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function
 Get_File_Size1(sFileToExamine: string
; bInKBytes: Boolean): string
;
 { 
 for some reason both methods of finding file size return 
 a filesize that is slightly larger than what Windows File 
 Explorer reports 
}
 var

   FileHandle: THandle;
   FileSize: LongWord;
   d1: Double;
   i1: Int64;
 begin

   //a- Get file size 
  FileHandle := CreateFile(PChar(sFileToExamine),
     GENERIC_READ,
     0, {exclusive}
     nil
, {security}
     OPEN_EXISTING,
     FILE_ATTRIBUTE_NORMAL,
     0);
   FileSize   := GetFileSize(FileHandle, nil
);
   Result     := IntToStr(FileSize);
   CloseHandle(FileHandle);
   //a- optionally report back in Kbytes 
  if
 bInKbytes = True then

   begin

     if
 Length(Result) > 3 then

     begin

       Insert('.', Result, Length(Result) - 2);
       d1     := StrToFloat(Result);
       Result := IntToStr(round(d1)) + 'KB';
     end

     else

       Result := '1KB';
   end
;
 end
;

 {****************************************************************************** 
Thanks to Advanced Delphi Systems here's another method which works just as 
well returning the same results 
*******************************************************************************}
 function
 Get_File_Size2(sFileToExamine: string
; bInKBytes: Boolean): string
;
 var

   SearchRec: TSearchRec;
   sgPath: string
;
   inRetval, I1: Integer;
 begin

   sgPath := ExpandFileName(sFileToExamine);
   try

     inRetval := FindFirst(ExpandFileName(sFileToExamine), faAnyFile, SearchRec);
     if
 inRetval = 0 then

       I1 := SearchRec.Size
     else

       I1 := -1;
   finally

     SysUtils.FindClose(SearchRec);
   end
;
   Result := IntToStr(I1);
 end
;



 procedure
 TForm1.Button1Click(Sender: TObject);
 begin

   if
 OpenDialog1.Execute then

     label1.Caption := Get_File_Size(Opendialog1.FileName, True);
 end
;

 {*******************************************************************************}

 function
 Get_File_Size3(const
 FileName: string
): TULargeInteger;
 // by nico 
var

   Find: THandle;
   Data: TWin32FindData;
 begin

   Result.QuadPart := -1;
   Find := FindFirstFile(PChar(FileName), Data);
   if
 (Find <> INVALID_HANDLE_VALUE) then

   begin

     Result.LowPart  := Data.nFileSizeLow;
     Result.HighPart := Data.nFileSizeHigh;
     Windows.FindClose(Find);
   end
;
 end
;

 procedure
 TForm1.Button1Click(Sender: TObject);
 begin

   if
 (OpenDialog1.Execute) then

     ShowMessage(IntToStr(Get_File_Size3(OpenDialog1.FileName).QuadPart));
 end
;

 {*******************************************************************************}

 function
 Get_File_Size4(const
 S: string
): Int64;
 var

   FD: TWin32FindData;
   FH: THandle;
 begin

   FH := FindFirstFile(PChar(S), FD);
   if
 FH = INVALID_HANDLE_VALUE then
 Result := 0
   else

     try

       Result := FD.nFileSizeHigh;
       Result := Result shl
 32;
       Result := Result + FD.nFileSizeLow;
     finally

       CloseHandle(FH);
     end
;
 end
;

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