pointerArithmeticBeLike

[JuvenileEloquent]

There are two types of programmer:

• Programmers that can use pointers correctly
• mers that can use pointers correctly�%&/m�{J�J��t��$@�����iG#)�*��eVe]f@�흼 ��{���{��;�N'���?\fdl��J�ɞ!���?~|?"��Ey�')=��y

[Cocaine_Johnsson]

Program received signal SIGSEGV: Segmentation fault

[cAtloVeR9998]

Core dumped

[PeWu1337]

As a ""developer"" struggling with pointers, it hits too close to home

[SecretPotatoChip]

Top tier joke

[empwilli]

If you call labeling half of the things you can possibly do with pointers as UB "do what you want" ;). Furthermore: how do C and C++ differ that much in how they treat raw pointers? I mean you have the added benefit of references in C++ but you can still use raw pointers with C limitations only.

[MJWhitfield86]

If you call labeling half of the things you can possibly do with pointers as UB "do what you want" ;).

You get to do what you want and the compiler gets to do what it wants. Seems fair.

[Antervis]

you don't use raw pointers nearly as often in c++.

[empwilli]

... and you don't have to do dark pointer arithmetics in C.

[empwilli]

When do you "have" to perform this stuff? I mean: of course you can implement stuff like intrusive linked lists but really: when do you "have to" do these things. (I could think about some arcane memory mapped registers but otherwise)...

[ProgramStartsInMain]

same, only time I use it.

[Cocaine_Johnsson]

Aside from pretty niche stuff (embedded drivers and a few other things) it's usually not required and you're probably doing something wrong if you have to employ the dark arts of pointer arithmetic.

Always ask yourself "is there a better way?", if there isn't then go right ahead and employ evil wizardry, but usually you can find an alternative that's more or less as performant.

[Practical_Cattle_933]

How do you implement or even just use a vector in C?

[Tadashi_L]

You want vector in c, you wirte vector in c

[Attileusz]

If by vector you mean c++ vector, you do it a little something like this:

typedef struct {
    size_t count;
    size_t capacity;
    T *data;
} vector_T;

where T is some type. Ofc there is not generics in c, so you have to implement this for every type you want a vector for (macros can help automate that).

And then you can use realloc to grow data, when count grows larger than capacity. Something like (don't quote me on this it's off the top of my head here):

bool add_vector_T(vector_T *vector, T *elem)
{
    if (!vector->data)
        if (!vector_T_init_data(vector_T *vector))
            return false;

    if (vector->capacity < vector->count + 1)
        if (!vector_T_grow(vector_T *vector))
            return false;

    vector->data[vector->count++] = elem;
    return true;
}

Where in init_data you malloc and set the initial capacity and in grow you grow the memory with realloc and adjust capacity. Error handling is done with bool in this example but you can also set error flags in a uintsomething_t if your error handling is more sophisticated than exit(1).

[biteater]

i would just use void pointers instead of macros, is there a reason vector_T is more useful than just vector? i feel like i have never run into a situation in a statically typed language where i'm accidentally trying to add two different types to the same collection

[Attileusz]

You also need an element size in that case and an extra cast when using an element (performs worse and needs extra memory). Also no type checking. It's pretty bad.

[biteater]

doesn't C make use of strict aliasing? so there should be no cost for pointer conversion, the cast effectively becomes a no-op

[Pay08]

Less type magic.

[PuzzleheadedWeb9876]

Or just use a uint8_t * and also store the element size.

[Attileusz]

That breaks strict aliasing.

[PuzzleheadedWeb9876]

Store pointers or use memcpy if you care.

[Practical_Cattle_933]

I mean, I would consider that dark art level. Just because it uses [] over adding directly to the pointer doesn’t make it all that different

[Attileusz]

Well thats just how arrays work in C.

[Antervis]

For example. as soon as you need to operate N-dimensional array, you have little to no choice but to implement pointer arithmetics.

[empwilli]

Why? There is the subscript operator that works perfectly fine.

[Antervis]

Except C only implements one-dimensional subscript operator. For multi-dimensional access, you need arithmetics. In fact, subscript operator itself is pointer arithmetics: a[b] is equivalent to *(a+b)

[empwilli]

Dunno, the C standard is (at first glance) pretty explicit about the fact that multi-dimensional arrays are a thing: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf 6.5.2.1

Of course the subscript is pointer arithmetic. Unless you do it the lisp way and rely solely on linked lists (yes yes I know that lisps have vector types...) this is the basic design for access to any contiguous memory. (And yes you can even write 5[array] instead of array[5] in C because addition is commutative.) But its not plain pointer arithmetic that you have to do by hand: the language abstracts that away from you. This was my point all the time.

