Re: smob pointer moving

[Noah Roberts]

Steve Tell wrote:

> > SCM db_open(SCM obj)
> > {
> >  Database *db = DB(db);
> >    
>
> I think you mean DB(obj) above.   Typo in email, or perhaps your real
> problem?
Actually it looks like it was very possibly a typo in code.  The 
argument was named db to begin with and I had decided to change it in 
favor of having that name for the converted variable - probably forgot 
to change the above.  Pretty embarasing actually :P

> One other thing wrong that I see here:  You're not checking that 
> obj really is a database smob before casting it and chasing the
> (possibly random) pointer.
Yeah, I hadn't gotten to that part in my searching - seems that finding 
thurough information on guile is a bit tough.  It is all out there, but 
scattered between various mailing lists, info pages, tutorials, and of 
course the source code itself, but I am beginning to get all the parts I 
require mapped out.

> (recent docs indicate that SCM_SMOB_PREDICATE() and SCM_ASSERT() are
> available for this, probably a better choice.)
That is what I found and preliminary testing indicates that it is what 
is "supposed" to be used....
SCM_ASSERT(SCM_SMOB_PREDICATE(db_id, obj), obj, SCM_ARG1, "db-open");

It was actually in this document that I found SCM_SMOB_DATA as well.

> >  printf("Database is at %p\n", db); 
> >      db->open();
> >  printf("db_open called.\n");
> >  return SCM_EOL;
> > }
Thanks for the info, it looks like it was plain sloppyness and not 
missinformation or lack of understanding that caused my problem.  After 
seing what caused the error I think it best to use SCM_SMOB_DATA in all 
cases so that my code is not relying on a specific implementation of 
smobs in case they change in later releases.  That probably won't 
happen, but better to use the existing macro than to make up my own, I 
just have to know about them first :P

Thanks,
NR