What is a String[*] and how do I cast it?

Question

I\'m currently in the unfortunate position of having to call a VBA macro from C#, via the COM Interop. The macro returns an array of strings and looks something like:

Answer 1

Your code was

var result = (string[])xlApp.Run("Foo", ... missing args ...);

As you have pointed out there is different behaviour with a 1-based array, with a zero-based array in VB your code does work.

You can get at the data like this

var result = (Array)xlApp.Run("Foo", ... missing args ...);

var stringsResult = result.Cast<string>[];

This gives you an IEnumerable of string

Answer 2

.NET supports such arrays (that have lower bound different from 0), you can create one using such snippet:

Array arr = Array.CreateInstance(typeof(string), new int[] { 5 }, new int[] {1});

The simplest way to convert such array to string[] is (although, it's copying data, on the other hands, those are just references, so if your arrays aren't too long, you won't get huge perf hit):

string[] x = new string[5];
Array.Copy(arr, 1, x, 0, 5);

Edit: Or using more general approach:

string[] x = new string[arr.GetLength(0)];
Array.Copy(arr, arr.GetLowerBound(0), x, 0, arr.GetLength(0));

Edit2: It also looks like casting arrays with lowerbounds != 0 works for fine, if there are more than 1 dimension, you can read more here, where Jon Skeet seems to answer why that happens.

Edit3: To make response less ambiguous, following djna's comments. This is how you could obtain string[] out of object returned by a method, that can't be cast to string[] directly, because it has lowerBound != 0:

Array arr = (Array)xlApp.Run("Foo", ... missing args ...); //Here I assume that .Run() method is returning object, or something that has to be casted to Array.
string[] result = new string[arr.GetLength(0)];
Array.Copy(arr, arr.GetLowerBound(0), result, 0, arr.GetLength(0)); // Here data is copied, but only references in this scenario