base class initialization

[Allen]

Hi all,

I have a derived class that inherits from two base classes. One of the
base class constructors takes as input a pointer that is initialized in the
other base class. How can I make sure the base classes are properly
initialized with the data they need when I call the derived class'
constructor?
--

Best wishes,
Allen

No SPAM in my email !!

[John Harrison]

Re: base class initialization


"Allen" <allen-terri-ng@att.SPAM.net > wrote in message
news:B_nWa.8296 0$0v4.5532056@b gtnsc04-news.ops.worldn et.att.net...[color=blue]
> Hi all,
>
> I have a derived class that inherits from two base classes. One of[/color]
the[color=blue]
> base class constructors takes as input a pointer that is initialized in[/color]
the[color=blue]
> other base class. How can I make sure the base classes are properly
> initialized with the data they need when I call the derived class'
> constructor?
> --
>
> Best wishes,
> Allen
>[/color]

Sounds like bad design, if the two bases classes are so closely linked
shouldn't they be a single class. Or maybe you should make the dependent
class a member of the derived class.

But if you write

class D : public B1, public B2
{
D();
};

Then it is guaranteed that B1 will be constructed before B2. So you can
write something like this

D::D() : B2(get_ptr_from _b1())
{
}

john

[Allen]

Re: base class initialization

Hi John,

"John Harrison" <john_andronicu s@hotmail.com> wrote in message
news:bgd2tg$mtt ad$1@ID-196037.news.uni-berlin.de...[color=blue]
>
> "Allen" <allen-terri-ng@att.SPAM.net > wrote in message
> news:B_nWa.8296 0$0v4.5532056@b gtnsc04-news.ops.worldn et.att.net...[color=green]
> > Hi all,
> >
> > I have a derived class that inherits from two base classes. One of[/color]
> the[color=green]
> > base class constructors takes as input a pointer that is initialized in[/color]
> the[color=green]
> > other base class. How can I make sure the base classes are properly
> > initialized with the data they need when I call the derived class'
> > constructor?
> > --
> >
> > Best wishes,
> > Allen
> >[/color]
>
> Sounds like bad design, if the two bases classes are so closely linked
> shouldn't they be a single class. Or maybe you should make the dependent
> class a member of the derived class.[/color]

What I'm trying to do is extend a window encapsulation class. Base
class A is the window and DDraw object (I didn't write it). Base class B is
the DSound object (which needs the window handle created by Base class A).
My derrived class extends the functionality of Base class A (blitting,
sprites, etc) and adds sound from Base class B.
I'll probably just make them members instead of inheriting.
--

Best wishes,
Allen

No SPAM in my email !!


[color=blue]
>
> But if you write
>
> class D : public B1, public B2
> {
> D();
> };
>
> Then it is guaranteed that B1 will be constructed before B2. So you can
> write something like this
>
> D::D() : B2(get_ptr_from _b1())
> {
> }
>
> john
>
>[/color]

[Allen]

Re: base class initialization

Oh yeah, Base class A doesn't init the window handle in the constructor.

"Allen" <allen-terri-ng@att.SPAM.net > wrote in message
news:nMyWa.8351 6$0v4.5576530@b gtnsc04-news.ops.worldn et.att.net...[color=blue]
> Hi John,
>
> "John Harrison" <john_andronicu s@hotmail.com> wrote in message
> news:bgd2tg$mtt ad$1@ID-196037.news.uni-berlin.de...[color=green]
> >
> > "Allen" <allen-terri-ng@att.SPAM.net > wrote in message
> > news:B_nWa.8296 0$0v4.5532056@b gtnsc04-news.ops.worldn et.att.net...[color=darkred]
> > > Hi all,
> > >
> > > I have a derived class that inherits from two base classes. One[/color][/color][/color]
of[color=blue][color=green]
> > the[color=darkred]
> > > base class constructors takes as input a pointer that is initialized[/color][/color][/color]
in[color=blue][color=green]
> > the[color=darkred]
> > > other base class. How can I make sure the base classes are properly
> > > initialized with the data they need when I call the derived class'
> > > constructor?
> > > --
> > >
> > > Best wishes,
> > > Allen
> > >[/color]
> >
> > Sounds like bad design, if the two bases classes are so closely linked
> > shouldn't they be a single class. Or maybe you should make the dependent
> > class a member of the derived class.[/color]
>
> What I'm trying to do is extend a window encapsulation class. Base
> class A is the window and DDraw object (I didn't write it). Base class B[/color]
is[color=blue]
> the DSound object (which needs the window handle created by Base class A).
> My derrived class extends the functionality of Base class A (blitting,
> sprites, etc) and adds sound from Base class B.
> I'll probably just make them members instead of inheriting.
> --
>
> Best wishes,
> Allen
>
> No SPAM in my email !!
>
>
>[color=green]
> >
> > But if you write
> >
> > class D : public B1, public B2
> > {
> > D();
> > };
> >
> > Then it is guaranteed that B1 will be constructed before B2. So you can
> > write something like this
> >
> > D::D() : B2(get_ptr_from _b1())
> > {
> > }
> >
> > john
> >
> >[/color]
>
>[/color]

[John Harrison]

Re: base class initialization


"Allen" <allen-terri-ng@att.SPAM.net > wrote in message
news:InzWa.8019 7$3o3.5513415@b gtnsc05-news.ops.worldn et.att.net...[color=blue]
> Oh yeah, Base class A doesn't init the window handle in the constructor.
>[/color]

If I understand correctly you need a handle from DDraw for DSound, but DDraw
does not create the handle for you in its constructor. Maybe this?

class MyClass : public DDraw
{
public:
MyClass()
{
// do whatever it takes to get a handle in DDraw
Handle h = get_handle();
sound = new DSound(handle);
}
private:
DSound* sound;
};

Ugly.

john

[Allen]

Re: base class initialization

Hi John,

Roughly, yes that is correct. The problem with that is that I want some
of the second classes methods (DSound) exposed publicly through my derived
class (which is why I was trying to inherit it in the first place--so I
could just use "using" to expose the methods I wanted). Of course making it
a private member doesn't allow that. So I guess what I'll have to do is
declare member pointers to the methods I want access to.
--

Best wishes,
Allen

No SPAM in my email !!


"John Harrison" <john_andronicu s@hotmail.com> wrote in message
news:bgegse$njn v2$1@ID-196037.news.uni-berlin.de...[color=blue]
>
> "Allen" <allen-terri-ng@att.SPAM.net > wrote in message
> news:InzWa.8019 7$3o3.5513415@b gtnsc05-news.ops.worldn et.att.net...[color=green]
> > Oh yeah, Base class A doesn't init the window handle in the constructor.
> >[/color]
>
> If I understand correctly you need a handle from DDraw for DSound, but[/color]
DDraw[color=blue]
> does not create the handle for you in its constructor. Maybe this?
>
> class MyClass : public DDraw
> {
> public:
> MyClass()
> {
> // do whatever it takes to get a handle in DDraw
> Handle h = get_handle();
> sound = new DSound(handle);
> }
> private:
> DSound* sound;
> };
>
> Ugly.
>
> john
>
>[/color]