Member Initializer Lists in C++ (Constructor Initializer List)

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[@samdavepollard]

watched this earlier today and have just written my first constructor initializer list i confess, i'm feeling pretty gangster right now

[@LoxagosSnake]

Lost it at the closed captions. "Hello guys my name is a cheddar"

[@FoxSensei]

Cheddar Bob

[@olliert4840]

@@nijucow i ALWAYS hear: " My name is 'Ocherno' "

[@tedchirvasiu]

I always hear it: "My name is the Cyano"

[@Plasticcaz]

I didn't realize this actually had performance benefits. When I first saw them, I thought they were just a nifty way of writing constructors.

[@mryup6100]

Exactly, needs better documentation.

[@DaRealPielover1987]

Hey Cherno. Just want to say that this series is one of the best I've seen on youtube. I've been in the industry for about a year now but having refreshers like these are always good. Like I haven't actually thought about why I use member initializer lists in years since I've just gotten in the habit of doing so. I'm looking forward to more videos so that I can fully recommend this series to more novice programmers.

[@chromoxd7958]

*Charno

[@1Naif]

Also you cant initialize *const* members without using "Member initializer".

[@SrogaPoziomka]

I was going to write same thing. :)

[@annahakobian7371]

if I'm not mistaken reference types also must be initialized in the initializer list

[@venkateswarans1012]

What about static .?

[@patrikjankovics2113]

@@venkateswarans1012 Well, those will be initialized by default I think, because you can access them without creating an object

[@jatinchadha7740]

Basically all members which should be initialized at time of declaration should be written in initializer list like const , references etc.

[@hexi3064]

Member Initializer List allows you to use references as properites of a class. (Without using it, you cannot do it because references has to have assigned values while being created.)

[@joshs2475]

Don't forget Member Initializer Lists can also be used for initializing const member variables as well!

[@deltarambo6230]

Basically, all data-members which should be initialized at time of declaration, such as const , references, etc., must be included in the constructor's initializer list.

[@drkerberos]

Mind blown @The Cherno. As I said in a earlier video and will say now you are the best C++ teacher and course on KZbin. To the way you describe subjects to asking the biggest question of why you would need to use them and giving an example. To be honest I thought I would never be able to learn programming and actually learning the materials until I went to college and forced myself but I was wrong. I wish I found this channel sooner than I did. Big props to you though in helping everyone and making this playlist. I can't wait to learn more from the rest of the videos and then try and make a simple project later on.

[@zfighter3]

Holy cow. It's like a constant stream of videos!! I use some of your videos as reference for my high school classes. Cheers!

[@lucha6262]

This video should come before the virtual functions video!

[@lucha6262]

Greatgreat video though, I will forever use this from now on!

[@GreenFlame16]

Cherno makes both C++ and teaching C++ look easy Heck, been reading some Stanley Lippman and that dork just sux ass explaining, and the book is a fucking minotaur maze. While Chemo makes it crystal clear and enjoyable. I just feel like I'm having a great company and we speak same language. I feel so much better watching these. Thank you, Cherno, you bring a lot to this world

[@farsanrashid5601]

Great work! I would like add two things though, I am not really sure why 2:48 "make sure you always initialize your variables in the same order that they are declared in when you declared them as members" If the order of initialization only matters on the order of member declaration when using initialization list it should not matter in which order I initialized them, it would matter if I had not used initializer list and initialized inside curly braces. Second the main reason that initialization by list is better is that it only calls the constructor but if I initialize inside curly braces a copy assignment is performed after the constructor. Scott meyers 55 ways item 4. Again keep up the good work.

[@touchdepp4507]

You just keep the order the same as your members to not confuse yourself. Try something like Entity:m_x(5),m_y(m_x+1) and flip the order.

[@turdle69420]

i mean, he explicitly states that it could mess up depending on the compiler. and feels like he's mostly encouraging this for good practice.

[@mytech6779]

Should use uniform initialization '{}' instead of '()' because it will warn on implicit narrowing conversions. '()' will silently allow, for example, an int to be truncated to a char. So this is better public: Entity() : m_Name{"Unknown"}, x{0}, y{0}, z{0} { std::cout

[@Karolis554]

and also Initializer list is helpfull when you have to initialize "const" variables/objects inside a class, because you can't overwrite const objects with "=" operator :)

[@deltarambo6230]

Basically, all data-members which should be initialized at time of declaration, such as const , references, etc., must be included in the constructor's initializer list.

