of the draft and 6.7.4 para 6, IMO, at any given time, the value of the object will be indeterminable (the value can come from either the external definition/internal definition based on how and where what choice the compiler had made. What's the difference between constexpr and const? The constant returned was: This is a viable solution. Do we have a static initialisation order fiasco while initialising variables inside the class. constexpr variable is guaranteed to have a value available at compile time. How to smoothen the round border of a created buffer to make it look more natural? How to Use the JavaScript Fetch API to Get Data? To declare a variable or procedure as static, use the static keyword. #define uses token-pasting to insert the specified value into the shader code whereever it occurs; the shader itself will see the token as if you simply hard-coded it at every occurrence instead.. A static const variable in, in actuality, a variable. Hide or show elements in HTML using display property, Difference between var and let in JavaScript. How to use a VPN to access a Russian website that is banned in the EU? Why is it so much harder to run on a treadmill when not holding the handlebars? Would salt mines, lakes or flats be reasonably found in high, snowy elevations? Static variable: A static variable in JavaScript is basically a property of the class which is not used on the object of the class but is used in the class itself. But static here means that it remains alive, doesn't get garbaged, opposite of dynamic in that sense. Is there a higher analog of "category with all same side inverses is a groupoid"? These represent a value, not a memory address. We could say that the difference lies in when the value of the variable is known throughout the lifecycle of the application. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. static int a = 10; But the difference is that, #define replaces foo by the value, static const is an instruction so it increments the instruction pointer to the next instruction and it uses 1 additional register to store the value. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. This means that. However the bigger picture question here is which is the more proper way of creating and using these values. stackoverflow is also for easy questions for those who know, but difficult for those who don't. C++ global variable that can be changed only in one method, possible? Typing constexpr express your intent of a compile time value in a much more explicit way than const. A static keyword is been used to declare a variable or a method as static. 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For the readonly keyword, the latest value is known by the runtime. The first difference is the timeslot which initializes the const or readonly variables. What is the difference between const int*, const int * const, and int const *? The const variable is used for declaring a constant or fixed value whose value cannot be changed. The correct form would be: An exception to this is when you define a constant in a function. whereas static const members or const variable could either mean a compile time value or a runtime value. As such, it cannot be called with the object's name, but only with the class's name. const restricts your ability to modify the value. @jagannath : yes, he could, but what if he is a very skilled fortran programmer, surrounded by fortran programming books, having a C source code to debug under pressure and no clue where to look ? whereas static const members or const variable could either mean a compile time value or a runtime value. Difference between self::$bar and static::$bar in PHP. rev2022.12.9.43105. This default value means that a single copy of the variable is created and shared among all objects. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. To assign a constant or fixed value to a variable, use the const keyword. Fan of making things beep, blink and fly. By default a const is static and we cannot change the value of a const variable throughout the entire program. How to append HTML code to a div using JavaScript ? score:64. constexpr variable is guaranteed to have a value available at compile time. The common of these two keywords is that they both cover immutable data types, meaning the value cannot change throughout the life of the application. Why is apparent power not measured in Watts? We could say that the difference lies in when the value of the variable is known throughout the lifecycle of the application. Appropriate translation of "puer territus pedes nudos aspicit"? Sed based on 2 words, then replace whole line with variable. ( A simple thought.. To know the number of objects created for a class we can put a static variable and do ++ in constructor), Value persists between different function calls. The const keyword is used for defining constant value for a variable. You can use the static keyword on methods, properties, classes, constructors, etc. However, for calling a static method within another static method, we can make use of this keyword. How could my characters be tricked into thinking they are on Mars? 2. In this section, we will describe the difference points between both variables. It might read better if the text " exists to a " was changed to " exists for a ". Printing dum from object: 1 X=9; //Correct. However, there seems to be a different behavior for doubles. A const variable is a variable that has a fixed value and remains the same throughout the program. Below is a practical implementation of using JavaScript static keyword within a class: In the above program code, we can see that a static method is created within a class and when it is invoked, it calls the statement within the static method of the class. Name of a play about the morality of prostitution (kind of). I was wrong to use the term "scalar" types in my answer. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? What is the difference between ++i and i++? Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, The static keyword and its various uses in C++, Initializing constexpr with const: Different treatment for int and double, using constants in header file with ODR compliance. Within a function, the second version can be computed from parameters. This keyword ensures that a variable instance or property of an object cannot be modified after initialization, and such attempts will result in an exception. Connect and share knowledge within a single location that is structured and easy to search. static is a variable. One more thing, in C++17, constexpr static data member variables will be inline too. Should I avoid static constexpr local variables? is used to make it a read-only variable. However, static are different from the variables in the sense that static variables retain their values for the whole of the program ie their lifetime is of the program or until the memory is de allocated by the program by using dynamic allocation method. See 6.7.4. para 3 and a related footnote on the next page (possibly). Making statements based on opinion; back them up with references or personal experience. If the programmer tries to modify its value the compiler shows an error, this is because as soon as we have declared a variable as constant it tells the compiler that this is a fixed value and should be prevented from making any changes to it. Making statements based on opinion; back them up with references or personal experience. How is the merkle root verified if the mempools may be different? The value of a static variable can be modified. To declare a variable/function as static we used the static keyword. so the order obviously doesn't matter. The common of these two keywords is that they both cover . The differences between the two qualifiers are as follows: How to convert Set to Array in JavaScript? Personally, I prefer the first version, because the fact that a variable is a constant is more important to me than its scope. It depends on what you need the value for. These fields can either be initialized when declared or at the constructor of our object. static_assert not working inside class template definition. The variable dum is a class variable. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What is the difference between #include and #include "filename"? The const is constant type data, or static const is constant but storage specifier is static. A const keyword is been used to assign a constant or a fixed value to . How did muzzle-loaded rifled artillery solve the problems of the hand-held rifle? constexpr simply performs an early check of the "constness" of initializer. A field marked static is the same for every instance of a class. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? What is a tooltip and how to create it in Bootstrap ? If you make a variable constexpr it will be initialized on compile time, so that will increase compilation time, but will make run time faster? static value may exists into a function and can be used in different forms and can have different value in the program. How to convert a std::string to const char* or char*. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Thus, whenever the programmer tries to modify a const value, an error gets displayed that the const value cannot be changed. Set the value of an input field in JavaScript. Not the answer you're looking for? Penrose diagram of hypothetical astrophysical white hole. Both initializations are fine, from the compiler side. A constant member is defined at compile time and cannot be changed at runtime. C++ semantics of `static const` vs `const`. Despite being very similar, these keywords use different binary versioning. The const is a type . All rights reserved. Why does the USA not have a constitutional court? The GCC assembly in your edit proves nothing. Why is the federal judiciary of the United States divided into circuits? While const is initialized at compile time, readonly keyword allow the variable to be initialized either at compile time or runtime. Moreover, immunity of integral static objects to ordering problems of static initialization is a very important feature of the language. At the highest level, if we want to differentiate the readonly and const keywords. arduino avr-gcc C Programming. That mean it's in some way the equivalent of declaring the variable as global, but only accessible in the function. If the value isn't known at compile time, it's a compilation error, not a slower function. static const : "static const" is basically a combination of static(a storage specifier) and const(a type qualifier). Must static objects generally be initialized? Ready to optimize your JavaScript with Rust? Constants are declared as a field, using the const keyword and must be initialized as they are declared. #define myvalue = 2). Appealing a verdict due to the lawyers being incompetent and or failing to follow instructions? 1980s short story - disease of self absorption. If the static modifier is applied to a class then you cannot instantiate the class using the new keyword. For in-depth information on this subject, check out this thread in the Arduino Forums: Const vs #define - Arduino Forum. Let's discuss. Historically, the declaration specifier was an unordered list of keywords and type names, so: static unsigned int const var; static unsigned const int var; static int unsigned const var . The longer answer: More on the keywords than you wanted to know (right from the standards): Has the same semantics mostly except as noted in the short answer. Typesetting Malayalam in xelatex & lualatex gives error. Constant variables however are prevented from changing. Declaring a static variable in an object has the effect that this value is the same for all instances of the object. 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. Developed by JavaTpoint. This deprecation was removed in C++11 for various reasons (see here). @Mr.C64 When you are creating some class, which will be used as a parameter of template, here is the good time to use constexpr: all members are constexpr, whereas. memory-usage. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. JavaScript const can be used with objects and arrays also. In this article, we discussed these three keywords: const, readonly, and static readonly with the proper examples. Constant: A constant variable in JavaScript is a variable that has a constant or a fixed value which remains the same ie. Does a 120cc engine burn 120cc of fuel a minute? if the value is used in a different assembly, the original needs to be updated and the value changed. Thanks for contributing an answer to Stack Overflow! Typing constexpr express your intent of a compile time value in a much more explicit way than const. I'm not asking "constexpr" vs. "const", but vs. This is especially important if the variable is declared in a function, since it guarantees the initialization will only take place at the first call to the function. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. JavaScript static can be used with classes and methods also. This guide will walk you through the nifty details and what you need to know to properly utilize these keywords in your applications. You need not define a static variable while declaring. Static means static instance (in memory) vs dynamic instance (on the stack. Now let's look at the Java keyword static. How to add an object to an array in JavaScript ? A static variable can get an initial value only one time. Meaning of 'const' last in a function declaration of a class? Deprecation of the static keyword no more? That means you can omit the out of line definition of static constexpr variables, but not static const. I mean, the inline definitions are already allowed to expose different behavior. Typing constexpr express your intent of a compile time value in a much more explicit way than const. We can use the static keyword for making a static value, a static function, with classes, operators, properties and work as a utility function for the application or websites. Thanks for contributing an answer to Stack Overflow! The const keyword is used for defining constant value for a variable. How to calculate the number of days between two dates in JavaScript ? Though in practice the compiler will . Why is Singapore considered to be a dictatorial regime and a multi-party democracy at the same time? Then if you have no way of determine the value of your variable at compile time, then the compiler will tell you about it and you can do something about it. JavaScript static is labeled by a keyword known as the 'static' keyword. JavaTpoint offers too many high quality services. In case you are using this context via class, you can access them through the name of the class. Difference between require() and include() in PHP. const or static const. JavaScript const is labeled by a keyword known as the 'const' keyword, where we declare a const variable and initialize it with a constant value. It basically doesn't matter. constexpr vs. static const: Which one to prefer? For defining compile-time constants of integral types like the following (at function and class scope), which syntax is best? Constants can't be changed, static variables have more to do with how they are allocated and where they are accessible. What is the difference between const int*, const int * const, and int const *? The static keyword is used for defining static properties and methods in a javascript class program. Have a look at a book or the standard. The const variable is basically used for declaring a constant value that cannot be modified. Copyright 2011-2021 www.javatpoint.com. It is equivalent to a global variable who's usage scope is the scope of the block they have been declared in, but their value's scope is global. Printing dum from class: 1. Const is nothing but "constant", a variable of which the value is constant but at compile time. The static keyword can be accessed on the class definition only. Please mail your requirement at [emailprotected] Duration: 1 week to 2 week. Also, with C++0x until C++11 the use of the static keyword was deprecated for declaring objects in namespace scope. However, one might say that constexpr is a feature designed specifically for that purpose so it fits better stylistically. For integer types constexpr does not offer anything extra over what const already did. A bank account might have a static variable that represents the interest rate, for . Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 2 Answers. If you do it, it will complain. Any kind of modification in its value is not possible once it is declared. Should I give a brutally honest feedback on course evaluations? You must assign a value to it. Constant variables cannot be changed. Share. Divide global declarations into two categories: constants declare constant values. In JavaScript, the static keyword is used with methods and classes too. In the following code, we have declared a variable as const and using document.write() method, we have displayed its value. The static keyword can be accessed on the class definition only. const is equivalent to #define but only for value statements(e.g. It can be used on fields, but not on local variables. Apr 12, 2011 at 4:24pm. In languages like C and C++, it is meaningless to declare static global variables, but they are very useful in functions and classes. Are there breakers which can be triggered by an external signal and have to be reset by hand? Check if an array is empty or not in JavaScript. That's the advantage of a constexpr variable. These two concepts are not mutually exclusive, and can be used together. However, we can re-declare the const variable in different block scope as it is allowed. There are a few more nuances of C++'s static that I leave out here. The static methods are the utility functions that are used for creating or cloning the objects. The value of a static variable is set at the run time and is a kind of global value that can be used for the instance of the specified class. The const in const char * makes p point