My earlier work in C, C++ and C#

My earlier work in C, C++ and C#

Posted on by David

Cplus.About.com screenshotThe tutorials I wrote on C++ and C# on cplus.about.com between 2006 and 2013 are all a bit dated now. Both languages have been updated several times since 2013 when I stopped writing for About.com. But thanks to the Wayback machine you can view all of my work from the early stages in Mid 2006 to the finish in July 2013.  I owe the copyright to this material so I can reuse it as I wish.

On this page, there’s an index to 43 C tutorials, most written by me.  So as a little side task, I’m downloading these, cleaning them up, fixing the odd error and adding them to this website via the Tutorials page. Some but not all are also available on the ThoughtCo website which is the reinvention of About.com.

Ironically I got better at writing for them towards the end. About.com had been very successful back in the late 90s when the web was still fairly new but could never sustain that and declined more or less from the year 2000. I think the highest daily viewing figure I ever got was 12,000 pages but some of the others (particularly Southern Cooking) got in the millions.

I recommend you visit archive.org earlier in the day as it slows up a bit once the USA wakes up typically around 1.00 PM (GMT). Given the volume of stuff it stores, it is a totally amazing place.

An example of what you can do with MonoGame

An example of what you can do with MonoGame

Posted on by David

OpenVIII screenshotMonoGame is not just for mobile, as I’ve been doing. Open VIII is a Final Fantasy VIII game engine written in C#/MonoGame and currently works on Windows and Linux (not sure about Mac). Other games in the series have been ported to other platforms but not FFVIII, so that’s why the project was started.

The instructions for Open VIII on Windows suggest Visual Studio 2017 but I imagine 2019 might also work as MonoGame 3.8 has templates for it.  As the project says “OpenVIII is an open-source complete Final Fantasy VIII game engine rewrite from scratch powered in OpenGL making it possible to play the vanilla game on wide variety of platforms including Windows 32/64 bit, Linux 32/64 bit and even mobile!”

As with virtually all open source reimplementations, you will have to provide your own game assets such as images and sound. You can do this apparently by buying the original game on Steam. I took a look and sure enough it’s there and there’s an official remastering by Square Enix. I’m not sure why the Steam search brings up FF VII as well but hey that’s search for you… I’ve added a permanent link to the C#/MonoGame links page.

Steam Final Fantasy VIII

Adding Security to Web apps and Games

Adding Security to Web apps and Games

Posted on by David
Security
Image by Darwin Laganzon from Pixabay

Because I’m developing a server game, data has to flow in both directions. That means it might be read (by ‘tapping’ e.g. using utilities like WireShark) or maybe even spoofed. Obviously this would be a bad thing.

Now I’m obviously not going to say how exactly I plan to protect it. Here are a few ideas.

  1. Encrypt all data. I already do this with an SSL certificate. Apple for example block network connections that aren’t secured.
  2. Include checksums and other ways of checking that the data originated from where it purported to. A poor way of doing this would be to always include a constant value and check for its presence. The idea is good but if someone managed to disassemble an app, they might spot it and it would be game over. The principle is sound but not a constant value.
  3. I like the idea of a time based constant but it needs careful implementation. The idea is that every hour say a new constant is calculated. Now there are several issues with this: how do you derive the constant so that the server and mobile apps know what constants should be? One way would be a pseudo random number generator and there are many algorithms. So long as both client and server (which are programmed in different languages) can manage this then that’ is not bad. Another issue is “time dislocation”. My mobile and server may not be exactly in sync. It might only be a fraction of a second or maybe longer if they are on different time zones.  One way round this is to keep the last say two or three values and check not jut the current one but the one before that as well.  We’re not bothered about the time so much as when the hour changes.
  4. Or a simpler method, just have a list of constant values. And an index which is incremented every hour. It wraps round at the end. This is virtually the same as 3. but without the pseudo random number generator.
  5. Include a secure hash of the main data. This is like a digital certificate created from a document. It guarantees that the document hasn’t been tampered with because the certificate is created from the contents of the document. The only thing here is, the data must include a value from 3 or 4 to verify the document so a spoofer doesn’t just send their own data and a secure hash of that!

