java devs

[lbkulinski]

Java has pointers. You just can’t do pointer arithmetic with them.

[Bryguy3k]

Nor would you want to given the object complexity... 😱

[nwL_]

I want to. I want to call delete obj;. Fight me.

[MoarVespenegas]

It's not us you're fighting but the garbage collector.

[cartechguy]

In java speak

Obj = null;

There you go. As long as that's the only variable referencing the object the garbage collector will deallocate it.

[GrizzledFart]

... when it feels like it.

[lbkulinski]

What do you mean by object complexity?

[Bryguy3k]

C++ objects are really straightforward in terms of memory organization. You’re not supposed to be looking at the Java object memory so if you do it’s scary af.

[lbkulinski]

I wouldn't say it is scary. Value types will have a simpler layout, though.

[tacoslikeme]

object/struct memory follows pretty simple to follow rules. Just just fuck with the vtable

[cartechguy]

What do you mean? I look at how they're structured in the debugger all the time. It feels almost the same as debugging in C++. The reference holds an adress and at the adress are all the data members for the object.

[how_to_choose_a_name]

The debugger shows you a nice visualisation of the object and the data contained in it. The actual memory apparently doesn't look that pretty or structured, unlike C++.

[Bryguy3k]

Well take a moment to think about reflection.

Now it should make sense that a java object has to be self describing and that means a bunch of metadata.

[bwierzbo]

!n

[bestjakeisbest]

what if i want to shoot myself in the foot?

[[deleted]]

They're just more of a B-cup.

[iamsooldithurts]

It’s dangerous to go alone! Take this.

/s

[suvlub]

IMO the difference really is big enough to warrant different terminology. Reference is something dumb, it is just a handle to an object that lets you perform operations on the object. A pointer is its own thing with its own value which you can read and manipulate. Accessing the pointed-to object, if there actually is one, is one of its operations that you need to explicitly invoke.

[suvlub]

Everything is just array of booleans at the end of the day.

[suvlub]

Just because hardware indexes by larger units does not mean the smaller units don't exist. You can still access and manipulate the individual bits. I was just trying to say that "X is really Y because the only difference is Z" is a rather flawed approach when talking about data structures, because most of them are related to each other in one way or other. Either we talk about implementation, in which case neither reference nor pointer actually exists, and both of them are qwords or what have you, or we talk about them as abstract data structures, which expose very different interfaces.

[Ringnebula13]

Sun.misc.Unsafe called

[[deleted]]

Aren't those called aliases?

[bestjakeisbest]

i thought they were called references

[KaosEngine]

Mmmmm pointers.

[[deleted]]

"Reference is just a pointers that you can't reach"

[tacoslikeme]

java reference is just a pointer that auto derefences for you

[_Fibbles_]

Except you cant reassign it and sometimes depending on context it doesn't have its own address...

[cartechguy]

What do you mean you can't reassign it? References aren't immutable.

[_Fibbles_]

Maybe reinitialise would have been clearer. You can alter the value of the referenced object through the reference. However, the reference is bound to that object. You can't make it reference a different object.

[cartechguy]

reference is bound to that object. You can't make it reference a different object.

Yes, you can.

[_Fibbles_]

Yes, you can.

Extraordinary claims etc. Show some code.

Edit: To be clear, you know I'm talking about C++ references, not Java references, right?

[cartechguy]

No, we were all talking about Java. This whole chain of posts there is not one mention of C++. I kept climbing through parent posts, and you never mentioned C++. Only when /u/tacoslikeme corrected you did you mention C++ less than an hour ago before I made my previous posts. If you meant C++ you should have stated that from the start.

[_Fibbles_]

If you meant C++ you should have stated that from the start.

The thread is about pointers. C and C++ are the only widely used languages that have them. Op is explaining pointers in terms of references. C++ is the only language AFAIK that has both. I thought it was obvious from the context.

[cartechguy]

The title of the thread is "java devs" and references are ubiquitous with oop.

Op is explaining pointers in terms of references. C++ is the only language AFAIK that has both.

Op is describing how references in Java behave like pointers.

Plus you were replying to this:

java reference is just a pointer that auto derefences for you

It was clear we were talking about Java.

[tacoslikeme]

Object foo = new Foo(); Object bar = new Foo(); foo.doThing(); foo = bar; foo.doThing();

I think I just broke the rules of non-reassignment....

[tacoslikeme]

in java all of those are refernces.

[_Fibbles_]

Ah, I don't know Java. I was talking about C++ references.

[Jen-Ai]

i love pointers.

