The right way to test for undef in XS code is using !SvOK(sv).

PL_sv_undef is a perl scalar with the undef value, but it is not the only one. It is just for convenience, to not have to instantiate a new scalar on every place where an undef is required.

sv_undef is a macro that expands to PL_sv_undef

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

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