to const char. Simple and short answer is memory is allocated for static and const only once. I've created a separate question for that here. Here I have created a class named Variables and defined all three variables, so first let's . static means local for compilation unit (i.e. You (and everyone else so far) omitted the third alternative: static const int var = 5; #define var 5. enum { var = 5 }; Ignoring issues about the choice of name, then: If you need to pass a pointer around, you must use (1). Static vs. Const in JavaScript. Strictly speaking a Constant should have slightly better performance (1 nanosecond instead of 2 probably) because it's value is set at compile-time whereas a static readonly value is loaded at runtime.. The output of the following is shown below: Below is a practical implementation of using JavaScript const keyword: In the above code, it is seen that the const variable is assigned with a value but when we try to re-assign another value, an error is thrown which tells that the value described as const cannot be changed. The value of the constant variable cannot be modified. What is the difference between a static and const variable? Should one or the other be preferred in modern C++ code, and why? When an expression references a specific constant, the compiler embeds the value at compile-time. A static variable exists to a function, or class, rather than an instance or object. As long as we are talking about declaring compile-time constants of scalar integer or enum types, there's absolutely no difference between using const (static const in class scope) or constexpr. A common use of const and static together is within a class definition to provide some sort of constant. How to create Static Variables in JavaScript ? Since (2) is apparently an option, you don't . Sudo update-grub does not work (single boot Ubuntu 22.04). statics declare global variables. http://duramecho.com/ComputerInformation/WhyHowCppConst.html. The first, const, is initialized during compile-time and the latter, readonly, initialized is by the latest run-time. In order to access the static keyword for non-static methods, one needs to invoke them using the class name. If the constant is only constant for the lifetime of the function and may change depending on on how/when the function is called, use const. Hence, the output of the above code is: In this section, we understood that static as well as const variable have different roles and are used for different purposes where a static variable can be used for a class method or property and a const variable is used for initializing a const value for an array, variable or an object. volatile. What's the difference between constexpr and const? These represent a memory address. The changes in the assembly are not reflected until it is recompiled. It's not really exactly the same is it? The value for a const variable cannot be reassigned. The readonly fields are stored in dynamic memory, the values are accessible only at runtime. Asking for help, clarification, or responding to other answers. As such, static variables are only initialized once. PHP7static:MY_CONST vs self:MY_CONST vs SomeClass:MY_CONST,php,php-7,Php,Php 7, self:MY_CONSTSomeClass:MY_CONSTstatic:MY_CONST self:MY_CONST class . This definition holds the FullName property of the class which is initialized at runtime, but the compilation still succeeds due to the nature of the readonly keyword. Or to avoid writing static in front of all static functions? Static variable are private to the file and only accessible within the program code and not to anyone else. Also during program after increment of decrement their value may change but const in constant during the whole program. What happens if you score more than 99 points in volleyball? A static const variable at function scope is pretty much the same, but instead of having a automatic storage duration, it has static storage duration. static const vs #define vs enum. Why did the Council of Elrond debate hiding or sending the Ring away, if Sauron wins eventually in that scenario? constexpr vs. static const: Which one to prefer? The full "compile time constant" treatment is only applied to, "rules of constant initialization prevent local. Performance while key is leaving out the entire issue of when it it appropriate to . @litb: Because, inline definition of functions are not allowed to have modifiable static object definitions in C99. Find centralized, trusted content and collaborate around the technologies you use most. constant variables are specific to each individual instance of a type but their values are known and fixed at compile time and it cannot be changed at runtime. In the case of a static variable, its value is set at the runtime itself and it is a global value that can be used by the instance of the class. By this, we can say that macro is better than static constants but the difference is minimum. Call this function with the following statement: The above gives us the following console output. Static variables are common across all instances of a type. a single C++ source code file), or in other words it means it is not added to a global namespace. 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. const makes internal linkage the default, and all global variables have static lifetime. As a demand in the comment section, here's a more detailed explanation about static const in function scope. Did neanderthals need vitamin C from the diet? Any idea? We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. This is the most common thing one would reach for and would replace static as we know it today in almost all cases. The specialty of these variables is that they need to have a value at compile time and, by default, they are static. Static variables in the context of a class are shared between all instances of a class. C99 borrowed the use of const from C++. Java's static vs. final keywords. Are the S&P 500 and Dow Jones Industrial Average securities? Convert a string to an integer in JavaScript. As @Nawaz says, those two examples do different things, and without any mention of their intended uses it's impossible to decide which is "better". Difference between static class and singleton pattern? In order to access the static keyword for non-static methods, one needs to invoke them using the class name. In a function, it remains a persistent variable, so you could for instance count the number of times a function has been called. We make use of both static and const variables in different languages. rev2022.12.9.43105. There are the following difference points which will let us understand the difference between the two: Static Const; The static keyword is used for defining static properties and methods in a javascript class program. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. As long as we are talking about declaring compile-time constants of scalar integer or enum types, there's absolutely no difference between using const (static const in class scope) or constexpr. Multiple definition of inline functions when linking static libs. As far as I know, static global variables are not deprecated in C, since there are no namespaces. To use a const variable, we use a 'const' keyword and input value. Why did the Council of Elrond debate hiding or sending the Ring away, if Sauron wins eventually in that scenario? But the first variant has the same behavior in C, so that may be a good reason to use it. So if one object modifies its value then the modified value is visible to other objects as well. Examples of frauds discovered because someone tried to mimic a random sequence. This would print: A static const local variable is a variable that does not change and is initialized or constructed only once; the first time the function is called. Change in the value is reflected immediately, the assembly does not need to be recompiled. I tried this sample code with Godbolt's CE: and for the static const case this is the generated assembly by GCC 6.2: Although at -O3 in both cases I get the same (optimized) assembly: I tried this simple code (live on Ideone): which shows that const int k1 is evaluated at compile-time, as it's used to calculate constexpr int k2. Find centralized, trusted content and collaborate around the technologies you use most. answered Aug 17, 2012 at 12:41. user743382. The readonly keyword is a special modifier which bears significant resemblance to the const keyword. Differences between Functional Components and Class Components in React, Difference between TypeScript and JavaScript, Form validation using HTML and JavaScript. This static variable is stored into the data segment of the memory and its value is shared among all the objects/instances created in that particular class. The static modifier is used to declare a static member, this means that the member is no longer tied to a specific object. you can have multiple static variables in different c++ source code files with the same name and no name conflicts. Static methods are essentially utility functions for constructing or copying objects. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Another usage of statics involves objects. Where does the idea of selling dragon parts come from? In this beginner C++ tutorial, we will talk about static keyword and how it is used in C++ object-oriented programming. In C++, the anonymous namespace is preferred to static for file scope variables. Difference between static and const variables. Not sure if it was just me or something she sent to the whole team. which does not change throughout the program. Share. Can someone explain the difference between a static and const variable? Constants are set at compile-time itself and assigned for value types only. Should teachers encourage good students to help weaker ones? Therefore, const variables are used for compile-time constants. Received a 'behavior reminder' from manager. The compileTime variable tells you this is initialized beforehand. The idea behind both keywords is the same. A const value can be accessed globally or locally, but a global constant can never be window object properties. How to remove a character from string in JavaScript ? constexpr is an extension and generalization of the concept that was originally implemented in C++ through const with a constant initializer. A variable where value can't be modified once after declaration is know as constant variable where as in read only variable we can make separation in between declaration and initialization. The const variable is mostly used to declare a non-modifiable constant value. In the same program mentioned above, let's make the dum a const as well: Though static has been manageable to understand, const is messed up in c++. Does a 120cc engine burn 120cc of fuel a minute? We would like to mark a variable to hold its value during the execution of the application and not allow modification. Why would Henry want to close the breach? C# facilitates keywords like const, readonly, and static readonly which can be confusing at a time when you need them the most. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 3. static means local for compilation unit (i.e. The const keyword converts nothing more but a constant. Are there any other differences between the two? Is it appropriate to ignore emails from a student asking obvious questions? ) Static variables exist for the duration of the program. static keyword defines the scope of variables whereas const keyword defines the value of variable that can't be changed during program execution. Mail us on [emailprotected], to get more information about given services. Author James Lewis. How to Open URL in New Tab using JavaScript ? http://duramecho.com/ComputerInformation/WhyHowCppConst.html. const. const is just constant, meaning can't be modified. A const is a promise that you will not try to modify the value once set. Static variables are for the class (not per object). Difference between Static vs Const. For example, if you set the constant variable like "const int a=5", then