Learn how to use SWIG to create Perl modules that interface to libraries written in C or C++.

1. EASY NATIVE WRAPPERS WITH
SWIG
2014 Barcelona Perl Workshop

2. Text
Every time you open a pipe to a program to do something
that Perl already knows how to do, God kills a kitten.
- @pplu_io
!
Check CPAN to save kittens.

4. Going Native
Obscure/Propietary libraries
Legacy code
Code Optimization*
Test harness
Glue

5. XS

6. XS is an interface description file format
used to create an extension interface
between Perl and C code (or a C library)
which one wishes to use with Perl.
-perlxs 1:1

7. “Hooking Perl to C using XS requires you to write a
shell.pm module to bootstrap an object file that has
been compiled from C code, which was in turn
generated by xsubpp from a.xs source file
containing pseudo-C annotated with an XS interface
description.”
–Brian D. Foy, “Perl Best Practices”

8. “Hooking Perl to C using XS requires you
to write a shell.pm module
to bootstrap an object file
that has been compiled from C code,
which was in turn
generated by xsubpp
from a.xs source file
containing pseudo-C
annotated with an XS interface description.”
–Brian D. Foy, “Perl Best Practices”

9. “If that sounds horribly complicated,
then you have achieved an accurate
understanding of the use of xsubpp.”
–Brian D. Foy, “Perl Best Practices”

10. Inline::C
It’s C, but Inline!

11. Inline::C
#!/usr/bin/env perl
use strict;
use Inline C => << 'END_C';
void hello() {
printf("Hello, world!");
}
END_C
!
hello();

12. How does it work?

13. Live demo

14. SWIG
Simplified
Wrapper and
Interface
Generator

15. “SWIG is an interface compiler that connects
programs written in C and C++ with scripting
languages such as Perl, Python, Ruby, and Tcl.”
– http://www.swig.org/exec.html

16. Purpose
Prototyping & Debugging
Systems Integration
Build extension modules

17. SWIG
Open Source (GPL)
Created in 1995 by Dave Beazley
Support for a couple dozen languages by 2014
http://www.swig.org/

18. Supported Languages
Tcl
Python
Perl
Java
Ruby
PHP
Ocaml
Pike
C#
Scheme
Modula-3
Lua
Common Lisp
R
Octave
Go
D
Javascript
http://www.swig.org/compat.html#SupportedLanguages

19. Interface definition
/* File : example.i */
!
%module example
!
%inline %{
extern int gcd(int x, int y);
extern double Foo;
%}

20. C file
/* File : example.c */
!
/* A global variable */
double Foo = 3.0;
!
/* Compute the greatest common divisor of positive
integers */
int gcd(int x, int y) {
int g;
g = y;
while (x > 0) {
g = x;
x = y % x;
y = g;
}
return g;
}

21. Build Wrapper
swig -perl example.i

22. Compile & Link (Ideal)
cc -c example_wrap.c
!
cc -c example.c
!
ldd example_wrap.o example.o -o
example.so

23. Compile & Link (Real World)
cc -c -fno-common -DPERL_DARWIN -fno-strict-aliasing -
pipe -fstack-protector -I/usr/local/include -I/opt/
local/include -I/Users/arturo/perl5/perlbrew/perls/
perl-5.10.1/lib/5.10.1//darwin-2level/CORE/
example_wrap.c
!
cc -c -fno-common -DPERL_DARWIN -fno-strict-aliasing -
pipe -fstack-protector -I/usr/local/include -I/opt/
local/include -I/Users/arturo/perl5/perlbrew/perls/
perl-5.10.1/lib/5.10.1//darwin-2level/CORE/ example.c
!
env MACOSX_DEPLOYMENT_TARGET=10.3 cc -bundle -
undefined dynamic_lookup -L/usr/local/lib -L/opt/
local/lib -fstack-protector example_wrap.o example.o
-o example.bundle

24. Hello, SWIG!
perl runme.pl
The gcd of 42 and 105 is 21
Foo = 3
Foo = 3.1415926

25. Getting There
Simpler interface file
Add SWIG to build chain

26. (#|%)include
%module MyModule
%{
#include "mymodule.h"
%}
!
%include "mymodule.h"

27. Makefile.PL
use 5.008000;
use Config;
use ExtUtils::MakeMaker;
use vars qw($version);
$version='0.1';
my $cmd = qq{swig -outdir lib -o Fact_wrap.c -perl Fact.i};
print "Executing $cmdn";
system($cmd);
if($?==-1) {
die("failed to execute: $!");
} elsif($?>0) {
die("Error creating perl wrapper: $?");
}
WriteMakefile(
NAME => 'Fact',
VERSION => $version,
PREREQ_PM => {},
DEFINE => '-DMACOSX '.$Config{ccflags},
INC => '',
OBJECT => '$(O_FILES)',
clean => {
FILES => 'lib/Fact.pm Fact_wrap.c',
},
PMLIBDIRS => [ 'lib', 'lib/Fact' ],
);

28. Live demo!

29. structs
struct Vector {
double x,y;
};
package Vect::Vector;
use vars qw(@ISA %OWNER %ITERATORS %BLESSEDMEMBERS);
@ISA = qw( Vect );
%OWNER = ();
%ITERATORS = ();
*swig_x_get = *Vectc::Vector_x_get;
*swig_x_set = *Vectc::Vector_x_set;
*swig_y_get = *Vectc::Vector_y_get;
*swig_y_set = *Vectc::Vector_y_set;
…

30. Sane Accessors
my $v = Vect::Vector->new();
$v->{x}=3;
$v->{y}=4;

31. Distribute on CPAN
No need to force swig dependency
Include the generated wrapper (*_wrap.c, *.pm)
Include the interface definition as a courtesy

32. Tip of the Iceberg
C++
Exceptions
Typemaps
%perlcode

33. ++$learn
http://www.slideshare.net/daoswald/getting-started-with-
perl-xs-and-inlinec
Cozens, Simon. “Advanced Perl Programming”
Orwant, Jon. “Computer Science & Perl Programming”
http://www.swig.org/

34. Q&A

35. Thank you!
@codehead
javier@rodriguez.org.mx
scribd.com/javierrgz