Stack vs Heap Memory - Simple Explanation

[@michaeltheisen]

These ideas were saved in my head as a sequence of words for the entirety of my undergrad. If 5 short minutes you managed to actually help me understand a huge gap in my understanding. Thank you so much.

[@alexhyettdev]

You're welcome Michael, I am glad it helped.

[@saumyojitdas4212]

​@@alexhyettdev public class Main { String s = "ABC"; public static void main(String[] args) { Main obj = new Main() ; System.out.println(obj.s); } } in this above code String object is created in heap and also of class. So 2 objects in heap. But isn't the string object Abc resides inside class object in the heap?that's why we are calling it obj.s

[@rembautimes8808]

Good video very in-depth

[@crazychase443]

i feel the exact same way!! this random collection of words and statements now i feel like concrete concepts in my brain

[@aborda0987]

@@alexhyettdev Quick question. You mentioned that when a pointer/ref in the stack is deleted, the value it points to dangles around the heap until the GC collects it, but what happens in a language like C++ there is not GC? Would that become a memory leak?

[@kohltonpeterson3287]

This is one of the best programming related videos I have ever watched. It cleared up so much of my confusion in C++.

[@alexhyettdev]

Thank you!

[@JakeSouthernCalifornia]

Alex, you made my day. I would call you one of the best instructors! Your explanations are flawless. You explain perfectly in context. For instance, where you explain why variables are not accessible outside the method.

[@alexhyettdev]

Jake, you made my day! Thank you for the lovely comment. I am glad you found it helpful!

[@christymathew9035]

YOU ARE LITERALLY CAPABLE OF REPLACING 99 PERCENT OF TEACHERS WHO PATHETICALLY FAILED TO TEACH ME THIS CONCEPT. THE CLARITY WITH WHICH YOU JUST EXPLAINED IT SHOWS THE TRUE MASTERCLASS YOU ARE IN. I WISH I DINT WASTE MONEY IN COLLEGE WHEN PEOPLE LIKE YOU EXIST. LOVE YOU SIR ❤

[@luminuslux]

Not gonna lie, i cant state enough how explanations like this can massively improve your understanding of why code works the way it does. Just learning to code is one thing, but understanding whats behind all of it and WHY whatever thing actually is happening, can definitly up your game. Im not a pro by any means, but i think stuff like this is very important. The visual presentation also makes it way easier to follow and connect the concepts - so thx for that 😊

[@alexhyettdev]

Thank you, I am glad you enjoyed the video. I find it helps with remembering everything as well. If you can understand something then it tends to stick in your mind a bit better.

[@Pratik0917]

Fab explanation.. Saw many videos however nobody has explained clearer than you..Thank you

[@Tanessok]

Thank you sir. Good Explanation. Please, I wish you make a video on "Why in Java, Do Local Variables Used in Lambdas Have to Be Final or Effectively Final?" and please make the explanations at the memory level too, so we can understand all the mechanics behind it.

[@awys5]

I've been coding, and teaching code for the past 4 years. This video blew me away. Explained everything so well, and was incredibly easy to follow. Sorry, Alex, I will be stealing this! Amazing work, and you've got a new fan! Thank you!

[@scubagoblin]

Reading a book right now that explains this concept rather poorly over 20 pages. You managed to grant me understanding in 5 minutes, and now I can continue reading past the chapter. Thank you, great explanation!

[@alexhyettdev]

You’re welcome! I am glad I could help you understand it. Hopefully more fun than reading 20 pages of that book.

[@fuadadio]

Your videos are awesome and very clear. Can't wait for a full CS playlist. Thanks for what you do for the community Alex.

[@bitwisedevs469]

Finally a much simpler with actual sample code that explain the whole stack and heap stuff. Now I understand why and when OOM occurs in app, the usual suggestion is to increase heap size but said to be slow or when we do recursion recklessly we get stackoverflow.

[@b25671]

I've seen multiple videos of you now... you can explain the essence of things very well. It's a talent. Very good. Thank you!

[@sonederbr]

The best explanation/animation ever.

[@alexhyettdev]

Thank you!

