What is 'long?' data type?

Question

I am going over some code written by another developer and not sure what 'long?' means:

protected string AccountToLogin(long? id)
      {
         string loginName = "";
         if (id.HasValue)
         {
            try
            {....

Answer 1

long? is a 64 bit, nullable integer

to clarify, nullable means it can be null or an integer number ( 0, 1... etc. )

Answer 2

long is an Int64, the ? makes it nullable.

Answer 3

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.

Answer 4

"long?" is a nullable 64-bit signed integer. It's equivalent to Nullable<Int64>.

Answer 5

long? is a nullable type. This means that the id parameter can have a long value or be set to null. Have a look at the HasValue and Value properties of this parameter.

Answer 6

Got an error attempting to answer: It's a nullable type declaration.