"J.Barfurth" <techview@bfk-net.de> writes:

>BTW: MSVC6 (again - sorry) refuses to compile the expression 'new const
>T()'. Is this standard ?

The expression 'new const T()' is well-formed, and so MSVC6's behaviour
does not conform to the standard.

Here's some non-normative quotes to that effect.

 | 5.3.4 - New [expr.new]
 ...
 | [Note: the
 | type-id may be a cv-qualified type, in which case the object created
 | by the new-expression has a cv-qualified type. ]

 | 7.1.5.1 - The cv-qualifiers [dcl.type.cv]
 ...
 | -5- [Example:
 ...
 | const int* ciq = new const int (3);

The normative wording also allows it -- see the syntax for new
expressions, new-type-id, and type-id.

--
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3        |     -- the last words of T. S. Garp.
---
[ comp.std.c++ is moderated.  To submit articles, try just posting with ]
[ your news-reader.  If that fails, use mailto:std-c++@ncar.ucar.edu    ]
[              --- Please see the FAQ before posting. ---               ]
[ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html              ]

Nathan Myers schrieb in Nachricht <7egn1k$4r1$1@shell7.ba.best.com>...
>
>J.Barfurth<techview@bfk-net.de> wrote:
>>Nathan Myers schrieb in Nachricht <7edokk$mgo$1@shell7.ba.best.com>...
>>>There is no such thing as a const object on the heap.
>>
>>Does this mean, that 'new' actually ignores top-level constness ? Like:
>>    const T* p = new const T();          // *p is _actually_ non-const
>>    const_cast<T*>(p)->change();    // results are well-defined
>
>Yes.  There is no operator const_new().  Operator new() returns
>a non-const pointer which is passed to the constructor.

I was talking about new-expressions, NOT operator new(). For auto const
objects having c'tors and/or d'tors, the compiler reserves a piece of
non-const memory (i.e. no ROM) to pass to the constructor as well. Actual
constness applies to these objects only after construction and before
destruction.
Wouldn't the expression 'p = new const T()' result in the following
sequence:

    void* memory= operator new(sizeof(T));    // maybe sizeof(T const) ?
    c'tor call T::T(),  passing static_cast<T*>(memory) as construction time
this-pointer
    p = &'make object const'( *static_cast<T*>(memory));

where >>const T& 'make object const'(T&)<< would be the imagined operation
'activating' an object's constness after the constructor has finished. It
would be this 'operation', that would yield undefined behavior of the
inverse const_cast.

BTW: MSVC6 (again - sorry) refuses to compile the expression 'new const
T()'. Is this standard ? I couldn't find such a statement. IMHO it would be
inconsistent.


-- J   rg



[ comp.std.c++ is moderated.  To submit articles, try just posting with ]
[ your news-reader.  If that fails, use mailto:std-c++@ncar.ucar.edu    ]
[              --- Please see the FAQ before posting. ---               ]
[ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html              ]