Re: A subtle access issue (may be advanced :-) )

"Alf P. Steinbach" <>
Sun, 30 Aug 2009 14:17:06 +0200
* James Kanze:

On Aug 29, 11:25 pm, "Alf P. Steinbach" <> wrote:

* James Kanze:

On Aug 29, 9:11 am, "Alf P. Steinbach" <> wrote:

The following code compiles as-is with g++ and Comeau
Online, but not when then the commented lines are

#include <stddef.h>

template< class T > T* create();

class Base
template< class T > friend T* create();
     static void* operator new( size_t size )
         return ::operator new( size );

// static void operator delete( void* p )
// {
// ::operator delete( p );
// }

     virtual ~Base() {}

class Derived
     : public Base
     Derived() {}
     virtual ~Derived() {}

template< class T >
T* create() { return new T; }

int main()

With uncommenting the commented code both compilers
complain that the Derived destructor can't access
Base::operator delete.

Correctly (more or less).

As you write further down, you don't *know* that.

I do with regards to the new expression. The operator delete
must be accessible in the context of the new expression.

The operator delete is accessible in the context of the new expression, since
that expression appears in a friend function.

And neither do I. :-)

But one might suspect that the destructor needing access is
correct wrt. to the standard, and that the standard therefore
ideally should be corrected, for access has nothing to do with
machine code.

I agree in principle; if that's what the standard says (and I
seem to recall that it is), then it's pretty ugly. On the other
hand, the authors of the standard do consider implementation
issues, and generally dislike requiring something that can't
reasonably be implemented.

MSVC has no problem compiling the code with commented block uncommented.

It's very easy to implement.


- Alf

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