Create a cmd window and write to it from C# application

Question

I am developing a C# component for Grasshopper for Rhino. As I am running some pretty heavy iterative analysis I would like to output results continuously to a cmd window ju

Answer 1

Your approach is wrong: You currently don't write to a console window. Instead you created a process by starting cmd.exe and write to the standard input pipe of that process. cmd.exe is not aware of that. It's not the same as typing in a console via your keyboard, and even that can have strange effects.
Imagine you output a new line character, so cmd.exe might try to "execute" what you output before as a command.

The correct way is to invoke AllocConsole. With this call you can create a console window for your process and use it simply via Console.WriteLine().

When you finished your work and logging, you'll eventually need to close and free this console again via FreeConsole.

So import these two native methods:

internal sealed class NativeMethods
{
    [DllImport("kernel32.dll")]
    public static extern bool AllocConsole();

    [DllImport("kernel32.dll")]
    public static extern bool FreeConsole();
}

And use them in your code:

NativeMethods.AllocConsole();

// start work
Console.WriteLine("log messages...");

// finished work

NativeMethods.FreeConsole();

---

Note that FreeConsole() will close the console window, so all your log messages get lost. And a console only has a so large buffer and you can't scroll back to older messages if the leave the buffer.

So it may be a better idea to simply write your log messages into a file that you can analyze later.

Answer 2

Create a Console App in Visual Studio. In VS 2017 it looks like this (on the start page):

Console apps open a command console automatically. Then you can write to it with

Console.WriteLine("hello");

The console closes automatically when the program terminates. So make sure to call Console.ReadKey(); at the end, if you want to keep it open.