Destructors not called when I terminate a console app with Ctrl-C
Hello,
on windows, when I enter Ctrl-C while any console app is running, QT-Creator shows a negative exit code, for example -1073741510.
On Linux, I also see a negative return code plus a remark that the application finished unexpectedly. If I set the GUI language to german it says that the application crashed (in german words).
Is that normal or a technical problem? Example source to reproduce:
- int main(int argc, char *argv[]) {
- return app.exec();
- }
I think, it’s fairly impossible to make a mistake in that simple application.
15 replies
When you close your app using CTRL+C, your app.exec() method doesn’t return. Your app is killed by an unix signal called SIGINT [en.wikipedia.org]).
If you’re looking for last second clean-up, you should use QCoreApplication::aboutToQuit [doc.trolltech.com] signal
Thanks for yout hint. I tried it but it does not work under windows, unfortunately. I do not see my debug message from the slot that I assigned to aboutToQuit() and I still get random exit codes when I pres Ctrl-C.
Did I understand you correctly, that it is normal that app.exec() does not return, so the program is simply killed without any cleanup (except that the OS closes file handles ans some other stuff).
Sorry if I couldn’t made myself clear, but aboutToQuit will not work for CTRL+C.
I’ve just tried to say that aboutToQuit is safer for cleanup’s, because I thought you’re trying to do that on destructos.
About your last comment: Afaik yes… However you can watch for unix signals [doc.qt.nokia.com]. There is an interesting thread about it on stackoverflow [stackoverflow.com].
chk if this faq [developer.qt.nokia.com] helps, and if you can take a similar approach to handle CTRL+C
kalle: Ctrl-C does send SIGTERM, not SIGKILL.You can not catch SIGKILL, that one will always kill the application (and is what if send via the command “kill -9 <PID>”).
Afaik no.
SIGTERM is the default signal sent by kill (without -9)
SIGINT is the signal sent by terminal when you press ctrl-c.
http://en.wikipedia.org/wiki/SIGINT_ [en.wikipedia.org])
http://en.wikipedia.org/wiki/SIGTERM [en.wikipedia.org]
[edit: fixed link / chetankjain]
I am already familiar with signal catching under Linux and Im sure that this would be the solution for my question if I would only deveop for Linux. However, Im currently more interested in Windows.
Anyway, the abnormal program termination is not really a problem to me. I just wondered if the error message in QT Creator and the random exit code indicate a problem or if that is normal.
My understanding is now that it is normal to see a abnormal termination warning and a random exit code when I press Ctrl-C because the QCoreApplication.exec() method does not return, so the program does not return a defined exit code.
@danilocesar: Qt applications already handle signals: The nice thing is that the operating system enforces this, so there is no code required in Qt (always the best way to implement anything;-). If the defaults do not work for you, then you can override it. So where is the problem?
What needs to happen when a signal is received is usually platform dependent, so there is little to win by proving an abstraction in Qt.
i have written a console application.
now suppose if i send SIGINT to the application, will it get terminate immediately.??
or it will complete all the pending stuff and then return.??
[EDITED: aboutToQuit signal may help, once the SIGINT is received and event loop returns, this signal will be emitted and clean up can be done in the slot connected to it… right.??]
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