Re: [orbitcpp-list] Strings and sequences

[Phil D. <ph...@us...>]

Andreas Kloeckner wrote:
> 
> On Tue, Apr 18, 2000 at 05:34:47PM +0000, Phil Dawes wrote:
> > CORBA 2.3 requires that strings in structs and sequences be
> > initialised to "". This is solved for structs by using the String_mgr
> > class, whose constructor allocates an empty string.  However,
> > sequences present problems for the current implementation because we
> > use the ORBit C alloc functions for allocating sequences, and there is
> > no such 'empty string' requirement in the latest C spec.
> 
> I do not yet have the 2.3 spec. Arrays have no such requirement, right?
> Whereas every other aggregate (e.g., union, exception) falls under the
> struct'n'sequence rule?

I'm afraid arrays do have that requirement in 2.3:

Page 46 of the cpp mapping:
"If the array element is a string, wide-string or an object reference,
then the mapping uses the same type as for structure members. That is,
the default constructor for string elements and wide string elemnts
initializes them to the empty string"



> In that case, arrays is the special case and I think we'd like to name the
> new _mgr types you mention below like _mgr and _arraymgr.
> 
> > Candidate solution:
> >
> > We redefine operator new[] each time we create a sequence, which
> > invokes the underlying C allocation function. We then use the operator
> > new[] in allocbuf() instead of calling the C allocation function
> > direct. This should insure that the String_mgr constructor gets called
> > appropriately.
> 
> why not use the c allocation func in _allocbuf and do a placement new
> afterwards?

What's a placement new?
If you mean iterate over the sequence newing each element, then this
wont work because the seqence is an array of values (i.e. String_mgrs)
not pointers.

> 
> > Note that this approach must be used with any variable length type
> > containing a string. e.g.:
> 
> I can already see a needsConstructorInAggregates() method materialize
> in front of my eyes :[
> 

I'm using isVariableLength() to deduce this, since both sequences and
strings must initialise their members.

I've written an implementation which uses operator new[], by extending
the sequence template class hierarchy so that a new Elem type is defined
in the variable length sequence template on instansiation. This elem
type has its own operator new[] defined.

I've now got problems with operator new[], which I'll explain in the
next email.

Cheers,

Phil.