Chapter 9

I'll add a line for the GList* type:

GList *          T_GLIST

The next section in a typemap is the INPUT section. An INPUT typemap describes 

how to translate from an SV* to the specified type. It is used when an XSUB takes 

the type as a parameter. Since gnome_mime_get_keys() returns GList* and nothing 

I'm wrapping uses a GList* as a parameter, I'll leave this one unimplemented:

INPUT

T_GLIST

        croak("GList * input typemap unimplemented!");

Next comes the OUTPUT section, which specifies how to turn the type into an SV*:

OUTPUT

T_GLIST

        $arg = GList_to_AVref($var);

Typemap code uses two placeholder variables: $arg and $var. In an OUTPUT typemap, 

$var is a variable of the type being output and $arg is the SV* to be returned. As you 

can see, my OUTPUT typemap calls the GList_to_AVref() function. This function 

doesn't exist in either Perl or Gnome, so I'll have to write it!

Where to place external functions like GList_to_AVref() is a matter of pref 

erence. Some XS coders prefer to put them in a separate .c file compiled and 

linked separately. I prefer to place them in the C section above the XSUB decla 

rations, and that's the way I'll do it here (see Listing 9 10).

Listing 9 10. GList_to_AVref() Function Included in MIME.xs

#include "EXTERN.h"

#include "perl.h"

#include "XSUB.h"

#include 

SV * GList_to_AVref(GList *list) {

  GList *iter;       // list iterator

  AV *av = newAV();  // initialize new array

  // iterate through GList

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

    // push data onto array

    av_push(av, newSVpv(iter >data,0));

  }

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