why range base loop doesn't work for arrays in heap, but works for the arrays in stack

Question

Here I'm trying to user c++11 range base loop for tow integer arrays. one declared using new keyword and other not.

#include <iostream>
#include <stdlib.h>

#define ARRAY_LENGTH 100    

int main()
{
          int* heap_array = new int[ARRAY_LENGTH];
          int stack_aray[ARRAY_LENGTH];

          for(int i=0; i < ARRAY_LENGTH; i++)
          {
            int val = (rand() % ARRAY_LENGTH) + 1;
            heap_array[i] = val;
            stack_array[i] = val;
          }

          for(int& i : stack_array){ std::cout << i << std::endl;}
          for(int& i : *heap_array){ std::cout << i << std::endl;} // compile error

          delete[] heap_array;
          return 0;
}

Why range base loop doesn't work for the array declared with new keyword? my view is it doesn't matter heap or stack both are heap_array & stack_array are pointers to the first element.

http://stackoverflow.com/questions/1461432/what-is-array-decaying Anyways, `*heap_array` is `int`, so what did you expect from it? And please, look at the docs before asking to see that there is no magic involved and that range based for is a mere syntactic sugar that uses `std::begin` and `std::end` to know the range. And `std::end` with a pointer does not make sense. — LogicStuff, Aug 21 '16 at 09:48
No. Arrays decay to pointers when necessary, but they're not the same thing. Take `sizeof stack_array` (`ARRAY_LENGTH * sizeof(int)`) compared to `sizeof heap_array` (`sizeof(int*)`), for example. — Ry-, Aug 21 '16 at 09:48
@NayanaAdassuriya, `stack_array` is an array, not a pointer; it can be used like a pointer sometimes, because, in certain contexts, an array-to-pointer conversion may be performed — chill, Aug 21 '16 at 09:50

Frank Puffer · Answer 1 · 2016-08-21T09:52:55.233

4

Your heap_array isn't really an array but a raw pointer to an int. A raw pointer does not know anything about the number of elements allocated.

edited Aug 21 '16 at 09:52

answered Aug 21 '16 at 09:46

Frank Puffer

8,135
2
20
45

why range base loop doesn't work for arrays in heap, but works for the arrays in stack

1 Answers1