Calling D DLL from C# and passing/retrieving string variables

[Trass3r]

>         [DllImport("mydll.dll",
>             CallingConvention = CallingConvention.Cdecl,
>             SetLastError = false, CharSet = CharSet.Auto)]
>             private static extern bool concatenate(
>                 string str1, // in
>                 string str2, // in
>                 StringBuilder strResult); // out

Question is if that StringBuilder really is equal to a char* in this case.