return char array from a function in c

I've updated my answer to reflect your comment. I don't think this is a dupe of "Can a local variable's memory be accessed outside its scope?". If you want to return a single-dimension array from a function, you would have to declare a function returning a pointer as in the following example @zett42 True, I actually should point it out as a potential flaw in this approach. You will need to delete the memory after writing, like: However, I highly don't recommend doing this (allocating memory in callee and deleting in caller). Big applications can have hundreds of functions. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? But it is not. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? @Elephant Comments aren't for asking questions - long segments of code are unreadable. Not the answer you're looking for? The memory pointed at by str is now never destroyed. If commutes with all generators, then Casimir operator? is it needed? How can I write a function which returns array with repeating strings grouped together? Now, in mycharstack() the string is stored on stack I guess, so as "ch" goes out of scope, it should not be able to return the string. Why does Acts not mention the deaths of Peter and Paul? How a top-ranked engineering school reimagined CS curriculum (Ep. Why is processing a sorted array faster than processing an unsorted array? I NEED to end up with a char array rather than a string type purely because the char array is used to contain a pump port name ie "COM7" and is used as an argument in createfile() function to open the port to writting (actually a char pointer) this function does not accept string types. Don't know. What were the most popular text editors for MS-DOS in the 1980s? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. A minor scale definition: am I missing something? Returning objects allocated in the automatic storage (also known as "stack objects") from a function is undefined behavior. A char array is returned by char*, but the function you wrote does not work because you are returning an automatic variable that disappears when the function exits. Does a password policy with a restriction of repeated characters increase security? The fact that it's an array has nothing to do with it. This allows you to encapsulate an array in a vector or a similar structure: You have two options for returning an array in C++. which is basically what Marjin said. To keep everyone but the zealots happy, you would do something a little more elaborate: Just remember to free the allocated memory when you are done, cuz nobody will do it for you. And will come across the right way of returning an array from a function using 3 approaches i.e. Ubuntu won't accept my choice of password, Reading Graduated Cylinders for a non-transparent liquid. Where in the array would the compiler put your char? Let us write a program to initialize and return an array from function using pointer. Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? It's safe to say the OP's code is more complicated than returning some fixed values (there would be no point). C compiler reports a warning message on compilation of above program. because the "%s" expects a matching string to be passed, and in c an array is not a string unless it's last character is '\0', so for a 2 character string you need to allocate space for 3 characters and set the last one to '\0'. Even if changed, returning a pointer to a global variable is horrible practice to begin with. this implementation will cause memory corruption due to malloc(sizeof(array_t*)); it should be malloc(sizeof(array_t)); (no star). you'd better add the kind of code you write in the tags. It doesn't affect the space that you just allocated by malloc; furthermore, since this space isn't referenced any more, it will remain allocated but unused until your program exits. Why refined oil is cheaper than cold press oil? If the string length goes beyond the specified length, just its first 4 characters will be stored. What's the function to find a city nearest to a given latitude? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The pointer and the string it might point to are two seperate things. It will automatically deallocate the reserved memory when the scope exits (you don't have to call, You can change the size of the "array" dynamically after construction (using the. Why is it shorter than a normal address? If you are not going to change the chars pointed by the returnValue pointer ever in your programme, you can make it as simple as: This function creates allocates a memory block, fills it with the following: And then returns the address off the first element 't'. What differentiates living as mere roommates from living in a marriage-like relationship? What "benchmarks" means in "what are benchmarks for?". Be careful, though, to either agree on a fixed size for such calls (through a global constant), or to pass the maximum size as additional parameter, lest you end up overwriting buffer limits. If #2 is true, then you want to allocate the strings, process the strings, and clean them up. So you can accept the output array you need to return, as a parameter to the function. Which was the first Sci-Fi story to predict obnoxious "robo calls"? Does the 500-table limit still apply to the latest version of Cassandra? What problem do you foresee? 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Or use a std::vector in C++. @Quentin Oh do come one I just addressed what the OP said exactly. But an array of strings in C is a two-dimensional array of character types. My solution doesn't have the problem of returning a pointer to a local variable, because hard-coded strings are static by definition. So you have 3 options: Use a global variable: char arr [2]; char * my_func (void) { arr [0] = 'c'; arr [1] = 'a'; return arr; } @Alexander: Good point. But it is pretty weird. You also need to consume your line end characters where necessary in order to avoid reading them as actual data. that might change size depending on the values I pass into the function through the main function. Thanks for contributing an answer to Stack Overflow! Array : Return a pointer to array from a function in C++?To Access My Live Chat Page, On Google, Search for "hows tech developer connect"As I promised, I hav. And additionally what if the string added is dynamically allocated by cin >> string? I appreciate but I think people need to understand with example not by word that's why I gave this link, and if you did not like, it's Ok. @SimonF. How do I use these pointers to arrays properly without gtting a type error? May not be a problem but for large arrays this could be a substantial cost. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Does that program even compile? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Wow. @ontherocks: this question is wrong ;-) you should not reassign the pointer in the first place. However, you can return a pointer to array from function. To learn more, see our tips on writing great answers. You should also specify the length of the destination field when using scanf ("%s", array_name). To learn more, see our tips on writing great answers. What if we have the following: SET_ERROR_MESSAGE(false, (returnErrorCppString().c_str())); where the capital letters represent a macro that takes varargs. Boolean algebra of the lattice of subspaces of a vector space? is that even possible? Another thing is, you can't do this char b [] = "Hallo";, because then the character array b is only large enough to handle Hallo. How do I iterate over the words of a string? If you want it as a return value, you should use dynamic memroy allocation, You should be aware of the fact that the array as filled above is not a string, so you can't for instance do this. Returning multi-dimensional array from function is similar as of returning single dimensional array. How can I remove a specific item from an array in JavaScript? Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0. Before we learn that, let's see how you can pass individual elements of an array to functions. Finally there is the problem that the return type is "pointer to char", while you're attempting to return an array of arrays of pointers to char. "Modern" as in C++11/14/17. C arrays degrade to pointers. Thanks! Loop (for each) over an array in JavaScript. However with use of the return value optimisation (. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? You are writing a program in C++, not C, so you really should not be using raw pointers at all! Image Processing: Algorithm Improvement for 'Coca-Cola Can' Recognition. How can I remove a specific item from an array in JavaScript? That thing on the stack is just a pointer variable and you return the value of the pointer (the address it stores) by value. 1. const char* ptr; . Return pointer pointing at array from function C does not allow you to return array directly from function. How a top-ranked engineering school reimagined CS curriculum (Ep. What are the advantages of running a power tool on 240 V vs 120 V? So you see, it's not a "C string" issue but the problem of returning a pointer to a local variable (static or not) So, my possible solutions: 1) return dynamic allocated memory which the caller has to free () 2) manage an static array of buffers which elements you rotate through with each call Multi-dimensional arrays are passed in the same fashion as single dimensional. How a top-ranked engineering school reimagined CS curriculum (Ep. We learned to pass array and return array from a function. rev2023.5.1.43405. To make more sense of it all, you might also want to read this: What and where are the stack and heap? Embedded hyperlinks in a thesis or research paper. @abligh It doesn't matter whether title and main question exactly match. So I'm correct in thinking the returned string does not go out of scope because it is an object return type but a char array does because its only a pointer and not the entire array returned? For the "What you want:" part, Yossarian was faster than me. How do I check if an array includes a value in JavaScript? Asking for help, clarification, or responding to other answers. In C programming, the collection of characters is stored in the form of arrays. In modern C++ a better approach is to return a standard library container like std::vector, instead of raw pointers. Also I find it useful to write a simple array of string implementation which has a minimal API for data manipulation. Further applying [0] on that character is ill-formed since there is no subscript operator for arguments char and int. char str [] = "C++"; you need the return type to be char(*)[20]. This is also supported in C++ programming. ), it would look something more like this instead: Not so nice, is it? while 'int function' or 'float function' will do just fine without using pointer on the function. The declaration of strcat () returns a pointer to char ( char * ). It takes literally 30 seconds to add a note: you should be calling free from the caller function". Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? NULL-terminated character arrays) from unmanaged code to managed code. One convention is one you said. The reason that the first is preferred is because it re-enforces proper disposal of allocated memory. I ran your cod eand it's giving me, Returning const char* array from function, How a top-ranked engineering school reimagined CS curriculum (Ep. From the linked FAQ "Arrays are not pointers, though they are closely related (see question 6.3) and can be used similarly." There is no array. If we had a video livestream of a clock being sent to Mars, what would we see? My ultimate goal is to have char * array from a function. And then returns the address off the first element 't'. How do I make a fuction that returns an array that I am able to read in a different function? This temporary object is then copied to the client before it is destroyed. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Does a password policy with a restriction of repeated characters increase security? Asking for help, clarification, or responding to other answers. The function doesn't need to know the buffer size unless there is a possibility for an overflow. In C programming, you can pass an entire array to functions. It complains about returning address of a local variable. Use dynamic allocation (the caller will have the responsibility to free the pointer after using it; make that clear in your documentation), Make the caller allocate the array and use it as a reference (my recommendation). var functionName = function() {} vs function functionName() {}, How to insert an item into an array at a specific index (JavaScript). Usually in C, you explicitly allocate memory in this case, which won't be destroyed when the function ends: Be aware though! Trying to still use it will most likely cause your application to crash. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. It is not possible to return an array out of a function, and returning a pointer to an array would simply result in a dangling pointer. Loop (for each) over an array in JavaScript, tar command with and without --absolute-names option. In the example below I made it a global. char* Groceries:: getList () const // Returns the list member. Can I use my Coinbase address to receive bitcoin? In the code shown, there is no array, rather a pointer to a chunk of dynamically allocated memory. I disagree. How does it work correctly? Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? The assignment returnValue = "test" makes the returnValue variable point to a different space in memory. char* is a pointer to char (or array of chars). Making statements based on opinion; back them up with references or personal experience. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? 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. Effect of a "bad grade" in grad school applications. Like so: What I expected it will return the Halloworld when i run it. char* get_name () { char *string = malloc (4); strcpy (string, "ANA"); return string; } Remember that you need to match every call to malloc with a call to free. @Zac: Conceptually, first a temporary string object is created from the char array. I just use a char* function and return arr; and it segfaults when I try to output. How to initialize static member array with a result of a function? Do: Making statements based on opinion; back them up with references or personal experience. get a proper answer. C program to sort an array using pointers. @iksemyonov True, but I'll leave that for another question :), First things first: how would you return an. Which means any changes to array within the function will also persist outside the function. Returning or not returning allocated memory is a matter of convention. How do I declare and initialize an array in Java? How to insert an item into an array at a specific index (JavaScript), Sort array of objects by string property value, Improve INSERT-per-second performance of SQLite. To learn more, see our tips on writing great answers. The declaration of strcat() returns a pointer to char (char *). I won't downvote, that would be unfair, but a better answer would explain the problems with his initial code. Why is reading lines from stdin much slower in C++ than Python? Almost indentical and they have the same issue -, How a top-ranked engineering school reimagined CS curriculum (Ep. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. if you want to allocate the string "hello world" on the heap, then allocate a buffer of sufficient length (. You'll need it larger than Hallo, and the rest will be filled with 0x00, or NUL. Find centralized, trusted content and collaborate around the technologies you use most. rev2023.5.1.43405. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Why is processing a sorted array faster than processing an unsorted array? Take a look at: Please also pass the capacity as argument, it's too fragile this way. Did the drapes in old theatres actually say "ASBESTOS" on them? Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Output changes when I put my code into a function. Answer: Because C (and C++) just does not allow returning array-typed values. Are there any canonical examples of the Prime Directive being broken that aren't shown on screen? Warnings involving reading file into char array in C, What "benchmarks" means in "what are benchmarks for?". You can't return a double* from a function with double return type. In main() no ones freeing the allocated memory. How to access two dimensional array using pointers in C programming? Not the answer you're looking for? A normal char[10] (or any other array) can't be returned from a function. You'll also need to keep track of the length yourself: 2) Allocate space for the array on the stack of the caller, and let the called function populate it: Since you have a predetermined size of you array you can in-fact return the array if you wrap it with a struct: You can return a pointer for the array from a function, however you can't return pointers to local arrays, the reference will be lost. How to check whether a string contains a substring in JavaScript? As char* is a pointer, assigning into it changes the pointer. Why did US v. Assange skip the court of appeal? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Asking for help, clarification, or responding to other answers. may i know why we must put pointer on the function? You've declared doc as an automatic variable. How do I determine the size of my array in C? Function should return char *. You would benefit from reading an introduction to the C programming language. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? a NULL) at the end. In the last chapter, we looked at some code for converting an integer into a string of digits representing its value. How to set, clear, and toggle a single bit?

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