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SameDateTime

Function SameDateTime( const A, B : TDateTime) : Boolean

Example​

procedure ScriptEvent(var Value: variant);
var
  LeftValue, RightValue: TDateTime;
begin
  LeftValue := EncodeDateTime(2026, 7, 16, 8, 30, 15, 125);
  RightValue := EncodeDateTime(2026, 7, 16, 8, 30, 15, 125);
  Value := SameDateTime(LeftValue, RightValue); // True
end;

Usage​

SameDateTime reports whether two values normalise to the same millisecond date/time timestamp.

Parameters

NameTypeDescription
ATDateTime, constFirst date/time value.
BTDateTime, constSecond date/time value.

Returns

True when both converted timestamps have the same date integer and the same millisecond-of-day integer; otherwise False.

Behaviour

  • The comparison is symmetric and includes year, month, day, hour, minute, second and millisecond.
  • Numerically different floating values can compare equal when they convert to the same millisecond timestamp.
  • Values one encoded millisecond apart compare unequal.
  • No timezone conversion occurs; the values are compared exactly as encoded.

Errors

No exception is expected for valid finite TDateTime values. Any core conversion exception propagates unchanged.

Usage notes

Use this routine for encoded field equality. It does not establish that two separately tagged timezone values represent the same UTC instant because TDateTime contains no timezone tag.

Additional Technical Info​

SameDateTime compares two values after converting each to Delphi's integer date/time timestamp representation. Date and time must match at millisecond resolution.

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

Implementation

The DateUtils import binds to Delphi 37.0 System.DateUtils.SameDateTime. It calls DateTimeToTimeStamp for each argument and compares both TTimeStamp.Date and TTimeStamp.Time. The conversion handles Delphi's pre-epoch sign representation and maps the floating value to millisecond fields.

Edge cases and quirks

  • This is millisecond equivalence, not bitwise Double equality and not an arbitrary floating tolerance.
  • Sub-millisecond differences that map to the same timestamp are intentionally ignored.
  • The timestamp conversion makes valid pre-epoch and cross-epoch values comparable by their encoded date/time fields.
  • Free Pascal exposes the same API but documents its comparison via CompareDateTime; installed Delphi's direct timestamp comparison is the Velox terminal.
  • Invalid or non-finite raw values can fail during timestamp conversion rather than returning a defined Boolean.

Side effects

None.

Performance and concurrency

Constant-time conversion of two values and integer comparison. No I/O, allocation of long-lived resources or shared mutable state.

Related entries

External references

Created 2026-07-15