@bender@twtxt.net Hell yeah, that sounds like a good day!

Ta, @prologic@twtxt.net! Assuming you mean 13, it’s just some old shed in an orchard. I reckon the owners keep some of their tools in there. They are all over the place around here. To me they look like they were all built like 50 odd years ago or maybe more, not sure. I could be completely wrong. I just like the look of them and actually wanted to capture the dark sky with the rolling in thunderstorm, but my camera had totally other plans. Didn’t work out at all.

@movq@www.uninformativ.de Hahaha, this is so cool! :‘-D

@kat@yarn.girlonthemoon.xyz And tasty! :-) Turns out there’s marzipan in the bunny belly. Yum-yum!

@bender@twtxt.net Thanks! The rain rapidly cooled off the 17°C to just 10°C. I certainly appreciated that. The weather is coming from the west here, so I thought you’ve sent it our way. Let me try to return it. :-)

Today’s stroll was really nice. Just around 11km in total I’d reckon. We had a barbie at a mate’s garden where everybody went on a hunt for an easter basket. Oh boy, what a preparation that must have been! Baking the bunnies, dying the eggs, mixing the bear leek butter and so on. That’s dedication, let me tell you. :-)

Image

It was the first time this year that we had half proper April weather and a thunderstorm in general. It started off with clear sky and lovely sunshine. Right after arvo lunch it started to rain, so we went into the hut. Then, the sun returned.

On the way back with the growling thunder in the distance coming closer and closer we escaped the rain just perfectly. A minute or two after we reached the car, wet stuff started coming down the sky. Not even half a minute after opening the front door, it poured like crazy. Lucky twice today. There’s beautiful sunshine again by now. It smells absolutely great after the rain. I love it!

https://lyse.isobeef.org/waldspaziergang-2025-04-21/

@movq@www.uninformativ.de Oh, that’s beautiful!

I opened up all the photos in new tabs and went through them. For a second, I wondered that it was snowing at your place right now. :-D

That made me realize that so far we basically had nearly no April weather whatsoever. May might be full of it then, let’s see. :-)

@prologic@twtxt.net @movq@www.uninformativ.de @bmallred@staystrong.run @ionores@twtxt.net Thank you! Yeah, the yellow meadows look truly awesome.

Watching “Happy People: A Year in the Taiga” in German the evening before, this thing totally looked like a trap to us. So, we decided to sit on another, more rustic bench nearby. :-) Oh neat, it turns out, there is a much longer four part series of the documentary in English on YouTube. Highly recommended! This is part one: https://www.youtube.com/watch?v=fbhPIK-oBvA

Judging by the surroundings, I think this is actually a forest altar or something of that nature. But it looks like they started with the chappel’s reinforcement steel and then they ran out of money before completing it or even placing the concrete forms. :-P

Yeah, 78 might be photo of the month. It’s one of my favorites.

A mate and I had an amazing but also exhausting hike to the highest of the Three Emperor Mountains yesterday with perfect weather conditions. Sunny 18°C, blue sky with barly a cloud and a little welcoming breeze, just beautiful.

Image

Mt. Stuifen is 757 meters above sea level, has a small shelter and a barbie area and is still the most boring one of the three. It’s also the one farthest away from me. Not sure why it has two summit crosses, but both aren’t at the summit. The third, makeshift one at the real summit was gone by now. Four years ago, somebody had cobbled one together and put it up.

We bought our tucker at a local bakery on our way. This was the first time I tried a Teufelsbrezel (lit. devil’s pretzel), a lye pretzel with pepper. Haven’t come across that anywhere else. But I can certainly recommend that, it’s yummy.

We were glad when we were finally back home after some 26 or 27km. I won’t do much today and let my feet rest. Another friend called for a much, much shorter hike tomorrow.

Enjoy the 92 photos: https://lyse.isobeef.org/wanderung-auf-den-stuifen-2025-04-19/

@bender@twtxt.net Exactly. I suspect it was because of sqlitebrowser also accessing the database in parallel to debug the original issue.

