Programming Perl in C

Then a loop is run for count iterations calling hv_iternextsv(). The call takes 

three parameters, the HV* for the hash, a pointer to a char* to store the key, and a 

pointer to an integer to store the length of the key. The function returns an SV* for 

the value of this key.

Storing Values

Values are stored in a hash using the hv_store() function. For example, the 

following stores the value 100 under to key fuel_remaining in hv:

SV *sv_value = newSViv(100);

hv_store(hv, "fuel_remaining", strlen("fuel_remaining"), sv_value, 0);

The last value allows you to pass in a precomputed hash value; setting it to 0 tells 

Perl to compute the hash value for you. Notice that this function doesn't have the 

restrictions that av_store() does HVs grow automatically, and you don't have to 

extend them manually to store new values.

Deletion

An entire HV can be cleared with the hv_clear() function:

hv_clear(hv); // %hv = ();

Or you can use it to clear just a single key:

hv_delete(hv, "foo", strlen("foo"), 0); // delete $hv{foo}

Reference Values (RV)

In Perl, complex data structures are built using references. For example, if you 

want to create an array of hashes, you do it by assigning references to arrays as 

hash values:

%hash_of_arrays = (

   foo => [ 1, 2, 3 ],

   bar => [ 4, 5, 6 ],

);

In the Perl API, references are represented by SVs containing RV values. Much like SVs

can contain IV or PV values, SVs can also contain RV values that reference other objects.

18

189

9