Thanks for watching, hope you enjoyed the video! Don't forget to check out hostinger.com/cherno and use code "cherno" to get up to 91% OFF yearly web hosting plans! ❤

I'd really like more of such design pattern content. Big fan btw, great content.

There is one important functional difference between a namespace and a singleton class. In a namespace, all of the data is initialized/loaded into memory when the program first starts; this might be undesirable sometimes when we don't want all the data initialized until we actually need it. In contrast, singleton instances are only loaded during the first call to the "Get()" method.

Great content from an experienced developer. I would note that technically there's a little functional difference between static member variables and local static variables. When you moved the static inside the Get() function, you made the initialization order deterministic. Local static variables are initialized the first time control passes through the declaration. This makes it safe to call one singleton from another singleton. Also local static variables are thread-safe beginning with C++11 (except when --fno-threadsafe-statics is used in GCC). Plain old static member variables aren't thread safe, and the undefined initialization order causes a nightmare situation. This is less of an issue with ints and floats, but if a singleton contains a class, like a string, you're in a really big trouble. Especially when you're using one singleton/static from the constructor of another singleton/static, and you have no way of knowing which one gets initialized first, and if you're out of luck. You may be using a variable that hasn't even been constructed or assigned yet. The destruction order is an even bigger mess than the initialization order, so stay away from custom destructors that rely on other statics. The object being destructed may be using an object that has already been destructed earlier.

Yes! Please, do cover more Design Patterns! Side question: can you type and talk like that or is that edited? Regards!

YAY! More C++ :)

I am so damn happy this series is back. Have been waiting for a c++ video for so long!!

Cherno, have you considered covering more design patterns in the C++ series? Thanks!

This is HUGE in embedded programming because we have to often interface with C libraries. The singleton pattern allows us to interface with C callbacks but still use dependency injection for unit test. I love your videos. You are doing this right. C++ is the best language ever made and you are making this accessible

One use case for C++ singleton that makes sense to me is the case where you have several classes with a common base class. Each of the derived classes could be a singleton, benefiting from reused code and encapsulation and they're similar enough to where it makes sense to derive them all from a single base virtual class. In this case, the base class takes care of most of the structure - making it reusable. Then the singleton derived classes have just a few minor differences for each of their use cases.

Keep it up, i am a student that is c++ geek. I learnt a lot through you.

A Log Class is a good example of a singleton. You just need a way to log things so you instantiate the Log singleton and can do Log.warning("something"). Other examples are in plugin architectures where a singleton can act as an API interface. You want to provide a certain class of functionality, then there is a singleton for that and you bind to it by registering handlers etc.

more design patterns please!! you're by far the best C++ teacher on yt

OMG, You're even married, Lol, Its been 7 years man, since I followed your channel and waited for you to release more videos, KZfaq recommendations have brought us back together lol.

Great Video. First ran across singletons on a Java project (where, as you point out, everything is a class). Since then, used it occasionally if needed to reuse some object that was 'expensive' to create. One was where a lengthy connection to another server database had to be established. Each query on the object was stand-alone, but creation took time. So we created once in a singleton and then all the code could 'get' and 'query' without having to recreate the connection all the time.

More c++ ep please!

Les goooooo. Hell yeah, more c++ content. 🔥🔥

I particularly would like to see a video on the Command pattern, since I've been told its useful for game dev.

Me and my friend had to give a 40 minute presentation about the Design Pattern, specifically using C++ as well. Singletons are, from what we've seen most of the time disliked and sometimes treated as an anti-pattern even. Now, Singletons do have their limited uses, so there's that. But how to construct one and especially how to destruct one or worse, doing that AND being in concurrent environment, that is a real piece of work. What Cherno did in construction was a Meyers Singleton, i.e. the local static one. There's also the way of allocating the singleton on a heap and checking if the pointer is null and if so, creating the Singleton, otherwise just returning the pointer as a reference. Threading usually involves something like double checked locking (you don't want to construct two singletons, that'd defeat their purpose) or something that ensures a single call of the constructor. Destruction is pretty funny too - you can either ignore possible problems or think of the Keyboard-Display-Logger problem and think of the Phoenix Singleton (where you basically remake the Singleton anew) or the Longevity Singleton, which requires a lot more work. If someone has a need to know more about Singletons, I recommend Modern Design Patterns in C++ or the original Design Patterns by GoF. Tbh, once we did that presentation, I started to see Singletons a lot more. E.g. my browser uses files to lock the processes and guess what, that's a Singleton. Never seen it before the presentation.