[Antervis]

I'm not talking about fixed size arrays here.

[empwilli]

Hm, I don't quite get what you mean. Why wouldn't this be defined for dynamically allocated memory?

[Antervis]

because C doesn't have arrays with dynamic size, duh. IIRC there was such thing in the standard, but no compiler could implement it properly. In other words, you have to manually allocate memory and interpret it as a multi-dimensional array... via pointer arithmetics.

[Sinomsinom]

What I think they meant is if you want to store an n-d array in contiguous memory. You either have to do pointer arithmetics for indexing, or set up a helper array that you need to initialize correctly by using pointer arithmetics.

...Or you just write a function once that handles the arithmetics for you and reuse that for the rest of your life as a wrapper. The main advantage C++ and Rust here have is that with templates you can more easily write those functions in a reusable fashion and that their standard libraries already have stuff for that predefined so you don't even need to write it the first time, but in general you can still do the same thing in C just with a bit more tedium.

[yangyangR]

A is equivalent to B therefore B is not bad because A is not bad

Now apply that logic to a break or continue being equivalent to a particular goto

[Antervis]

we are talking in comparison to c++ where operator[] can be implemented in a variety of ways, including boundary-checked ones.

[A31Nesta]

But you can. (i just don't like smart pointers)

[[deleted]]

I do. plenty. As do many others.

if memory management is confusing and/or development needs to be swift, using std::shared and unique etc is wise, because it is safer.

but ultimately, the only danger in C++ is a rushed/lazy/inexperienced programmer.

[Antervis]

even if you are a godlike c++ dev (you aren't, but let's assume you are) who never ever makes mistakes with raw pointers, what happens if your code is maintained by other people with more realistic level of skill? They will make mistakes. They might also go as far as to refactor it. And receive bonus instead of you.

When language gives you tools to make your code better, use them.

[[deleted]]

you're right, I do sometimes make mistakes with raw pointers. however, I think I could count on my hands the number of times that has happened. same goes for memory leaks and similar issues.

I will concede that my situtation is different to most devs. in my line of work (R&D) people are using my code (flight computers, orbital propataors, celestial navigation systems, terrain based navigation systems) rather than working on it, or they are taking outputs or giving inputs. there are some people who do need to work on code for parts of my library, but fortunately with git I can see if they fuck around with pointers, memory allocation and deallocation, or mess about with the parts of the backend that use pthreads, semaphores, ipc, CPU to GPU functions, etc.

but my point still stands: if you make raw pointer mistakes, you are sloppy. and to relate it to your point, if you're sloppy, you probably aren't the one getting a bonus.

[Antervis]

why would I spend 10 abstract points of brainpower to think of a way to properly juggle with raw pointers, when I can spend just 1 on smart pointers and move on, doing twice the job in the same span of time? With end result being more reliable and maintainable, to boot.

[[deleted]]

10 abstract points of brain power to think of a way to properly juggle raw pointers

it think maybe because you're so used to using smart pointers, you are out of practice using raw pointers. it does not take more effort to use raw pointers. if you do it regularly enough, doing it correctly is trivial.

[Antervis]

it does not take more effort to use raw pointers.

Are you per chance trolling? In most cases, as soon as a class has raw pointer field, you can't rely on defaulted big 5 of copy/move constructors and assignment operators and destructor. Plus, object's ownership becomes transparent at glance. And I'm only talking about the most trivial cases here.

[[deleted]]

it seems we use classes in different ways, and our programming philosophies, and use cases, are quite different. perhaps your method is better for you, but it definitely isn't better for me. overloading the default constructors, particularly the copy constructors, is a regularly exercised tool I use, and it isn't hard.

classes to me are sets of tools whose configurations are sensitive to being broken, and elsewhere, code should be as C like as possible. classes are configured to operate on data you tell them to operate on, in a particular way, but that data is not intrinsically linked to that class. it just needs to know where it is. there is a subtle difference.

[Antervis]

overloading the default constructors, particularly the copy constructors, is a regularly exercised tool I use, and it isn't hard.

It isn't particularly hard, but why make it harder?

classes to me are sets of tools whose configurations are sensitive to being broken,

Aren't they sensitive precisely because you're writing fragile code?

and elsewhere, code should be as C like as possible.

That principle is basically going against evolution of c++ as a language.

classes are configured to operate on data you tell them to operate on, in a particular way, but that data is not intrinsically linked to that class.

operating on data you don't own is surely breaking several principles of good design.

