EncodeDateWeek

Function EncodeDateWeek(const AYear, AWeekOfYear: Word;
  const ADayOfWeek: Word): TDateTime

Example

procedure ScriptEvent(var Value: variant);
begin
  // Monday of ISO week 1 in 2026 is 29 December 2025.
  Value := EncodeDateWeek(2026, 1, 1);
end;

Usage

EncodeDateWeek encodes an ISO week-numbering year, week and Monday-based weekday as a midnight TDateTime value.

Parameters

Name	Type	Description
AYear	Word, const	ISO week-numbering year 1..9999, which can differ from the result's calendar year near New Year.
AWeekOfYear	Word, const	ISO week 1..52, or 1..53 for an ISO year that contains week 53.
ADayOfWeek	Word, const	Monday 1 through Sunday 7. The script declaration requires this argument.

Returns

The selected ISO weekday at 00:00:00.000 as a TDateTime.

Errors

An invalid year, unavailable week number or weekday outside 1..7 raises EConvertError.

Additional Technical Info

EncodeDateWeek converts ISO 8601 week-date fields to a calendar date. ISO weeks begin on Monday; week 1 is the week containing the year's first Thursday, so a result can lie in the preceding or following calendar year.

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

Implementation

The DateUtils import binds directly to Delphi 37.0 System.DateUtils.EncodeDateWeek. Validation calls WeeksInAYear and checks the weekday. The implementation encodes 1 January of AYear, obtains its ISO weekday, then adds an offset for the requested week/day adjusted by whether the year's opening days belong to the previous ISO year.

Edge cases and quirks

• AYear is an ISO week year, not necessarily the calendar year returned. Early January can belong to the prior ISO year; late December can belong to the next one.
• Week 53 is valid only when that ISO year actually has 53 weeks.
• Unlike the underlying Delphi declaration's default weekday of Monday, the generated Velox script declaration exposes no default; supply ADayOfWeek explicitly.
• Weekdays use Monday 1, unlike DayOfWeek, which uses Sunday 1.
• The returned value is timezone-neutral and at midnight.

Side effects

None.

Performance and concurrency

Constant bounded calendar arithmetic with no allocation or shared state.

Related entries

• DecodeDateWeek converts a date back to ISO week fields.
• DayOfTheWeek uses the same Monday-based weekday numbering.

External references

• Embarcadero System.DateUtils.EncodeDateWeek
• Free Pascal EncodeDateWeek - the public Free Pascal page also lists a two-argument overload; Velox exposes only the explicit three-argument declaration.

Created 2026-07-15