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StartOfTheDay

Function StartOfTheDay( const AValue : TDateTime) : TDateTime

Example​

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

Usage​

StartOfTheDay returns the encoded date at midnight by truncating the supplied TDateTime.

Parameters

NameTypeDescription
AValueTDateTime, constValue whose time portion is removed.

Returns

Trunc(AValue) as a TDateTime, representing midnight on the encoded date for valid values.

Behaviour

  • Hour, minute, second and millisecond information is discarded.
  • Ordinary valid pre-epoch values truncate to their encoded midnight integer.
  • No calendar lookup, timezone conversion or clock read occurs.
  • Reapplying the function to its result is idempotent.

Errors

No exception is expected for valid finite values. Core floating conversion behaviour applies to invalid values.

Usage notes

Use this for an inclusive encoded lower boundary. EndOfTheDay returns 23:59:59.999, not an exclusive next-day boundary.

Additional Technical Info​

StartOfTheDay removes the encoded time portion and returns midnight on the same encoded date.

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

Implementation

The DateUtils import calls System.DateUtils.StartOfTheDay. The installed function consists of one raw Trunc(AValue) operation; it does not decode or re-encode the fields.

Edge cases and quirks

  • This is raw floating-point truncation towards zero, relying on Delphi's TDateTime representation.
  • The routine does not validate the raw value; arbitrary non-finite values are outside its supported contract.
  • A timezone-aware concept of “day start” may differ because the encoded value has no zone or daylight-saving rules.
  • Free Pascal provides the same-name operation; current Delphi source defines the exact Velox terminal.

Side effects

None.

Performance and concurrency

Constant-time truncation with no allocation, I/O or shared state.

Related entries

  • EndOfTheDay returns the day's final encoded millisecond.
  • DateOf uses the same raw date-part operation.

External references

Created 2026-07-15