So far, I have not found the exact reason why some replies don’t show up. When I do not filter for unread messages and show all, though, I actually see them. So, there’s that.

Today is the day where everything is falling apart. Suddenly, I get: SQL logic error: cannot start a transaction within a transaction

Aha, they all had to do with a dropped feed. I suspect the internal bookkeeping with root paths couldn’t keep up.

I just noticed that my unread messages counter was off by quite a bit. It showed 8, but I only saw one unread message. Even after restarting my client, which recalculates the number of unread messages, it remained at eight. Weird. Looking in the database revealed that this is indeed correct.

Apparently, my query to build up the message tree must be incorrect. It somehow misses seven messages. They all are orphaned, maybe that’s a clue. However, generating missing root messages (and thereby including the replies) typically works just fine. Hmm.

@movq@www.uninformativ.de Hopefully at your neighbors and not your building. :-S Keep your pecker up!

I just heard the fire brigade respond here with their compressed air sirens, too.

If you let fire take effect properly, it helps to reduce density.

That’s an interesting research article about Wallbleed, a memory disclosure vulnerability in the Great Firewall of China. They reverse-engineered the buggy DNS query processing code that injects a response if the hostname should be censored: https://gfw.report/publications/ndss25/data/paper/wallbleed.pdf

@movq@www.uninformativ.de Lol! Yeah, nobody wants to see you bring your coal-powered forklift into the gym. :-D

Even though I really do like the shell, I always use Dolphin to mount my digicam SD card and copy the photos onto my computer. I finally added a context menu item in Dolphin to create a forest stroll directory with the current date in order to save some typing:

Image

The following goes in ~/.local/share/kservices5/ServiceMenus/galmkdir.desktop:

[Desktop Entry]
Type=Service
X-KDE-ServiceTypes=KonqPopupMenu/Plugin,inode/directory
Actions=Waldspaziergang;

[Desktop Action Waldspaziergang]
Name=Heutigen Waldspaziergang anlegen…
Icon=folder-green
Exec=~/src/gelbariab/galmkdir "%f"

In order to update the KDE desktop cache and make this action menu item available in Dolphin, I ran:

kbuildsycoca5

The referenced galmkdir script looks like that:

#!/bin/sh
set -e

current_dir="$1"
if [ -z "$current_dir" ]; then
    echo "Usage: $0 DIRECTORY" >&2
    exit 1
fi

dir="$(kdialog \
    --geometry 350x50 \
    --title "Heutigen Waldspaziergang anlegen" \
    --inputbox "Neues Verzeichnis in „$current_dir“ anlegen:" \
    "waldspaziergang-$(date +%Y-%m-%d)")"
mkdir "$current_dir/$dir"
dolphin "$current_dir/$dir"

This solution is far from perfect, though. Ideally, I’d love to have it in the “Create New” menu instead of the “Actions” menu. But that doesn’t really work. I cannot define a default directory name, not to mention even a dynamic one with the current date. (I would have to update the .desktop file every day or so.) I also failed to create an empty directory. I somehow managed to create a directory with some other templates in it for some reason I do not really understand.

Let’s see how that works out in the next days. If I like it, I might define a few more default directory names.

@bender@twtxt.net Oooofff, I’m panting for breath when just thinking about that! I’ll immediately stop complaining. :-) I already forgot that a jacket over my jumper would have been nice. I’m happy to be cold.

We had some nice 22°C today. But after work, it got rather windy and cloudy, temps rapidly dropped so just 14°C. Still a nice stroll to our backyard mountain. https://lyse.isobeef.org/waldspaziergang-2025-04-16/

@movq@www.uninformativ.de For sure, an app for that is very silly. I’ve just seen signs in participating shops in my town. That’s how I know of this concept.

