smob pointer moving

[Noah Roberts]

I have been trying to figure out how to get a C++ class working in guile 
through smobs.  I have suceeded in getting it to create an instance, and 
the print call works appropriately.  However, when I am calling a 
specific method (only one tried so far) the pointer to the object has 
been altered so that it no longer points at the correct 'this'.  Here is 
some relevant pieces of code:

class Database
{
 char *filename;
public:
 Database(char *name); // prints filename
 ~Database() { printf("Database freed.\n"); }
 void open(); // prints filename
};


#define DB(X) ((Database*)(SCM_CDR(X)))

int print_db(SCM obj, SCM port, scm_print_state *pstate)
{
 char string[32];
 sprintf(string, "#<db %p>", DB(obj));
 scm_puts(string, port);
 return 1;
}
SCM db_create_new(SCM filename)
{
 Database *db;
 SCM smob_blob;
 printf("db_create_new called.\n");
 if (SCM_STRINGP(filename))
   {
     db = new Database(SCM_STRING_CHARS(filename));
     SCM_NEWCELL(smob_blob);
     SCM_SETCAR(smob_blob, db_id);
     SCM_SETCDR(smob_blob, (SCM)(db));
    
     return smob_blob;
   }
 else return SCM_BOOL_F;
}

SCM db_open(SCM obj)
{
 Database *db = DB(db);
 printf("Database is at %p\n", db); 
     db->open();
 printf("db_open called.\n");
 return SCM_EOL;
}

 scm_c_define_gsubr("db-create-new", 1, 0, 0, (SCM (*)(...))db_create_new);
 scm_c_define_gsubr("db-open", 1, 0, 0, (SCM (*)(...))db_open);

 scm_set_smob_print(db_id, print_db);

Right now, Database simply prints out some information.  When db-open is 
called from guile I get a crash or "frm" is the filename spit out by 
Database.

Here is some sample output:
guile> (define d (db-create-new "SNTH"))
db_create_new called.
Database SNTH requested at 0x809d210.
guile> d
#<db 0x809d210>
guile> (db-open d)
Database is at 0x805ed78
DB frm OPEN
db_open called.
()
guile> d
#<db 0x809d210>
guile>

as you can see, when db-open is called the pointer returned by the DB 
macro is not correct, why?

Thanks for any help,
NR