Problem with copying an array to another and not modifying the original array, Can not initialize struct inside a struct-C2224 Error, Assign Array in C (array contains a struct type), C++, expression must be a modifiable lvalue, Returning string for struct pointer prints random results. Because we know the size a priori, we can do the reallocation, before inserting. And one of the common ways to access these array values are by using indices like s[0] or tmp[0]. The l-value has the array type, but the r-value is the decayed pointer type, so the assignment is between incompatible types. Note that this still take O(N) time for N elements. Really. Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Is this a ragged array or is it a monolithic single block allocation. Why is there no 'pas' after the 'ne' in this negative sentence? Why does one have to iterate through the array copying index by index? There are several ways to do this. Anthology TV series, episodes include people forced to dance, waking up from a virtual reality and an acidic rain, Physical interpretation of the inner product between two quantum states. Similarly, tmp[1] and tmp[2] point to 5 and 2 chars respectively. How To Print Array In C++ Without Loop - Techinima.com What are the basic rules and idioms for operator overloading? C Program to Check whether the Given Number is a Prime. Works fine and fast for POD types. And if you want to print a variable amount of chars: Usefull for arrays of chars that do not end in \0, Yes its possible to print an array without loop you have to just use goto statemenet to make a loop and if condition to check. Also, you could perform your reverse with a single pass and without allocating a whole array in memory by just swapping the values in place one by one: Because both s and tmp are memory addressees. Circlip removal when pliers are too large. Thanks for contributing an answer to Stack Overflow! Initializing a different array in each iteration of a loop in C, initialize an array from another array in C, initializing an array without using a for loop. What would naval warfare look like if Dreadnaughts never came to be? This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. Internally, Python also work with loops. Writing a general print function for arrays in C. In C is there a way to print an array of unknown size with a single formatted print statement? rev2023.7.24.43543. I probably should just put an if (s[i] != '\n' || s[i] != '\0') in the in the first while loop. create same length size char array. Method 5 is a tweak on Method 4 - copy the array into a vector and then append it. Asking for help, clarification, or responding to other answers. Conclusions from title-drafting and question-content assistance experiments Memcpy returns contents of C array as pointers, How do I print an 2D array by means of a pointer? Yes, it's technically O(n). Knowing that the array has all the elements consecutive, and each element occupies 1 byte, accessing the element 8 is accessing the start of the array plus 8, that is *(myArray + 8) or myArray[8]. So if you do a memcpy() of a, you're doing a shallow copy of that pointer. Good option - generally fast-ish and clear. I could build nested loops to copy every char by hand but I hope there is a better way. How can kaiju exist in nature and not significantly alter civilization? Why the ant on rubber rope paradox does not work in our universe or de Sitter universe? How difficult was it to spoof the sender of a telegram in 1890-1920's in USA? How can I pass and store an array of variable size containing pointers to objects? I've tried to use memcpy with this lines: But I'm getting a: Program received signal: EXC_BAD_ACCESS, If the multidimensional array size is given at compile time, i.e mytype myarray[1][2], then only a single memcpy call is needed. Alas, it's slow. Connect and share knowledge within a single location that is structured and easy to search. if not, you will corrupt memory. rev2023.7.24.43543. How to rewrite Ackermann function in non-recursive style? Making statements based on opinion; back them up with references or personal experience. Is not listing papers published in predatory journals considered dishonest? strcpy (name, temp); copy temp back to name and voila works perfectly. How to initialize an array to something in C without a loop? Making statements based on opinion; back them up with references or personal experience. Please include what you tried, and where it went wrong, and what you wanted it to do. Find centralized, trusted content and collaborate around the technologies you use most. As to why the "decay to pointer value" semantic was introduced, this was to achieve a source code compatibility with the predecessor of C. You can read The Development of the C Language for details. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I've re arranged my answer. When you return, x is still holding on to the same array, but you have modified the values in that array. Initialize the array with values. What are some compounds that do fluorescence but not phosphorescence, phosphorescence but not fluorescence, and do both? Bjarne agrees. What would kill you first if you fell into a sarlacc's mouth? Geonodes: which is faster, Set Position or Transform node? How to avoid conflict of interest when dating another employee in a matrix management company? Making statements based on opinion; back them up with references or personal experience. It will still point to ab. Why is reading lines from stdin much slower in C++ than Python? Is saying "dot com" a valid clue for Codenames? Is it better to use swiss pass or rent a car? If a crystal has alternating layers of different atoms, will it display different properties depending on which layer is exposed? The only way to set an arbitrary amount of bytes to the same value in constant time is with a very large magnet. Instead, you can say dataArray + dataArraySize to get the pointer without having to dereference it first. Nor does C really have a string type. I found this link on wikipedia with a peculiar code snippet showing just how 'plasticine' C can be! Thanks for contributing an answer to Stack Overflow! How did this hand from the 2008 WSOP eliminate Scott Montgomery? I agree with you in that the comment may be not appropriate for a newbie and can lead to confusion. Are there any practical use cases for subtyping primitive types? The array can be copied by iterating over an array, and one by one assigning elements. I would ditch the multi-dimensional aspect and go with a flat buffer of size nn. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. There is no dangling pointer in his code, assigning tmp to s just modifies the local copy of the pointer to the array. Connect and share knowledge within a single location that is structured and easy to search. But it's not difficult to write a custom print function for this. You can't directly do array2 = array1, because in this case you manipulate the addresses of the arrays (char *) and not of their inner values (char). In addition to the methods presented above, you need to make sure you use either std::Vector.reserve(), std::Vector.resize(), or construct the vector to size, to make sure your vector has enough elements in it to hold your data. @Rahav, impossible to tell without testing, but, blogs.msdn.com/b/michael_howard/archive/2004/11/02/251296.aspx, Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. Short answer to almost ALL questions on the form "Can you do X as easy in C as Python?" No. Another alternative when unable to construct would be. Try experimenting and see what happens when you do things like this: What happens when you modify the array directly in attemptModifyArray, you are just overwriting a local copy of the address of the array x. The reason strncpy() behaves this somewhat odd way, is because it was not actually originally intended as a safe way to copy strings. remember that this can only be used for POD types. It entirely depends on how your "multidimensional array" is constructed. I've amended it. With the following code you can get a two columns range i (a1:b10) nto a variant array and then copy the column 2 of that array to another array without looping: Code: Sub test () Dim arrTest As Variant Dim arrCopy As Variant arrTest = Range ("a1:b10") arrCopy = Application.WorksheetFunction.Index (arrTest, 0, 2) End Sub. Does glide ratio improve with increase in scale? On the other hand it is probably a faster O(N) than the one you code by hand (or at least no slower). Your tmp array was declared on stack and so when your method completes, the memory used to hold the values will be freed because of scoping. 27 I'm looking for a smart way to copy a multidimensional char array to a new destination. Why the ant on rubber rope paradox does not work in our universe or de Sitter universe? What information can you get with only a private IP address? C: Copy array without knowing its type - Stack Overflow The second solution displays the string in reverse order without changing the string - whereas the exercise requests that the string is reversed without printing it. To cut a long story short Method 4, using vector::insert, is the best for bsruth's scenario. Thanks for contributing an answer to Stack Overflow! Can I opt out of UK Working Time Regulations daily breaks? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. You can only assign arrays the way you want as part of a structure assignment: If your arrays are passed to a function, it will appear that you are allowed to assign them, but this is just an accident of the semantics. For maintainability, consider what you're doing - the for loop may be more readable and easier to understand. (Most likely memcpy() is implemented with a loop, so the effect is as if you had nested loops.). What should I do after I found a coding mistake in my masters thesis? Within that function, you cannot use. To learn more, see our tips on writing great answers. I consider it a shortcut, and avoid using it unless the array or data structure is too large to conveniently initialise every element. This is what is called spaghetti code and the reason goto is frowned upon, because it makes the code very hard to follow. You can simulate A[i][j] with A[i + jwidth]. Can I spin 3753 Cruithne and keep it spinning? Your code is incorrect though. C++ vector.assign (contents of char array) works in WinXP-32, fails in Win10-64; why? In pictures, your data might look like this: tmp points to a contiguous block of 3 char * values. And it will work with any data type, not just char: (Yes, the code above is granted to work always and it's portable). How to copy a char array in C? - Stack Overflow Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. strcpy(name, temp); copy temp back to name and voila works perfectly. Thanks to all of you who answered. I'd stay away from memcpy() unless you can be sure that the values are plain-old data (POD) types. Thus, the line array2[i] = array1[i-1]; executes