@movq@www.uninformativ.de You just have to dress yourself up in a dog custume to pee on a tree, fence post or house wall. :-P

Depending on the hour, town halls and also graveyards are typically good options for public toilets. But yeah, you have to find them first. And then, there might be the “Nette Toilette”: https://www.die-nette-toilette.de/ (Unfortunately, you can’t see on the website which towns and cities participate in that concept. :-()

@movq@www.uninformativ.de Heck yeah, that’s an awesome shot!

@bender@twtxt.net Yup, we run an ejabberd.

This 8 bit trip is really cool! https://www.youtube.com/watch?v=pCm1fKZGvl47

@prologic@twtxt.net So, this flag isn’t doing exactly what you thought it does? Or is there a bug in the implementation itself?

@prologic@twtxt.net Ta! :-)

@bender@twtxt.net @ionores@twtxt.net Yep, it’s extremely seldom that a photo turns out looking better than reality. Very rarely does that happen. But basically never with sunsets. ;-) Maybe once a leap year I’m very surprised to wonder how that subject wasn’t better in person but actually on film.

A mate and I met at the scout yard to prepare an upcoming workshop. Boy did we have an amazing sunset when we left. The photos don’t reflect it, it was a hell lot more beautiful in person: https://lyse.isobeef.org/plaetzle-2025-04-11/

Image

@anth@a.9srv.net Hahaha, for a second I thought that you implemented word splitting according to Swiss (.ch) rules. :-D

Btw, both manpage links string(2) and getields(2) (it’s missing an f) point into nothingness: http://a.9srv.net/src/wordwrap.2.html

I can’t help but notice line 9: http://a.9srv.net/src/wordwrap.c

And I reckon your finger slipped one key to the right for quore: http://a.9srv.net/src/litclock.1.html

Cool stuff! :-)

@bender@twtxt.net @movq@www.uninformativ.de Thanks! I’ll think about switching to higher resolution teasers in the future. The reasoning behind the thumbnails is to avoid wasting traffic. Maybe folks in the outback or on expensive mobile networks appreciate it. Yeah, they could disable images in general.

That’s a dang cool story from Apollo 11 where priority queues saved the day: https://www.nasa.gov/history/alsj/a11/a11.1201-fm.html

Hit by the arvo sun rays behind the window I was convinced that it is t-shirt weather. Deep blue sky, yeah, for sure! It turned out to be just 15°C and declining, though. So, I had to wear my jacket on today’s windy stroll. Pretty nice. Didn’t take many photos, but there you go: https://lyse.isobeef.org/waldspaziergang-2025-04-10/

Image

@movq@www.uninformativ.de Holy crap, that’s really crazy!

Hahaha, you got me. When I read your first sentence I thought you were going to tell about your Wayland experience in comparison to X11. :-D

@movq@www.uninformativ.de @ionores@twtxt.net Thank you! Nope, still a petting farm over here. The only dangerous (to humans) animals are boars and ticks. But I only ever encountered a wild hog once in my entire life so far. Luckily, it took off and didn’t attack me. Ticks, on the other hand, regularly attack me.

@bender@twtxt.net @prologic@twtxt.net Thanks mates!

Another nice stroll in nature last week: https://lyse.isobeef.org/waldspaziergang-2025-04-03/

Image

@thecanine@twtxt.net Hahaha, woofcome back! :-)

@kat@yarn.girlonthemoon.xyz It’s very well hidden, it took me a while to find that. Go to “Settings” in the menu bar up top → “Profile and Privacy” (already selected) → on the right at “User Info” → “1 Muted” → click the link with the minus in the circle at the message you want to unmute.

