CONST in C++

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In this video we're going to take a look at the const keyword and how it works with pointers, references, and class methods.
Series Playlist ► • C++
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[@jean-naymar602]

For people having trouble remembering the order in which const keyword is to be used, here's a quick tip. You have to read it backward, like the compiler does. For instance : -const int * A; ==> "A is a pointer to an int that is constant." (or, depending on how you prefer to write it) int const* A; ==> "A is a pointer to a const int" but both are the same as explained in the video. -int * const A; ==> "A is a const pointer to an int." -const int* const A; ==> "A is a const pointer to an int that is constant". EDIT : As mentionned by simo simo in the comments bellow, const int * A does not mean that A actually points to a const variable. It just means that the compiler will not allow you to modify the pointed value *through* A. for instance : int val = 10; int const * a = &val; *a = 30; //this will NOT compile, you're not allowed to modify "val" through "a". val = 30; //this will compile. Same with : int val = 10; int val2 = 30; const int * const A = &val; A = &val2; //will NOT compile : you can't modify what A points to. *A = 30; //will NOT compile : you can't modify val through A val = 30; //this will compile, val is not constant

[@h.hristov]

Jean-Nay Mar Awesome tip. Thanks :)

[@afterbunny257]

lol, it works out perfectly!

[@TheBellite]

Great tip! Thanks.

[@kmattrichards64]

this has to be the best explanation, awesome!

[@suryarocks8647]

Thanks

[@inserteunnombreapropiado9079]

More simply: a _const_ is like a: "if I modify this, please give an error calling me an idiot because I modified a _const_ ".

[@yashbhatt4498]

Const can be modified but in terms of constant there is no such a thing cuz it's literal...

[@HornyVegan]

Your C++ vids are the best on youtube, don't stop ^^

[@websurfer5283]

If people like, please visit his patreon page. I will certainly be contributing come 1st of next month. As I think u get a months benefit from start of each month.

[@jeremymesloh1981]

Agreed!

[@mjthebest7294]

Also check ChiliTomatoNoodle, he is impressive as well. :)

[@rudiger86]

Can’t stop, won’t stop

[@Aragubas]

true x3

[@KeybladeMasterCam]

The C in C++ stands for Cherno. I'm convinced.

[@chhayanksharma3926]

you mean Charno?

[@victormamede7004]

What about the C in C?

[@chhayanksharma3926]

@@victormamede7004 The C in C stands for C++

[@chhayanksharma3926]

@@AbhishekBM it stands for C

[@Brahvim]

@@chhayanksharma3926 *C -Sorry, shouldn't question a joke :joy:-

[@rayysw]

"const is basically sort of like a promise that you give, in which you promised that something will be constant, that is it's not going to change. However, it's just a promise and you can bypass that whole 'promise', and you can break your promise just like you can in real life." I came here to learn more about C++ but I get legit life lesson instead...

[@cexplr2431]

"C++ man ... That's how it rolls.." HAAHAHAHAH

[@basedworldsk8]

I'm taking a upper division c++ class at uni with a really old professor who can't teach.... you're saving my life

[@parth46767]

"Now let's put const everywhere"

[@serkanozturk4217]

Personal notes: - reading backwards helps understanding what is constant - making a class method constant says that that method will not change any of the class member - defining a function outside of the class and passing class instance as a constant reference makes sure that the instance won’t change. Thus, any method in that function must be const, otherwise you get error

[@sroentoel]

Bucky teaches the cpp fundamental level, you teach the advanced one. Brilliant guys on KZbin

[@fburnrostro95]

ah @thenewboston is indeed ol' reliable

[@alexandergonzalez5975]

sroentoel Is Bucky coming back?

[@rajesh09ful]

I Second that, also feel Master Bo Qian need a mention here, most def

[@rajesh09ful]

I Second that, also feel Master Bo Qian need a mention here, most def

[@MsJavaWolf]

@@rajesh09ful Yes his videos are great. I think he stopped uploading sadly.

[@nahuelarjona]

Funny short story, demonstrating all acquired Cherno-skills: I went ahead and compiled the code showed on <a href="#" class="seekto" data-time="173">2:53</a>. I wanted to see *if I could force a change to the const MAX_AGE using the a pointer* . *The code:* _const int MAX_AGE = 90;_ _int* a = new int;_ _a = (int*)&MAX_AGE;_ _*a = 85;_ _std::cout

[@thanostitan.infinity]

wow! that's amazing seriously! I had this doubt too, and was thinking and playing with it to understand it. So double wow and thanks haha.

[@spyrex3988]

its been 2 years but thats crazy

[@swaw11]

Thanks! I did the same and was confused!

