What is the specification of Hexadecimal Date format in SQL server?

Question

SQL Server Management studio generated value of datatype "Date" into following string: CAST(0x38320B00 AS Date).

I need to convert it into classical .NET datetime (i have the string in c# app). I know that if it were SQL Server DateTime it would be 2 times longer Hex number and first part would specify number of days from 1.1.1900, and second part would specify number of 1/300th seconds from the noon.

I thought that respectively in SQL Server Date datatype this would be just first part of DateTime (time part omitted) however it's not. When I try following snippet i get exception:

Int32 high = Int32.Parse("38320B00", NumberStyles.HexNumber);
DateTime start = new DateTime(1900, 1, 1);
start = start.AddDays(high);

So what does this number specify?

Answer 1

The DATE type is stored internally as a 3-byte integer, representing the number of days since 1 January 0001.

The hex value that you have is in little-endian format, so you'll need to flip it into big-endian before you can use it in C# DateTime calculations:

string hexString = "38320B00";

// convert the first 6 characters to bytes and combine them into an int
// we can ignore the final two characters because the DATE type is a
// 3-byte integer - the most-significant-byte should always be zero
int days = byte.Parse(hexString.Substring(0, 2), NumberStyles.HexNumber)
    | byte.Parse(hexString.Substring(2, 2), NumberStyles.HexNumber) << 8
    | byte.Parse(hexString.Substring(4, 2), NumberStyles.HexNumber) << 16;

DateTime dt = new DateTime(1, 1, 1).AddDays(days);

Console.WriteLine(dt);    // 12/12/2009 00:00:00