this value for "a" will be constant in whole of your program. The non-static methods cannot access static members. The Const qualifier is applied to the variable declaration to specify the fact that the value of the variable will not be changed. Another important difference is that const variables can be referenced through "ClassName.VariableName", while readonly can be referenced through "InstanceName.VariableName". To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The first line ( static const int.) The default constants are static, and we cannot change the value of the const variable throughout the program. The static keyword is used for defining static properties and methods in a javascript class program. How to get value of selected radio button using JavaScript? Why are they then limited to non-modifiable object definitions and forbidden to use identifiers with internal linkage? Why before ALL functions (except for main()) there is a 'static' keyword? A static variable is a class property that is used in a class and not on the instance of the class. Plus, it has to check if the value is initialized each time the function is called. It wouldn't be philosophically sound to use the word constant -- or the Java keyword const-- to describe this field. Which one to prefer depends on what you're going to use them for. By default, this would throw a compile time error because you are expected to provide a value to the constant before compilation. The value declared replaces the name of the variable before compilation. In managed languages, the only way to have the effect of a global variable is to declare it as static. There are also static global variables which are static variables declared outside of both a function and a class. And also discuss the similarities and differences between const, readonly, and static readonly keywords. Apart from these theoretical difference descriptions, let's have a look over an example of both through which we can understand the use and working of the static and const variable. unlike constants, static variable values can be changed at runtime. Why is the federal judiciary of the United States divided into circuits? The variable is stored on the data segment area of the memory, and the same value is shared among every instance created in a class. Trying to access it via an object just informs the compiler that it is a variable of which class. To use a static variable, we use the static keyword. On the other hand, static has been the source of many debates (in both languages) because of its often confusing semantics. How do you run JavaScript script through the Terminal? Still, it is probably wiser to use the second version: not because the first one is ill-formed, but because of misbehaving compilers and static . No exception is thrown, the runTime indicates that this variable will have its value initialized with the class' constructor. To learn more, see our tips on writing great answers. I have introduced the differences and similarities to the best of my abilities and I hope you found what you were looking for. The value for a static variable can be reassigned. Or using static const: static const uint8_t REGISTER_MOTOR_1_MODE = 0x44; static const uint8_t REGISTER_MOTOR_2_MODE = 0x47; (Obviously I have more than just two registers I need to declare, but I thought two would illustrate the point just fine) c++. A property of the const variable is that we cannot change or modify its value throughout the program. Static: Constant: The static methods are basically utility functions creating or making a copy of an object. Disch (13742) If the constant will be the same every time the function is called, use static const. Therefore, readonly variables are used for the run-time constants. For the const keyword, the value must be known by compile time. Const, readonly, static readonly - keywords that perform a similar action but have an important difference: Const - is a variable whose value is constant and is assigned at compile time. Additionally, as long as such objects remain odr-unused, they require no definition, which further demonstrates that they won't be used as run-time values. Michael, it's the other way around, in this matter VS follows the standard, while gcc doesn't. I found this in the standard 9.4.2/4 - If a static data member is of const integral or const enumeration type, its declaration in the class definition can specify a constant-initializer which shall be an integral constant expression (5.19). C++ What's the difference between the way compiler accesses static members and accesses ordinary members? is used for making the variable a class variable. @litb: If it is non-const, then per footnote "120) Since an inline definition is distinct from the corresponding external definition and from any other corresponding inline definitions in other translation units, all corresponding objects with static storage duration are also distinct in each of the definitions." This means that if you have code such as "static int a=0" in a sample function, and this code is executed in a first call of this function, but not executed in a subsequent call of the function; variable (a) will still have its current value (for example, a current value of 5), because the static variable gets an initial value only one time. As an example, take a look at a constant. The static determines the lifetime and visibility/accessibility of the variable. Example: Below is the implementation of const keyword in JavaScript. Constant variable VS Read only Variable. To get another level of indendation for the unknown namespace block and increase cyclomatic complexity? Do you know the reason for that restriction? Static can be assigned for reference types and set at run time. Ad the "little bit slower" part: not only because it has to initialize the value the first time the function is called, but it also has to determine at run time at every call, @Mr.C64: Yes, it is. 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static const'' vs #define 2022