System.FilePos Function

Returns the current file position.

Pascal

function FilePos(var F): Longint;

C++

Longint FilePos( F);

File

System

Description

In Delphi code, use FilePos on the file variable of an open file to determine the current position in the file. If the current position in the file is at the very beginning, FilePos returns 0. Otherwise, FilePos returns the byte offset from the beginning of the current position.

FilePos will not work on a file that is not open.

Note: {$I+} handles runtime errors using exceptions. When using {$I-}, use IOResult to check for I/O errors.

Delphi Examples:

Copy Code

{
FileSize, Seek, FilePos example
This example displays a open dialog when the user clicks a button. When the user selects the file, it reports the size of the file, seeks to halfway through the file, and reports the file position at that point.
Note:   This example assumes the compiler flag $IOCHECKS ON ($I+). That is, it expects errors to generate exceptions rather than checking IOResult to be sure that I/O routines succeed.
} 
procedure TForm1.Button1Click(Sender: TObject);
var
   f: file of Byte;
   size: Longint;
   S: string;
   y: Integer;
begin
  if OpenDialog1.Execute then
  begin
    AssignFile(f, OpenDialog1.FileName);
    Reset(f);
    try
      size := FileSize(f);
      S := 'File size in bytes: ' + IntToStr(size);
      y := 10;
      Canvas.TextOut(5, y, S);
      y := y + Canvas.TextHeight(S) + 5;
      S := 'Seeking halfway into file...';
      Canvas.TextOut(5, y, S);
      y := y + Canvas.TextHeight(S) + 5;
      Seek(f, size div 2);
      S := 'Position is now ' + IntToStr(FilePos(f));
      Canvas.TextOut(5, y, S);
    finally
      CloseFile(f);
    end;
  end;
end;