Pointers explained:

543 points · 77 comments · view on lemmy.world

77 Comments

lime@feddit.nu · 108 pts · 76d

they used to call him the deref king back in college

lian_drake@lemmy.world · 73 pts · 75d (11 replies)

Worse version of this

ZILtoid1991@lemmy.world · 6 pts · 75d

Null termination is no longer recommended, use fat pointers instead!

mbp@slrpnk.net · 3 pts · 75d (8 replies)

Why would I want to be shown the concept of pointers by an eight year old?

WrathEnchanter@europe.pub · 15 pts · 75d (6 replies)

I'll have you know, she's canonically 300 years old

wieson@feddit.org · 15 pts · 75d (4 replies)

Nah, she's 5 or younger. She lied about being 6 (school age) to get adopted. It's a very wholesome story (if you disregard the war, political intrigue and terrorism).

mnemonicmonkeys@sh.itjust.works · 5 pts · 75d (1 reply)

And the fact that Anya's best friend is trying to break up Anya's parents because she has a crush on the dad

HeyThisIsntTheYMCA@lemmy.world · 1 pts · 74d

Hey if you knew Lloyd and not Yor you might do the same. Dudes a hottie.

HeyThisIsntTheYMCA@lemmy.world · 2 pts · 74d

El terrorismo makes it more holesome.

WrathEnchanter@europe.pub · 2 pts · 74d

I was just making a joke

mbp@slrpnk.net · 2 pts · 75d

🙄

rizzothesmall@sh.itjust.works · 5 pts · 75d

It's a good reference (lol) even if it's getting downvoted

hoohoohoot@fedinsfw.app · 0 pts · 41d
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NullPointerException@lemmy.ca · 67 pts · 76d (15 replies)

Wait. It’s been a long time but shouldn’t be int*** -> int** -> int* -> int ?

Susaga@sh.itjust.works · 83 pts · 76d (11 replies)

I think int*** is meant to be pointing at int**, but the image is just unclear about where everything is in perspective.

dohpaz42@lemmy.world · 28 pts · 75d (9 replies)

Pretty sure the image is clear:

int*** -> int*
int** -> int
Int* -> int

Clarity doesn’t mean correct. But that’s probably why it’s posted here. 🤷‍♂️

mexicancartel@lemmy.dbzer0.com · 9 pts · 75d

int** is inside a TV, and persumably int* must be inside another TV(even though uts not edited in). The image perespective is showing one thing inside the other, inside the other. So when when int*** points the TV it reference int**, which reference int* which reference int. Its just edited very bad

Susaga@sh.itjust.works · 8 pts · 75d (1 reply)

RT*** isn't pointing at RT*, he's pointing at the TV showing RT**. The fact you think otherwise is what makes the image unclear. I'm not sure why you insist on them being wrong.

_tasten_tiger@feddit.org · 0 pts · 73d

But that doesn't hold up, because RT** isn't pointing at a TV containing RT* only RT*** is pointing at an TV containing RT** RT* and RT

MonkderVierte@lemmy.zip · 2 pts · 75d (5 replies)

What's the * for again?

Monument@piefed.world · 4 pts · 75d (3 replies)

It’s to check to see if commenters know how to escape the symbol. Congratulations! You passed!

Source: I made it up.

MonkderVierte@lemmy.zip · 5 pts · 75d (2 replies)

You don't need to escape standalone *. At least not on Lemmy.

Monument@piefed.world · 3 pts · 75d

Well, I thought my misinformation was funny.

Valmond@lemmy.dbzer0.com · 2 pts · 74d

You can't escape it, it will always get you.

HeyThisIsntTheYMCA@lemmy.world · 2 pts · 74d

That one's a typo

obviouspornalt@fedinsfw.app · 15 pts · 75d

I mean, that's pretty much what happens to me every time I try to use pointers, so the meme checks out.

Quibblekrust@thelemmy.club · 7 pts · 75d

terranoid@lemmy.cafe · 7 pts · 76d

yep this is just someone misunderstanding pointers lol

Dialectical_Specialist@quokk.au · 3 pts · 75d

That's not the end of the chain either, right?

