how to get the file size?

2 things that in some cases produce "logical" errors and are probably among the hardest bugs to track down.

one addition to kiranmahales code:
- since filemode is a global variable, you might want to save initial value and restore it otherwise you might encounter issues later on in your project (happened to me)

one addition to lokis code:
- flags are usually ORed not +ed. even though at first sign adding them get the same result, one might wrongfully use addition out of habbit in a case where this is not happening (for example when the flag is already defined, the value is not known precisely, but another flag must be made available)
in this particular case, it's ok to use addition, but keep in mind not to get use to it and better use ORing just to be on the safe side

Hi,

Both examples above open the file. The following is another example:

function GetFileSize(const strFile: string): Int64;
var
  h: THandle;
  FindData:TWin32FindData;
begin
  result := 0;
  h := windows.FindFirstFile(PChar(strFile), FindData);
  if (h > 0) then begin
    // File found.
    result := (Int64(FindData.nFileSizeHigh) shl 32) + FindData.nFileSizeLow;
  end;
  windows.FindClose(h);
end;

Regards, Geo

if youre pointing to files on NTFS volumes there are differences between the logical filesize and the filesize it really needs on the disk (this can vary due to compression or sparsing)

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;

You can use GetFileAttributesEx
http://windowssdk.msdn.microsoft.com/en-us/library/ms685877.aspx

Advandages:
*) It does not open the file
*) It does not traverse a directory to find the file
*) It returns 2 DWORDS for the file size, so it supports files larger than 4 Gb.

> *) It does not traverse a directory to find the file

Not really. It does. The code in my comment above also gets the same type of structure - 2 DWORDs - and makes one Int64 as a result.

> *) Not really. It does.

Where do you base that?
It's a native function (on >=98, >=2000), not an emulation...
And event if it does this internally, everything in inside kernel32.dll, no ring switching for each file => greater speed.

Function GetMyNewFileSize(fnm: string): Int64;
var
  srec:   TSearchRec;
begin
  // resolves file size to 64bits instead of just 32bits (as some other methods)
  // AND (on my computer) it is more than twice as fast as methods which cause the file to be opened

  result:=0;

  if SysUtils.FindFirst(fnm,faAnyFile-faDirectory-faVolumeID,srec)=0 then
    begin
      result:=Int64((srec.FindData.nFileSizeHigh shl 32)+srec.FindData.nFileSizeLow);
      SysUtils.FindClose(srec);
    end;
end;

David_Ward: test your code against the one from geobul (08/30/2006 08:16AM CEST), i bet the pure API call is the fastest one instead using long routes out of delphis sysutil...