I guess the question says it all, but, what happens if someone closes a c++ console app? As in, clicks the "x" in the top corner. Does it instantly close? Does it throw some sort of exception? Is it undefined behavior?
Closing a c++ console app with the "x" in the top corner throws an CTRL_CLOSE_EVENT which you could catch and process if you set a control handler using the SetConsoleCtrlHandler function. In there you could override the close functionality and perform whatever you wished to do, and then optionally still perform the default behavior.
I imagine that the console process just gets unceremoniously killed by the OS. If you want to trap this event and do something it looks like the SetConsoleCtrlHandler function is the way to do it.
See also:
How to handle a ctrl-break signal in a command line interface
Console Event Handling
On Linux and other Unix systems, the console runs as a separate process. As you close the shell, it sends the SIGHUP signal to the currently active process or processes that are not executed in the background. If the programmer does not handle it, the process simply terminates. The same signal is sent if you close the SSH session with a terminal and an active process.
SIGBREAK is raised on Windows.
Related
Some programs pop "Save before exit?" message when terminating.
And I wonder if I can implement this with C++ console application.
So I tried some standard functions like signal and atexit.
But they only work when:
main() returns (atexit)
sending interrupt through Ctrl+C (on Windows, SIGINT)
an error occurs (SIGABRT)
So yeah, how? Is it only possible with GUI application?
In comments, you said:
I want exit events to happen when that 'X' button is pressed(On windows).
That's part of GUI I guess.
Than what kind of request is sent to program when the exit button of the console is pressed?
You can use SetConsoleCtrlHandler() to register a user defined callback function that receives a CTRL_CLOSE_EVENT notification when the console window is closed:
A signal that the system sends to all processes attached to a console when the user closes the console (either by clicking Close on the console window's window menu, or by clicking the End Task button command from Task Manager).
I am working on a TCP server that I'm developing on CLion under Windows 10.
I would like my program to be able to end properly, when I click on "stop" my program. I thought CLion was sending a signal, but after trying to catch them all, it looks like it does not.
So my question is, how does CLion stop running the program? Is it possible to detect it within the program?
Thank you in advance.
I found my answer here.
According to this link, signals are actually used :
Click this button to terminate the current process externally by means
of the standard shutdown script. Clicking the button once invokes soft
kill allowing the application to catch the SIGINT event and perform
graceful termination (on Windows, the Ctrl+C event is emulated). After
the button is clicked once, it is replaced with icon run tool window
kill indicating that subsequent click will lead to force termination
of the application, e.g. on Unix SIGKILL is sent.
I have just got this problem for a few days. Before, I've always thought that letting the program exit by returning from main and clicking close the console window is the same way to end the program.
However, I've found that they are different. Since my program opens a camera which is an object. And closing the console windows does not destroy or clean up the object. So the next time I have error to open the camera again
I just need a confirm if this is true?
Then why only until now I can see the problem?
Closing a console window in Windows, kills the running program (or stack of running programs). Unless it has registered a handler for this event, it gets no chance to clean up. If you want solution, register a handler.
Hm, consulting the documentation, wait a few secs…
OK, look up SetConsoleCtrlHandler.
Closing a running console application will kill the process, not giving you the chance for any clean up code. I guess you could hook a windows message loop to trap the WM_CLOSE message and do proper cleanup, but at the end of the day, you just shouldn't kill the process.
Using the Win32 API in Visual C++, I want to create a program under the Windows subsystem that allocates a console with AllocConsole and writes to it with WriteConsole. However, if the user closes the console, the process should keep running in the background. As it stands, I can't get that to happen. When X is pressed on the console title bar, the process exits.
Is there any particular way of doing this?
Thanks in advance!
The key is to respond to the Console Control Event that is raised when the user attempts to close the console. You can then call FreeConsole to detach your program from the console, and let the console be destroyed. That should keep your program running.
Additional info:
If the process is terminated when the HandlerRoutine exits, then my suggestion didn't work as expected. If that's the case, then you might have a problem. You can try hooking the SC_CLOSE system message, and do the FreeConsole there before passing the message on. That might work, although I don't know what it'll do if the user presses Ctrl+C or Ctrl+Break.
The problem is that the control handler exits the process. It might be that calling FreeConsole in the HandlerRoutine is too late.
I am using SDL for an OpenGL application, running on Linux. My problem is that SDL is catching SIGINT and ignoring it. This is a pain because I am developing through a screen session, and I can't kill the running program with CTRL-C (the program the computer is running on is connected to a projector and has no input devices).
Is there a flag or something I can pass to SDL so that it does not capture SIGINT? I really just want the program to stop when it receives the signal (ie when I press ctrl-c).
Ctrl-C at the console generates an SDL_QUIT event. You can watch for this event using SDL_PollEvent or SDL_WaitEvent, and exit (cleanly) when it is detected.
Note that other actions can generate an SDL_QUIT event (e.g. attempting to close your main window via the window manager).
I have found an answer:
The SDL_INIT_NOPARACHUTE flag will capture fatal signals so that SDL can clean up after itself. It works for things like SIGSEGV, but apparently SIGINT is not fatal enough.
My solution is to reset the signal handler to SIGINT after SDL has been initialised:
SDL_Init(SDL_INIT_VIDEO | SDL_INIT_NOPARACHUTE);
signal(SIGINT, SIG_DFL);
Thanks Cache for you input, it put me on the right track.
Michael
In SDL_quit.c, there's a check for hints to determine whether the signal handlers should not be used in SDL_QuitInit(). Not sure if this existed in older versions when the original question was asked, but may be handy for those coming here fresh.
Just tested on my Windows application, I can now receive all signals properly again, using:
SDL_SetHint(SDL_HINT_NO_SIGNAL_HANDLERS, "1");
SDL_Init(...);
Passing the SDL_INIT_NOPARACHUTE initialisation flag to SDL_Init "Prevents SDL from catching fatal signals".
See: http://www.libsdl.org/cgi/docwiki.cgi/SDL_Init
If you're not actually using an event loop for some reason, you can use SDL_QuitRequested in your "poll stuff" loop.