constexpr variables are not just initialized at compile time, but constexpr implies const and immutable state is always the right way. This is the case when your variable is initialized by a constant expression, that is, an expression that can be evaluated at compile time. Where are static variables stored in C/C++? Learn more, Initialization of global and static variables in C, C++ static member variables and their initialization, Implicit initialization of variables with 0 or 1 in C, A non-static initialization block in Java. Kindly throw some light if all are correct or some modification is required. And the linker usually tries to pull unresolved symbols from Generally, a download manager enables downloading of large files or multiples files in one session. Within a partial class, the meaning of textual order is specified by 14.5.6.1. . If T is an aggregate class and the braced-init-list has a single element of the same or derived type (possibly cv-qualified), the object is initialized from that element (by copy-initialization for copy-list-initialization, or by direct-initialization for direct-list-initialization). Back to my case, then I can have the line "static int x" inside my "main" just before x is being used? gcc (or any other C compiler) allocates zero-initialized variables with static storage duration in the .bss section. Everything allocated in that section will be zero-initialized on program startup. Everything allocated in that section will be zero-initialized on program startup. Its a problem too essential to ignore but too challenging to master. Can we declare final variables without initialization in java. How to pass a 2D array as a parameter in C. There is, however, a category of variables that can (and should) be initialized before the program starts: static variables. Global (namespace) variables or static class members 1 live for the entire execution of the program: they must be initialized before main () is run and destroyed after execution finishes. static int x = 5; static int y; The static variable x is stored in the initialized data segment and the static variable y is stored in the BSS segment. A program that demonstrates static variables in C is given as follows If other is an rvalue expression, move constructor will be selected by overload resolution and called during copy-initialization. @yCalleecharan: if x is only used by main, then you should declare it inside of main. One big problem with static variable initialization is that it is not always clear if a variable is being initialized at compile time or at runtime. The variables are initialized with values and displayed as follows , Enjoy unlimited access on 5500+ Hand Picked Quality Video Courses. Asking for help, clarification, or responding to other answers. What happens if you score more than 99 points in volleyball? Can you please clarify? 3) Static variables (like global variables) are initialized as 0 if not initialized explicitly.For example in the below program, value of x is printed as 0, while value of y is something garbage. So whats the problem with the linker? Prior to C# 6.0, scope was always identified by the variable declaration placement within code. Name of a play about the morality of prostitution (kind of), 1980s short story - disease of self absorption. In other words, you want constexpr: The compiler is complaining because std::string defines a non-trivial destructor. Would salt mines, lakes or flats be reasonably found in high, snowy elevations? Lets consider the following application: The application just asks to create ZIP method. The only injection that is done is on. GetMap(). How do I tell if this single climbing rope is still safe for use? The reason for this is simple: All objects with static storage duration must be initialized (set to their initial values) before execution of main() starts. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? Initialization of static variables happens in two consecutive stages: static and dynamic initialization. 2) Otherwise, non-local static and thread-local variables are zero-initialized. Thanks for the link. Not the answer you're looking for? A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. application (the linker doesnt include them in the unresolved set of A public static means of getting the reference to the single created instance, creating one if necessary. Const Qualifier in C; Initialization of static variables in C; Understanding register keyword in C; Understanding extern keyword in C; Storage Classes in C; we declared day as the variable and the value of Wed is allocated to day, which is 2. 1.-3.You cannot exactly know when it happens and so you cannot depend on it. This post is motivated by one important We can put static members (Functions or Variables) in C++ classes. dont land in read-only data section in the binary. use. In C language both the global and static variables must be initialized with constant values. If static field variable initializers are present in the class of the static constructor, they're executed in the textual order in which they appear in the class declaration. The static variable is only initialized once, if it is not initialized, then it is automatically initialized to 0. But in that circumstance, it will just work. There are two forms of static initialization: 1) If possible, constant initialization is applied. destructor with side effects; it shall not be eliminated even if it Difference Between malloc() and calloc() with Examples, Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc(). Allows you to configure the application's middleware. It is a way to tell the compiler what type of data is in a variable during taking input using scanf() or printing using printf(). If I have a global static variable x like in this code, What will be difference if I opted to initialize x to a value first say as in. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. The C standard 6.7.8/10 has description on this. I've prepared a valuable bonus if you're interested in Modern C++! A static variable means that the object's lifetime is the entire execution of the program and it's value is initialized only once before the program startup. If you need more than an expression, you could refactor the initialization into a static method and invoke that. The exact timing of static constructor execution is implementation-dependent, but is subject to the following rules: The reason static constructors should be avoided is because the compiler injects code everywhere any method of the class is called to check that the static constructor has been called. The static constructor for a class What do you mean by "even if the internal representation of those values is not all bits zero" ? Why is the federal judiciary of the United States divided into circuits? Here is the syntax of static variables in C language, static datatype variable_name = value; Here, datatype wrap it into a static method with a static variable: And every time you want to access the container you have to call comment Is there any reason on passenger airliners not to have a physical lock between throttles? This linker behaviour might be a problem when you have a lot of Global (namespace) variables or static class members1 live for the entire execution of the program: they must be initialized before main() is run and destroyed after execution finishes. When static constructor is not defined in class, static fields are initialized just before their use. Each time a new variable of the class is instantiated the constructor will run. simple fix might work: To be sure that the container is ready for the first addition we can In my first case where I didn't assign a value to x, does the compiler implicitly know that x is to be set to zero as it's a static variable? and some from the client app. This behavior is actually allowed by the C++ standard. i've updated the question. static constructors of two. yes, in C#, static variables are not declared within method. Should v initialize like this. Static variable can be defined inside or outside the function. By default, it is zero. So be sure to have tests for such cases. initialized - so we can add new items. Whereas, Definition of a variable says where the variable gets stored. In what way is a static constructor slower than the equivalent initializers declared on the individual static fields? Rsidence officielle des rois de France, le chteau de Versailles et ses jardins comptent parmi les plus illustres monuments du patrimoine mondial et constituent la plus complte ralisation de lart franais du XVIIe sicle. What is difference between declaration and initialization in C programming? appears to be unused. An ordinary variable is limited to the scope in which it is defined, while the scope of the static variable is throughout the program. Re " the compiler injects code everywhere any method of the class is called to check that the static constructor has been called." blank screen and error: The C++ standard isnt explicit about the linking model of static The negative of this approach is that it will bloat the final exe size. Im wearing my yellow underwear; its a new years tradition in this part of the world. How to say "patience" in latin in the modern sense of "virtue of waiting or being able to wait"? A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. fenbf/CompressFileUtil/factory_in_static_lib. These variable are created when the block in entered or the function is called and destroyed after exiting from the block or when the call returns from the function. Dynamic initialization happens at runtime for variables that cant be evaluated at compile time2. class-key - one of class, struct and union.The keywords class and struct are identical except for the default member access and the default base class access.If it is union, the declaration introduces a union type. Add a new light switch in line with another switch? Hence, static class without constructor and non-static call will not work for me. If no static field is accessed within a static method and that Why are static variables considered evil? acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Full Stack Development with React & Node JS (Live), Fundamentals of Java Collection Framework, Full Stack Development with React & Node JS(Live), GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Understanding volatile qualifier in C | Set 2 (Examples). External static variable with Examples in C. How are variables scoped in C - Static or Dynamic? Closed 5 days ago. The initializers run immediately prior to the execution of the static constructor. Learn More If no other initialization is not. So a value which is not known at translation time cannot be used for initialization of static variables. But explicitly setting it to 0 can help others no need to wonder about the same question :). In computer programming, lazy initialization is the tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.It is a kind of lazy evaluation that refers specifically to the instantiation of objects or other resources.. Therefore, they must be initialized with a constant value. Ready to optimize your JavaScript with Rust? If possible, initial values for static variables are evaluated during compilation and burned into the data section of the executable. What is the Python equivalent of static variables inside a function? Are there conservative socialists in the US? Typesetting Malayalam in xelatex & lualatex gives error. Why does the USA not have a constitutional court? One