Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!RHINO.NCSL.NIST.GOV!tebbutt
From: tebbutt@RHINO.NCSL.NIST.GOV (John Tebbutt)
Newsgroups: comp.protocols.iso.dev-environ
Subject: OPTIONAL SEQUENCES and pepy
Message-ID: <9103192154.AA06810@rhino.ncsl.nist.gov>
Date: 19 Mar 91 21:54:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: inet
Organization: National Institute of Standards and Technology (NIST)
Lines: 41

I have a problem relating to how an application can discern between an
OPTIONAL SEQUENCE which is present but empty, and one which is absent,
based on the pepy decoder generated local C structure.

For example, if I have an ASN.1 definition:

DistributedOperationsArgument ::=
        SET {
            originator[0]
                DistinguishedName
                OPTIONAL,

            targetObject[1]
                DistinguishedName
                OPTIONAL,
        
                ...
}

...where DistinguishedName ::= SEQUENCE OF SomethingOrOther,
the corresponding pepy generated struct looks like this:

struct DistributedOperationsArgument {
    int     optionals;
#define opt_DistributedOperationsArgument_aliasedRDNs (000000001)

    struct DistinguishedName *originator;

    struct DistinguishedName *targetObject;

                ...
};

Now, if originator == (struct DistinguishedName *)NULL, does that mean
(a) that originator was not present in the encoding, (b) that
originator was present but empty, or (c) either/both? In the case of
(a) or (b), what value of originator would indicate the converse?

Many thanks in advance for any insights.

        JT