@movq@www.uninformativ.de @kat@yarn.girlonthemoon.xyz Heck yeah, that’s crazy! :-) Fingers crossed! (tt also agrees with the right™ hash)

@prologic@twtxt.net @bender@twtxt.net @movq@www.uninformativ.de I’m going to join the party in Down Under. :-)

And we’re back to the regular landscape! Not only in subject but also photo orientation. No more silly portrait. I can’t recall it exactly, but I reckon that was one of ~20°C days. The evening sun was really crazy that day, made a great combination with the puddles: https://lyse.isobeef.org/waldspaziergang-2025-04-02/

Image

@prologic@twtxt.net Not sure if the confirmation helps at all. You just condition yourself to immediately press y on a daily basis.

Apart from that, aborting the removal should probably terminate the function with a non-zero exit code, something like return 1.

@movq@www.uninformativ.de Same! Another infrastructure apocalypse at work. Who needs reliable shit? Definitely not us.

@doesnm@doesnm.p.psf.lt Hahahaha, I heard this one before, but it’s brilliant! :-D

@prologic@twtxt.net Ta! :-)

Pretty sunset from last weekend: https://lyse.isobeef.org/abendhimmel-2025-03-30/

Image

@prologic@twtxt.net Spring cleanup! That’s one way to encourage people to self-host their feeds. :-D

Since I’m only interested in the url metadata field for hashing, I do not keep any comments or metadata for that matter, just the messages themselves. The last time I fetched was probably some time yesterday evening (UTC+2). I cannot tell exactly, because the recorded last fetch timestamp has been overridden with today’s by now.

I dumped my new SQLite cache into: https://lyse.isobeef.org/tmp/backup.tar.gz This time maybe even correctly, if you’re lucky. I’m not entirely sure. It took me a few attempts (date and time were separated by space instead of T at first, I normalized offsets +00:00 to Z as yarnd does and converted newlines back to U+2028). At least now the simple cross check with the Twtxt Feed Validator does not yield any problems.

And now, let’s finish it off with Besigheim’s old town. Only when we left, the sun peaked through the clouds. That was a bit unfortunate, but what can you do? It has some nice buildings. https://lyse.isobeef.org/besigheim-2025-03-30/

Image

Today, we had a cleanup day with the scouts. I estimate that we ended up with about half a metric ton of rubbish. Despite the heat it was really great fun.

Image

@prologic@twtxt.net In all my two Go projects I use modernc.org/sqlite and can’t complain. Works great for me.

@david@collantes.us This pink tree I featured in a few shots is a magnolia tree. I haven’t noticed any particular smell, it just looks pretty. :-) That’s a close-up: https://lyse.isobeef.org/bad-wimpfen-2025-03-28/18.jpg (I only noticed the spider and its web when I reviewed my photos.)

@thecanine@twtxt.net Happy to hear that. :-)

The photo series covering old stuff continues. This time, Gundelsheim. Actually, mostly the castle hotel Horneck, I hardly took any photos from the town itself. I really should have, though. Let me just blame… aehm… yeah, the rain! It’s totally the rain’s fault!! When it started to drizzle, I actually took the first photos, so it’s a total lie. https://lyse.isobeef.org/schlosshotel-horneck-in-gundelsheim-2025-03-30/

Image

@arne@uplegger.eu I’m very glad I only rarely have to deal with .docx & Co. And when I have to, 99% is in read mode only. Even though, I don’t think that Markdown is the best choice, I use it on a daily basis. Some things, like links, in reStructuredText are better in my opinion.

Jira just resists to switch to Markdown and forces us to use its silly markup language.

For real typesetting, LaTeX is the way to go. But I very, very rarely do that.

Hirschhorn also offers a nice old town. The castle with all its many buildings up the mountain is very beautiful. This is my absolutely favorite one, it just looks soo great:

Image

Walking back down the narrow stairs with all the crooked, well-worn steps of different heights and lengths was quite challenging.

https://lyse.isobeef.org/hirschhorn-2025-03-30/

@movq@www.uninformativ.de Awwwwww! Thank you, that is now in my collection. :-) The other ones aren’t bad either, very nice!