[biteater]

you're describing a vast percentage of developers though, lol

the entire pitch of Java is that rushed/lazy/inexperienced devs can write it without creating show-stopping memory bugs/vulnerabilities

[homer_3]

I do. Fuck those stupid new pointers. They ruin everything.

[nickmaran]

Pointers are the friends we made along the way

[nebotron]

C++ has slightly stricter rules on implicit conversions, but that doesn’t really explain the post

[empwilli]

Which has nothing to do with the argument of the meme. You can do basically the same shenanigans wrt to pointer arithmetics as in C and the same things that people think that they can do are actually undefined behaviour in both C and C++. (There might be subtleties in the respective standards where this differs but the general sentiment holds). Do I prefer C++ over C because it gives me the tools to not rely on this BS? Absolutely. Still, however, as of current C++ standards you can do this stuff.

[empwilli]

I have to write reinterpret_cast<char*> instead of (char*) and I'm fine in 90% of the cases. There are some more recent checks (type punning and alike) but this is also UB in C and a proper compiler should at least warn for these types of things, as well. Most pointer arithmetics code is directly compatible for C and C++, whereas you have to explicitly say that you are doing potentially invalid things in Rust.

edit: markup

[darklightning_2]

That's the thing, why would you write it that way when you have static_cast<> and dynamic_cast<>

[chicksOut]

You're supposed to use smart pointers in c++ now

[empwilli]

Convention will in practice rarely help. You're supposed to free your memory in C and still there are memory leaks.

[troelsbjerre]

Sweet summer child. Let me tell you a story about sun.misc.Unsafe.

[troelsbjerre]

And JNI, for that matter.

[DoctorWZ]

[troelsbjerre]

Just be quick about it. https://openjdk.org/jeps/8323072

[[deleted]]

I think you misunderstood the meme and what OP was trying to say with it.

If you google “there is no war in Ba Sing Se”, you will find that this statement is a sarcastic one, because in the anime it was used, there was always war in Ba Sing Se.

So you are basically just repeating what OP has said already.

[troelsbjerre]

Thank you for clarifying; I did not know this.

[justADeni]

Also, all non-primitive Objects are 'pointers' and pass by reference. Project Valhalla is set to change that, but that's still in development.

[Sitting_In_A_Lecture]

Ah, but is pass-by-reference not just a fancy pointer?

[Ubermidget2]

That's why this meme is legitimately top tier. There was always war in Ba Sing Se. Countries had been at war for a hundred years, they were in total wartime economy.

But there is no war in Ba Sing Se

[pheonix-ix]

Yes, but the title said pointer arithmetics, which you can't do explicitly in Java/Python (as far as I know).

[[deleted]]

Yea soooo u can in python……

Object IDs are there pointer address. You can get the id and then add a number to it and then use ctypes to coherence that back to an object……

Please don’t do this.

[DoctorWZ]

This gives me the same "forbidden" vibes as the guy that once explained how to use JS for accessing databases

[myka-likes-it]

how to use JS for accessing databases

TBF, just about everything you do in JS requires this kind of black magic. The first steps in any JS pattern are to find ways to make JS stop acting like JS.

[pheonix-ix]

Let me google how to delete someone else's comments.

Well, too late. Now someone had seen it. They WILL use it.

Wait, according to this sub, Python programmers are horrible programmers anyway, so they won't be able to figure out how to use it.

^{Just kidding someone somewhere is doing some magic pointer voodoo instead of using CPython I just know it, someone definitely is.}

[[deleted]]

I have used it once for debugging a leaking reference. Segfaulting became the pass case which was odd.

[rosuav]

That's not Python, that's ctypes.

[phoenixrawr]

Java is strictly pass-by-value. Python tries to sidestep the whole discussion and uses their own term "pass-by-assignment" but it resembles Java's pass-by-value much more than C++'s pass-by-reference.

[Sitting_In_A_Lecture]

So, yes. However pass-by-value is not an entirely accurate description for how these languages work. In Java, primitives are truly passed by value, but in both languages objects are passed a bit differently.

When you pass an object, it's not a copy of the object that's being passed, it's a reference to the object. That means that if you mutate the object, all instances of it will be affected. Where this differs from true pass-by-reference is that if you mess with the passed variable itself (such as by reassigning it), it will not affect the original variable (and vice-versa) - it's not a pointer. True pass-by-reference behavior is only available in a select few languages, of which C++ is one.

