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DecodeDate

procedure DecodeDate(const DateTime: TDateTime; var Year, Month, Day: Word);

Example​

procedure ScriptEvent(var Value: variant);
var
  YearValue, MonthValue, DayValue: Word;
begin
  DecodeDate(EncodeDate(2026, 7, 18), YearValue, MonthValue, DayValue);
  Value := YearValue * 10000 + MonthValue * 100 + DayValue; // 20260718
end;

Usage​

DecodeDate writes the calendar year, month and day components of a TDateTime value to caller variables.

Parameters

NameTypeDescription
DateTimeTDateTime, constEncoded value to decode. Its time component is ignored for the date outputs.
YearWord, varOverwritten with the Gregorian year for a valid value.
MonthWord, varOverwritten with 1..12 for a valid value.
DayWord, varOverwritten with 1..31 as permitted by the decoded month/year.

Behaviour

The output is based entirely on the encoded calendar date. The procedure does not return a success flag and does not preserve previous output values.

Errors

Valid values do not raise. Unsupported non-finite or overflowing timestamp inputs have no function validation; any RTL numeric exception propagates.

Additional Technical Info​

DecodeDate decomposes the calendar portion of a TDateTime into separate year, month and day outputs. All three caller variables are overwritten.

The example is fictional, deterministic and source-reviewed. It was not executed by the documentation workflow.

Implementation

The modified PascalScript runtime registers the procedure directly to Delphi 37.0 System.SysUtils.DecodeDate. It calls the RTL's DecodeDateFully, discarding that helper's day-of-week result. DecodeDateFully converts the value to a Delphi timestamp, splits its day count across 400-, 100-, four- and one-year Gregorian cycles, then walks the common/leap month table.

Edge cases and quirks

  • A negative TDateTime does not automatically mean an invalid/BC date. Ordinary dates before the 1899 epoch are valid and decode normally under Delphi's negative representation.
  • When the converted timestamp date is before 1 January of year 1, Delphi writes 0 to all three outputs and returns no error flag. The first supported day itself decodes normally. Callers processing arbitrary raw numeric values must check for Year = 0.
  • A valid 0.0 value decodes to 1899, 12, 30; it is not failure.
  • The script declaration uses var, while current Delphi/FPC documentation may show out in some generated signatures. In this binding all outputs are written, so their incoming values have no meaning.
  • No timezone conversion occurs before decoding.

Side effects

Only the three caller variables are changed.

Performance and concurrency

Constant bounded calendar arithmetic/table scanning, no allocation or shared state. Separate caller variables are safe in concurrent executions.

Related entries

External references

Created 2026-07-15