I wasn't aware of this change in static member variables but it islogical and is a necessary extension with constexpr to also prohibit separate initialization. An array is a collection of items of the same data type stored at contiguous memory locations. static const char FLVSIGNATURE[3]; 1. initialize it in declaration (header file), error C2131: expression did not evaluate to a constant, error C2737: 'public: static char const * const FlvHeader::FLVSIGNATURE': 'constexpr' object must be initialized, 3. Another challenge comes about if you pass string to another function so the other function can write into the array. a Latin word meaning "about" or "around" . If you believe this to be in error, please contact us at team@stackexchange.com. Thanks for contributing an answer to Stack Overflow! How to professionally decline nightlife drinking with colleagues on international trip to Japan? Possible ranges of variables that are defined by inequalities. I'm really looking forward to C++14's expanded constexpr. If a function type is declared with the const type qualifier (through the use of typedef), the behavior is undefined. I don't know why you insist on having an array, since just naming each string would give you names that are intimately tied to the contents, but there are valid reasons to have an array, e.g. What is the status for EIGHT man endgame tablebases? The definition of a template static data member is a template-declaration (14p1). Or does it have to be defined outside the class as before C++11? @Dainus: the MSVC compiler has an optimisation called 'string pooling' which will put a single copy of identical strings into a read-only segment if it can guarantee that uses of them are read-only. auto (*p)[42] = &a; is valid if a is an lvalue of type int[42] . What should be included in error messages? @MaciejPiechotka: Well, thank god Unix rejected the microsoft-sponsored annex k. @JohnBode - thanks, and those are good points. I prompt an AI into generating something; who created it: me, the AI, or the AI's author? can I declare a static array with constexpr function, Initialize a static constexpr member in templated class. How one can establish that the Earth is round? Question 0 Sign in to vote User-1039984109 posted Hi all probably a stupid question, but is it possible to define a constant char array? HTML XML "C" "c". If the build system isn't braindead, integration is less text than your comment :) As much as. Whats the relationship between a heap and the heap? More info here: I think Dainius is suggesting that in many cases the error is that the variable itself should be marked. static const char* Title[] = { "first", "second", "third" }; Check out this little blurb on initialization. is a constant expression. An array is a collection of items of the same data type stored at contiguous memory locations. This would be a possible implementation: class fred { static char *a = "1234"; static char *b = "ab"; static char c [4]; public: fred () { strcpy (fred::c, fred::b); strncat (fred::c, fred::a . rev2023.6.29.43520. To expand on my comment, the X macro technique can be used for this. Static Arrays in C - Computer Notes "No, forget about using preprocessor macros: yuck!" Is it legal to bill a company that made contact for a business proposal, then withdrew based on their policies that existed when they made contact? Why is there inconsistency about integral numbers of protons in NMR in the Clayden: Organic Chemistry 2nd ed.? The C standard insists that if any part of an array is initialized, it all is. GDPR: Can a city request deletion of all personal data that uses a certain domain for logins? I prompt an AI into generating something; who created it: me, the AI, or the AI's author? How about parsing strings at compile-time? }; Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I would think the compiler would be smarter than that, Incorrect. Thanks for contributing an answer to Stack Overflow! So in this case, it's better to do it yourself. In this case the OP isn't actually storing copies of string literals, but pointers to string literals. Was the phrase "The world is yours" used as an actual Pan American advertisement? How AlphaDev improved sorting algorithms? @AquilaRapax There are actually quite a few reasons for writing the definition the way you did. A static data member of literal type can be declared in the class definition with the constexpr specifier; if so, its declaration shall specify a brace-or-equal-initializer in which every initializer-clause that is an assignment-expression is a constant expression. What is the earliest sci-fi work to reference the Titanic? But of course you haven't mentioned the biggest obstacle: how are you going to refer to those strings in that array? "static const" vs "#define" vs "enum" - GeeksforGeeks This article is being improved by another user right now. Presumably this is in relation to the way constant expressions are handled in terms of ODR (that is a constexpr member isn't required to have a definition so long as it is only used in compile-time constant expressions - see the answer ecatmur gave). How does one transpile valid code that corresponds to undefined behavior in the target language? You'll have to do externs. Merging them together is the pre-mature optimization. How do I fill in these missing keys with empty strings to get a complete Dataset? In that language, a const-qualified variable does count as a constant expression. Copying "september" over that string is an obvious memory overrun. The best answers are voted up and rise to the top, Not the answer you're looking for? class MyParameters { public: }; I get the error: members static const. For more information on the basic source character set, universal character names, and using characters from extended codepages in your source code, see Character sets. Thanks for all replies, it is really helpful. Connect and share knowledge within a single location that is structured and easy to search. 