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DayOf

Function DayOf(const AValue: TDateTime): Word

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := DayOf(EncodeDate(2026, 7, 18)); // 18
end;

Usage​

DayOf returns the day-of-month component of a TDateTime value in the range 1 through 31.

Parameters

NameTypeDescription
AValueTDateTime, constDate/time value whose day-of-month is required. Time and timezone meaning do not affect the component.

Returns

A Word from 1 to 31 for a valid date.

Behaviour

The date portion alone determines the result. Leap years and month lengths matter to the validity of the original date, but no separate month-length calculation is performed here.

Errors

Valid TDateTime values do not raise. Unsupported non-finite or out-of-domain values are not validated by the binding.

Additional Technical Info​

DayOf extracts the calendar day within the month from a TDateTime. For a valid Delphi date, the result is between 1 and 31.

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

Implementation

The DateUtils import binds directly to Delphi 37.0 System.DateUtils.DayOf. It calls System.SysUtils.DecodeDate(AValue, Year, Month, Result) and discards the decoded year and month.

Edge cases and quirks

  • DayOfTheMonth is an exact wrapper around DayOf in the installed Delphi source; it does not use a different ordinal convention.
  • Raw TDateTime values before Delphi's supported year 1 boundary cause DecodeDate to return zero components. In that unsupported case this function can return 0, outside the documented valid range, rather than raising locally.
  • The value 0.0 is valid and represents 30 December 1899, so DayOf(0.0) returns 30.
  • No timezone conversion occurs. A UTC and local value with different encoded dates can return different components.

Side effects

None.

Performance and concurrency

Constant-time calendar decoding with no allocation or shared state.

Related entries

External references

Created 2026-07-15