 

Adding an SSL Cert

Adding an SSL Cert

Posted on by David

SSL connectionThese days, if you have a website or even a game server then you probably should have an SSL (or TLS to be more precise) certificate. Have you heard of telnet? It’s an old protocol that allows you to connect to a remote computer and issue commands. Do you know why you don’t hear of it any more? Because it was designed for an era where hackers didn’t spend all their time attempting to compromise computers. Telnet, like FTP has a flaw. Passwords and login details are sent in the clear. Not hashed, or encrypted.

Why don’t I use SSH to connect to it? I do. SSH has more functionality than SSL and is very good for encrypting remote connections. SSL needs a certificate, whereas SSH doesn’t but many think you should use a SSH certificate as a substitute for username/password and I intend to. If you’re not sure of the technical differences between SSL and SSH, this article isn’t a bad place.

So today I paid for an SSL certificate. I’d pointed a domain I had handy to the vps a few days ago, to give DNS a chance to settle, (24 hours max but usually much less) paid £20 for five years of SSL cert and installed it today. Thankfully, virtualmin which I use for configuring the server makes it straightforward to request a SSL by generating the CSR (Certificate Request an Private Key) . This blog uses an SSL cert from the same place (CheapSSL). Despite the low price the certificates are very good.

Although the world won’t see what the cert is protecting, you almost have to have them nowadays. This is for the connection between smartphone and server. As I found today, Apple is ramping up security and Google is doing the same. I have iOS 14 on my iPhone (upgraded yesterday) and it refused to connect to WiFi in my local coffeeshop. Their certificate doesn’t expire for another month but I suspect it is now over 398 days old. As far as Apple is concerned, that certificate is past its use by date. This is Apple’s new policy since earlier this year. My wife’s iPhone, still on iOS 13 connected quite happily.

For those who have bought a multi-year certificate as I have today, it just means you have to generate another CSR and install a newer certificate once every 400 days or so. I’ve started taking screenshots of the details so I get them correct! I believe Google is moving to this 398 day maximum as well.

So the commands from smartphone to game server are now sent over https and encrypted in flight as are the results. It’s one less thing to worry about.

 

 

Quake II – still a favourite

Quake II – still a favourite

Posted on by David

Quake II screenshotOh I do play much newer games such as Far Cry 5 which I’ve completed recently but Quake II was a favourite of mine back in 1997 when I bought it. I’m more of a Quake than a Doom person. Unfortunately for me, my then PC couldn’t run it. It was only two years old as well.  But I got a new PC in 1998 and that played it just fine. I’m not saying I’m a saddo but I can play it through on the hardest level without losing a life.

The reason I mention it because of an article I came across that described the different ID Tech Game engines and the games made with each engine. All have been open sourced (Up to ID Tech 4). Quake II was written using the ID Tech 2 engine itself written in C and assembler.

For some reason the link to Quake II source code is wrong in that article but you can find it on GitHub. In one of 18 of ID Tech’s 18 repositories there.

If you are interested in downloading and trying to understand the Quake II source code, I strongly recommend you read Fabien Sangard’s walkthough of the code.

How to measure the area of a circle

How to measure the area of a circle

Posted on by David

Odd ShapesWell if you remember maths (or math for US readers), you’ll know that the area of a circle is pi X r X r where r is the radius and pi is that 3.14159 number.

But what if you are given a weird shape instead of a circle? Like some of those in the picture.

There’s a method called Monte Carlo because of the casino there. In effect you simulate throwing darts at the shape (say printed out and stuck on the wall). You throw thousands or millions of darts and count how many hit the particular shape and how many darts were thrown in total. You only count those that hit the rectangular paper; those that miss it don’t count.

