When using qtcreator, inherit a QWidget class

class xxx:public QWidget

{

Q_ OBJECT

explicit xxx(QWidget* parent=0);

};

Then, undefined reference to ` VTable for XXX:: XXX appears in build

Solution: turn off the qtreactor in order not to destroy some structures

Then enter the directory where the program is stored to execute

qmake xxx.pro

Then open qtreactor to build, and the error disappears