Re: [Dbi-interbase-devel] set_txn_param fix confirmed

[Daniel R. <dan...@gm...>]

it was the first time i was using XS...

why it is better? 
* short answer: because it now works :-)
* long answer: 
because SvRV dereferences a Perl reference (RV*) and returns an SV*, AV* or HV*. 
to which one you have to cast it to can be figured out using SvTYPE. to check if a SV*
contains a reference you can use SvROK....(SvRV should always be used in combination 
with SvROK -> value = SvRV(SvROK(reference));

but av_fetch() returns a SV** which is only a pointer to an SV*, not a RV*, so dereferencing
a non RV* crashes Perl....

see http://www.perldoc.com/perl5.6/pod/perlguts.html for explaination of these macros,
and http://www.perldoc.com/perl5.6/pod/perlxs.html for an XS manual,
http://www.perldoc.com/perl5.6/pod/perlxstut.html for a (still incomplete) XS tutorial, 
http://gisle.aas.no/perl/illguts/ for detailed description of Perl data structures

rgds
-daniel


----- Original Message ----- 
From: "Mark D. Anderson" <md...@di...>
To: <dbi...@li...>
Sent: Wednesday, August 01, 2001 7:02 PM
Subject: [Dbi-interbase-devel] set_txn_param fix confirmed


> thanks for the fix in 28.4.
> 
> for us XS neophytes, what was the bug?
> 
> why is 
>             svp = av_fetch(av, j, FALSE);
>             if ( strEQ( SvPV_nolen(*svp), "read_committed" )) 
> 
> better than
>                     sv = (SV*)SvRV(*av_fetch(av, j, FALSE));
>                     if ( strEQ( SvPV(sv, PL_na), "read_committed" )) {
> 
> -mda
> 
> 
> 
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