TDateTime
│ English (en) │ suomi (fi) │
TDateTime is stored as a double, the integer part representing days and the fractional part being fraction of a day. The integer part is the number of days that have passed since December 30, 1899, and can be a negative number. The fractional part reflects the fraction of a 24-hour day without regard to the sign of the TDateTime value, so care must be taken when computing negative TDateTime values with a fractional part.
Methods exist in Sysutils (datetimeroutines) that allow reading, writing and calculating with TDateTime, converting to and from a number of formats.
The following table displays examples of TDateTime values and their corresponding dates and times:
| Double Value | 'dd-mm-yyyy hh:nn:ss' |
|---|---|
| -1.75 | 29-12-1899 18:00:00 |
| -1.5 | 29-12-1899 12:00:00 |
| -1.25 | 29-12-1899 06:00:00 |
| 0 | 30-12-1899 00:00:00 |
| 1.25 | 31-12-1899 06:00:00 |
| 2.25 | 01-01-1900 06:00:00 |
| 25569 | 01-01-1970 00:00:00 (Unix Epoch) |
| 36152.5 | 23-12-1998 12:00:00 (FPC 1.0 Beta2) |
| 36526 | 01-01-2000 00:00:00 |
| 44927 | 01-01-2023 00:00:00 |
Get current time
Unit SysUtils function Now retrieves the current system date and time.
function Now : TDateTime; Adding and subtracting TDateTime
Unit DateUtils function DaysBetween tell number of whole days between two DateTime values.
function DaysBetween ( const ToDate, FromDate : TDateTime ) : Integer; Unit DateUtils function WeeksBetween tell number of whole weeks between two DateTime values.
function WeeksBetween( const ToDate, FromDate : TDateTime ):Integer;
program DateProject1; uses SysUtils,DateUtils; const DateFormatChars = 'dd"/"mm"/"yyyy'; var DateTime1, DateTime2: TDateTime; begin DateTime1 := now; DateTime2 := DateTime1 + 4*7; //28 days later WriteLn('Current date is '+ FormatDateTime( DateFormatChars, DateTime1 )); WriteLn('28 days later date is '+ FormatDateTime( DateFormatChars, DateTime2 )); WriteLn('Number of days is '+ ( DaysBetween( DateTime1 ,DateTime2)).ToString ); WriteLn('Number of weeks is '+ ( WeeksBetween( DateTime1 ,DateTime2)).ToString ); ReadLn; end. Set Date
Unit SysUtils function EncodeDate to set the date.
function EncodeDate ( const Year, Month, Day : Word ) : TDateTime; Compare two TDateTime
program CompareTwoDateTime; uses SysUtils, DateUtils; var firstDate, secondDate: TDateTime; begin firstDate := EncodeDate(2000, 2, 29); secondDate := EncodeDate(2018, 8, 11); if DaysBetween( firstDate, secondDate) = 0 then WriteLn('Both dates are same') else if firstDate < secondDate then WriteLn('First date is earlier') else WriteLn('First date is later'); ReadLn; end. See also
- Date and time format ISO 8601
- RFC 1123 Time Format
- datetimeroutines in the
sysUtilsunit
