[squeak-dev] [FFI] Endless C structs and unions

Dear list,
  I have a couple of questions, I started to play with FFI, so these
are newbie ones, my intention is to port the ZOOM library. I was there
happily writing ExternalStructure's until I found one that kills the
VM. Then I've realized I have some basic doubts about FFI:

1) I have this C struct

    odr Struct Reference
    ===============
        int direction
        int error
        unsigned char * buf
        int top
        int size
        int pos
        const unsigned char * bp
        NMEM mem
        struct Odr_private * op

which I wrote (with a lot of brilliant inspiration) like:

ZOOMODR class>> fields
        "  self defineFields  "
        ^ #(
                (direction  'long')
                (error      'long')
                (buf        'char *')
                (top         'long')
                (size        'long')
                (pos         'long')
                (bp          'char *')
                (mem       'ZOOMNMem')
                (odrPrivate 'void *')  " ========= HERE ========= "
        )

I don't know if this exists, the HERE means : I want to avoid to write
an external structure for this...

        Odr_private Struct Reference
        =====================
            struct odr_constack * stack_first
            struct odr_constack * stack_top
            const char ** tmp_names_buf
            int tmp_names_sz
            struct Odr_ber_tag odr_ber_tag
            yaz_iconv_t iconv_handle
            int error_id
            char element [80]
            void(* stream_write )(ODR o, void *handle, int type,
const char *buf, int len)
            void(* stream_close )(void *handle)
            int can_grow
            int t_class
            int t_tag
            int enable_bias
            int choice_bias
            int lenlen
            FILE * print
            int indent

After a look at the fields, I supose I do not care about the contents
of that struct. It is ok the

... (odrPrivate 'void *') ...

magic line to "stop" these C structs?
If not, is there a way to say "I don't care what follows from here"
(i.e. pass automagically nil to that pointer) ?

2)
    Z_NamePlusRecord Struct Reference
    =================================
    Z_DatabaseName * databaseName
    int which
    union {
       Z_External *   databaseRecord
       Z_DiagRec *   surrogateDiagnostic
       Z_FragmentSyntax *   startingFragment
       Z_FragmentSyntax *   intermediateFragment
       Z_FragmentSyntax *   finalFragment
    } u

Is there something special to do about an union in the #fields method?

Thanks in advance.

Hernán

Hernán Morales Durand wrote:
Yes, this will work fine.

Just declare it as any pointer you'd like and provide methods for the
particular conversions you need.

Cheers,
   - Andreas

On 30-Mar-09, at 10:49 AM, Andreas Raab wrote:

> Hernán Morales Durand wrote:
>> I have a couple of questions, I started to play with FFI, so these
>> are newbie ones, my intention is to port the ZOOM library. I was  
>> there
>> happily writing ExternalStructure's until I found one that kills the
>> VM. Then I've realized I have some basic doubts about FFI:

You might want to download a copy of Sophie from http://opensophie.org/
and start, hit cmd-period at some point to get a debugger up, then a  
browser

To support os-x navigation services we had to code up quite a bit of  
ugly structure accessors.
No Unions tho

--
=
=
=
========================================================================
John M. McIntosh <[hidden email]>
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
=
=
=
========================================================================

Andreas, John, thank you very much!

Hernán

2009/3/30 John M McIntosh <[hidden email]>: