String[] pointer to void* and back

[anonymous via Digitalmars-d-learn]

On Thursday, 18 September 2014 at 21:35:50 UTC, seany wrote:
> Yes, thank you, I corrected that.
>
> However, if this v is a member of a class, like
>
>
>
> import std.stdio;
> import std.conv;
> import core.vararg;
>
> struct S
>   {
>     void *v;
>   }
>
> class C
> {
>
>
>   S* sx = new S;
>
>   void dothings()
>   {
>      string[] ss = ["1", "2", "4"];

ss is a local variable. I.e., ss.ptr and ss.length are on the
stack.

>      string[] *s;
>      void *vv;
>
>      s = &ss;
>      vv = s;

vv now holds a pointer to the stack.

>
>      sx.v = vv;

Here, the pointer to the stack escapes the function. Don't do
that! When dothings returns, its portion of the stack becomes
unoccupied. Other functions will re-use it and stomp over the
data. The escaped pointer then points to some completely 
unrelated data.

>
>   }
>
> }
>
>
> void main() {
>
>      C c = new C;
>      c.dothings();
>      writeln("done");
>
>      string[]* sh;
>      sh = cast(string[]*)c.sx.v;
>      writeln(sh);        // upto this, works, the same pointer 
> as set in
>                          // c.dothings(), checked with write 
> instructions
>
>      string[] si = *sh;
>      writeln(si);
> }
>
>
>
> and then casted back, then i notice that it does not work. 
> Wondering why.