subclass initialization

[Jay Wolfe]

Hello,

I'm guessing I can't do this, but can I do work in a subclass before its
parent class initialization?

I've got 2 classes, class A & subclass B:

class A
{
public:
A(): x(0), y(0) {}
...
}

class B: public A
{
//bunch of definitions
}

So, normally for subclass B I'd initialize as

B::B() : A()
{
do_some_work_here();
}

Is it possible to execute 'do_some_work_here()' BEFORE the parent class
initialization?

Thank you,

Jay

[red floyd]

Jay Wolfe wrote:
class B: public A

{
//bunch of definitions
}

So, normally for subclass B I'd initialize as

B::B() : A()
{
do_some_work_here();
}

Is it possible to execute 'do_some_work_here()' BEFORE the parent class
initialization?

No. B's constructor doesn't start until the A portion is fully constructed.

[Rolf Magnus]

Jay Wolfe wrote:

Hello,

I'm guessing I can't do this, but can I do work in a subclass before its
parent class initialization?

You're right. You can't do this.

[Pete Becker]

Jay Wolfe wrote:

B::B() : A()
{
do_some_work_here();
}

Is it possible to execute 'do_some_work_here()' BEFORE the parent class
initialization?

Yes, with a little change. But it's a hack.

class A
{
public:
A(int): x(0), y(0) {}
...
}

class B: public A
{
int do_some_work_here();
}

B::B() : A(do_some_work_here())
{
}

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Alan Johnson]

Jay Wolfe wrote:

Hello,

I'm guessing I can't do this, but can I do work in a subclass before its
parent class initialization?

I've got 2 classes, class A & subclass B:

class A
{
public:
A(): x(0), y(0) {}
...
}

class B: public A
{
//bunch of definitions
}

So, normally for subclass B I'd initialize as

B::B() : A()
{
do_some_work_here();
}

Is it possible to execute 'do_some_work_here()' BEFORE the parent class
initialization?

Thank you,

Jay

This is a bit hackish, but you could make a separate class that did the
work in its constructor, and derive from that as well. You would be
exploiting the fact that base classes are initialized in order of
declaration. For example:

class do_work
{
public:
do_work() { do_some_work_here() ; }
} ;
class B : public do_work, public A
{
....
} ;
The do_work class will be initialized before A. If you want more
information, see the boost utility template here:
http://boost.org/libs/utility/base_from_member.html

-Alan

[lou zion]

Thanks to all! A couple of hacks to try is better than nothing!

Jay

[Rolf Magnus]

Pete Becker wrote:

Jay Wolfe wrote:

B::B() : A()
{
do_some_work_here();
}

Is it possible to execute 'do_some_work_here()' BEFORE the parent class
initialization?

Yes, with a little change. But it's a hack.

class A
{
public:
A(int): x(0), y(0) {}
...
}

class B: public A
{
int do_some_work_here();

do_some_work_here should be static, because the member variables of B are
not yet initialized and thus must not be accessed anyway.
}

B::B() : A(do_some_work_here())
{
}

[Pete Becker]

Rolf Magnus wrote:

class B: public A
{
int do_some_work_here();

do_some_work_here should be static, because the member variables of B are
not yet initialized and thus must not be accessed anyway.

I wouldn't know. I haven't seen its code.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)