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copy char* to another char

    copy char* to another char

    If total energies differ across different software, how do I decide which software to use? Performance & security by Cloudflare. What is the difference between char s[] and char *s? Powered by Discourse, best viewed with JavaScript enabled, http://www.cplusplus.com/reference/cstring/strncpy/. To be supersafe, you should use strncpy to copy and strnlen to get the length of the string, bounded by some MAX_LENGTH to protect from buffer overflow. That's why the type of the variable is Making statements based on opinion; back them up with references or personal experience. In that case x[i].name = a[i].name would have worked just fine and you could also use the standard algorithm library for copy. and Yes, you will have to look after it and clean it up. char linkCopy [sizeof (link)] That creates a char array (aka string) on the stack that is the size of a pointer (probably 4 bytes). Inside this myTag array I am going to store the RFID tag numbers. Literature about the category of finitary monads, "Signpost" puzzle from Tatham's collection, Checking Irreducibility to a Polynomial with Non-constant Degree over Integer, Futuristic/dystopian short story about a man living in a hive society trying to meet his dying mother. Your main problem in your second attempt is that you can't assign to an array that way. No. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. until you crash). To learn more, see our tips on writing great answers. You've just corrupted the heap. I'm trying without success to copy a char array to another one. How to check if a string "StartsWith" another string? The sizeof (char) is redundant, but I use it for consistency. How to convert a std::string to const char* or char*. How do I count the number of occurrences of a char in a String? Are there any canonical examples of the Prime Directive being broken that aren't shown on screen? I totally forgot that the increment assigns a new value for my. This is often an indication that other memory is corrupt. Which one to choose? Connect and share knowledge within a single location that is structured and easy to search. Why in the Sierpiski Triangle is this set being used as the example for the OSC and not a more "natural"? Not the answer you're looking for? let's say: i call methodone(p); and i then want to assign the result to lkey, how do i do that? Why does contour plot not show point(s) where function has a discontinuity? Note that strdup is inexplicably not standard C. Use the following instead: char* my_strdup(char* str) {len = strlen(str)+1; res = malloc(len); if (res != NULL) memcpy(res, str, len); return res;} (Messy here, feel free to include it sean.bright). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. the pointer. Can I general this code to draw a regular polyhedron? Your n char needs to be 5 bytes big (4 characters + null-terminater). On what basis are pardoning decisions made by presidents or governors when exercising their pardoning power? What are the advantages of running a power tool on 240 V vs 120 V? You define returnString[] but it only lives within the scope of the function. @LokiAstari: The OP said explicitly "other than strcpy". It also makes code more readable. Have the function copy/cat the data like i showed above. Thanks for your explanation it was very helpful, Thanks for your suggestion it was helpful, Copy a single character from a character array to another character array in C, https://www.geeksforgeeks.org/c-program-replace-word-text-another-given-word/. What were the most popular text editors for MS-DOS in the 1980s? char is defined to be 1 byte wide by the standard, but even if it weren't sizeof is defined in terms of char, not byte width. Which is often 4 or 8 depending on your processor/compiler, but not the size of the string pointed to. Generating points along line with specifying the origin of point generation in QGIS. But I think the statement you are looking for is. strncpy must be the worst designed function in the entire C API. What if i want to perform some modifications on p and then assign it to lkey? Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? Better stick with std::string, it will save you a LOTS of trouble. Find centralized, trusted content and collaborate around the technologies you use most. Solution: Make a copy of s for counting the characters: Even better, you could refactor the length counting part into a reusable function called strlen. Understanding pointers is necessary, regardless of what platform you are programming on. Loop (for each) over an array in JavaScript, Checking Irreducibility to a Polynomial with Non-constant Degree over Integer. How about saving the world? How a top-ranked engineering school reimagined CS curriculum (Ep. How to insert an item into an array at a specific index (JavaScript), Sort array of objects by string property value. Some answers, including the accepted one are a bit off. First off you do: that is wrong, that assumes every char is 1 byte which it depends on the platform. How to combine several legends in one frame? What if i want to perform some modifications on p and then assign it to lkey? Making statements based on opinion; back them up with references or personal experience. Then, here: You try to copy n characters starting from the null terminator, and you end up reading past the end of the array which has undefined behaviour. :-)): if memory is not a problem, then using the "easy" solution is not wrong of course. std::vector<unsigned char> v ( buf, buf + datalen ); The vector constructor will copy all the data from buf [0] to buf [datalen - 1] and will deallocate the memory when the vector goes out of scope. Not the answer you're looking for? However, the location is not in read-only memory: you just malloc'd it. No, you are not copying the string, you are accessing the same string through a Cloudflare Ray ID: 7c0754bcaf2702bd EDIT: memcpy is very likely to be faster in any architecture, strcpy can only possibly perform better for very short strings and should be avoided for security reasons even if they are not relevant in this case. Making statements based on opinion; back them up with references or personal experience. You need strcpy. I assume that the second call to your function overwrites the contents of the buffer created by the first call. Embedded hyperlinks in a thesis or research paper. if (ptrFirstEqual && ptrFirstHash && (ptrFirstHash > ptrFirstEqual)) { Embedded hyperlinks in a thesis or research paper. - dcds Jan 22, 2015 at 14:26 Add a comment 8 Winnie the Pooh is getting another R-rated reimagining, this time featuring Christopher Robin as a burnout who embarks on drug-fueled fantasy adventures. Connect and share knowledge within a single location that is structured and easy to search. so when it's ok I have a char **content that has the old content, and a char **temp that has the new content and I want to replace my char **content by temp.. and thus points to read-only memory. rev2023.4.21.43403. copy can move. Connect and share knowledge within a single location that is structured and easy to search. Cheers, @ibiza: lKey needs to be a caller-allocated buffer, then you can. There are several actions that could trigger this block including submitting a certain word or phrase, a SQL command or malformed data. You're headed in the wrong direction.). char * ptrFirstHash = strchr (bluetoothString, #); const size_t maxBuffLength = 15; Now when I call this function from external application, I get this error: AccessViolationException: Note that this is not where original points, but where original is However, it's not a good idea to mix up std::string and C string routines for no good reason. Is this plug ok to install an AC condensor? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Fixed. My first (naive) attempt was to create another char* and set it equal to the original: This doesn't work, of course, because all I did was cause them to point to the same place. Also lKey=p won't work either -- it just copies the local address of p into the local variable lKey. char c[] has the same size as a pointer. So the location is definitely safe to write. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Why does Acts not mention the deaths of Peter and Paul? Not the answer you're looking for? Looking for job perks? Looking for job perks? Asking for help, clarification, or responding to other answers. Now I have a problem where whenever I try to make a delete[] variable the system gets lost again. rev2023.4.21.43403. You need to copy some bytes from one place to another, where you have pointers to both locations. In case, the input is smaller, you'll again hit UB. you can't do what you want very easily ( and possibly not at all depending on your application ). I don't want to look after every allocated memory. Why is char[] preferred over String for passwords? actionBuffer[actionLength] = \0; // properly terminate the c-string How about saving the world? It does not nessesary to be a string. Looking for job perks? Can I general this code to draw a regular polyhedron? No wonder you are getting a null string. Remember that a char* is just an address of a memory location. 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. Can I use my Coinbase address to receive bitcoin? Then you can continue searching from ptrFirstHash+1 to get in a similar way the rest of the data. Effect of a "bad grade" in grad school applications. How to check for #1 being either `d` or `h` with latex3? 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. original is a const pointer meaning you cannot reassign it. I assumed that "strncpy" was subsumed in that condition. This website is using a security service to protect itself from online attacks. Added a simple implementation of strdup() so anyone can happily use it. Add a comment. Not the answer you're looking for? When a gnoll vampire assumes its hyena form, do its HP change? to set the initial value of i. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Attempted to read or write protected memory. What is the difference between char s[] and char *s? you cannot do. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. (Now you have two off-by-one mistakes. I just put it to test and forgot to remove it, at least it does not seem to have affected! Why does contour plot not show point(s) where function has a discontinuity? I want to use such a function to save code. What was the actual cockpit layout and crew of the Mi-24A? Basically, I need to copy an array of char pointers to another array of char pointers. You just assign the pointer copy with the address of the string literal which address is also stored in the original pointer. You're seeing gonk afterwards because there is no null-terminator \0. Why did US v. Assange skip the court of appeal? What is Wario dropping at the end of Super Mario Land 2 and why? but anyway, why use it if you have other functions that are guaranteed to be available? You can't copy it using assignment operator. How would you count occurrences of a string (actually a char) within a string? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Generic Doubly-Linked-Lists C implementation, There exists an element in a group whose order is at most the number of conjugacy classes. However, it's not a good idea to mix up std::string and C string routines for no good reason. In case, the input is smaller, you'll again hit UB. Therefore i am up voting the post that has been down-voted. