What happens if I initialize an array to size 0?

Question

Let's say I have a function like:

void myFunc(List<AClass> theList)
{
   string[] stuff = new string[theList.Count];
}

and I pass in an empty list.

Will stuff be a null pointer? Or will it be a pointer to some random place in memory that is uninitialized?

Answer 1

stuff will be a reference to an array with length theList.Count with all entries initialized to default(string), which is null.

Answer 2

Why should it? It will just point to an array of size 0, which is perfectly valid.

I think the confusion here arises from the ambiguity of representing the absence of data either bye an array of size 0 set to null (or between an empty string and a string reference set to null for that matter). Both are valid ways to indicate such absence and it would arguably make more sense to have only one. Hence, on some databases an empty string equals the NULL value and vices versa and some programming languages (I think, new versions of C# are one of them) allow to specify references to never be null, also eliminating said ambiguity.

Answer 3

If theList is an actual List object, and is merely empty, then theList.Count is going to return 0. Which means that the declaration becomes

string[] stuff = new string[0];

In other words, stuff will just be an array (of strings) with length 0.

Answer 4

This is fine code. You will get an Array object with zero items (allocations) in it.

Answer 5

It will create an empty array object. This is still a perfectly valid object - and one which takes up a non-zero amount of space in memory. It will still know its own type, and the count - it just won't have any elements.

Empty arrays are often useful to use as immutable empty collections: you can reuse them ad infinitum; arrays are inherently mutable but only in terms of their elements... and here we have no elements to change! As arrays aren't resizable, an empty array is totally immutable.

Answer 6

The following is in the C# language specification:

• The computed values for the dimension lengths are validated as follows. If one or more of the values are less than zero, a System.OverflowException is thrown and no further steps are executed.
• An array instance with the given dimension lengths is allocated. If there is not enough memory available to allocate the new instance, a System.OutOfMemoryException is thrown and no further steps are executed.

So for a length of zero, memory is allocated.

Answer 7

As long as you ensure that your List<> that you actually pass in to the method was initialized somewhere, like

List<Stuff> myStuff = new List<Stuff>;

the list will not point to null. It will be a list of zero Stuffs.