PL_sv_undef is a perl scalar that has the value undef.

There can be other perl scalars with the undef value. Actually, you can create then using SV *a = newSV(0).

With a == &PL_sv_undef you are not testing if they contain the same value but if they are both pointers to the same scalar!

In reply to Re^4: 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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