Step 3 - Use the memcpy() function to copy the const char* to the char*. How a top-ranked engineering school reimagined CS curriculum (Ep. How to calculate euler constant or euler powered in c++? Does the C++ standard allow for an uninitialized bool to crash a program? @isal sizeof (char*) is 4 or 8 bytes depending on if you're on a 32 or 64 bit platform. Same as above, does double the work though it is good to point out that you must choose how to handle s being too big to fit in c. All of the examples using char c[256]{} instead of char c[256] are potentially doing double the work. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Something without using const_cast on filename? int main(int argc, char *argv[]) ^^^^^ That is the second parameter does not have qualifier const.. Secondly argv[1] has type char *.There is no any sense to compare it with a character literal similar to '1234'.As for string literal "1234" when it may not be used in the case label. free() dates back to a time. String literals are constant and shouldn't be modified, older compilers might allow assigning them to char * but more modern compilers will only allow assignment to const char* (or const char[]), e.g. You might use strncpy if t1->name was a fixed-size array instead (though many people prefer to use strlcpy). Each method has its own advantages and disadvantages, so it is important to choose the right method for your specific use case. How about saving the world? How a top-ranked engineering school reimagined CS curriculum (Ep. How to copy contents of the const char* type variable? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? However, it is generally not recommended to modify data that is intended to be constant, as it can lead to unexpected behavior in your program. Otherwise go for a heap-stored location like: You can use the non-standard (but available on many implementations) strdup function from : or you can reserve space with malloc and then strcpy: The contents of a is what you have labelled as * in your diagram. You can either call malloc () and then use strcpy (), or call strdup () which will do both things for you: int A (const char* name) { name = "Here you GO!"; char* new_name = strdup (name); printf ("%s\n", new_name); return 0; } Does the 500-table limit still apply to the latest version of Cassandra? The common but non-standard strdup function will allocate new space and copy a string. problems with convert const char* to char* in c - Stack Overflow Is there a weapon that has the heavy property and the finesse property (or could this be obtained)? String to array char* - Programming Questions - Arduino Forum Is anyone offer some suggestion how to solve that. However "_strdup" is ISO C++ conformant. The difference is the {} at the end of char c[256]{}. Find centralized, trusted content and collaborate around the technologies you use most. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Thanks for contributing an answer to Stack Overflow! Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. @JaviMarzn It would in C++, but not in C. Some even consider casting the return of. - WindyFields Sep 14, 2017 at 3:21 1 Side note: to use in a printf, you can use something like "%.256s", sizeof(c) only works if chars are 1byte. It does matter. You can't (really) "convert" a pointer to char to a single char. Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Don't write your own string class. One that takes you from pointers through chars and c-strings to switch/case statements. I.e. rev2023.4.21.43403. thank you for this explanation, it really helps. What is the difference between char * const and const char *? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So the C++ way: There's a function in the Standard C library (if you want to go the C route) called _strdup. You can also likely use 255 in place of 256 (if you init c to zeros and dont touch ther 255th item) or set the 255th element to '\0' explicitly if required. How to copy contents of the const char* type variable? So change code to: You need fix how your array is being initialized as you are initializing only one character (and we assume you want full string to be copied). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. What is the difference between const int*, const int * const, and int const *? How would you count occurrences of a string (actually a char) within a string? You declared MyEepromArray as an array of pointers to the const strings, it can't be changed by simple way. But moving strings from one place to another is efficient.. casts away the const. When using the const_cast operator, be aware that modifying data that is intended to be constant can lead to unexpected behavior in your program. And for the case str0 = str1; I don't understand why it won't work, because str0 points to nothing, while str1 points to a const string literal, so if I now make str0 point to what str1 is pointing to, it should be fine, but it is not. this should compile: Even if your compiler allows assignment to char * you should always use const char* to prevent hard to trace crashes when you try to modify a string literal. It's part of homework and I'm not allowed to post it online sorry, You don't have to post your actual code, only a simple, Please note that in C way you should call. (IMHO std::remove (const char*) should be std::remove_file (std::string const&) or at least std::remove_file (const char . If total energies differ across different software, how do I decide which software to use? The first method uses C++ type casting feature called const_cast, it allows you to remove the const-ness of a variable, so you can modify it. I compile this with visual studio. Secondly argv[1] has type char *. I believe sizeof is in fact tied to the sizeof a char (regardless of whether a char is 8 bits). Even better, use implicit conversion: filename = source; It's actually not conversion, as string has op= overloaded for char const*, but it's still roughly 13 times better. Here's an example of what I'm working with: I have a const char *, I need to set the "name" value of test to the const char. Short story about swapping bodies as a job; the person who hires the main character misuses his body. free (value); // now do some other stuff with Thanks for contributing an answer to Stack Overflow! Parabolic, suborbital and ballistic trajectories all follow elliptic paths. OK, that's workable. Doing double the work is not necessarily bad but given the optimal version is simple there's no reason not to use it. The trouble with a pure * though is you need to know how long it is. C convert const char * to char - Stack Overflow To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Whats wrong here? Looking for job perks? The choice and simply test. Why did DOS-based Windows require HIMEM.SYS to boot? Effect of a "bad grade" in grad school applications, A boy can regenerate, so demons eat him for years. You cannot copy from a const char *s = std::string("x").c_str(); though, because the pointer is dangling, and attempting to access the pointed data would have undefined behaviour. 