Because : int -> &int -> &&int

Or can you not use the address operator like that? It also might be int& &, I failed cs2200 on this exact type of technicality

DrCake@lemmy.world · 41 pts · 76d (1 reply)

Rumble Tumble Games in the wild

MrQuallzin@pie.eyeofthestorm.place · 12 pts · 75d

Seeing him break containment is wild

MrNesser@lemmy.world · 30 pts · 75d (1 reply)

Didn't expect to see the Drift King here

Jumi@lemmy.world · 9 pts · 75d

Drift King? You mean Dan the Villian

dangrousperson@feddit.org · 11 pts · 75d

as a python script kiddie, this is way over my head, but upvoted because of RT Game

14th_cylon@lemmy.zip · 8 pts · 76d (2 replies)

Why should the left one in the rectangle be int**? It doesn't make sense to me, they are both clearly just int*

What am i missing?

ImgurRefugee114@reddthat.com · 9 pts · 76d

I they're supposed to be pointing at each other but the edit didn't really work because his arm is pointing too far away

Skipcast@lemmy.world · 4 pts · 75d

Perspective innit

MonkderVierte@lemmy.zip · 8 pts · 75d (8 replies)

So, googling it, the general premise is you should use smart pointers instead to avoid crashes. Got it.

DahGangalang@infosec.pub · 10 pts · 75d (2 replies)

Smart pointers implies C++, which is not the right answer.

MonkderVierte@lemmy.zip · 6 pts · 75d (1 reply)

Unlike many other programming languages, which are often picked up on the go from tutorials found on the Internet, few are able to quickly pick up C++ without studying a well-written C++ book. It is way too big and complex for doing this. In fact, it is so big and complex, that there are very many very bad C++ books out there. And we are not talking about bad style, but things like sporting glaringly obvious factual errors and promoting abysmally bad programming styles.

https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list

mnemonicmonkeys@sh.itjust.works · 6 pts · 75d

Considering that most of the "answers" I've found on StackOverflow were complete dogshit, I'm wary of this reading list

HeyThisIsntTheYMCA@lemmy.world · 5 pts · 74d

Uh

I think I'll just let the cat drive instead

CanadaPlus@lemmy.sdf.org · 4 pts · 75d (3 replies)

They all have footguns that cause different crashes.

If you want to do explicit memory access without inevitable safety problems, you need Rust. That's the whole hype with Rust.

MonkderVierte@lemmy.zip · 1 pts · 74d (2 replies)

But... per-process-isolation is a hardware feature, no?

CanadaPlus@lemmy.sdf.org · 2 pts · 74d

Sure, that may be (it's definitely not in userspace). But don't forget it works by crashing your program.

psud@aussie.zone · 2 pts · 71d

So you really should implement it in your compiler so you don't contravene it

Technus@lemmy.zip · 7 pts · 76d (7 replies)

Real talk: is there any practical use-case for T*** of any pointee type?

palordrolap@fedia.io · 22 pts · 76d (6 replies)

Dynamically allocated multidimensional arrays.

Technus@lemmy.zip · 12 pts · 75d (1 reply)

Ah right, so that would be a 3D array.

  • T* is a single row of T
  • T** is a list of rows
  • T*** is a list of "layers" in the third dimension

This would be incredibly hazardous to pass around as a bare pointer with no context, though. I'd expect to see this in a struct that, at minimum, also includes fields for the size of each dimension.

BartyDeCanter@piefed.social · 8 pts · 75d

This Sparta C. We live for danger.

Auth@lemmy.world · 8 pts · 75d

Tesseract Array

MonkderVierte@lemmy.zip · 1 pts · 75d (2 replies)

Where?

palordrolap@fedia.io · 3 pts · 75d (1 reply)

In the C programming language. Or do you mean which C project specifically? Because as Technus surmises in their response, it's usually a better idea to set up aliases (typedefs or heck, even #defines) so that you're offloading some of the mental strain keeping track of the layers, and that's likely to be what happens in production code.

But the underlying data type is still T***.

MonkderVierte@lemmy.zip · 1 pts · 75d
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LovableSidekick@lemmy.world · 5 pts · 75d

C# delegates enter the chat and nod.

Flames5123@sh.itjust.works · 4 pts · 75d (14 replies)

Now that explain the & part of the pointers that I never really understood.

