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StartOfTheMonth

Function StartOfTheMonth( const AValue : TDateTime) : TDateTime

Example​

procedure ScriptEvent(var Value: variant);
var
  InputValue: TDateTime;
begin
  InputValue := EncodeDateTime(2026, 7, 16, 14, 30, 5, 125);
  Value := StartOfTheMonth(InputValue); // 1 July 2026 00:00:00.000
end;

Usage​

StartOfTheMonth returns midnight on the first day of the supplied value's encoded calendar month.

Parameters

NameTypeDescription
AValueTDateTime, constValue that supplies the calendar year and month.

Returns

An encoded TDateTime for the first day of the decoded month at midnight.

Behaviour

  • All clock fields and the original day-of-month are discarded.
  • Calendar month/year fields are decoded correctly for valid pre-epoch values.
  • No timezone or locale operation is performed.
  • Reapplying the function is idempotent.

Errors

Decode or encode exceptions propagate unchanged.

Usage notes

Use StartOfAMonth when the year and month are supplied independently.

Additional Technical Info​

StartOfTheMonth returns midnight on day one of the calendar month encoded by 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.StartOfTheMonth. Delphi decodes year, month and day from AValue, discards the original day, then calls EncodeDate(decodedYear, decodedMonth, 1).

Edge cases and quirks

  • The boundary is encoded calendar midnight, not a timezone-aware instant.
  • Invalid or non-finite raw input can raise while decoding.
  • Free Pascal describes the compatible calendar boundary; installed Delphi's decode/encode chain governs Velox.

Side effects

None.

Performance and concurrency

Constant-time field decoding and date encoding with no I/O.

Related entries

External references

Created 2026-07-15