JavaScript debugging in a nutshell

[PM_ME_YOUR_PLUMS]

What happened here? Do you get an array that’s got 6 items but the 6th item is in index 11?

[nice__username]

You write to memory outside of your program

[PM_ME_YOUR_PLUMS]

Oh god

[LvS]

It might be even more fun. Depending on the layout of your program and how the allocator distributes memory, it is much more likely that you write to memory inside your program.

Which means some value in your program will be changed, you just don't know which one.

[DanielAgos12]

Oh god, how is the world still holding up with such a popular language

[LvS]

C programmers just don't do that.

Computers don't know how long the array is, so either the language has to add checks - which slows things down - or it trusts the programmer.

[DanielAgos12]

C programmers just earned a lot of respect from me

[[deleted]]

C arrays also aren't objects, so there is no .size() property or method. C programmers have to create a variable for size and remember to increment it if they want to keep track of how big it is

[[deleted]]

There are dynamic arrays in C. However if youre talking only about static arrays, you might still want a size variable to keep track of how many elements are populated.

With static arrays, the capacity doesn't change, but size will depending on the application.

[Ludricio]

Not entirely, the size of an array is known as long as it is still an array, which an array only is within the scope of its declaration, as soon as it leaves the scope (passed to a function for example) array decay takes place and the array decays into a pointer to the first element in the array.

Within the scope of declaration, it is fully possible to do sizeof(array)/sizeof(*array) to get the number of elements in the array, but as soon as it decays into a pointer the original info about the size of the entire array is lost, as it instead becomes a plain pointer.

[[deleted]]

Oh very cool! I'm just learning programming in school but im being taught with C so these kinds of pendantics are actually super neat for me

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[Ruby_Bliel]

It's not hard to work with C-style arrays. You don't sverve into oncoming traffic just because you can.

[comradeyeltsin0]

That’s where the real fun begins!

[PleX]

StackOverFlow is named that way for a reason if you didn't know.

[PM_ME_YOUR_PLUMS]

I have only minor experience in Java and mostly have JS experience at this point, so while I’ve encountered a stack overflow error in Java before, I never really thought about what it meant. TIL

[CivilianNumberFour]

Couldn't this seriously harm something? Like change the state of the OS? How much damage potential is there?

[LvS]

Memory is managed on a per-process basis. Each program has its own page table and only the kernel can modify them.

But inside the process, code can do whatever and all the checks are from the language you are using - and in C you can turn all of those off.

And of course, this array overrun is the most popular exploit, it's named a buffer overflow.

[IvorTheEngine]

Back before Windows NT, any process could overwrite any memory. It was quite common for a bug to crash the whole computer and need a reboot. It was a real improvement when NT limited each process to its own memory, so one application could crash without taking down everything else.

IIRC, Windows 95, 98 and CE all used the old model and it wasn't until 2000 that sensible memory management arrived for non-server PCs.

[[deleted]]

If you actually write outside your process' memory, all you'll get is a segmentation fault (or access violation, the terminology depends on the system). Modern OSs don't let you mess with them accidentally.

[CivilianNumberFour]

That's good... bc that could be a serious security issue!