ZILtoid1991@lemmy.world · 6 pts · 75d (12 replies)

The & operator references the value.

int i;
int* p = &i;

In C++, the & at the function argument makes it a reference type (safe pointer).

void someFunction(int& refVal) {
    [...]
}
Flames5123@sh.itjust.works · 1 pts · 75d (11 replies)

As someone who likes working with higher level languages, I never understood the pass by reference or even referencing different pointers. It never stuck out to me as useful in what I want software to do. It’s too close to hardware.

lime@feddit.nu · 10 pts · 75d (7 replies)

if you're working with higher level languages you pass-by-reference all the time. give a list to a function to modify it? that's by reference. giving an event handler function to a framework? that's by reference. setting a property on an object? that's usually by reference.

funkless_eck@sh.itjust.works · 0 pts · 75d (6 replies)

the list is the helpful part to understanding it.

it would be terrible if, with bar being a list and foo being a member of the list

 if foo in bar: return true

modified the list. So yeah, you want to look at the list not edit the list, it's a pointer.

lime@feddit.nu · 4 pts · 75d

other way round surely? if you want to modify the original object, use a pointer. if you don't, use a copy.

gerryflap@feddit.nl · 2 pts · 75d

Your example doesn't make sense to me. Why would you modify the entire list by checking if something is in it? Also, you can totally edit the list via a pointer, that's how you're supposed to edit the list if you want any performance. Otherwise you'd be copying the list on every modification, which is terribly inefficient

Sylvartas@lemmy.dbzer0.com · 1 pts · 75d (3 replies)

A pointer to the list would allow you to modify whatever's at that pointer's address though. If you want to look at the list and not edit it you pass by const reference 99% of the time (or you pass a copy) and if your language doesn't have that I don't like it.

captcha_incorrect@lemmy.world · 2 pts · 75d (2 replies)

I still don't get the point of pointers.

I want my language to pass by reference. I give a variable to a function and the variable in the function scope should be a reference to the same place in memory as the original variable.

How can pointers help me here? What value does it provide? Genuine question.

Sylvartas@lemmy.dbzer0.com · 2 pts · 75d

I want my language to pass by reference. I give a variable to a function and the variable in the function scope should be a reference to the same place in memory as the original variable.

I'm not even a C++ wizard or anything (though it's my most advanced language) so I'm not gonna argue that is good or bad, that sounds fine to me for a wide range of applications already.

But the way is see it, pointers kinda allow you to use "raw memory" which is an actual thing that's gonna be handled by the program one way or another, and it's a way to relatively refer to memory for example. As some guy on stackoverflow put it "That guy at the end for the bar" vs "Bob" can be very useful. Especially when using data structures you don't know the size of at compile time.

Sylvartas@lemmy.dbzer0.com · 10 pts · 75d (1 reply)

Most of the time you pass by reference for more outputs, or by const ref to avoid copying a big-ass data structure (which is not always straightforward, with structures smaller than a pointer, which are pretty big in 64 bits architecture, you lose more to the ref overhead than to the copy IIRC)

DahGangalang@infosec.pub · 4 pts · 75d

Another reason I commonly see: to change the structure / "main pointer" to a data structure (esp during freeing and cleanup).

ZILtoid1991@lemmy.world · 1 pts · 75d

Reference values are quite useful, such as:

double valOut;
if (parseDouble(valOut) == 0) { //Argument of parseDouble is ref type, no & needed for input, no exceptions needed for error handling
    [...] //No error, code executed normally
} else {
    [...] //Erroreus input
}
dejected_warp_core@lemmy.world · 4 pts · 75d

*x = dereference or "point to". Treats the variable x as containing a pointer value. Evaluates to a variable existing at the address in x.

&x = reference or "get address of". Evaluates to the address of x.

They're complimentary operators, so *(&x) cancels out and is equvalent to just x.

refalo@programming.dev · 4 pts · 74d

that's not LaurieWired

Quibblekrust@thelemmy.club · 4 pts · 75d (1 reply)

Am I a computer scientist now?

ZILtoid1991@lemmy.world · 0 pts · 75d

No, you need to learn a lot more. Other programming concepts, programming paradigms, algorithms, and many more.

HeyThisIsntTheYMCA@lemmy.world · 3 pts · 74d (1 reply)

Uh I'm a charisma class (with unfortunate base stats) what's int

zerofk@lemmy.zip · 3 pts · 74d

It’s what makes mages turn those squiggly lines on paper into fireballs.

Not clerics though, they’re different.

Deconceptualist@leminal.space · 3 pts · 75d (2 replies)

The placement of the labels is a bit sloppy but I think it tracks. The character in the middle (int*) is pointing at int, then the one on the left (int**) is pointing at the middle one (int*), etc

What I want to know: what is that shirt and where do I get it?

addie@feddit.uk · 2 pts · 75d (1 reply)

He dereferenced a pointer to the 1970s and retrieved the shirt that way.

Deconceptualist@leminal.space · 2 pts · 75d

So it's like a mystical artifact of the computational Big Bang? You deref a pointer to the very beginning of Unix time and bam, suddenly you're styling like Richard Stallman?

itkovian@lemmy.world · 3 pts · 75d

So, confusing, nonetheless.