Good afternoon everyone, I would like to know if it is customary to delete global variables on the destructor in qt? For example: <<<<<< Global.h Extern MainWindow *newWindow; Extern QWidget *newWidget; Global.cpp MainWindow *newWindow; QWidget *newWidget; <<<<<< MainWindow.h class MainWindow : public QObject { …. MainWindow(); ~MainWindow(); }; MainWindow.cpp MainWindow::MainWindow() { newWidget = new QWidget; } MainWindow::~MainWindow() { delete newWidget; newWidget = nullptr; } <<<<<<< Int main() { QApplication a; newWindow = new MainWindow; return a.exec(); } Is it done the way I wrote above? And how do I clear the memory for newWindow?

But it depends on what you do with with newWidget after you created it via newWindow = new MainWindow; in MainWindow::MainWindow() . Do you really do nothing with it, as you show? It is true that if your code is exactly as you show, nothing more, then, yes, you should delete newWidget; in MainWindow::~MainWindow() . On the other hand, since you delete newWindow immediately after creating it and before calling a.exec() your application has no windows at all. Returning from a.exec() does not "clear any memory" or do anything itself. If the intention is to create a main window, show it, run the UI and then exit (e.g. when the user closes the window) then from C++ most people would create the main window on the stack rather than heap / new so no delete ing: int main() { QApplication a; MainWindow newWindow; newWindow.show(); return a.exec(); }

You don't delete the Mainwindow instance anywhere. Don't use global variables - none of them is needed in your example.Or properly clean them up after usage.

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Freeing up memory for global variables

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Christian Ehrlicher
Lifetime Qt Champion
wrote on last edited by

#21

A global scoped pointer to a QObject will be destroyed after QCoreApplication is gone so it will likely crash. Fix your code and don't use global variables.
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