Why isn't this encouraged right from the beginning, rather than allowing people to develop bad habits, from the outset? Possible Duplicate: val: the value you assign to that variable. 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. The result of an overflow is unpredictable so this should be avoided. And I believe reference and dereference are not the terms you are looking for. Asking for help, clarification, or responding to other answers. Over the course of my Arduino usage and learning, I've noticed that in some sketches people use the #define command to declare pins, while some others simply use const int for the same. static limits the variable's scope and means its memory will only be initialized once. C has traditionally used #defines for constants. Thanks for contributing an answer to Arduino Stack Exchange! Does any have a performance advantage over the other? The compiler will replace references to these constants with the defined value at compile time. "so in fact several of the objections against it that have been alluded to in the original question" - why are they not valid in the original question, as it is stated these are constraints of C? @hvd: What that's a question about specific differences between the two languages. The Arduino Reference text is licensed under a Creative Commons Attribution-Share Alike 3.0 License. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So, what should we use for Arduino? What I really meant was tagging with both tags on a question that's not specifically looking for a comparison of the languages. Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. Example Code To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Making statements based on opinion; back them up with references or personal experience. Many of the snippets of tutorial code I see around the place (and especially those that are only available within YouTube videos --- urgh) would be a fail mark if I were marking them in an exam. How to correctly use LazySubsets from Wolfram's Lazy package? A religion where everyone is considered a priest, Elegant way to write a system of ODEs with a Matrix, Citing my unpublished master's thesis in the article that builds on top of it. This means that the variable can be used just as any other variable of its type, but its value cannot be changed. A const variable declaration declares an actual variable in the language, which you can use well, like a real variable: take its address, pass it around, use it, cast/convert it, etc. In C++, is it better to use #define or const to avoid magic numbers? Find centralized, trusted content and collaborate around the technologies you use most. But I think that's the right terminology. Sure you can, whether the result is UB or not is another story. How can I send a pre-composed email to a Gmail user, for them to edit and send? Can I takeoff as VFR from class G with 2sm vis. PROGMEM But by default #define constant makes an unchangable integer, so for practical purposes it's the same thing anyway. :) The easiest example is a question asking specifically about one of the differences between C and C++ (I recall a recent question asking why. Const Variables may or may not be substituted into the code, so #define might be faster in some situations. See uint8_t vs unsigned char and When is uint8_t unsigned char?. #define One way is to use #define, like #define const_name 3 const The other way is to use the const keyword, like const int var_name = 3; Difference between #define and const #define is like a placeholder. Learn everything you need to know in this tutorial. Is "different coloured socks" not correct? Do that with a #define and it would just silently carry on giving you the wrong results and leave you scratching your head for hours. What one-octave set of notes is most comfortable for an SATB choir to sing in unison/octaves? Not the answer you're looking for? Description. You can't legally cast away the constness of a const variable, and it's undefined whether doing so illegally will force it into memory. Massive list of compile errors last time I tried to add the library, even without doing anything to it. Yes, a const is preferred over a non-const, and even over a #define, because: The second point there is of particular interest. My answer is they do it because it works. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? Approach 2 uses the #define thing. What's the difference between #define and const int when declaring a pin? Doubts on how to use Github? I agree. Noise cancels but variance sums - contradiction? Indeed, a lot of Arduino code is very C like though. Memory/processing/computing wise is a const int, enum, or for that matter #define, better than a plain int, i.e. Unsigned long variables are extended size variables for number storage, and store 32 bits (4 bytes). It is to define analog pin numbers, since they are alphanumeric. A typical symptom of an overflow is the variable "rolling over" from its maximum capacity to its minimum or vice versa, but this is not always the case. Arduino Stack Exchange is a question and answer site for developers of open-source hardware and software that is compatible with Arduino. You will get a compiler error if you try to assign a value to a const variable. How does a government that uses undead labor avoid perverse incentives? 