[@TheKingofkatz]

Incredible video series that will remain relevant for years to come. Nice work man, appreciate it.

[@passionfruit7617]

confirmed

[@BOTHLine]

First of all really thank your for all the videos. Even though the most concepts may be known by a lot of people already, it's interesting to see what happens behind the scenes. For example the Initializer lists. I knew they would be better in terms of performance in some situations.. but I never actually knew why and when especially. I didn't even feel the need to look it up. But I just like to know things like those, so these videos are really interesting and helping me out! And I like it, you are not discriminating primitive types nor classes!

[@serkanozturk4217]

Personal Notes: - Way of constructing objects by assigning members values - Not only a coding style, if you don't use that you initialize objects twice , one when declaring the member, and the other one when assigning it to a different object again inside constructor which takes parameters

[@prometheus8439]

you deserve as much as subscribers as PewDiePie

[@allenvicencio5156]

Wanted to say thanks! Your videos are great and are a huge help to me in understanding C++.

[@wearyadventurer404]

"hey little guys my name is a chadder and welcome back to my say plus plus series" xD

[@samarthsrivastava6220]

@TheChernoProject Man! You rock!!!. I was having trouble understanding this but you made it so simple with ur examples. Thanks!

[@mamoudgad4210]

I just want to thanks for this great content one of the best c++ courses on KZbin

[@BlackJar72]

Yay! I finally am back online and can catch up with these awesome videos!

[@MiddleCross378]

Thank you, exactly what I was looking for.

[@ymahmoodi5817]

Some think that I do not understand is that even after moving m_Example(8) in to initializer list, the Example m_Example is still in line 22, and as Cherno said, because it is in member region it does not mean that it will nor run and create an instance. So, why now does not create an instance!

[@matt-g-recovers]

Very cool, I like this style vs Java

[@b_01_aditidonode43]

amazing explaination and that is amazing effect there when you said like and the like button actually glowed , woah mindblown

[@h.hristov]

Thanks for the daily uploads :D

[@legendarytwister3656]

i didnt know that. thanks, ive watched alot of your videos you are doing great work. cheers

[@DaemonJax]

You didn't mention that you can also give the intializer list a private static function to initialize a member variable. Sometimes you need to do something more complicated than just a simple assignment. Maybe that's a new language feature in 14, 17, or 20. Dunno. You can also give it a constructor for a nested class or whatever. The initializer list is kinda clunky tbh but I feel forced to use it, but the only real downside is that when using the initializer list AND you want to use the constructor for other things to set up the class without using a secondary manually called init function, you're FORCED to implement it in the header instead of the source file so you can't hide the implementation details... holy run-on sentence, Batman. That's a weird design decision... flaw, if you ask me. Some other stuff is also weird... like you can't use a static function for array initialization in the initialization list. You. Just. Can't.

[@toast_on_toast1270]

Love you man, C++ for life

[@smileynetsmileynet7922]

So far, I've left initializers out of pnfha, because what I would have had the option to do is make a function with 2 bodies. Maybe it wouldn't be that way later in development though...

[@eruston]

Great video, very easy to understand, bought the book: ‘effective c++ third ed.’ Great compliment to that book.

[@gamelovers4974]

You are the best cherno.

[@dhu1090]

YOU ARE AMAZING!

[@ghostradiodelete]

"if we....were to....move this...." haha thanks William Shatner, that was very helpful. In all seriousness though I really dig these videos and am looking forward to the opengl series.

[@meelz812]

Cherno does not miss

[@TheSunscratch]

Photo on the wall is awesome!

[@asterisk4424]

Dude thank you so much I love your videos

[@stormwaker]

I cannot think of another KZbinr with such a high likes to dislikes ratio under his videos. Is this how perfection looks like?

[@yavuzselimcagan5233]

It's really good to learn that.

[@adrianhurtado8323]

Thank you for this!

[@leixun]

*My takeaways:* Why should we use member initializer lists 3:10: clean code and speed advantage

[@georgei2480]

Mr. Cherno . You are my hero

[@teosurch]

Thank you! Finally got the new constructor syntaxis ( a(a1) like instead of this->a = a1 );

[@barellevy6030]

Appreciate you! Great content! Thank you!

