Leaving a pointer to it on the stack

[Adam D. Ruppe]

On Thursday, 13 August 2020 at 20:04:59 UTC, Andre Pany wrote:
> Hi,
>
> in the specification 
> https://dlang.org/spec/interfaceToC.html#storage_allocation 
> there is this paragraph:
> "Leaving a pointer to it on the stack (as a parameter or 
> automatic variable), as the garbage collector will scan the 
> stack."
>
> I have some trouble to understand what does this mean. Given 
> this example:
>
> ```
> import std;
>
> void main()
> {
> 	int* i;
> 	sample(&i);
> 	writeln(*i);
> }
>
> extern(C) export void sample(int** i)
> {
> 	*i = new int();
> 	**i = 42;
> }
> ```
>
> Int variable is created on the heap. How do I leave a pointer 
> on the stack?

You just did - the `int* i` is a pointer left on the stack for 
the duration of `main` so the GC won't collect it until after 
main returns.

But after main returns, even if `sample` kept a copy of it 
somewhere in some other location, the GC might reap it...