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). The caller won't even see a difference. You should be using the assignment (=), like. char n [5] = { '\0' }; // Initializes the array to all \0 strncpy (n, input, 4); Share Improve this answer Follow answered Sep 23, 2013 at 16:03 Daniel A. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. stored. Assuming endPosition is equal to lastPosition simplifies the process. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Like sean.bright said strdup() is the easiest way to deal with the copy. Looking for job perks? It's not them. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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! 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 increment s. So it no longer points to the beginning of the input string. Hi Alexander, I am facing a similar problem and I found your answer useful. Effect of a "bad grade" in grad school applications. Plot a one variable function with different values for parameters? 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. char actionBuffer[maxBuffLength+1]; // allocate local buffer with space for trailing null char Use the functions designed for this: strncpy(). You can email the site owner to let them know you were blocked. Flutter change focus color and icon color but not works. What if i want to perform some modifications on p and then assign it to lkey? Why is char[] preferred over String for passwords? I've tried to implement a basic system like this; What's wrong? Your n char needs to be 5 bytes big (4 characters + null-terminater). // handle buffer too small It does not nessesary to be a string. Can I connect multiple USB 2.0 females to a MEAN WELL 5V 10A power supply? Also - being perdantic you need const char * const t1 = "hello" - but the standard gives a lot of tolerance on that subject. 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. Cheers, @ibiza: lKey needs to be a caller-allocated buffer, then you can. Basically, I need to copy an array of char pointers to another array of char pointers. Why xargs does not process the last argument? What does 'They're at four. Therefore when you copy you are just copying to memory location 0, which is illegal. https://www.geeksforgeeks.org/c-program-replace-word-text-another-given-word/ as well as fixing the issue mentioned by Sourav Ghosh and you should have it. Why does Acts not mention the deaths of Peter and Paul? If you want to create a copy of the array you should write #include <string.h> //. let's say: i call methodone(p); and i then want to assign the result to lkey, how do i do that? char str [] = "Hello World"; char *result = (char *)malloc (strlen (str)+1); strcpy (result,str); Share Improve this answer Follow answered Jan 22, 2015 at 13:11 Rajalakshmi 681 5 17 I want to implement strcpy () in my own way. The idea is to read the parameters and values of the parameters from char * "action=getData#time=111111". c string strcpy unsigned-char Share Improve this question Follow hm, ok, although I prefer the app to crash in that case, because if your strings aren't null-terminated you did something wrong before. You just deal with two mallocs in main and 2 free's in main after you use them. rev2023.4.21.43403. How is white allowed to castle 0-0-0 in this position? How to check if a string "StartsWith" another string? Or perhaps you want the string following the #("time") and the numbers after = (111111) as an integer? How to combine several legends in one frame? To learn more, see our tips on writing great answers. Your IP: Copy part of a char* to another char* Using Arduino andresilva September 17, 2018, 12:53am 1 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*. Asking for help, clarification, or responding to other answers. ', referring to the nuclear power plant in Ignalina, mean? - dcds Jan 22, 2015 at 14:26 Add a comment 8 This is part of my code: This is what appears on the serial monitor: The idea is to read the parameters and values of the parameters from char * "action=getData#time=111111", but it seems that the copy of part of the char * affects the original value and stops the main FOR. Not the answer you're looking for? Making statements based on opinion; back them up with references or personal experience. I used strchr with while to get the values in the vector to make the most of memory! How to check if a string "StartsWith" another string? 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. Connect and share knowledge within a single location that is structured and easy to search. Making statements based on opinion; back them up with references or personal experience. I assume that the second call to your function overwrites the contents of the buffer created by the first call. Futuristic/dystopian short story about a man living in a hive society trying to meet his dying mother. How would you count occurrences of a string (actually a char) within a string? Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987? English version of Russian proverb "The hedgehogs got pricked, cried, but continued to eat the cactus". @LokiAstari: The OP said explicitly "other than strcpy". I am fairly new to C programming and trying to improve. When it is done it should return a pointer to the char. Looking for job perks? Simply assigning them just makes an "alias" of it, a different name that points to the same thing. - tab Aug 18, 2013 at 23:07 Yes it's always going to be 1, but it is good practice to get into the habit of doing that. Looking for job perks? How a top-ranked engineering school reimagined CS curriculum (Ep. I have tried the following, but it causes a crash: EDIT: My apologies, I was trying to simplify the examples, but I left some of the longer variable names in the second example. Why in the Sierpiski Triangle is this set being used as the example for the OSC and not a more "natural"? Asking for help, clarification, or responding to other answers. Which was the first Sci-Fi story to predict obnoxious "robo calls"? Now when I try it out my output is simply: Try not incrementing s before you start copying it to p. I notice that in your first for loop you increment s until it points at a null, and then later use that pointer value to start your string copy. However, the location is not in read-only memory: you just malloc'd it. Find centralized, trusted content and collaborate around the technologies you use most. Also, using std::array instead of a raw C array for you "array of structures" might be a better option (does not degenerate . What are the advantages of running a power tool on 240 V vs 