[@Nicolas-L-F]

Insanely useful video, didn't think i'd learn that much in just under 6 minutes, thank you.

[@RYANCARNEY-dc2qe]

This video actually answered all my questions about how the stack and heap work together. Great explanation!

[@patrickmccarthy7124]

The analogy of a stack of books provided much needed clarity for me. I appreciate the video mate!

[@alexhyettdev]

You’re welcome, I am glad it was helpful.

[@Saad.Makhdumi]

Very good explanation, in short amount of time. I hope all IT folks see this video and understand these topics. Thank you Alex.

[@AhmedAlsabsab]

Finally I understand the difference in few words and short time... keep doing videos like this

[@0bsy96]

My jaw dropped when you explained what happens to variables declared in the stack, I never made the connection between this fact and the scope of variables, thank you soooo much !!!

[@nikolabosevski1435]

Samee heree, I've never even thought of why we couldn't call variables from different scopes, i just took it for granted this opened my eyes

[@TheHermitProcess]

I'd be extremely weary of taking this for fact. It is up to the compiler to generate scoping rules, as far as I know. Look into it a bit more.

[@brunofilgueiras3518]

such a clear explanation couldn't get better thanks Alex

[@austinhummel5439]

I can't put into words how helpful this video was. Thank you Alex!

[@Misteribel]

3:01 small correction. A const is NOT allocated on the heap. In fact, it's embedded on the call site at compile time (in C#/F#/VB), the reference is removed (you can test this: create a const in another lib, reference and use it in your lib. Compile. Now update the const in the referenced lib and recompile, but do not recompile your lib. You'll see it did not change on the call site). What you probably want is readonly, which, in your example at 3:01, would then be allocated on the heap.

[@benessilfie]

This explanation was exactly what I needed! thank you Alex

[@alexhyettdev]

You’re welcome I am glad it helped!

[@i_am_dumb1070]

Thank you very much i was not able to understand this concept even after reading and watching a lot of videos now i have a good understanding of this

[@alexhyettdev]

That’s great! I am glad I helped.

[@i_am_dumb1070]

@@alexhyettdev if possible can you please explain the anonymous function part i didn't get it

[@basedd64]

Perfect, really good explanation. Thank you!

[@alexsal6069]

This is an excellent video about how the memory works, I love the last part about asynchronous methods. Thank you for this awesome content. I wish you could speak more about asynchronous functions. 😃

[@orrymr]

Wow, absolutely brilliant video. Thank you, sir!

[@tylerlwsmith]

Incredible. Even though I've been a professional developer for six years, I was having a crisis of confidence tonight because I've worked with languages where I never have to worry about this directly. I was asking myself, "Do I even know anything about computers if I don't know the difference between the stack and the heap?" Five minutes and twenty-seven seconds later, I feel like I have a solid understanding of the difference and I'd be capable of talking about this intelligently. Thank you 🙏

[@alexhyettdev]

I have been a developer for 12 years and I went through exactly the same thought process before making this video. I am really glad it helped you.

[@___gg421]

Same here just went through a training where some memory management stuff was covered and I felt like an imposter. This made it all make sense

[@mojizze]

Finally, i now understand the differences between these two. Thank you for the video

[@alexhyettdev]

You're welcome 😊

[@csanid1]

hey this is an excellent video! i'd never thought or read about the link between variable scope and memory. thank you so much!

[@aelesbao]

This video needs to be promoted higher on KZbin. Anyone who wants to learn Rust should start from here before diving into the borrow checker.

[@alexhyettdev]

Thank you. I am glad it is useful for people learning Rust as well. Some of the C# references might not be applicable but hopefully the rest is. I need to learn rust as well actually!

[@agun214]

hell yeah. idk how you did it but that finally made sense. i had to have heard the stack of books analogy before, but this is probably the first time seeing it played out with actual books imma have to watch this again

[@GG-sw9vm]

that was a clean description of stack and heap. Never knew about anonymous function being a heap, but it makes sense

[@alexhyettdev]

Thanks I am glad you liked it 👍

[@potatopotato4676]

Your explanations are immaculate! You'll definitely make it big if you want to. I am glad I caught your channel early at 18.4k subscribers

[@alexhyettdev]

I appreciate that! Will be making more videos soon.

