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Postings from May 2004
Tony Cook wrote:
> On Thu, May 27, 2004 at 12:45:02AM -0700, Stas Bekman wrote:
>
>>So how do I check in C whether the passed variable (or a random sv) is
>>undef or not if comparing to &PL_sv_undef doesn't work? am I missing some
>>obvious RTFM section? I've read: 'perlguts:=head2 AVs, HVs and undefined
>>values'
>>but it doesn't seem to be related. There were many other references to
>>undef in the perl manpages, but I didn't find anything useful.
>
>
>>From perldoc perlguts:
>
> If you want to know if this variable (or any other SV) is
> actually "defined", you can call:
>
> SvOK(SV*)
>
> I've always used this, but the documentation in perlapi:
>
> SvOK Returns a boolean indicating whether the value is
> an SV.
>
> bool SvOK(SV* sv)
>
> doesn't really lead you to it.
Why pp_defined doesn't use it then?
But I guess both doc places could be fixed.
Moreover the original problem came from the autogenerated xs => C process, for
converting a standard char * argument:
#line 451 "URI.c"
char * RETVAL;
dXSTARG;
[...]
if (items < 2)
val = NULL;
else {
val = (char *)SvPV(ST(1), val_len);
}
not only it's messed up formatting-wise, it should probably have the SvOK in
it and not issue:
Use of uninitialized value in subroutine entry at
or may be it's a goodness that it does it. I suppose in order to allow undefs
to be passed as arguments, one has to change the prototype of the xs function
to accept SV* instead of char* and do the conversion manually.
If it's not a goodness I'd rather see it do:
if (items < 2 || (items == 2 && !SvOK(ST(1))))
val = NULL;
else {
val = (char *)SvPV(ST(1), val_len);
}
(in my example it's the second argument that's char *, but can be undef as
well, therefore it's 2 items and ST(1)), but that may cause segfaults when an
author weren't expecting users to pass undefined value as a char * variable.
--
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Stas Bekman JAm_pH ------> Just Another mod_perl Hacker
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