Dare I say, your playlist of C++ videos are the best in the universe so far, youtube aside. I can not thank you enough. If I had the financial ability, Id definitely join the patreon group, not for the extra access but just to show my support for the greatest C++ videos on the net. Who knows, maybe I will get there soon.

Loving the content! Could you possibly do a video on iterators? As far as what they are, how you can use them in a queue/linked list implementation, etc

Thanks cherno for all these videos. I binge watched you whole series almost a week ago so that I can be comfortable with c++ again(even more now). It really helped me to understand c++ codebase of mlpack organization, I even made a PR on it which is almost accepted. Thanks a lot.

this is called Meyer's singleton and after c++11 it is thread safe too, but has an overhead cost of the Get functuion because of the internal locking mechanism

Thanks for your great videos, can you please make a tutorial about DESIGN PATTERNS

I'm bagging you: more design patterns! great video!

We use a lot of static function variables in methods especially for fixes that should not break ABI (Introducing variables or reordering may break ABI). The best advantage from this approach is the guarantee for MT safety when initialization the variable - either better if the variable is a class. Something you didn't mention (Or I missed it) is MT thread safety which is the crucial point for singleton initialization. (Refers to the famous double-if-lock pattern).

Good video! Only thing I missed is the downsides of the singleton pattern. For example, they are pretty much untestable in unit tests. And then there is threading issues. Also, the initialization order fiasco. In my opinion, this pattern has so many issues and too few benefits to balance it out.

I love your video. Some explanations (e.g. the linkedin explanation ) are confusing because they use complicated classes as their demo. I really liked how you didn't bother making a working random generator function and focused on singletons!

I used them in ue4 as a game audio programmer and found them to be tricky to work with. The engine instantiates the Singleton as expected but tweaks to the Singleton data doesn't show until the entire engine is rerun. That makes iterating on designs a lengthy trial. Otherwise it's a handy way to get your world actors to survive between map transitions.

You forgot to mention the most important thing. It's a antipattern and should not be used except few rare exceptions. It adds hidden dependencies into the whole codebase, makes unit testing harder and causes lots of pain and costs few years later.

Although useful for begginers Singletons are an anti-pattern and end up coupling your code and make it difficult to test. Try creating an IoC (inversion of control), which is basically an object you inject into a constructor that has single references to you global objects. A framework that uses reflection to do this is super useful.

Already knew about singletons, but super helpful that I learned how to circumvent the cumbersome declaration of the static instance in the translation unit.

So I'm kind of learning the business at work, being introduced to embedded programming (from being a tech previously), and we commonly use classes for single instance objects... because it's embedded code on an MCU and there's no reason to have more of something like a Hardware class. The hardware class usually initializes a microcontroller and stuff. We do something like this to override the new operator: template T* static_allocate( void ) { static type Object[ (sizeof( T ) + sizeof( type ) - 1U ) / sizeof( type ) ]; return reinterpret_cast( &Object[ 0U ] ); }; Then a class can be instantiated statically in memory with "new Hardware;" which will have a bunch of init functions in the constructor. Hardware( void ); virtual ~Hardware( void ) { } void* operator new( size_t ) { return static_allocate ( ); } void operator delete( void * ) { } I'd be really curious to see what your thoughts are on something like this. Is there any point in doing this and not using a namespace? Functions are called in the application layer sometimes from the Hardware class, but it's really just a global instance this way... something like " Hardware::uart_print("Hello"); "

"Let's just pick on Java" xD sad Java noises

Glad to hear you say you're just getting started! Can't wait!

17:25 cant you just have a class with everything static instead of a namespace so you can have private / public

I make the pointer static and initialize that to NULL. The get_instance method checks the static pointer for NULL and will instantiate it if NULL, so one instance.

Thank you The cherno. This is great, just what I need. I wish you can look at more design patterns in future, I mean yuo realyy explain in a way that makes it easy to understand.

A question ! Is there any advantage of Singletons over pure static class ? (With static methods and attributes, and private constructor) i.e: class Random{ public: static float Float(){return m_number;}; private: Random(){}; static float m_number; }; float Random::m_number = 0.5; int main(){ std::cout

This was pretty useful and easy to understand. Thank you!

