Convenience macro to get the REGEXP from a SV. This is approximately equivalent to the following snippet:

            

              
              
if (SvMAGICAL(sv))
    mg_get(sv);
if (SvROK(sv))
    sv = MUTABLE_SV(SvRV(sv));
if (SvTYPE(sv) == SVt_REGEXP)
    return (REGEXP*) sv;
            
          

NULL will be returned if a REGEXP* is not found.

Returns a boolean indicating whether the SV (or the one it references) is a REGEXP.

If you want to do something with the REGEXP* later use SvRX instead and check for NULL.