I get passed an SV* and want to make sure it is a valid string. How to do that?

Consider this sv: 

SV = PVMG(0x2492968) at 0x1e759c8
  REFCNT = 1
  FLAGS = (PADMY,GMG,SMG,pIOK)
  IV = 123456
  NV = 0
  PV = 0x1f76868 "123foobar"\0
  CUR = 9
  LEN = 16
  MAGIC = 0x1f83b18
    MG_VIRTUAL = &PL_vtbl_taint
    MG_TYPE = PERL_MAGIC_taint(t)

[download]
It is an IV and has an invalid buffer assigned.

How can I do something like $x.=''?

I thought SvUPGRADE($buffer, SVt_PV) is the answer but that changes nothing.

Thanks

In reply to XS question by tfoertsch

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.