way to make sure that So as a result, 2 is printed. IMHO the best way to solve it is by refactoring the code to break the initialization dependency of globals across compilation units. Why are static variables considered evil? A First Look at Classes. compile time) is ideal, thats why your compiler will try to perform it whenever it can. This initializes all static fields on object creation. I have two compression method implementations: Zip and Bz. Declaration of a variable is for informing the compiler of the following information: name of the variable, type of value it holds, and the initial value if any it takes. Closed 5 days ago. The effects of list-initialization of an object of type T are: . The code for Visual Studio can be found here: A non-static initialization block in Java; Java static block; Why interfaces don't have static initialization block when it can have static methods alone in java? Connect and share knowledge within a single location that is structured and easy to search. Output: 1 1. If refactoring is not an option, one common solution is the Initialization On First Use. Static variables can be initialized outside the member function or class definition. In C and Objective-C, you define static constants and variables associated with a type as global static variables. A static object of class type will use the default constructor if you do not initialize it. initialization: Resulting Context Implementing Singleton in C# results in the following benefits and liabilities: Benefits. Bad news is that this isnt as nice, safe, or efficient as static initialization, but isnt inherently bad either. If the initial value of a static variable cant be evaluated at compile time, the compiler will perform zero-initialization. 2 To subscribe to this RSS feed, copy and paste this URL into your RSS reader. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14.The name follows the tradition of naming language versions by the publication year of the specification, though it was formerly named C++0x because it was expected to be published One big problem with static variable initialization is that it is not always clear if a variable is being initialized at compile time or at runtime. It may print 14 or 0 (all static variables are at least zero-initialized during static initialization), depending if the dynamic initialization of A happens before B or not. Why are static variable not always in context in the Visual Studio debugger. The static field variable initializers of a class correspond to a sequence of assignments that are executed in the textual order in which they appear in the class declaration . Using of cached values avoids object allocation and the code Static in C. Static is a keyword used in C programming language. C99 borrowed the use of const from C++. By default, it is zero. Inside a function, you can initialize a static variable using the static keyword. You might consider noting that The C99 standard specifies this, someone finding this answer might still be in a position where they have to work around old compilers. If the programmer didn't do this explicitly, then the compiler must What are the default values of static variables in C? AFAIK, an. The rubber protection cover does not pass through the hole in the rim. When would I give a checkpoint to my D&D party that they can return to if they die? rev2022.12.9.43105. Yet, unfortunately, the linker will happily ignore it if linking from Skip to content Courses For Working Professionals Data Structure & Algorithm Classes (Live) Even though mostly written for my own understanding, my hope is that the curious programmer finds my writings entertaining. The flag variable will be initialized at compile time to a known starting value. One way to make sure that variables are const-initialized (i.e. You can refer to a function's arguments inside that function by using its arguments object. Examples of frauds discovered because someone tried to mimic a random sequence. Here is the syntax of static variables in C language, static datatype variable_name = value; Here, datatype The datatype of variable like int, char, float etc. A member variable plays a major role in a class as it is used to store a data value. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. The effects of reference initialization are: If the initializer is a braced-init-list ( {arg1, arg2,}), rules of list initialization are followed. It might be tricky to notice that some of Thanks. I said inside a function, because global variables are static by default, so theres no need to For example, following program fails in compilation. Initialization of an ArrayList in one line. (They all have the same basic value in memory.). by static variables i mean fields. the Standard: variable with static storage duration has initialization or a is initialized before main() kicks in and later you have all the types The syntax of the C programming language is the set of rules governing writing of software in the C language.It is designed to allow for programs that are extremely terse, have a close relationship with the resulting object code, and yet provide relatively high-level data abstraction.C was the first widely successful high-level language for portable operating-system development. Static variables (like global variables) are initialized as 0 if not initialized explicitly. If an object that has static storage duration is not initialized explicitly, In other words, std::string("3.4.1") is not a constant expression so we cant force the compiler to const-initialize it! @Tim Post: C90 also specifies this initialization behavior of statically allocated variables, however I have heard that there are a few older compilers that don't follow this rule. It can be used with both variables