DecodeTime

procedure DecodeTime(const DateTime: TDateTime;
  var Hour, Min, Sec, MSec: Word);

Example

procedure ScriptEvent(var Value: variant);
var
  HourValue, MinuteValue, SecondValue, MilliSecondValue: Word;
begin
  DecodeTime(EncodeTime(14, 30, 45, 125),
    HourValue, MinuteValue, SecondValue, MilliSecondValue);
  // Outputs: 14, 30, 45, 125
  Value := MilliSecondValue;
end;

Usage

DecodeTime writes the hour, minute, second and millisecond time-of-day components of a TDateTime value.

Parameters

Name	Type	Description
DateTime	TDateTime, const	Encoded value whose time-of-day is decoded.
Hour	Word, var	Overwritten with 0..23.
Min	Word, var	Overwritten with 0..59.
Sec	Word, var	Overwritten with 0..59.
MSec	Word, var	Overwritten with 0..999.

Behaviour

All four output variables are overwritten. Date-only values return four zeros. Any calendar date combined with the same time returns the same outputs.

Errors

Valid finite values do not raise. Unsupported non-finite/overflowing numeric values can propagate timestamp-conversion errors.

Additional Technical Info

DecodeTime decomposes a TDateTime value's time of day into hour, minute, second and millisecond outputs. The calendar date is ignored.

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

Implementation

The modified PascalScript runtime registers directly to Delphi 37.0 System.SysUtils.DecodeTime. The RTL converts the value to TTimeStamp, takes its integer millisecond-of-day field, then uses division/remainder operations to split it into minutes/milliseconds and hours/minutes/seconds.

Edge cases and quirks

• Effective precision is one millisecond. Smaller differences in the underlying Double are rounded/normalised by timestamp conversion and cannot appear in the outputs.
• Negative pre-epoch TDateTime values use Delphi's magnitude-based fractional-time convention; timestamp conversion extracts that intended time of day rather than returning negative fields.
• The procedure performs no timezone conversion. It reports whatever wall-clock fields are encoded in the number.
• The script declaration uses var, while Free Pascal documentation may show out. Incoming output-variable values do not affect the result.
• A zero input is both a valid date epoch at midnight and a time-only midnight; all time outputs are zero in either interpretation.

Side effects

Only the four output variables are changed.

Performance and concurrency

Constant-time integer division/remainder operations with no allocation or shared state.

Related entries

• DecodeDate returns calendar components.
• DecodeDateTime writes all seven date/time outputs.
• CompareTime compares times through the same millisecond-scale model.

External references

• Embarcadero System.SysUtils.DecodeTime - documents the exact Delphi routine.
• Free Pascal DecodeTime - documents the compatible decomposition and parameter-mode difference.

Created 2026-07-15