Writing C Modules with XS

  // loop over args by pairs and fill in parameters

  for(x = 0; x < items; x+=2) {

    char *key = SvPV(ST(x), PL_na);

    if (strEQ(key, "filename")) {

    filename = SvPV(ST(x+1), PL_na);

  } else if (strEQ(key, "default_type")) {

    // ...

The preceding block uses the ST macro to access the SVs passed in as arguments. The 

strEQ() function is used to compare the keys to the available parameter names. When 

a match is found, the value is assigned to one of the variables initialized in the PREINIT

section. After that, a series of conditionals determines which gnome_mime_type function 

to call:

  // call the appropriate function based on arguments

  if (read_file && default_type != NULL) {

    RETVAL = gnome_mime_type_or_default_of_file(filename, default_type);

  } else if (read_file) {

    // ...

With the new named parameter style, the test cases will need adjusting:

# test some simple mime file_type recognitions

is(Gnome::MIME::file_type(filename => "foo.gif"),  image/gif ,  "test .gif");

is(Gnome::MIME::file_type(filename => "foo.jpg"),  image/jpeg , "test .jpg");

is(Gnome::MIME::file_type(filename => "foo.html"),  text/html , "test .html");

# test defaulting

is(Gnome::MIME::file_type(filename => "", default_type => "text/html"),

   "text/html", "test default");

# ...

Using Perl

The XSUB shown previously gets the job done, but at the cost of some long and rel 

atively complicated C code. An easier way to get the same functionality is to divide 

the module into an XS back end and a Perl front end. The XS layer will provide a 

thin wrapper around the existing API, and the Perl front end will add the code 

necessary to support a friendly interface.

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