and functions, i.e., we can declare a static variable and static function as well. All class objects have access to a static member. You are probably reading this because you code in C++. -1 Of course you know when a static ctor is called. Some of them register from the static library After static initialization, dynamic initialization takes place. How is the merkle root verified if the mempools may be different? Initialization of an ArrayList in one line, Improve INSERT-per-second performance of SQLite. Hence, during static initialization all static variables are either const-initialized or zero-initialized. What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. static variables are automatically initialised to zero (i.e. Here is the syntax of static variables in C language. How to dynamically allocate a 2D array in C? Unless the dynamic initialization is deferred, see, The compiler can promote initialization for non-constant expressions to compile time under certain conditions, see. You've got this garbled. If possible static constructor should be avoided in a class. How to deallocate memory without using free() in C? In C static variables and initialization There is a nice answer here: Just a short excerpt: First of all in ISO C (ANSI C), all static and global variables must be initialized before the program starts. You could also set a breakpoint there. 3.2.28 config.middleware. static or class variables (with an Object type) are initialized with null, because the compiler can't check if they are initialized at compile time. This program will always consistently print 14, as it is guaranteed that A will always be initialized before B. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Extending Python with C or C++. The initialization of static variables in a C++ class is the process of assigning values to the static variables. the methods are declared and defined in a separate static library: Notice that in the client app we only include CompressionMethod.h. A staticvariable in a block is initialized only one time, prior to program execution, whereas an autovariable that has an initializer is initialized every time it comes into existence. If no other initialization is present, all static data is initialized to zero when the first object is created. By using this website, you agree with our Cookies Policy. See 6.7.8/10 in the C99 Standard (PDF document) If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. static . The static constructor for a class C++11 is a version of the ISO/IEC 14882 standard for the C++ programming language. Variable-length arrays. static field variable initializer FAILS in online compiler but works in VS. Why does compiler optimization break my code? The compiler has little chance to initialize such variables before execution starts: How is it supposed to know what arguments will be passed to a function?, or if a given code block will be reached? It is allocated for the lifetime of program. 14.5.6.2 Static field initialization. If no static field is accessed within a static method and that static method is called. Disclaimer: Any opinions expressed herein are in no way representative of those of my employers. But how about linkers and using such approach in static libraries.? Initialization of such static variables is indeterminately sequenced with respect to all other dynamic initialization except if the program starts a thread before a variable is initialized, in which case its initialization is unsequenced (since C++17). how-to-initialize-const-member-variable-in-a-class By using our site, you All data and information provided on this site is for informational purposes only. Thanks for contributing an answer to Stack Overflow! Static variables are initialized only once. Here is the syntax of static variables in C language, static datatype Interesting facts about data-types and modifiers in C/C++, Difference between float and double in C/C++, Understanding volatile qualifier in C | Set 2 (Examples). I've recently released a new book on Modern C++: The container that is used inside the factory is prepared and This blog explores a variety of topics that Ive stumbled across in my journey as a software developer. When true, eager load the application when running Rake tasks.Defaults to false.. 3.2.30 config.reload_classes_only_on_change. Dynamic initialization will be inevitable in some cases, not everything can be done at compile time, for example: The future looks bright, however. Asking for help, clarification, or responding to other answers. When should it be destroyed? The static constructor for a class It is quite easy to add new built-in modules to Python, if you know how to program in C. Such extension modules can do two things that cant be done directly in Python: they can implement new built-in object types, and they can call C library functions and system calls.. To support extensions, the Python API (Application How do I tell if this single climbing rope is still safe for use? It's a bit advanced but I'm understanding :). This turns into a very serious issue if the initialization of a variable in a.cpp depends on another one defined b.cpp . the types are not available! Find centralized, trusted content and collaborate around the technologies you use most. The suggestion to always avoid a useful feature, instead of only avoiding it when a performance TEST, on production code, demonstrates a problem, is distasteful at best. class is created. That means that std::string is probably allocating some resource that must be freed upon destruction, in this case memory. static (->) (self parent static ) Does balls to the wall mean full speed ahead or full speed ahead and nosedive? The static member variables in a class are shared by all the class objects as there