string[] to char**

[Ali Çehreli]

On 03/23/2012 08:48 AM, simendsjo wrote:
 > What's the best way to convert char** from string[]?

In C, char** communicates transfer of ownership. Is that what you are 
trying to do? Are you going to pass a slice to a C function to be filled 
in by that C function?

Such functions usually assign to *str. In that case you can use the 
"make slice from raw pointer" method below. I hope others will answer my 
concern in the comment below:

import std.stdio;
import std.c.stdlib;
import std.c.string;

void C_func_with_an_out_parameter(char ** str)
{
     *str = cast(char*)calloc(1, 10);
     (*str)[0] = 'A';
     (*str)[1] = '\0';
}

void main()
{
     char * p;
     C_func_with_an_out_parameter(&p);

     char[] slice = p[0..strlen(p)];     // <-- make a D slice

     /*
      * Note: I don't think that the memory that
      * std.stdlib.calloc() returns is managed by the GC. For
      * that reason, I don't think it will be safe to share the
      * element with another slice and expect normal behavior
      * of element-sharing between slices.
      *
      * In other words, this would be risky:
      *
      *     char[] anotherSlice = slice;
      */
     writeln(slice);

     free(p);
}

Ali