[@mryup6100]

This is amazing. Code changer for sure y'all!

[@AdityaPrasad007]

3:17 why why!! thank you for asking that. wow... performance issues. good enough for me.

[@filippovolpe746]

Doesn't "... :m_Example(Example(8)) ..." Implicitly use the copy constructor? It hasn't been overloaded with a cout so it doesn't appear in the terminal.

[@chiyungchu9463]

Why not immediate initialize them inside the class instead of inside constructor?

[@ashtonkusmaul6907]

what if you used like std::string& then would it still douplicate it

[@johnk6598]

Would default arguments be another way to accomplish this?

[@pawankumarmeena6737]

you are my hero

[@qandos-nour]

thank you you are the best

[@krec348]

YES! DAILY VIDEOS :D

[@donovantheprogrammer2989]

I'm a bit confused about 4:10. You're saying the member will be constructed twice: once in the default constructor, and again with the "Unknown" string value. Where I'm confused is that the default constructor is already being used in your example to set the string to "Unknown" already. So is there a second "hidden" default constructor some where else?

[@zoeres]

So, to explain it as best I can: Every class has a default constructor. If you don't implement one on your own there will be an empty one there. Every member class variables that an object has are instantiated via default constructor when the object is instantiated, that is before the code inside of that object's constructor is ran, but after it's initializer list, unless initialized already. If you've hidden the constructor of the class you are initializing (by making it private or protected), or if you have member variables that are constants or reference types you have to initialize them either in the initializer list or in their declaration (doing it at declaration time doesn't allow you to pass them any parameters so be wary of that).

[@imninja4220]

in short, constructors assign the variables to a new value while member initialiser list simply initialise them

[@flecko5]

Good summary

[@Nick-lx4fo]

Thank you

[@MrDivad006]

5:55, this is so confusing. Why would it run that code before the code in the constructor?

[@Netrole]

It runs the code so the variables you are assigning values to in the constructor actually exist

[@tessa10001]

amazing, thanks

[@sergeyklassen9696]

Great video! Did you change the audio settings? Sounds different.

[@wsk3184]

What if I want to initilize some member object based on some condition? E.g. class Test{ private: Object a; public: Test(int b) { if (b > 0) a = Object(b + 10); else a = Object(b - 10); } } Based on what You said Object will be created twice. Can this be avioded is this example?

[@mikhailsobol3895]

In this particular case, you can use ternary operator Test(int b) : a(b > 0 ? Object(b + 10) : Object(b - 10)) {}

[@Rob-nx1dz]

Test(int b) : a(b > 0 ? b + 10 : b - 10) { } should work I think

[@wsk3184]

Sure, but what if the condition is more complex ? Additional else if.

[@Rob-nx1dz]

for really complex conditions i think there is no way but nesting those one-line-ifs... at least I can't think of anything better

[@Trogzul]

Like many other have mentioned, you can use the ternary operator. If the condition is really complex, you can use a lambda (Which he hasn't covered in depth yet), or just create a function, example: hastebin.com/omaliderat.cpp I personally would prefer just using a function rather than a lambda in most cases, but that depends on the situation.

[@vyomraj3389]

Wow thanks!

[@ilyosbeknajmiddinov6754]

Hello I have a question can we use c++ for web application's the part of backend ? can you teach how to create web-backend or desktop applications or how can we use c++ for mobile (some percentage) please give me answer.

[@AviPars]

Look at webassembly

[@l3aIIin23]

Thanks!

[@SruVekDiaries]

Ur videos are awesome bro..Keep it up...u r genius

[@meh1672]

These video's are the best! :D

[@dr3mro]

we need a series of wxwidgets :)

[@anton_98]

I am quite sure, that if you try this in Release mode, then you get the same result with init list and without.

[@joseponce6250]

brillant!!

[@我有一个朋友-i2u]

Today's hair is also just perfect.

[@ohmnamo7056]

wow ...gr8 explanation.....thanks a lot...

[@reguret2976]

you can't initialize const and reference members without the initializer, ty for the vid very helpful :)

[@mint6276]

A heads up: you can't initialize inherited values this way unless you redefine them.

