undefined reference to 'vtable ...'

[SixDegrees]

Also, make sure you've added both the header and the implementation files to your .pro file.

[schnitzel]

try cleaning the project, remove debug/release folders, remove the makefiles and the .pro.user file, then open the project again and rebuild.

[ChrisW67]

You need to provide the implementations for two virtual functions (one pure) you declare:

QRectF boundingRect() const;
QPainterPath shape() const;

QRectF boundingRect() const;
QPainterPath shape() const;

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and the error goes away.

[GUIman]

Thank you very much... I am an idiot