gistfile1.pas

function TxtFileRecCount(const Filename: string): integer;
var
  FS : TFileStream;
  buffer : string;
  red, i : integer;
begin
  result := 0;

  if FileExists(Filename) then begin
    SetLength(buffer, $FFFF);
    FS := TFileStream.Create(Filename, fmOpenRead or fmShareDenyNone);
    try
      red := FS.Read(buffer[1], $FFFF);
      while red > 0 do begin
        if red < $FFFF then
          SetLength(buffer, red);

        for i := 1 to red do
          if buffer[i] = #10 then
            Inc(result);

        if red = $FFFF then
          red := FS.Read(buffer[1], $FFFF)
        else
          red := 0;
      end;
    finally
      FS.Free;
    end;
  end;
end;