120 V? original points to the start of the string "TEST", which is a string literal How a top-ranked engineering school reimagined CS curriculum (Ep. You define returnString[] but it only lives within the scope of the function. Actually the problem is strcpy(p,s1.c_str()); since p is never set to anything but NULL. Eliminate p (it is doing nothing here), and copy the data from s1 directly to lkey, Not to beat on you, but the indentation scheme is a travesty, please cop a good style from somewhere ( google 1tbs ). What is the difference between char s[] and char *s? You can with a bit more work write your own dedicated parser. This is often an indication that other memory is corrupt. Find centralized, trusted content and collaborate around the technologies you use most. No, you are not copying the string, you are accessing the same string through a What were the poems other than those by Donne in the Melford Hall manuscript? Is there a generic term for these trajectories? rev2023.4.21.43403. Not the answer you're looking for? How to set, clear, and toggle a single bit? Work from statically allocated char arrays. Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs. Find centralized, trusted content and collaborate around the technologies you use most. Please explain more about how you want to parse the bluetoothString. However, it's not a good idea to mix up std::string and C string routines for no good reason. I think your problem is no pointer to the dest argument in the strncpy function. You need to pre-allocate the memory which you pass to strcpy. Solution 1. Fixed. J-M-L: Start him off with strncpy. Making statements based on opinion; back them up with references or personal experience. What were the poems other than those by Donne in the Melford Hall manuscript? Short story about swapping bodies as a job; the person who hires the main character misuses his body. What was the actual cockpit layout and crew of the Mi-24A? 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 need to have memory allocated at the address. I like C primer plus by Steven Prata. If you are passing a buffer into the function then you probably want simply this (and remove p). (Now you have two off-by-one mistakes. To copy a single char one at a time, you can simply use the assignment , like. So the location is definitely safe to write. This is a real issue with strtok() and strtok_r() on non-BSD system where strsep is not available. How about saving the world? The myTags array is saved in the EEPROM. The action you just performed triggered the security solution. The question does not have to be directly related to Linux and any language is fair game. ;), "You do not strcpy a string you have just strlen'd" - Sure you do, when you don't save off the result of the strlen :P. sizeof(link) will return the length of the pointer, not the length of the string. Attempted to read or write protected memory. Sizeof(array) will return the size of the array IF it is declared in the same function, if it is passed as a pointer then it will return the size of the pointer. Has depleted uranium been considered for radiation shielding in crewed spacecraft beyond LEO? You're headed in the wrong direction.). You are currently viewing LQ as a guest. Asking for help, clarification, or responding to other answers. This is often an indication that other memory is corrupt. 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 is the difference between char s[] and char *s? Arrays in C++ (an C) have a pointer to the first item (character in this case). Connect and share knowledge within a single location that is structured and easy to search. I would prefer to worry more that the author is using unsafe techniques so I can convert to std::string quicker. Checks and balances in a 3 branch market economy. rev2023.4.21.43403. 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. Not the answer you're looking for? What does 'They're at four. Find centralized, trusted content and collaborate around the technologies you use most. His question is about the pointers and constants (char []literals in this case). Beware of buffer overruns! Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, oh my god thank you! How to check for #1 being either `d` or `h` with latex3? I think he wants to copy it leaving the original string literal intact. What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? is it bad style to make a var global if I need it in every function? Asking for help, clarification, or responding to other answers. This website is using a security service to protect itself from online attacks. Why is reading lines from stdin much slower in C++ than Python? Added a simple implementation of strdup() so anyone can happily use it. So in case of your code fragment it will copy as many characters as there are characters in . Did the drapes in old theatres actually say "ASBESTOS" on them? I used this solution: I also tried. How about saving the world? Why is char[] preferred over String for passwords? You need to copy some bytes from one place to another, where you have pointers to both locations. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Note that if you want to print the address of a variable with printf, you Add a pointer to the destination for the strncpy function. What does 'They're at four. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. actionBuffer[actionLength] = \0; // properly terminate the c-string To learn more, see our tips on writing great answers. tar command with and without --absolute-names option, Tikz: Numbering vertices of regular a-sided Polygon. sizeof (char) is guaranteed to be 1. You need to pre-allocate the memory which you pass to strcpy. I totally forgot that the increment assigns a new value for my. What is Wario dropping at the end of Super Mario Land 2 and why? Can I connect multiple USB 2.0 females to a MEAN WELL 5V 10A power supply? a p = new char [s1.length ()+1]; will do it (+1 for the terminating 0 character). You still need to put a null-terminating char (\0) at the end. How do I stop the Flickering on Mode 13h? 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*. Using an Ohm Meter to test for bonding of a subpanel. The caller won't even see a difference. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How to convert a std::string to const char* or char*. To my understanding, you are trying to concatenate two character strings. How would you count occurrences of a string (actually a char) within a string? Why typically people don't use biases in attention mechanism? What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. A minor scale definition: am I missing something? Some answers, including the accepted one are a bit off. Why is char[] preferred over String for passwords? What's better to do is: plus malloc is expensive in terms of CPU time and you don't free it. 