[@balajia.t1487]

A nice and concise explanation . Wishing you all the best for better reach of your subsequent tutorials so a lot from community would benefit

[@amalekilawlor2922]

Wow this was an incredible series of topics, thank you!

[@alexhyettdev]

Thanks, I’m glad you enjoyed it!

[@nomymathieu-petrin5672]

A hidden gem !!! Thanks you so much, I understand it so much better now !!!!

[@alexhyettdev]

I am glad it helped!

[@SSn0wx]

Great explanation. I do mostly web development, but I've been getting into low-level programming recently, and your video really helped me reach out into my bucket of programming concepts and rearrange a bunch of previous knowledge I had about computers into something more clear and concise. Thanks!

[@alexhyettdev]

You're welcome, glad I could help!

[@johndzikunu9986]

This is good. Have learned some things I could not know in a year.

[@alexhyettdev]

That’s great I am glad you learned something from it. Thank you for commenting.

[@TonttuTorvinen]

Awesome video, very short and to point.

[@Ali_Pxll]

Man you're a savior thanks for the clear explanation

[@alexhyettdev]

Thanks, glad I could help

[@chocolate_Almonds]

Dude, that was awesome. You explained what I tried to wrap my head around in college courses, in 5 minutes. ily :)

[@alexhyettdev]

Thank you! 👍

[@Soupie62]

How does garbage collection handle memory fragmentation? Is there a heap defrag utility? Do you wipe the heap when a program ends? What is multiple programs / threads run concurrently? Now I need to check the rest of your videos for answers. Thank you for starting my journey.

[@rmcgraw7943]

In C#, async methods that complete sync, before you await them, will not go onto the heap, hence the reason we have ValueTask now. However, if you use a ValueTask struct and it doesn’t complete sync, then you incur a hit of boxing, allocation, and deallocation (GC collect), which makes it a tiny bit more expensive than the regular Task class. One more thing. If you cast any value type to an Interface type, it will go onto the heap, even if it’s a struct or value type.

[@wajdwael8775]

That is a great, clear, and easy explanation, thank you.

[@Mythical_Beastinator]

Very well explained. Thank you!

[@alexhyettdev]

Thank you, I am glad you liked it!

[@may8128]

Loved the explanation !

[@alexhyettdev]

Thank you! I am glad it was helpful.

[@timi_t_codes]

Thanks for this simple and straight to the point explanation

[@alexhyettdev]

You’re welcome!

[@Zmey5656]

Thank you, very simple and useful explanation

[@vfryhn2]

Such a great explanation

[@alexhyettdev]

Thank you! I am glad you liked it.

[@mithunkinarullathil643]

Very good explanation, thank you.

[@itsurguy7756]

Hello sir at 3:20 in the video you say that in must run times there is a garbage collector that will clean the memory from the stored memory location after it has finished execution. Not sure if you know but with in C and C++ language we do not have a garbage collector I was told. So in C and C++ we delete pointers manually after block execution. So, Actually C and C++ are not garbage collecting languages.

[@dorianneto2859]

Such an intuitive and simple explanation!

[@alexhyettdev]

Thank you, I am glad it was helpful.

[@milehighgaragespeedshop1065]

Excellent explainer and graphics THX

[@alexhyettdev]

You’re welcome, I am glad you like it.

[@satyabharadwaj7779]

Asynchronous methods don't run on different threads. They run on a single thread but with a flexible event loop mechanism

[@obama213]

While asynchronous methods can run on different threads, they do not necessarily have to. Aync execution can also involve single-threaded environments. E.g.: with event loops (JavaScript / Python's asyncio)

[@gavinmeeker287]

Really great video! This helped so much

[@alexhyettdev]

Thank you I appreciate the kind words. I am glad it was helpful.

[@Freepackman]

absolutely brilliant explanation, thanks a lot

[@alexhyettdev]

Thanks, I am glad it was useful!

