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, date/time values are stored as a packed 32-bit integer, which you can retrieve by casting a DosDateTime value to an unsigned 32-bit integer:
// Retrieve the packed integer form of a DOS date/time.
var packedDateTime = (DosDateTime)dosDateTime;
To create a DosDateTime you use the constructor in either of two ways. First, if you already have a DOS date/time as a packed 32-bit integer, you can use this integer when creating the DosDateTime:
// Create DosDateTime from packed integer.
var dosDateTime = new DosDateTime(0x28217DA5);
Alternately, you can create a DosDateTime using the components of the date and time:
// Create DosDateTime from the date and time components.
var dosDateTime = new DosDateTime(1984, 2, 29, 12, 30, 0);
The second form can also be used to create a DosDateTime with just the date components if you don’t have a time.
With a DosDateTime value, you can convert it to standard .Net date and time types.
var dosDateTime = new DosDateTime(0x85D63C0);
// Convert DosDateTime to date object.
var dosDateTimeDateOnly = dosDateTime.ToDateOnly();
// Convert DosDateTime to date & time object.
var dosDateTimeDateTime = dosDateTime.ToDateTime();
// Convert DosDateTime to time object.
var dosDateTimeTimeOnly = dosDateTime.ToTimeOnly();
Conversions can also go the other way. Starting with a .Net date or time object, you can create the DosDateTime equivalent:
var myDate = new DateOnly(1999, 12, 31);
// Convert to DosDateTime.
var dosDateTime = myDate.ToDosDateTime();
As DosDateTime implements the ISystemTime interface, you can wrap it in the SystemTimeWithGregorianCalendar decorator to add date & time conversion information. This wrapper adds properties for Year, Month, Day, Hour, Minute, and Second. A wrapped DosDateTime can then be used interchangeably with the original value as both have the ISystemTime interface. If you have a decorated DosDateTime value, you can still get back the original value like so:
// Getting back original date/time.
var dosDateTime = decoratedDosDateTime.AsDosDateTime();