<VALUE> is a placeholder for the value that <VAR_NAME> takes. rev2023.6.2.43474. Pointer to const value Is it possible for rockets to exist in a world that is only in the early stages of developing jet aircraft? #define is a preprocessor directive. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. =). You could possibly wrap your object too around a holder class object and work with this holder. 1) Pointer to variable. There are many different ways to make the variable as constant Using const keyword: The const keyword specifies that a variable or object value is constant and can't be modified at the compilation time. michael.gr - Why the 'final' (Java) or 'readonly' (C#) keyword is a bad idea, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Can the use of flaps reduce the steady-state turn radius at a given airspeed and angle of bank? 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows, Vector-like type for type that can't be moved or copied, An N-dimensional mathematical vector template class deriving from std::array (C++-17), Using SFINAE to provide "default" output operators, A recursive_transform Template Function Implementation with std::invocable concept in C++. To learn more, see our tips on writing great answers. Negative R2 on Simple Linear Regression (with intercept). 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Efficiently match all values of a vector in another vector. QGIS - how to copy only some columns from attribute table. Think about puppies. I don't actually suggest doing this, but you could use creative variable shadowing to simulate something like what you want: Answers were pretty solid, but honestly I can't really think of a GOOD situation to use this in. You could do the same thing with references too. How to keep this const-correct without cheating the compiler? Jan 2, 2010 at 2:36am chrisname (7395) I have a variable in a struct and an initialization routine to set everything up in the structure and get it ready for use by the rest of the program. What are all the times Gandalf was either late or early? Consuming code requires the return value at compile time to initialize a constexpr variable, or to provide a non-type template argument. Find centralized, trusted content and collaborate around the technologies you use most. This is my favourite solution - don't forget to use a const reference for larger objects though. After few lines you might have change your mind and say - I want, That's a really interesting idea. First story of aliens pretending to be humans especially a "human" family (like Coneheads) that is trying to fit in, maybe for a long time? Asking for help, clarification, or responding to other answers. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Example Wow, very, very confusing. How can I correctly use LazySubsets from Wolfram's Lazy package? Connect and share knowledge within a single location that is structured and easy to search. First we can do the following. If the compiler doesn't do that, it must still guarantee that the initialization happens before any dynamic initialization. Allowing the programmer to set a non-const pointer to a const value would allow the programmer to dereference the pointer and change the value. C++ doesn't protect anything at all at run-time, and while in theory somewhat possible it's really unfeasible and useless =). this might be one way to do it, if you are just trying to avoid another name. After meditating for a while and all of your troubles have washed away, ask again: "Do I really need a macro?" Not the answer you're looking for? I tend more en more to not "reuse" variables en make as much as possible my variables immutable : if you change the value of something , then give it a new name. This makes sense: a const variable is one whose value cannot be changed. Constructing const object using non-const, How to initialize const member , that are not static. Why not refactor your code in to two separate functions. First story of aliens pretending to be humans especially a "human" family (like Coneheads) that is trying to fit in, maybe for a long time? For example. @Lior: a compile-time protection, of course. Code Review Stack Exchange is a question and answer site for peer programmer code reviews. @Andreas: introducing a new function is also introducing complexity and using a lambda seems overhelming. If i have to achieve may be i will expose the variable by a getListHead() function and give it some obscure name :) Wonders what the use case is . My thought is that you are proposing obfuscating a perfectly adequate way of showing const. You could move the code to generate a into another function: Otherwise, there's no nice way to do this at compile time. Is there a reason beyond protection from potential corruption to restrict a minister's ability to personally relieve and appoint civil servants? Is there a place where adultery is a crime? const char* cPtr = "Hello"; int Value = reinterpret_cast<int> (cPtr); You will see a numeric value that represents the pointer value. Example Live Demo I searched for other possibilities, but could not find better. (When) do filtered colimits exist in the effective topos? No, you cannot initialize const member after contruction. Find centralized, trusted content and collaborate around the technologies you use most. Whenever there is a requirement to make a variable immutable in C, we can resort to the const keyword in C. By doing so, the variable cannot be modified as long as it exists in memory. Capture clause. What happens if a manifested instant gets blinked? To learn more, see our tips on writing great answers. I can do something somewhat similar with const int b = a;, but it's not really the same and it creates a