@thecanine@twtxt.net My apologies, mate! :-( As @david@collantes.us pointed out, this was definitely not my intent at all.

For the easter egg hunt, I first looked for a hidden image map link on the pixel dog in the right lower corner itself. Maybe one giant pixel just links to somewhere else, I figured. But I couldn’t find any and then quickly moved on. Hence, I naturally viewed the HTML source. Because where else would be a good hiding place for easter eggs, right?

Next, I noticed the <font> tags. I thought I had read quite some time ago that they are not an HTML5 thing, but wasn’t entirely sure about it. So, I asked the W3C HTML validator. Sure enough. I thought I let you know about the violations. If somebody had found a mistake on my site, I’d love to hear about it, so I could fix it. I’m sorry that my chosen form of report didn’t resonate with you all that well. I reckoned you’ll also find it a bit funny, but I was clearly very wrong on that.

I actually followed the dog cow link to the video, so I ended up on the easter egg. However, I didn’t recognize it as such. ¯_(ツ)_/¯ Oh well.

Regarding my message about the browser quirks: I read your answer that you were arguing against the HTML validator findings. Of course, everybody can do with their sites whatever they likes.

@movq@www.uninformativ.de Sorry for being completely offtopic, but that’s a really cute bird! :-)

A hike to the highest mountain in the Odenwald, the Katzenbuckel, lit. cat hillock. It was very windy and the sun very rarely showed its face, so it was quite chilly. Nice scenery, nevertheless. Surprisingly, this ski-jumping hill is still in operation. I’ve never expected this in a hundred years, judging by its state. https://lyse.isobeef.org/katzenbuckel-2025-03-29/

Image

@arne@uplegger.eu ;-)

@bender@twtxt.net Hahaha, YMMD! :-D

@movq@www.uninformativ.de @xuu@txt.sour.is That sounds like kat! :-)

Is there some Makefile shenanigans going on maybe? $V and $C being swallowed by the Makefile. I fell in that trap again the other day.

@movq@www.uninformativ.de Oh yeah, take some pictures when you do. :-)

@bender@twtxt.net @eapl.me@eapl.me @xuu@txt.sour.is @movq@www.uninformativ.de Glad you all agree. :-D My SOAP knowledge is extremely rusty, I luckily had not to deal with that crap anymore for quite some years now. I even couldn’t remember the XML declaration and had to look it up. ;-)

@movq@www.uninformativ.de Yeah, I’m also disappointed each and every time.

Let me introduce you to the much superior version 4 instead: https://lyse.isobeef.org/tmp/twxm4.xml

@thecanine@twtxt.net And this is exactly why there are quirks modes in browsers…

I’m actually glad I don’t have to deal with all this web shit and work with compilers that hit me in the face when I do something illegal. :-)

@arne@uplegger.eu Oh no, you are in front of the line!!

Eberbach is nowhere near Bad Wimpfen in comparison, but still has a nice historic old town: https://lyse.isobeef.org/eberbach-2025-03-29/

Image

Bad Wimpfen has a pretty cool old town with timber framed houses. Looks really beautiful: https://lyse.isobeef.org/bad-wimpfen-2025-03-28/

Image

@thecanine@twtxt.net I found it! This looks like colored easter eggs when squinting.

@kat@yarn.girlonthemoon.xyz They all just wanted to be friends with a cool gal like you. ;-) It’s sad that putting things openly on the internet just waits to be raided by script kiddies, bots or spammers eventually.

@movq@www.uninformativ.de Yeah, like nearly all of them. There is the so called Bannwald, where it typically is not allowed to log, but there’s only one in my entire county and I haven’t even visted it. I should change that. https://de.wikipedia.org/wiki/Bannwald

@movq@www.uninformativ.de Hahaha, geil! :-D

@movq@www.uninformativ.de Haha, that’s cool! :-D

@movq@www.uninformativ.de That’s really great! I can’t tell the difference to the original. :-)

This time, I brought my cam along. We checked out a piece of ex-forest they’ve cut down. It looks terrible now. :-( At least the spruce resin smell was nice. https://lyse.isobeef.org/waldspaziergang-2025-03-27/

Image

@eapl.me@eapl.me According to an update of the article, others have suggested the same.

