Why does closing a console that was started with AllocConsole cause my whole application to exit? Can I change this behavior?

Solution 1:

Ah, yes, this is one of the caveats of using the Windows console subsystem. When the user closes the console window (regardless of how the console was allocated), all of the processes that are attached to the console are terminated. That behavior makes obvious sense for console applications (i.e., those that specifically target the console subsystem, as opposed to standard Windows applications), but it can be a major pain in cases like yours.

The only workaround that I know of is to use the SetConsoleCtrlHandler function, which allows you to register a handler function for Ctrl+C and Ctrl+Break signals, as well as system events like the user closing the console window, the user logging off, or the system shutting down. The documentation says that if you're only interested in ignoring these events, you can pass null for the first argument. For example:

[DllImport("kernel32")]
static extern bool SetConsoleCtrlHandler(HandlerRoutine HandlerRoutine, bool Add);

delegate bool HandlerRoutine(uint dwControlType);

static void Main()
{
    AllocConsole();
    SetConsoleCtrlHandler(null, true);
    while (true) continue;
}

That works perfectly for Ctrl+C and Ctrl+Break signals (which would have otherwise caused your application to terminate as well), but it doesn't work for the one you're asking about, which is the CTRL_CLOSE_EVENT, generated by the system when the user closes the console window.

Honestly, I don't know how to prevent that. Even the sample in the SDK doesn't actually allow you to ignore the CTRL_CLOSE_EVENT. I tried it in a little test app, and it beeps when you close the window and prints the message, but the process still gets terminated.

Perhaps more worryingly, the documentation makes me think it is not possible to prevent this:

The system generates CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, and CTRL_SHUTDOWN_EVENT signals when the user closes the console, logs off, or shuts down the system so that the process has an opportunity to clean up before termination. Console functions, or any C run-time functions that call console functions, may not work reliably during processing of any of the three signals mentioned previously. The reason is that some or all of the internal console cleanup routines may have been called before executing the process signal handler.

It's that last sentence that catches my eye. If the console subsystem starts cleaning up after itself immediately in response to the user attempting to close the window, it may not be possible to halt it after the fact.

(At least now you understand the problem. Maybe someone else can come along with a solution!)

Solution 2:

Unfortunately there's nothing you can do to really alter this behaviour.

Console windows are "special" in that they're hosted by another process and do not allow sub-classing. This limits your ability to modify their behaviour.

From what I know, your two options are:

1. Disable the close button altogether. You can do this with the following code fragment:

HWND hwnd = ::GetConsoleWindow();
if (hwnd != NULL)
{
   HMENU hMenu = ::GetSystemMenu(hwnd, FALSE);
   if (hMenu != NULL) DeleteMenu(hMenu, SC_CLOSE, MF_BYCOMMAND);
}

2. Stop using consoles altogether, and implement your own text output solution.

Option #2 is the more complicated option but would provide you the greatest control. I found an article on CodeProject that implements a console-like application using a rich edit control to display the text (rich edit controls have the ability to stream text like the console, so they are well suited to this sort of application).

Solution 3:

On closing the console window obtained using AllocConsole or AttachConsole, the associated process will exit. There is no escape from that.

Prior to Windows Vista, closing the console window would present a confirmation dialogue to the user asking him whether the process should be terminated or not but Windows Vista and later do not provide any such dialogue and the process gets terminated.

One possible solution to work around this is avoiding AttachConsole altogether and achieving the desired functionality through other means.

For instance in the case described by OP, console window was needed to output some text on Console using Console static class.

This can be achieved very easily using inter-process communication. For example a console application can be developed to act as an echo server

namespace EchoServer
{
    public class PipeServer
    {
        public static void Main()
        {
            var pipeServer = new NamedPipeServerStream(@"Com.MyDomain.EchoServer.PipeServer", PipeDirection.In);
            pipeServer.WaitForConnection();

            StreamReader reader = new StreamReader(pipeServer);

            try
            {
                int i = 0;
                while (i >= 0)
                {
                    i = reader.Read();
                    if (i >= 0)
                    {
                        Console.Write(Convert.ToChar(i));
                    }
                }
            }
            catch (IOException)
            {
                //error handling code here
            }
            finally
            {
                pipeServer.Close();
            }
        }
    }
} 

and then instead of allocating/attaching a console to the current application, the echo server can be started from within the application and Console's output stream can be redirected to write to the pipe server.

class Program
{
    private static NamedPipeClientStream _pipeClient;

    static void Main(string[] args)
    {
        //Current application is a Win32 application without any console window
        var processStartInfo = new ProcessStartInfo("echoserver.exe");

        Process serverProcess = new Process {StartInfo = processStartInfo};
        serverProcess.Start();

        _pipeClient = new NamedPipeClientStream(".", @"Com.MyDomain.EchoServer.PipeServer", PipeDirection.Out, PipeOptions.None);
        _pipeClient.Connect();
        StreamWriter writer = new StreamWriter(_pipeClient) {AutoFlush = true};
        Console.SetOut(writer);

        Console.WriteLine("Testing");

        //Do rest of the work. 
        //Also detect that the server has terminated (serverProcess.HasExited) and then close the _pipeClient
        //Also remember to terminate the server process when current process exits, serverProcess.Kill();
        while (true)
            continue;
    }
}

This is just one of the possible solutions. In essence the work around is to allot the console window to its own process so that it can terminate without affecting the parent process.