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From: "news.xs4all.nl" <sbierman@idfix.nl>
Subject: Re: Reference to base class pointer
Date: 1999/05/20
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The same problem holds for converting a Derived ** to a Base **. This is not
allowed for the following reason:

class Base { };

class Derived1 : public Base { };

class Derived2 : public Base { };

void foo()
{
    Derived1 d1;
    Derived1 *p1 = &d1;
    Derived2 d2;
    Derived2 *p2 = &d2;
    Base **pp = &p1; /* convert Derived1** to Base**, not allowed */
    *pp = p2; /* convert Derived2* to Base *, allowed */
    /* At this point p1 which is a
        Derived1 pointer is pointing to
        a Derived2 variable.
        Possible disaster!!
    */
}

Your example is simply a variation of the same principle.


Silvio Bierman


Gernot wrote in message <37428FB3.5DC7@eae.com>...
>I've just changed some existing code and abandonded using pointers to
>pointers. Instead I'm using references to pointers now, which greatly
>improves readability. But still my compiler keeps telling me that it
>cannot cast a reference to a pointer to class Derived to a reference to
>a Base class pointer.
>Simple question: Is that standard-conforming behaviour or can I hope for
>a new compiler version?
>
>Just for clarity, the essential code:
>
>class Base
>{
>};
>
>class Derived : public Base
>{
>};
>
>void foo( Base*& rpBase );
>
>int main()
>{
>  Derived* pDerived = NULL;
>  foo( pDerived );            // This is the error!
>...

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