So, I have this: I would prefer using std::string for this, but if you like char* and the str functions, at least initialize p before using strcat: And you don't have to deallocate p somewhere. I think it may be improved to have only the final, How to concatenate a const char* in compile time, stackoverflow.com/questions/4077369/concatenate-boostmplstring, forum.vingrad.ru/forum/topic-314085/anchor-entry2241007/0.html#, Why on earth are people paying for digital real estate? (Ep. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Synopsis #include < string.h > char *strcat (char *dest, const char *src); char *strncat (char *dest, const char *src, size_t n); Description The strcat () function appends the src string to the dest string, overwriting the terminating null byte ('\0') at the end of dest, and then adds a terminating null byte. Is speaking the country's language fluently regarded favorably when applying for a Schengen visa? How can I do this ? fileDescriptor = Can anyone please explain me the difference between char *p and char p ? What is the Modified Apollo option for a potential LEO transport? const char* desc) { My aim with this string concatenation stuff was mostly to avoid going into template meta-programming techniques too much (except that it is needed, afaik, for number-to-string conversion). Now this is the kind of question for which I'm missing the "Must show minimal understanding" close reason. 103 S Bucy Ave Bartlesville, OK 74003-2212, Customer Reviews are not used in the calculation of BBB Rating, BBB Tip: Hire a trusted roofing contractor to repair, replace roof, Need to file a complaint? In almost all situations inet 127.0.0.1 what is the difference b/w char in C and C++.and give me the examples. mpl::string size limit is 32 elements. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. And I need to incorporate following in my code. BBB encourages you to check with the appropriate agency to be certain any requirements are currently being met. This is a common example: This looks quite simple, especially the second loop where the strings (Ep. std::apply applies the the given function (first argument) on all the elements of the given tuple (second argument). Optimization Experiment: Recursion vs. Iteration (with a twist! Zachry sets the standard for excellence in executing major industrial EPC capital projects. But thanks again to C++11, the standard library provides a std::array (docs) class template to represent static arrays and it can be constructed and copied at compile-time, via constexpr constructors. I want to do System.out.println(char1+char2+char3. BBB Business Profiles are subject to change at any time. Thnx in advance. Why did the Apple III have more heating problems than the Altair? to use strcat/wcscat. By the way, the namespace detail { namespace { is simply there to make sure that the class templates inside it are not going to conflict by name with other parts of the library (this is what the "detail" is for), and that they will not be unecessarily exported from the compiled library (which is what the namespace { is for, it's an anonymous namespace that hides everything from the linker). I solved the problem: I simply did: char* p = new char[strlen(metadata.getRoot())+strlen(metadata.getPath())+1]; strcat(p,metadata.getRoot()); strcat(p,metadata.getPath()); args2->fileOrFolderPath = p; function(args2->fileOrFolderPath); and in the fucntion I delete the variable. Concatenate two strings Find centralized, trusted content and collaborate around the technologies you use most. So, we need to avoid the use of such a sequence of arrays, which implies merging all the arrays into one array. Arduino Stack Exchange is a question and answer site for developers of open-source hardware and software that is compatible with Arduino. Travelling from Frankfurt airport to Mainz with lot of luggage. Arun. Remove outermost curly brackets for table of variable dimension, Travelling from Frankfurt airport to Mainz with lot of luggage, Commercial operation certificate requirement outside air transportation. const char* var1 = "some string"; const char* var2 = "some other string"; // how do i generate this in some rational way? We work with customers to plan, build and renew their most critical facilities, so they can achieve their immediate and long-term goals, all at the highest safety standards. Please begin by refreshing the page to see if your location populates the Near field. International Association of Better Business Bureaus. How can i concatenate a const char with char array? Zachry Brands, Inc. 2008 2023. Nevertheless, it is still at least twice as much as the plain version with run-time strings (std::string) concatenation. One possible solution is to involve construct a compile-time tree of strings, instead of a list, which is also non-trivial. Limit is 32 symbols. @Guy.D , create an array of suitable size before calling the function and just pass a pointer to it. end of the destination string so that the actual copying can start. BTW, is there any reason to have fileOrFolderPath const? We utilize asprintf function to store the passed integer as a character string. Is a dropper post a good solution for sharing a bike between two riders? This is essentially the approach used by Sprout (that vijayan121 refers to above). How to format a JSON string as a table using jq? If you've been following my posts here on Daniweb, you might find this odd, because I generally discourage recursion