visual c++ - Array allocation in C++ on stack with varying length -

this question has answer here:

• c++: why int array[size] work? 3 answers

i surprised find out possible allocate varying-length array on stack in c++ (such int array[i];). seems work fine on both clang , gcc (on os/x) msvc 2012 don't allow it.

what language feature called? , official c++ language feature? if yes, version of c++?

full example:

#include <iostream>  using namespace std;  int sum(int *array, int length){     int s = 0;     (int i=0;i<length;i++){         s+= array[i];     }     return s; }  int func(int i){     int array[i]; // <-- feature i'm talking     (int j=0;j<i;j++){         array[j] = j;     }      return sum(array, i);  }  int main(int argc, const char * argv[]) {     cout << "func 1 "<<func(1)<<endl;     cout << "func 2 "<<func(2)<<endl;     cout << "func 3 "<<func(3)<<endl;      return 0; } 

you're looking @ gcc's variable length arrays. that's gnu extension , not standard c++.