Re: how can i allocate an objekt with initialization???

[Dave Thompson <david.thompson1@worldnet.att.net>]

On Mon, 06 Dec 2004 14:34:13 +0100, Martin Krischik
<martin@krischik.com> wrote:

> > Ole-Hjalmar Kristensen wrote:
> > the corresponding C++ example should have been:

> >    a &my_object = b(1);
> 
> I have seen this before and I am wondering if it is actualy valid. Because:
> where is the result of the b(1) constructor call been stored? a& can only
> hold a reference to retun value. 

In a temporary which persists as long as the reference, 12.2p5. In
practice this means the stack frame is extended. Since C++ references
cannot be reseated, and the type of an initializer is AFAICS always
statically known, this isn't terribly valuable, but it does work.

> Is this not a variation on the classic > mistake.
> 
> int&
> f ()
>   {
>   auto int retval = 5;
> 
>   // do something
> 
>   return retval;
>   }
> 
That's different. auto objects explicitly have lifetime of the block
in which they are declared hence allocated. And since under the covers
the reference is only a pointer, this returns a stale pointer.

(Aside: auto is the default storage class where it applies, to local
variables, so does not need to be and usually is not given explicitly.
Especially since in C++ and C99 'implicit int' is gone and the type
specifier must be present in the beginning part of a declaration. In
fact there have been semiserious proposals to 'recycle' the keyword
'auto' to a new meaning since its existing one is so unnecessary.)
- David.Thompson1 at worldnet.att.net