one problem is when I use const_cast
, it says it is undeclared. For null-terminated strings, strlen can get you that size (and so it works with strncpy). You can however extract one single character from a string. Thanks for contributing an answer to Stack Overflow! strcpy copies the characters pointed by str1 into the memory pointed by str0. You're getting mixed up between char (character) and char * (string). If you really want the raw point out of an std::string you can use the c_str() method and it will return you a const char* - I strongly advise against it, unless you have to pass it to a function that only accepts const char*. @Caleth that may be true but older compilers might not have fully implemented the c++ standard (in fact most current compilers probably aren't fully compliant with c++), I think older versions of gcc certainly allowed this. Anther problem is when I try to use strcpy to combine them together, it pops up segmentation fault. Didn't verify this particular case which is the apt one, but initialization list is the way to assign values to non static const data members. You might use strncpy if t1->name was a fixed-size array instead (though many people prefer to use strlcpy). How about saving the world? Find centralized, trusted content and collaborate around the technologies you use most. Can my creature spell be countered if I cast a split second spell after it? You were on the right track using strcpy, because const_cast is C++ only. n_str is of type std::string and str0 is char*, there's no overloaded operator that allows this. I tried to use strcpy but it requires the destination string to be non-const. How about saving the world? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. I believe sizeof is in fact tied to the sizeof a char (regardless of whether a char is 8 bits). Extracting arguments from a list of function calls, QGIS automatic fill of the attribute table by expression. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? you are to fast! He also rips off an arm to use as a sword. It is useful when you want to pass the contents. You need to pre-allocate the memory which you pass to strcpy. Is there a weapon that has the heavy property and the finesse property (or could this be obtained)? In the first case, you can make filename point to any other const char string, in the second, you can only change that string "in-place" (so keeping the filename value the same, as it points to the same memory location). - Mike Seymour Dec 13, 2013 at 7:37 According to the documentation ( msdn.microsoft.com/en-us/library/kdzttdcb.aspx) beginthreadex wants a void*. 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. For the manual memory management code part, please see Tadeusz Kopec's answer, which seems to have it all right. 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). @Tronic: Even if it was "pointer to const" (such as, @Tronic: What? free() dates back to a time. As you only want to read the string, you want it to be const. From Prince Harry's tell-all memoir to King Charles III's ascension to the throne, there has been no shortage of royal family news in the last year. Why does Acts not mention the deaths of Peter and Paul? We already have too many of them, C compilers, not "older compilers". Which language's style guidelines should be used when writing code that is supposed to be called from another language? Making statements based on opinion; back them up with references or personal experience. Thank you. also wrong. How would you count occurrences of a string (actually a char) within a string? What is Wario dropping at the end of Super Mario Land 2 and why? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Gahhh no mention of freeing the memory in the destructor? So now what s points to is undefined, If you were not creating the string in that line it would be safe. 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. What was the actual cockpit layout and crew of the Mi-24A? Here, the destination string is the char* variable and the source string is the const char* variable. What should I follow, if two altimeters show different altitudes? i will study this carefully. I agree that the best thing (at least without knowing anything more about your problem) is to use std::string. i should change them dynamically through serial. How to Make a Black glass pass light through it? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Also you can not use strings as switch/case labels. How do I stop the Flickering on Mode 13h? Find centralized, trusted content and collaborate around the technologies you use most. How about saving the world? Where reinterpret_cast would probably just directly convert to char, without any cast safety. and want to copy this const char string* to a char*! Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? Understanding the probability of measurement w.r.t. How to Make a Black glass pass light through it? He also rips off an arm to use as a sword. 2) The pointer to const char* becomes invalid as soon as you hit a semicolon in the statement where qPrintable was used. Not the answer you're looking for? Effect of a "bad grade" in grad school applications. 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; } I'm very new to C, I'm getting stuck using the strncpy function.\. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. It is always wrong. You can access the any individual character in a string using normal array indexing, so for your example you could say: thanks again - your answer really helped, i wish it were possible to mark more than one answer as correct. How about saving the world? @Phlucious, because: 1) qPrintable returns const char* not char*, str.toLocal8Bit ().data () returns char*. Making statements based on opinion; back them up with references or personal experience. sizeof (*s) is 1, as it's the same as sizeof (char) which is specified in the C specification to be equal to one. Fixed it by making MyClass uncopyable :-). If doesn't have to cover anything complex. display those problems. To prevent possible type overflow you could do this: const char char_max = (char) ( ( (unsigned char) char (-1)) / 2); int i = 128; char c = (i & char_max); // Would always result in positive signed values. How a top-ranked engineering school reimagined CS curriculum (Ep. Without that {} the c array is only allocated. Generating points along line with specifying the origin of point generation in QGIS. Why is it shorter than a normal address? tar command with and without --absolute-names option, Counting and finding real solutions of an equation. const_cast is a C++ thing; it doesn't exist in C. If you want to use strcpy, you can't just use an uninitialised pointer (i.e. