Quick int pointer allocation question

[Steven Schveighoffer]

On Fri, 14 Sep 2012 13:03:37 -0400, bearophile <bearophileHUGS at lycos.com>  
wrote:

> monarch_dodra:
>
>>> int *p = [5].ptr;
>>>
>>> -Steve
>
> But see this benchmark:
>
>
> void main() {
>      auto pointers = new int*[1_000_000];
>      foreach (int i, ref p; pointers)
>          p = [i].ptr;
>      foreach (i; 0U .. 4_000_000_000U) {}
> }
>
>
> On my 32 bit system its RAM commit is about 23 MB. The pointers array  
> takes about 4 MB. This means each "int" takes about 19 bytes of heap RAM  
> instead of 4. Each int allocates some data (capacity) to extend the  
> array.

That has nothing to do with using array literals -- it has to do with the  
fact that the minimum heap block is 16-bytes (or 4 ints wide).  Extra 3  
bytes is probably for overhead and static data.

If instead of p = [i].ptr; you did p = new int; *p = i;

You would get the same exact behavior.

No way around this, unless you want to do custom allocators.

-Steve