Writing C Modules with XS

    // store the key/value pair in

    hv_store(hv, key, strlen(key), value, 0);

  }

  // return a reference to the new hash

  RETVAL = newRV_noinc((SV *)hv);

OUTPUT:

  RETVAL

CLEANUP:

  g_list_free(keys);

The XSUB starts with a return type of SV:

SV *

type_data(type)

  const gchar * type

Since the subroutine will return a reference to a hash, the return type must be 

SV*. Next, several local variables are declared in a PREINIT block, including two 

GLists. The GList type is the Gnome API's linked list type. The CODE body starts by 

initializing the HV that will be returned to the user:

  // initialize hash

  hv = newHV();

Next, I call gnome_mime_get_keys() and begin iterating over the GList:

  // get GList of keys for this type

  keys = gnome_mime_get_keys(type);

  // iterate through keys

  for (iter = keys; iter; iter = iter >next) {

    // get the key from the iterator

    key = iter >data;

If keys returns a NULL pointer, then this loop won't be executed, and an empty hash 

will be returned to the user. Next, the key value pairs are stored in the HV:

    // create a new SV and load it with the value for this key

    value = newSVpv(gnome_mime_get_value(type, key), 0);

    // store the key/value pair in

    hv_store(hv, key, strlen(key), value, 0);

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