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Is this even the correct approach? Here, the destination memory location is the char* variable, the source memory location is the const char* variable, and the. Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? No need to do anything. Next I put (char *)string.c_str () but this only causes an unhandled exception. How can I convert const char* to char[256]. Please when you post also post the code that was used to print out data as problems such as these in a lot of cases depend on what you call to print out data. Extracting arguments from a list of function calls. Which was the first Sci-Fi story to predict obnoxious "robo calls"? What is Wario dropping at the end of Super Mario Land 2 and why? It works now, however it says that strncpy is a function on char but I'm using the sizeof char *. How to set, clear, and toggle a single bit? char* myChar = const_cast<char*>(myString); For example, to get the first character of the first argument to your program, you can do e.g. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? What is the difference between const int*, const int * const, and int const *? There are a few ways to convert a const char* to a char* in C++. - Zdeslav Vojkovic Sep 28, 2012 at 10:30 How can I control PNP and NPN transistors together from one pin? @gman Potentially, the optimal answer is still to not use. In your first example, tmp is an lvalue of type mutable pointer to const char, so a reference can be bound to it without issue. What does 'They're at four. Why is char[] preferred over String for passwords? Find centralized, trusted content and collaborate around the technologies you use most. Does the C++ standard allow for an uninitialized bool to crash a program? When you have non-const pointer, you can allocate the memory for it and then use strcpy (or memcpy) to copy the string itself. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. You can implicitly convert char * into const char *. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Embedded hyperlinks in a thesis or research paper. To learn more, see our tips on writing great answers. To learn more, see our tips on writing great answers. Each method has its own advantages and disadvantages, so it is important to choose the right method for your specific use case. It's always important to understand the trade-offs and implications of the different approaches, and making the right decision will depend on the specific requirements of your program. What risks are you taking when "signing in with Google"? This is considered bad practice, but you should think of const as a strong suggestion of the original programmer, not to modify it. Connect and share knowledge within a single location that is structured and easy to search. It's bad habit to use sizeof when you want to know how any elements not how many bytes. What is the difference between const int*, const int * const, and int const *? Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. cannot convert 'const char **' to 'const char*'. 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. Note: warnings need to be fixed, as the compiler knows the C language better than you or I. Not the answer you're looking for? If you make any changes, particularly adding a new string constant before "Test", you will find that the pointer you stored in EEPROM points to where "Test" used to be. of strncpy, which works (i.e. only allocates a single char and value-initializes it to length+1. Is there a weapon that has the heavy property and the finesse property (or could this be obtained)? I allocated t1->name = malloc(sizeof(s)) and then used strncpy. You need to add 1 to length after copying in order to copy null character (as strlen returns only number of chars without null character; see more here). So const char* c_ptr = s.toLocal8Bit ().constData (); does not make any sense. 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. this allocates space for a struct test; enough space for the pointer name, but not any memory for the pointer to point to. You declared MyEepromArray as an array of pointers to the const strings, it can't be changed by simple way. How do I stop the Flickering on Mode 13h? Find centralized, trusted content and collaborate around the technologies you use most. str0 = (char*) str1; or use std::string class template library for managing strings.std::string owns the character buffer that stores the string value. Something like: (This function actually exists, under the name strcpy_s in C 2011, but Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? However "_strdup" is ISO C++ conformant. strncpy() copies not more than length characters. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Why are players required to record the moves in World Championship Classical games? Unfortunately C++ didn't add an array size function until C++ 17 (std::size) so we're left to make our own. I would recommend using std::string everywhere so you don't have to manage the memory yourself. elsewhere.). The second and the third methods use two library functions strcpy() and memcpy() respectively to copy the content of const char* to char* variable. #include <algorithm>. What did you intend to declare with this line - a string of 12 characters or an array of 12 strings?