Was this a) a real difficult question? b) a really stupid question that
I should find the answer to in a FAQ? c) a really silly question, because
no one sane person would do what I'm doing? d) somehow while the post made
it to the news server, it didn't make it to the mailing list, and everyone
else is reading the list from there?
In case it's d, I repost. In case it's any of a-c, I wouldn't mind to be
told.
Erland Sommarskog ([EMAIL PROTECTED]) writes:
> Perl version Active State Perl, Build 809.
>
> I'm working with a module that will permit programmers to connect to SQL
> Server through SQLOLEDB. Part is Perl, part is XS. There is an object
> representing a connection, and this is a tied hash. I have fought
> several battles with this thing called magic, and my main weapon have
> been to guess and to what appears to work.
>
> There are a bunch of options with my object that I need to retrieve in the
> XS code. To this end I wrote these two routines:
>
> static SV **fetch_from_hash (SV* olle_ptr, hash_key_id id) {
> HV * hv;
> hv = (HV *) SvRV(olle_ptr);
> return hv_fetch(hv, hash_keys[id], strlen(hash_keys[id]), FALSE);
> }
>
> static SV * fetch_option(SV * olle_ptr, hash_key_id id) {
> // Fetches an option from the hash, and only returns an SV, if there is
a
> // defined value.
> SV **svp;
> SV * retsv = NULL;
> svp = fetch_from_hash(olle_ptr, id);
> if (svp != NULL) {
> mg_get(*svp);
> if (SvOK(*svp)) {
> retsv = *svp;
> }
> }
> return retsv;
> }
>
> I found that if I did not add the call to mg_get, SvOK would not return
> TRUE. This appears to work, but now I have run into a situation where
> the call to mg_get causes an access violation. Some pieces of the Perl
> code:
>
> @ISA = qw(Exporter DynaLoader Tie::StdHash);
> ...
> sub FETCH {
> my ($self, $key) = @_;
> if (not exists $myattrs{$key}) {
> croak("Attempt to fetch undefined OlleDB attribute '$key'");
> }
> if ($key eq "SQL_version" and not defined $self->{$key}) {
> # If don't have it, we must retrieve it, and save it.
> my %sqlversion = $self->internal_sql(
> "EXEC master.dbo.xp_msver 'ProductVersion'")
> $self->{SQL_version} = $sqlversion{'Character_Value'};
>
> And this call to internal_sql will pass the command to SQL Server to
> retrieve the result. Except for a minor difference this is the same
> code path as for any other command. But this is where I get the
> access violation in mg_get. I suppose the reason is that since I
> come from the FETCH method, *svp is not magic at this point. But
> how can I tell? Or should I check *svp for a true value in some
> better way than I do?
>
> I believe that I should be to workaround this by adding some extra
> parameter that prevents me from fetching options when coming from
> FETCH. I would still be interesting to learn how I am supposed to
> deal with this situation.
>
>
--
Erland Sommarskog, Stockholm, [EMAIL PROTECTED]