vehemently. What is the Modified Apollo option for a potential LEO transport? What is the number of ways to spell French word chrysanthme ? sbanlab1:ksh# ifconfig -a | egrep "flags|inet" | awk -F' ' '{print $1,$2}' Description of the illustration ''concat.gif''. Here is a test program: The resulting code, after compilation, is simply a linked-list being formed in the read-only data section of the executable, as seen in these assembly listings: There is definitely some overhead to this scheme (as with any use of a linked-list), but the important part here is that there is no initialization code needed, the strings can simply be read off from read-only memory. strncat() Concatenate strings base1 and base2 are simply the tuple base of foo1 and foo2. Resize the allocated memory if necessary. How do you concatenate characters in java? concat() - Arduino Reference So, back to the problem at hand, how does one go about putting together two strings if one cannot copy or change anything? We are focusing on helping our current and future clients navigate through the energy transition by lowering the carbon footprint of those facilities. I'm not sure you guys clearly understand what i'm trying to do, everything is seperate from eachother, everything is modular, but i need to know where a call . The role of the gen_index_seq class template is to recursively construct a sequence of indices from 0 to N-1 in the form of a variadic argument pack (the S in index_seq). 2) Wide string literal. Pure functional programming is a big part of C++, because there are two additional programming languages hidden in the C++ language, and they are pure functional languages. The rules of the game with constexpr is pretty much the same as for TMP, because they are both compile-time meta-programming languages, but const-expressions are made to create compile-time values, as opposed to types (in TMP). Connect and share knowledge within a single location that is structured and easy to search. To learn more, see our tips on writing great answers. Twines support a special 'null' value, which always concatenates to form itself, and renders as an empty string. | AS-Safe Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Is there a distinction between the diminutive suffixes -l and -chen? First, you should use std::string or std::vector<char>, second you can always convert to const char* when you eventually need it. In other words, the "detail" hides things, by convention, during compilation, and the un-named namespace hides things during linking. the intermediate results sums up to 5500! It is not a coincidence that the class is now called "list" and has a pointer called "head". It initialize from UTF-8 strings without problem. CONCAT - Oracle Help Center BBB is here to help. 103 S Bucy Ave. Bartlesville, OK 74003-2212. I'm using C so am limited to char pointers and arrays. Here is ready to go header file StaticString.h: Thanks for contributing an answer to Stack Overflow! The advantage of this approach is that there are only different instantiations of the std::array for different N (for each unique string length in your program), which should dramatically reduce the template instantiation depth required compared to the tuple-array version. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This business has 0 complaints. function <cstring> strcat char * strcat ( char * destination, const char * source ); Concatenate strings Appends a copy of the source string to the destination string. English equivalent for the Arabic saying: "A hungry man can't enjoy the beauty of the sunset", Different maturities but same tenor to obtain the yield, Relativistic time dilation and the biological process of aging. we dont use strcat anymore. local variables). Concatenate char* and char* into a char*? : r/arduino - Reddit int fileDescriptor; Commercial operation certificate requirement outside air transportation. BBB asks third parties who publish complaints, reviews and/or responses on this website to affirm that the information provided is accurate. Zachry Group is North America's pacesetter in turnkey engineering, construction, maintenance, turnaround and fabrication services to the energy, chemicals, power, manufacturing and industrial sectors. strcat is declared in the header file string.h while efgh strcat searches for the first occurrence of the null-character, so if you want to use strcat, you must first initialise result. Will just the increase in height of water column increase pressure or does mass play any role in it? Another solution, which I present below, is to build a compile-time array of string literals instead. with the search for the allocation we can write this function more BBB Business Profiles may not be reproduced for sales or promotional purposes. User does not have to select a country if they click this link. #include How can I remove a mystery pipe in basement wall and floor? I have made a number of trials in that vein, and I thought it was interesting to explain some of the issues that occurred. It only takes a minute to sign up. Returns true: success. Has a bill ever failed a house of Congress unanimously? I suspect what is happening is that it ignores the const on the argument, but it can't then modify the buffer because it's defined as const elsewhere in the code. In simple words, constants don't get "exported". C++ has a built-in method to concatenate strings. I'm trying to write a method which will return the extension of a file given the file's name, e.g. See Copying Strings and Arrays. What is the problem? 