results. The sample code does work in 5.0.2 but my project won't since it needs 5.7 as it needs QtCharts. When using 5.9.2 I did have install libmesa-dev to fix a missing file (GL/gl.h). Then I got another error "-error: cannot find -lGL" and to fix that I had to install libgl1-mesa-dev. When using 5.7 I never encountered these errors but I hadn't uninstalled the mesa libraries prior to installing 5.7.

                My previous install of Qt ran smoothly on Ubuntu 14.10 and continued to run smoothly even when upgrading to 16.10. My impression is that I have an Ubuntu library that isn't correct.

                JonBJ 1 Reply Last reply
                0
                • banditoB bandito

                  So I used the degugger which output nil. As for commenting out MainWindow, that didn't help. I also tried QMainWindow instead with the same results. The sample code does work in 5.0.2 but my project won't since it needs 5.7 as it needs QtCharts. When using 5.9.2 I did have install libmesa-dev to fix a missing file (GL/gl.h). Then I got another error "-error: cannot find -lGL" and to fix that I had to install libgl1-mesa-dev. When using 5.7 I never encountered these errors but I hadn't uninstalled the mesa libraries prior to installing 5.7.

                  My previous install of Qt ran smoothly on Ubuntu 14.10 and continued to run smoothly even when upgrading to 16.10. My impression is that I have an Ubuntu library that isn't correct.

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

                  @bandito

                  My impression is that I have an Ubuntu library that isn't correct

                  Or, depending on what you mean, my impression is that you have an inconsistent set of Qt libraries, among themselves or in combination with Ubuntu ones.

                  You can't even construct a QApplication object, never mind about getting as far as windows/UI.

                  You need to completely sort out your Qt library installation on your Ubuntu before going any further.

                  banditoB 1 Reply Last reply
                  1
                  • JonBJ JonB

                    @bandito

                    My impression is that I have an Ubuntu library that isn't correct

                    Or, depending on what you mean, my impression is that you have an inconsistent set of Qt libraries, among themselves or in combination with Ubuntu ones.

                    You can't even construct a QApplication object, never mind about getting as far as windows/UI.

                    You need to completely sort out your Qt library installation on your Ubuntu before going any further.

                    banditoB Offline
                    banditoB Offline
                    bandito
                    wrote on last edited by
                    #12

                    @JNBarchan
                    I wouldn't know how to do that. I installed it with the online installer. I thought it was supposed to care of that for you.

                    1 Reply Last reply
                    0
                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #13

                      How many versions of Qt did you install ?
                      Do you also have the Qt dev packages from your distribution installed ?

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                      banditoB 1 Reply Last reply
                      0
                      • SGaistS SGaist

                        How many versions of Qt did you install ?
                        Do you also have the Qt dev packages from your distribution installed ?

                        banditoB Offline
                        banditoB Offline
                        bandito
                        wrote on last edited by bandito
                        #14

                        @SGaist

                        I used the online installer to install 5.9.2. Then I used the MaintenanceTool to remove 5.9.2 and then install 5.7.

                        The error regarding GL/gl.h missing, GL/gl.h is a file from a system library and not a Qt library. That's why I feel its a system error and not a qt error.

                        1 Reply Last reply
                        0
                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #15

                          The GL error is a classic one that has been answered many times already: you are missing the OpenGL development package.

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                          1 Reply Last reply
                          1
                          • banditoB Offline
                            banditoB Offline
                            bandito
                            wrote on last edited by bandito
                            #16

                            Well I got it going. I installed Ubuntu 17.10 64bit version and Qt 5.7 with the online installer. The library in questions to fix the missing GL/gl.h file appears to be libgl1-mesa-dev.

                            Update:

                            I also got it to install correctly on Ubuntu 16.10 64bit using the online installer. Had to install the exact same library as 17.10 64 bit libgl1-mesa-dev. Works like a charm.

                            1 Reply Last reply
                            1

                            • Login

                            • Login or register to search.
                            • First post
                              Last post
                            0
                            • Categories
                            • Recent
                            • Tags
                            • Popular
                            • Users
                            • Groups
                            • Search
                            • Get Qt Extensions
                            • Unsolved