error: ‘SIGNAL‘ was not declared in this scope 未在此范围内声明。
connect(ui->Btnshowhello,SIGNAL(clicked(bool),this,SLOT(BtnshowhelloSlot()));
其他错误导致的此报错。。
是SIGNAL后括号忘了。
【QT】error: 'SIGNAL' was not declared in this scope
原文：https://www.cnblogs.com/wxl845235800/p/10751797.html