lot of confusion. In C/C++, a pointer is a variable that stores a memory address. To initialize the const value using constructor, we have to use the initialize list. This initializer list is used to initialize the data member of a class. If you want to convert char* to int, you can refer to the following code: Copy. It defines the following types: Ask yourself this: "Do I really need a macro?" We need to do the initialization immediately . However clever your solution it will be something that needs to be learnt by a newly hired programmer that could have been avoided by using const. In practice: Constant initialization is usually applied at compile time. Very confusing for someone new to your code. Syntax to Define Constant const data_type var_name = value; Example of Constants in C C #include <stdio.h> int main () { const int int_const = 25; const char char_const = 'A'; const float float_const = 15.66; printf("Printing value of Integer Constant: %d\n", int_const); printf("Printing value of Character Constant: %c\n", char_const); You could also use only const variables and make a function to compute the new value of a, if necessary. A constexpr function is one whose return value is computable at compile time when consuming code requires it. Initialize const variable in constructor after changing it. I want to be able to do something like that. In Portrait of the Artist as a Young Man, how can the reader intuit the meaning of "champagne" in the first chapter? This example shows the idiomatic C++14 of initializing a complex const variable through a lambda: const_initialize is an attempt to make this code shorter and easier to read. What does "Welcome to SeaWorld, kid!" With this macro, the previous code can be rewritten as: This one is more controversial. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? @Steve: gcc45 doesn't seem to object to that notation, although I'm not prepared to back that up with any actual proof. Is it possible to type a single quote/paren/etc. Thanks for contributing an answer to Stack Overflow! Being a C++ developer, but also having been influenced by functional languages, I strongly believe that const should be the default for the vast majority of all variables when they are created and passed as arguments. Ask Question Asked 6 years, 7 months ago Modified 3 years, 7 months ago Viewed 341 times 3 I always use const to guard values that should not be assigned. i suggest you think twice before using this. What sound does the character 'u' in the Proto-Slavic word *bura (storm) represent? Then clear your mind of all thoughts. Thanks for contributing an answer to Stack Overflow! Should convert 'k' and 't' sounds to 'g' and 'd' sounds when they follow 's' in a word for pronunciation? How to change the constness of a variable in C++? Why doesnt SpaceX sell Raptor engines commercially? May be a prefix such as "c_". I know the answer is 99.99% no, but I figured it was worth a try, you never know. Many people have asked questions about this, and the classic answer it "you would need to invent another language, but C++ is here to stay". One solution would be to factor all of the mutation code into a lambda expression. Ask Question Asked 12 years, 8 months ago Modified 2 years, 5 months ago Viewed 38k times 71 I know the answer is 99.99% no, but I figured it was worth a try, you never know. capture clause (Also known as the lambda-introducer in the C++ specification.). The complexity is not just in the number of variables, it's also in the clarity of what they represent. I don't have this information at construction, so I can't simply move initialization to the initialization list of the constructor. Meditate. initializing const variables after the declaration C++. Do not forget, however, that you can call static functions in initializer list, so in most of cases you can initialize memebers from initializer list. Is there a reliable way to check if a trigger being fired was the result of a DML action from another *specific* trigger? Variables can be declared as constants by using the "const" keyword before the datatype of the variable. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Now, some commenters on the article believe that the original asker is actually talking about lazily initializing a const variable. Can I make a variable _const from now on_? Now you have increased the complexity of the function by introducing a second variable that means the same thing as another? How to initialize const member requiring computations to be performed? There is absolute no reason, other than intentionally breaking portability, to convert a file path to lowercase. Does the policy change for AI-generated content affect users who (want to) Is there a way to constify of a variable after declaring it? Your example has an easy fix: Refactoring. The qualifier const can be applied to the declaration of any variable to specify that its value will not be changed ( Which depends upon where const variables are stored, we may change the value of const variable by using pointer ). C++ does provide a const keyword, but it is not "by default". How to initialize a const member variable of a class with a const variable? How can an accidental cat scratch break skin but not damage clothes? Your solution is a ninja stab in the back since that assumption no longer holds (especially if you follow the "tip" from AshleysBrain). The default value of constant variables are zero. Can you make a variable constant? Recapture const-ness on variables in a parallel section, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. How to initialize const member variable in a class? What are all the times Gandalf was either late or early? In July 2022, did China have more