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. One other issue is using magic numbers. this sets MyEepromArray [2] to a const char string, Powered by Discourse, best viewed with JavaScript enabled, To write the default configuration on eeprom, send the command: DEF from the serial line, To write the word test, send the command from serial: RW:test, To read all the contents of the eeprom, send the command from the serial line: RR. Was Aristarchus the first to propose heliocentrism? elsewhere.). Also you can not use strings as switch/case labels. Making statements based on opinion; back them up with references or personal experience. How to Make a Black glass pass light through it? What should I follow, if two altimeters show different altitudes? The owner always needs a non-const pointer because otherwise the memory couldn't be freed. You need to start with a basic C tutorial. Not the answer you're looking for? Find centralized, trusted content and collaborate around the technologies you use most. char const* implies that the class does not own the memory associated with it. For more definitive answer please show a full code. Asking for help, clarification, or responding to other answers. Is there a way around? C++ : How can I convert const char* to string and then back to char What did you intend to declare with this line - a string of 12 characters or an array of 12 strings? In most cases, it is better to create a new char* variable and copy the contents of the const char* to the new variable, rather than modifying the original data. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Can my creature spell be countered if I cast a split second spell after it? If total energies differ across different software, how do I decide which software to use? How about saving the world? If doesn't have to cover anything complex. Whether all string literals are distinct (that is, are stored in nonoverlapping objects) is implementation dened. :-S. This answer confused me a little, so I'm clarifying for other readers. Much appreciate.. You are getting segmentation fault, because new_name points nowhere. Has the Melford Hall manuscript poem "Whoso terms love a fire" been attributed to any poetDonne, Roe, or other? When you have non-const pointer, you can allocate the memory for it and then use strcpy (or memcpy) to copy the string itself. one problem is when I use const_cast, it says it is undeclared. What is the difference between char * const and const char *? What is Wario dropping at the end of Super Mario Land 2 and why? In practice, because strncpy may leave a string without a \0 terminator, it's best to avoid it. Better stick with std::string, it will save you a LOTS of trouble. Connect and share knowledge within a single location that is structured and easy to search. In MyEepromArray[12] i enter the following data: and i should change them dynamically through serial. @keanehui1 no. please post your code. Find centralized, trusted content and collaborate around the technologies you use most. rev2023.4.21.43403. How to cast the size_t to double or int 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. You can implicitly convert char * into const char *. I think the confusion is because I earlier put it as. "Signpost" puzzle from Tatham's collection. What are the differences between a pointer variable and a reference variable? won't be null terminate if s is longer then 255 bytes, As it's an array you can do sizeof(c) to get its size and use it in via safe string functions that allow you to pass an n to them. const char* original = "TEST"; char* copy; copy = original; original points to the start of the string "TEST", which is a string literal and thus points to read-only memory. What is Wario dropping at the end of Super Mario Land 2 and why? And at the end you might consider using just an array of fixed size that is initialized to maximum path. But you can copy the string. if you want an char array, you should do. I searched quite a while to find the answer, but I could only find a solution for C++ that didn't seem to work for C. I'm trying to convert argument of const char * to char to use in my switch statement. The "string" is NOT the contents of a. Looking for job perks? C++ How to remove \\0 char from std::string - Stack Overflow The const qualifier instructs the compiler to not allow data modification on that particular variable (way over simplified role of const, for more in-depth explanation use your favorite search engine and you should be able to find a bunch of articles explaining const). if the target is too long (the third argument) , the trailing end will be completely padded with NULs. gcc 4.8.4 allows it with a deprecation warning, They issue a diagnostic, telling you your program isn't C++. The sizeof(char) is redundant, but I use it for consistency. What is the difference between const int*, const int * const, and int const *? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. That's potentially double the work. Thanks for contributing an answer to Stack Overflow! You are getting segmentation fault, because new_name points nowhere. You can lookup. What is scrcpy OTG mode and how does it work? Here, the destination string is the char* variable and the source string is the const char* variable. What is Wario dropping at the end of Super Mario Land 2 and why? How to convert a std::string to const char* or char*. What is the difference between char s[] and char *s?