Advanced Perl Programming

Adding Extensions

In the preceding pages, we created C applications that made calls to the Perl library, parsed scripts, and sent data between Perl and C space. In the meantime, we studiously avoided the issue of extensions, if you recall, by passing NULL to perl_parse instead of the address of an initialization subroutine. This means that we could not make use of any C-based extensions in the scripts, even common ones such as Socket and SDBM — clearly an unacceptable solution for real applications.

In this section, we learn a simple way of making standard and custom extensions accessible to the embedded Perl interpreter.

The initialization subroutine, which we will refer to as xs_init, is responsible for calling the initialization routines for all statically linked extensions. If you prefer dynamic loading, xs_init simply needs to initialize the built-in dynamic loader.

Instead of handcoding xs_init, we rely on a very convenient module called ExtUtils::Embed to produce it for us. This module is packaged with the Perl distribution, and is used like this:

perl -MExtUtils::Embed -e xsinit -- -o xsinit.c -std IO::Socket DBI

The -M option is identical to saying "use ExtUtils::Embed;“. This invocation produces a file called xsinit.c with a publicly available function called xs_init, which in turn contains the code to initialize all the standard modules (thanks to the -std argument), and the two custom modules, IO::Socket and DBI.

How does this module know what is standard or whether we ...