NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/17736

Text File | 1996-08-05 | 4.3 KB | 190 lines

Path: siemens.ch!news
From: [e-mail] (Waeckerlin Marc)
Newsgroups: comp.lang.c++
Subject: Re: Circular Usage (forward declaration?)
Date: 17 Apr 1996 08:57:37 GMT
Organization: Siemens Schweiz AG
Message-ID: <[e-mail]>
References: <[e-mail]>
    <[e-mail]>
    <[e-mail]> <[e-mail]>
NNTP-Posting-Host: 150.10.54.28
In-reply-to: [e-mail]'s message of 17 Apr 1996 08:41:21 GMT

Hi there

You have the same problem in other cases (yes I know there is an endless loop):

class B;

class A
{
  public:
    void b(B &x)
    {
      x.a(*this);
    }
};

class B
{
  public:
    void a(A &x)
    {
      x.b(*this);
    }
};


It does not even work with pointers:

class B;

class A
{
  public:
    void b(B *x)
    {
      assert(x);
      x->a(this);
    }
};

class B
{
  public:
    void a(A x)
    {
      assert(x);
      x->b(this);
    }
};


-> is there a solution or not?
BTW: regarding the smart p[ointer example below - I know, that circular
     references and smart pointers normally don't work tokether, but you
     don't know how smart *these* smart pointers may be ;-) ...


regards



In article <[e-mail]> [e-mail] (Waeckerlin Marc) writes:

> From: [e-mail] (Waeckerlin Marc)
> Newsgroups: comp.lang.c++
> Date: 17 Apr 1996 08:41:21 GMT
> Organization: Siemens Schweiz AG
>
> Hi
>
> Thank you for the answers.
>
> I know this way, but it does not work in my case, since the members "x"
> absolutely must be no pointers.
> Speaking more exactly, they are pointers, but they are smart pointers.
> In another example, you could get somnething like this, where "CPointer"
> is a smart pointer:
>
> class CCompany
> {
>   protected:
>
>     CPointer<CEmployee> m_emp;
>
>   public:
>
>     set(CEmployee &p_emp)
>     {
>       m_emp = &p_emp;
>     }
> };
>
>
> class CEmployee
> {
>   protected:
>
>     CPointer<CCompany> m_comp;
>
>   public:
>
>     set(CCompany &p_comp)
>     {
>       m_comp = &p_comp;
>     }
> };
>
>
> Best Regards
> Marc
>
> In article <[e-mail]> Rob Stewart <[e-mail]> writes:
>
> > From: Rob Stewart <[e-mail]>
> > Newsgroups: comp.lang.c++
> > Date: Wed, 17 Apr 1996 00:40:17 -0400
> > Organization: Datalytics, Inc.
> >
> > Enno Sandner wrote:
> > >
> > > In article <[e-mail]> [e-mail] (Waeckerlin Marc) writes:
> > >
> > >    How do you realize this in C++:
> > >    (the whole problem is much more complex, but it can be reduced to that)
> > >
> > >    class A
> > >    {
> > >        B x;
> > >    };
> > >
> > >    class B
> > >    {
> > >        A x;
> > >    };
> > >
> > > There's no way -- use pointers or references instead, i.e. dynamicly
> > > allocate the appropriate instance of class 'A' or class 'B'.
> > >
> > >         Enno
> >
> > Enno is correct, except you also need to forward declare one of
> > the classes:
> >
> > class B;
> >
> > class A
> > {
> >    B* px;
> > };
> >
> > class B
> > {
> >    A x;
> > };
> >
> > --
> > Rob Stewart    | My opinions are generally my own.  They do
> > Datalytics, Inc.| not necessarily reflect those of my employer.
> >
--
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