I'm finding 
  if(valuesv == &sv_undef)

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never tests true and 
!SvOK(valuesv)

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tests true when valuesv is undef - of course. What I'm not sure is what the original author might have meant by the first test above - perhaps it should have been SvOK in which case it was bug, perhaps something else.

In reply to Re^2: testing for undef in perl XS code (in DBD::ODBC) by mje
in thread testing for undef in perl XS code (in DBD::ODBC) by mje

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