Compiler does not produce .o file , just a moc_.o and moc_.cpp files.

[ddze]

@kshegunov ,

dynamic_cast did not work, but the reinterpret_cast compiled ok.

[kshegunov]

@ddze

dynamic_cast did not work, but the reinterpret_cast was ok.

You shouldn't use reinterpret_cast, it's not for that purpose. What's the problem with the dynamic_cast?

[ddze]

@kshegunov

here is the ...

error: cannot dynamic_cast 'event->QDragEnterEvent::<anonymous>.QDragMoveEvent::<anonymous>.QDropEvent::source()' (of type 'class QObject*') to type 'class IBase*' (target is not pointer or reference to complete type)
IBase source = dynamic_cast<IBase>(event->source());
^

seems like that dynamic_cast cannot cast if the object is not instantiated completely ...

[kshegunov]

@ddze

IBase source = dynamic_cast<IBase>(event->source());

I don't see the stars ...! dynamic_cast works only on pointers (or references), so this line is quite simply invalid. You can't have polymorphic cast on an object, it just doesn't make sense. You can however do it on a pointer to that object.

IBase * source = dynamic_cast<IBase *>(event->source());

Should work just fine.

[ddze]

@kshegunov

here is the line IBase *source = dynamic_cast<IBase*>(event->source()); , not the pointer

[kshegunov]

@ddze
Okay then, your previous post didn't reflect that. Anyway, have you included the header where the IBase class resides?

PS:
Oh, I see, because you pasted the code as text, and the forum parser recognised the the asterisks and made the text italic ... heh.

[ddze]

@kshegunov

you are 100% correct , it was the header file missing .... . The other project has the header IBase , that is why it compiles .... probably I deleted it accidentally or by trying the things out. (Should use a diff from now on)

[ddze]

once on this topic , what would happen if one has a cross-reference include headers ?

I noticed few times that only if I declare a class forward declaration skipping an include of the header to be able to compile. Would in that case be ok to use reinterpret_cast as the dynamic_cast may needed the full header?

probably this applies

An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. The resulting value is the same as the value of expression. (since C++11)

Ref: reinterpret_cast

[kshegunov]

@ddze
No, not at all. dynamic_cast is polymorphic cast, it goes looks up the virtual table and makes safe casting for object pointers. reinterpret_cast is a different kettle of fish entirely, it just switches from one "interpretation" of data to another (whence the name). So it's completely legal to cast pretty much anything with reinterpret_cast but it's a bad idea, because it can be quite error-prone.

You can do this:

struct SomeStruct
{
    int a;
    double b;
    QString x;
};

SomeStruct * variable = new SomeStruct;
char * bytes = reinterpret_cast<char *>(variable);  //< This is valid, compiles and runs just fine. Only problem is, you may accidentally modify memory that's not yours ...

And you have the whole structure as an array of bytes ... but it's ill advised to do such things in general. reinterpret_cast is similar to the functionality the union provides.
So as rule of thumb, do not use reinterpret_cast.

[ddze]

@kshegunov

Thanks a lot.