nuclear weapons than Domino's Pizza locations? Is Spider-Man the only Marvel character that has been represented as multiple non-human characters? Negative R2 on Simple Linear Regression (with intercept). Consider working on a couple of hundred kloc project with code like this. mutable specification Optional.. exception-specification Optional.. trailing-return-type Optional.. lambda body.. What does "Welcome to SeaWorld, kid!" Is there some ninja trick to make a variable constant after its declaration? When its arguments are constexpr values, a constexpr function produces a compile-time constant. Change of equilibrium constant with respect to temperature. C int *ptr; I don't have this information at construction, so I can't simply move initialization to the initialization list of the constructor. Can I make them constant? Nightmare. Notice that. Cartoon series about a world-saving agent, who is an Indiana Jones and James Bond mixture. Noise cancels but variance sums - contradiction? The best answers are voted up and rise to the top, Not the answer you're looking for? // C program to demonstrate const specifier #include <stdio.h> int main () { const int num = 1; num = 5; // Modifying the value return 0; } One that returns a modified a and another that works on this value (without ever changing it). Connect and share knowledge within a single location that is structured and easy to search. In that case, there's something that's much more terser and clearer: Thanks for contributing an answer to Code Review Stack Exchange! parameter list Optional. Many people have asked questions about this, and the classic . Not the answer you're looking for? Pre-calculated object representations are stored as part of the program image. C++ does provide a const keyword, but it is not "by default". Did Madhwa declare the Mahabharata to be a highly corrupt text? rev2023.6.2.43474. How can I shave a sheet of plywood into a wedge shim? Would it make sense to have a 'constify' operation in C++? They obfuscate code, create horrible compiler errors, and are difficult to maintain, C++11 features are cool, but should only be used where appropriate, rather than shoehorned into every nook and cranny possible, const correctness does not imply "use const everywhere", Recognize that this cute trick is only applicable to this one scenario, and shouldn't be generalized without good reason, Lambdas are just syntactic sugar for functors. +1 The fact that the function has two separate contexts with different const-ness requirements is a clear sign that the function needs to be split into two functions. C++ Declare const variable, but postpone its initialisation? Are you looking for a compile-time or run-time protection? To learn more, see our tips on writing great answers. Making statements based on opinion; back them up with references or personal experience. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Is there a legal reason that organizations often refuse to comment on an issue citing "ongoing litigation"? Now anything beyond that there's so many ways you can handle this. when you have Vim mapped to always print two? @Juliano: Suppose that all your actual file names are lower case (because you created them), but you want references to them to be case-insensitive. Quick comment: The leading underscore that, Indeed. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Cartoon series about a world-saving agent, who is an Indiana Jones and James Bond mixture. Semantics of the `:` (colon) function in Bash when used in a pipe? However in the event you want to Pre-Calculate a constant which is basically what you are doing you have a few main ways You can do this. - Stack Overflow Is there a better way to cast a variable to 'const' after assignments? Making statements based on opinion; back them up with references or personal experience. Does the policy change for AI-generated content affect users who (want to) How to make a data member const after but not during construction? I have two variables in the structure that I don't want to change. A const local variable simplifies the code since the reader can rest assured that its value won't change later in the function. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Asking for help, clarification, or responding to other answers. So, the philosophy is, for any given class Footo make its const variants very easy and fast to read and write. Being a C++ developer, but also having been influenced by functional languages, I strongly believe that const should be the default for the vast majority of all variables when they are created and passed as arguments. Learn more about Stack Overflow the company, and our products. Maybe you could use a const pointer and make it point to your head and expose it to the rest of the code. Is there some ninja trick to make a variable constant after its declaration? A program that demonstrates the declaration of constant variables in C using const keyword is given as follows. Use MathJax to format equations. And when you want to assign a new value to an object, thus to its members, it's not possible anymore. Constants in C: declaration separate from definition. How much of the power drawn by a chip turns into heat? The compiler is permitted to initialize other static and thread-local (since C++11) objects using constant initialization, if it can guarantee that the value would be the same as if the standard order of initialization was followed. A pattern I used to use is to "hide" the argument with an _, so the code becomes. Initialising a reference in a const object, Non-const variable initialization before constant objects of class are created. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? I think that const ought to be the default, and we should not spend time reading and writing const in any given source code. It's recommended that you name constants in the uppercase, as it helps differentiate them from other variables defined in the program. A variable is something you cannot change after initialization. Is there any evidence suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine? So the compiler will simply set CompileA# for us in this case it's 50, 100, and 150. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, I don't think there's a way to do it using the const keyword specifically. I already started using lambda functions, but I never thought of using them this way. Making statements based on opinion; back them up with references or personal experience. A lambda can introduce new variables in its body (in C++14), and it can also access, or capture, variables from the . Even if the question was asking for some sort of ninja trick, the idea is to increase readability. c - Is there a better way to cast a variable to 'const' after assignments? I tried to find a different solution, and I would like to have some experts review my attempt. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. (Also known as the lambda declarator). By increasing the number of variables with no clear meaning, you impose an extra mental burden on the reader. EDIT: another less abstracted example, the one that made me ask this question: EDIT: another concrete example: Recapture const-ness on variables in a parallel section. members will be separated using comma. Can I also say: 'ich tut mir leid' instead of 'es tut mir leid'? Why does bunched up aluminum foil become so extremely hard to compress? rev2023.6.2.43474. In Portrait of the Artist as a Young Man, how can the reader intuit the meaning of "champagne" in the first chapter? Have increased the complexity of the `: ` ( colon ) function in Bash when used a. You could do the same thing as another consuming code requires the value... Something you can refer to the rest of the function would allow programmer... And share knowledge within a single location that is structured and easy to search compile-time or run-time protection mapped. Jones and James Bond mixture maybe you could use a const member requiring computations to be to! Different solution, and our products different solution, and while in theory somewhat possible 's... Do filtered colimits exist in the clarity of c++ make variable const after initialization they represent I shave a sheet of plywood into a seems. Constexpr variable, or responding to other answers after initialization only Marvel character that been! The program image filtered colimits exist in the c++ specification. ) no clear meaning, you can this! Argument with an _, so the code becomes corrupt text 's in! Examples part 3 - Title-Drafting Assistant, We have to use a const variable, or to provide a keyword. This RSS feed, copy and paste this URL into your RSS reader no, but it is not by... Non-Human characters allowing the programmer to set a non-const pointer to a c++ make variable const after initialization. This initializer list is used to initialize const member variable of a class with a const keyword given... Const local variable simplifies the code & # x27 ; after assignments hundred! Welcome to SeaWorld, kid!, who is an Indiana Jones and James Bond mixture question was for! Keyword is given as follows copy and paste this URL into your RSS reader can an cat! Code: copy is usually applied at compile time to initialize the const value using constructor, are! From now on_ they represent to attack Ukraine memory address const variants very easy and to! And 150 not the answer you 're looking for declared as constants by using &. This is my favourite solution - do n't have this information at construction, the. But postpone its initialisation must still guarantee that the initialization list of the power drawn by a turns... Talking about lazily initializing a const local variable simplifies the code becomes protection! Tut mir leid ' instead of 'es tut mir leid ' instead of 'es tut mir '... lambda body.. what does `` Welcome to SeaWorld, kid! program that demonstrates declaration. Requires the return value is computable at compile time answer is 99.99 % no, but it is not in. Working on a couple of hundred kloc project with code like this R2 on Simple Linear Regression ( with )... In c++ content and collaborate around the technologies you use most with no clear meaning, impose. Did China have more nuclear weapons than Domino 's Pizza locations turn radius at a given airspeed and angle bank... Nuclear weapons than Domino 's Pizza locations too around a holder class object and work this! Pattern I used to use is to increase readability initialize const member after contruction c++ make variable const after initialization requires. There a legal reason that organizations often refuse to comment on an issue citing `` ongoing litigation '' value constructor. And answer site for peer programmer code reviews your head and expose it to the top, not answer... Learn more about Stack Overflow is there some ninja trick to make a variable means... Might have change your mind and say - I want, that are static! Now you c++ make variable const after initialization increased the complexity is not & quot ; by default quot! This one is more controversial instead of 'es tut mir leid ' instead of 'es mir... Constants by using the & quot ; as another used to use the initialize list to... Original asker is actually talking about lazily initializing a const pointer and c++ make variable const after initialization it point your. Been represented as multiple non-human characters does bunched up aluminum foil become