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. How about saving the world? White 186k 46 364 443 It might not be entirely clear that you are 0 -ing the entire array in the first line. 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. Find centralized, trusted content and collaborate around the technologies you use most. We already know that the C-String handling feature are inherently unsafe and thus you take a closer look at features that use/see them. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? Improve INSERT-per-second performance of SQLite. Understanding pointers is necessary, regardless of what platform you are programming on. 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*. Note that this is not where original points, but where original is 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. Improve this answer. You obviously can. How about saving the world? - BoBTFish :-)): if memory is not a problem, then using the "easy" solution is not wrong of course. Why does Acts not mention the deaths of Peter and Paul? In your code you don't have memory allocated to use and you didn't set p to point to that memory address. Short story about swapping bodies as a job; the person who hires the main character misuses his body. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It seems like this should be easy, but I am really struggling. Work from statically allocated char arrays, If your bluetoothString is action=getData#time=111111, would find pointers to = and # within your bluetoothString, Then use strncpy() and math on pointer to bring the substring into memory. You're seeing gonk afterwards because there is no null-terminator \0. How about saving the world? 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. On whose turn does the fright from a terror dive end? in order to fill the above with space gaps so that I can get a proper tokenization of ALL my payload. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Remember that a char* is just an address of a memory location. In your code you don't have memory allocated to use and you didn't set p to point to that memory address. Embedded hyperlinks in a thesis or research paper. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Share Now, you can't write to a location via a const char *. How to check for #1 being either `d` or `h` with latex3? PaulS: This is often an indication that other memory is corrupt. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The strings may not overlap, I.e. But I think the statement you are looking for is. I tried this and does not work.. printed. I am deliberately not using strtok(). It helped a lot, I did not know this way of working with pointers, I do not have much experience with them. 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. English version of Russian proverb "The hedgehogs got pricked, cried, but continued to eat the cactus", Short story about swapping bodies as a job; the person who hires the main character misuses his body. So there's a bit wrong with that code. Checks and balances in a 3 branch market economy. Is it safe to publish research papers in cooperation with Russian academics? @john , and thats saying a lot since there are some many bad ones :/, My suggestion (assuming C++11) is just using, It might not be entirely clear that you are. 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 probably want to write: char linkCopy [strlen (link)+1]; strncpy (linkCopy,link,strlen (link)+1); Share. On whose turn does the fright from a terror dive end? If total energies differ across different software, how do I decide which software to use? Can I general this code to draw a regular polyhedron? You do not strcpy a string you have just strlen'd. strncpy(actionBuffer, ptrFirstEqual+1, actionLength);// http://www.cplusplus.com/reference/cstring/strncpy/ I've a simple question about string/char. Embedded hyperlinks in a thesis or research paper. 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. Same as the second one, but this time the address of the copy variable is Embedded hyperlinks in a thesis or research paper. char c[] has the same size as a pointer. How a top-ranked engineering school reimagined CS curriculum (Ep. You are on the right track, you need to use strcpy/strncpy to make copies of strings. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Can anyone give me a pointer in the right direction? What would be the best way to copy unsigned char array to another? What were the most popular text editors for MS-DOS in the 1980s? Why should I use a pointer rather than the object itself? But following problem persists: in C, you have to look after the malloced memory, the char array you are declaring is on the stack, and will be gone after the function returns, only the malloc memory will hang around. 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. strcpy does not allocate a buffer, it just takes a memory address to copy the data to. Making statements based on opinion; back them up with references or personal experience. you cannot do. How can I remove a specific item from an array in JavaScript? Inside this myTag array I am going to store the RFID tag numbers. You probably want to write: You don't say whether you can use C++ instead of C, but if you can use C++ and the STL it's even easier: Use newString as you would have used the C-style copy above, its semantics are identical. Where have you allocated memory to the pointer p? The sizeof will give you the size of the pointer. I am doing this but I this is not my main target. Which was the first Sci-Fi story to predict obnoxious "robo calls"? That is why I said to be careful. p is a pointer to memory that is not allocated. Looking for job perks? A minor scale definition: am I missing something? Prints the numerical address in hexadecimal format of the variable original. strcpy does not allocate a buffer, it just takes a memory address to copy the data to. Why did US v. Assange skip the court of appeal? Parabolic, suborbital and ballistic trajectories all follow elliptic paths. How to copy contents of the const char* type variable? Attempted to read or write protected memory. You do not have to assign all the fields. a p = new char [s1.length ()+1]; will do it (+1 for the terminating 0 character). Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity?