How to use ConsoleCancelEventHandler several times

Question

I've been busy coding a application that functions as a frontend: it has a GUI taking command line options with buttons and things like that and passing them to a command line .exe. It uses the console of the application to display the output of the command line app. This works fine, but when using Ctrl+C or trying to close the console window, the GUI closes too, which is not really what I want. However, letting the program output with it's own console is not possible because it batch-processes files and every file would pop up it's own console.

The program is written in C++ with MSVC 2012 and uses .NET. I tried Console::CancelKeyPress to at least get Ctrl+C behave as I want it to (stop the command-line app but not the GUI) but have some trouble with this.

My code

private: System::Void OnCancelKeyPressed(System::Object^  sender, System::ConsoleCancelEventArgs^  e) {
         e->Cancel = true;
     }
private: System::Void GetConsoleReady() {
         COORD c;
         FreeConsole();
         AllocConsole();
         c.X = 80; c.Y = 8000;
         SetConsoleScreenBufferSize(GetStdHandle(STD_OUTPUT_HANDLE),c);
         Console::Clear();
         Console::TreatControlCAsInput = false;
         Console::CancelKeyPress += 
             gcnew ConsoleCancelEventHandler(this, &Form1::OnCancelKeyPressed);  
     }

This gets called every time a user tries to run a batch of files to process. After running the batch, the console is released with FreeConsole(). The first time it works nice and using Ctrl+C kills the command line app but the processing in the GUI continues, running other commands and finally using FreeConsole(). However, when trying to do this a second time, it kills the GUI as well. I tried to add this before adding the new event to remove the previous event

             Console::CancelKeyPress -= 
             gcnew ConsoleCancelEventHandler(this, &Form1::OnCancelKeyPressed);

But somehow that raises an error on adding the handler, but only the second time: An unhandled exception of type 'System.IO.IOException' occurred in mscorlib.dll, Additional information: De parameter is onjuist.

That last part is Dutch for 'wrong argument', and the debugger says it chokes on readding the ConsoleCancelEventHandler.

If I try to add the event handler only once by adding it when loading of the form it does nothing.

What is going on here?

The console runs in the same process context as the GUI. So any issues or uncaught exceptions will terminate the entire application. That's why you see the GUI as well getting closed. Could you post entire code? Also one solution would be to spawn a new process for every batch file, which will not affect the GUI app to be closed unexpectedly..../ — Rahul Sundar, Apr 29 '13 at 20:27

score 0 · Answer 1 · edited May 23 '17 at 10:31

Have you considered running the batch in a different process? You can then display the output of the batch process by reading from the stdout (and stderror) of the spawned process.

If you are using .net then take a look at Process.RedirectStandardOutput (example here Capturing console output from a .NET application (C#)).

If you hide the spawned process then there is no way for the user to interact with it / close it. Your main application remains in complete control and there are no issues with ctrl-c etc.

How to use ConsoleCancelEventHandler several times

1 Answers1

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