Just updated the program to take on board your helpful critique.

use strict;
use warnings;

my $point = pack 'f2', 1.2, 2.3;
func(undef);    # pass in 'NULL pointer'
func($pointer);

Inline C => <<'C_END';

typedef struct { float x, y; } Point;

void func(SV *buf) {
   if (!SvOK(buf)) {
       printf("got a null pointer\n");
   }
   else if (SvPOK(buf) && SvCUR(BUF) == sizeof(Point)) {
       Point *point = (Point *)SvPV_nolen(buf);
       printf("x=%.2f, y=%.2f\n");
   }
   else {
       croak("invalid scalar");
   }

}

C_END
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