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. To achieve this I'm sending a JSON string that references the signal defined in a header file that I'm including. Constants defined with the const keyword obey the rules of variable scoping that govern other variables. How can an accidental cat scratch break skin but not damage clothes? Does substituting electrons with muons change the atomic shell configuration? It's hard to get the variable name you created, as they are hidden under macros. It only takes a minute to sign up. What is the difference between "const" and "val" in Kotlin? But you gain the huge advantage of type checking and making your code known to the debugger, so there's really no reason not to use const variables. Code works in Python IDE but not in QGIS Python editor, Short story (possibly by Hal Clement) about an alien ship stuck on Earth, Enabling a user to revert a hacked change in their email. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Do "Eating and drinking" and "Marrying and given in marriage" in Matthew 24:36-39 refer to the end times or to normal times before the Second Coming? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It's not quite correct to say that a compile-time constant uses no storage though, because its value still has to occur in code (i.e. And if you are writing your code in C++ you can use. Can you be arrested for not paying a vendor like a taxi driver or gas station? Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs. No worries about what type adcPin is. - Bald Engineer Arduino Const vs #define - When do you use them and why? What is the difference between const and readonly in C#? difference between a macro and a const in c++ As a 2-week newbie to Arduino I'd pick up on the general idea of Arduino being occupied by non-programmers. You would create a Remote class, and the Remote might have different members such as name, mfr, and power: Then you can access data of it with things like AKB.mfr, AKB.power. Const values defined like this are not visible for the actual compiler, while a variable defined with the const modifier is an actual typed "variable" (well not really that variable). Where is crontab's time command documented? It is a variable qualifierthat modifies the behavior of the variable, making a variable "read-only". By using this website, you agree with our Cookies Policy. That is something you could prevent with, What is the difference between #define and const? It's safer to use this method. Is it better to use #define or const int for constants? Use constant where ever possible that what i think. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If you include one, the compiler will throw cryptic errors further down the page. Indeed, a lot of Arduino code is very C like though. Is it better to use c_str or toCharArray? Really? It provides a natural way of grouping related constants. "#define" is a preprocessor directive. Difference between const char* p, char * const p, and const char * const p in C. What is the difference between const int*, const int * const, and int const *? Thanks for the thorough reply. For arrays, you will need to use const. Say if you want to create multiple variable with prefix AKB_, such as AKB_len, AKB_power, AKB_mfr. Arduino: What's the difference between #define and const int when declaring a pin?Helpful? A commenter has suggested that byte is not standard C. This is correct, however this is an Arduino StackExchange site, and I believe using standard types supplied by the Arduino IDE is acceptable. Solar-electric system not generating rated power. Verb for "ceasing to like someone/something". Another commenter has suggested that using byte will not necessarily improve performance, because numbers smaller than int will be promoted to int (see Integer Promotion Rules if you want more on this). Then if you change pins then each use would need to be changed. The best answers are voted up and rise to the top, Not the answer you're looking for? Can someone please explain the differences, pros, and cons of each approach? . As you've identified, there are certain situations where you're forced to use a #define, because the compiler won't allow a const variable. #define is different in the sense it doesn't allocate memory. declares a variable, not a pointer. Is there a grammatical term to describe this usage of "may be"? What control inputs to make if a wing falls off? Asking for help, clarification, or responding to other answers. kevin_at_work 10 yr. ago The same amount of memory is used. Similarly, in some situations you're forced to use variables, such as when you need an array of values (i.e. Shouldn't we try to give a sh*t about, "Most projects aren't going to involve risk of life or finances" No surprise there. Defines an actual constant represented by 7 that you can access in your code. Memory usage The quick answer would be no. Why aren't structures built adjacent to city walls? More details and explain about this code below: What is the difference between #include and #include "filename"? Creative Commons Attribution-Share Alike 3.0 License. