compiled program error

[tcak via Digitalmars-d]

On Sunday, 7 June 2015 at 18:59:00 UTC, John Nixon wrote:
> While developing with D (DMD64 D Compiler v2.067.0 on MacOS 
> 10.10.3) I had a program with an unexpected behaviour
> and I reduced it to the minimal form below. The error as 
> indicated in the comment is that the function call pvi_calc 
> changes int_1 when I think it should not. The result copied 
> below.
>
> I hope this helps. Kind regards
> John Nixon
>
>
> import std.stdio;
> int n,cp;
> double[] pvi,int_1,int_2;
>
> void pvi_centre(const int centre){
>   int_1=pvi_calc(centre);
>   writeln("int_1 = ",int_1);
>   int_2=pvi_calc(n-1-centre);//pvi_calc is changing int_1!
>   writeln("int_1 = ",int_1);
>   return;}
>
> double[] pvi_calc(const int n1){
>   for(int i=0;i<=n1;++i)pvi[i]= 1;
>   return pvi;}
>
> int main(){
>   n=10;
>   pvi.length=n;
>   int_1.length=int_2.length=n;
>   pvi_centre(cp);
>   return 0;}
> ~
>
> int_1 = [1, nan, nan, nan, nan, nan, nan, nan, nan, nan]
> int_1 = [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

There is only one "pvi" array at all. So, pvi_calc function 
modifying that only one, and returns it back.

When you first call pvi_calc, int_1 points to pvi array. When you 
call it second time, int_2 points to same pvi array again.

Since both of them points to same array, value of int_1 (actually 
value of pvi array) changes.