[@BinGanzLieb]

puh thats is crazy and error-prone for beginners. i have to keep that in mind, thank you

[@forbidden-cyrillic-handle]

​@@BinGanzLieb Just don't try to break your promise and you'll be benefiting from const.

[@ehsan18t]

Man! I never understand this const properly. I learned everything I could find in books, lectures and other c & c++ videos on KZbin. But this is the only video that solved all of my confusion on const. Thanks a lot man.

[@TheJorge100]

For anyone still struggling. A good way to read these statements is from right to left. Example: const int * (pointer to an int constant), int const * (pointer to a constant int), int * const (constant pointer to an int), const int* const (constant pointer to a constant integer)

[@soniablanche5672]

Every programming language ever: let's create a "constant" array ... then change the values inside it :^)

[@thomascreel6522]

the size is constant

[@cvbattum]

@@thomascreel6522 That's true for all arrays. As soon as you change the size, you reassign it with a different array, so it's no longer the same array with the old size. Now, of course, const prevents that and only that.

[@thomascreel6522]

@@cvbattum No, the number of elements in the array is immutable and you must create a new array of a different size and move the old array elements into it.

[@AlFredo-sx2yy]

@@thomascreel6522 uh... that's exaclty what the other guy said tho...

[@rafaelmenna8384]

That’s why we have (tuples) in python.

[@LucidStew]

Learned a few things, and this clarified my thinking on const greatly, so thank you, sir.

[@786balgoo]

You saved my life cherno... I love your tutorials and I would love it even more if you make 2d game tutorials in c++.

[@reflectiveradiosity6664]

Was really confused and this made it a whole bunch clearer, again your videos are straight to the point, and relatively easy to follow! Thanks!

[@Weredah]

Thank you so much for clearing up const's I really appreciate this series :D

[@pixarfilmz4769]

This is how I see c++: const *int &int const ***const const *** &const

[@MsJavaWolf]

We had something like that as questions in university, but every reasonable programmer avoids stuff like that.

[@angelstojanov2346]

Same here, when I studied C I had a test with an expression full of illogical pointers

[@bombrman1994]

schools teach and test programming using the worse method and discouraging students so much. In my C++ course i thought about droping the class so many times bcuz of my mark, on the other side i have good understanding on C++. It never makes sense bcuz schools care for mark and never for the diamond someone got in his brain

[@haroldfinch360]

If you have a good understanding of C++, how can your grades be bad then?

[@bombrman1994]

Harold Finch because when my mother language is not English and the question in a test is a paragraph long asking to write a single line code. That’s when I start making mistakes. Programming instructors are not often found in every school

[@TheBellite]

Gold! As a longtime hobbyist programmer who's new to C++, these videos are amazingly helpful.

[@karmaindustrie]

const bool confusion = true;

[@kushnayak1619]

ok

[@karmaindustrie]

@@kushnayak1619 I want to know the mindset that led you to write "ok" and I also want to know the mindset that led somebody to give you a like after at most 8 hours. Because I want to benefit from the law of attraction fully.

[@kushnayak1619]

@@karmaindustrie ok

[@karmaindustrie]

@@kushnayak1619 So I guess the answer is: You don't really want to benefit from the law of attraction. What a pity. I want to inform you that I am very cool.

[@karmaindustrie]

@@kushnayak1619 And also, to all the other people: It looks like you are liking your own comments because you got one like again after 23 minutes. This feels like a psychological disease to me, right now :) - Correct me if I'm wrong. Plausible. Try.

[@manonthedollar]

Thank you for all your videos! I just finished working through a C++ book, and I'm at the point where I try to make my first "thing," and I go "uh oh I still don't know anything." These videos are excellent for solidifying my understanding of things that I remember reading about, but do not yet have an instinct to know if I'm using them correctly yet in my own work.

[@Prashantkumar-pn6qq]

<a href="#" class="seekto" data-time="208">03:28</a> "Now let's start adding const everywhere" - Cherno be like - let the games begin baby😂

[@more_than_just_sentient]

Hey, I saw just two videos and clicked the sub button , your videos are really high quality and I left with a lot of answers than questions when I finish watching . Keep up the hard work . Cheers .

[@AviPrakriti]

These videos are addictive. I am coding for long time and know most of it, still watching this playlist is so refreshing. I feel like exploring every details of C++ all over again and play with it. Great job @TheCherno! Your Game Engine series is also another gem engine! Big thanks

[@YogeshSharma-hg4lx]

Geming engine lol

[@Hetp111]

Thanks! The level of depth you go in is amazing!

[@dhu1090]

You are so knowledgeable!! I don't know how I'd learn C++ without you!! 🙏🏻

[@romanprykhodchenko1551]

You are the best!!! Really structured and easy to understand lessons!) Very useful for any kind of the projects) Thanks bro!

[@shvideo1]

Comprehensive and to the point. A great tutorial. Crystal clear. Thanks a lot for your effort.

[@RoaiDude1]

You are seriously the best code teacher I've seen and I bought something like fifty udemy courses.. keep the good work and combining assembly and c++ together! Its great and im learning alot even as a long time java programmer! Thank you a lot!!!

[@tyroneslothdrop9155]

Thank you for using a dark theme with your coding examples. It makes a massive difference.

[@rhyscabonita5933]

As someone who's only approaching intermediate: Ahhhh.... Wait, holy. hell. what?!?.... Okay.. What.

[@Deadshot-fz5gx]

I feel that bro

[@MirrorsEdgeGamer01]

@@Deadshot-fz5gx Me too.

[@furkanmacit4040]

i have been searching c++ videos in several platforms for two weeks i think i have finally found a good one

[@TheMR-777]

Hey man, I've never seen these in-depth concepts before in my University! Many thanks for this!

[@yacinemathurin2013]

For people having trouble with the (const Entity& e), it's just that the function can't accept any instruction able to change the object (one of it's parameters) as you've set it const.

[@4wen_main]

These kind of details will take us countless hours to grasp from reading a book (with omission often), this is amazing.

[@mkhadka123]

you are a reason I fell in love with c++ language again, your c++ videos are simply awesome :)

[@0x_Anakin]

You have the best c++ tutorials in youtube dude

[@unstablethermalpaste3366]

You are the best one I found so far with a clear eng accent that is able to help me learn C++. No offense to other KZbinrs with strong accents.

[@alecmather]

Literally amazing video, just answered all my questions about const (and more) in 12 minutes, you're a GANGSTER

[@ashiinsane90]

bro your channel is a gold mine i just started learning C++ also new to programming but your vids help alot. would love to see u do games like asteroids and snake etc with C++

[@YektaSarioglu]

Simple and clear explanation. Keep up the good work, friend 👍

[@10bokaj]

dud, your knowledge exceeds the physical barrier of the realm

[@raymondyoo5461]

What a clarity I found here :) Thank you soooooo much!

[@jekku2045]

You really did make me understand what const's are and how do they work, have been trying to find answer to it from so many websites and videos I can't believe I now understood it all. Really thank you so much!!

[@eyalpery8470]

Thanks! Refactored my whole program at work

[@TW19567]

Absolutely the clearest explanation of const out there!

[@nedboulter9187]

Really nice tutorial, I already know C++ and I just ran across this, but it still cleared a couple of things up, in terms of the mutable keyword at whatnot. I will probably keep watching these in case there is anything else I missed :) :)!!

[@sachinnair8375]

Thanks man ..... your tutorials are very clear to follow.✌️

[@piyushphodu]

this video is the best const in C++ explanation till date i ever watched

[@mikedoeren5960]

The best video on the const keyword, and it's not even close. Good stuff!

[@calecacciatore5422]

dont forget that const makes a variable local to the file. that is, only visible in the actual translation unit. you can have 2 const variables with the same name in different files and it will compile fine. so basically they re implicitly static.

[@GfastGao]

Man, I start to think if I really should pledge through patreon to this series, because you are the correct one for me. INDEED.

[@KishanKumar-mz3xr]

Easy to remember like this: * const -> pointer(*) is constant(const) const * -> constant(const) value at pointer(*)

[@rcookie5128]

daym, so much to take care of when working with const stuff..

[@ericrussell5304]

In some ways the opposite is true. If you get const right in your program, you'll have to worry less about what you do with your objects. Without const it would be like having a bunch of global variables that might get changed without warning. With const, I can give you an const object and not worry about you changing it...like a map's key.

[@AdityaKumar-xw2yx]

Dude you are great!! you have really make the things very simple!!

[@gorilla543210]

/* my note of CONST Use for 3 cases */ 1. const int* a => can't modify the value store in a (address) 2. int* const a => can't modify the address which a points to 3.use in member function which promise not to modify the data member of the class => add const to all member functions which don't modify data members , since it might be const reference! p.s. add "mutable" if you want to break the promise wrap up const int* const Getter() consr {}

[@siAppDesign]

Nice summary Thank you

[@aubreymatende6497]

im loving these videos, i am asking if you can make a video on friend functions

[@sangdilbiswal30]

this is a complete video I was looking for thanks sir.

[@kartikxramesh]

This was such a good video!!! Multiple *holy shit* moments for me throughout the video. This is better than Breaking Bad ngl.

