C# – Debugging: Attach to Process for Console App running inside cmd.exe

So, I've written tools with both a GUI and a CLI. The hard part was figuring out which one to open - in our case, though, the CLI version had required parameters, so I just opened the GUI if there weren't any parameters. Then, if they did want a console, call a function that looks something like:

private const int ATTACH_PARENT_PROCESS = -1;
private const int ERROR_INVALID_HANDLE = 6;
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool AttachConsole(int dwProcessId);
[DllImport("kernel32.dll")]
static extern bool AllocConsole();
[DllImport("kernel32.dll")]
static extern bool FreeConsole();

private static bool StartConsole()
{
  if (!AttachConsole(ATTACH_PARENT_PROCESS)) // try connecting to an existing console  
  {  
      if (Marshal.GetLastWin32Error() == ERROR_INVALID_HANDLE) // we don't have a console yet  
      {  
          if (!AllocConsole()) // couldn't create a new console, either  
              return false;  
      }
      else
          return false; // some other error
  }
  return true;
}

Returns whether the console was created. Don't forget to FreeConsole() when you're done!

In our case, of course, if we don't create a console, we create a GUI. It'd be just as easy to create either a console or no UI, though.

EDIT: That totally didn't answer the question in the edit that wasn't there when I started writing that, of course. Other than that our hack was just checking whether it was called with command-line parameters or not.

Use Console.KeyAvailable so that you only call ReadKey when you know it won't block:

Console.WriteLine("Press ESC to stop");
do {
    while (! Console.KeyAvailable) {
        // Do something
   }       
} while (Console.ReadKey(true).Key != ConsoleKey.Escape);