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EncodeDateMonthWeek

Function EncodeDateMonthWeek(const AYear, AMonth, AWeekOfMonth,
  ADayOfWeek: Word): TDateTime

Example​

procedure ScriptEvent(var Value: variant);
begin
  // Week 1 of July 2026 starts on Monday 29 June.
  Value := EncodeDateMonthWeek(2026, 7, 1, 1);
end;

Usage​

EncodeDateMonthWeek encodes an ISO month-week year, owning month, week number and Monday-based weekday as a midnight TDateTime.

Parameters

NameTypeDescription
AYearWord, constOwning calendar year 1..9999.
AMonthWord, constOwning month 1..12.
AWeekOfMonthWord, constISO month-week number 1..5.
ADayOfWeekWord, constISO weekday: Monday 1 through Sunday 7.

Returns

The selected weekday at midnight. The returned calendar month may differ from AMonth where the partial days at a month edge belong to its first or last ISO month week.

Errors

An invalid year, month, week number or weekday raises EConvertError. The exception propagates into the script.

Additional Technical Info​

EncodeDateMonthWeek converts ISO-style month-week fields into a date. A month week starts on Monday, and week 1 is the first week containing at least four days of the named month. Consequently, the result can fall in an adjacent calendar month.

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.EncodeDateMonthWeek. Validation checks only the broad year/month/week/weekday ranges. The implementation encodes the first of AMonth, finds its Monday-based weekday, calculates an offset from (AWeekOfMonth - 1) * 7 + ADayOfWeek - 1, then shifts that offset according to the ISO four-day ownership rule.

Edge cases and quirks

  • AWeekOfMonth describes ISO month ownership, not the simple ordinal occurrence used by EncodeDayOfWeekInMonth.
  • The first week can start in the previous month. Likewise, a Monday, Tuesday or Wednesday at the end of a month can belong to week 1 of the following month.
  • Broad validation permits every combination of week 1..5 and weekday 1..7. The calculated date is not required to remain inside AMonth; that is part of this function's design.
  • The script exposes all four parameters and no defaults.
  • The result has millisecond value zero and carries no timezone.
  • Free Pascal offers a compatible routine, but dialect-specific validation and edge calculation should not be assumed identical beyond the documented contract.

Side effects

None.

Performance and concurrency

Constant bounded calendar arithmetic with no allocation or shared state.

Related entries

External references

Created 2026-07-15