C# Hello World (NixOS)

Nov. 11, 2022, edited on Mar. 22, 2023

Install Mono And .Net SDK

C# requires .Net as runtime to execute, so we need install .Net SDK first:

nix-shell -p dotnetCorePackages.sdk_6_0 mono

Hello World

The structure of C# source looks like this, it uses .cs as file extensions.

// hello_world.cs
using System;

namespace com.example {
    class HelloWorld {
        static void Main(string[] args) {
            Console.WriteLine("Hello World");
        }
    }
}

The writing style is similar to Java and C++:

The using is used for import a namespace
The entry function is Main, with similar writing style in Java.
The Console.WriteLine method just likes the printf function in C. This method is import from System namespace.

Compile and Execute

Using csc to compile source code after installed mono packages:

csc hello_world.cs

After compile done, it will generate hello_world.exe in current directory:

$ file hello_world.exe 
hello_world.exe: PE32 executable (console) Intel 80386 Mono/.Net assembly, for MS Windows

Run Hello World:

$ mono hello_world.exe
Hello World

VSCode Extensions

We need to install two extensions:

C#
Mono Debug

The debug functionality in C# extensions only available in Windows, In Linux we need to install Mono Debug extensions for Debug. The flowing Nix expression describe how to install those extensions to system:

environment.systemPackages = with pkgs; [
  (vscode-with-extensions.override {
    vscode = vscodium;
    vscodeExtensions = with vscode-extensions; [
      vscode-extensions.ms-dotnettools.csharp
    ] ++ pkgs.vscode-utils.extensionsFromVscodeMarketplace [
      {
        name = "mono-debug";
        publisher = "ms-vscode";
        version = "0.16.3";
        sha256 = "sha256-6IU8aP4FQVbEMZAgssGiyqM+PAbwipxou5Wk3Q2mjZg=";
      }
    ];
  })
];

Debug

Mainly refer to this posts in CSDN: https://blog.csdn.net/qinyuanpei/article/details/57419539

.vscode/tasks.json: Create a task to compile c# source with -debug mode:

{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build", // A label to identify task
            "command": "csc", // Run `csc -debug ${file}`
            "type": "shell",
            "args": [
                "-debug",
                "${file}"     // ${file} will be replaced to the file to compile
            ],
        }
    ]
}

.vscode/launch.json: Execute program and start debugger by Mono Debug extensions:

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "mono",
            "name": "Launch",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}.exe", 
            "cwd": "${workspaceFolder}",
            "preLaunchTask": "build",
            "runtimeExecutable": "mono",
            "console": "integratedTerminal",
        }
    ]
}

If Vscode failed and tips with can’t found Mono Runtime, just set up the runtimeExecutable field to absolute path of mono in previous configuration.

Now we can add breakpoint and press F5 to debugging: