use Inline (
    C           => 'DATA',
    BUILD_NOISY => 1,
    clean_after_build => 0,
    warnings => 10,
);

# perl stuff

# more perl stuff...

__DATA__
__C__
#include <stdio.h>

// checks if array is indeed an arrayref and sets array_sz to its size and
// returns 1 else returns 0 (not an array)
int is_array_ref(
	SV *array,
	size_t *array_sz
){
	if( ! SvROK(array) ){ fprintf(stderr, "is_array_ref() : warning, input '%p' is not a reference.\n", array); return 0; }
	if( SvTYPE(SvRV(array)) != SVt_PVAV ){ fprintf(stderr, "is_array_ref() : warning, input ref '%p' is not an ARRAY reference.\n", array); return 0; }
	// it's an array, cast it to AV to get its len via av_len();
	// yes, av_len needs to be bumped up, it's $#array
	int asz = 1+av_len((AV *)SvRV(array));
	if( asz < 0 ){ fprintf(stderr, "is_array_ref() : error, input array ref '%p' has negative size!\n", array); return 0; }
	*array_sz = (size_t )asz;
	return 1; // success, it is an array and size returned by ref, above
}

int func(
	SV *inp,
	SV *out
){
	AV *av, *av2;
	size_t i, j, asz;
	if( is_array_ref(out, &asz) ){
		printf("Case1: @out\n");
		// we have an \@R, e.g. func(\@R)
		 av = (AV *)SvRV(out);
		// but first clear any contents
		if( asz > 0 ) av_clear(av);
	} else if( SvROK(out) ){
		printf("Case3: \\$out\n");
		// we have a scalar ref, e.g. func(\$x)
		av = newAV();
		sv_setsv(SvRV(out), (SV *)av);
	} else {
		printf("Case2: $out\n");
		// we have a scalar e.g func($x);
		av = newAV();
		sv_setsv(out, (SV *)av);
	}
        // and fill it in
	for(i=0;i<5;i++){
		av2 = newAV();
		av_extend(av2, 3);
		av_push(av, (SV *)av2);
		for(j=0;j<3;j++){
			av_store(av2, j, newSViv(42));
		}
	}
	return 0; // success
}