Then you divide the number of hits by the number thrown, multiply it by the width and height of the picture (which is rectangular or square) and that is a close approximation to the area. In more advanced ,maths/math, this method is sometimes used to calculate the integral of a function. The integral is the area under the function. Some complicated functions are particularly hard to integrate, so using a Monte Carlo method can solve it for you.

I’ll publish a C program to run Monte Carlo on an image in a day or two.

An alternative way of measuring the area is by using recursion. I discussed it in this article Using recursive fill to count maps.

C11 and C17 support in MSVC

C11 and C17 support in MSVC

Posted on by David

 

The letter C
Image by Peggy und Marco Lachmann-Anke from Pixabay

Microsoft have announced that they will be supporting both C11 and C17 in Visual Studio 2019 version 16.8 Preview 3. All the required features but not optional features and not VLAs (Variable Length Arrays) which is considered unsafe.

One of the complaints has been that Microsoft always prioritised C++ over C for many years. C was supported inasmuch as it was needed for C++. Until fairly recently C++ was a superset of C and you could compile C program as C++. Just change the extension to .cpp.

That said, I will probably continue to write C code as C99 for now and take a look at the C11/C17 features such as restrict, stdnoreturn and so on.  Note C17 is considered a bit of a bug fix for C11.

The joys of setting up a server

The joys of setting up a server

Posted on by David

Virtualmin install script runningThis is for my MMO game. I need a backend server, so yesterday I signed up for a vps service. I picked Ubuntu 20.04 LTS which I’ve used before and received the login details. I use Putty to log in via SSH and WinSCP for browsing, copying files.  Installing Apache2 is actually very easy. Likewise PHP. I didn’t install MySQL which might have been a mistake, so I had a LAP system (Linux, Apache, PHP) rather than LAMP.

What I did do sensibly was pay for a backup snapshot service.  When I logged in first I did an sudo apt update then upgrade. Then I took a snapshot.

And I needed it. My exact configuration was Apache 2.4 with PHP 7.4. Apache worked when I tested it but PHP didn’t. Well from the command line the PHP command worked and I could see the version but it didn’t work with Apache.  I created a PHP script with phpinfo in it but instead when I browsed to it, it downloaded the script rather than ran it.

This is usually the case that httpd.conf needs some AddType statements only there isn’t an httpd.conf anymore in Apache 2.4. I did locate a mime.conf but adding AddType into that and restarting Apache made no difference. I eventually wasted about three hours on it yesterday. However in my searches I came across mention of Virtualmin and so today I restored to the snapshot and ran the Virtualmin open source script. Luckily Ubuntu 20.04 LTS was one of the supported distros and Virtualmin installed without a hitch. It’s very impressive. The screenshot is of virtualmin installing. Thankfully all the bars on the right were green…

Back about 12 years ago when I first started experimenting with Linux and websites, i came across Webmin and used it extensively. Virtualmin installed both WebMin and Usermin. It has changed substantially in the time since I last used it. It surprised me a little because for years Ubuntu and Webmin didn’t seem to get on and Ubuntu recommended not to install it.

Anyway I now have a server that runs PHP. The backend will be running .NET Core once installed, but it’s just as easy to use Apache and PHP for receiving order files (from mobile). PHP is just to simplify getting those files onto and off the server.

My code is buried in the Arctic!

My code is buried in the Arctic!

Posted on by David

Svalbard taken from a cruise ship in 2015It’s true. Well my code and that of thousands of others on Svalbard, a set of islands halfway between Norway and the North pole. I’ve actually been to Svalbard on a cruise a few years back. It was cold and a bit damp. That’s one of a bunch of photos I took.

GitHub shipped 21 terabytes to be stored in long term storage under the ice. It should be good for a few hunded years at least so thats my backups taken care of. I wish!

Normal blogging will be resumed tomorrow. Hey after 200 posts I’m allowed a semi-off topic post once in a while!