[[Lepe]]

No sé si incumplo alguna norma del foro o licencia de Borland, si algún moderador lo sabe, que no dude en eliminar este mensaje e informarme de ello.

El código de la vcl es:

Código Delphi [-]

const   SInvalidDayOfWeekInMonth = '(%d, %d, %d, %d) is not a valid DayOfWeekInMonth quad';

procedure DecodeDayOfWeekInMonth(const AValue: TDateTime; out AYear, AMonth,
  ANthDayOfWeek, ADayOfWeek: Word);
var
  ADay: Word;
begin
  DecodeDate(AValue, AYear, AMonth, ADay);
  ANthDayOfWeek := (ADay - 1) div 7 + 1;
  ADayOfWeek := DayOfTheWeek(AValue);
end;

function EncodeDayOfWeekInMonth(const AYear, AMonth, ANthDayOfWeek,
  ADayOfWeek: Word): TDateTime;
begin
  if not TryEncodeDayOfWeekInMonth(AYear, AMonth, ANthDayOfWeek, ADayOfWeek, Result) then
    InvalidDayOfWeekInMonthError(AYear, AMonth, ANthDayOfWeek, ADayOfWeek);
end;

function TryEncodeDayOfWeekInMonth(const AYear, AMonth,
  ANthDayOfWeek, ADayOfWeek: Word; out AValue: TDateTime): Boolean;
var
  LStartOfMonth, LDay: Word;
begin
  LStartOfMonth := DayOfTheWeek(StartOfAMonth(AYear, AMonth));
  if LStartOfMonth <= ADayOfWeek then
    LDay := (ADayOfWeek - LStartOfMonth + 1) + 7 * (ANthDayOfWeek - 1)
  else
    LDay := (7 - LStartOfMonth + 1) + ADayOfWeek + 7 * (ANthDayOfWeek - 1);
  Result := TryEncodeDate(AYear, AMonth, LDay, AValue);
end;


procedure InvalidDayOfWeekInMonthError(const AYear, AMonth, ANthDayOfWeek,
  ADayOfWeek: Word);
begin
  raise EConvertError.CreateFmt(SInvalidDayOfWeekInMonth, [AYear, AMonth,
    ANthDayOfWeek, ADayOfWeek]);
end;

Quizás esta función la tenga ya:

Código Delphi [-]
function DayOfTheWeek(const AValue: TDateTime): Word;
begin
  Result := (DateTimeToTimeStamp(AValue).Date - 1) mod 7 + 1;
end;

Saludos