"Doug Chamberlin" <dchamberlin@...> wrote in message
news:4.3.2.7.2.20010904175236.020b6540@......

> At 9/4/2001 04:25 PM (Tuesday), Martijn Tonies wrote:
> > > > where can I find information about UDFs arguments 'by descriptor'?
>
>
> If we had a standard descriptor definition and FB could be told to pass
> arguments to UDFs using it then the UDFs could detect NULLs being passed.
> This would be a big improvement! If UDFs could also return values via
> descriptors they could return NULL states as well.

Look into jrd\ibase.h under
"Blob passing structure". The definitions are there. Both the blob passing
structure (different than the internal blob struct) and the descriptor (same
for internal and external use) have been defined. Basically you get the
type, the scale, the length, the sub_type (or charset+collation, depending
on the type), the flags and the address of the data. The three available
flags are documented, too and one of them is DSC_null.

The FBUDF is a first demonstration of descriptor usage.

C.
--
Claudio Valderrama C. - http://www.cvalde.com - http://www.firebirdSql.org
Independent developer
Owner of the Interbase® WebRing