c - How do I gracefully exit an X11 event loop?

Question

Almost every tutorial I find tells me to do this for my event loop:

XEvent event;

while (true)
{
    XNextEvent(display, &event);

    switch (event.type)
    {
        case Expose:
            printf("Expose
");
            break;

        default:
            break;
    }
}

However, clicking the X to close the program results in this message.

XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 10 requests (10 known processed) with 0 events remaining.

It is indeed strange to me that the examples suggest using an infinite loop. That doesn't sound natural, and my other X11 programs don't do that. So I searched around. I found out how to capture the window close event.

Atom wmDeleteMessage = XInternAtom(mDisplay, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, window, &wmDeleteMessage, 1);

XEvent event;
bool running = true;

while (running)
{
    XNextEvent(display, &event);

    switch (event.type)
    {
        case Expose:
            printf("Expose
");
            break;

        case ClientMessage:
            if (event.xclient.data.l[0] == wmDeleteMessage)
                running = false;
            break;

        default:
            break;
    }
}

That works. It exits without errors. ... But I refuse to believe this is the normal way to do things. I mean, is this the only way to properly exit an X11 app? It seems like a lot of work just to capture the close event. How do I make a 'proper' event loop? Why is the close event so deeply buried? What am I missing?

question from:https://stackoverflow.com/questions/10792361/how-do-i-gracefully-exit-an-x11-event-loop

Answer 1

There are no such things as "exit button" or "application" or "close event" in X11. This is by design.

Window decorations, exit buttons and many the other things we depend upon are not built into X11. They are implemented on top of the core X11 instead. The name of the particular set of conventions responsible for wmDeleteMessage is ICCCM, look it up.

Xlib only deals with the core X11 protocol. No built-in close event there.

There are toolkits that make dealing with ICCCM and all other things that are not built into X11 easier (GTK, wxWindows, Qt, ...) You probably want to use one of those.