Situation

I am developing a program that combines GUI and console output.

The program converts the input image into a monochromatic BMP.

If the argument is empty, the program will pop up a file dialog to let the user select an image.

Off-topic Note: monochromatic ≠ single channel (or grayscale). Monochromatic means that the image is either black or white and has only one bit per pixel.

For simplicity, I created a WinForm project and added some logic to the Program.cs which includes some Console.WriteLine() statements.

Problem

However, when I run the program in terminal, the console output is not shown.

Attempt

I tried the following solution:

Program.cs

using System.Runtime.InteropServices;

internal static class Program 
{
    [STAThread]
    static void Main(string[] args)
    {
        AllocConsole();
        // ...
    }
}

[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool AllocConsole();

This actually works, but there’s a problem: what it actually does is to create a new console window. What I want is to print the output to the terminal window where I ran the program.

Solution

Finally I found a working solution which is way too simple:
Go to the project properties, and change the output type to Console Application.

Or, you can edit the .csproj file and change the OutputType to Exe.

<OutputType>Exe</OutputType> 

It will not break the GUI, and the console output will be shown in the terminal window now.