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IsInLeapYear

Function IsInLeapYear(const AValue: TDateTime): Boolean

Example​

procedure ScriptEvent(var Value: variant);
var
  InputValue: TDateTime;
begin
  InputValue := EncodeDate(2024, 7, 18);
  Value := IsInLeapYear(InputValue); // True
end;

Usage​

IsInLeapYear reports whether the calendar year encoded by a TDateTime is a Gregorian leap year.

Parameters

NameTypeDescription
AValueTDateTime, constEncoded date/time whose calendar year is inspected.

Returns

True when the decoded year is a Gregorian leap year; otherwise False.

Behaviour

  • The month, day and time fields do not affect the result.
  • The operation reads the encoded calendar year; it does not convert the value through a timezone.
  • Valid pre-epoch dates are decoded by their calendar year in the same way as later dates.

Important usage notes

  • An invalid or non-finite encoded value can fail while the year is decoded rather than returning False.
  • This tests the proleptic Gregorian calendar used by Velox, not a historically varying local calendar.

Usage notes

Use the result as the documented field or date predicate only. It does not establish a timezone, business calendar or input provenance.

Additional Technical Info​

IsInLeapYear reports whether the calendar year encoded by a TDateTime is a Gregorian leap year.

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

Implementation

The DateUtils import binds directly to Delphi 37.0 System.DateUtils.IsInLeapYear. It extracts the calendar year with YearOf and passes that year to IsLeapYear, which applies the Gregorian divisible-by-4, century and divisible-by-400 rules.

Side effects

None.

Errors

There is no wrapper exception handling. Invalid or non-finite encoded values can raise during decoding or produce non-useful comparisons rather than a meaningful Boolean.

Performance and concurrency

Constant-time field decoding or comparison with no external I/O. The routine uses no shared mutable state.

Related entries

External references

Created 2026-07-15