195 131. Date: Wed, 28 Jun 2023 08:36:04 +0900: From: Takashi Sakamoto <> Subject: Re: [PATCH][next] ALSA: oxfw: make read-only const array models static Also, if you mark an array with read-only, you are marking the pointer to the array, not the array itself. static const char* const values[] = {"string one", "string two"}; The idea is to put the two consts on either side of *: the left belongs to char (constant character), the right belongs to char* (constant pointer-to-character). Use {{ }} Double Curly Braces to Initialize 2D char Array in C. The curly braced list can also be utilized to initialize two-dimensional char arrays. Const : is a type qualifier. [C++], Use const int by reference to create static array, initialize const char[] as non-static class member. 585), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Undefined reference to static constexpr char[], Initializing Constant Static Array In Header File, Difference between function pointers to class member functions vs arbitrary function pointer, constexpr and static member declaration with templete class, Initialization of const array of const in a template C++ class, C++ static const array initialization in template class, Initialization of static constexpr member array in gcc 4.8. An array is a sequence of objects of the same type that occupy a contiguous area of memory. Define &c. &c synonyms, &c pronunciation, &c translation, English dictionary definition of &c. Abbr. It is confusing (at least IMHO), but the constexpr specification requires the initializer to be at the point of declaration, not the point of definition. You already have a working solution but you say "it would be easier on the system to have 2 separate arrays". Why do you want to do it in separate files? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Do native English speakers regard bawl as an easy word? It qualifies the pointer type to which the array type is transformed. Why is there a drink called = "hand-made lemon duck-feces fragrance"? A type qualifier is used to express additional info about a value through type system. Code Review Stack Exchange is a question and answer site for peer programmer code reviews. When contacting us, please include the following information in the email: User-Agent: Mozilla/5.0 _iPhone; CPU iPhone OS 15_3_1 like Mac OS X_ AppleWebKit/605.1.15 _KHTML, like Gecko_ Version/15.3 Mobile/15E148 Safari/604.1, URL: stackoverflow.com/questions/11093283/how-to-initialize-static-member-char-array-with-code. Frozen core Stability Calculations in G09? Spaced paragraphs vs indented paragraphs in academic textbooks. I'll leave that to those more qualified. Construction of two uncountable sequences which are "interleaved". The example posted by the OP is indeed yuck. And as you can see, this C++ feature was extended in C++11 for other types as long as they are constexpr. rev2023.6.29.43520. Do I understand correctly, the first const is for the string and the second for the array? What should be included in error messages? C - Wikipedia I can hide, C++11 Initializing class static const array, How Bloombergs engineers built a culture of knowledge sharing, Making computer science more humane at Carnegie Mellon (ep. how do you declare and use a static constant array inside a class - C / C++ Why is inductive coupling negligible at low frequencies? You can write either char string [] = "october"; Objects declared with const-qualified types may be placed in read-only memory by the compiler, and if the address of a const object is never taken in a program, it may not be stored at all. struct FlvHeader The possibly constrained (since C++20) auto specifier can be used as array element type in the declaration of a pointer or reference to array, which deduces the element type from the initializer or the function argument (since C++14), e.g. If you are OK with not using C for the generator, then either C++ or Python or Perl or even bash would yield a more robust generator at less than 1/3 the size. 