Chapter 8

Creation

You can create a new RV using the newRV_inc() function:

SV *sv = newSVpv("foo",0); // $sv = "foo";

SV *rv = newRV_inc(sv);    // $rv = \$sv;

This function officially takes an SV* as a parameter, but it can actually be used with 

any Perl type that you can cast to an SV* (such as an AV* or an HV*). This pattern is 

repeated across the entire RV API instead of having separate functions for SV, AV,

and HV references, there is a single API, and you must cast everything to and from 

SV*. For example, the following creates the hash of arrays data structure shown earlier:

HV *hash_of_arrays_hv = newHV();

AV *foo_av            = newAV();

AV *bar_av            = newAV();

// fill in arrays

push_av(foo_av, newSViv(1));

push_av(foo_av, newSViv(2));

push_av(foo_av, newSViv(3));

push_av(bar_av, newSViv(4));

push_av(bar_av, newSViv(5));

push_av(bar_av, newSViv(6));

// create references and assign to hash

hv_store(hash_of_arrays_hv, "foo", 3, newRV_inc((SV*)foo_av), 0);

hv_store(hash_of_arrays_hv, "bar", 3, newRV_inc((SV*)bar_av), 0);

Once created, an RV can be distinguished from a normal SV using the SvROK

macro. For example, this code would print  ok  twice after the preceding code:

if (SvROK(*(hv_fetch(hash_of_arrays_hv, "foo", 3, 0)))) printf("ok\n");

if (SvROK(*(hv_fetch(hash_of_arrays_hv, "bar", 3, 0)))) printf("ok\n");

Another way to create a reference is to use one of the sv_setref functions. 

These functions take an initialized SV and one of the value types (IV, UV, and so on) 

and creates a new SV. They then make the SV passed as an argument a reference to 

the new SV. Here are some examples:

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