[@Sparky579]

Hello for my future self, I know I'll be watching this many times in the future

[@rajcodes100]

Great Video thanks - I learnt some new stuff here .

[@NefKamerzon]

"Haha, point out" That was comedy gold

[@Zentamusic]

soooo helpful man thanks

[@MitLiebezurMusik]

This channel is awesome!!! Thank you for sharing your knowledge :)

[@hts2370]

very clear explanation

[@can3792]

i am on the patreon and donated . i cant thank you enough. please carry on taking video in c++ :)😀 keep up the good work

[@rjle2446]

Super helpful. Thank you!

[@handover007]

You are the best tutor on the planet .

[@ezequielzion]

te amo cherno acá te estamos viendo con un amigo muchas gracias!!!!

[@PythonisLove]

awesome explanation

[@informativecontent4778]

man o man you are awesome and most the programming i learnt is beacuse of you and buckey

[@celestialmaat9462]

I spent like 20 minutes and then looked you up🤯🤯🤯! Thanks

[@zuhail339]

I really like how he does sarcasm in the middle of a serious lesson ! But I guess that's how it rolls😂

[@xintong3635]

Really helpful, thanks a lot

[@mryup6100]

Well, I finally underatand! Thanks Cherno! Const has always confused me.

[@nidhalabidi69]

a great explanation thank you !!

[@syedrizvi2687]

Love your videos, thank you so much!

[@gunrunjk]

Thanks for detail explanation. :)

[@vineethnarayanavakicherla7219]

Good explaination cherno sir

[@IshakHeor]

One of the best teachers ever!!!

[@NexGenSlayer]

Love your videos! So helpful. Could you bring back the suspenseful music though, it engages the audience making the videos even more exciting! Also, what happened to you mic from the first videos in this series (it sounds like you are recording with mono in a smaller room)?

[@jawadelmokhliss1214]

thanks for the effort

[@thelstan8562]

Amazing! Thanks a lot!

[@davidl.castillo7517]

really good video !! I love it.!!

[@mytech6779]

Thinking way back to my short time with C. Constant was a term used when using the preprocessor directive #define to name literal values. The purpose was similar to why you might use a named function rather than writeing inline statements(only need to write it or change it in one place), the question is why not simply assign the value to a variable name. The given reason was that it helped produce faster running and more compact machine code because the compiler must consider that variables are potentially ... variable and mutable at run time while constant literals don't change at run time and can be more easily handled by the compiler in the optimizing stage. Of course that book was from 1993, compiler optimizers have improved enough since that they can likely take up the slack if the programmer takes the easy route like declaring a variable when a constant literal value is the intent. And that was C89 not C++14

[@pedrodeazeredonogueira9661]

you are a LEGEND legend

[@lewisb8634]

Fantastic video Cherno as usual, thank-you for uploading! What is your opinion on using const everywhere possible? I came across big flame war on StackOverflow recently between people that supported the 'security' and 'consistency' of using const wherever physically possible and those that said it was an eyesore. We're talking about using const literally everywhere - a simple 2 line function that takes in one integer to use in some quick calculation? It must take in a const int because the value is not modified. Would you say it is an eyesore to have it everywhere or do you think there is some benefit?

[@choosyguytest719]

Fantastic, thank you!

[@greggas87]

"One thing I'll point out, just quickly - haha 'point out' ... " .. Had to laugh here

[@tsibulsky4900]

Thank you very much for your videos 👍 Very useful

[@autogenes]

This is one of the more entertaining episodes :D

[@arihanttonage7436]

Best explanation

[@ahmadshbat8363]

you have my like, THNAKS MAN!

[@hpeterh]

Pretty clear, thank you. It should be noted, if a global variable is declared as "const" or a variable is declared "static const", then it is placed by the linker into a non writable CODE or CONST segment. When it is written to by some pointer trickery, an access violation exception will probably happen.

[@vinniciusrosa8284]

THANK YOU SO MUCH

[@jimmylander2089]

I keep coming back to this video because I always forget what const means depending on its position and it's so ANNOYIIIIIINNNNGGGG

[@youssefmuhamad3213]

Awesome video, you saved me

[@jingfenghong2312]

Thank you. Could you also introduce a little bit more about return constant, return reference and return constant with reference? I'm confused about these three things.

[@372leonard]

are you ever gonna do function pointers?

[@Steven-tw7iz]

Paul Leonard Boon I definitely think he should. That would be an awesome topic

[@Hopsonn]

I hope not, that is more a C thing. In C++, "std::function" should be used

[@brod515]

Why are you Guys on this playlist