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IsValidDateDay

Function IsValidDateDay(const AYear, ADayOfYear: Word): Boolean

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := IsValidDateDay(2024, 366); // True
end;

Usage​

IsValidDateDay validates a year and one-based ordinal day against that Gregorian year's length.

Parameters

NameTypeDescription
AYearWord, constGregorian year; valid range 1 through 9999.
ADayOfYearWord, constOne-based ordinal day to validate.

Returns

True for ordinal days 1–365 in a common year or 1–366 in a leap year, provided the year is 1–9999.

Behaviour

  • Day 1 is the first day of the year; there is no day zero.
  • Day 366 is accepted only in a Gregorian leap year.
  • No conversion or normalisation is attempted.

Important usage notes

  • The Word parameter excludes negative values but still permits values far above 366; those return False.
  • Validation uses a proleptic Gregorian year, not a historical regional 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​

IsValidDateDay validates a year and one-based ordinal day against that Gregorian year's length.

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.IsValidDateDay. It verifies the supported year range and checks ADayOfYear from 1 through DaysInAYear(AYear).

Side effects

None.

Errors

There is no wrapper exception handling. Ordinary out-of-range Word fields return False rather than raising.

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