If I instantiate an array like this:
int array = new int;
It's 0. It can't be null, as null isn't a valid
From section 220.127.116.11 of the C# 5 specification:
All elements of the new array instance are initialized to their default values (§5.2).
And from section 5.2:
The default value of a variable depends on the type of the variable and is determined as follows:
- For a variable of a value-type, the default value is the same as the value computed by the value-type’s default constructor (§4.1.2).
- For a variable of a reference-type, the default value is null.
Initialization to default values is typically done by having the memory manager or garbage collector initialize memory to all-bits-zero before it is allocated for use. For this reason, it is convenient to use all-bits-zero to represent the null reference.
(As an implementation detail, there's some trickiness around the first bullet point. Although C# itself doesn't allow you to declare a parameterless constructor for value types, you can create your own parameterless constructors for value types in IL. I don't believe those constructors are called in array initialization, but they will be called in a
new X() expression in C#. It's outside the realm of the C# spec though, really.)