Writing C Modules with XS

After adding this XSUB to the end of MIME.xs, I'll edit my test.pl to read 

as follows:

use Test::More  no_plan ;

BEGIN { use_ok( Gnome::MIME ); }

# test some simple mime type recognitions

is(Gnome::MIME::gnome_mime_type("foo.gif"),   image/gif ,  "recognizes .gif");

is(Gnome::MIME::gnome_mime_type("foo.jpg"),   image/jpeg , "recognizes .jpg");

is(Gnome::MIME::gnome_mime_type("foo.html"),  text/html ,  "recognizes .html");

Now a normal perl Makefile.PL, make, and make test run will build and test the 

new module.

XSUB Anatomy

As you can see in the preceding section, an XSUB resembles a C function signature 

in K&R format. The first line contains the return type of the function. Then comes 

a line containing the function name and a list of parameters. Finally, a line per 

parameter specifies the type of each parameter. Here's an annotated version of the 

previous example (note that XS doesn't actually allow comments inline with 

XSUBs, so this won't compile):

char *                     # returns a string

gnome_mime_type(filename)  # takes a single parameter named filename

     char *filename        # filename is a string

This is the simplest possible type of XSUB it maps a C function directly to a 

Perl function with the same parameters and return type. The xsubpp compiler takes 

this definition and produces C code in the generated MIME.c (see Listing 9 5). This 

C code makes use of functions in the Perl API introduced in the previous chapter. 

For example, to translate the incoming SV into a char *, MIME.c contains this line:

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

The ST macro provides access to the argument array of an XSUB, but the rest of the 

call should be familiar.

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