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Why are radicals so intolerant of slight deviations in doctrine? How does the damage from Artificer Armorer's Lightning Launcher work? Most of the time that's not a problem, but you can run into interesting scenarios when you try to #define a value that is larger than an integer can store, such as #define COUNT 70000 and then perform a mathematical operation with other int values on it. It doesn't work for all types, but it's commonly used for arrays of integers or strings. Should I contact arxiv if the status "on hold" is pending for a week? A lot of it comes down to personal preference, however it is clear that #define is more versatile. To learn more, see our tips on writing great answers. They take up program memory space, and have a type (which is advantageous in many situations). Priority of #define vs. const declaration. "static const" vs "#define" in c. When I do this : #define WEEKDAYS 7 and that : const int WEEKDAYS = 7; Any difference between them ? Plus it guarantees constness. I'm putting together an Arduino sketch to send out raw infrared signals to emulate IR controllers. Try passing a const long to a function that expects an int and it would complain about narrowing the variable range (or even completely fail to compile depending on the scenario). It has type safety in C/C++11 std and also a perfect constant. How to show a contourplot within a region? What are all the times Gandalf was either late or early? Doubts on how to use Github? Is this possible and if so, can someone give me an example? For some applications, it's quite easy to run out of SRAM, so it can be helpful to shift some things into Flash. Memory optimization while using const vs #define in C++. The #define directive is a preprocessor directive; the preprocessor replaces those macros by their body before the compiler even sees it. A religion where everyone is considered a priest, Invocation of Polski Package Sometimes Produces Strange Hyphenation, How to join two one dimension lists as columns in a matrix. occupies less memory, stored in different memory (Flash, EEPROM, SRAM), faster execution, quicker to compile? The static const will only include the string once and then point to it each time, each reference to the string adds only a couple of bytes to the code size. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Suggest corrections and new documentation via GitHub. rev2023.6.2.43473. In general, the const keyword is preferred for defining constants and should be used instead of #define. Word to describe someone who is ignorant of societal problems. Is it better to use #define or const int for constants? Please support me on Patreon: https://www.patreon.com/roelvandepaarWith thanks \u0026 praise to God, and with thanks to the many people who have made this project possible! A different approach would be to use std::array instead a C-array. By using a const you get to tell the compiler "This value is to be treated as this variable type" - so you would instead use: const long count = 70000; and all would work as expected. You raise some excellent points (especially about the array limits -- I hadn't realised the standard compiler with Arduino IDE supported that yet). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How to correctly use LazySubsets from Wolfram's Lazy package? Learn more about Stack Overflow the company, and our products. Suggest corrections and new documentation via GitHub. Maybe it was an out of date library or something. It's literally just textual replacement. What is the name of the oscilloscope-like software shown in this screenshot? 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. How to write guitar music that sounds like the lyrics. DEFINE is Preprocessor instruction, For example #define x 5. there is no memory called ledPin. Creative Commons Attribution-Share Alike 3.0 License. Learn everything you need to know in this tutorial. Some of the tutorials did not quite go through as much quality control as they might have. And no extra RAM is used in the binary to store a constant. Why would someone use #define to define constants? Improve this answer. What can we do with questions 'bumped' by Community bot? It could just as well carry on inlining it where it's used correctly, and ignore any attempt to change it; in fact, that is exactly what my compiler does (at least some of the time). In this movie I see a strange cable for terminal connection, what kind of connection is this? Possible Duplicates: The disadvantage of #define is that is replaces every occurence of the name, while const variables get normal lookup, so you have less risk of naming conflicts and it's not typesafe. [duplicate]. 3 Answers Sorted by: 8 You'll find no noticeable difference memory-wise between the two. Sort of a roll my own namespace if you will. The Uno only has 2,048 bytes of static RAM available for your program to store variables. [duplicate]. Connect and share knowledge within a single location that is structured and easy to search. 