C++ / Qt5.1.1 - Call virtual function in another class

mad-hatter

Windows 10 - GCC 5.3
Qt Creator 4.5.2
Based on Qt 5.10.1 (MSVC 2015, 32 bit)

Hello,

I'm getting the following compile errors.
path\generated\plugin\gear\obj\divideoptions.o:-1: In function ZN7derivedC4Ev': error: undefined reference to vtable for derived'
path\generated\plugin\gear\obj\divideoptions.o:-1: In function ZN16LC_DivideOptions8execCommEP18Document_InterfaceP7QWidget7QString': error: undefined reference to derived::getData(QHash<int, QVariant>*)'

Help please;

Regards

class Plug_Entity
{
public:
    virtual ~Plug_Entity() {}

    //! Obtain the entity data.
    /*!
    * The data is a QHash with the EDATA keys relevant to the type of entity
    *  \param data pointer to a QHash<int, QVariant> to store the entity data.
    */
    virtual void getData(QHash<int, QVariant> *data) = 0;
	...
	...
};

class derived : public Plug_Entity //in document_interface.h
{
    Q_OBJECT
public:
    virtual void getData(QHash<int, QVariant> *data);
    virtual void updateData(QHash<int, QVariant> *data);
    virtual void getPolylineData(QList<Plug_VertexData> *data);
    virtual void updatePolylineData(QList<Plug_VertexData> *data);
    virtual void move(QPointF offset);
    virtual void moveRotate(QPointF const& offset, QPointF const& center, double angle);
    virtual void rotate(QPointF center, double angle);
    virtual void scale(QPointF center, QPointF factor);
    virtual QString intColor2str(int color);
};

QHash<int, QVariant> *data;
    auto obj = new derived ;
    obj->getData(data);
    qDebug() << data;
    delete obj;

raven-worx

@mad-hatter
did you already try a full rebuild?

mad-hatter

Thanks for your reply.

Yes.
Ran clean, qmake & rebuild

aha_1980

@mad-hatter

might be a silly question, but do you link against this object?

mad-hatter

@aha_1980 - Thanks for your reply.

This is the first time I've tried to call a virtual function (I don't know if I'm doing it correctly).
I don't know what you mean by linking against this object.

aha_1980

hi @mad-hatter,

'undefined reference' means the linker cannot find a symbol.

therefore my question, if you link against the compiled object file containing your class.

to recreate the error, a minimal compilable example would be nice.

Regards

SGaist

Hi,

Usually the vtable error comes from add/removing the Q_OBJECT macro in your QObject derived class without re-running qmake. Is that your case ?

mad-hatter

@SGaist

Hello,

Ran qmake and rebuild all.
I'm still getting errors.

I don't know what to do about "virtual ~Plug_Entity() {}".

I'm making an error, but don't know what.

Regards

*document_interface.h*
class Plug_Entity
{
public:
    virtual ~Plug_Entity() {}
    virtual void getData(QHash<int, QVariant> *data) = 0;
    virtual void updateData(QHash<int, QVariant> *data) = 0;
    virtual void getPolylineData(QList<Plug_VertexData> *data) = 0;
    virtual void updatePolylineData(QList<Plug_VertexData> *data) = 0;
    virtual void move(QPointF offset) = 0;
	virtual void moveRotate(QPointF const& offset, QPointF const& center, double angle)=0;
    virtual void rotate(QPointF center, double angle) = 0;
    virtual void scale(QPointF center, QPointF factor) = 0;
    virtual QString intColor2str(int color) = 0;
};

class base : public Plug_Entity //in document_interface.h
{
public:
    virtual void getData(QHash<int, QVariant> *data);
    virtual void updateData(QHash<int, QVariant> *data);
    virtual void getPolylineData(QList<Plug_VertexData> *data);
    virtual void updatePolylineData(QList<Plug_VertexData> *data);
    virtual void move(QPointF offset);
    virtual void moveRotate(QPointF const& offset, QPointF const& center, double angle);
    virtual void rotate(QPointF center, double angle);
    virtual void scale(QPointF center, QPointF factor);
    virtual QString intColor2str(int color);
    //virtual ~Plug_Entity() {} //error: declaration of '~Plug_Entity' as member of 'base'
};

class derived : public base
{
public:
    void getData(QHash<int, QVariant> *data);
    void updateData(QHash<int, QVariant> *data);
    void getPolylineData(QList<Plug_VertexData> *data);
    void updatePolylineData(QList<Plug_VertexData> *data);
    void move(QPointF offset);
    void moveRotate(QPointF const& offset, QPointF const& center, double angle);
    void rotate(QPointF center, double angle);
    void scale(QPointF center, QPointF factor);
    QString intColor2str(int color);
    //~Plug_Entity() {} //error: declaration of '~Plug_Entity' as member of 'derived'
};

*Code:-*
    QHash<int, QVariant> *data;
	
    base *p;
    derived obj1; //error: undefined reference to `vtable for derived'
    p = &obj1;

    p->getData(data); //error: undefined reference to `derived::getData(QHash<int, QVariant>*)'
    qDebug() << data;

JonB

@mad-hatter

I don't know what to do about "virtual ~Plug_Entity() {}".

It looks like you want all your methods in Plug_Entity to be pure virtual, including the destructor. So in Plug_Entity maybe you want virtual ~Plug_Entity() = 0;, and in base you (kind of) meant virtual ~Plug_Entity() {} ?

But, in your derived classes (base & derived), you (must not) try to define a destructor for class Plug_Entity, you must define it for the class you are in! So base will have:

virtual ~base() {}

and derived will have:

virtual ~derived() {}

That is what the error message is telling you!

jsulm

@mad-hatter You can't define a destructor of a base class in a derived class! So, adding ~Plug_Entity() {} in derived is invalid. Simply add ~derived() {}.
See https://www.geeksforgeeks.org/pure-virtual-destructor-c/