Your explanation seems fitting. I just don’t get why people don’t use feed readers anymore. Anyway.

@xuu@txt.sour.is Yeah, it will be delayed. Oh well. That’s just the way it is. :-)

@movq@www.uninformativ.de Hahaha, that filename! :-D 100 times better than I could ever play.

@xuu@txt.sour.is If the unread counter becomes negative, wouldn’t that mean I have that many more read messages? :-D

@bender@twtxt.net You’re spot on, it’s important to not introduce classical bugs!

@movq@www.uninformativ.de Oh dear. :-( Have they fixed it?

@prologic@twtxt.net @movq@www.uninformativ.de I had a t-shirt with this one or the other decade ago. :-)

“Unread messages: -1”: Well, classic off by one error. I gotta have to hunt that down.

@movq@www.uninformativ.de That’s not very retrocomputing!

@eapl.me@eapl.me Interesting! Two points stood right out to me:

1. Why the hell are e-mail newsletters considered a valid option in the first place? Just offer an Atom feed and be done with it! Especially for a blog of this very type. This doesn’t even involve a third party service. Although, in addition he also links to Feedburner, what the fuck!? No e-mail address or the like is needed and subject to being disclosed.

2. When these spam mailers want to prevent resubscribing, then for fuck’s sake, why don’t they use a hash of the e-mail address (I saw that in yarnd) for that purpose? Storing the e-mail address in clear text after unsubscribing is illegal in my book.

@movq@www.uninformativ.de I see, fair point, yeah.

@movq@www.uninformativ.de Yikes! I didn’t know about about:compat. Crazy!

@xuu@txt.sour.is Wow, that’s a giant graveyard. In my new database I have 16,428 messages as of now. Archive feed support is not yet available, so it’s just the sum of all the 36 main feeds.

@david@collantes.us Ah shit, sorry, you’re right! :-D

There are 82.108 read statuses, but only 24.421 messages in the cache. In contrast to the cache with the messages, the read statuses are never cleaned up when a feed was unsubscribed from. And the read statuses also contain old style hashes, before we settled on the what we have today. Still a huge difference. Hmm.

Thanks, @movq@www.uninformativ.de!

My backing SQLite database with indices is 8.7 MiB in size right now.

The twtxt cache is 7.6 MiB, it uses Python’s pickle module. And next to it there is a 16.0 MiB second database with all the read statuses for the old tt. Wow, super inefficient, it shouldn’t contain anything else, it’s a giant, pickled {"$hash": {"read": True/False}, …}. What the heck, why is it so big?! O_o

@movq@www.uninformativ.de You could also just use a tiling window manager. :-) As a bonus, it doesn’t waste dead space, the window utilizes the entire screen. To also get rid of panels and stuff, put the window in fullscreen mode.

If I didn’t mess this up, 61 feeds reduced down to 36.

I now subscribed to most feeds in my Go tt reimplementation that I already followed with the old Python tt. Previously, I just had a few feeds for testing purposes in my new config. While transfering, I “dropped” heaps of feeds that appeared to be inactive.

This might motivate me to actually “finish” the new client, so that it could become my daily driver. No need to use the old software stack any longer. Let’s see how bad this goes.

@movq@www.uninformativ.de Yeah, most of the graphical applications are actually KDE programs:

• KMail – e-mail client
  
• Okular – PDF viewer
  
• Gwenview – image viewer
  
• Dolphin – file browser
  
• KWallet – password manager (I want to check out pass one day. The most annoying thing is that when I copy a password, it says that the password has been modified and asks me whether I want to save the changes. I never do, because the password is still the same. I don’t get it.)
  