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. Frozen core Stability Calculations in G09? Do native English speakers regard bawl as an easy word? char x = FlvHeader::FLVSIGNATURE[0]; The only way I can make it compile if I have exactly one string that is wrapped in a struct (Parameter). integral or enumeration) static constexpr data member is that its use in lvalue-to-rvalue conversion is not odr-use; you would only need to define it if taking its address or forming a const reference to it. [] The member shall still be defined in a namespace scope if it is odr-used (3.2) in the program and the namespace scope definition shall not contain an initializer. Overline leads to inconsistent positions of superscript, Novel about a man who moves between timelines. In the first case, the size of the array is taken from the size of the initializer. Why copy constructor argument should be const in C++? c++ - How to create a static const array of const char* - Stack Overflow How Bloombergs engineers built a culture of knowledge sharing, Making computer science more humane at Carnegie Mellon (ep. It'd look as follows: If you use cmake, then you probably shouldn't be writing such a generator in C since it'll end up being 10x (or worse!) Frozen core Stability Calculations in G09? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Not the answer you're looking for? When they are used as array sizes, the resulting arrays are VLAs. So the OP's example should work with only section 1 and without section 2 for compliant c++11. Practice What is an array? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. As commend said I mixed a bit char[] with char*, that is not good as they differs a bit. of static d ata member 'const Fruit::Value Fruit::VALUES [4]' of 585), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned, error: default initialization of an object of const type 'const char', Setting static const char[] to a predefined static const char[] fails, How to initialize static const char array for ASCII codes [C++], Initialization of static array from constant string, How to create a static const array of const char*, static char array in C initialized with strings. Initialize Char Array in C | Delft Stack Can you take a spellcasting class without having at least a 10 in the casting attribute? A common problem is the number of elements to Strs[], Lengths[] will differ due to a maintenance error. Turn off the optimisation to see 'normal' behaviour. its like its calculating the sizeof string before it is changed by strcpy but the length after. initializing a static const array inside a class - c++, static const array initialized in the .cpp file, C++ static constant array initialization inside class, Novel about a man who moves between timelines. How Bloombergs engineers built a culture of knowledge sharing, Making computer science more humane at Carnegie Mellon (ep. How to cycle through set amount of numbers and loop using geometry nodes? Agreed. to throw a compile time divide by zero error if you're about to overflow the array. Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog This makes it easier to calculate the position of each element by simply adding an offset to a base value, i.e., the memory location of the first element of the array (generally denoted by the name of the array). Connect and share knowledge within a single location that is structured and easy to search. Any attempt to modify an object whose type is const-qualified results in undefined behavior. In any case, I'd expect the compiler to whine if the type was too narrow. Simply hardcoding them is 'magic numbers'. The definition of a template static data member is a template-declaration (14p1). Can renters take advantage of adverse possession under certain situations? @John Bode's comment(s) are correct, and there are ways to mitigate these risks. Learn more about Stack Overflow the company, and our products. or (C-cedilla) is a Latin script letter, used in the Albanian, Azerbaijani, Manx, Tatar, Turkish, Turkmen, Kurdish, Kazakh, and Romance alphabets. Does a constant Radon-Nikodym derivative imply the measures are multiples of each other? Why do you want to do it in separate files? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. rev2023.6.29.43520. So I came up with my current solution, though kind of a pain in the backside, I have this. No special purpose here, I would just like to see is it possible to do it. What do you do with graduate students who don't want to work, sit around talk all day, and are negative such that others don't want to be there? Never is really long time, but you should avoid initialization char[] to string, because, "string" is const char*, and you are assigning it to char*. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Because of the restrictions on constexpr I had actually forgotten about the requisite for static members to be defined outside of the class, until I tried accessing a static constexpr array. The disadvantage is that it looks pretty bizarre first time you see it, and others maintaining your code might be boggled. Making statements based on opinion; back them up with references or personal experience. Is it possible to "get" quaternions without specifically postulating them? Find centralized, trusted content and collaborate around the technologies you use most. rev2023.6.29.43520. None of this stuff should be manually tweaked by humans - it's a total waste of time, and obscure macros doesn't help with readability either. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. }. I just want to use the new features of C++ cause I love C++. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This related question provides the correct way of defining the array member, but I'm interested as to the implications on this definition in a class template. 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. Making statements based on opinion; back them up with references or personal experience. And as you can see, this C++ feature was extended in C++11 for other types as long as they are constexpr. Traditional C-style arrays are the source of many bugs, but are still common, especially in older code bases. 01000011 01100011. If it's C++ you could wrap this array about a class and create a static instance of it. &c - definition of &c by The Free Dictionary . One confusing thing here: The declaration in the class is not a definition but has an initializer. Is it bad practice to store certain values as strings? https://www.odysee.com/@LarrySanger:7/letter-c-sanger-academy:d, , https://ar.wikipedia.org/w/index.php?title=C&oldid=62760375. where foo is another array of char. Do I owe my company "fair warning" about issues that won't be solved, before giving notice? Update crontab rules without overwriting or duplicating. Well if it's in a class it would make sense wouldn't it? It's a much better solution that code generation, since code generation increases complexity and the chances for bugs. What is the term for a thing instantiated by saying it? How can I handle a daughter who says she doesn't want to stay with me more than one day? I was reading a thread titled "strlen vs sizeof" on CodeGuru, and one of the replies states that "it's anyways [sic] bad practice to initialie [sic] a char array with a string literal.". Maybe I can define a constexpr string (with null terminator) and parse the string at compile-time. Each individual type in the C type system has several qualified versions of that type, corresponding to one, two, or all three of the const, volatile, and, for pointers to object types, restrict qualifiers. The best answers are voted up and rise to the top, 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. I need an array that contains a constexpr of some strings. What do gun control advocates mean when they say "Owning a gun makes you more likely to be a victim of a violent crime."? First is initialization and it is allowed in header for integer types since C++03. Very useful but I can see why it's difficult. Connect and share knowledge within a single location that is structured and easy to search. I think the "bad practise" idea comes from the fact that this form : makes implicitly a strcpy from the source machine code to the stack. { Can the supreme court decision to abolish affirmative action be reversed at any time? Array declaration - cppreference.com Australia to west & east coast US: which order is better? I don't want to usestatic const char FLVSIGNATURE[3], "Since the static member is potentially initialized in a separate module constexpr can't be applied.". { "file", "name", "line", "column", nullptr }; static const octave_fields bt_fields (bt_fieldnames); Octave has moved beyond C++0x and now allows C++11 standards. And the more generated bits you have, the more you end up with a wheen of wee files which is bad news for readability. How to declare and initialize a static const array as a class member? Why assigning string to const char* is possible? : r/cpp_questions - Reddit Is there a better way to do this? C. - Wikipedia In the second two cases, the size of the array is specified as part of the declaration (8 and MAX_MONTH_LENGTH, whatever that happens to be). What is the earliest sci-fi work to reference the Titanic? Would limited super-speed be useful in fencing? Does the paladin's Lay on Hands feature cure parasites? const-qualified compound literals do not necessarily designate distinct objects; they may share storage with other compound literals and with string literals that happen to have the same or overlapping representation. Does the paladin's Lay on Hands feature cure parasites? More precisely, most references to the array name. I guess this is one of the remaining bugs that has C++11 implementation FYI the "Edit and Continue" requires this option to be on. So always do one of the following: It's anyways bad practice to initialie a char array with a string literal. If it is just a problem of VC++ 2015 RC, maybe I could suggest VC++ team to fix it. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. This forum has migrated to Microsoft Q&A. And other unspecified things of the same class; and so forth. end note]The member shall still be dened in a namespace scope if it is odr-used (3.2) in the program and the namespace scope denition shall not contain an initializer.". passed to the class constructor): Another possible solution is: }; hard-coding Nine. For example, consider the below snippet: int arr[5] = {1, 2, 3, 4, 5}; This initializes an array of size 5, with the elements {1, 2, 3, 4, 5} in order. An implementation is within it's rights to put it in read-only storage and/or to share the same char array with other occurrences of the same string literal. @liuyanghejerry These are two separate things here. Why is there inconsistency about integral numbers of protons in NMR in the Clayden: Organic Chemistry 2nd ed.? The edit has some useful additions!