XS is an interface through which a Perl program can call a C_programming_language language subroutine. The letters stand for eXternal Subroutine, or xsub, where external means external to Perl, i.e. written in some other language.
It may be desirable for a Perl program to invoke a C subroutine in order to
handle very CPU or memory intensive tasks
interface with harware or low-level system facilities
make use of existing C subroutine libraries
The Perl , the word guts suggesting the highly technical nature of the material.
Subroutine libraries in Perl are called modules , and modules that contain xsubs are called XS modules . Perl provides a framework for developing, packaging, distributing, and installing modules. To create an XS module, a programmer
runs h2xs to create an empty module
adds the C subroutines
specifies the calling interfaces to the C subroutines, using a specialized glue language (also referred to as XS)
compiles, tests, and installs the module with make
Once an XS module is installed, it can be loaded into a Perl program with a use statement, like an ordinary Perl module. Once the module is loaded, the C subroutines can be called from Perl code, as if they were written in Perl.
XS modules are not without drawbacks
They are difficult to write and maintain
The can only be installed if
a C compiler is available
the headers that the Perl interpreter was compiled against are available
New versions of Perl may break binary compatibility; if this happens, all XS modules must be recompiled.
It is also possible to write XS modules that wrap C++ code. Doing so is mostly a matter of wrestling with the module build system. Details on how to do this are given [http://www.johnkeiser.com/perl-xs-c++.html here].
=Related Topics=
Perl
=References=
Jenness, Tim & Cozens, Simon (2002). Extending and Embedding Perl . Greenwich: Manning Publications Co. ISBN 1930110820
=External links=
[http://search.cpan.org/dist/perl/pod/perlguts.pod perlxs] Perl XS application programming interface
[http://search.cpan.org/dist/perl/pod/perlguts.pod perlxstut] Perl XS tutorial
[http://search.cpan.org/dist/perl/pod/perlguts.pod perlguts] Perl internal functions for those doing extensions
[http://search.cpan.org/dist/perl/pod/perlguts.pod perlapi] Perl API listing (autogenerated)
[http://world.std.com/~swmcd/steven/perl/pm/xs/intro/index.html XS Mechanics] tutorial
[http://www.johnkeiser.com/perl-xs-c++.html Perl and C++] building XS modules for C++