• KPatience – card game
  
• Kdenlive – video editor
  
• Kleopatra – certificate manager
  

Qt:

• VLC – video player
  
• Psi – Jabber client (I happily used Kopete in the past, but that is not supported anymore or so. I don’t remember.)
  
• sqlitebrowser – SQLite browser
  

Gtk:

• Firefox – web browser
  
• Quod Libet – music player (I should look for a better alternative. Can’t remember why I had to move away from Amarok, was it dead? There was a fork Clementine or so, but I had to drop that for some unknown reason, too.)
  
• Audacity – audio editor
  
• GIMP – image editor
  

These are the things that are open right now or that I could think of. Most other stuff I actually do in the terminal.

In the past™, I used the Python KDE4 bindings. That was really nice. I could pass most stuff directly in the constructor and didn’t have to call gazillions of setters improving the experience significantly. If I ever wanted to do GUI programming again, I’d definitely go that route. There are also great Qt bindings for Python if one wanted to avoid the KDE stuff on top. The vast majority I do for myself, though, is either CLI or maybe TUI. A few web shit things, but no GUIs anymore. :-)

Oh, it’s called “unsubscribe”.

@movq@www.uninformativ.de Oh, right, a type would be good to have! :-D

@movq@www.uninformativ.de Where can I join your club? Although, most software I use is decentish in that regard.

I just noted today that JetBrains improv^Wcompletely fucked up their new commit dialog. There’s no diff anymore where I would also be able to select which changes to stage. I guess from now on I’m going to exclusively commit from only the shell. No bloody git integration anymore. >:-( This is so useless now, unbelievable.

@kat@yarn.girlonthemoon.xyz Pointers can be a bit tricky. I know it took me also quite some time to wrap my head around them. Let my try to explain. It’s a pretty simple, yet very powerful concept with many facets to it.

A pointer is an indirection. At a lower level, when you have some chunk of memory, you can have some actual values sitting in there, ready for direct use. A pointer, on the other hand, points to some other location where to look for the values one’s actually after. Following that pointer is also called dereferencing the pointer.

I can’t come up with a good real-world example, so this poor comparison has to do. It’s a bit like you have a book (the real value that is being pointed to) and an ISBN referencing that book (the pointer). So, instead of sending you all these many pages from that book, I could give you just a small tag containing the ISBN. With that small piece of information, you’re able to locate the book. Probably a copy of that book and that’s where this analogy falls apart.

In contrast to that flawed comparision, it’s actually the other way around. Many different pointers can point to the same value. But there are many books (values) and just one ISBN (pointer).

The pointer’s target might actually be another pointer. You typically then would follow both of them. There are no limits on how long your pointer chains can become.

One important property of pointers is that they can also point into nothingness, signalling a dead end. This is typically called a null pointer. Following such a null pointer calls for big trouble, it typically crashes your program. Hence, you must never follow any null pointer.

Pointers are important for example in linked lists, trees or graphs. Let’s look at a doubly linked list. One entry could be a triple consisting of (actual value, pointer to next entry, pointer to previous entry).

  _______________________
 /               ________\_______________
↓               ↓         |              \
+---+---+---+   +---+---+-|-+   +---+---+-|-+
| 7 | n | x |   | 23| n | p |   | 42| x | p |
+---+-|-+---+   +---+-|-+---+   +---+---+---+
      |         ↑     |         ↑
       \_______/       \_______/

The “x” indicates a null pointer. So, the first element of the doubly linked list with value 7 does not have any reference to a previous element. The same is true for the next element pointer in the last element with value 42.

In the middle element with value 23, both pointers to the next (labeled “n”) and previous (labeled “p”) elements are pointing to the respective elements.

You can also see that the middle element is pointed to by two pointers. By the “next” pointer in the first element and the “previous” pointer in the last element.

That’s it for now. There are heaps ;-) more things to tell about pointers. But it might help you a tiny bit.