Thank you so much! Your videos are so good. Thanks to you I learned some little details that are important to know about C++. I would love to see more on idioms. The only idiom everyone seems to use for tutorials is the pimpl idiom.

Love this series, more design patterns please!!!!

The indirection is a great idea. I have never thought of it like this 👍

In general singletons have some overhead for the function calls and initialization when you need to access. In addition, it's hard to reason about initialization and shutdown order so I completely avoid them in my engine. Instead I have a class that contains static instances of all the engine components. I can explicitly control startup and shutdown this way. It's not perfect though as c++ guarantees initialization before access in multithreaded environments, however, I've found that even with this performance cost, it's about 50% faster than using singletons

You C++ classes are simply brilliant. Thank you.

FWIW, Singeltons are used quite a bit in embedded designs to control access to hardware.

The C++ series is back! Hell yeah!

Your fast typing is so satisfying

This video is exactly what I needed, it helps me think of how to organize my code better. Would love to see more design pattern videos!

I use Singletons at work, and I learned something. Deleting the copy constructor. When I researched this topic I had not seen this part before. You did not touch on the part of deleting the actual singleton, Im not sure if its actually an important thing to look into when using Singletons, but I have heard there is a particular way to actually delete the singleton in order to evade memory leaks?,

i can see some chap on code interview ... " i can name function a "float" ... cherno does it ... "

So singletons are basically the overcomplicated version of namespaces with public and private sections (yes, I know there is no pub, and priv sections for namspaces)...

I just made a tic tac toe c++ game and my main downside was that I had to call “TicTacToe main;” at the beginning of the file. I went on KZfaq and this is the first thing I saw! Thanks man!

1. create a private object inside a class..(mark it as static -> meaning that object is specific to an object //not shared with other objects) 2. mark constructor as private 3. make a public function to access that private object(return type is pass by reference because to refer an object that already being created not making a copy of it)

I really like your explanation very much, the way you construct the solution makes things more easy, Please add video on all the other class Design Patterns

In other languages I would stuff my game state into a singleton. And then I tried it in c++ and wow, mistakes were made. I can't even describe to you how deep the cyclic dependency error crap went...

I use singletons just if you must be able to reinit the object, for example restarting a server etc. Then you can just reassign the object and don't have to worry about those variables

Best C++ tutorials on the internet. Hostinger better be giving you some good money.

BTW You don't need to define static variables in outside the class in c++17 , you can use inline static keyword Learned a lot from you😊

Cherno you saved my life with this video (again) thx for the great tutorial

Singleton as class allows "optional singletons", so I can have singleton, but i can benefit to able create a new standalone instance for some special purpose. Singletons as class can also extend some interface. Putting instance to static variable outside of function Get is slightly faster, then having it inside of the function Get because every-time the Get() it called, it must ask, whether the instance is already initialized. There is also some locking protocol to ensure MT safety. This doesn't applied to outside variable. However there is also benefit to having the static variable inside of the function. If the singleton is never used, it is also never initialized, which can help with performance in the such case.

For the random generator you could have just entered a comment saying // I rolled a dice for this number. I am joking, your channel is great.

I think a big advantage of singletons is that you can put init code in the constructor and not worry about calling it manually. Advantage or disadvantage, depending on if the init code relies on some other singleton that may or may not have been initialized

in short: - declare a class with a public Get()-function, a private constructor and define the static singleton instance somewhere - exec functions with Singleton::Get().function() OR alias Singleton first with Singleton& instance = Singleton::Get() and then use alias to call functions: instance.function() - don't forget to delete the copy constructor: Singleton(const Singleton&) = delete; you can also put the instantiating part into the Get() function of the class, as static variables will not be instantiated twice.

Excellent! I finally find some useful C++ tutorial on KZfaq! Thanks!

Man, I honestly don't see why I would use this. I mean, when you understand it, it becomes clear, but the fact is that you _have_ to understand a thing that could really be simpler and shorter. Am I missing something? Do singletons have any advantages compared to namespaces in C++?

Good theoretical explanation while keeping it simple. Plus, a relevant example. Great video!

