procedure TFrm_main.writelog(str: string);
var
  F: TextFile;
  S,FilePath: String;
  qFileStream:   TFileStream;
begin
  FilePath := ExtractFilePath(ParamStr(0)) +'logfile.ini';
  If  not FileExists(FilePath)   then
  begin
    qFileStream   :=   TFileStream.Create(FilePath,   fmCreate);//这里用打开写方式。可设其他常量值看帮助。
    qFileStream.Seek(0,   sofromEnd);
    qFileStream.Free;
  end;
  AssignFile(F,   FilePath);
  Append (F);
  Writeln(F,str);
  CloseFile(F);
end;