[SOLVED] [Class Inheritance] Need tips on creating a hierarchic class structure

loladiro

I guess your testroot inherits QWidget? In that case it has to have a similar constructor to your CQp class and you have to call that constructor.

valandil211

You guessed right, but I don't understand what you mean.

loladiro

@
class testroot : public QWidget
{
Q_OBJECT
public:
testroot(QWidget *parent = 0) : QWidget(parent)
{}
}

CQp::CQp(QWidget *parent) :
testroot(parent)
{
}
@

valandil211

Thanks!

Do you have any good reference book that talks about this kind of inheritance? My code now compiles, but I haven't the slightest idea why. I read about inheritance before, but it's always demonstrated in simple cases, and rarely with abstract classes.

Thanks, @loladiro!

dangelog

[quote author="Joey Dumont" date="1308751406"]
and when I try to compile, it complains that 'QWidget' is not a direct base of CQp. True. But I if make it a parent class to CQp explicitly, it complains that class CQp inherits QWidget from two places. Is there a way around that?[/quote]

What the compiler is telling you is that from a constructor you can call only direct base constructors.

That is, if you have an inheritance chain like this
@
A --> B --> C
@
(C inherits from B, B from A) then from C::C() you can call B::B(), but not A::A(), because it's not a direct base for C.

The offending line is obviously the call to the QWidget ctor here, since "testcase" is a direct base for CQp, and QWidget is a non-direct base:

[quote author="Joey Dumont" date="1308751406"]
@#include "cqp.h"

CQp::CQp(QWidget *parent) :
QWidget(parent)
{
}
@
[/quote]

valandil211

And by using,

@ CQp::CQp(QWidget *parent):
testroot(parent);

{
}
@

what am I changing to the inheritance chain?

dangelog

You're not changing the inheritance graph (which is defined by the class definition); that's a call to a base constructor from your constructor. You're now calling a costructor of a direct-base (allowed) instead of a non-direct base (forbidden).

loladiro

Nothing, but you are calling the constructor of your base class (which is the only constructor your are allowed to call in C++).

valandil211

Thanks for both your simultaneous answers!

Now, will I be able to instantiate the tests that are at the far end of the inheritance graph by using QWidget signals like show() and such? My guess is no, but if so my abstract classes organization scheme falls apart.

Any thoughts?

loladiro

Yes you will! Signals/Slots are inherited just like methods (because they are methods).

valandil211

Oh, I just got it. Thanks for your patience!