273 likes. As for the error you're seeing when using a parameter, I've wrote some tests to see why it doesn't break when using a const local variable. What do you think? The resulting binaries are, all in all, 2.3% smaller with this scheme. Did you malloc enough memory for it ? I make it string and it need to concatenate. Output: All you really need to know is that this is what we can do with the above code: which doesn't sound that impressive given that we could just write: However, where it really starts to pay off is when we realize we can do something like this: which you obviously could never do with normal code, or MACROs, or even do too easily with template meta-programming. Well, the whole point of the RTTI is to provide information on the type of objects, and a string representation of that name is a pretty central part of that (as well as a hash value). Find centralized, trusted content and collaborate around the technologies you use most. How to replace any char with newline char. We detect that you are visiting from Germany. Improve INSERT-per-second performance of SQLite, How to convert a std::string to const char* or char*. Connect and share knowledge within a single location that is structured and easy to search. This question appears to be off-topic because it asks things which are essential for the language and can be read up in a good tutorial. The last. To learn more, see our tips on writing great answers. So, even though the final result is just one final value and everything else is washed away by the optimizer, the path to get there can be very strenuous. So, everything has to be turned into a recursion (which is always possible, if you didn't know that already). Any form of iteration will require that you modify some kind of a variable (e.g., loop counter, termination condition, etc. rev2023.7.7.43526. As a matter of policy, BBB does not endorse any product, service or business. [duplicate]. How can i concatenate a const char with char array? See Copying Strings and Arrays . It's represented by the character surrounded by single quotation marks. And his answer too (8-th message): Why (tf) you want to do this? At Zachry, citizenship has always been the foundation of the way we do business. Shouldn't you use "calloc" or change first "strcat" to "strcpy"? Pure functional programming works on two fundamental principles: there are only values, and values can never change. Ordinary string literals are static arrays of chars (const char[N]) which are not directly copyable. Why did Indiana Jones contradict himself? #include "Hello " already have a space. What is args2->fileOrFolderPath ? Do I have the right to limit a background check? What is the difference between const int*, const int * const, and int const *? strncat - C++ Users LLVM: llvm::Twine Class Reference FILE* stream, Can you work in physics research with a data science degree? ", is a static array, which is what the constructor of literal_str takes in. are actually copied. In that library, concatenation is implemented by turning the string literal into a variadic template argument pack of chars and then unpacking it as a sequence of chars that brace-initialize an array of chars of the same size. const char* var3 = "some string/some other string"; Specifically, I'm looking to concatenate var1 + "/" + var2 and have the result be of type char*. Here are the essential mechanisms for doing this merger of the static arrays: which is similar to the previous approach, but instead of unrolling the two arrays of char-arrays into a larger array of char-arrays, we unroll the two char-arrays into one larger char-array. @Tobi: strcpy starts writing to the first character of result. and technology enthusiasts meeting, networking, learning, and sharing knowledge. I am passed these char* s from a third-party library with a C interface so I can't simply use std::string instead. Or get a good book or tutorial. As an added little bonus, you can also use this literal string list class to perform some compile-time integer to string conversions: The method is simple. since how can one otherwise ensure the allocated size of the buffer is Asking for help, clarification, or responding to other answers. Please select the region that you would like to explore today. Python zip magic for classes instead of tuples. What is wrong, though, is that you can't return a pointer to a locally declared array from a function. dont use stpcpy which might seem more natural since we are handling Please take a look, @Nelfeal I know, but this version of the class template is as close to the original version as possible. The best answers are voted up and rise to the top, Not the answer you're looking for? The problem is that people won't read the link. concat const char * with char Which prints out "Hello, World!" (17 answers) Closed 9 years ago. And as you probably know, this can, in principle, store a long list of strings all concatenated together. The problem is that the concatenation operator assumes that the second literal string list is not an actual list but only a single node. Static const/constexpr data members that are defined inside a class declaration have no linkage, i.e., they disappear after compilation. as expected. So, I found a major problem with the implementation that I posted originally. int main(){ What does that have to do with compile-time string concatenation? They follow the string-copying System.out.print(char1); System.out.print(char2); System.out.print(char3); Or at least, one could know them if one keeps track of the How do I concatenate const/literal strings in C? Making statements based on opinion; back them up with references or personal experience. I need to put "Hello World" in str3. This is a hybrid of constexpr syntax and template meta-programming. Haven't really looked into C++11 too seriously yet. So, the addition operator takes care of generating two sequences of indices (one for each string array) to address each element of the tuple of char arrays within each string array. @Tobi Weihaar yeah ,the dest buffer can not be const ,because you are changing it . I am passed these char* s from a third-party library with a C interface so I can't simply use std::string instead. 