Inverse function of FormatDateTime

Question

I am looking for a function to reverse any string (YYYYMDD,YY/MM/DD,YYMMDD,...) created by the function FormatDateTime to datetime.

example

I have a string-date in format YYYYMMDDcreated by FormatDateTime

mydatestr:=FormatDateTime('YYYYMMDD',Mydate); 

now how I can convert mydatestr to DateTime again?

UPDATE

these functions

function StrToDate(const S: string): TDateTime; overload;
function StrToDate(const S: string;
  const FormatSettings: TFormatSettings): TDateTime; overload;

function StrToDateTime(const S: string): TDateTime; overload;
function StrToDateTime(const S: string;
  const FormatSettings: TFormatSettings): TDateTime; overload;

do not support passing a string with the format to convert.

I am looking something like this

Mydatetime:=InvFormatDatetime('20091225','yyyymmdd');

or

Mydatetime:=InvFormatDatetime('20090108','yyyyddmm');

Answer 1

It is quite easy with existing solution, StrToDateFmt function in rxDateutil.pas unit from RX package, which can be downloaded here: http://sourceforge.net/projects/rxlib/

EDIT:

Mentioned above function and StrToDateFmt from rxDateutil.pas are doing exactly what you expect, converting string to datetime using specified string mask, the code is too large to be included as this unit contains also other date functions, some of them required for converting string to date.

Example of use:

Result := StrToDateFmtDef('MM/DD/YYYY', '11/11/2011', Now);