How to store a TDateTime in the Registry

Converting it to a string and then back is not always satisfactory as people can change their date and time formats and we do not want to impose any restrictions on the software. TDateTime is a float, so we can store it as a binary value.

~~~~~~~~~~~~~~~~~~~~~~~~~
program DateRegistry;

uses
   Windows,
   Dialogs,
   Registry,
   SysUtils;


{$R *.RES}

procedure SaveDate
  (const sKey: string;
   const sField: string;
   aDate: TDateTime) ;
begin
   with TRegistry.Create do
   begin
     RootKey := HKEY_CURRENT_USER;
     if OpenKey(sKey, True) then
     begin
       WriteBinaryData(sField, aDate, SizeOf(aDate)) ;
       CloseKey;
     end;
     Free;
   end;
end;

function ReadDate
   (const sKey: string;
    const sField: string) : TDateTime;
begin
   // default: return 0
   Result := 0;

   with TRegistry.Create do
   begin
     RootKey := HKEY_CURRENT_USER;
     if OpenKey(sKey, False) then
     begin
       try
         ReadBinaryData(sField, Result, SizeOf(Result)) ;
       except
       end;
       CloseKey;
     end;
     Free;
   end;
end;

var
   dDate: TDateTime;

begin
   // save the date
   SaveDate('\DateTimeDemo', 'LastDate', Now) ;

   // retrieve it
   dDate := ReadDate('\DateTimeDemo', 'LastDate') ;

   // show it
   ShowMessage(DateTimeToStr(dDate)) ;
end.
~~~~~~~~~~~~~~~~~~~~~~~~~

Delphi tips navigator:
» How to Convert a String of Integers into an Array of Byte
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