[android] Mobile C

September 18, 2017 Leave a comment

If you want to develop a C or Python program on your Android device, try Mobile C. Write your program, press a button, and it’s compiled (or interpreted) and executed. Several languages are supported: C, C++ 11, Python 3, JavaScript, Lua.

Categories: android, python Tags:

web server on localhost

September 14, 2017 Leave a comment

I wanted to share a 3.3 GB big zip file with my students.

I love Python, so I chose this simple trick: “python3 -m http.server“. It starts a web server and makes the content of the current directory available. I shared the URL with my students (10 people) and they started to download the big file at the same time. And it turned out that Python was not a good choice here since only 1 person could download the file and the others had to wait. This solution is single-threaded :(

I hate Node.js but this time it provided the winning solution. Node.js’s async nature was perfect for the job, it could serve several clients. The download rate was not super fast, but at least it worked (and it worked well).

The following tip is from here.

$ sudo npm install http-server -g
[sudo] password for jabba: 
/trash/opt/node-v5.1.0-linux-x64/bin/http-server -> /trash/opt/node-v5.1.0-linux-x64/lib/node_modules/http-server/bin/http-server
/trash/opt/node-v5.1.0-linux-x64/bin/hs -> /trash/opt/node-v5.1.0-linux-x64/lib/node_modules/http-server/bin/http-server

I couldn’t launch it with “http-server“, but the full path “/trash/opt/node-v5.1.0-linux-x64/lib/node_modules/http-server/bin/http-server” did the trick.

Categories: python Tags: , ,

Outgoing port tester

August 31, 2017 Leave a comment

If you want to test if you can make outgoing port connections, use this web service: http://portquiz.net . To specify a port (e.g. 8080), use the address http://portquiz.net:8080 . If the page does not load and your request eventually times out, outgoing traffic to the specified port is probably blocked on your local network (check your firewall).

Categories: network Tags: , ,

[manjaro] Make C# debugger work in Visual Studio Code

Under Manjaro / Arch you use Visual Studio Code with the C# extension. Everything works fine except the C# debugger.

I found the solution here: https://github.com/OmniSharp/omnisharp-vscode/issues/1323 . The debugger on Manjaro / Arch is not supported officially, so we need to do some tricks. In VS Code open the user settings and add this line:

"csharp.fallbackDebuggerLinuxRuntimeId": "ubuntu.16.04-x64"

Uninstall the C# extension, restart VS Code, and re-install the C# extension. Open a .cs file and the extension will download some packages, including the debugger for Ubuntu 16.04 (as we specified it in the settings).

However, the *.so files of the Ubuntu debugger rely on a specific version of the package “icu”.

$ cd ~/.vscode/extensions/ms-vscode.csharp-1.11.0/.debugger
$ find *.so -type f | xargs ldd 2> /dev/null | grep not\ found
        liblldb-3.6.so => not found
        libvsdebugeng.so => not found
        libvsbaseservices.so => not found
        libvsbaseservices.so => not found
        libicuuc.so.55 => not found
        libicui18n.so.55 => not found

The last 2 lines are interesting: we need version 55 of the package “icu“. “yaourt icu” revealed that I had version 59 installed, but version 55 can be installed too with “yaourt icu55“. The two versions can co-exist. When installed, restart VS Code and debugging should work now.

The solution was found at https://github.com/OmniSharp/omnisharp-vscode/issues/1323 . A big thanks for starquake.

Categories: csharp, manjaro Tags:

In C#, ++c and c += 1 are not always equivalent

July 2, 2017 1 comment
csharp> char c = 'a'
csharp> ++c
csharp> c += 1
(1,7): error CS0031: Constant value `1' cannot be converted to a `char'
Categories: csharp Tags: ,

Getting started with C# on Linux

June 30, 2017 Leave a comment

I’ve heard lots of good things about C# but I’ve never tried it. I saw some codes and thought “fine, it’s like Java”. As I also have Linux on my primary machine, I was not interested in Microsoft technologies. However, a few years ago .NET Core was open sourced and it reached version 1.0 (now it’s 1.1). It’s a cross platform framework and it works well under Linux too, so I thought it was time to try it. Project Mono has also existed for a long time but .NET Core comes directly from Microsoft.

Under Manjaro, install these packages with yaourt: dotnet, dotnet-cli, dotnet-sdk. We will also try Mono, so install the package mono too. For Ubuntu, see the instructions here: https://www.microsoft.com/net/core#linuxubuntu .

Create a project

Create a folder for holding your C# projects, e.g. ~/CSharpProjects (optional), and create a folder for a sample project (e.g. ~/CSharpProjects/Sample). Enter it, and create a source file called hello.cs with the following content:

using System;
using static System.Console;
using System.Linq;

namespace SampleApp
    class MainClass
        public static void Main(string[] args)
            WriteLine("Hello World!");

Compile with Mono

If you installed Mono, you have the command “csc” (C Sharp Compiler).

$ csc hello.cs
$ mono hello.exe 
Hello World!
$ chmod u+x hello.exe
$ ./hello.exe 
Hello World!

Compile with dotnet

Now let’s use the official command-line tools. You can also delete the file “hello.exe”. I suppose you are in the project’s folder. Issue the following command:

$ dotnet new console

It creates a project file (with extension .csproj), and a sample file called Program.cs . As we already have hello.cs, Program.cs is not needed so simply delete it (leave only one source file, but it doesn’t matter which one). Then,

$ dotnet restore    # installs some necessary packages, using the .csproj project file
Restoring packages for /home/jabba/Dropbox/csharp/Sample/Sample.csproj...
$ dotnet run        # compile and run
Hello World!

The binary output is here: bin/Debug/netcoreapp1.1/Sample.dll . If you use the command “dotnet”, you get a .dll, not an .exe . However, it can be executed:

$ cd bin/Debug/netcoreapp1.1
$ ./Sample.dll 
Hello World!
$ dotnet Sample.dll 
Hello World!

When you are ready with the development and ready for deployment, issue this command:

$ dotnet publish
Microsoft (R) Build Engine version 15.1.1012.6693
Copyright (C) Microsoft Corporation. All rights reserved.

  Sample -> /home/jabba/Dropbox/csharp/Sample/bin/Debug/netcoreapp1.1/Sample.dll

According to the docs, “dotnet publish compiles the application, reads through its dependencies specified in the project file, and publishes the resulting set of files to a directory. The dotnet publish command’s output is ready for deployment to a hosting system (for example, a server, PC, Mac, laptop) for execution and is the only officially supported way to prepare the application for deployment.”


Mono ships a REPL too called “csharp”.

$ csharp 
Mono C# Shell, type "help;" for help

Enter statements below.
csharp> 1+1

Visual Studio Code support

Programming C# with VS Code is a joy. When you open a .cs file, the editor offers immediately to install the official C# extension. In order to execute a program, install the Code Runner extension. Then, add the following lines to your user settings:

    "code-runner.executorMap": {
        // "python": "python3",
        // "csharp": "echo '# calling mono\n' && cd $dir && csc /nologo $fileName && mono $dir$fileNameWithoutExt.exe",
        "csharp": "echo '# calling dotnet run\n' && dotnet run"

Choose either Mono or dotnet.


If you have Linux, no problem, you can try C#. I started to play with it yesterday, but I like it. It seems a saner language than Java :)