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6). 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6), C++ Concating strings result in "invalid operands of types const char* and const char", How to append const char* to a const char*. The other language is that of constexpr expressions, a relatively new feature added to the standard in 2011 (C++11). Well, even though this sounds like a difficult restriction, it does grant a side benefit: if nothing can change, things are persistent, i.e., they will always be there, unmodified. CONCAT returns char1 concatenated with char2. (WARNING: If you're not ready for it, reading what follows could blow your mind!). <cstring> strncat char * strncat ( char * destination, const char * source, size_t num ); Append characters from string Appends the first num characters of source to destination, plus a terminating null-character. Input: Countering the Forcecage spell with reactions? Why did Indiana Jones contradict himself? is almost always unnecessary to use strcat. bge0: Hello, strncat or wcsncat functions defined in What is wrong, though, is that you can't return a pointer to a locally declared array from a function. I create an array of mpl::string in compile time. When are complicated trig functions used? Be the first to review! When you return the array from the function you return an address that is (currently) within the stack. Accidentally put regular gas in Infiniti G37, My manager warned me about absences on short notice. // string_operators.cpp // compile with: /clr // In the following code, the caret ("^") indicates that the // declared variable is a handle to a C++/CLI managed object. When you try that out and you've issues, come here. Why do complex numbers lend themselves to rotation? sufficient?) Concatenating strings would only require a + between the strings, but concatenating chars using + will change the value of the char into ascii and hence giving a numerical output. Is there a distinction between the diminutive suffixes -l and -chen? strncat(3): concatenate two strings - Linux man page Doing fancy stuff like that with variadic templates has not been a joyful experience for me. Just imagine that ten strings of 100 bytes each have to be What you need to so is: 1) count the number of characters in the string foo. concatenate char array in C Ask Question Asked 13 years, 5 months ago Modified 1 year, 3 months ago Viewed 331k times 57 I have a a char array: char* name = "hello"; I want to add an extension to that name to make it hello.txt How can I do this? are you calling by value or by reference ? Thanks for contributing an answer to Stack Overflow! I think you should make the extra. from overwrites the null byte marking the end of to. Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? Mind you, this is still just a draft. How to concatenate two const char*? @Jarod42 it is not duplicate. If one were to use "normal" string concatenation code to create some global string objects (instead of the constexpr constants in the test code above), there would be a much larger amount of overhead to account for the initialization code that needs to run in order to construct those global objects. Although TMP can be used to compute values (i.e., as static members of types), it's very inefficient to do so because of the overhead in compilation times and code-bloat (e.g., symbols, useless code, etc. | See POSIX Safety Concepts. What's the difference between constexpr and const? Will just the increase in height of water column increase pressure or does mass play any role in it? Topline Construction | Better Business Bureau Profile For the second string we search the already stored 100 string - Return a char concatenation A simply char array will do. c++ - const char* concatenation An equivalent definition for wcscat would be: Programmers using the strcat or wcscat function (or the Compiling xpp (The X Printing Panel) on SL6 (RHEL6 essentially): (Ep. The end effect of this is that the final string array contains a copy of both original string arrays, one set after the other in a single tuple. Find centralized, trusted content and collaborate around the technologies you use most. They'll just copy your code and only make the minimum amount of changes necessary to get it to compile in their program. This can be returned from APIs to effectively nullify any concatenations performed on the result. Has a bill ever failed a house of Congress unanimously? results of the various function calls. At that point, I had to switch over to run-time code (e.g., using std::string or C-style functions) to form those compound strings. There are five kinds of character literals: Ordinary character literals of type char, for example 'a' UTF-8 character literals of type char ( char8_t in C++20), for example u8'a' Where should I put a plot that summarizes my entire thesis? But then it is very inefficient const char* format="%*s\e; Find centralized, trusted content and collaborate around the technologies you use most. Making statements based on opinion; back them up with references or personal experience. 295 likes. String and character literals (C++) | Microsoft Learn There are four ways of solving the problem - all of them have their pitfalls. Hopefully I won't get a system-wide crash this time! 5 11 Related Topics When practicing scales, is it fine to learn by reading off a scale book instead of concentrating on my keyboard? The reason you want to copy or assign data in general is because the source of that data is not persistent, i.e., it could disappear or change some time in the future. 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Concatenation of non constant character array with a string, Simple word translator, return error: invalid array assignment, Memory leakage caused by String Concatenation, How to decrease delay for String concatenation + Arduino Due, String type replace function can't replace with no char, Different maturities but same tenor to obtain the yield. Non-definability of graph 3-colorability in first-order logic. I don't know the reason about BOOST_MPL_STRING_MAX_LENGTH. To replace ',' with newline @Toby: There is absolutely no reason to declare p as const, because you are trying to change it, so remove the const, but you really have to initialise p (by setting it to 0 or by using strcpy before using strcat). It does have the advantage that is generates an actual char array (as opposed to linked-list of literals), which makes other operations like substring and iterators a lot easier (not to mention that it relieves some of the linking constraints on the objects being concatenated, which is very nice), but it is also a very heavy compile-time mechanism to put in play. Sprout is certainly not as bad as using Boost.MPL for this purpose, but it is still pretty heavy. Is it possible to concatenate two strings of type `const char *` at compile time? While compiling using a const char * for the pointer I'm using as the target I get this warning: As it states, const is discarded and it works as expected. const char* declaration, could someone explain how it works? Explanation 1) Ordinary string literal. A lot of time is wasted finding the How to make it? If I wanted to do that, I would probably use a similar approach. There are a couple more fancy little things in the code (like a compile-time FNV-1a hashing function), but that was the important part. can you be more specific for solution 3 ? Privacy Policy. How can I concatenate two object of this class template in order to have all the tuple member of both class as an object of the same class template. However, the compilation times nearly doubled. This principle is well explained by this simple class that "stores" a compile-time string: This is what is called a literal class because it fulfills a number of basic requirements, and it has a constructor marked with constexpr, meaning that if its inputs are compile-time constants, then the object created will be itself a compile-time constant (yes, you heard that right, the compiler will create the object at compile-time!). For the BBB EU Privacy Shield independent dispute resolution program, please click here. and create a String word like this.. Please click on the country abbreviation in the search box below to change to a different country location. Canady Construction and Handyman Service. Yes, I was aware of that implementation. But i need a complete string (not array): How do "string" from "array_mpl_strings"? fprintf(stream,format,shift,"",desc); How to replace any character in a file with a newline character using sed .. Btw, your code has a memory leak since you don't free. Read Reviews Be the First to Review! How to concatenate a char * and a const char*? How can I concatenate two object of this class template in order to have all the tuple member of both class as an object of the same class template. Not the answer you're looking for? (looks like trying to make things complicated just for the sake of it) Compile-time character strings are hardly really needed. <string> string operator+ function <string> std:: operator+ (string) C++98 C++11 Concatenate strings Returns a newly constructed string object with its value being the concatenation of the characters in lhs followed by those of rhs. Most string operations like getting the total size, getting an individual char (indexing), computing a FNV-1a hash, or converting to a run-time string (std::string) is rather straight-forward to implement (but again, everything must be done recursively, because compile-time calculations imply recursion as the only option). const char* desc; @Toby: When you say "this doesn't work", do you also mean the std::string solution? 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. The functions described in this section concatenate the contents of a string or wide string to another. Zachry Group Apperently lambdas also support closures! Extract data which is inside square brackets and seperated by comma. The following code example demonstrates concatenating and comparing strings. I have a class template which is based on a std::tuple and only consist of that tuple.