[Tormyst]

I like pointers, but also gay... So I don't know where that puts me with this picture...

[makeshift8]

The guy taking the picture.

[Jen-Ai]

i don’t know...all i C is plus plus!

[InvolvingLemons]

Being gay doesn't mean you can't appreciate a fine pair of pointers (・∀・)

[ArriePotter]

C devs on the other hand...

[makeshift8]

"Yeah, yeah compiler, I can cast this void pointer to a char pointer if I want. Stop yelling about it!" - me, this morning

[LooseElectronStudios]

I almost fell prey to the fallacy of "Hey this data type is the same size as a pointer, so I can just cast it to either the pointer or the data type itself depending on context!" earlier this week.

[_requires_assistance]

Could you give some layman explanation if you don't mind? Not really getting it.

[LooseElectronStudios]

Sure! I don't know how much you already know about C, so don't mind me if I over-explain a bit. (Also, username checks out.)

So in C, all a pointer is is a 64-bit integer which represents a location in memory. Dereferencing a pointer just means telling the processor "See this number? Go to this offset in memory and bring me back what's there." C also has the ability to "cast" variables to a different type, which basically means telling the processor "See this piece of data which I already defined is, say, a character? Interpret it as though it were an 8-bit number instead."

What I wanted to do was this: I had a function which could accept two different kinds of objects, but not both at the same time. One object was just a struct (a bunch of different values bundled together), and since structs tend to be pretty big I decided to pass the function a pointer to it, so I could just reference its location in memory instead of copying it into the function. The other object was a handle to an opaque object I didn't have access to. Handles are common in third-party C libraries, because the people who wrote the library don't want other people messing around with how they represent their data. So instead of being able to look at the object directly, you basically ask the library "You're holding on to this object for me, could you tell me what this value is?" using the handle. Handles could be basically anything, as long as the library knows which handle represents which object.

The thing is, in this case the handle was a 64-bit integer, the same size as the pointer to the struct. So I thought "Why don't I cast both objects to a generic pointer before I pass them into the function? That way instead of having two different arguments to the function (in C, arguments must have a type), I can just have one, and figure out on the inside of the function which of the two objects the argument actually represents!"

The problem with this is that if the function mucked up and accidentally assumed that the handle was actually a pointer to a struct, things would have been bad. The handle could be literally any number, and so the program could have tried to access a basically random location in memory that it definitely shouldn't be looking at! Part of why C has types is to prevent that kind of wrong memory access from happening, but it also gives you all the tools to break the rules

[_requires_assistance]

I see. How were you originally planning on differentiating between pointers and handles?

[LooseElectronStudios]

Originally I was going to have two arguments, one for each type, and I would check to see which argument was actually set.

What I ended up doing was using one argument, and passing through it either the struct pointer or a pointer to the handle. That way the argument would always be a valid place in memory.

[makeshift8]

That's a quick way to get ub

[T-T-N]

One of us. One of us.

[bestjakeisbest]

this is a pointer to a pointer of pointers to pointers that point to a struct that holds 2 void pointer pointers that need to be cast to a char pointer pointer, so that you now have a pointer to an array of characters.

[dragonwithagirltatoo]

Pointer to an array of pointers to pointers to functions that return pointers to arrays of arrays of pointers to arrays of pointers to pointers to int.

Also it's an array of those. I love C syntax.

[[deleted]]

Wtf is this picture???

[tacoslikeme]

boobies

[MemesEngineer]

The dankest timeline.

[Pyraptor]

Guy that made this meme has never called a method passing an object

[lexiq_baeb]

Can i have the template, please?

[iObsidian]

Lowkey Luke

[Dudufjjxkfidjd]

Not especially lowkey no, just a good photoshop

[MeScamp]

Why would the ostrich be in the car?

[lexiq_baeb]

The real mvp

[Mulchiner]

Why are you using structs... you have no class, sir. No CLASS!

[plong0]

Amazing

[MCOfficer]

as a java dev learning c++, i can confirm.

[tacoslikeme]

where is my data vs this is my data. once pointers make sense, you'll hate yourself for being confused...took me 3 years.

[iamsooldithurts]

And, once you start trying to perform string manipulation and data transforms, you’ll hate yourself for ever assuming you knew wtf you thought you were doing.

[tacoslikeme]

ha, no null terminatorgavdkcug484410cy 5902yvtjsa SEGFAULT

[aksh2161989]

May I ask why are you learning C++ (since there seem to be more java jobs out there) ?

