CHAPTER 9  

Writing C Modules 

with XS

N

OW THAT YOU

'

RE A

 Perl API yellow belt, it's time to learn to write Perl modules in C. 

XS is the name for the toolkit used to create most of the existing C modules on 

CPAN. It consists of two pieces: the XS language for expressing interfaces and the 

xsubpp compiler that generates C code from XS.

A Real World Example

This section will use a real world module as an example Gnome::MIME. 

Gnome::MIME will provide an interface to the Gnome system's MIME handling 

routines. The Gnome system is a desktop and component system for UNIX like 

operating systems produced by the Free Software Foundation.

1

 You can find more 

information at the Gnome Web site: http://gnome.org.

CPAN already has a Perl module that provides a binding to some of Gnome, 

although not to the MIME functions at present; you can find the Gnome module, 

written by Kenneth Albanowski and Paolo Molaro, on CPAN.

The Gnome MIME functions come from the packages gnome mime and 

gnome mime info. They provide functions to guess MIME types given a file and 

functions to retrieve information about a MIME type. A MIME type is a standardized 

system for describing the type of a file. Example MIME types that you might be 

familiar with are text/html, image/gif, and application/pdf. MIME types are used 

in many applications, from Web browsers to e mail programs to operating systems. 

You can find more information on the MIME types in RFC 2046, which is available 

here (among many other locations): http://www.rfc editor.org/rfc/rfc2046.txt.

This example module is, by nature, platform specific and will only work on 

UNIX systems with Gnome installed. However, the basic techniques demonstrated 

can be used to create cross platform XS modules.

1. See http://www.fsf.org.

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