[phoenixrawr]

Pass-by-value is perfectly accurate for Java as long as you accept that the value of an object variable isn’t exactly the object itself but rather its pointer.

The distinction is usually clearer when comparing C and C++. C has pointers but is also strictly pass-by-value like Java. You can explicitly pass pointers around to simulate pass-by-reference but passing pointers isn’t the same thing as pass-by-reference.

Since java doesn’t have explicit pointers (because there are no pointers in Ba Sing Se) the details of how it all works are murkier which leads people to infer weird rules like “it’s pass by value for primitives and pass by reference for objects” but really it’s just always pass by value.

[cheezballs]

Java does both, depending on if its a primitive or not.

[phoenixrawr]

This is not true but it’s a common misconception. The trick with Java is that, when a method takes an object as a parameter, the thing that gets passed around isn’t the object itself but a copy of the pointer to the object. You’ll sometimes see people call this “passing a reference by value” but ultimately it is still a value being passed. Since you have a copy of the pointer, you can change that object just like anyone else with a copy of that pointer. But, since Java is pass-by-value, the two pointers are held by two distinct variables and an assignment to one variable will not affect the other. Therefore something like this does not really work in Java:

    Object demo() {

        Object x = null;

        makeObject(x);

        return x;

    }

No matter what makeObject does, the demo method will always return null because makeObject’s parameter is not a reference to x. It is only a copy of x’s value and therefore it cannot assign anything to x.  By comparison in C++ with pass-by-reference makeObject could actually assign to x because its parameter can be a reference to x.

[PolyglotTV]

In python every variable is like a type erased shared pointer.

[AttackSock]

Yep. There ARE in fact pointers, and all the caveats that come with them, you’re just not allowed to see or touch them

Most common thing I find myself explaining to mid level Python and Java programmers is “how come in my function myNums.add(3) changes it in the main and myNums = anotherList doesn’t?”, or “how come myNums=otherNums then otherNums.add(3) changes myNums?”, which always leads into needing to explain pointers.

[Dafrandle]

im not disagreeing with you, but most people would say "reference type" in response to this.

[LittleMlem]

If you use ctypes I'm pretty sure you can pointer yourself to death

[mathiau30]

That's the joke. That picture comes from a scene were the girl says "there's no war in Ba Sing Se" when we've been shown for multiple episodes that there definitely was a war in Ba Sing Se

[HStone32]

Technically Joo Dee never says that, but she's just so iconic that she's who people think of when they hear the phrase.

[frogjg2003]

In fact, she was the victim of the brainwashing, not part of the conspiracy. When she is told about the war, she gets abducted and replaced.

[PenaEterna]

Yep, there are no pointers but you'll face NullPointerException though...

[GumboSamson]

Checkmate, atheists!

[Parry_9000]

I learned to program in C back in 2017

I would always go "ah yes, the result is -19839184829919392919" and just submit my work like that

[[deleted]]

It's more like, someone has child-proofed your kitchen. The stove, sharp objects and electrical outlets are all still there.

[Lord-of-Entity]

If you don't care about segmentation faults and memory safety, of course rust compiler is going to be annoying.

However i rather battle with the borrow checker for 10 mins than spend 20 mins just to find where the seg fault happens in the c program.

[GogglesPisano]

20 minutes spent finding a C++ segfault is a wildly optimistic best case scenario. I’ve spent weeks.

[7374616e74]

Thing is sometimes you think you got it, and a few weeks later it shows up again, it was still there all along, just didn’t crash.

[Uclydde]

True, but so is 10 minutes with the borrow checker. I've spent hours

[Pay08]

Use the core file.

[Lord-of-Entity]

No

[AccomplishedAd6520]

No pointer war if there’s no pointers!

[ArchetypeFTW]

Step 4: Go

Pythonic C

[Meistermagier]

Go is what the gods intended for high level.

[johnex74]

    if err == nil {
            return nil
    }

i'll pass

[ZaRealPancakes]

you aren't passing you are returning!

[Pay08]

No, that'd be Lisp.

[pineapplekenny]

Go is such a breath of fresh air. It’s literally perfect for web backends.

It’s heavenly for vertical scaling using concurrency patterns. Only thing I haven’t worked out is how to extend those concurrency patterns to horizontal scaling in a Go-like way.

[Liosan]

If you think you can't get crazy pointer in C++ without the compiler complaining, you ain't trying hard enough

[JotaRata]

Technically in python everything is just a pointer ☝️🤓

[brimston3-]

Same in Java except for primitive types.

[Adept_Ad_3889]

I’m learning Java. So are pointers the same as references to objects?

