Writing C Modules with XS

  // free glist passed into function

  g_list_free(list);

  // return a reference to the new array

  return sv_2mortal(newRV_noinc((SV *)av));

}

The code for the function should be easy enough to understand. It simply 

takes a GList* and adds each data item contained inside to an array, returning a 

new mortal reference to the array constructed. Notice that the function also frees 

the GList*:

  // free glist passed into function

  g_list_free(list);

This could just as well have been done in a CLEANUP block, but putting it in the 

typemap function provides the cleanest access for the XSUB.

With this XSUB in place, the test code is updated to use the new interface:

# test get_keys and get_value

$keys = Gnome::MIME::get_keys("image/gif");

isa_ok($keys,  ARRAY , "get_keys return");

foreach $key (@$keys) {

  ok(Gnome::MIME::get_value("image/gif", $key), "got value for \"$key\"");

}

The best way to learn to program typemaps is to examine the typemaps that 

come with Perl. You'll find them in a file called typemap in the library directory 

where the ExtUtils modules are installed. On my system, the path to typemap is 

/usr/lib/perl5/5.6.1/ExtUtils/typemap, but different platforms will place the file 

in different locations.

Learning More about XS

The examples in this chapter have explored many useful XS programming tech 

niques. However, there are many useful commands and options that I didn't have 

space to cover. Included with Perl is perlxstut, a tutorial that covers much the 

same ground as this chapter. Also included with Perl is perlxs, an exhaustive ref 

erence to all of XS.

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