Use DOS date/time

Date & time values for the MS-DOS operating system are a pair of packed 16-bit integers representing the date and time of an event — typically a change to an object in the file system. Valid values range from 1 January 1980 to 31 December 2107. You can read more about the format in Microsoft’s documentation.

DOS date/time values are represented by the DosDateTime type. Internally the value is stored as a packed 32-bit integer, which you can retrieve by casting a DosDateTime to an unsigned 32-bit integer:

// Retrieve the packed integer form of a DOS date/time.
var packedDateTime = (uint)dosDateTime;

Create a DosDateTime

You can construct a DosDateTime in either of two ways. If you already have a packed 32-bit integer, pass it to the constructor:

// Create DosDateTime from a packed integer.
var dosDateTime = new DosDateTime(0x28217DA5);

Alternatively, construct it from the individual date and time components:

// Create DosDateTime from date and time components.
var dosDateTime = new DosDateTime(1984, 2, 29, 12, 30, 0);

The component constructor also has a date-only form for when you have no time:

// Create DosDateTime from date components only.
var dosDate = new DosDateTime(1984, 2, 29);

Component values are validated. Year must be 1980–2107, month 1–12, day 1–31, hour 0–23, and minute and second 0–59; out-of-range values throw ArgumentOutOfRangeException.

Convert to and from standard .NET types

var dosDateTime = new DosDateTime(0x85D63C0);

// Convert DosDateTime to a date object.
var dosDateTimeDateOnly = dosDateTime.ToDateOnly();

// Convert DosDateTime to a date & time object.
var dosDateTimeDateTime = dosDateTime.ToDateTime();

// Convert DosDateTime to a time object.
var dosDateTimeTimeOnly = dosDateTime.ToTimeOnly();

Conversions also go the other way:

var myDate = new DateOnly(1999, 12, 31);

// Convert to DosDateTime.
var dosDateTime = myDate.ToDosDateTime();

Add date & time semantics

Because DosDateTime implements ISystemTime, you can wrap it in a SystemTimeWithGregorianCalendar decorator to expose Year, Month, Day, Hour, Minute, and Second properties. A wrapped value can be used interchangeably with the original, and you can get the original back:

// Getting back the original date/time.
var dosDateTime = decoratedDosDateTime.AsDosDateTime();

See The system-time model for how the decorator fits together.