Get array starting with offset

Question

I am using C#, and it's rather annoying that I can't send an array starting from a certain point like in C++.

suppose this code:

int[] array = new int[32];
foobar (array + 4); //send array starting from the 4th place.

this is a weird syntax for C# because we don't have any usable pointers, but surely there's a way to do it? There's .Skip(), but I think it produces a new array, which is something I do not like.

What are my options?

Answer 1

You could just pass the offset to the function itself as a parameter. The function will then simply loop through the elements from [array + offset] to array.Length. That, or copy the sub-array into a new array, but that is probably not optimal.

Answer 2

You might want to pass it as an IEnumerable<int> rather than as an array. You can then use skip and it will simply move the iterator over the number of elements skipped. Used this way, you won't have to use ToArray() and create a copy of the portion of the array in question. Of course, IEnumerable may not be appropriate for what you want to do, but that's difficult to tell from your question.

public void FooBar( IEnumerable<int> bar )
{
  ...
}

int[] array = new int[32];
FooBar( array.Skip(4) );

Answer 3

I can appreciate what you are trying to do but you can't (and shouldn't try to) send a reference to "part of an array." In C#, arrays are objects, not pointers. That's an important distinction. Sending a reference to "part of an object" just doesn't make sense.

How should "part of an object" act when you pass it to a method?

• What would array.Length return?
• What if the called method sorts the array (just it's part of the array)?
• What if the array is self-referential (i.e. array elements references other parts of the array)? Are you somehow "locked out" of accessing array elements not passed into the method?
• Does the called method now need to check a flag to know if they have the "full object?" That would break a lot of existing code.

If your method needs only part of the array (and you don't want to create a local copy), the best solution would be to pass the array reference and any other information you need to access the portion you need.

Enjoy,

Robert C. Cartaino

Answer 4

.NET has the System.ArraySegment wrapper – unfortunately, it's completely useless since it doesn't implement IEnumerable.