8. Asking for help, clarification, or responding to other answers. error: cannot convert 'char**' to 'char*' for argument '1' to 'char* strcpy(char*, const char*)', error: cannot convert 'char**' to 'char*' for argument '1' to 'char* strcpy(char*, const char*)', i don't get that error ;-). We already have too many of them, C compilers, not "older compilers". How about saving the world? Understanding the probability of measurement w.r.t. Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? Why did DOS-based Windows require HIMEM.SYS to boot? a is your little box, and the contents of a are what is in the box! okay, but then i spend hours looking for that through endless garbage. What is the difference between const int*, const int * const, and int const *? This line puts a null terminating zero at the end. To learn more, see our tips on writing great answers. Asking for help, clarification, or responding to other answers. char* myChar = const_cast<char*>(myString); There are many different ways to copy a const char* into a char []: #include <cstring> const char *s = "x"; char c [256] {}; std::strncpy (c, s, 255); #include <algorithm> #include <cstring> const char *s = "x"; char c [256] {}; std::copy_n (s, std::min (std::strlen (s), 255), c); Find centralized, trusted content and collaborate around the technologies you use most. What risks are you taking when "signing in with Google"? How about saving the world? of strncpy, which works (i.e. 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. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. However, it's not a good idea to mix up std::string and C string routines for no good reason. how can I compile this code? Where reinterpret_cast would probably just directly convert to char, without any cast safety. Copying strings is an expensive operation. How about saving the world? How to combine several legends in one frame? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Is anyone offer some suggestion how to solve that. How do I iterate over the words of a string? Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Getting a "char" while expecting "const char", Using an Ohm Meter to test for bonding of a subpanel. for gcc, at a minimum, use: '-Wall -Wextra -pedantic'. In the more general case, you may have to use strlen, to ensure that the string you have fits in the target buffer (without ever forgetting to add 1 to the results, for the \0). Why is it shorter than a normal address? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So const char* c_ptr = s.toLocal8Bit ().constData (); does not make any sense. You allocate mem for just 1 char. Why does Acts not mention the deaths of Peter and Paul? Connect and share knowledge within a single location that is structured and easy to search. It takes two arguments, the destination string, and the source string. That would look like the following: Note that the size argument to strncpy should always be the size of the destination, not the source, to avoid writing outside the bounds of the destination buffer. Now, there's another reason to mark your . Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? In your second example, (const char*)s creates a temporary const char* object. 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. How about saving the world? That they still give you an executable doesn't change what C++ is defined as, how to convert const char [] to char * in c++. 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. Ouch! Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? "Signpost" puzzle from Tatham's collection. Making statements based on opinion; back them up with references or personal experience. How would you count occurrences of a string (actually a char) within a string? What is scrcpy OTG mode and how does it work? It takes three arguments, the destination memory location, the source memory location and the number of bytes to be copied. Is there a way around? How a top-ranked engineering school reimagined CS curriculum (Ep. Making statements based on opinion; back them up with references or personal experience. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. You need to do that before you copy to it. Thanks for contributing an answer to Stack Overflow! Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987? (IMHO std::remove (const char*) should be std::remove_file (std::string const&) or at least std::remove_file (const char . "strdup" is POSIX and is being deprecated. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. Find centralized, trusted content and collaborate around the technologies you use most. 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. What is the difference between const int*, const int * const, and int const *? His writes exactly 256 bytes. Finally I just tried char *test = string.c_str () but that's not compatible with const either. But moving strings from one place to another is efficient. This is not straightforward because how do you decide when to stop copying? The common but non-standard strdup function will allocate new space and copy a string. gcc 4.8.4 allows it with a deprecation warning, They issue a diagnostic, telling you your program isn't C++. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. If you want to have another one at compile-time with distinct values you'll have to define one yourself: Notice that according to 2.14.5, whether these two pointers will point or not to the same memory location is implementation defined. How is white allowed to castle 0-0-0 in this position? When using the strcpy() or memcpy() method, be sure to properly allocate and deallocate memory for the char* variable to avoid memory leaks. In your case, strcpy alone is fine, since you've just allocated a sufficiently large buffer. 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. rev2023.4.21.43403. you can copy the String variable, but MyEepromArray [2] needs to point to a char array that it can be copied into. Secondly argv[1] has type char *. Failure to properly deallocate memory can lead to memory leaks in your program. I'm guessing you are given a const because something has marked it "not ok for you to change" ie read only. What was the actual cockpit layout and crew of the Mi-24A? 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. e.g. Why should C++ programmers minimize use of 'new'? free() dates back to a time. The "string" is NOT the contents of a. Even worse, it will leave the buffer non-null-terminated if the input string is longer than the buffer. It is always wrong. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, C++: How to convert 'const char*' to char, How to convert a std::string to const char* or char*. Making statements based on opinion; back them up with references or personal experience. rev2023.4.21.43403. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Is it a good practice to free memory via a pointer-to-const, How to convert a std::string to const char* or char*. English version of Russian proverb "The hedgehogs got pricked, cried, but continued to eat the cactus". I prefer to use that term even though it is somewhat ambiguous because the alternatives (e.g. Is there a weapon that has the heavy property and the finesse property (or could this be obtained)? What is Wario dropping at the end of Super Mario Land 2 and why? @MarcoA. Hi, I have to replace a string value in a specific char* array and then write it in eeprom: char * MyEepromArray[12]; //array char String Valore;// string value to insert in array location coming from serial MyEepromArray[2]=Valore.c_str();// i convert String to const char* an put it on array position 2 EEPROM.put(0, MyEepromArray); //I write the whole array in eeprom but the eeprom is not . To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Here are three methods you can use: It is important to note that converting a const char* to a char* allows you to modify the data that the char* points to. Thanks for contributing an answer to Stack Overflow! Now, you can't write to a location via a const char *. I agree that the best thing (at least without knowing anything more about your problem) is to use std::string. do you want to do this at runtime or compile-time? 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. Something without using const_cast on filename? How do I stop the Flickering on Mode 13h? Otherwise, you can allocate space (in any of the usual ways of allocating space in C) and then copy the string over to the allocated space. (I know it can work under 'g++' compiling) I think the confusion is because I earlier put it as. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Is there a generic term for these trajectories? If the string is local variable - this code should works fine inside the same scope as the Valore has. First of all the standard declaration of main looks like. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? You could change char *str = "C++ Language"; to char str []="C++ Language;" Initializing the pointer directly with constant string is not supported by most compilers. What were the poems other than those by Donne in the Melford Hall manuscript? What is Wario dropping at the end of Super Mario Land 2 and why? For more definitive answer please show a full code. rev2023.4.21.43403. Generating points along line with specifying the origin of point generation in QGIS. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. When a gnoll vampire assumes its hyena form, do its HP change? Anyways, non-static const data members and reference data members cannot be assigned values; you should use initialization list with the constructor to initialize them. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, How to convert a std::string to const char* or char*. One that takes you from pointers through chars and c-strings to switch/case statements. You haven't allocated space for new_name. Problem with this answer is if s is more than 255 characters there will be no terminating 0 at the end of c. Whether that's important or not is really up to you but 999 times out of 1000 it probably is important. How to calculate euler constant or euler powered in c++? On whose turn does the fright from a terror dive end? Looking for job perks? Realloc is not resizing array of pointers. Not the answer you're looking for? str0 = (char*) str1; or use std::string class template library for managing strings.std::string owns the character buffer that stores the string value. Note: warnings need to be fixed, as the compiler knows the C language better than you or I. strncpy() copies not more than length characters. English version of Russian proverb "The hedgehogs got pricked, cried, but continued to eat the cactus". if you want an char array, you should do. 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. How to Make a Black glass pass light through it? 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. Is this even the correct approach? printMe takes an lvalue reference to a mutable pointer to const char. What are the advantages of running a power tool on 240 V vs 120 V? Again, even you change that to something like "1234", still it would be incorrect, as it will not give you the intended value, and strings cannot be used for case statement values. You need to start with a basic C tutorial. What should I follow, if two altimeters show different altitudes? What does "up to" mean in "is first up to launch"? 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). Here is a fixed version of your code: First of all the standard declaration of main looks like. Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? Not the answer you're looking for? How a top-ranked engineering school reimagined CS curriculum (Ep. What is Wario dropping at the end of Super Mario Land 2 and why? What is Wario dropping at the end of Super Mario Land 2 and why? How a top-ranked engineering school reimagined CS curriculum (Ep. tar command with and without --absolute-names option, Counting and finding real solutions of an equation. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. What was the actual cockpit layout and crew of the Mi-24A? You were on the right track using strcpy, because const_cast is C++ only. How a top-ranked engineering school reimagined CS curriculum (Ep. I'd like to make str0 same as str1 while runtime(after compilation), I don't know how to do it. C++ : How to convert 'wchar_t *' to 'const char *'To Access My Live Chat Page, On Google, Search for "hows tech developer connect"So here is a secret hidden . thanks, i didn't realize strings could not be used in switch statements. How to convert a std::string to const char* or char*. Thanks UKHeliBob for the welcome. Connect and share knowledge within a single location that is structured and easy to search. You can however extract one single character from a string. Find centralized, trusted content and collaborate around the technologies you use most. How a top-ranked engineering school reimagined CS curriculum (Ep. What is the difference between char * const and const char *? Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? C++ copy a part of a char array to another char array. I forgot about those ;). Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, problems with convert const char* to char* in c, https://stackoverflow.com/questions/252782/strdup-what-does-it-do-in-c. the way you're using it, it doesn't copy the terminating \0. if I do this, and it works, is it the same as your solution? Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? - Wander3r Aug 3, 2018 at 9:12 1 Use std::string in C++ - Clonk Aug 3, 2018 at 9:13 Related question: stackoverflow.com/questions/20944784/ - vishal Aug 3, 2018 at 9:18 1 I'm having a really tough time figuring this out. Each method has its own advantages and disadvantages, so it is important to choose the right method for your specific use case. Thanks for contributing an answer to Stack Overflow! 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*. However, in your situation using std::string instead is a much better option. Edit: Even better use strdupas Miroslav suggests. Without that {} the c array is only allocated. "Signpost" puzzle from Tatham's collection. What is the difference between char * const and const char *? Can my creature spell be countered if I cast a split second spell after it? It has never been correct C++ to assign a string literal to a. Effect of a "bad grade" in grad school applications. Not the answer you're looking for? "Signpost" puzzle from Tatham's collection. i did studied this for hours, just need a hint. 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. How to copy contents of the const char* type variable? Making statements based on opinion; back them up with references or personal experience. rev2023.4.21.43403. Thanks for contributing an answer to Stack Overflow! Anther problem is when I try to use strcpy to combine them together, it pops up segmentation fault. without allocating memory first? 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. 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. 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. In which case you can do the following: By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Sure, my point was it was hypocritical to criticize the strncpy answer doing extra work is since your own example does extra work. @gman Abel's answer also (potentially) unnecessarily copies null characters into the buffer when the string is shorter. But this will probably be optimized away anyway. To learn more, see our tips on writing great answers. Find centralized, trusted content and collaborate around the technologies you use most. Here, I've used an exception, but you can use error handling of your choice, if this is not an option for you. i will study this carefully. Can my creature spell be countered if I cast a split second spell after it? Is there a weapon that has the heavy property and the finesse property (or could this be obtained)? 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. rev2023.4.21.43403. With it c is not only allocated but also initialized to 0 for all 256 characters. thank you for this explanation, it really helps. Connect and share knowledge within a single location that is structured and easy to search. If total energies differ across different software, how do I decide which software to use? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. warning: incompatible pointer to integer conversion initializing 'char' with an expression of type 'const char *' [-Wint-conversion], warning: overflow converting case value to switch condition type (825373492 to 52) [-Wswitch]. And at the end you might consider using just an array of fixed size that is initialized to maximum path. Extracting arguments from a list of function calls, QGIS automatic fill of the attribute table by expression. What is Wario dropping at the end of Super Mario Land 2 and why? Why is it shorter than a normal address? Nothing comes back to me. Looking for job perks? That is the second parameter does not have qualifier const. 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. characters are part of the string object. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. That's why the type of the variable is const char*. Looking for job perks? OK, that's workable. a p = new char [s1.length ()+1]; will do it (+1 for the terminating 0 character). Please read about RAII to understand why all of the solutions with manual memory management are bad: cppreference , wiki. You will have to store the characters, not just a pointer to them. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Looking for job perks? There is no any sense to compare it with a character literal similar to '1234'. Why do men's bikes have high bars where you can hit your testicles while women's bikes have the bar much lower? There's no general way, but if you have predetermined that you just want to copy a string, then you can use a function which copies a string. As for string literal "1234" when it may not be used in the case label. Looking for job perks? needs an array of pointers, not chars, You can't put character pointers in EEPROM, OP used EEPROM.put() method, which can store a char array string type, passed by pointer (however depends on realization). How about saving the world? Just for understanding code easily. str0 is of type char*, str1 is of type const char*. What differentiates living as mere roommates from living in a marriage-like relationship? This is the source code which I am testing. 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. If you need a const char* from that, use c_str(). What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? 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). What were the most popular text editors for MS-DOS in the 1980s? Connect and share knowledge within a single location that is structured and easy to search. @JaviMarzn It would in C++, but not in C. Some even consider casting the return of. What does "up to" mean in "is first up to launch"? 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. Embedded hyperlinks in a thesis or research paper, Understanding the probability of measurement w.r.t. tar command with and without --absolute-names option. this allocates space for a struct test; enough space for the pointer name, but not any memory for the pointer to point to. Find centralized, trusted content and collaborate around the technologies you use most. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Connect and share knowledge within a single location that is structured and easy to search. Is safe but slower. But you can copy the string. Use a std::string to copy the value, since you are already using C++. ], will not make you happy with the strcpy, since you actually need some memory for a copy of your string :). As you only want to read the string, you want it to be const. The hyperbolic space is a conformally compact Einstein manifold. Asking for help, clarification, or responding to other answers. Here, the destination string is the char* variable and the source string is the const char* variable. How to cast the size_t to double or int c++? But if you insist on managing memory by yourself, you have to manage it completely. Step 1 - Create a variable of type const char*. 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).