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. The aim of the code is to be given a string and split it on finding a blank space. Better stick with std::string, it will save you a LOTS of trouble. Work from statically allocated char arrays. of course you need to handle errors, which is not done above. rev2023.4.21.43403. What were the poems other than those by Donne in the Melford Hall manuscript? a p = new char[s1.length()+1]; will do it (+1 for the terminating 0 character). 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. Here you actually achieved the same result and even save a bit more program memory (44 bytes ! Cheers, @ibiza: lKey needs to be a caller-allocated buffer, then you can. The strcpy() function copies the string pointed to by src, including the terminating By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. tar command with and without --absolute-names option, Tikz: Numbering vertices of regular a-sided Polygon. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. and the destination string dest must be large enough to receive the copy. printed. Also lKey=p won't work either -- it just copies the local address of p into the local variable lKey. 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. Looking for job perks? ', referring to the nuclear power plant in Ignalina, mean? char c[]= "example init string"; is exactly the same thing as char *c = "example init string"; On Linux, it would put that string literal in the ELF object file's .rodata section, then move merely the address-of into the pointer variable. The idea is to read the parameters and values of the parameters from char * "action=getData#time=111111". To be supersafe, you should use strncpy to copy and strnlen to get the length of the string, bounded by some MAX_LENGTH to protect from buffer overflow. 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. Why do men's bikes have high bars where you can hit your testicles while women's bikes have the bar much lower? Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? ', referring to the nuclear power plant in Ignalina, mean? Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Which was the first Sci-Fi story to predict obnoxious "robo calls"? Has depleted uranium been considered for radiation shielding in crewed spacecraft beyond LEO? Why is char[] preferred over String for passwords? Note that if you want to print the address of a variable with printf, you What does 'They're at four. First thing first - you cannot do char* t1 = "hello";; Simply because string literals are constant, and any attempt to modify them trough t1 will result in undefined behavior. Why does this function work?I don't think that this is the proper way to copy a char* in C. It does not copy the string. Essentially, I want to create a working copy of this char*. Looking for job perks? I replaced new char(varLength) with new char(10) to see if it was the size that was being set, but the problem persisted. Actually the problem is strcpy(p,s1.c_str()); since p is never set to anything but NULL. Simply assigning them just makes an "alias" of it, a different name that points to the same thing. How to check if a string "StartsWith" another string? Start him off with strncpy. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, oh my god thank you! Use the functions designed for this: strncpy(). Can I connect multiple USB 2.0 females to a MEAN WELL 5V 10A power supply? 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*. Short story about swapping bodies as a job; the person who hires the main character misuses his body. Image Processing: Algorithm Improvement for 'Coca-Cola Can' Recognition. You should be using the assignment (=), like. How a top-ranked engineering school reimagined CS curriculum (Ep. Short story about swapping bodies as a job; the person who hires the main character misuses his body. But since you tagged this as c++, consider using std::string instead of a char array, unless you have a particular reason for using a char array. "Signpost" puzzle from Tatham's collection. You try to copy n characters starting from the null terminator, and you end up reading past the end of the array which has undefined behaviour. Your issue is that a char[] only live within the scope of the function (unless its global). To learn more, see our tips on writing great answers. I am doing this but I this is not my main target. @Zee99 strcpy just copies the data. char **content; that contains lines of text, and in order to change some lines I create a. char **temp; and copy (with strncpy) whatever I need from content to temp. PaulS: I'm surprised to have to start with new char() since I've already used pointer vector on other systems and I did not need that and delete[] already worked! Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So in case of your code fragment it will copy as many characters as there are characters in . rev2023.4.21.43403. How would you count occurrences of a string (actually a char) within a string? Solution 1. You do not have to assign all the fields. Can my creature spell be countered if I cast a split second spell after it? const char*. Not the answer you're looking for? That tells you that you cannot modify the content pointed to by the pointer. White 186k 46 364 443 It might not be entirely clear that you are 0 -ing the entire array in the first line. How is white allowed to castle 0-0-0 in this position? }. What was the actual cockpit layout and crew of the Mi-24A? For example: unsigned char q [1000]; unsigned char p [1000]; strcpy (q,&p); The above code does not work, it gives me error saying "cannot convert parameter 1 from unsigned char [1000] to char *". Here's the pseudo code: Thanks for contributing an answer to Stack Overflow! A minor scale definition: am I missing something? Then, the usage of strncpy() also looks wrong, you're not passing a char *, as required for the first argument. strcpy does not allocate a buffer, it just takes a memory address to copy the data to. Why is it shorter than a normal address? Embedded hyperlinks in a thesis or research paper. Why should I use a pointer rather than the object itself? You are currently viewing LQ as a guest. Since C++ doesn't have assignment operators from constant character pointer to character array, you have to copy memory manually. Connect and share knowledge within a single location that is structured and easy to search. I appreciate your suggestion, but I am giving credit to litb as I used his answer to solve my problem. I am deliberately not using strtok(). I want to write a function which takes in const char* and copies it to a new allocated char memory. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Improve INSERT-per-second performance of SQLite. if you have the option of C++, then you can use smart pointers, but in C, you either have to preallocate, or you manage your malloced memory, yes but I am trying to create this function so I don't have to look after every string i am creating. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, C: array of pointers pointing to the same value. What is the difference between 'typedef' and 'using' in C++11? So you have to change the logic behind the use and the declaration of returnString[]. c string strcpy unsigned-char Share Improve this question Follow Use strlen, or use strdup. a p = new char [s1.length ()+1]; will do it (+1 for the terminating 0 character). 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*. You need to pre-allocate the memory which you pass to strcpy. Actually the problem is strcpy(p,s1.c_str()); since p is never set to anything but NULL. If you know the string you're duplicating can never be longer than X bytes, you can pass X into strndup and know it won't read beyond that. This is often an indication that other memory is corrupt. You still need to put a null-terminating char ( \0) at the end. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. ', referring to the nuclear power plant in Ignalina, mean? Find centralized, trusted content and collaborate around the technologies you use most. Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs. Coding Badly, thanks for the tips and attention! I tried a naive content=temp; without results of course. Now, you can't write to a location via a const char *. It helped a lot, I did not know this way of working with pointers, I do not have much experience with them. Understanding pointers on small micro-controllers is a good skill to invest in. If the arg to strdup is not null-terminated, you could go reading through memory indefinitely (i.e. What is scrcpy OTG mode and how does it work? Find centralized, trusted content and collaborate around the technologies you use most. When it is done it should return a pointer to the char. @Zee99 strcpy just copies the data. I.e. Your third parameter to strncpy () has the same problem. Froe Char), Mugen Tutorial How To Copy A Move From One Char To Another. Something doesn't smell right on this site. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, You're returning the address of an automatic variable, you can't really avoid it. It's not them. Not the answer you're looking for? What you can do is this: or. I'm having a weird problem to copy the part of a char* to another char*, it looks like the copy is changing the contents of the source char*. i don't know about others. Where have you allocated memory to the pointer p? Why xargs does not process the last argument? If you are passing a buffer into the function then you probably want simply this (and remove p). Please include what you were doing when this page came up and the Cloudflare Ray ID found at the bottom of this page. How about saving the world? Or perhaps you want the string following the #("time") and the numbers after = (111111) as an integer? we simply use the strcpy function to copy the array into the pointer. sean.bright, before i added a commentary to my answer about strdup, i did a quick googlesearch, finding that at least windows ce doesn't ship that posix function. On whose turn does the fright from a terror dive end? As an alternative to the pointer managment and string functions, you can use sscanf to parse the null terminated bluetoothString into null terminated statically allocated substrings. Is there a generic term for these trajectories? 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. Share Improve this answer Follow edited May 11, 2016 at 17:56 answered May 11, 2016 at 17:41 Sourav Ghosh To subscribe to this RSS feed, copy and paste this URL into your RSS reader. You don't need to free() it, it is a stack object and will be disposed of automatically. Looking for job perks? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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 are on the right track, you need to use strcpy/strncpy to make copies of strings. Looking for job perks? You do not strcpy a string you have just strlen'd. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What would be needed instead of lKey=p so that the caller will correctly receive the new value in lkey? You increment s. So it no longer points to the beginning of the input string.

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