is only one copy of them in the memory, regardless of the number of objects of the class. What are the criteria for a protest to be a strong incentivizing factor for policy change in China? compile time) is by declaring them constexpr, this will force the compiler to treat them as constant expressions and perform their evaluation and initialization at compile time. e.g. And, as always, you can do a lot of self damage if you are not careful. Today is the last day of the year. Here, MyStruct::a will be const-initialized, because 67 is a compile time constant, i.e. I read a lot of answers saying that one must initialize a const class member using initializing list. It appears that there are no explicit rules and our classes might not be I mentioned that the two points are satisfied by the following fact from Affordable solution to train a team and make them project ready. constexpr must be your first choice when declaring global variables (assuming you really need a global state to begin with). Anyone who has been doing this long enough knows that variable initialization is everything but trivial. variables that are initialized and destroyed at runtime: local (block-scope) variables, function arguments, non-static class members, etc. Within a single compilation unit, static variables are initialized in the same order as they are defined in the source (this is called Ordered Dynamic Initialization). How to deallocate memory without using free() in C? Obtain closed paths using Tikz random decoration on circles. but there must exist some description about these. Generally, a download manager enables downloading of large files or multiples files in one session. The variable from my last article about factories and self-registering executes before any of the static This is a problem, if we create an std::string at compile time the managed memory must be somehow copied into the binary as well, as it wont be available when the executable is run! which they end up in the factory container doesnt matter. a static library. The static variables are alive till the execution of the program. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 5 How to initialize a static reference to a variable inside the class, for use in nested classes I need to save in Class static ref to a variable for use in nested classes in a Explanation Zero-initialization is performed in the following situations: 1) For every named variable with static or thread-local (since C++11) storage duration that is not subject to constant initialization, before any other initialization. This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s). sure about the order of initialization across one application built from Here we will see how to initialize the private static member variables initialization in C++. From there I read "The only solution to these problems is to write the code so that all initialization of statics/globals is done in runtime, just before the variable is used". and want to know if these points are logical and that's how CLR works? When static keyword is used, variable or data members or functions can not be modified again. class is being registered. To learn more, see our tips on writing great answers. All class objects have access to a static member. Generally, it may be put only between digit characters. How static variables in member functions work in C++? Difference between static class and singleton pattern? Should teachers encourage good students to help weaker ones? Thanks for contributing an answer to Stack Overflow! object files, it gets even trickier when you rely on symbols from a Static Member does two things; it creates Singleton Object of the class by doing initialization in class constructor, and second this static members does is to call a non-static method 'run()' to handle Request (by bridging with Phalcon). We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Namely when either the first instance of the class is created or when any static member (method, field) is accessed for the first time. Therefore, they must be initialized with a constant value. Here is an example of static variables in C language, In the above program, two variables are declared, one is static and another is non-static. variable_name This is the name of variable given by user. initialization Such variables have static storage duration. These variables are members of a class. So if we have two classes like Foo and Bar, the order in Its a, #1-#3 are almost certainly wrong. : attr - (since C++11) any number of attributes, may include alignas specifier class-head-name - the name of the class that's being defined, optionally This is a bit of a contradiction - as we wanted to have self-registering In most cases, the static initialization approach is sufficient. Dynamic initialization of static variables suffers from a very scary defect: the order in which variables are initialized at runtime is not always well-defined. @yCallee: If some architecture's NULL is at 0x1000, then the pointer will be initialized to 0x1000 instead of 0. Did neanderthals need vitamin C from the diet? Predict the output of following C programs. We make use of First and third party cookies to improve our user experience. If your goal is to initialize the static variable in your header file (instead of a *.cpp file, which you may want if you are sticking to a "header only" idiom), then you can work around the initialization problem by using a template. Moreover, for static variables, Zero As discussed, variables with static storage duration must be initialized once before the program starts and destroyed after execution terminates. The format specifier in printf() and scanf() are mostly the same but there is some difference which we will see. Initialization of static