Re: C++ mapping of OUT variable-length structures

[Diego Sevilla Ruiz <dsevilla ditec um es>]

Hi!

On Wed, Apr 24, 2002 at 04:04:55PM +0200, ERDI Gergo wrote:
| According to a CORBA/C++ spec I've found on the web, the mapping of OUT
| arguments for variable-length structures is T*&. However, I see that there
| are auxillary _out classes in the main ORBit2/C++ branch. 
| So my questions are:
| 	1, What's the point of these _out classes?

I hope I can explain it well... Please, take a look at H&V book, pages
300-302. The question is that as the _out types are allocated by the
callee, (and are passed by reference), there must be a way to deallocate
the previous owned reference if you use a _var type. That is, the
pointer contained in the call (the value of the T*&) must be 0 (NULL),
so the _out type constructor ensures this for just pointers (for
instance char*) and for _var classes. This is: 

1) it frees any memory allocated with the internal _var variable before 
calling the method if the actual _var variable is passed as an _out 
parameter, and

2) it sets any pointer to null (if not using a _var variable).

| 	2, Where should the allocation happen? Should the server allocate
| the structure? Should it be allocated by the client before doing the call?
| Both? Neither?

The structure must be allocated by the implementation code for this
object written by the object implementation programmer.

| 
| Right now in my ORBit/C++ branch I'm allocating/deallocating on the client
| side via the new/delete operators, but it would be very easy to modify
| this scheme to do the Right Thing.

In the C++ mapping (contrary to the C mapping) out types are always
allocated by the callee and freed by the caller.

> So what does the CORBA/C++ spec say
| about this?
| 

Hope I explained it well...

	Best regards.
	diego.

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