[@waiitwhaat]

"I don't discriminate between primitive type and class type" I'll cheers to that. (I code in Python)

[@alexisreynolds4277]

I just realized his voice sounds exactly like the character Lawrence (Prince Naveed's butler) in the Disney movie, the princess & the frog.

[@jubranoo]

what does const std::string& GetName() means? why did we put the & sign in the return type ?

[@jubranoo]

@Peterolen can we say that all what references do is to avoid unnecessary copies ?

[@sunitjoshi3573]

Wouldn’t this be an issue since any changes to the “outside” string will cause changes in the initialized class? Is the normal, copy-Val a safer option for classes?

[@NeZversSounds]

Another frustration explained!

[@Strikerz0r]

I don't quite get it. Is this just if you use an overloaded constructor in addition to the default constructor? Or should you just use it always?

[@TKcKoucher]

Would it be correct to use member lists to initialize variables in a struct? I'm using a struct to group a bunch of variables (integers, small arrays, etc.) that are going to be filled with data once I read a binary file using .read() from std::ifstream. Even in this case, should I be using a member initializer list instead of initializing these variable inside the constructor?

[@adamhendry945]

Can you please do a video on padding and alignment as well as the pIMPL idiom?

[@rajahoomi]

You MUST use initializer list if you have CONST member variables. Complied error if not

[@cooltuque]

If the default constructor initializes a member variable to some default value. Wouldn't it be simpler to just assign the default value when declaring it?

[@kamilwisniewski1080]

you can also do something like this #include class a; int main() { a obj1; std::cout

[@1tsyB1tsy]

Loving your videos but the room your recording in has a nasty resonance at 2kHz -4kHz, consider some acoustic dampening panels!

[@VanBhardwaj]

they are 3 years old. This won't help now :P

[@varuntaneja7073]

You used this in one of your previous videos (maybe the virtual functions) and I was so damn confused . ps : I get it now

[@chrispanov8167]

Hey Cherno, i have a question. Why can't i do this (no pun intended here haha): Entity(int x, int y) : this->x(x), this->y(y) {} So that's my constructor. And when i use a member initializer list with the this function it gives me an error "expected an identifier"

[@lightps5515]

What is the downside of initializing a variable in the header instead of the constructor especially for the primitive data types?

[@popplestones886]

Do you use inititializer lists just with constructor or can / should you use on regular functions?

[@amrtcpp6203]

thanks man , you save me

[@emilfransson2984]

Would this->name = "Unknown"; act the same as name = "Unknown";? Would I still get two copies, and wasting one?

[@jeremyphillips2047]

does this mean that languages like java are stuck creating the extra throwaway objects?

[@simonmaracine4721]

No. Only C++ can create objects like this: Object obj (it's the same as Object obj = Object()). Unlike Java who can only create objects like this: Object obj = new Object().

[@cubedude76]

Is this also how I should be initializing struct members variables?

[@fadyhany6818]

in this video exactly in 00:12 you said " initialize our class member functions " i think you meant " class member ( the variables that are members in the class ) " not " member functions " , right ?

[@valentinamerturi2330]

greate video!

[@robinmaes8818]

When you don't use initializer list and you construct a member class twice, does the first instance get destructed when the second one is constructed or does this happen afterwards?

[@jordanclarke7283]

Plus there is the case where your class member has NO default constructor and requires parameters passed to create. Then you NEED the initialiser list.

[@desrucca]

6:39 What if theres another Constructor for Entity which takes Example object as a parameter , and i want to define m_Example as the Example object on the parameter. the code, looks like this Entity(Example x) : m_Example(x) {} Is it possible? Or is it gonna throw error instead? If it is possible, what if the Example class also has constructor that takes Example object as it parameter ( Example(Example e) {} ) ?

[@xr_xharprazoraxtra5428]

🔴HELP : I have 3 constructors : a default constructors with no parameters, a constructor with a parameter, and a copy constructor the constructor with the parameter works fine. the copy constructor works fine, but for the default constructor, C++ says "expression must have class type but it has type "ClassName (*)()"" what is going on and how to fix it ?

[@sruthisrinivasan3622]

I just have a doubt here! when there were two classes example and entity. You called example from entity. Don't you need to override?