redardless of whether the inner for loop finds a duplicate. C program to copy all elements of one array to another When laying trominos on an 8x8, where must the empty square be? rev2023.7.24.43543. Thanks for the insight. The same applies if you have a pointer to a pointer: Assuming that malloc() succeeds, now you have ppa pointing to the first of a sequence of 10 contiguous int * values. Making statements based on opinion; back them up with references or personal experience. With the function signature given in the question, you avoid calling strlen() twice per line of input. There's an interesting sub-thread in this thread about arrays and pointers It is most likely more efficient to resize your vector up front if you know the size ahead of time, and not use the back_inserter. C Program to Copy All the Elements of One Array to Another Array Does glide ratio improve with increase in scale? I have function, it receive pointer to array and pointer to function and should return new array with order defined by function passed in parameter. I believe that leads to: Compile this with -DTEST to include the test program and without to have just the function reverse() defined. At the most basic level, a pointer to type T points to one object of type T. For example: Now, pi points to one int. To learn more, see our tips on writing great answers. I understand the following is invalid: What is the proper way to copy the array? I don't want to have to do the standard loop to push_back all the values individually, it would be nice if I could just copy it all using something similar to memcpy. The difference between the stack and the heap. How do you copy the contents of an array to a std::vector in C++ without looping? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. As others suggested, it looks like this is an array of pointers rather than a multi demetional array. How would I copy an array to a new array if i want the new array to not be dependent on the original array in C++. Can a creature that "loses indestructible until end of turn" gain indestructible later that turn? And if the vector is already there, a vec.clear(); vec.insert(vec.begin(), a, a + n); would work as well. You cannot assign one array to another array by a simple assignment, unlike some other languages (PL/1, for instance; Pascal and many of its descendants too - Ada, Modula, Oberon, etc.). If you s = tmp, both pointers would point to the same array. Not the answer you're looking for? 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. The above code will print the array without using a loop. @dmckee: Thanks for that. And how is it going to affect C++ programming? Since I don't know how many times my function will be called before it is time to process the data, I need a dynamic storage structure, so I chose a std::vector. If you give the ''n'' value(here n is size of array) as input to user, then you don't know what value will the user give. Finally, note that C-style arrays are perfectly valid containers for most STL algorithms--the raw pointer is equivalent to begin(), and (ptr + n) is equivalent to end(). is not supported in c. You have to use functions like strcpy() to do it. Let me clarify the second moral a little bit. After running arrSorted contain garbage, @MattyT what is the point of method 5? (array of string to another array of string), copy a char array to another char array of arrays, copy array of char to another without strcpy in c. Can a Rogue Inquisitive use their passive Insight with Insightful Fighting? People often trip over the fact that memcpy sizes in bytes, and they write things like these: You can protect yourself here by using language features that let you do some degree of reflection, that is: do things in terms of the data itself rather than what you know about the data, because in a generic function you generally don't know anything about the data: Note that you don't want the "&" infront of "myGlobalArray" because arrays automatically decay to pointers; you were actually copying "nums" to the address in memory where the pointer to the myGlobalArray[0] was being held. memcpy vs for loop - What's the proper way to copy an array from a pointer? For example, in Python, if we take a list as an array it directly prints the whole array for a single line of code. Thanks for contributing an answer to Stack Overflow! Now i want to initialize all elements of this array to 0. Line integral on implicit region that can't easily be transformed to parametric region. Why do capacitors have less energy density than batteries? Edit: This isn't a dangling modifier as pointed out in the comments of this answer. Also, do you need to use C-strings? These are not strings at all, so forget all about the string functions in the library. Is it a concern? @bradtgmurray: I think any reasonable implementation of the "two iterators" vector constructor I suggested above would call std::distance() first on the two iterators to get the needed number of elements, then allocate just once. How to initialise array dynamically with a default value? Maybe this should be a comment on one of the other answers, as you do not actually propose a solution. English abbreviation : they're or they're not. But if your compiler is good enough to optimize it, it's optimizing it, Yes. How many alchemical items can I create per day with Alchemist Dedication? this works perfectly ), The manpage for strncpy() even states "Warning: If there is no null byte among the first n bytes of src, the string placed