variables should be simple, but off course it isnt. I havent investigated whats going on there, but I realized that a Most of the time the compiler must deal with dynamic variables, i.e. This is because the values of these variables must be known before the value Any value to initialize the variable. They are local to the block. Dynamic Initialization: Here, the variable is assigned a value at the run time. 1. Zero runtime overhead, early problem diagnosis, and, as we will see later, safe. The value of this variable can be altered every time the program is being run. i.e., declaration gives details about the properties of a variable. There is, however, a category of variables that can (and should) be initialized before the program starts: static variables. The static variables are alive till the execution of the program. Member variables are further classified into three types: Local variable; Instance variable; Class/Static variable; Let me discuss each one of them: Note that the above programs compile and run 2011-2022, Bartlomiej Filipek In this post, Ive given a few found ideas how to solve the problem, but Bx: Method invokes inefficient floating-point Number constructor; use static valueOf instead (DM_FP_NUMBER_CTOR) Using new Double(double) is guaranteed to always result in a new object whereas Double.valueOf(double) allows caching of values to be done by the compiler, class library, or JVM. What you can do is have a private static field in you class that is assigned a dummy value when the default (or other non static) constructor is called. You probably dont want this object to be instantiated every time the program runs, but rather create it once and embed it into the executable as read-only memory. pimpl vs Abstract Interface - a practical tutorial, Randomizing lines from a file, a tool in VC++ 2017. Where does the idea of selling dragon parts come from? Different ways of initializing a variable in C. Method 1 (Declaring the variable and then initializing it) int a; a = 5; Method 2 (Declaring and Initializing the variable together): The static variables are alive till the execution of the program. How to pass a 2D array as a parameter in C? 2) Static variables are allocated memory in data segment, not stack segment. the s_registered variables are then initialized in the Dynamic part. Compiler persist the variable till the end of the program. This is called constant initialization. The default value of static variable is zero. Find centralized, trusted content and collaborate around the technologies you use most. Templated static variables can be initialized in a header, without causing multiple symbols to be defined. i.e., memory for the variable is allocated during the definition of the Static variables with explicit initialization are always initialized to zero (or null-pointer, depending on the type). When does static class initialization happen? As the compiler translates your program it must decide how to deal with variables introduced: When should a variable be initialized? For the static variables, we have to initialize them after defining the class. Both of the above programs dont compile in C. We get the following compiler error in C. In C, static and global variables are initialized by the compiler itself. The following code is an example of a static variable, which shows the declaration and initialization of a static variable. I would be interested to know which books in C discuss such issues. If the programmer didn't do this explicitly, then the compiler must set them to zero. Note that the above programs compile and run fine in C++, and produce the output as 10. This is called the Static Initialization Order Fiasco. It cannot be put at the beginning (_121) or the end of the value (121_ or 121.05_), next to the decimal in floating point values (10_.0), next to the exponent character (1.1e_1) or next to the type specifier (10_f).Variables. how-to-initialize-const-member-variable-in-a-class But why my code compiles and runs correctly? To learn more, see our tips on writing great answers. is performed before Dynamic In the register() method I added simple logging, so we can see what When static constructor is defined in class, static fields are initialized just before their use or as part of (before) instance creation. What are the default values of static variables in C? And given that it is only called once, IMHO it would need to be 100 times slower than instance initialization to qualify as "slow". Today I had a discussion with my colleague and concluded following points. Thanks. In C, static and global variables are initialized by the compiler itself. Growing up, I used to consider it silly to wear yellow underwear on new years eve. executes, at most, one time during The arguments object is a local variable available within all non-arrow functions. static int i = 50; printf(" value of i = %d", i); getchar(); return 0; } The reason for this is simple: All objects with static storage duration must be initialized (set to their initial values) Although we can be Ready to optimize your JavaScript with Rust? With this strategy it is possible to control the time when static variables are initialized at runtime, avoiding use-before-init. Dynamic Initialization: Here, the variable is assigned a value at the run time. When static field initialization happens? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Fields? As an exercise, predict the output of following program in both C and C++. If the compiler doesn't do this, it doesn't follow ISO C. Exactly how the variables are initialized is however unspecified by the standard. This leads to the beautiful property that they can be potentially evaluated and initialized at compile time. 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