invalid application of 'sizeof' to incomplete type 'QStaticAssertFailure<false>' at QGlobal.h

Question

I am currently migrating a huge project from Qt 4.x to 5.2.1, Everything has been rather good until this error, which I find incredibly confusing because its located at the Qt files, and I believe the solution must be applied somewhere else, not in the qglobal.h located at 5.2.1\mingw48_32\include/QtCore/qglobal.h. The error must be happening somewhere else.

Heres the error:

..........\Qt5\5.2.1\mingw48_32\include/QtCore/qglobal.h:681:85: error: invalid application of 'sizeof' to incomplete type 'QStaticAssertFailure' enum {Q_STATIC_ASSERT_PRIVATE_JOIN(q_static_assert_result, COUNTER) = sizeof(QStaticAssertFailure)} ^

..........\Qt5\5.2.1\mingw48_32\include/QtCore/qglobal.h:686:47: note: in expansion of macro 'Q_STATIC_ASSERT' #define Q_STATIC_ASSERT_X(Condition, Message) Q_STATIC_ASSERT(Condition) ^

..........\Qt5\5.2.1\mingw48_32\include/QtCore/qobject.h:520:5: note: in expansion of macro 'Q_STATIC_ASSERT_X' Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro::Value, ^

Here's the piece of code in qglobal.h

// Intentionally undefined
template <bool Test> class QStaticAssertFailure;
template <> class QStaticAssertFailure<true> {};

#define Q_STATIC_ASSERT_PRIVATE_JOIN(A, B) Q_STATIC_ASSERT_PRIVATE_JOIN_IMPL(A, B)
#define Q_STATIC_ASSERT_PRIVATE_JOIN_IMPL(A, B) A ## B
#ifdef __COUNTER__
#define Q_STATIC_ASSERT(Condition) \
    enum {Q_STATIC_ASSERT_PRIVATE_JOIN(q_static_assert_result, __COUNTER__) = sizeof(QStaticAssertFailure<!!(Condition)>)}
#else
#define Q_STATIC_ASSERT(Condition) \
    enum {Q_STATIC_ASSERT_PRIVATE_JOIN(q_static_assert_result, __LINE__) = sizeof(QStaticAssertFailure<!!(Condition)>)}
#endif /* __COUNTER__ */
#define Q_STATIC_ASSERT_X(Condition, Message) Q_STATIC_ASSERT(Condition)
#endif

I have tried everything and have researched all about it, but didnt find a proper solution. I have wasted all day in this annoying piece of code. I hope someone can shed some light on the matter.

Thankyou very much.

EDIT: I searched for all the documents that included qglobal.h, but none of them make use of any assert funcion, so I dont know what could be triggering such error. Theres no way that the qglobal.h is wrong, so it must be something of the source code.

EDIT2: I managed to isolate the lines that trigger the error, apparently the compilation output gave more information than I thought, but it was so 'separated' that I thought it was a warning and had nothing to do. Here is the code from my application. The two commented lines are the ones that trigger the error. Sorry for my mistake.

bool ISPSModel::removeGraphics(GraphicsPrimitive* _gtr) {

    for (int _i = 0; _i < ispss.size(); _i++) {

        for (int _j = 0; _j < ispss[_i]->graphicsObjects.size(); _j++) {

            if (ispss[_i]->graphicsObjects[_j] != _gtr)
                continue;

            if (ispss[_i]->graphicsObjects.contains(_gtr)) {

                //beginRemoveRows(indexFromItem(ispss[_i]->m_item), _gtr->getData(DATA_ROLE).value<ISPSItem*>()->row(), _gtr->getData(DATA_ROLE).value<ISPSItem*>()->row());
               //_gtr->getData(DATA_ROLE).value<ISPSItem*>()->remove();
                ispss[_i]->removeGraphics(ispss[_i]->graphicsObjects[_j]);
                endRemoveRows();
                return true;
            }
        }
    }

    return false;
}

Its this part the one that causes the error:

value<ISPSItem*>()

Heres the other part of the compilation error that I had ignored, in case it can help:

..........\Qt5\5.2.1\mingw48_32\include/QtCore/qobject.h: In instantiation of 'T qobject_cast(QObject*) [with T = ISPSItem*]': ..........\Qt5\5.2.1\mingw48_32\include/QtCore/qvariant.h:695:51: required from 'static T QtPrivate::QVariantValueHelper::object(const QVariant&) [with T = ISPSItem*]' ..........\Qt5\5.2.1\mingw48_32\include/QtCore/qvariant.h:101:37: required from 'static ReturnType QtPrivate::ObjectInvoker::invoke(Argument) [with Derived = QtPrivate::QVariantValueHelper; Argument = const QVariant&; ReturnType = ISPSItem*]' ..........\Qt5\5.2.1\mingw48_32\include/QtCore/qvariant.h:810:64: required from 'T qvariant_cast(const QVariant&) [with T = ISPSItem*]' ..........\Qt5\5.2.1\mingw48_32\include/QtCore/qvariant.h:348:36: required from 'T QVariant::value() const [with T = ISPSItem*]' ..\marssies\ispswidget.cpp:785:109: required from here EDIT3: I left those 2 lines commented and kept migrating the application, until I got the same error in another file, this is the line:

Im getting the same error in another .cpp using a different class, but what they have in common is the .value<Type>();

Notify* _n = ui.notifyBox->model()->data(index, Qt::UserRole).value<Notify*>();

So definitely its the .value<Type>(); what throws the error, now the only thing left is to find a way around it.

Here is the object ISPSItem in case its useful:

class ISPSItem : public QObject {

public:
    enum Level {ROOT_LEVEL = 1,
                    ISPS_LEVEL,
                        GRAPHICS_LEVEL
                    } level;

    ISPSItem(ISPSItem* = NULL, Level = ROOT_LEVEL, int = -1);
    ~ISPSItem();

    ISPSItem* parentItem() {return _parentItem;}

    ISPSItem* child(int);
    void appendChild(ISPSItem*);
    void insertChild(ISPSItem*, int);
    int childCount() const {return children.size();}

    int row() const;
    int newNodeRow(Level);
    void remove();

private:
    QList<ISPSItem*> children;
    ISPSItem* _parentItem;
    void remove(ISPSItem*);
};
Q_DECLARE_METATYPE(ISPSItem*)

Answer 1

Add this before you use ISPSItem as a QVariant cast:

Q_DECLARE_METATYPE(ISPSItem)

To solve the problem you need to add your class to QMetaType, the macro do that.

Q_DECLARE_METATYPE(Type)

This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. It is needed to use the type Type as a custom type in QVariant.

Good look!

Answer 2

I see this problem when I change signals variable type but at the same time I forgot changing slots descriptions.For example; I have a signal slot : this is signal-> setResult(bool res); this is slot -> setResult(bool res){}

I change signal's type signal -> setResult(QString res); slot -> setResult(bool res); /////WHEN I FORGOT CHANGING THIS ASSERT THIS EXP

Answer 3

After getting much information about the error and the sources that trigger it I conclude, that the root cause could be in using QObject subclasses in QVariant, especially when calling QVariant::value() function. As Qt docs say:

If the QVariant contains a pointer to a type derived from QObject then T may be any QObject type. If the pointer stored in the QVariant can be qobject_cast to T, then that result is returned. Otherwise a null pointer is returned. Note that this only works for QObject subclasses which use the Q_OBJECT macro.

I believe, that adding Q_OBJECT macro to these classes (ISPSItem) declaration will solve the problem.