variable-length-array

I wrote a C program that accepts integer input from the user, that is used as the size of an integer array, and using that value it declares an array of given size, and I am confirming it by checking the size of the array. Code: #include <stdio.h> int main(int argc, char const *argv[]) { int n; scanf("%d",&n); int k[n]; printf("%ld",sizeof(k)); return 0; } and surprisingly it is correct! The program is able to create the array of required size. But all static memory allocation is done at compile time, and during compile time the value of n is not known, so how come the compiler is able to

I heard from many people that variable length array, introduced in C99, are terrible. Some guys on IRC said a minute ago « I don't think C++ will get VLA's, strousoup made some very negative comments about them ». What are the reasons why those people hate VLAs? VLAs allocate arrays on the stack, in runtime, making it harder, or even impossible to determine the stack size used at compile time. Since the stack has a rather small amount of memory available (in comparison with the heap), many worry that VLAs have a great potential for stack overflow. The upcoming version of the MISRA-C coding

Looking at this question: Why does a C/C++ compiler need know the size of an array at compile time ? it came to me that compiler implementers should have had some times to get their feet wet now (it's part of C99 standard, that's 10 years ago) and provide efficient implementations. However it still seems (from the answers) to be considered costly. This somehow surprises me. Of course, I understand that a static offset is much better than a dynamic one in terms of performance, and unlike one suggestion I would not actually have the compiler perform a heap allocation of the array since this

I've always wondered how I could get away with this: int main(int argc, char **argv) { printf("%p %s %d\n", &argv[1], argv[1], strlen(argv[1])); char copy[strlen(argv[1]) + 1]; strcpy(copy, argv[1]); printf("%p %s %d\n", &copy, copy, strlen(copy)); return 0; } The char array copy gets allocated anyway and the program runs fine, printing out the original and the copy. And Valgrind doesn’t complain about anything. I thought dynamic arrays weren’t possible in C without malloc. Was I wrong? This is a C99 feature and could be implemented on prior versions by the compiler . Variable-length automatic

n3639 proposed the adoption of c99 's variable-length-array s into C++14 (at least for the first dimension.) But the latest I've been able to find lists n3639 as: Features in the first CD of C++14, subsequently removed to a Technical Specification Did this ever make it into a Technical Specification, or was it lost in the hand off? The reason for my question is, I've noticed this code: void f(size_t n) { int a[n]; for (size_t i = 0; i < n; ++i) a[i] = 2 * i; sort(a, a + n); } This fails to build in Visual Studio 2015 and in gcc (when the "-pedantic" flag is used.) Works fine under gcc5.1, but

I am trying to write a function that takes an array of an variable size in c. void sort(int s, int e, int arr[*]){ ... } It says that for variable length arrays, it needs to be bounded in the function declaration. What does that mean? I am using xcode 4.0, with the LLVM compiler 2.0. Thanks for the help. If you're not using the C99 variable length arrays, the usual solution is to pass in a pointer to the first element, along with any indexes you want to use for accessing the elements. Here's a piece of code that prints out a range of an array, similar to what you're trying to do with your sort

This question already has an answer here: Variable Length Array overhead in C++? 2 answers How does Variable Length arrays (VLA) take space in memory? I have observed that VLAs do not take continuous memory space, can anyone please confirm the same?? void func(const IplImage *imgSrc, IplImage *imgDest) { uchar *data = (uchar *)imgSrc->imageData; // get the image data int height = imgSrc->height; int width = imgSrc->width; int step = imgSrc->widthStep; int stepSobel = imgDest->widthStep; //Calculate Sobel of Image uchar *dataSobel = (sobelStart + stepSobel); //**Declaration of VLAs** int

I have the following code which could not be complied. using namespace std; void f(int); template<typename T1, size_t N> void array_ini_1d(T1 (&x)[N]) { for (int i = 0; i < N; i++) { x[i] = 0; } } What is the proper way to pass the array if the main is something like below. int main() { int a; cin >> a; int n = a / 4; f(n); return 0; } void f(int n) { int arr[n]; array_ini_1d(arr); } error: no matching function to call to array_ini_1d.............. I don't think the compiler can deduce the size of a variable-length array in a template. Also, don't forget to forward declare f before you use it.