variable-length-array

问题 Based on a comment of someone in another thread: VLAs introduce more problems than they solve, because you never know if the declaration is going to crash for x being too large for the stack. This code will overflow because sizeof(a) is too long for the stack: #include <stdio.h> #include <stdlib.h> int main(void) { int n = 100000000; int a[4][n]; printf("%zu\n", sizeof(a)); return 0; } But this one can not because sizeof(a) is 8 (the size of a pointer in my computer): #include <stdio.h>

问题 I'm trying to understand what "best practice" (or really any practice) is for passing a multidimensional array to a function in c is. Certainly this depends on the application, so lets consider writing a function to print a 2D array of variable size. In particular, I'm interested in how one would write the function printArry(__, int a, int b) in the following code. I have omitted the first parameter as I'm not exactly sure what that should be. void printArry(_____, int a, int b){ /* what goes

问题 I understand what variable length arrays are and how they are implemented. This question is about why they exist. We know that VLAs are only allowed within function blocks (or prototypes) and that they basically cannot be anywhere but on the stack (assuming the normal implementation): C11, 6.7.6.2-2: If an identifier is declared as having a variably modified type, it shall be an ordinary identifier (as defined in 6.2.3), have no linkage, and have either block scope or function prototype scope

问题 I understand what variable length arrays are and how they are implemented. This question is about why they exist. We know that VLAs are only allowed within function blocks (or prototypes) and that they basically cannot be anywhere but on the stack (assuming the normal implementation): C11, 6.7.6.2-2: If an identifier is declared as having a variably modified type, it shall be an ordinary identifier (as defined in 6.2.3), have no linkage, and have either block scope or function prototype scope

问题 This question already has answers here : C compile error: “Variable-sized object may not be initialized” (7 answers) C error “variable-sized object may not be initialized” [duplicate] (3 answers) gcc complains: variable-sized object may not be initialized (3 answers) Closed last year . On initializing a Variable length array compiler gives an error message: [Error] variable-sized object may not be initialized Code snippet: int n; printf("Enter size of magic square: "); scanf("%d",&n); int

问题 No, wait, bear with me... VLAs were always a GCC extension, but they were adopted by C99: [C99: 6.7.5.2/4]: If the size is not present, the array type is an incomplete type. If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used in declarations with function prototype scope; such arrays are nonetheless complete types. If the size is an integer constant expression and the element type has a known constant size

问题 This function has been asked a few times on here but I am interested in a particular case. Is it possible to have the size of the array passed defined by an additional argument? As an example, let's say I want a function to print a 2D array. However, I the array may not have the same dimensions every time. It would be ideal if I could have additional arguments define the size of that array. I am aware that I could easily switch out the n for a number here as needed but if I have more complex

问题 This question already has an answer here : Why am I being allowed to use a const qualified variable as an array size in C? (1 answer) Closed 6 years ago . GCC compiles the following function void f(int i) { int a[i]; } I was under the impression that you can only initialize arrays with constant length. Is this supposed to compile, and will it do what I expect it to? 回答1: C99 added variable length arrays. And gcc adds this to c89 as an extension with -std=gnu89 option (the default with gcc ).

问题 I've a bootstrap modal which contains a table of users. I can select a user from the table and on clicking 'save', the details of selected user is displayed and I get an alert stating 'Data saved successfully!'. The alert is at the end of the 'saveData()' method in my code. However, even when no row is selected from the table, when I click on save, I still get the same alert 'Data saved successfully!'. How do I ensure, that the alert only shows up if the details of a selected used is added?

问题 I tried this but it is not working ! can any one help me please this is very important :( #include <iostream> using namespace std; int a[100][100]; void read(int a[][100],int n) { int i,j; for(i=0;i<n;i++) for(j=0;j<n;j++) cin>>a[i][j]; } int main () { int n; cin>>n; int a[n][n]; read(a,n); } 回答1: The unclear syntax to pass array by reference is: void read(int (&a)[100][100], int n) resulting in #include <iostream> void read(int (&a)[100][100], int n) { for(int i = 0; i < n; i++) for(int j =