Question

With reference to MSDN, It is stated that “You can set the lower bound of an Array, but the lower bound of an ArrayList is always zero”

If i declare an array a[10], the lower bound is always a[0].

Is this the lower bound specified there? If yes, How can we set the lower bound of an array, Since the index of an array always starts with a[0].

Or is the lower bound stated in the link is something different?

Note: I know the link point to the contents of .NET Framework 1.1 but still curious to know what exactly they have mentioned.

Answer 1

You can create an array with a non-zero lowerbound using Array.CreateInstance.

Note that you won’t be able to cast that to a Foo[] (where Foo is the relevant type) unless you also make it multidimensional. There are two types of array inside the CLR – a vector (zero based, single dimensional) and an array (can be multi-dimensional and have non-zero lower bound).

A T[] in C# always corresponds to a vector, whereas a T[][] corresponds to an array. So you can do:

int[][] rectangle = (int[][]) Array.CreateInstance(typeof(int),
                                       new int[]{2, 2}, // lengths
                                       new int[]{-1, -1}); // lower bounds

but this will fail:

int[] rectangle = (int[]) Array.CreateInstance(typeof(int),
                                       new int[]{2}, // length
                                       new int[]{-1}); // lower bound

Likewise you can’t cast it to IEnumerable<int> or IList<int> – although you can iterate over it with IEnumerable just fine.

Personally I would avoid using non-zero lower-bounded arrays like the plague. They’re slow, and painful to work with.