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QT deployed executable crashes on some computers

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  • Pablo J. RoginaP Pablo J. Rogina

    @Lati said in QT deployed executable crashes on some computers:

    Strangely, there is no sign about the crash caused by getenv.

    Well, it looks like the culprit isn't getenv() but the way the return value from that function is used within the DLL later on. From man getvenv:

    The getenv() function returns a pointer to the value in the environment, or NULL if there is no match.

    so programXRootDirectory becomes NULL when the variable is not set, and the world ends...

    L Offline
    L Offline
    Lati
    wrote on last edited by Lati
    #29

    @Pablo-J-Rogina
    Exactly! No-one would guess the crash is due to getenvsince all indications were showing that it was either false libraries or graphic card issue.

    @JonB
    I am not deploying anything on that screen. The screenshot is after I clicked on F5 to debug the code and the path of the Qt5Cored.dll is from Qt's installation directory (Qt is installed on D: drive, as I mentioned). getenv crashes on my computer, as well as the deployed executable crashes on the computers if the environmental variable doesn't exist. It is very easy to test by writing a small application.

    JonBJ 1 Reply Last reply
    0
    • L Lati

      @Pablo-J-Rogina
      Exactly! No-one would guess the crash is due to getenvsince all indications were showing that it was either false libraries or graphic card issue.

      @JonB
      I am not deploying anything on that screen. The screenshot is after I clicked on F5 to debug the code and the path of the Qt5Cored.dll is from Qt's installation directory (Qt is installed on D: drive, as I mentioned). getenv crashes on my computer, as well as the deployed executable crashes on the computers if the environmental variable doesn't exist. It is very easy to test by writing a small application.

      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by JonB
      #30

      @Lati said in QT deployed executable crashes on some computers:

      It is very easy to test by writing a small application.

      char *p = getenv("ProgramXROOT");
      // or
      char *p = getenv("AnythingElseWhichDoesntExist");
      

      won't crash. It will set p to NULL/nullptr.

      If the program continues and does not check for that, assuming that p will not be null, it may crash. That is all @Pablo-J-Rogina and I are saying.

      Pablo J. RoginaP 1 Reply Last reply
      0
      • fcarneyF Offline
        fcarneyF Offline
        fcarney
        wrote on last edited by
        #31

        @Lati said in QT deployed executable crashes on some computers:

        programXRootDirectory

        It would be interesting to know what the data type is for this variable. I could not get QString to crash or misbehave.

        {
                char* null = nullptr;
        
                QString test = "hallo";
                qInfo() << "before init null";
                test = QString(null);
                qInfo() << test;
                qInfo() << "after init null";
        
                QString test2 = "hallo again";
                qInfo() << "before assign null";
                test2 = null;
                qInfo() << test2;
                qInfo() << "after assign null";
            }
        

        C++ is a perfectly valid school of magic.

        L 1 Reply Last reply
        0
        • fcarneyF fcarney

          @Lati said in QT deployed executable crashes on some computers:

          programXRootDirectory

          It would be interesting to know what the data type is for this variable. I could not get QString to crash or misbehave.

          {
                  char* null = nullptr;
          
                  QString test = "hallo";
                  qInfo() << "before init null";
                  test = QString(null);
                  qInfo() << test;
                  qInfo() << "after init null";
          
                  QString test2 = "hallo again";
                  qInfo() << "before assign null";
                  test2 = null;
                  qInfo() << test2;
                  qInfo() << "after assign null";
              }
          
          L Offline
          L Offline
          Lati
          wrote on last edited by Lati
          #32

          @fcarney
          You can reproduce the issue with the following example (at least it crashes on my computer:)):

          main.cpp

          #include "mainwindow.h"
          #include <QApplication>
          
          int main(int argc, char *argv[])
          {
              QApplication a(argc, argv);
              MainWindow w;
              w.show();
              return a.exec();
          }
          

          mainWindow.h:

          #ifndef MAINWINDOW_H
          #define MAINWINDOW_H
          
          #include <QMainWindow>
          
          QT_BEGIN_NAMESPACE
          namespace Ui { class MainWindow; }
          QT_END_NAMESPACE
          
          class MainWindow : public QMainWindow
          {
              Q_OBJECT
          
          public:
              MainWindow(QWidget *parent = nullptr);
              ~MainWindow();
          
              // Senex root directory
              std::string notExistEnvVar;
          
          private:
              Ui::MainWindow *ui;
          };
          #endif // MAINWINDOW_H
          

          mainWindow.cpp

          #include "mainwindow.h"
          #include "ui_mainwindow.h"
          
          MainWindow::MainWindow(QWidget *parent)
              : QMainWindow(parent)
              , ui(new Ui::MainWindow)
          {
              ui->setupUi(this);
          
              notExistEnvVar = getenv("notExistEnvVar");
          }
          
          MainWindow::~MainWindow()
          {
              delete ui;
          }
          

          Compiled with MSVC2015 64bit.

