long? 형식은 nullable 가능하게 됨 ( null값 허용 )

함수명(long? id) 이렇게 쓰일때가 있다.

long?의 의미는

long은 Int64와 동일하며

?의 의미는 nullable (널값을 허용한다는 의미)

long is the same as Int64

long data type

The ? means it is nullable

A nullable type can represent the normal range of values for its underlying value type, plus an additional null value

Nullable Types

Nullable example:

int? num = null;
if (num.HasValue == true)
{
    System.Console.WriteLine("num = " + num.Value);
}
else
{
    System.Console.WriteLine("num = Null");
}

This allows you to actually check for a null value instead of trying to assign an arbitrary value to something to check to see if something failed.

I actually wrote a blog post about this here.

출처: https://stackoverflow.com/questions/3893143/what-is-long-data-type