virtual inheritance.

[Radde]

Hello,
when i run the below code.. I get output

A()
A()
B()
C()
D()

dont know? why in this sequence?

#include<iostre am.h>

class A
{
public:
A()
{
cout<<"A()"<<en dl;
}
};

class B: public A
{
public:
B()
{
cout<<"B()"<<en dl;
}
};
class C: public virtual A
{
public:
C()
{
cout<<"C()"<<en dl;
}
};

class D: public B,public C
{
public:
D()
{
cout<<"D()"<<en dl;
}
};

void main()
{
D d;
}

But when i make class B : public virtual A{}
and class C : public A(}

i get output
A()
B()
A()
C()
D()

how is this??

I get same output even if i dont use virtual inheritance(sam e as
above)..This is agreeable..But i dont know the first one and second
one?? I realy didnt understand the constructor calling mechanism..

Cheers..

[Victor Bazarov]

Re: virtual inheritance.

Radde wrote:[color=blue]
> [...initialisati on of virtual base subobject seems out of order...]
> how is this??[/color]

All you need to know is that virtual base subobjects are constructed by
the most derived class' constructor's initialiser list.
[color=blue]
> [...][/color]

V

[Mark P]

Re: virtual inheritance.

Radde wrote:[color=blue]
> Hello,
> when i run the below code.. I get output
>
> A()
> A()
> B()
> C()
> D()
>
> dont know? why in this sequence?
>
> #include<iostre am.h>
>
> class A
> {
> public:
> A()
> {
> cout<<"A()"<<en dl;
> }
> };
>
> class B: public A
> {
> public:
> B()
> {
> cout<<"B()"<<en dl;
> }
> };
> class C: public virtual A
> {
> public:
> C()
> {
> cout<<"C()"<<en dl;
> }
> };
>
> class D: public B,public C
> {
> public:
> D()
> {
> cout<<"D()"<<en dl;
> }
> };
>
> void main()
> {
> D d;
> }
>[/color]

Here's my understanding:

First constructed is the virtual A, then D inititiates B and C, and B
initiates A, so A is constructed again, followed by B, then C, and
finally D.
[color=blue]
> But when i make class B : public virtual A{}
> and class C : public A(}
>
> i get output
> A()
> B()
> A()
> C()
> D()
>
> how is this??[/color]

Again, first virtual A, then D initiates B and C, so B is constructed
first then for C we get A and C in that order, and finally D.
[color=blue]
>
> I get same output even if i dont use virtual inheritance(sam e as
> above)..This is agreeable..But i dont know the first one and second
> one?? I realy didnt understand the constructor calling mechanism..
>
> Cheers..
>[/color]

Basically the virtual constructors are called first and then what's left
over is called in depth-first left-to-right order.

[leonardo77]

Re: virtual inheritance.

All you need to know is that you should first read the C++-FAQ-Lite!
:->)) Site:"parashift .com\c++-faq-lite" ,look for virtual inheritance.

Isn't the FAQ supposed to handle cases like this?

_______________ _______________ _______________ ____________

leo77

There is nothing new in this universe...