in dest will not be null-terminated.". Just copy each element from the array and push it into the back of the vector. Asking for help, clarification, or responding to other answers. It is more clear if you think of it from the memory point of view, and not from language point of view. Since I can only edit my own answer, I'm going to make a composite answer from the other answers to my question. s = tmp means that s should point to the same memory location as tmp. Why the ant on rubber rope paradox does not work in our universe or de Sitter universe? c functions below only c++ you have to do char array then use a string copy then user the string tokenizor functions c++ made it a-lot harder to do anythng. Whilst this code snippet is welcome, and may provide some help, it would be. Who counts as pupils or as a student in Germany? To learn more, see our tips on writing great answers. Improve this answer. How can I animate a list of vectors, which have entries either 1 or 0? It could be a constant, or it could be a variable, depending upon i, or the phase of the moon, or a random number, or anything else. So if your question is if there are some predefined functions for printing arrays, the answer is no, provided that the array isn't a string. You forgot to multiply newPos and cPos by elemSize. You cannot assign arrays, the names are constants that cannot be changed. s and tmp are both pointers so doing s = tmp will simply make s point at the address where tmp lives in memory. Connect and share knowledge within a single location that is structured and easy to search. Geonodes: which is faster, Set Position or Transform node? Now, to copy all elements from source to dest array, you just need to iterate through each element of source . When you have a pointer to a pointer in C, you have to know how the data is going to be used and laid out in the memory. This is the reason to use vector.push_back(), you can't write past the end of the vector. Defining a array globally will also initialize with 0. Looking for story about robots replacing actors. @Alex: Yes: you could sort an array of pointers, but it changes the semantics in several ways. Lets consider this code: After compilation and execution, these 10 bytes are stored together at a given location in memory. It's meaning is clear, it's (usually) the fastest and it works for any objects. Like so: As @Prof. Falken mentioned in a comment, strncpy can be evil. Copy an array column to a different array w/out looping Make sure your target buffer is big enough to contain the source buffer (including the \0 at the end of the string). How I can insert an array of floats returned by a lambda into a vector of floats? Example: Input: First Array: a [5] = {3, 6, 9, 2, 5} Output: First Array : a [5] = {3, 6, 9, 2, 5} Second Array : b [5] = {3, 6, 9, 2, 5} Explanation: Copy elements from array a to b and then print the second array elements In certain cases, you could use snprintf() as well. Can someone help me understand the intuition behind the query, key and value matrices in the transformer architecture? C / C++ How to copy a multidimensional char array without nested loops? 4 K&R did not use your solution - they wrote for C89, not C99, but your solution uses a VLA (variable-length array) which was only added in C99. Can someone help me understand the intuition behind the query, key and value matrices in the transformer architecture? Is copying in a loop less efficient than memcpy()? Make sure you thoroughly grasp these three concepts and you won't go far wrong. Populating a class's member vector through constructor that takes a pointer to type. You cannot do the assignment s = tmp; Arrays cannot be assigned in C. Pointers can though, but a pointer is not an array. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. stackoverflow.com/questions/4707012/c-memcpy-vs-stdcopy/, Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. Why would God condemn all and only those that don't believe in God? c - Why can't I copy an array by using `=`? - Stack Overflow Copying contents of a char array into another. For large arrays this might help. It currently shows what you've written. If you need to guarantee the fastest speed and you know your type is a POD type then I would recommend the resize method in Thomas's answer: avoid the memcpy, I say. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. So, your array parameter in your function is really just a pointer. Do US citizens need a reason to enter the US? Add a comment. :-). If a crystal has alternating layers of different atoms, will it display different properties depending on which layer is exposed? Making statements based on opinion; back them up with references or personal experience. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Alas, it's slow. if you don't have the array dimensions, then you can't copy it with a loop either. Why is a dedicated compresser more efficient than using bleed air to pressurize the cabin? Why would God condemn all and only those that don't believe in God? (The name of an array gets promoted to a pointer to its first element when used as a value though, so if 's' were a pointer you'd be right. You can do it with any other value which, as bytes, consists of the same value in each byte. #include <bits/stdc++.h>. Why is a dedicated compresser more efficient than using bleed air to pressurize the cabin? Is there a word for when someone stops being talented? Perhaps it was edited?
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