          1 Reply Last reply
          0
          • fcarneyF Offline
            fcarneyF Offline
            fcarney
            wrote on last edited by fcarney
            #33

            You are getting an exception because you are assigning nullptr to std::string. Assign to

            char* ptr = getenv("notExistEnvVar");
            if(ptr != nullptr)
              notExistEnvVar = ptr;
            

            getenv is not crashing

            Edit:
            or use QString

            QString str = getenv("notExistEnvVar");
            

            C++ is a perfectly valid school of magic.

            JonBJ L 2 Replies Last reply
            2
            • fcarneyF fcarney

              You are getting an exception because you are assigning nullptr to std::string. Assign to

              char* ptr = getenv("notExistEnvVar");
              if(ptr != nullptr)
                notExistEnvVar = ptr;
              

              getenv is not crashing

              Edit:
              or use QString

              QString str = getenv("notExistEnvVar");
              
              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by
              #34

              @fcarney Thank you :)

              1 Reply Last reply
              1
              • JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by
                #35

                For std::string s = nullptr, see https://stackoverflow.com/questions/10771864/assign-a-nullptr-to-a-stdstring-is-safe/10771938. Accepted answer:

                Requires: s shall not be a null pointer.

                Since the standard does not ask the library to throw an exception when this particular requirement is not met, it would appear that passing a null pointer provoked undefined behavior.

                1 Reply Last reply
                2
                • fcarneyF Offline
                  fcarneyF Offline
                  fcarney
                  wrote on last edited by
                  #36

                  @JonB said in QT deployed executable crashes on some computers:

                  undefined

                  !!!UNDEFINED!!!
                  The end is nigh!

                  Good find!

                  C++ is a perfectly valid school of magic.

                  1 Reply Last reply
                  0
                  • JonBJ JonB

                    @Lati said in QT deployed executable crashes on some computers:

                    It is very easy to test by writing a small application.

                    char *p = getenv("ProgramXROOT");
                    // or
                    char *p = getenv("AnythingElseWhichDoesntExist");
                    

                    won't crash. It will set p to NULL/nullptr.

                    If the program continues and does not check for that, assuming that p will not be null, it may crash. That is all @Pablo-J-Rogina and I are saying.

                    Pablo J. RoginaP Offline
                    Pablo J. RoginaP Offline
                    Pablo J. Rogina
                    wrote on last edited by
                    #37

                    @JonB said in QT deployed executable crashes on some computers:

                    won't crash. It will set p to NULL/nullptr.

                    The problem is not the assignment... the problem comes once you have assigned NULL to the pointer and then you try using it

                    Upvote the answer(s) that helped you solve the issue
                    Use "Topic Tools" button to mark your post as Solved
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                    Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

                    1 Reply Last reply
                    1
                    • fcarneyF fcarney

                      You are getting an exception because you are assigning nullptr to std::string. Assign to

                      char* ptr = getenv("notExistEnvVar");
                      if(ptr != nullptr)
                        notExistEnvVar = ptr;
                      

                      getenv is not crashing

                      Edit:
                      or use QString

                      QString str = getenv("notExistEnvVar");
                      
                      L Offline
                      L Offline
                      Lati
                      wrote on last edited by Lati
                      #38

                      @fcarney

                      Obviously, the person who wrote the library didn't know this (to be honest, I didn't know it as well, I have never used getenv). And this is how bugs happened, right? :)

                      But interesting thing is that there is no sign about the crash and no-one had an idea about it (including me). I would still look at the error somewhere else if I wouldn't test the code on one of the problem computer.

                      Anyway, thank you for the clarification.

                      JonBJ 1 Reply Last reply
                      0
                      • L Lati

                        @fcarney

                        Obviously, the person who wrote the library didn't know this (to be honest, I didn't know it as well, I have never used getenv). And this is how bugs happened, right? :)

                        But interesting thing is that there is no sign about the crash and no-one had an idea about it (including me). I would still look at the error somewhere else if I wouldn't test the code on one of the problem computer.

                        Anyway, thank you for the clarification.

                        JonBJ Offline
                        JonBJ Offline
                        JonB
                        wrote on last edited by
                        #39

                        @Lati
                        For the record, getenv() has been in the C runtime libraries since the 1970s(!) There has to be a way for it to tell you that the selected environment variable does not exist (without crashing!), and that is of course by returning 0. I and millions of other coders have been using that behaviour ever since :)

                        In your case, whoever wrote the code which does not check for that will doubtless have been working in an environment where that ProgramXROOT variable did always exist, and hence never witnessed the unanticipated behaviour.

                        OOI, how have you resolved this? Did you actually change that library's code to fix and recompile, or have you just told your end users they must have that environment variable defined?

                        jsulmJ L 2 Replies Last reply
                        1
                        • JonBJ JonB

                          @Lati
                          For the record, getenv() has been in the C runtime libraries since the 1970s(!) There has to be a way for it to tell you that the selected environment variable does not exist (without crashing!), and that is of course by returning 0. I and millions of other coders have been using that behaviour ever since :)

                          In your case, whoever wrote the code which does not check for that will doubtless have been working in an environment where that ProgramXROOT variable did always exist, and hence never witnessed the unanticipated behaviour.

                          OOI, how have you resolved this? Did you actually change that library's code to fix and recompile, or have you just told your end users they must have that environment variable defined?

                          jsulmJ Offline
                          jsulmJ Offline
                          jsulm
                          Lifetime Qt Champion
                          wrote on last edited by
                          #40

                          @JonB @Lati
                          Yes, "man getenv" shows this:
                          "RETURN VALUE
                          The getenv() function returns a pointer to the value in the environment, or NULL if there is no match."
                          It is the responsibility of the caller to check its return value and reacting accordingly...

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

                          1 Reply Last reply
                          2
                          • JonBJ JonB

                            @Lati
                            For the record, getenv() has been in the C runtime libraries since the 1970s(!) There has to be a way for it to tell you that the selected environment variable does not exist (without crashing!), and that is of course by returning 0. I and millions of other coders have been using that behaviour ever since :)

                            In your case, whoever wrote the code which does not check for that will doubtless have been working in an environment where that ProgramXROOT variable did always exist, and hence never witnessed the unanticipated behaviour.

                            OOI, how have you resolved this? Did you actually change that library's code to fix and recompile, or have you just told your end users they must have that environment variable defined?

                            L Offline
                            L Offline
                            Lati
                            wrote on last edited by Lati
                            #41

                            @JonB I am not one of that millions of coders (or even if I used it, I never had problems).

                            In the code, I replaced the getenv part using _dupenv_s as following (which will be valid with the next release):

                                char* buf = nullptr;
                                size_t sz = 0;
                                if (_dupenv_s(&buf, &sz, "programXROOT") == 0 && buf != nullptr)
                                {
                                    programXRootDirectory = buf;
                                    free(buf);
                                }
                                else
                                {
                                    QMessageBox msgBox;
                                    msgBox.setText("Environmental variable is missing!");
                                    msgBox.exec();
                                }
                            

                            Actually, after installation of this application, user has to create this environmental variable before starting the application. And seems like all the users have created the variable and there was no issue so far. But if a user would forget about this, it would be nightmare to find out the reason.

                            JonBJ 1 Reply Last reply
                            0
                            • L Lati

                              @JonB I am not one of that millions of coders (or even if I used it, I never had problems).

                              In the code, I replaced the getenv part using _dupenv_s as following (which will be valid with the next release):

                                  char* buf = nullptr;
                                  size_t sz = 0;
                                  if (_dupenv_s(&buf, &sz, "programXROOT") == 0 && buf != nullptr)
                                  {
                                      programXRootDirectory = buf;
                                      free(buf);
                                  }
                                  else
                                  {
                                      QMessageBox msgBox;
                                      msgBox.setText("Environmental variable is missing!");
                                      msgBox.exec();
                                  }
                              

                              Actually, after installation of this application, user has to create this environmental variable before starting the application. And seems like all the users have created the variable and there was no issue so far. But if a user would forget about this, it would be nightmare to find out the reason.

                              JonBJ Offline
                              JonBJ Offline
                              JonB
                              wrote on last edited by JonB
                              #42

                              @Lati
                              Again for the record, the _dupenv_s (which btw is MSVC-only) you mention has nothing to do with the issue you are talking about. The extra parameters it takes are to do with copying the value, if found, into your own buffer. If it's not found:

                              If the variable is not found, then buffer is set to NULL, numberOfElements is set to 0, and the return value is 0 because this situation is not considered to be an error condition.

                              So the issue will rear its head again if code later tries to dereference the buf from the &buf passed in. Just as with the return result from getenv().

                              Purely as a by-the-by, I presume you are aware in the code you show (which perhaps is only intended as an example):

                                      programXRootDirectory = buf;
                                      free(buf);
                              

                              This would not be a good idea --- programXRootDirectory is left pointing to freed memory! You'll get a different error/crash/behaviour if you then dereference that :)

                              1 Reply Last reply
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