[@alejandropoirier6493]

Amazing explanation, greetings from Chile

[@alexhyettdev]

Thank you! Hi 👋 from UK 🇬🇧

[@kwaku_2023]

@4:23 what do you mean by the anonymous function is pushed on top of the stack and not have access to what previous level down? You mean even variables within main?

[@skankhunt__42]

3:54 Good Video but in object oriented the static variables dont go into the heap. zero-initialized static data goes in bbs and non-zero-initialized data goes in data

[@EugeneDaveAstator]

Awesome video! Id like to add that in csharp async doesnt always equal multithreading, and since it uses internal statemachine which is a class, asyncs may get allocated on the heap

[@alexhyettdev]

Yes it’s a good point!

[@kasunsaumya3151]

Simply love your explanations.. Clean and deep..

[@alexhyettdev]

Thank you! 🙏

[@JHatLpool]

Very nice explanation. Thanks !

[@4rjunc]

straight to the point 💯

[@leeeric6292]

Many thanks to your video, this KZbin is valuable, so I read word by word carefully. And I find at 03:55, about the static variable, which is different from what you mentioned in your flvog (the link you provide in descriptions). In ur flvog, in para "where do static variable live", there you said static variables even if they are value types are not stored on the stack or the heap...need clarify? Thanks.

[@alexhyettdev]

Thanks for spotting the discrepancy! I need to update my blog to make things clearer. Basically it is an implementation detail. In C# static variables are part of the MethodTables on the "High Frequency Heap". Which is a special part of the Heap memory for static variables and internal data structures. In C and C++ they are stored on the Data Segment, which is a special part of the memory for storing static variables and internal data structures. :) Sound familiar? If you look up Data Segment and High Frequency Heap they are both in the same place in memory. By the looks of things they are just slightly different implementations of the same thing. There is an old article here that explains it in depth: web.archive.org/web/20140724084944/msdn.microsoft.com/en-us/magazine/cc163791.aspx Jon Skeet also has a good article on it as well: jonskeet.uk/csharp/memory.html

[@leeeric6292]

@@alexhyettdev Thanks for your response and your KZbin.

[@paulventura3118]

Great explanation! Thanks Alex!

[@alexhyettdev]

You’re welcome!

[@miladfahimi4787]

that was flawless thanks a million man

[@alexhyettdev]

You're welcome, I am glad you liked it.

[@PabloDeLafuria]

Great video, great explanation! Thanks

[@AdrianTregoning]

Create more content, you'll be to a million subscribers within a few short years I have no doubt. Your content is pure gold, thank you for explaining this so clearly.

[@alexhyettdev]

Thank you 🤞🏻. Regular content will be back again in September. I have had some family commitments that has put a stopper to my videos this month.

[@AdrianTregoning]

@@alexhyettdev fully understand. Good luck! I quit my full time job as a mechanical engineer to become a programmer/coder of sorts. Bit tough being a student at age 41 but for me I made the decision to ultimately spend more time with my family. Have a super day further.

[@polimorphic13]

Excellent explanation. Thank you so much.

[@tejassravanthikasulanati4733]

thats lot of info, more than what i was looking for. 👍

[@khaledmoazedi4317]

hey Alex ! it was very great to find your videos on this topic ! so clear and easy . can i grant your permission to translate your videos in persian by my voice and re share them on a channel for persian people to use them?

[@triphazard2906]

lovely explanation, thank you for this

[@alexhyettdev]

You’re welcome! I am glad it was useful.

[@rembautimes8808]

Loved the garbage collector animation. Very nice and funny

[@gantushigsaruul2489]

Thank you for easy to understand and great video

[@davidjiang7929]

Thanks for the great explanations!

[@Ahmed1Hussein]

you actually help me understand a lot ,thank you sir

[@alexhyettdev]

You’re welcome!

[@mehtubbhai9709]

@Alex Hyett As always, you give the best explanation of whatever programming topics that you cover. Please keep up the great work and keep the content coming. I'm a fan :)

[@alexhyettdev]

Thank you, I am glad you like them!

[@iDeveloper92]

Excellent breakdown!

[@alexhyettdev]

Thank you!

