Hi,
On Friday 10 January 2014, 程梁 wrote:
> Following is my example code:
>
> int main(int argc, char *argv[])
> {
> QApplication app(argc, argv);
> QLabel *label = new QLabel;
> label->show();
> return app.exec();
> }
>
> label should live longer than app so there might be unsafe because any
> QPaintDevice must have a QApplication. I'm not sure am I right? That's
> all main widgets should create on stack in main() in order to avoid such
> things? Or there is no such requirement?
In this particular case it should not present a problem because of the
mechanism how app.exec() returns: when the last visible widget is closed the
main event loop (i.e. app.exec()) exits and main ends (also killing the app
object). Meaning: all widgets are already invisible. Otherwise, if it is
killed with qApp->close(), the last action that QApplication takes is to
unmap (close) all windows.
Of course the code would be cleaner if you told the QLabel to kill itself on
closure:
label->setAttribute(Qt::WA_DeleteOnClose);
Konrad
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