Somewhat inspired by your suggestion, and taking some things from the original generated C code, I've currently got something like this: 
struct bar*
create_event(foo_sv)
  SV* foo_sv
  struct type_foo* foo = NULL;
  CODE:
    if ( SvROK(foo_sv)) {
      SV *tmp = (SV*) SvRV(foo_sv);
      if ( SvOK (tmp)) {
        foo = (struct type_foo*) SvIV(tmp);
      }
    } else {
      warn( "Foo::create_bar() -- foo is not an SV reference" );
      XSRETURN_UNDEF;
    }

    RETVAL = my_c_create_bar(foo);
  OUTPUT:
    RETVAL

[download]
which successfully avoids the warning message I was getting originally. Unfortunately, this is one of those bits of code someone else wrote originally and didn't write tests for, so now I need to go and actually write some tests to make sure this works right.

In reply to Re^2: Passing NULL pointer through XS without "Use of uninitialized value in subroutine entry" by kscaldef
in thread Passing NULL pointer through XS without "Use of uninitialized value in subroutine entry" by kscaldef

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.