dynamic_cast<const B&>

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2 total messages Started by Martin E. Nordberg III Fri, 22 Mar 1996 02:20

#3772

Author: Martin E. Nordberg III
Date: Fri, 22 Mar 1996 02:20

30 lines
1756 bytes

    I just installed MS VC++ 4.1.  The following code (strained 
from my larger code) now fails to compile:

    class A { virtual ~A() };
    class B : public A {};

    void test( const A&  a )
      {
        const B& b = dynamic_cast<const B&>( a );
          // gives "... error ... cannot use dynamic_cast to 
          // convert from 'const A &' to 'const B &' "
      }

    Did Microsoft goof or did I?  The draft standard (Sect. 5.2.6) 
seems to equate a reference to an lvalue for dynamic_cast, but 
gives no clear wording for this case.  The same problem happens 
for const A* to const B*.
    If the new MSVC++ behavior is correct, why?
(Eagerly awaiting BC++ 5.0, hope it really works with MFC)

-- 
Martin E. Nordberg III
Quintessoft Engineering, Inc.
"Visualizing new patterns of software development."
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Re: dynamic_cast<const B&>

#3790

Author: Nathan Myers, http://www.cantrip...
Date: Sun, 24 Mar 1996 04:43

28 lines
1669 bytes

Martin E. Nordberg III wrote:
> 
>   I just installed MS VC++ 4.1.  The following code (strained
> from my larger code) now fails to compile:
> 
>     class A { virtual ~A() };
>     class B : public A {};
> 
>     void test( const A&  a )
>       { const B& b = dynamic_cast<const B&>( a ); }
> 
>   Did Microsoft goof ... ?

"Heh heh heh."

But seriously... new implementations from the Draft are bound to 
have mistakes.  What's important is whether they get fixed after
attention is called to them.  I'll be interested to see whether
the next release still has this bug.

Nathan Myers
ncm@cantrip.org  http://www.cantrip.org/
---
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