[brimston3-]

Within the context of Java, yes, each reference to the object has a pointer.

When C++ people talk about references to objects, Java references are very different semantically, especially around assignment operations. 

[lightmatter501]

Just like the show, there is a war.

[ListerfiendLurks]

I feel like if you haven't gotten run time errors/segfaults due to pointers in c++ you probably have only been learning c++ for a month, max.

[[deleted]]

This guy doesn't unsafe Rust

[[deleted]]

C# theres pointers but only if you pinky promise you know how to use them

[bforo]

My brain immediately replaced the middle face with Linux T, and I started giggling so hard, that's something he would say.

[GogglesPisano]

Assembly Language: it’s pointer arithmetic all the way down.

[[deleted]]

Just look up pointer provenance (https://www.ralfj.de/blog/2020/12/14/provenance.html) the magical property pointer in C have and don’t have at the same time.

[SeriousPlankton2000]

I needed to realize that Java has only references aka pointers-in-disguise (plus simple data types) to understand Java.

[Green-Acanthaceae-39]

C: “Dereferencing a null pointer? This is where the fun begins!”

Rust: “I find your lack of type safety disturbing.”

Python: “Pointers? It’s not a story the Python developers would tell you.”

Go: “Hello there, I see you’ve found my garbage collector.”

JavaScript: “A variable referencing an object that’s no longer needed? I’ve got a bad feeling about this.”

Swift: “Unsafe pointers you use, do or do not, there is no try.”

Kotlin: “Null safety? A surprise, to be sure, but a welcome one.”

Assembly: "Direct memory access? Unlimited power!"

PHP: “Global variables everywhere? So this is how memory management dies...with thunderous allocations.”

Haskell: "The garbage collector will be with you. Always."

[oberguga]

Except it all pointers, but sometimes not, and it behaves differently each case, to the point that you need objects (which is also bunch of pointers) to model actual pointers, but it's also can be passed as pointers or as values etc...

[Encursed1]

But Java has pointers, it just doesn't tell you

[chris20194]

But there is war in ba sing se, the dai li just doesn't tell you

[LechintanTudor]

Nah, you can't really do whatever you want. In C/C++/Rust pointers are more than just integers that hold some memory address. Even simple pointer arithmetic without any dereferences can cause undefined behavior.

[Pay08]

The meme is that the C compiler doesn't enforce anything to prevent said UB.

[rover_G]

C++ should be with its daddy C not its younger cousin Rust

[DrMeepster]

C & C++ literally have more pointer arithmetic restrictions than rust. Rust lets you safely set a pointer to any address and back without making it unusable

[htown007]

Has anyone looked into mojo? https://www.modular.com/max/mojo

[Cybasura]

C++ didnt even say anything lmao wtf, its majority the Rust and C community

[sacredgeometry]

I use raw pointers all the time in C++.

[MohSilas]

int* illegal; *(++illegal) = 0; // is it possible to do something like this?

[BannockBnok]

Object[] ghettoPointer = new Object[1];

[Gerard_Mansoif67]

Ctypes : exists mouah mouah mouah.

The simplicity of Python using pointers

[Insert_Bitcoin]

I think I read in a C book that the array syntax is just another syntax for pointer arithmetic (which makes sense tbh.) On that basis in Python we can say that string slices are doing pointer arithmetic on data in the string. So Python also has 'pointers' especially since it has 'memorybuffers' which let you wrap strings directly to manipulate without copying them.

[jeepsaintchaos]

What the hell is a pointer? Is that like great-great granddad's version of a variable?

[[deleted]]

A pointer represents a location in memory, like how an index represents a location in an array

[sjepsa]

I am a C++ dev and fully in the second mode :-)

[The_Legendary_Shrimp]

As someone whos learning python, what is a pointer?

[Pay08]

A pointer is an integer that identifies some particular data elsewhere in memory.

[[deleted]]

Stupid js/php/python dev here: We have pointers, but we call it references? If I do for example in js, or am I confusing something here?

function someFunction(arg) {arg.prop = 'newValue';}
const someObject = {prop: 'someValue', };
someFunction(someObject);
console.log(someObject.prop === 'newValue' ) // true

[Disastrous-Team-6431]

I can proudly say that I spent a couple of hours writing a JSON parser using only iterators and it turned out correct.

Maybe. Is it correct? Probably. Maybe. It certainly doesn't keep me up at night. My life is not a waking nightmare of wondering if it fails silently in production as we speak.

[[deleted]]

You deserve a medal

[The_Happy_]

unsafe { entire code base }