Advanced Perl Programming

SWIG Features

Having completed a tour of the extension process, let’s zoom in for a closer look at SWIG’s compendium of features. We mentioned earlier that SWIG handles a useful subset of ANSI C/C++, which means support for data structures as well as functions. Specifically, it supports the following:

Constants and global variables

A C variable can be exported into Perl space as a scalar variable of the same name. SWIG supports the fundamental C data types, enums, and #defined constant values. Variables of complex or user-defined types are automatically mapped to a pair of get/set accessor functions.

Pointers

Every pointer is treated as a void * by default, regardless of whether it is a char** or Matrix* or double ***. This strategy works especially well for user-defined types, because most C libraries don’t expect you to dereference such pointers. For example, fopen returns a FILE *, which is simply handed over to fread() and fwrite(). In Perl, this pointer is available as a scalar, and Perl doesn’t have to know whether the pointer refers to an array, structure, or a typedef. On the other hand, if you want a Vector * to a list of integer-valued scalars, you will have to help SWIG out by providing a typemap.

Typemaps

Not every data type is a simple conversion from Perl to C or vice versa. SWIG (like xsubpp) provides a way for you to write arbitrary transformations, such as converting a Perl array to a 10-by-10 matrix. To write a typemap, you need to know Perl’s API for accessing its ...