字符串截取，SubString

procedure TForm12.btn1Click(Sender: TObject);
var
  wokao: string;
begin
  wokao := 'abcde_fg';
  ShowMessage(IntToStr(wokao.IndexOf('_')));//5
  ShowMessage(wokao.Substring(0,wokao.IndexOf('_')));//abcde
end;