animation - Having issue with animating Qt Widget with QTimer(exit with code 255)? -

i want animate qt widget qtimer (without animation system) , painting,so put timer , starting point in enterevent , in timercall slot make border bigger , on... doesn't run , application exit code 255:

.h

#include <qtwidgets> class qwidget; class qpainter; class qtimer;  class sample : public qwidget {     q_object public:     sample(qwidget *parent = 0);     ~sample(); private:     qtimer *timer;     int weight=1, step=1; protected:     virtual void paintevent(qpaintevent *);     virtual void enterevent(qevent *); public slots:     void timercall(); }; 

.cpp

sample::sample(qwidget *parent)     : qwidget(parent) {    connect(timer,signal(timeout()),this,slot(timercall())); }  sample::~sample() {}  void sample::paintevent(qpaintevent * ) {     qpainter painter(this);     painter.setpen(qpen(qt::black,weight));     painter.setrenderhint(qpainter::antialiasing);     qrect rectangle=qrect (10,10,width()-20,height()-20);     painter.drawrect(rectangle); }  void sample::enterevent(qevent *) {     timer->start(100); }  void sample::timercall() {     weight+=1;     if (step > 10) {         timer->stop();     }     step++;     repaint(); } 

and when remove line code:

connect(timer,signal(timeout()),this,slot(timercall())); 

in enterevent application crash happened.

private:     qtimer *timer; 

you never create object referenced timer pointer.

declare qtimer timer instead, it's internal object there's no need use pointer.