QT--MessageBox --multi button

QMessageBox messageBox(this);
  messageBox.setText("删除测量坐标数据前是否备份？");
  messageBox.setWindowTitle("提示");

  QPushButton* okButton = messageBox.addButton("是", QMessageBox::YesRole);
  QPushButton* cancelButton = messageBox.addButton("否", QMessageBox::NoRole);
  QPushButton* returnButton = messageBox.addButton("取消", QMessageBox::RejectRole);