Chapter 9

  // make sure we have a filename parameter

  if (filename == NULL) croak("Missing required parameter filename.");

  // 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) {

    RETVAL = gnome_mime_type_of_file(filename);

  } else if (default_type != NULL) {

    RETVAL = gnome_mime_type_or_default(filename, default_type);

  } else {

    RETVAL = gnome_mime_type(filename);

  }

OUTPUT:

  RETVAL

The XSUB starts with syntax for a variable argument function that mimics 

C's syntax:

const char *

file_type(...)

Note that unlike C's . . . , you don't need to have at least one fixed parameter.

Next, I set up a number of local variables in a PREINIT block. The contents of 

PREINIT are placed first in the output XSUB. In some cases this is essential, but in 

this case it's merely a convenient place for local declarations:

PREINIT:

  char *filename     = NULL; // variables for named params

  char *default_type = NULL;

  IV read_file       = 0;

  IV x;                      // loop counter

Next comes the CODE block proper, where the automatic XS variable items is 

used to check the number of parameters:

  // check that there are an even number of args

  if (items % 2) croak("Usage: Gnome::MIME::file_type(k => v, ...)");

and then iterate through the key/value pairs:

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