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StartOfTheWeek

Function StartOfTheWeek( const AValue : TDateTime) : TDateTime

Example​

procedure ScriptEvent(var Value: variant);
var
  InputValue: TDateTime;
begin
  InputValue := EncodeDateTime(2026, 7, 16, 14, 30, 5, 125); // Thursday
  Value := StartOfTheWeek(InputValue); // Monday 13 July 2026
end;

Usage​

StartOfTheWeek returns midnight on Monday of the supplied value's ISO week.

Parameters

NameTypeDescription
AValueTDateTime, constValue whose Monday-based week boundary is required.

Returns

The encoded date of the containing week's Monday at 00:00:00.000.

Behaviour

  • Monday values return their own date at midnight.
  • Tuesday through Sunday move back one through six whole encoded days.
  • The result can fall in a different calendar month or year.
  • No timezone or daylight-saving rules are applied.

Errors

Core conversion errors propagate.

Usage notes

Use StartOfAWeek when ISO year/week/weekday numbers are already known.

Additional Technical Info​

StartOfTheWeek returns encoded midnight on the Monday that begins the ISO week containing AValue.

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

Implementation

The DateUtils import binds to System.DateUtils.StartOfTheWeek. Delphi calculates Trunc(AValue) - (DayOfTheWeek(AValue) - 1). DayOfTheWeek obtains a Monday-one value from Delphi's timestamp date.

Edge cases and quirks

  • The function uses ISO Monday as the first day regardless of Windows/user locale week-start preferences.
  • It returns an encoded field boundary, not necessarily the UTC instant at which a local timezone's Monday began.
  • Invalid raw input can fail in truncation/timestamp conversion.
  • Free Pascal documents the same Monday-based boundary.

Side effects

None.

Performance and concurrency

Constant-time timestamp/date arithmetic with no I/O or shared state.

Related entries

External references

Created 2026-07-15