[@Erhannis]

4:20 Can't you, though? For instance, passing &localVariable to a function call I think lets that function access localVariable by reference. I think that's a common mechanism for setting multiple output values. (Similarly, around 2:10 it says that the values of reference types are always stored on the heap, but &localVariable gives you a reference to a stack value, doesn't it?)

[@alexhyettdev]

It is going to be different for different languages. Each has its own way of implementing stack and heap. Yes in the case where you are passing a local value variable by reference to another function, I believe that function gets a reference to the local variable in memory even though it is in the stack.

[@MarcoLenzo]

This video was very good! I really like the way you explain!

[@alexhyettdev]

Thank you! I am glad you liked it.

[@Black_Cats_]

Good video. One question: In the case of results from asynchronous methods, once the asynchronous function completes, who cleans up the result in the heap that was left over by the async function?

[@alexhyettdev]

Generally they will be cleaned up by the garbage collector in the same way other objects on the heap are.

[@Black_Cats_]

@@alexhyettdev thanks for your response

[@ragtop63]

Well done! Very good video.

[@jesusromero9167]

Great explanation!

[@JanosTech]

Fantastic explanation, thanks mate!

[@alexhyettdev]

You’re welcome! I am glad you liked it.

[@jacobL1172]

Learning Redux right now, so very helpful! Definitely subscribing.

[@alexhyettdev]

Awesome, thank you!

[@tibebetech4867]

Thank you!

[@alexhyettdev]

You're welcome, I am glad you liked my video.

[@chitoan77]

Can you re-check this one? I think something is incorrect with global or static variables. We basically have 4 segments: Stack, Heap, Code Segment, and Data Segment. Global or static variables, including constants like `const int MAX_AGE = 99`, are not stored on the heap. They are typically stored in the Data segment of the memory, specifically in the initialized data section. The Data segment is a part of the memory that contains static and global variables. These variables are allocated and initialized before the program starts executing. The initialized data section of the Data segment holds variables that have explicit initial values, such as the MAX_AGE constant in your example.

[@vikingghost117]

I haven't coded in over a year. I had a dream where I was traversing a world on some quest to explain stack vs heap to all these people getting it wrong, and I knew they were wrong but didn't know why. Soon as I woke up I came here. Now I can sleep at night again. Thanks! 😂 It was an..(Explain you're a nerd without saying you're a nerd XD)... moment.

[@alexhyettdev]

I am glad I can help you sleep at night! 😂

[@tannguyen_91]

amazing, this help me understand everything

[@kinnetikira]

The static variables are supposed to be stored in the Data Segment not Stak or Heap. the video mentions that static variables are stored in the heap.

[@younesmdarhrialaoui643]

Great explanation!

[@alexhyettdev]

Thanks! I’m glad it was helpful!

[@Cruz0e]

what does "heap has higher overheads" mean...? higher cost? I assume (seeing that little 'watch' with pointer at high) that you mean for example it's slower, because it's more complicated for the "machine code" to add to the heap?

[@alexhyettdev]

Yes higher overheads as in performance. It is slower to add to the heap compared to the stack.

[@AXkj3mmy]

Thank you! This was great

[@mattp6460]

great explanation thanks

[@jamiewalker6296]

Is this what a memory leak is? If something like c++ that doesn’t have garbage collection or something gets left on the heap is that memory leaks or is that something else?

[@alexhyettdev]

Yes exactly, languages like C++ which don't have a garbage collector need the programmer to release the memory correctly. If they don't then memory stays allocated on the heap and can't be accessed by anything causing a memory leak.

[@TejAgarwal]

Really nice explanation but I have one doubt, I used to think that global variables are stored outside of both stack and heap in a dedicated area for global and static variables. Would be great if someone could clarify on that.

[@thankzcomputer]

thanks dude

[@juliaclaire68]

thank you! very clear

[@alexhyettdev]

You're welcome Julia, thank you for commenting.

[@dflosounds]

Great explanation! Thank you! My only bit of feedback would be to stay on the graphic visualizations longer. The constant switching between the visualizations and the shot of you talking is a bit jarring and makes it harder to focus.