What I missed in your video is the ability to control when the singleton instance is deleted again. This can be important, for example, when analyzing memory leaks. Without explicit control, the singleton instance is only deleted "too late", so that it is always detected as memory leak (provided that the singleton instance allocates dynamic memory, which of course is rather irrelevant for the random number generator from your example).

Would definitely to see some other design patterns video. Love your style of teaching and examples.

I recently used a singleton for a SDL wrapper. I wrote an initializer class in the protected field of the window class with a static instance of that initializer such that once the user instantiate a window, it will initialize SDL automatically in the constructor of the static initializer object and de-initialize it at the end of the main in the destructor of the initializer. I've not yet used singletons in other ways than the one I described and I simply don't use them that much.

Note: function local static variables (depending on implementation) can have guards for thread safety, which make accesses take longer. This can be particularly problematic when it's a pointer because of the dependency stall.

loved the video. Please make more Design pattern tutorials like observer pattern, Factory pattern, the decorator pattern etc.

YES. EDUCATIONAL C++. MORE OF THIS PLEASE.

Please do more design patterns! Your content is great and your explanation is very clear and elaborate!!

GOODNESS ME, 14:09! That is a lot of speed! Edited? Typed? I can't figure out! Haha.

I think speaking of Singletons without mentioning dependency injection is somewhat pointless, as you actually covered that without the implementation being derived from somewhere above, the singleton class can be simply replaced by a namespace and have the same functionality. Since I'm far not a c++ expert, I actually wonder in what ways can a dependency injection implemented in c++. I can imagine ways of doing that, but I don't really think those are good ways, so perhaps covering that part may be good.

14:06 Is this real time typing? That's insane :D

We need more of this

6:53 a singleton is organized global variables

Great vid, One of my use cases for Singlton in real life is database connection, for every request you get, it's better to establish 1 connection to the database, and use it throughout the code, instead of re-establishing connection for every query which will slow down your app.

yes. please make more such videos

It would be nice to follow up this with a comparison to the Monostate design pattern.

Greetings, Cherno. I think the singleton pattern is very very important. In your video material you showed the case of singleton object being copied. I think, that was a great misuse of singleton paradigm, because it must not be ever copied but only got by reference or pointer. Could the "explicit" runeword make your example more prone of errors? Or any other ways?

Hey Cherno.. Great content and well explained. Expecting more videos on other design patterns as well..!!

Best learning. Please make such videos on as much Design patterns as possible to implement in C++. Awaiting

This is the best C++ playlist on KZfaq, Hope i know it earlier, but i think some topics are missing.

The biggest benefit of a singleton is the fact that it has a destructor, so you can free the resources you have used without forcing the user to call it. Also, a static function variable can have a minor performance hit if your singleton is not a POD type, because it has to check if it has been initialized or not everytime you call the function, and do it in a thread-safe manner.

You can have private members in a namespace by using an anonymous inner namespace.

Everyone: * Singletons are bad! * Singletons are obsolete! * Don't use singletons, ffs! Someone: * What is actually bad about singletons? * Why is depending on interface classes better than depending on one given implementation. * How to ditch singletons in legacy code The Cherno: * SINGLETONS Anyways, you have great videos for beginners and even advanced programmers, because C++ is super complicated and no one knows everything. Singletons are starting to be problematic inside large code where everything depends on 4 singletons such as logger, serializer, licenses, rights and you want some code to bypass all of this and just want to make unit test pretending you have certain rights, all licences, data are deserialized from memory object instead of file and log messages are discarded.

More videos on c++ design patterns please.

guys, am I in a paradise? 1.Yan's video every single day 2. I asked him to tell us about gamedev patterns in the comments a couple videos ago.

a database handler a logger are also good examples for singletons

hey Chemo been following ya since I got a interest on game devolopment past 5 years. recently been doing turotials on learning gamedev with c++ n defently looking forward to more content to advance my learning. :)

Can you talk about other Design Patterns that you use in C++?

Please add seperate playlist and videos exclusively explaining design patterns in depth

What about an another singleton kind: class MyClass { ...members... } myClass; its a typedef or is same as singleton pattern in C++?

I use a singleton for my data provider where I have to keep track of every request sent within a certain timeframe regardless of originating class

website company: *charges money* me with a linux server: ill do it myself

Thank you a lot for the great content. Please don't stop making such great videos. I will certainly contribute to your Patreon account once I start a full-time job.

The very best video i'd seen. 🤯 Thanks for all