Documentation of 'Property of class preceded by question mark' [duplicate]

Question

This question already has answers here:

What is the purpose of a question mark after a type (for example: int? myVariable)? (9 answers)

Closed 5 years ago.

I have class that uses a ulong ParentId { get; set; }and I needed it to be nullable. Because if the entity (of this class) is added to the database, and has no parent, it must be null and not 0. So I remembered vaguely something about preceding it with a question mark. And it works. See the code below.

class ExampleClass
{
    public ulong ?ParentId { get; set; }
}

Question: Does anyone know where to find the documentation for this?

Answer 1

You may check Using Nullable Types and Nullable Types

Answer 2

For value type which can be nullable - http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx Question mark after a value type is same as Nullable<T>