TryEncodeDate

function TryEncodeDate(Year, Month, Day: Word;
  var Date: TDateTime): Boolean;

Example

procedure ScriptEvent(var Value: variant);
var
  EncodedDate: TDateTime;
begin
  if TryEncodeDate(2028, 2, 29, EncodedDate) then
    Value := EncodedDate
  else
    Value := 0;
end;

Usage

TryEncodeDate validates Gregorian year, month and day fields and assigns their midnight date only on success.

Parameters

Name	Type	Description
Year	Word	Gregorian year 1..9999.
Month	Word	Month 1..12.
Day	Word	One-based day valid for the supplied month and year.
Date	TDateTime, var	Receives the encoded midnight only when the function succeeds.

Returns

True when all fields form an encodable date; otherwise False.

Behaviour

• Successful output is at 00:00:00.000.
• Leap-year rules include the Gregorian century exception: 2000 is a leap year; 2100 is not.
• Validation is combination-aware, so 31 April and 29 February in a common year return False.

Errors

Expected field-range failures return False. Unexpected Velox errors can still raise instead of returning False.

Additional Technical Info

TryEncodeDate validates a Gregorian year, month and day and, on success, writes the corresponding midnight TDateTime. It reports invalid input with False instead of raising the normal date-encoding conversion exception.

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

Implementation

The modified PascalScript runtime registers a Velox adapter with the exact script signature above. That adapter delegates directly to installed Delphi 37.0 System.SysUtils.TryEncodeDate. The terminal selects the normal/leap-year month table, checks all ranges, accumulates preceding month lengths and converts the Gregorian ordinal to Delphi's day number.

Edge cases and quirks

• The script exposes Date as var, while the installed terminal declares an out parameter. For this unmanaged numeric type the terminal assigns it only on success. Treat its previous value as unchanged but not useful when the result is False; always branch on the Boolean.
• Fields are not normalised or carried. Month 13 and day 0 fail.
• The output has no timezone meaning. It is simply a Gregorian date at encoded midnight.
• Unlike EncodeDate, invalid fields do not raise EConvertError through this normal path.

Side effects

Writes Date only on success. No global state or I/O is used.

Performance and concurrency

Constant bounded calendar arithmetic with no allocation or shared mutable state.

Related entries

• EncodeDate raises when the same fields are invalid.
• TryEncodeDateTime combines date and millisecond time validation.
• IsValidDate validates without producing an output value.

External references

• Embarcadero System.SysUtils.TryEncodeDate
• Free Pascal TryEncodeDate

Created 2026-07-15