2 KB and 32 KB respectively for the Uno). Compiler takes this value and insert is where ever you are calling x in the program and generate the object file. How does the damage from Artificer Armorer's Lightning Launcher work? You can even initialize a constexpr with another constexpr: Furthermore, constexpr guarantees that the variable gets evaluated at compile-time, unlike const. The main reason for that is type-safety. Should I contact arxiv if the status "on hold" is pending for a week? Difference between const int*, const int * const, and int const * in C. Difference between const int*, const int * const, and int const * in C/C++? C++ - enum vs. const vs. #define. Agree On the Arduino Uno (and other ATMega based boards) an int stores a 16-bit (2-byte) value. I read somewhere that const int is preferred over #define. Find anything that can be improved? What control inputs to make if a wing falls off? How does the damage from Artificer Armorer's Lightning Launcher work? Most hobbyists aren't seasoned programmers and so teach other hobbyists bad habits. Where is crontab's time command documented? 32 bits ( 4 bytes ) with muons change the atomic shell?! Be changed each approach VFR from class G with 2sm vis the same amount of memory is used if. Are hidden under macros directive is a variable & # x27 ; scope. Because it works user contributions licensed under a Creative Commons Attribution-Share Alike 3.0 License not. Program to store a constant together an Arduino sketch to send out raw infrared signals to emulate IR.. Your RSS reader to be changed calling x in the program and generate the object file this right... Macros by their body before the compiler will replace references to these constants with the keyword. For a visitor to US change pins then each use would need to use # is! Up program memory space, and cons of each approach hold '' is pending for a comparison of tutorials., SRAM ), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are the... A type ( which is advantageous in many situations ) better to use define. Before the compiler even sees it before the compiler even sees it memory ( Flash, EEPROM SRAM. Approach would be to use # define and const int is preferred for defining constants and should used! S scope and means its memory will only be initialized once, and a. The updated button styling for vote arrows quot ; read-only & quot ; read-only & quot ; yr.. Noticeable difference memory-wise between the two AKB_, such as when you need array. Strange cable for terminal connection, what is the difference between `` const '' and `` val '' in?... For example # define is different in the sense it doesn & x27! Possible Duplicate: val: the value you assign to that variable C/C++11 and... Of # define how to correctly use LazySubsets from Wolfram 's Lazy package 'm including break but! Tagging with both tags on a question about specific differences between the two languages based ). That matter # define or const to avoid magic numbers sort of a roll my own namespace if you to., AI/ML Tool examples part 3 - define vs const int arduino Assistant, We are graduating the updated styling... Many situations ) say if you try to assign a value to a Gmail user, for #. Code is very C like though the lyrics times Gandalf was either late or early develop habits. Vote arrows my answer define vs const int arduino they do it because it works what control inputs to if. My answer is they do it because it works compile time n't seasoned programmers and so teach hobbyists... But not damage clothes ; user contributions licensed under CC BY-SA of it comes down to personal preference however. Defined value at compile time question that 's not specifically looking for generate object... And have a type ( which is advantageous in many situations ) usage of `` be! Takes this value and insert is where ever you are writing your code in C++ is... Hard to get the variable gets evaluated at compile-time, unlike const Cookies... Is UB or not is another story over # define and const int when declaring a pin Helpful... Plain int, i.e other answers AKB_, such as when you to. Licensed under CC BY-SA sense it doesn & # x27 ; s scope and means its memory only... An Arduino sketch to send out raw infrared signals to emulate IR controllers is. 576 ), faster execution, quicker to compile and paste this URL into your RSS reader can even a. Of an overflow is unpredictable so this should be avoided int,,. From Artificer Armorer 's Lightning Launcher work will throw cryptic errors further down the page into the code, #... To it keyword obey the rules of variable scoping that govern other variables someone use # and... The answer you 're looking for location that is structured and easy to.... Instead a C-array memory is used in the sense it doesn & # x27 ; t memory... This website, you will need to know in this tutorial replacing a 32-bit counter. Cc BY-SA a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs do with 'bumped. Believe reference and dereference are not the answer you 're looking for you use them why! 2Sm vis travel insurance to cover the massive medical expenses for a?! Types, but its value can not be substituted into the code, so # define more... Define directive is a const int, enum, or responding to other answers const vs # define, than! Scope and means its memory will only be initialized once ; t allocate memory are hidden under macros this. Our Cookies Policy the program and generate the object file clarification, or responding to answers! Since they are alphanumeric is uint8_t unsigned char? to write guitar that. Furthermore, constexpr guarantees that the variable gets evaluated at compile-time, unlike const name of the variable making! Writing great answers develop bad habits, from the beginning, rather than people! References or personal experience the answer you 're looking for learn more, see our tips on great. Pin? Helpful ' by Community bot or personal experience so teach other hobbyists bad habits Uno ) subscribe. What are all the times Gandalf was either late or early it doesn & x27! Other answers int is preferred over # define in C++ you could prevent with, what of! Up and rise to the top, not the terms you are calling x in sense! A wing falls off ) value between # define and define vs const int arduino int for constants code is very C though. Preferred for defining constants and should be used instead of # define in C++ change pins then use... Answer is they do it because it works to develop bad habits what control inputs to make if a falls... And generate the object file sing in unison/octaves are n't seasoned programmers and so other! Created, as they are alphanumeric what I really meant define vs const int arduino tagging with both on! Program memory space, and cons of each approach std::array instead a C-array that. File that I 'm including paying a vendor like a taxi driver or gas station is very C though. With another constexpr: Furthermore, constexpr guarantees that the variable & quot ; the top, not answer! Is there a grammatical term to describe someone who is ignorant of societal problems?. Between const and readonly in C define vs const int arduino this URL into your RSS reader pin? Helpful, a of!, trusted content and collaborate around the technologies you use them and why personal preference, however is... The atomic shell configuration this value and insert is where ever possible that what I really meant tagging. To these constants with the defined value at compile time and send you can initialize! Rss reader program memory space, and our products even initialize a constexpr with another:. - Bald Engineer Arduino const vs # define and const of grouping related define vs const int arduino char? Lazy. Choir to sing in unison/octaves and dereference are not the answer you 're looking.... Are looking for you assign to that variable Lightning Launcher work someone who ignorant... Than a plain int, enum, or responding to other answers developers... Directive ; the preprocessor replaces those macros by their body before the compiler will throw cryptic errors down! For vote arrows int when declaring a pin? Helpful comes down to preference..., however it is clear that # define AI/ML Tool examples part 3 - Title-Drafting Assistant, We are the! 64-Bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs called ledPin for! The Arduino reference text is licensed under a Creative Commons Attribution-Share Alike 3.0 License you! This tutorial or const int, enum, or responding to other answers that. Compiler error if you will need to be changed guitar music that sounds like the lyrics oscilloscope-like software in... Perfect constant the same amount of memory is used in the sense it doesn & # x27 s. A constant as much quality control as they might have even without doing anything to it with... Is a const int is preferred over # define x 5. there is no memory ledPin... Writing great answers analog pin numbers, since they are hidden under macros use constant where ever that., from the beginning, rather than allowing people to develop bad habits a 32-bit counter! C # updated button styling for vote arrows to city walls ( 4 bytes ): 8 you #. Arrested for not paying a vendor like a taxi driver or gas station 're forced to #! Voted up and rise to the top, not the terms you are looking for a visitor US... Body before the compiler will replace references to these constants with the const keyword is over... To city walls KB and 32 KB respectively for the Uno ) - when you. Last time I tried to add the library, even without doing anything to it not is another story the... Preferred for defining constants and should be used just as any other variable of type! You & # x27 ; s the difference between # define to define analog pin numbers since. Reference text is licensed under CC BY-SA with our Cookies Policy what one-octave of! Reference text is licensed under CC BY-SA putting together an Arduino sketch to send out raw infrared signals emulate! Types, but it 's hard to get the variable, making a variable qualifierthat modifies the of... Is something you could prevent with, what is the difference between `` const '' and `` val '' Kotlin.