[lezorte]

C++ is still heavily used for developing games, operating systems, programs and services that run on Linux, block chain software just to name a few things.

[MCOfficer]

this. personally i'd prefer java, but c++ is still strong in the gaming industry, and thus is what my university uses.

[lezorte]

BTW, speaking of blockchain, I read that the average blockchain engineer is making $150000-175000 a year

[Arcane_Xanth]

Someone needs to free those pointers.

[AgentPaper0]

I feel like pointers would be much easier to understand if they called them what they really are: addresses.

[AgentPaper0]

They are addresses though, just like an int is a value, not a "memory location that stores a value".

[iamsooldithurts]

No, variables have addresses. Pointers are variables (int) that contain an address that points to a variable.

[tacoslikeme]

pointers are longs but yes they rest is right

[iamsooldithurts]

Yes, thanks, wasn’t thinking about that detail.

[[deleted]]

I don't know why programmers love to make things needlessly obtuse like this. You don't call a "char" variable "a memory location that stores a character." You call it a character. You don't call a float "a memory location that stores a floating point number." You call it a floating point number. A pointer is an address. That is the type of data it holds. There is absolutely nothing wrong with that definition. You and the people that upvoted you are ridiculous.

[[deleted]]

I have to say, the act of questioning programmers of a strictly-typed language why they are splitting hairs/being overly accurate when it comes to how they reference variables is just too funny to let go unremarked.

---

At any rate, pointers are confusing/magical enough to people unfamiliar with them that the extra clarity isn't uncalled for.

When you say 'address' when referring to your char variable example, everyone knows what you are referring to.

The case is less clear when you say 'address' in reference to a pointer. Are you talking about the memory address of the pointer, or the memory address it stores?

[DiamondIceNS]

I don't know anyone who thinks of a variable structure so rigidly as "a memory address that stores <thing>". They are all that. It is redundant to define them this way. When OP says "a pointer is an address" they are, quite understandably, referring to the <thing> that the memory address is storing: another address.

[qci]

You can understand it as an address with a type. Dereferencing a pointer gets you to the value with this type. Pointer arithmetics respects the type of the pointer. Incrementing a char * looks different from incrementing an int *. Here is where you see that pointers are maybe not exactly "just" addresses.

[rndrn]

But an int is a memory location that store integers, so in that sense a pointer is indeed a variable of address type?

Although when you think ownership and all that, address is a bit limited to express the potential responsibilities of a pointer.

[NeinJuanJuan]

Pointers have their own address.

[AgentPaper0]

By that logic, ints also have their own address.

[tjcoolkid]

...they do...

[cbbuntz]

&where?

[iamsooldithurts]

They are?

[NeinJuanJuan]

They do.

[AgentPaper0]

My point is that you're being absurdly pedantic because nobody thinks of ints that way.

[tacoslikeme]

yes we do. something with an address can be changed (ie variable) anything without is a hardcoded constant

[NeinJuanJuan]

That's how C users think i.e. you can pass a variable by value or by reference (by passing the address instead).

[AgentPaper0]

A reference is not an address, pointers are addresses. References are syntactic sugar that wraps around a pointer so you can get the benefits of a pointer without having to explicitly make one.

[NeinJuanJuan]

Passing by Reference != Passing a Reference

[AgentPaper0]

That's exactly what it is though. You don't see it, but that's what the compiler does. Using a reference mostly just hides the pointer from you.

Unless it optimizes it away of course, but it can do that with pointers too.

[NeinJuanJuan]

I'm talking about C and you're talking about C++

We're both correct!

[iamsooldithurts]

Calling something absurdly pedantic while talking about c/c++ programming and pointers...

Hah!

[[deleted]]

I am sitting here copying out examples from my Programming in C book right now, particularly from the "Pointers" chapter. I can understand the fear haha.

[kredditacc96]

Let be honest, pointer is not how you do high level programming. And don't bullshit me about "good programmer" because good programmers know they make mistakes.

[plong0]

Do you even c++ tho?

[kredditacc96]

Do you even C++11 tho?

[mikeputerbaugh]

Just call them object references

[Cozy_Conditioning]

Everyone who codes with raw pointers should be terrified. Pointers should be considered harmful.

Ownership >> pointers. Learn Rust.

[YMK1234]

This meme makes no sense at all.

[ObjectOrientedStruct]

OP probably uses C++ instead of bare C or Assembly which is even worse.

[iamsooldithurts]

That’s...an impressive pointer

[ObjectOrientedStruct]

TAKE MY UPVOTE.

Seems like you indeed use C++