Chapter 9

Listing 9 5. C Function Generated by xsubpp for gnome_mime_type() XSUB

XS(XS_Gnome__MIME_gnome_mime_type)

{

    dXSARGS;

    if (items != 1)

               Perl_croak(aTHX_ "Usage: Gnome::MIME::gnome_mime_type(filename)");

    {

               char *         filename = (char *)SvPV(ST(0),PL_na);

               char *         RETVAL;

               dXSTARG;

               RETVAL = gnome_mime_type(filename);

      sv_setpv(TARG, RETVAL); XSprePUSH; PUSHTARG;

    }

    XSRETURN(1);

}

XSUB Techniques

The XSUB shown earlier is about as simple as an XSUB can be. However, there are 

many useful changes that can be made to enhance the usability and functionality 

of XSUBs.

Types and Typemaps

You might have noticed that the types used in the gnome_mime_type() XSUB 

are subtly different from those used in the actual function signature. In the 

gnome_mime_type() function, the return type is a const char * and the filename 

argument type is const gchar *, whereas the XSUB used char * for both. This was 

done because XS comes with a typemap for char *, but doesn't know anything 

about const char * and const gchar *. A typemap is a description of how to map 

Perl types to and from C types.

If you try to use the real types in an XSUB as follows:

const char *

gnome_mime_type(filename)

     const gchar *filename

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