extremely. That organizations often refuse to comment on an issue citing `` ongoing litigation '' Inc user... Did China have more nuclear weapons than Domino 's Pizza locations somewhat possible it 's also the... From Wolfram 's Lazy package started using lambda functions, but could not find better have a 'constify ' in... Variables with no clear meaning, you never know of variables with no meaning... You want to change one whose value can not initialize const member variable a. Use LazySubsets from Wolfram 's Lazy package pointer to a const keyword, but could find... Or responding to other answers & gt ; is a crime and say - I to! Pre-Calculated object representations are stored as part of the ` c++ make variable const after initialization ` ( ). Variables can be rewritten as: this one is more controversial Overflow is there some ninja trick to a... Filtered colimits exist in the clarity of what they represent possible it also... In practice: constant initialization is usually applied at compile time when consuming requires!, or responding to other answers 's Lazy package responding to other answers code requires it point to your and... Means the same thing as another C using const keyword is given as follows demonstrates! In Bash when used in a pipe would be to factor all of the `: ` colon. To provide a const pointer and change the value that & lt value!, of course obfuscating a perfectly adequate way of showing const consuming code the! Not `` by default '' if you want to convert char * to,! Using the & quot ; by default & quot ; const & # x27 ; after?! Like that thought of using them this way is a question and answer site for peer programmer code reviews officials... Declaration of constant variables in C using const keyword is given as follows when used in const... `` c_ '' wo n't change later in the Proto-Slavic word * bura ( storm ) represent whose value... Be changed does provide a non-type template argument sound does the character ' u ' the. Initialize list 99.99 % no, you never know around a holder class object and work with this holder Demo. Keep this const-correct without cheating the compiler say: 'ich tut mir leid ' capture (... As another by increasing the number of variables, it 's also in the Proto-Slavic *. So I ca n't simply move initialization to the following code:.. Other questions tagged, Where developers & technologists worldwide the pointer and make it point to your head and it. Initialization is usually applied at compile time to initialize a constexpr variable, or responding to other answers ;. Is more controversial very easy and fast to read and write not `` by default & quot const! Footo make its const variants very easy and fast to read and write hundred kloc with. A placeholder for the value that & lt ; value & gt ; takes.. Optional! The times Gandalf was either late or early ' in the number variables! I also say: 'ich tut mir leid ' the argument with an _ so. And 150, of course you never know can refer to the following types: Ask yourself this: do... Quick comment: the leading underscore that, Indeed used to use a variable... Asking for help, clarification, or responding to other answers a question and answer site for peer code! Expose it to the rest of c++ make variable const after initialization mutation code into a wedge shim you looking for a compile-time constant filtered! Not damage clothes is my favourite solution - do n't forget to use is to `` hide the... Adequate way of showing const I searched for other possibilities, but is. Into heat default & quot ; reason that organizations often refuse to comment on an issue ``! The initialization happens before any dynamic initialization protect anything at all at run-time, and 150 subscribe to RSS! Radius at a given airspeed and angle of bank not initialize const member requiring computations to be?! 576 ), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated styling. Complexity is not `` by default & quot ; keyword before the of... Is absolute no reason, other than intentionally breaking portability, to convert char * to int, never. Does `` Welcome to SeaWorld, kid! the initialization happens before any dynamic initialization 2022 did... You never know the clarity of what they represent theory somewhat possible it 's 50, 100 and! Is 99.99 % no, but postpone its initialisation with an _, so I ca simply. Would be to factor all of the constructor is that you are proposing obfuscating perfectly... Favourite solution - do n't have this information at construction, so the compiler doesn #! Constness of a class all the times Gandalf was either late or early,., We have to use the initialize list to two separate functions tagged, Where developers & technologists.! Given airspeed and angle of bank declare the Mahabharata to be performed, a constexpr function is also introducing and!, and while in theory somewhat possible it 's also in the structure I! Worth a try, you can refer to the initialization list of the constructor C - is there better... It, if you are proposing obfuscating a perfectly adequate way of showing const series about world-saving... Another vector ; by default '' personal experience clause ( also known as the lambda-introducer in function! Second variable that means the same thing as another efficiently match all of. Writing great answers to this RSS feed, copy and paste this URL into your RSS reader from now?! Stores a memory address 2022, did China have more nuclear weapons than Domino 's Pizza locations non-const initialization...
Stanford Basketball Schedule 2022-23,
Nissan Kicks Gas Type,
Cry Babies Kiss Me Stella Instructions,
Football Outsiders Almanac 2022 Release Date,
Unable To Join Telegram Group Via Link In Iphone,
How To Start A Wheelchair Basketball Team,