• mw (13/13) Oct 10 2023 Hi,
• H. S. Teoh (12/26) Oct 10 2023 This is an empty slice. It can refer to either stack or heap memory,
• mw (4/29) Oct 10 2023 How about the temporary array literal on the right hand side?
• ryuukk_ (42/55) Oct 10 2023 a is a static array, therefore it won't allocate any, it's a
• Imperatorn (2/15) Oct 10 2023 profile=gc
• Steven Schveighoffer (14/18) Oct 12 2023 ask the compiler:

mw <mw g.c> writes:

Hi,

I want to confirm: in the following loop, is the array literal 
`a` vs. `b` stack or heap allocated? and how many times?

void main() {

int[2] a;
int[] b;

int i;
While(++i <=100) {

   a = [i, i+1];  // array literal
   b = [i, i+1];

}

}


Thanks.

"H. S. Teoh" <hsteoh qfbox.info> writes:

On Wed, Oct 11, 2023 at 02:54:53AM +0000, mw via Digitalmars-d-learn wrote:
 Hi,
 
 I want to confirm: in the following loop, is the array literal `a` vs.
 `b` stack or heap allocated? and how many times?
 
 void main() {
 
 int[2] a;

This is stack-allocated. Once per call to the function.


 int[] b;

This is an empty slice. It can refer to either stack or heap memory,
depending on what's assigned to it.


 int i;
 While(++i <=100) {
 
   a = [i, i+1];  // array literal

`a` is overwritten in-place once per loop.


   b = [i, i+1];

[...]

A new array consisting of 2 elements is allocated, once per loop, and
assigned to b each time. Any arrays from previous iterations will be
collected by the GC eventually.


T

-- 
They pretend to pay us, and we pretend to work. -- Russian saying

mw <mw g.c> writes:

On Wednesday, 11 October 2023 at 03:15:30 UTC, H. S. Teoh wrote:
 On Wed, Oct 11, 2023 at 02:54:53AM +0000, mw via 
 Digitalmars-d-learn wrote:
 Hi,
 
 I want to confirm: in the following loop, is the array literal 
 `a` vs. `b` stack or heap allocated? and how many times?
 
 void main() {
 
 int[2] a;

 This is stack-allocated. Once per call to the function.


 int[] b;

 This is an empty slice. It can refer to either stack or heap 
 memory, depending on what's assigned to it.


 int i;
 While(++i <=100) {
 
   a = [i, i+1];  // array literal

 `a` is overwritten in-place once per loop.

How about the temporary array literal on the right hand side? 
It's stack / heap allocated? Or it's not in the language 
specification, but up to the (optimizing) compiler to decide?

   b = [i, i+1];

 [...]

 A new array consisting of 2 elements is allocated, once per 
 loop, and assigned to b each time. Any arrays from previous 
 iterations will be collected by the GC eventually.


 T

ryuukk_ <ryuukk.dev gmail.com> writes:

On Wednesday, 11 October 2023 at 02:54:53 UTC, mw wrote:
 Hi,

 I want to confirm: in the following loop, is the array literal 
 `a` vs. `b` stack or heap allocated? and how many times?

 void main() {

 int[2] a;
 int[] b;

 int i;
 While(++i <=100) {

   a = [i, i+1];  // array literal
   b = [i, i+1];

 }

 }


 Thanks.


a is a static array, therefore it won't allocate any, it's a 
memcpy

b will be heap allocated, and it'll do an allocate at each 
iteration


```D
void test_b()
{
     int[] a;
     int i;
     while (++i <= 100)
     {
         a = [i, i + 1];
         printf("%p\n", a.ptr);
     }
}
```

You can run this, and it'll print a different address each time


If you add `[]` it'll do range based copy (memcpy), but since the 
array is not initialized, it has a length of 0, so you only need 
to allocate once (either with GC or with malloc)

```D
void test_b()
{
     int[] a;
     int i;

     a.length = 2; // initialize the heap allocated array here

     // or with malloc:
     // auto ptr = malloc(int.sizeof * 2);
     // a = cast(int[]) ptr[0 .. int.sizeof * 2];

     while (++i <= 100)
     {
         a[] = [i, i + 1];
         printf("%p\n", a.ptr);
     }
}
```

Otherwise you'd get: ``core.exception.RangeError onlineapp.d(18): 
Range violation``

I don't use D with the GC, so my memory about it is probably 
foggy, but i'm pretty sure what i said is right, please anyone 
correct me if i'm wrong

Imperatorn <johan_forsberg_86 hotmail.com> writes:

On Wednesday, 11 October 2023 at 02:54:53 UTC, mw wrote:
 Hi,

 I want to confirm: in the following loop, is the array literal 
 `a` vs. `b` stack or heap allocated? and how many times?

 void main() {

 int[2] a;
 int[] b;

 int i;
 While(++i <=100) {

   a = [i, i+1];  // array literal
   b = [i, i+1];

 }

 }


 Thanks.

profile=gc

Steven Schveighoffer <schveiguy gmail.com> writes:

On 10/10/23 10:54 PM, mw wrote:
 Hi,
 
 I want to confirm: in the following loop, is the array literal `a` vs. 
 `b` stack or heap allocated? and how many times?

ask the compiler:

```d
void main()  nogc {

int[2] a;
int[] b;

int i;
while(++i <=100) {

   a = [i, i+1];  // array literal
   //b = [i, i+1]; // yes, this allocates, had to comment it out

}

}
```

-Steve