Issue Subclassing a Qlabel C++

Question

I am attempting to subclass a QLabel using a header file and I get the error on constructor

IntelliSense: indirect nonvirtual base class is not allowed

class foo : public QLabel
{
    Q_OBJECT

    foo(QWidget* parent = 0) :  QWidget(parent)
    {

    }

    void mouseMoveEvent( QMouseEvent * event )
    {
        //Capture this
    }

};

Any suggestions why this is happening and how I can fix it ?

You need use QLabel, instead QWidget in the constructor – grisha Jun 24 '14 at 17:19 — grisha, Jun 24 '14 at 17:19

László Papp · Accepted Answer · 2014-06-27T18:05:27.143

2

The problem is here:

foo(QWidget* parent = 0) :  QWidget(parent)

You are inheriting from QLabel, but you specify QWidget for the base. You should write this intead:

explicit foo(QWidget* parent = Q_NULLPTR) :  QLabel(parent)
//                                           ^^^^^^

Also, please use explicit for that constructor as well as Q_NULL_PTR or at least NULL instead of 0.

edited Jun 27 '14 at 18:05

answered Jun 24 '14 at 17:20

László Papp

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The last sentence, what's it for? – Tay2510 Jun 24 '14 at 17:46
1

@Tay2510: 1) Avoid implicit conversion. 2) Use nullptr with C++11. – László Papp Jun 24 '14 at 17:47

Issue Subclassing a Qlabel C++

1 Answers1